HVAC is the generic name for the industry that incorporates portable air conditioners, industrial electric fan heaters, large heaters, commercial dehumidifiers, man cooler fans, warehouse fans, portable ventilation fans, extractor fans, evaporative coolers, fan coil units and portable boilers.
Heating, ventilation, and air conditioning (HVAC) is the technology of environmental comfort within a confined space. The goal of HVAC is to provide thermal comfort and acceptable air quality within that environment. HVAC system design is considered a part of mechanical engineering and uses the principles of thermodynamics, fluid mechanics and heat transfer to achieve it’s primary aim. “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).
HVAC is an essential part factor in modern building design, be that residential structures such as modern family homes, high rise tower blocks, hotels or even sheltered accommodation such as retirement villages, medium to large industrial and office buildings, skyscrapers and hospitals. It is also equally important in vehicular design, with air conditioning systems expected in cars, trains, airplanes, ships and submarines. In atypical manufacturing environments such as marine environments, HVAC systems help ensure safe, healthy building conditions are maintained and regulated with respect to temperature and humidity, mainly by using fresh air from outdoors.
The V in HVAC refers to ventilation, this is the process of exchanging or replacing air in any space to provide improved indoor air quality which involves temperature control or oxygen replenishment, and also the removal of moisture, odours, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases or substances that contribute to an unpleasant environment. Additional benefits to proper ventilation are removal of undesirable smells and excessive moisture, while the continuous introduction of fresh, outside air, keeps the interior building air circulating thereby helping to prevent stagnation of the interior air.
Ventilation can include both the exchange of inside air for outside air as well as the circulation of the air within the building. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. There are several methods of ventilation used within the building and HVAC industries but they can all be divided into either mechanical/forced and natural types.
As the name suggest, the three main disciplines of HVAC are heating, ventilation, and air conditioning, which all relate to the provision of thermal comfort and acceptable indoor air quality by means of reasonable set up, operation, and maintenance costs. HVAC systems can be used in almost any environment, including domestic, industrial and commercial applications. HVAC systems generally provide ventilation, and maintain pressure relationships between spaces. The means of air delivery and removal from spaces is known as room air distribution.
As awareness of the importance of good indoor air quality grew, along with advancing technology in the field of thermal comfort, the design installation and control systems of HVAC functions have become integrated into one or more bespoke HVAC system. For very small buildings or older buildings specialists will normally estimate the capacity and type of system needed and then design an appropriate system, utlising the best suited refrigerant and components required to give the best effect. With larger buildings, building service designers, mechanical engineers, or building services engineers analyse the building then design and specify the bespoke HVAC systems. Speciality HVAC or mechanical contractors then fabricate, install and commission the systems. Building permits, permission from landlords and building regulations compliance inspections of the installations are normally required for all fixed installation systems regardless of the building size.
Although HVAC is generally concerned with the environmental control of individual buildings or other enclosed spaces (like NORAD’s underground headquarters), the systems used in some cases are an extension of a larger district heating (DH) or district cooling (DC) network, or a combined BHC network. When this is the case you tend to find the operating and maintenance aspects are simplified whereas energy metering becomes necessary to for accurate and fair billing for the energy used to operate the system, or indeed for any energy that is returned to the larger system, e.g. when one building in the DHC (or indeed room within a building) is using chilled water for air conditioning purposes and the warm water it returns to the system may be used in another building or room for heating, alternatively if it isn’t required for heating then it can be used for the overall heating-portion of the DHC network (in all likelihood with energy added to boost the temperature).
Basing HVAC on a larger network in this manner can greatly improve the economy of scale beyond what is often possible for individual buildings. It can also help make the most of renerable energy sources such as solar heat, the cold of winter, and the cooling potential in places close to large bodies of water such as rivers, lakes or seawater for use as part of a free cooling system and to enable seasonal thermal energy storage.
The theory behind HVAC is based on the studies, discoveries and inventions made by numerous scientists and engineers, most notable the likes of Nikolay Lvov, Michael Faraday, Willis Carrier, Edwin Ruud, Reuben Trane, James Joule, William Rankine, Sadi Carnot, however there were also many, many others who made valuable contributions.
A number of inventions made around the time of the century helped set the scene for the first comfort air conditioning system, which was designed in 1902 by Alfred Wolff (Cooper, 2003) which was iinstalled in the New York Stock Exchange, while Willis Carrier equipped the Sacketts-Wilhems Printing Company with the process AC unit later that same yar. The first school to offer an HVAC specific course is thought to be Coyne College all the way back in 1899.
