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Wikipedia

Heating, ventilation, and air conditioning

January 15, 2023

"HVAC" redirects here. HVAC may also refer to high-voltage alternating current.

Heating, ventilation, and air conditioning (HVAC)[1] is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR (as in the designation of HACR-rated circuit breakers).

Rooftop HVAC unit with view of fresh-air intake vent
Ventilation duct with outlet diffuser vent. These are installed throughout a building to move air in or out of rooms. In the middle is a damper to open and close the vent to allow more or less air to enter the space.
The control circuit in a household HVAC installation. The wires connecting to the blue terminal block on the upper-right of the board lead to the thermostat. The fan enclosure is directly behind the board, and the filters can be seen at the top. The safety interlock switch is at the bottom left. In the lower middle is the capacitor.

HVAC is an important part of residential structures such as single family homes, apartment buildings, hotels, and senior living facilities; medium to large industrial and office buildings such as skyscrapers and hospitals; vehicles such as cars, trains, airplanes, ships and submarines; and in marine environments, where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.

Ventilating or ventilation (the "V" in HVAC) is the process of exchanging or replacing air in any space to provide high indoor air quality which involves temperature control, oxygen replenishment, and removal of moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases. Ventilation removes unpleasant smells and excessive moisture, introduces outside air, keeps interior building air circulating, and prevents stagnation of the interior air. Methods for ventilating a building are divided into mechanical/forced and natural types.[2]

Overview

The three major functions of heating, ventilation, and air conditioning are interrelated, especially with the need to provide thermal comfort and acceptable indoor air quality within reasonable installation, operation, and maintenance costs. HVAC systems can be used in both domestic and commercial environments. HVAC systems can provide ventilation, and maintain pressure relationships between spaces. The means of air delivery and removal from spaces is known as room air distribution.[3]

Individual systems

See also: HVAC control system

In modern buildings, the design, installation, and control systems of these functions are integrated into one or more HVAC systems. For very small buildings, contractors normally estimate the capacity and type of system needed and then design the system, selecting the appropriate refrigerant and various components needed. For larger buildings, building service designers, mechanical engineers, or building services engineers analyze, design, and specify the HVAC systems. Specialty mechanical contractors and suppliers then fabricate, install and commission the systems. Building permits and code-compliance inspections of the installations are normally required for all sizes of buildings.

District networks

Although HVAC is executed in individual buildings or other enclosed spaces (like NORAD's underground headquarters), the equipment involved is in some cases an extension of a larger district heating (DH) or district cooling (DC) network, or a combined DHC network. In such cases, the operating and maintenance aspects are simplified and metering becomes necessary to bill for the energy that is consumed, and in some cases energy that is returned to the larger system. For example, at a given time one building may be utilizing chilled water for air conditioning and the warm water it returns may be used in another building for heating, or for the overall heating-portion of the DHC network (likely with energy added to boost the temperature).[4][5][6]

Basing HVAC on a larger network helps provide an economy of scale that is often not possible for individual buildings, for utilizing renewable energy sources such as solar heat,[7][8][9] winter's cold,[10][11] the cooling potential in some places of lakes or seawater for free cooling, and the enabling function of seasonal thermal energy storage. By utilizing natural sources that can be used for HVAC systems it can make a huge difference for the environment and help expand the knowledge of using different methods.

History

See also: Air conditioning § History

HVAC is based on inventions and discoveries made by Nikolay Lvov, Michael Faraday, Rolla C. Carpenter, Willis Carrier, Edwin Ruud, Reuben Trane, James Joule, William Rankine, Sadi Carnot, and many others.[12]

Multiple inventions within this time frame preceded the beginnings of the first comfort air conditioning system, which was designed in 1902 by Alfred Wolff (Cooper, 2003) for the New York Stock Exchange, while Willis Carrier equipped the Sacketts-Wilhems Printing Company with the process AC unit the same year. Coyne College was the first school to offer HVAC training in 1899.[13]

The invention of the components of HVAC systems went hand-in-hand with the industrial revolution, and new methods of modernization, higher efficiency, and system control are constantly being introduced by companies and inventors worldwide.

Heating

Main article: Central heating
"Heater" redirects here. For other uses, see Heater (disambiguation).

Heaters are appliances whose purpose is to generate heat (i.e. warmth) for the building. This can be done via central heating. Such a system contains a boiler, furnace, or heat pump to heat water, steam, or air in a central location such as a furnace room in a home, or a mechanical room in a large building. The heat can be transferred by convection, conduction, or radiation. Space heaters are used to heat single rooms and only consist of a single unit.

Generation

 
Central heating unit

Heaters exist for various types of fuel, including solid fuels, liquids, and gases. Another type of heat source is electricity, normally heating ribbons composed of high resistance wire (see Nichrome). This principle is also used for baseboard heaters and portable heaters. Electrical heaters are often used as backup or supplemental heat for heat pump systems.

The heat pump gained popularity in the 1950s in Japan and the United States.[14] Heat pumps can extract heat from various sources, such as environmental air, exhaust air from a building, or from the ground. Heat pumps transfer heat from outside the structure into the air inside. Initially, heat pump HVAC systems were only used in moderate climates, but with improvements in low temperature operation and reduced loads due to more efficient homes, they are increasing in popularity in cooler climates, they can also operate in reverse by cooling an interior.

Distribution

Water/steam

In the case of heated water or steam, piping is used to transport the heat to the rooms. Most modern hot water boiler heating systems have a circulator, which is a pump, to move hot water through the distribution system (as opposed to older gravity-fed systems). The heat can be transferred to the surrounding air using radiators, hot water coils (hydro-air), or other heat exchangers. The radiators may be mounted on walls or installed within the floor to produce floor heat.

The use of water as the heat transfer medium is known as hydronics. The heated water can also supply an auxiliary heat exchanger to supply hot water for bathing and washing.

Air

Main articles: Room air distribution and Underfloor air distribution

Warm air systems distribute the heated air through ductwork systems of supply and return air through metal or fiberglass ducts. Many systems use the same ducts to distribute air cooled by an evaporator coil for air conditioning. The air supply is normally filtered through air filters to remove dust and pollen particles.[15]

Dangers

The use of furnaces, space heaters, and boilers as a method of indoor heating could result in incomplete combustion and the emission of carbon monoxide, nitrogen oxides, formaldehyde, volatile organic compounds, and other combustion byproducts. Incomplete combustion occurs when there is insufficient oxygen; the inputs are fuels containing various contaminants and the outputs are harmful byproducts, most dangerously carbon monoxide, which is a tasteless and odorless gas with serious adverse health effects.[16]

Without proper ventilation, carbon monoxide can be lethal at concentrations of 1000 ppm (0.1%). However, at several hundred ppm, carbon monoxide exposure induces headaches, fatigue, nausea, and vomiting. Carbon monoxide binds with hemoglobin in the blood, forming carboxyhemoglobin, reducing the blood's ability to transport oxygen. The primary health concerns associated with carbon monoxide exposure are its cardiovascular and neurobehavioral effects. Carbon monoxide can cause atherosclerosis (the hardening of arteries) and can also trigger heart attacks. Neurologically, carbon monoxide exposure reduces hand to eye coordination, vigilance, and continuous performance. It can also affect time discrimination.[17]

Ventilation

Main article: Ventilation (architecture)

Ventilation is the process of changing or replacing air in any space to control the temperature or remove any combination of moisture, odors, smoke, heat, dust, airborne bacteria, or carbon dioxide, and to replenish oxygen. Ventilation often refers to the intentional delivery of the outside air to the building indoor space. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building may be divided into mechanical/forced and natural types.[18]

Mechanical or forced

Further information: Ventilation (architecture) § Mechanical systems
 
HVAC ventilation exhaust for a 12-story building

Mechanical, or forced, ventilation is provided by an air handler (AHU) and used to control indoor air quality. Excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air. However, in humid climates more energy is required to remove excess moisture from ventilation air.

Kitchens and bathrooms typically have mechanical exhausts to control odors and sometimes humidity. Factors in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent size) and noise level. Direct drive fans are available for many applications and can reduce maintenance needs.

In summer, ceiling fans and table/floor fans circulate air within a room for the purpose of reducing the perceived temperature by increasing evaporation of perspiration on the skin of the occupants. Because hot air rises, ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor.

Passive

Main article: Passive ventilation
 
Ventilation on the downdraught system, by impulsion, or the 'plenum' principle, applied to schoolrooms (1899)

Natural ventilation is the ventilation of a building with outside air without using fans or other mechanical systems. It can be via operable windows, louvers, or trickle vents when spaces are small and the architecture permits. ASHRAE defined Natural ventilation as the flow of air through open windows, doors, grilles, and other planned building envelope penetrations, and as being driven by natural and/or artificially produced pressure differentials.[2]

In more complex schemes, warm air is allowed to rise and flow out high building openings to the outside (stack effect), causing cool outside air to be drawn into low building openings. Natural ventilation schemes can use very little energy, but care must be taken to ensure comfort. In warm or humid climates, maintaining thermal comfort solely via natural ventilation might not be possible. Air conditioning systems are used, either as backups or supplements. Air-side economizers also use outside air to condition spaces, but do so using fans, ducts, dampers, and control systems to introduce and distribute cool outdoor air when appropriate.

An important component of natural ventilation is air change rate or air changes per hour: the hourly rate of ventilation divided by the volume of the space. For example, six air changes per hour means an amount of new air, equal to the volume of the space, is added every ten minutes. For human comfort, a minimum of four air changes per hour is typical, though warehouses might have only two. Too high of an air change rate may be uncomfortable, akin to a wind tunnel which has thousands of changes per hour. The highest air change rates are for crowded spaces, bars, night clubs, commercial kitchens at around 30 to 50 air changes per hour.[19]

Room pressure can be either positive or negative with respect to outside the room. Positive pressure occurs when there is more air being supplied than exhausted, and is common to reduce the infiltration of outside contaminants.[20]

Airborne diseases

Natural ventilation [21] is a key factor in reducing the spread of airborne illnesses such as tuberculosis, the common cold, influenza, meningitis or COVID-19. Opening doors and windows are good ways to maximize natural ventilation, which would make the risk of airborne contagion much lower than with costly and maintenance-requiring mechanical systems. Old-fashioned clinical areas with high ceilings and large windows provide the greatest protection. Natural ventilation costs little and is maintenance free, and is particularly suited to limited-resource settings and tropical climates, where the burden of TB and institutional TB transmission is highest. In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion. Natural ventilation requires little maintenance and is inexpensive.[22]

Air conditioning

Main article: Air conditioning

An air conditioning system, or a standalone air conditioner, provides cooling and/or humidity control for all or part of a building. Air conditioned buildings often have sealed windows, because open windows would work against the system intended to maintain constant indoor air conditions. Outside, fresh air is generally drawn into the system by a vent into a mix air chamber for mixing with the space return air. Then the mixture air enters an indoor or outdoor heat exchanger section where the air is to be cooled down, then be guided to the space creating positive air pressure. The percentage of return air made up of fresh air can usually be manipulated by adjusting the opening of this vent. Typical fresh air intake is about 10% of the total supply air.[citation needed]

Air conditioning and refrigeration are provided through the removal of heat. Heat can be removed through radiation, convection, or conduction. The heat transfer medium is a refrigeration system, such as water, air, ice, and chemicals are referred to as refrigerants. A refrigerant is employed either in a heat pump system in which a compressor is used to drive thermodynamic refrigeration cycle, or in a free cooling system that uses pumps to circulate a cool refrigerant (typically water or a glycol mix).

It is imperative that the air conditioning horsepower is sufficient for the area being cooled. Underpowered air conditioning systems will lead to power wastage and inefficient usage. Adequate horsepower is required for any air conditioner installed.

Refrigeration cycle

Main article: Heat pump and refrigeration cycle
 
A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporating coil, 4) compressor

The refrigeration cycle uses four essential elements to cool, which are compressor, condenser, metering device, and evaporator.

  • At the inlet of a compressor, the refrigerant inside the system is in a low pressure, low temperature, gaseous state. The compressor pumps the refrigerant gas up to high pressure and temperature.
  • From there it enters a heat exchanger (sometimes called a condensing coil or condenser) where it loses heat to the outside, cools, and condenses into its liquid phase.
  • An expansion valve (also called metering device) regulates the refrigerant liquid to flow at the proper rate.
  • The liquid refrigerant is returned to another heat exchanger where it is allowed to evaporate, hence the heat exchanger is often called an evaporating coil or evaporator. As the liquid refrigerant evaporates it absorbs heat from the inside air, returns to the compressor, and repeats the cycle. In the process, heat is absorbed from indoors and transferred outdoors, resulting in cooling of the building.

In variable climates, the system may include a reversing valve that switches from heating in winter to cooling in summer. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa. This allows a facility to be heated and cooled by a single piece of equipment by the same means, and with the same hardware.

Free cooling

Main article: Free cooling

Free cooling systems can have very high efficiencies, and are sometimes combined with seasonal thermal energy storage so that the cold of winter can be used for summer air conditioning. Common storage mediums are deep aquifers or a natural underground rock mass accessed via a cluster of small-diameter, heat-exchanger-equipped boreholes. Some systems with small storages are hybrids, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added-in because the storage acts as a heat sink when the system is in cooling (as opposed to charging) mode, causing the temperature to gradually increase during the cooling season.

Some systems include an "economizer mode", which is sometimes called a "free-cooling mode". When economizing, the control system will open (fully or partially) the outside air damper and close (fully or partially) the return air damper. This will cause fresh, outside air to be supplied to the system. When the outside air is cooler than the demanded cool air, this will allow the demand to be met without using the mechanical supply of cooling (typically chilled water or a direct expansion "DX" unit), thus saving energy. The control system can compare the temperature of the outside air vs. return air, or it can compare the enthalpy of the air, as is frequently done in climates where humidity is more of an issue. In both cases, the outside air must be less energetic than the return air for the system to enter the economizer mode.

Packaged vis-à-vis split system

Central, "all-air" air-conditioning systems (or package systems) with a combined outdoor condenser/evaporator unit are often installed in North American residences, offices, and public buildings, but are difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required.[23] (Minisplit ductless systems are used in these situations.) Outside of North America, packaged systems are only used in limited applications involving large indoor space such as stadiums, theatres or exhibition halls.

An alternative to packaged systems is the use of separate indoor and outdoor coils in split systems. Split systems are preferred and widely used worldwide except in North America. In North America, split systems are most often seen in residential applications, but they are gaining popularity in small commercial buildings. Split systems are used where ductwork is not feasible or where the space conditioning efficiency is of prime concern.[24] The benefits of ductless air conditioning systems include easy installation, no ductwork, greater zonal control, flexibility of control, and quiet operation.[25] In space conditioning, the duct losses can account for 30% of energy consumption.[26] The use of minisplits can result in energy savings in space conditioning as there are no losses associated with ducting.

With the split system, the evaporator coil is connected to a remote condenser unit using refrigerant piping between an indoor and outdoor unit instead of ducting air directly from the outdoor unit. Indoor units with directional vents mount onto walls, suspended from ceilings, or fit into the ceiling. Other indoor units mount inside the ceiling cavity so that short lengths of duct handle air from the indoor unit to vents or diffusers around the rooms.

Split systems are more efficient and the footprint is typically smaller than the package systems. On the other hand, package systems tend to have a slightly lower indoor noise level compared to split systems since the fan motor is located outside.

Dehumidification

Dehumidification (air drying) in an air conditioning system is provided by the evaporator. Since the evaporator operates at a temperature below the dew point, moisture in the air condenses on the evaporator coil tubes. This moisture is collected at the bottom of the evaporator in a pan and removed by piping to a central drain or onto the ground outside.

A dehumidifier is an air-conditioner-like device that controls the humidity of a room or building. It is often employed in basements that have a higher relative humidity because of their lower temperature (and propensity for damp floors and walls). In food retailing establishments, large open chiller cabinets are highly effective at dehumidifying the internal air. Conversely, a humidifier increases the humidity of a building.

The HVAC components that dehumidify the ventilation air deserve careful attention because outdoor air constitutes most of the annual humidity load for nearly all buildings.[27]

Humidification

Main article: Humidifier

Maintenance

All modern air conditioning systems, even small window package units, are equipped with internal air filters. These are generally of a lightweight gauze-like material, and must be replaced or washed as conditions warrant. For example, a building in a high dust environment, or a home with furry pets, will need to have the filters changed more often than buildings without these dirt loads. Failure to replace these filters as needed will contribute to a lower heat exchange rate, resulting in wasted energy, shortened equipment life, and higher energy bills; low air flow can result in iced-over evaporator coils, which can completely stop airflow. Additionally, very dirty or plugged filters can cause overheating during a heating cycle, which can result in damage to the system or even fire.

Because an air conditioner moves heat between the indoor coil and the outdoor coil, both must be kept clean. This means that, in addition to replacing the air filter at the evaporator coil, it is also necessary to regularly clean the condenser coil. Failure to keep the condenser clean will eventually result in harm to the compressor because the condenser coil is responsible for discharging both the indoor heat (as picked up by the evaporator) and the heat generated by the electric motor driving the compressor.

Energy efficiency

HVAC is significantly responsible for promoting energy efficiency of buildings as the building sector consumes the largest percentage of global energy.[28] Since the 1980s, manufacturers of HVAC equipment have been making an effort to make the systems they manufacture more efficient. This was originally driven by rising energy costs, and has more recently been driven by increased awareness of environmental issues. Additionally, improvements to the HVAC system efficiency can also help increase occupant health and productivity.[29] In the US, the EPA has imposed tighter restrictions over the years. There are several methods for making HVAC systems more efficient.

Heating energy

In the past, water heating was more efficient for heating buildings and was the standard in the United States. Today, forced air systems can double for air conditioning and are more popular.

Some benefits of forced air systems, which are now widely used in churches, schools, and high-end residences, are

  • Better air conditioning effects
  • Energy savings of up to 15-20%
  • Even conditioning[citation needed]

A drawback is the installation cost, which can be slightly higher than traditional HVAC systems.

Energy efficiency can be improved even more in central heating systems by introducing zoned heating. This allows a more granular application of heat, similar to non-central heating systems. Zones are controlled by multiple thermostats. In water heating systems the thermostats control zone valves, and in forced air systems they control zone dampers inside the vents which selectively block the flow of air. In this case, the control system is very critical to maintaining a proper temperature.

Forecasting is another method of controlling building heating by calculating the demand for heating energy that should be supplied to the building in each time unit.

Ground source heat pump

Main article: Geothermal heat pump

Ground source, or geothermal, heat pumps are similar to ordinary heat pumps, but instead of transferring heat to or from outside air, they rely on the stable, even temperature of the earth to provide heating and air conditioning. Many regions experience seasonal temperature extremes, which would require large-capacity heating and cooling equipment to heat or cool buildings. For example, a conventional heat pump system used to heat a building in Montana's −57 °C (−70 °F) low temperature or cool a building in the highest temperature ever recorded in the US—57 °C (134 °F) in Death Valley, California, in 1913 would require a large amount of energy due to the extreme difference between inside and outside air temperatures. A metre below the earth's surface, however, the ground remains at a relatively constant temperature. Utilizing this large source of relatively moderate temperature earth, a heating or cooling system's capacity can often be significantly reduced. Although ground temperatures vary according to latitude, at 1.8 metres (6 ft) underground, temperatures generally only range from 7 to 24 °C (45 to 75 °F).

Solar air conditioning

Main article: Solar air conditioning

Photovoltaic solar panels offer a new way to potentially decrease the operating cost of air conditioning. Traditional air conditioners run using alternating current, and hence, any direct-current solar power needs to be inverted to be compatible with these units. New variable-speed DC-motor units allow solar power to more easily run them since this conversion is unnecessary, and since the motors are tolerant of voltage fluctuations associated with variance in supplied solar power (e.g., due to cloud cover).

Ventilation energy recovery

Energy recovery systems sometimes utilize heat recovery ventilation or energy recovery ventilation systems that employ heat exchangers or enthalpy wheels to recover sensible or latent heat from exhausted air. This is done by transfer of energy from the stale air inside the home to the incoming fresh air from outside.

Air conditioning energy

The performance of vapor compression refrigeration cycles is limited by thermodynamics.[30] These air conditioning and heat pump devices move heat rather than convert it from one form to another, so thermal efficiencies do not appropriately describe the performance of these devices. The Coefficient of performance (COP) measures performance, but this dimensionless measure has not been adopted. Instead, the Energy Efficiency Ratio (EER) has traditionally been used to characterize the performance of many HVAC systems. EER is the Energy Efficiency Ratio based on a 35 °C (95 °F) outdoor temperature. To more accurately describe the performance of air conditioning equipment over a typical cooling season a modified version of the EER, the Seasonal Energy Efficiency Ratio (SEER), or in Europe the ESEER, is used. SEER ratings are based on seasonal temperature averages instead of a constant 35 °C (95 °F) outdoor temperature. The current industry minimum SEER rating is 14 SEER.[31] Engineers have pointed out some areas where efficiency of the existing hardware could be improved. For example, the fan blades used to move the air are usually stamped from sheet metal, an economical method of manufacture, but as a result they are not aerodynamically efficient. A well-designed blade could reduce the electrical power required to move the air by a third.[32]

Demand controlled kitchen ventilation

Main article: Demand controlled ventilation

Demand controlled kitchen ventilation (DCKV) is a building controls approach to controlling the volume of kitchen exhaust and supply air in response to the actual cooking loads in a commercial kitchen. Traditional commercial kitchen ventilation systems operate at 100% fan speed independent of the volume of cooking activity and DCKV technology changes that to provide significant fan energy and conditioned air savings. By deploying smart sensing technology, both the exhaust and supply fans can be controlled to capitalize on the affinity laws for motor energy savings, reduce makeup air heating and cooling energy, increasing safety, and reducing ambient kitchen noise levels.[33]

Air filtration and cleaning

Main article: Air filter
 
Air handling unit, used for heating, cooling, and filtering the air

Air cleaning and filtration removes particles, contaminants, vapors and gases from the air. The filtered and cleaned air then is used in heating, ventilation, and air conditioning. Air cleaning and filtration should be taken in account when protecting our building environments.[34]

Clean air delivery rate (CADR) is the amount of clean air an air cleaner provides to a room or space. When determining CADR, the amount of airflow in a space is taken into account. For example, an air cleaner with a flow rate of 30 cubic metres (1,000 cu ft) per minute and an efficiency of 50% has a CADR of 15 cubic metres (500 cu ft) per minute. Along with CADR, filtration performance is very important when it comes to the air in our indoor environment. This depends on the size of the particle or fiber, the filter packing density and depth, and the airflow rate.[34]

Industry and standards

The HVAC industry is a worldwide enterprise, with roles including operation and maintenance, system design and construction, equipment manufacturing and sales, and in education and research. The HVAC industry was historically regulated by the manufacturers of HVAC equipment, but regulating and standards organizations such as HARDI (Heating, Air-conditioning and Refrigeration Distributors International), ASHRAE, SMACNA, ACCA (Air Conditioning Contractors of America), Uniform Mechanical Code, International Mechanical Code, and AMCA have been established to support the industry and encourage high standards and achievement. (UL as an omnibus agency is not specific to the HVAC industry.)

The starting point in carrying out an estimate both for cooling and heating depends on the exterior climate and interior specified conditions. However, before taking up the heat load calculation, it is necessary to find fresh air requirements for each area in detail, as pressurization is an important consideration.

International

ISO 16813:2006 is one of the ISO building environment standards.[35] It establishes the general principles of building environment design. It takes into account the need to provide a healthy indoor environment for the occupants as well as the need to protect the environment for future generations and promote collaboration among the various parties involved in building environmental design for sustainability. ISO16813 is applicable to new construction and the retrofit of existing buildings.[36]

The building environmental design standard aims to:[36]

  • provide the constraints concerning sustainability issues from the initial stage of the design process, with building and plant life cycle to be considered together with owning and operating costs from the beginning of the design process;
  • assess the proposed design with rational criteria for indoor air quality, thermal comfort, acoustical comfort, visual comfort, energy efficiency, and HVAC system controls at every stage of the design process;
  • iterate decisions and evaluations of the design throughout the design process.

United States

Main article: American Society of Heating, Refrigerating and Air-Conditioning Engineers
See also: Section 608 EPA Certification

In the United States, HVAC engineers generally are members of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), EPA certified (for installation and service of HVAC devices), or locally engineer certified such as a Special to Chief Boilers License issued by the state or, in some jurisdictions, the city. ASHRAE is an international technical society for all individuals and organizations interested in HVAC. The Society, organized into regions, chapters, and student branches, allows the exchange of HVAC knowledge and experiences for the benefit of the field's practitioners and the public. ASHRAE provides many opportunities to participate in the development of new knowledge via, for example, research and its many technical committees. These committees typically meet twice per year at the ASHRAE Annual and Winter Meetings. A popular product show, the AHR Expo, has been held in conjunction with each winter ASHRAE meeting. The Society has approximately 50,000 members and has headquarters in Atlanta, Georgia.

The most recognized standards for HVAC design are based on ASHRAE data. The four volumes of most popular ASHRAE Handbooks are Fundamentals, Refrigeration, HVAC Applications, and HVAC Systems and Equipment. The current versions of the four handbooks are shown below:[37]

  • 2020 ASHRAE Handbook—HVAC Systems and Equipment
  • 2019 ASHRAE Handbook—HVAC Applications
  • 2018 ASHRAE Handbook—Refrigeration
  • 2017 ASHRAE Handbook—Fundamentals

Each volume of the ASHRAE Handbook is updated every four years. The Fundamentals Handbook includes heating and cooling calculations. The design professional must consult ASHRAE data for the standards of design and care as the typical building codes provide little to no information on HVAC design practices; codes such as the UMC and IMC do include much detail on installation requirements, however. Other useful reference materials include items from SMACNA, ACGIH, and technical trade journals.

American design standards are legislated in the Uniform Mechanical Code or International Mechanical Code. In certain states, counties, or cities, either of these codes may be adopted and amended via various legislative processes. These codes are updated and published by the International Association of Plumbing and Mechanical Officials (IAPMO) or the International Code Council (ICC) respectively, on a 3-year code development cycle. Typically, local building permit departments are charged with enforcement of these standards on private and certain public properties.

Technicians

HVAC Technician
Occupation
Occupation type
Vocational
Activity sectors
Construction
Description
Education required
Apprenticeship
Related jobs
Carpenter, electrician, plumber, welder

An HVAC technician is a tradesman who specializes in heating, ventilation, air conditioning, and refrigeration. HVAC technicians in the US can receive training through formal training institutions, where most earn associate degrees. Training for HVAC technicians includes classroom lectures and hands-on tasks, and can be followed by an apprenticeship wherein the recent graduate works alongside a professional HVAC technician for a temporary period.[citation needed] HVAC techs who have been trained can also be certified in areas such as air conditioning, heat pumps, gas heating, and commercial refrigeration.

United Kingdom

The Chartered Institution of Building Services Engineers is a body that covers the essential Service (systems architecture) that allow buildings to operate. It includes the electrotechnical, heating, ventilating, air conditioning, refrigeration and plumbing industries. To train as a building services engineer, the academic requirements are GCSEs (A-C) / Standard Grades (1-3) in Maths and Science, which are important in measurements, planning and theory. Employers will often want a degree in a branch of engineering, such as building environment engineering, electrical engineering or mechanical engineering. To become a full member of CIBSE, and so also to be registered by the Engineering Council UK as a chartered engineer, engineers must also attain an Honours Degree and a master's degree in a relevant engineering subject.[citation needed] CIBSE publishes several guides to HVAC design relevant to the UK market, and also the Republic of Ireland, Australia, New Zealand and Hong Kong. These guides include various recommended design criteria and standards, some of which are cited within the UK building regulations, and therefore form a legislative requirement for major building services works. The main guides are:

  • Guide A: Environmental Design
  • Guide B: Heating, Ventilating, Air Conditioning and Refrigeration
  • Guide C: Reference Data
  • Guide D: Transportation systems in Buildings
  • Guide E: Fire Safety Engineering
  • Guide F: Energy Efficiency in Buildings
  • Guide G: Public Health Engineering
  • Guide H: Building Control Systems
  • Guide J: Weather, Solar and Illuminance Data
  • Guide K: Electricity in Buildings
  • Guide L: Sustainability
  • Guide M: Maintenance Engineering and Management

Within the construction sector, it is the job of the building services engineer to design and oversee the installation and maintenance of the essential services such as gas, electricity, water, heating and lighting, as well as many others. These all help to make buildings comfortable and healthy places to live and work in. Building Services is part of a sector that has over 51,000 businesses and employs represents 2%-3% of the GDP.

Australia

The Air Conditioning and Mechanical Contractors Association of Australia (AMCA), Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH), Australian Refrigeration Mechanical Association and CIBSE are responsible.

Asia

Asian architectural temperature-control have different priorities than European methods. For example, Asian heating traditionally focuses on maintaining temperatures of objects such as the floor or furnishings such as Kotatsu tables and directly warming people, as opposed to the Western focus, in modern periods, on designing air systems.

Philippines

The Philippine Society of Ventilating, Air Conditioning and Refrigerating Engineers (PSVARE) along with Philippine Society of Mechanical Engineers (PSME) govern on the codes and standards for HVAC / MVAC (MVAC means "mechanical ventilation and air conditioning") in the Philippines.

India

The Indian Society of Heating, Refrigerating and Air Conditioning Engineers (ISHRAE) was established to promote the HVAC industry in India. ISHRAE is an associate of ASHRAE. ISHRAE was founded at New Delhi[38] in 1981 and a chapter was started in Bangalore in 1989. Between 1989 & 1993, ISHRAE chapters were formed in all major cities in India.[citation needed]

See also

References

  1. ^ "HVAC". Merriam–Webster Dictionary.
  2. ^ a b Ventilation and Infiltration chapter, Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, 2005
  3. ^ Designer's Guide to Ceiling-Based Air Diffusion, Rock and Zhu, ASHRAE, Inc., New York, 2002
  4. ^ Rezaie, Behnaz; Rosen, Marc A. (2012). "District heating and cooling: Review of technology and potential enhancements". Applied Energy. 93: 2–10. doi:10.1016/j.apenergy.2011.04.020.
  5. ^ Werner S. (2006). 2015-09-24 at the Wayback Machine
  6. ^ Dalin P., Rubenhag A. (2006). ECOHEATCOOL (WP5) Possibilities with more district cooling in Europe, final report from the project. Final Rep. Brussels: Euroheat & Power. 2012-10-15 at the Wayback Machine
  7. ^ Nielsen, Jan Erik (2014).
  8. ^ Wong B., Thornton J. (2013). . Renewable Heat Workshop.
  9. ^ Pauschinger T. (2012). Solar District Heating with Seasonal Thermal Energy Storage in Germany 2016-10-18 at the Wayback Machine. European Sustainable Energy Week, Brussels. 18–22 June 2012.
  10. ^ "How Renewable Energy Is Redefining HVAC | AltEnergyMag". www.altenergymag.com. Retrieved 2020-09-29.
  11. ^ ""Lake Source" Heat Pump System". HVAC-Talk: Heating, Air & Refrigeration Discussion. Retrieved 2020-09-29.
  12. ^ Swenson, S. Don (1995). HVAC: heating, ventilating, and air conditioning. Homewood, Illinois: American Technical Publishers. ISBN 978-0-8269-0675-5.
  13. ^ . Coyne College. Archived from the original on August 28, 2016.
  14. ^ Iain Staffell, Dan Brett, Nigel Brandon and Adam Hawkes (30 May 2014). "A review of domestic heat pumps".{{cite web}}: CS1 maint: multiple names: authors list (link)
  15. ^ (Alta.), Edmonton. Edmonton's green home guide : you're gonna love green. OCLC 884861834.
  16. ^ Bearg, David W. (1993). Indoor Air Quality and HVAC Systems. New York: Lewis Publishers. pp. 107–112.
  17. ^ Dianat, Nazari, I,I. "Characteristic of unintentional carbon monoxide poisoning in Northwest Iran- Tabriz". International Journal of Injury Control and Promotion. Retrieved 2011-11-15.
  18. ^ Ventilation and Infiltration chapter, Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, Georgia, 2005
  19. ^ "Air Change Rates for typical Rooms and Buildings". The Engineering ToolBox. Retrieved 2012-12-12.
  20. ^ Bell, Geoffrey. "Room Air Change Rate". A Design Guide for Energy-Efficient Research Laboratories. Retrieved 2011-11-15.
  21. ^ "Natural Ventilation for Infection Control in Health-Care Settings" (PDF). World Health Organization (WHO), 2009. Retrieved 2021-07-05.
  22. ^ Escombe, A. R.; Oeser, C. C.; Gilman, R. H.; et al. (2007). "Natural ventilation for the prevention of airborne contagion". PLOS Med. 4 (68): e68. doi:10.1371/journal.pmed.0040068. PMC 1808096. PMID 17326709.
  23. ^ "What are Air Ducts? The Homeowner's Guide to HVAC Ductwork". Super Tech. Retrieved 2018-05-14.{{cite web}}: CS1 maint: url-status (link)
  24. ^ "Ductless Mini-Split Heat Pumps". U.S. Department of Energy.
  25. ^ "The Pros and Cons of Ductless Mini Split Air Conditioners". Home Reference. 28 July 2018. Retrieved 9 September 2020.{{cite web}}: CS1 maint: url-status (link)
  26. ^ "Ductless Mini-Split Air Conditioners". ENERGY SAVER. Retrieved 29 November 2019.{{cite web}}: CS1 maint: url-status (link)
  27. ^ Moisture Control Guidance for Building Design, Construction and Maintenance. December 2013.
  28. ^ Chenari, B., Dias Carrilho, J. and Gameiro da Silva, M., 2016. Towards sustainable, energy-efficient and healthy ventilation strategies in buildings: A review. Renewable and Sustainable Energy Reviews, 59, pp.1426-1447.
  29. ^ "Sustainable Facilities Tool: HVAC System Overview". sftool.gov. Retrieved 2 July 2014.
  30. ^ "Heating and Air Conditioning". www.nuclear-power.net. Retrieved 2018-02-10.
  31. ^ "What Does SEER Stand For?". www.airrepairpros.com. 2015-09-07. Retrieved 2015-09-07.
  32. ^ Keeping cool and green, The Economist 17 July 2010, p. 83
  33. ^ "Technology Profile: Demand Control Kitchen Ventilation (DCKV)" (PDF). Retrieved 2018-12-04.
  34. ^ a b Howard, J (2003), Guidance for Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks, National Institute for Occupational Safety and Health, doi:10.26616/NIOSHPUB2003136, 2003-136
  35. ^ ISO. "Building environment standards". www.iso.org. Retrieved 2011-05-14.
  36. ^ a b ISO. "Building environment design—Indoor environment—General principles". Retrieved 14 May 2011.
  37. ^ "ASHRAE Handbook Online". www.ashrae.org. Retrieved 2020-06-17.
  38. ^ "About ISHRAE". ISHRAE. Retrieved 2021-10-11.

Further reading

  • (2012 (Second Printing)) by the International Code Council, Thomson Delmar Learning.
  • Modern Refrigeration and Air Conditioning (August 2003) by Althouse, Turnquist, and Bracciano, Goodheart-Wilcox Publisher; 18th edition.
  • The Cost of Cool.

External links

  •   Media related to Climate control at Wikimedia Commons

January 15, 2023
heating, ventilation, conditioning, hvac, redirects, here, hvac, also, refer, high, voltage, alternating, current, hvac, various, technologies, control, temperature, humidity, purity, enclosed, space, goal, provide, thermal, comfort, acceptable, indoor, qualit. HVAC redirects here HVAC may also refer to high voltage alternating current Heating ventilation and air conditioning HVAC 1 is the use of various technologies to control the temperature humidity and purity of the air in an enclosed space Its goal is to provide thermal comfort and acceptable indoor air quality HVAC system design is a subdiscipline of mechanical engineering based on the principles of thermodynamics fluid mechanics and heat transfer Refrigeration is sometimes added to the field s abbreviation as HVAC amp R or HVACR or ventilation is dropped as in HACR as in the designation of HACR rated circuit breakers Rooftop HVAC unit with view of fresh air intake vent Ventilation duct with outlet diffuser vent These are installed throughout a building to move air in or out of rooms In the middle is a damper to open and close the vent to allow more or less air to enter the space The control circuit in a household HVAC installation The wires connecting to the blue terminal block on the upper right of the board lead to the thermostat The fan enclosure is directly behind the board and the filters can be seen at the top The safety interlock switch is at the bottom left In the lower middle is the capacitor HVAC is an important part of residential structures such as single family homes apartment buildings hotels and senior living facilities medium to large industrial and office buildings such as skyscrapers and hospitals vehicles such as cars trains airplanes ships and submarines and in marine environments where safe and healthy building conditions are regulated with respect to temperature and humidity using fresh air from outdoors Ventilating or ventilation the V in HVAC is the process of exchanging or replacing air in any space to provide high indoor air quality which involves temperature control oxygen replenishment and removal of moisture odors smoke heat dust airborne bacteria carbon dioxide and other gases Ventilation removes unpleasant smells and excessive moisture introduces outside air keeps interior building air circulating and prevents stagnation of the interior air Methods for ventilating a building are divided into mechanical forced and natural types 2 Contents 1 Overview 1 1 Individual systems 1 2 District networks 2 History 3 Heating 3 1 Generation 3 2 Distribution 3 2 1 Water steam 3 2 2 Air 3 3 Dangers 4 Ventilation 4 1 Mechanical or forced 4 2 Passive 4 2 1 Airborne diseases 5 Air conditioning 5 1 Refrigeration cycle 5 2 Free cooling 5 3 Packaged vis a vis split system 5 4 Dehumidification 5 5 Humidification 5 6 Maintenance 6 Energy efficiency 6 1 Heating energy 6 2 Ground source heat pump 6 3 Solar air conditioning 6 4 Ventilation energy recovery 6 5 Air conditioning energy 6 6 Demand controlled kitchen ventilation 7 Air filtration and cleaning 8 Industry and standards 8 1 International 8 2 United States 8 2 1 Technicians 8 3 United Kingdom 8 4 Australia 8 5 Asia 8 5 1 Philippines 8 5 2 India 9 See also 10 References 11 Further reading 12 External linksOverview EditThe three major functions of heating ventilation and air conditioning are interrelated especially with the need to provide thermal comfort and acceptable indoor air quality within reasonable installation operation and maintenance costs HVAC systems can be used in both domestic and commercial environments HVAC systems can provide ventilation and maintain pressure relationships between spaces The means of air delivery and removal from spaces is known as room air distribution 3 Individual systems Edit See also HVAC control system In modern buildings the design installation and control systems of these functions are integrated into one or more HVAC systems For very small buildings contractors normally estimate the capacity and type of system needed and then design the system selecting the appropriate refrigerant and various components needed For larger buildings building service designers mechanical engineers or building services engineers analyze design and specify the HVAC systems Specialty mechanical contractors and suppliers then fabricate install and commission the systems Building permits and code compliance inspections of the installations are normally required for all sizes of buildings District networks Edit Although HVAC is executed in individual buildings or other enclosed spaces like NORAD s underground headquarters the equipment involved is in some cases an extension of a larger district heating DH or district cooling DC network or a combined DHC network In such cases the operating and maintenance aspects are simplified and metering becomes necessary to bill for the energy that is consumed and in some cases energy that is returned to the larger system For example at a given time one building may be utilizing chilled water for air conditioning and the warm water it returns may be used in another building for heating or for the overall heating portion of the DHC network likely with energy added to boost the temperature 4 5 6 Basing HVAC on a larger network helps provide an economy of scale that is often not possible for individual buildings for utilizing renewable energy sources such as solar heat 7 8 9 winter s cold 10 11 the cooling potential in some places of lakes or seawater for free cooling and the enabling function of seasonal thermal energy storage By utilizing natural sources that can be used for HVAC systems it can make a huge difference for the environment and help expand the knowledge of using different methods History EditSee also Air conditioning History HVAC is based on inventions and discoveries made by Nikolay Lvov Michael Faraday Rolla C Carpenter Willis Carrier Edwin Ruud Reuben Trane James Joule William Rankine Sadi Carnot and many others 12 Multiple inventions within this time frame preceded the beginnings of the first comfort air conditioning system which was designed in 1902 by Alfred Wolff Cooper 2003 for the New York Stock Exchange while Willis Carrier equipped the Sacketts Wilhems Printing Company with the process AC unit the same year Coyne College was the first school to offer HVAC training in 1899 13 The invention of the components of HVAC systems went hand in hand with the industrial revolution and new methods of modernization higher efficiency and system control are constantly being introduced by companies and inventors worldwide Heating EditMain article Central heating Heater redirects here For other uses see Heater disambiguation Heaters are appliances whose purpose is to generate heat i e warmth for the building This can be done via central heating Such a system contains a boiler furnace or heat pump to heat water steam or air in a central location such as a furnace room in a home or a mechanical room in a large building The heat can be transferred by convection conduction or radiation Space heaters are used to heat single rooms and only consist of a single unit Generation Edit Central heating unit Heaters exist for various types of fuel including solid fuels liquids and gases Another type of heat source is electricity normally heating ribbons composed of high resistance wire see Nichrome This principle is also used for baseboard heaters and portable heaters Electrical heaters are often used as backup or supplemental heat for heat pump systems The heat pump gained popularity in the 1950s in Japan and the United States 14 Heat pumps can extract heat from various sources such as environmental air exhaust air from a building or from the ground Heat pumps transfer heat from outside the structure into the air inside Initially heat pump HVAC systems were only used in moderate climates but with improvements in low temperature operation and reduced loads due to more efficient homes they are increasing in popularity in cooler climates they can also operate in reverse by cooling an interior Distribution Edit Water steam Edit In the case of heated water or steam piping is used to transport the heat to the rooms Most modern hot water boiler heating systems have a circulator which is a pump to move hot water through the distribution system as opposed to older gravity fed systems The heat can be transferred to the surrounding air using radiators hot water coils hydro air or other heat exchangers The radiators may be mounted on walls or installed within the floor to produce floor heat The use of water as the heat transfer medium is known as hydronics The heated water can also supply an auxiliary heat exchanger to supply hot water for bathing and washing Air Edit Main articles Room air distribution and Underfloor air distribution Warm air systems distribute the heated air through ductwork systems of supply and return air through metal or fiberglass ducts Many systems use the same ducts to distribute air cooled by an evaporator coil for air conditioning The air supply is normally filtered through air filters to remove dust and pollen particles 15 Dangers Edit The use of furnaces space heaters and boilers as a method of indoor heating could result in incomplete combustion and the emission of carbon monoxide nitrogen oxides formaldehyde volatile organic compounds and other combustion byproducts Incomplete combustion occurs when there is insufficient oxygen the inputs are fuels containing various contaminants and the outputs are harmful byproducts most dangerously carbon monoxide which is a tasteless and odorless gas with serious adverse health effects 16 Without proper ventilation carbon monoxide can be lethal at concentrations of 1000 ppm 0 1 However at several hundred ppm carbon monoxide exposure induces headaches fatigue nausea and vomiting Carbon monoxide binds with hemoglobin in the blood forming carboxyhemoglobin reducing the blood s ability to transport oxygen The primary health concerns associated with carbon monoxide exposure are its cardiovascular and neurobehavioral effects Carbon monoxide can cause atherosclerosis the hardening of arteries and can also trigger heart attacks Neurologically carbon monoxide exposure reduces hand to eye coordination vigilance and continuous performance It can also affect time discrimination 17 Ventilation EditMain article Ventilation architecture Ventilation is the process of changing or replacing air in any space to control the temperature or remove any combination of moisture odors smoke heat dust airborne bacteria or carbon dioxide and to replenish oxygen Ventilation often refers to the intentional delivery of the outside air to the building indoor space It is one of the most important factors for maintaining acceptable indoor air quality in buildings Methods for ventilating a building may be divided into mechanical forced and natural types 18 Mechanical or forced Edit Further information Ventilation architecture Mechanical systems HVAC ventilation exhaust for a 12 story building Mechanical or forced ventilation is provided by an air handler AHU and used to control indoor air quality Excess humidity odors and contaminants can often be controlled via dilution or replacement with outside air However in humid climates more energy is required to remove excess moisture from ventilation air Kitchens and bathrooms typically have mechanical exhausts to control odors and sometimes humidity Factors in the design of such systems include the flow rate which is a function of the fan speed and exhaust vent size and noise level Direct drive fans are available for many applications and can reduce maintenance needs In summer ceiling fans and table floor fans circulate air within a room for the purpose of reducing the perceived temperature by increasing evaporation of perspiration on the skin of the occupants Because hot air rises ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor Passive Edit Main article Passive ventilation Ventilation on the downdraught system by impulsion or the plenum principle applied to schoolrooms 1899 Natural ventilation is the ventilation of a building with outside air without using fans or other mechanical systems It can be via operable windows louvers or trickle vents when spaces are small and the architecture permits ASHRAE defined Natural ventilation as the flow of air through open windows doors grilles and other planned building envelope penetrations and as being driven by natural and or artificially produced pressure differentials 2 In more complex schemes warm air is allowed to rise and flow out high building openings to the outside stack effect causing cool outside air to be drawn into low building openings Natural ventilation schemes can use very little energy but care must be taken to ensure comfort In warm or humid climates maintaining thermal comfort solely via natural ventilation might not be possible Air conditioning systems are used either as backups or supplements Air side economizers also use outside air to condition spaces but do so using fans ducts dampers and control systems to introduce and distribute cool outdoor air when appropriate An important component of natural ventilation is air change rate or air changes per hour the hourly rate of ventilation divided by the volume of the space For example six air changes per hour means an amount of new air equal to the volume of the space is added every ten minutes For human comfort a minimum of four air changes per hour is typical though warehouses might have only two Too high of an air change rate may be uncomfortable akin to a wind tunnel which has thousands of changes per hour The highest air change rates are for crowded spaces bars night clubs commercial kitchens at around 30 to 50 air changes per hour 19 Room pressure can be either positive or negative with respect to outside the room Positive pressure occurs when there is more air being supplied than exhausted and is common to reduce the infiltration of outside contaminants 20 Airborne diseases Edit Natural ventilation 21 is a key factor in reducing the spread of airborne illnesses such as tuberculosis the common cold influenza meningitis or COVID 19 Opening doors and windows are good ways to maximize natural ventilation which would make the risk of airborne contagion much lower than with costly and maintenance requiring mechanical systems Old fashioned clinical areas with high ceilings and large windows provide the greatest protection Natural ventilation costs little and is maintenance free and is particularly suited to limited resource settings and tropical climates where the burden of TB and institutional TB transmission is highest In settings where respiratory isolation is difficult and climate permits windows and doors should be opened to reduce the risk of airborne contagion Natural ventilation requires little maintenance and is inexpensive 22 Air conditioning EditMain article Air conditioning An air conditioning system or a standalone air conditioner provides cooling and or humidity control for all or part of a building Air conditioned buildings often have sealed windows because open windows would work against the system intended to maintain constant indoor air conditions Outside fresh air is generally drawn into the system by a vent into a mix air chamber for mixing with the space return air Then the mixture air enters an indoor or outdoor heat exchanger section where the air is to be cooled down then be guided to the space creating positive air pressure The percentage of return air made up of fresh air can usually be manipulated by adjusting the opening of this vent Typical fresh air intake is about 10 of the total supply air citation needed Air conditioning and refrigeration are provided through the removal of heat Heat can be removed through radiation convection or conduction The heat transfer medium is a refrigeration system such as water air ice and chemicals are referred to as refrigerants A refrigerant is employed either in a heat pump system in which a compressor is used to drive thermodynamic refrigeration cycle or in a free cooling system that uses pumps to circulate a cool refrigerant typically water or a glycol mix It is imperative that the air conditioning horsepower is sufficient for the area being cooled Underpowered air conditioning systems will lead to power wastage and inefficient usage Adequate horsepower is required for any air conditioner installed Refrigeration cycle Edit Main article Heat pump and refrigeration cycle A simple stylized diagram of the refrigeration cycle 1 condensing coil 2 expansion valve 3 evaporating coil 4 compressor The refrigeration cycle uses four essential elements to cool which are compressor condenser metering device and evaporator At the inlet of a compressor the refrigerant inside the system is in a low pressure low temperature gaseous state The compressor pumps the refrigerant gas up to high pressure and temperature From there it enters a heat exchanger sometimes called a condensing coil or condenser where it loses heat to the outside cools and condenses into its liquid phase An expansion valve also called metering device regulates the refrigerant liquid to flow at the proper rate The liquid refrigerant is returned to another heat exchanger where it is allowed to evaporate hence the heat exchanger is often called an evaporating coil or evaporator As the liquid refrigerant evaporates it absorbs heat from the inside air returns to the compressor and repeats the cycle In the process heat is absorbed from indoors and transferred outdoors resulting in cooling of the building In variable climates the system may include a reversing valve that switches from heating in winter to cooling in summer By reversing the flow of refrigerant the heat pump refrigeration cycle is changed from cooling to heating or vice versa This allows a facility to be heated and cooled by a single piece of equipment by the same means and with the same hardware Free cooling Edit Main article Free cooling Free cooling systems can have very high efficiencies and are sometimes combined with seasonal thermal energy storage so that the cold of winter can be used for summer air conditioning Common storage mediums are deep aquifers or a natural underground rock mass accessed via a cluster of small diameter heat exchanger equipped boreholes Some systems with small storages are hybrids using free cooling early in the cooling season and later employing a heat pump to chill the circulation coming from the storage The heat pump is added in because the storage acts as a heat sink when the system is in cooling as opposed to charging mode causing the temperature to gradually increase during the cooling season Some systems include an economizer mode which is sometimes called a free cooling mode When economizing the control system will open fully or partially the outside air damper and close fully or partially the return air damper This will cause fresh outside air to be supplied to the system When the outside air is cooler than the demanded cool air this will allow the demand to be met without using the mechanical supply of cooling typically chilled water or a direct expansion DX unit thus saving energy The control system can compare the temperature of the outside air vs return air or it can compare the enthalpy of the air as is frequently done in climates where humidity is more of an issue In both cases the outside air must be less energetic than the return air for the system to enter the economizer mode Packaged vis a vis split system Edit Central all air air conditioning systems or package systems with a combined outdoor condenser evaporator unit are often installed in North American residences offices and public buildings but are difficult to retrofit install in a building that was not designed to receive it because of the bulky air ducts required 23 Minisplit ductless systems are used in these situations Outside of North America packaged systems are only used in limited applications involving large indoor space such as stadiums theatres or exhibition halls An alternative to packaged systems is the use of separate indoor and outdoor coils in split systems Split systems are preferred and widely used worldwide except in North America In North America split systems are most often seen in residential applications but they are gaining popularity in small commercial buildings Split systems are used where ductwork is not feasible or where the space conditioning efficiency is of prime concern 24 The benefits of ductless air conditioning systems include easy installation no ductwork greater zonal control flexibility of control and quiet operation 25 In space conditioning the duct losses can account for 30 of energy consumption 26 The use of minisplits can result in energy savings in space conditioning as there are no losses associated with ducting With the split system the evaporator coil is connected to a remote condenser unit using refrigerant piping between an indoor and outdoor unit instead of ducting air directly from the outdoor unit Indoor units with directional vents mount onto walls suspended from ceilings or fit into the ceiling Other indoor units mount inside the ceiling cavity so that short lengths of duct handle air from the indoor unit to vents or diffusers around the rooms Split systems are more efficient and the footprint is typically smaller than the package systems On the other hand package systems tend to have a slightly lower indoor noise level compared to split systems since the fan motor is located outside Dehumidification Edit Dehumidification air drying in an air conditioning system is provided by the evaporator Since the evaporator operates at a temperature below the dew point moisture in the air condenses on the evaporator coil tubes This moisture is collected at the bottom of the evaporator in a pan and removed by piping to a central drain or onto the ground outside A dehumidifier is an air conditioner like device that controls the humidity of a room or building It is often employed in basements that have a higher relative humidity because of their lower temperature and propensity for damp floors and walls In food retailing establishments large open chiller cabinets are highly effective at dehumidifying the internal air Conversely a humidifier increases the humidity of a building The HVAC components that dehumidify the ventilation air deserve careful attention because outdoor air constitutes most of the annual humidity load for nearly all buildings 27 Humidification Edit Main article Humidifier Maintenance Edit All modern air conditioning systems even small window package units are equipped with internal air filters These are generally of a lightweight gauze like material and must be replaced or washed as conditions warrant For example a building in a high dust environment or a home with furry pets will need to have the filters changed more often than buildings without these dirt loads Failure to replace these filters as needed will contribute to a lower heat exchange rate resulting in wasted energy shortened equipment life and higher energy bills low air flow can result in iced over evaporator coils which can completely stop airflow Additionally very dirty or plugged filters can cause overheating during a heating cycle which can result in damage to the system or even fire Because an air conditioner moves heat between the indoor coil and the outdoor coil both must be kept clean This means that in addition to replacing the air filter at the evaporator coil it is also necessary to regularly clean the condenser coil Failure to keep the condenser clean will eventually result in harm to the compressor because the condenser coil is responsible for discharging both the indoor heat as picked up by the evaporator and the heat generated by the electric motor driving the compressor Energy efficiency EditHVAC is significantly responsible for promoting energy efficiency of buildings as the building sector consumes the largest percentage of global energy 28 Since the 1980s manufacturers of HVAC equipment have been making an effort to make the systems they manufacture more efficient This was originally driven by rising energy costs and has more recently been driven by increased awareness of environmental issues Additionally improvements to the HVAC system efficiency can also help increase occupant health and productivity 29 In the US the EPA has imposed tighter restrictions over the years There are several methods for making HVAC systems more efficient Heating energy Edit In the past water heating was more efficient for heating buildings and was the standard in the United States Today forced air systems can double for air conditioning and are more popular Some benefits of forced air systems which are now widely used in churches schools and high end residences are Better air conditioning effects Energy savings of up to 15 20 Even conditioning citation needed A drawback is the installation cost which can be slightly higher than traditional HVAC systems Energy efficiency can be improved even more in central heating systems by introducing zoned heating This allows a more granular application of heat similar to non central heating systems Zones are controlled by multiple thermostats In water heating systems the thermostats control zone valves and in forced air systems they control zone dampers inside the vents which selectively block the flow of air In this case the control system is very critical to maintaining a proper temperature Forecasting is another method of controlling building heating by calculating the demand for heating energy that should be supplied to the building in each time unit Ground source heat pump Edit Main article Geothermal heat pump Ground source or geothermal heat pumps are similar to ordinary heat pumps but instead of transferring heat to or from outside air they rely on the stable even temperature of the earth to provide heating and air conditioning Many regions experience seasonal temperature extremes which would require large capacity heating and cooling equipment to heat or cool buildings For example a conventional heat pump system used to heat a building in Montana s 57 C 70 F low temperature or cool a building in the highest temperature ever recorded in the US 57 C 134 F in Death Valley California in 1913 would require a large amount of energy due to the extreme difference between inside and outside air temperatures A metre below the earth s surface however the ground remains at a relatively constant temperature Utilizing this large source of relatively moderate temperature earth a heating or cooling system s capacity can often be significantly reduced Although ground temperatures vary according to latitude at 1 8 metres 6 ft underground temperatures generally only range from 7 to 24 C 45 to 75 F Solar air conditioning Edit Main article Solar air conditioning Photovoltaic solar panels offer a new way to potentially decrease the operating cost of air conditioning Traditional air conditioners run using alternating current and hence any direct current solar power needs to be inverted to be compatible with these units New variable speed DC motor units allow solar power to more easily run them since this conversion is unnecessary and since the motors are tolerant of voltage fluctuations associated with variance in supplied solar power e g due to cloud cover Ventilation energy recovery Edit Energy recovery systems sometimes utilize heat recovery ventilation or energy recovery ventilation systems that employ heat exchangers or enthalpy wheels to recover sensible or latent heat from exhausted air This is done by transfer of energy from the stale air inside the home to the incoming fresh air from outside Air conditioning energy Edit The performance of vapor compression refrigeration cycles is limited by thermodynamics 30 These air conditioning and heat pump devices move heat rather than convert it from one form to another so thermal efficiencies do not appropriately describe the performance of these devices The Coefficient of performance COP measures performance but this dimensionless measure has not been adopted Instead the Energy Efficiency Ratio EER has traditionally been used to characterize the performance of many HVAC systems EER is the Energy Efficiency Ratio based on a 35 C 95 F outdoor temperature To more accurately describe the performance of air conditioning equipment over a typical cooling season a modified version of the EER the Seasonal Energy Efficiency Ratio SEER or in Europe the ESEER is used SEER ratings are based on seasonal temperature averages instead of a constant 35 C 95 F outdoor temperature The current industry minimum SEER rating is 14 SEER 31 Engineers have pointed out some areas where efficiency of the existing hardware could be improved For example the fan blades used to move the air are usually stamped from sheet metal an economical method of manufacture but as a result they are not aerodynamically efficient A well designed blade could reduce the electrical power required to move the air by a third 32 Demand controlled kitchen ventilation Edit Main article Demand controlled ventilation Demand controlled kitchen ventilation DCKV is a building controls approach to controlling the volume of kitchen exhaust and supply air in response to the actual cooking loads in a commercial kitchen Traditional commercial kitchen ventilation systems operate at 100 fan speed independent of the volume of cooking activity and DCKV technology changes that to provide significant fan energy and conditioned air savings By deploying smart sensing technology both the exhaust and supply fans can be controlled to capitalize on the affinity laws for motor energy savings reduce makeup air heating and cooling energy increasing safety and reducing ambient kitchen noise levels 33 Air filtration and cleaning EditMain article Air filter Air handling unit used for heating cooling and filtering the air Air cleaning and filtration removes particles contaminants vapors and gases from the air The filtered and cleaned air then is used in heating ventilation and air conditioning Air cleaning and filtration should be taken in account when protecting our building environments 34 Clean air delivery rate CADR is the amount of clean air an air cleaner provides to a room or space When determining CADR the amount of airflow in a space is taken into account For example an air cleaner with a flow rate of 30 cubic metres 1 000 cu ft per minute and an efficiency of 50 has a CADR of 15 cubic metres 500 cu ft per minute Along with CADR filtration performance is very important when it comes to the air in our indoor environment This depends on the size of the particle or fiber the filter packing density and depth and the airflow rate 34 Industry and standards EditThe HVAC industry is a worldwide enterprise with roles including operation and maintenance system design and construction equipment manufacturing and sales and in education and research The HVAC industry was historically regulated by the manufacturers of HVAC equipment but regulating and standards organizations such as HARDI Heating Air conditioning and Refrigeration Distributors International ASHRAE SMACNA ACCA Air Conditioning Contractors of America Uniform Mechanical Code International Mechanical Code and AMCA have been established to support the industry and encourage high standards and achievement UL as an omnibus agency is not specific to the HVAC industry The starting point in carrying out an estimate both for cooling and heating depends on the exterior climate and interior specified conditions However before taking up the heat load calculation it is necessary to find fresh air requirements for each area in detail as pressurization is an important consideration International Edit ISO 16813 2006 is one of the ISO building environment standards 35 It establishes the general principles of building environment design It takes into account the need to provide a healthy indoor environment for the occupants as well as the need to protect the environment for future generations and promote collaboration among the various parties involved in building environmental design for sustainability ISO16813 is applicable to new construction and the retrofit of existing buildings 36 The building environmental design standard aims to 36 provide the constraints concerning sustainability issues from the initial stage of the design process with building and plant life cycle to be considered together with owning and operating costs from the beginning of the design process assess the proposed design with rational criteria for indoor air quality thermal comfort acoustical comfort visual comfort energy efficiency and HVAC system controls at every stage of the design process iterate decisions and evaluations of the design throughout the design process United States Edit Main article American Society of Heating Refrigerating and Air Conditioning Engineers See also Section 608 EPA Certification In the United States HVAC engineers generally are members of the American Society of Heating Refrigerating and Air Conditioning Engineers ASHRAE EPA certified for installation and service of HVAC devices or locally engineer certified such as a Special to Chief Boilers License issued by the state or in some jurisdictions the city ASHRAE is an international technical society for all individuals and organizations interested in HVAC The Society organized into regions chapters and student branches allows the exchange of HVAC knowledge and experiences for the benefit of the field s practitioners and the public ASHRAE provides many opportunities to participate in the development of new knowledge via for example research and its many technical committees These committees typically meet twice per year at the ASHRAE Annual and Winter Meetings A popular product show the AHR Expo has been held in conjunction with each winter ASHRAE meeting The Society has approximately 50 000 members and has headquarters in Atlanta Georgia The most recognized standards for HVAC design are based on ASHRAE data The four volumes of most popular ASHRAE Handbooks are Fundamentals Refrigeration HVAC Applications and HVAC Systems and Equipment The current versions of the four handbooks are shown below 37 2020 ASHRAE Handbook HVAC Systems and Equipment 2019 ASHRAE Handbook HVAC Applications 2018 ASHRAE Handbook Refrigeration 2017 ASHRAE Handbook FundamentalsEach volume of the ASHRAE Handbook is updated every four years The Fundamentals Handbook includes heating and cooling calculations The design professional must consult ASHRAE data for the standards of design and care as the typical building codes provide little to no information on HVAC design practices codes such as the UMC and IMC do include much detail on installation requirements however Other useful reference materials include items from SMACNA ACGIH and technical trade journals American design standards are legislated in the Uniform Mechanical Code or International Mechanical Code In certain states counties or cities either of these codes may be adopted and amended via various legislative processes These codes are updated and published by the International Association of Plumbing and Mechanical Officials IAPMO or the International Code Council ICC respectively on a 3 year code development cycle Typically local building permit departments are charged with enforcement of these standards on private and certain public properties Technicians Edit HVAC TechnicianOccupationOccupation typeVocationalActivity sectorsConstructionDescriptionEducation requiredApprenticeshipRelated jobsCarpenter electrician plumber welderAn HVAC technician is a tradesman who specializes in heating ventilation air conditioning and refrigeration HVAC technicians in the US can receive training through formal training institutions where most earn associate degrees Training for HVAC technicians includes classroom lectures and hands on tasks and can be followed by an apprenticeship wherein the recent graduate works alongside a professional HVAC technician for a temporary period citation needed HVAC techs who have been trained can also be certified in areas such as air conditioning heat pumps gas heating and commercial refrigeration United Kingdom Edit The Chartered Institution of Building Services Engineers is a body that covers the essential Service systems architecture that allow buildings to operate It includes the electrotechnical heating ventilating air conditioning refrigeration and plumbing industries To train as a building services engineer the academic requirements are GCSEs A C Standard Grades 1 3 in Maths and Science which are important in measurements planning and theory Employers will often want a degree in a branch of engineering such as building environment engineering electrical engineering or mechanical engineering To become a full member of CIBSE and so also to be registered by the Engineering Council UK as a chartered engineer engineers must also attain an Honours Degree and a master s degree in a relevant engineering subject citation needed CIBSE publishes several guides to HVAC design relevant to the UK market and also the Republic of Ireland Australia New Zealand and Hong Kong These guides include various recommended design criteria and standards some of which are cited within the UK building regulations and therefore form a legislative requirement for major building services works The main guides are Guide A Environmental Design Guide B Heating Ventilating Air Conditioning and Refrigeration Guide C Reference Data Guide D Transportation systems in Buildings Guide E Fire Safety Engineering Guide F Energy Efficiency in Buildings Guide G Public Health Engineering Guide H Building Control Systems Guide J Weather Solar and Illuminance Data Guide K Electricity in Buildings Guide L Sustainability Guide M Maintenance Engineering and ManagementWithin the construction sector it is the job of the building services engineer to design and oversee the installation and maintenance of the essential services such as gas electricity water heating and lighting as well as many others These all help to make buildings comfortable and healthy places to live and work in Building Services is part of a sector that has over 51 000 businesses and employs represents 2 3 of the GDP Australia Edit The Air Conditioning and Mechanical Contractors Association of Australia AMCA Australian Institute of Refrigeration Air Conditioning and Heating AIRAH Australian Refrigeration Mechanical Association and CIBSE are responsible Asia Edit Asian architectural temperature control have different priorities than European methods For example Asian heating traditionally focuses on maintaining temperatures of objects such as the floor or furnishings such as Kotatsu tables and directly warming people as opposed to the Western focus in modern periods on designing air systems Philippines Edit The Philippine Society of Ventilating Air Conditioning and Refrigerating Engineers PSVARE along with Philippine Society of Mechanical Engineers PSME govern on the codes and standards for HVAC MVAC MVAC means mechanical ventilation and air conditioning in the Philippines India Edit The Indian Society of Heating Refrigerating and Air Conditioning Engineers ISHRAE was established to promote the HVAC industry in India ISHRAE is an associate of ASHRAE ISHRAE was founded at New Delhi 38 in 1981 and a chapter was started in Bangalore in 1989 Between 1989 amp 1993 ISHRAE chapters were formed in all major cities in India citation needed See also EditAir speed HVAC Architectural engineering ASHRAE Handbook Auxiliary power unit Electric heating Fan coil unit Glossary of HVAC terms Head end power Hotel electric power Mechanical engineering Outdoor wood fired boiler Radiant cooling Sick building syndrome Uniform Codes Uniform Mechanical Code Ventilation architecture World Refrigeration Day WrightsoftReferences Edit HVAC Merriam Webster Dictionary a b Ventilation and Infiltration chapter Fundamentals volume of the ASHRAE Handbook ASHRAE Inc Atlanta GA 2005 Designer s Guide to Ceiling Based Air Diffusion Rock and Zhu ASHRAE Inc New York 2002 Rezaie Behnaz Rosen Marc A 2012 District heating and cooling Review of technology and potential enhancements Applied Energy 93 2 10 doi 10 1016 j apenergy 2011 04 020 Werner S 2006 ECOHEATCOOL WP4 Possibilities with more district heating in Europe Euroheat amp Power Brussels Archived 2015 09 24 at the Wayback Machine Dalin P Rubenhag A 2006 ECOHEATCOOL WP5 Possibilities with more district cooling in Europe final report from the project Final Rep Brussels Euroheat amp Power Archived 2012 10 15 at the Wayback Machine Nielsen Jan Erik 2014 Solar District Heating Experiences from Denmark Energy Systems in the Alps storage and distribution Energy Platform Workshop 3 Zurich 13 2 2014 Wong B Thornton J 2013 Integrating Solar amp Heat Pumps Renewable Heat Workshop Pauschinger T 2012 Solar District Heating with Seasonal Thermal Energy Storage in Germany Archived 2016 10 18 at the Wayback Machine European Sustainable Energy Week Brussels 18 22 June 2012 How Renewable Energy Is Redefining HVAC AltEnergyMag www altenergymag com Retrieved 2020 09 29 Lake Source Heat Pump System HVAC Talk Heating Air amp Refrigeration Discussion Retrieved 2020 09 29 Swenson S Don 1995 HVAC heating ventilating and air conditioning Homewood Illinois American Technical Publishers ISBN 978 0 8269 0675 5 History of Heating Air Conditioning amp Refrigeration Coyne College Archived from the original on August 28 2016 Iain Staffell Dan Brett Nigel Brandon and Adam Hawkes 30 May 2014 A review of domestic heat pumps a href Template Cite web html title Template Cite web cite web a CS1 maint multiple names authors list link Alta Edmonton Edmonton s green home guide you re gonna love green OCLC 884861834 Bearg David W 1993 Indoor Air Quality and HVAC Systems New York Lewis Publishers pp 107 112 Dianat Nazari I I Characteristic of unintentional carbon monoxide poisoning in Northwest Iran Tabriz International Journal of Injury Control and Promotion Retrieved 2011 11 15 Ventilation and Infiltration chapter Fundamentals volume of the ASHRAE Handbook ASHRAE Inc Atlanta Georgia 2005 Air Change Rates for typical Rooms and Buildings The Engineering ToolBox Retrieved 2012 12 12 Bell Geoffrey Room Air Change Rate A Design Guide for Energy Efficient Research Laboratories Retrieved 2011 11 15 Natural Ventilation for Infection Control in Health Care Settings PDF World Health Organization WHO 2009 Retrieved 2021 07 05 Escombe A R Oeser C C Gilman R H et al 2007 Natural ventilation for the prevention of airborne contagion PLOS Med 4 68 e68 doi 10 1371 journal pmed 0040068 PMC 1808096 PMID 17326709 What are Air Ducts The Homeowner s Guide to HVAC Ductwork Super Tech Retrieved 2018 05 14 a href Template Cite web html title Template Cite web cite web a CS1 maint url status link Ductless Mini Split Heat Pumps U S Department of Energy The Pros and Cons of Ductless Mini Split Air Conditioners Home Reference 28 July 2018 Retrieved 9 September 2020 a href Template Cite web html title Template Cite web cite web a CS1 maint url status link Ductless Mini Split Air Conditioners ENERGY SAVER Retrieved 29 November 2019 a href Template Cite web html title Template Cite web cite web a CS1 maint url status link Moisture Control Guidance for Building Design Construction and Maintenance December 2013 Chenari B Dias Carrilho J and Gameiro da Silva M 2016 Towards sustainable energy efficient and healthy ventilation strategies in buildings A review Renewable and Sustainable Energy Reviews 59 pp 1426 1447 Sustainable Facilities Tool HVAC System Overview sftool gov Retrieved 2 July 2014 Heating and Air Conditioning www nuclear power net Retrieved 2018 02 10 What Does SEER Stand For www airrepairpros com 2015 09 07 Retrieved 2015 09 07 Keeping cool and green The Economist 17 July 2010 p 83 Technology Profile Demand Control Kitchen Ventilation DCKV PDF Retrieved 2018 12 04 a b Howard J 2003 Guidance for Filtration and Air Cleaning Systems to Protect Building Environments from Airborne Chemical Biological or Radiological Attacks National Institute for Occupational Safety and Health doi 10 26616 NIOSHPUB2003136 2003 136 ISO Building environment standards www iso org Retrieved 2011 05 14 a b ISO Building environment design Indoor environment General principles Retrieved 14 May 2011 ASHRAE Handbook Online www ashrae org Retrieved 2020 06 17 About ISHRAE ISHRAE Retrieved 2021 10 11 Further reading EditInternational Mechanical Code 2012 Second Printing by the International Code Council Thomson Delmar Learning Modern Refrigeration and Air Conditioning August 2003 by Althouse Turnquist and Bracciano Goodheart Wilcox Publisher 18th edition The Cost of Cool External links Edit Media related to Climate control at Wikimedia Commons Retrieved from https en wikipedia org w index php title Heating ventilation and air conditioning amp oldid 1127435210, wikipedia, wiki, book, books, library,

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