With the advent of the industrial revolution came the development, refinement and invention of HVAC components. This allowed for modernisation, greater efficiency, and system control as new ‘the new science’ gained a greater foothold and drew the attention of inventors and companies willing to invest.
Heaters are appliances such as industrial electric space heaters, or whole house systems such as central heating, whose purpose is to generate heat (i.e.) warmth) for a building or environment. Central heating systems generally comprise a central heat source such as a boiler, furnace, or heat pump to heat the medium used to transport the heat around the system, with water, steam and air the most commonly used substances. The heat source and pump used to circulate the medium around the system tend to be all housed in one location such as an airing cupboard, furnace room, or boiler room. The heat generated will then be transferred by convection, conduction, or radiation.
Heaters can use a multitude of fuel types, including sol.id, liquids an gases. Another very popular heat source is electricity, especially industrial, commercial where 3 phrase electrical supplies allow much bigger output industrial electric fan heaters. Fan heaters generally comprise heating elements composed of high resistance wire such as Nichrome and a fan. This principle is also used for baseboard heaters and other portable heater types. These commercial electric heaters are often used as back up or supplemental heat for heat pump systems.
During the 1950’s heat pumps saw a rise in popularity and large growth in Japan and throughout the United Stated. Heat pumps can extract heat from one source, such as environmental air, exhaust air from a building, or even the ground and transfer it to something else; the air within a building for example. Initially, heat pump HVAC systems were only really viable in moderate climates. However, as the technology improved and homes became ever more efficient, thereby minimising loads, this greatly improved their ability to perform at lower temperatures and has seen popularity grow in cooler climate area’s as well.
Water or steam
When using heated water or steam to transport the heat around a system, piping (traditionally copper but more often plastic these days) is used to distribute the heat around the various rooms and environments. Modern hot water boiler heating systems have a standard pump to move hot water around the distribution system, whereas older systems would have been gravity-fed. Once in the room to be heated the heat is transferred to the surrounding air using radiators, hot water coils (hydro-air), or other similar types of heat exchanger. The radiators are generally mounted on walls or installed within the floor for underfloor heating.
The science of using water as a heat transfer medium is called hydronics. With many modern combi boilers the hot water they create is also used to supply hot water to taps for bathing and washing, via an auxiliary plate heat exchanger.
Warm air systems use supply and return duct work (essentially just big pipes) to distribute a medium of heated air throughout a structure. The ducting is generally manufactured of metal or fiberglass tubes and fitted to the ceilings within a building, over the last few years it has become quite fashionable to leave the duct exposed. It is also not unusual for this type systems to use the same duct work for the distribution of air cooled by an evaporator coil for air conditioning. The air supply is cleaned via filters or air cleaners to remove or reduce dust, pollen particles and other airborne pollutants.
Although the use of furnaces, diesel/parafin heaters, boilers (solid and liquid fuel but not portable electric boilers or industrial electric fan heaters)are all commonly used methods of providing indoor heat there is the possibility of incomplete combustion as well as the emission of carbon monoxide, nitrogen oxides, formaldehyde, volatile organic compounds, and other unpleasant byproducts of combustion. As we know, the process of combustion requires oxygen therefore incomplete combustion will occur when there is insufficient oxygen; the inputs are fuels contain numerous contaminants and therefore the can be harmful, most dangerously carbon monoxide, which as a tasteless, odourless gas can be particularly dangerous is potential lethal as it can build up without being immediately obvious.
With the above in mind it is particularly relevant to ensure proper ventilation is used where carbon monoxide is a potential byproduct of providing heat.It takes a concentration of just 1000 ppm (0.1%) for carbon monoxide to become lethal however, even at lower concentrations of just several hundred ppm, the effects of exposure can be felt as headaches, fatigue, nausea, and vomiting.
Carbon monoxide molecules bind with the part of blood cell call haemoglobin to form carboxyhaemoglobin. Haemoglobin is responsible for transporting oxygen from the lungs to where it is needed throughout the body in the blood, however once bound with carbon monoxide it will severely restrict its ability to do so. The primary health concerns associated with carbon monoxide poisoning are the cardiovascular and neurobehavioral effects. Carbon monoxide exposure can cause atherosclerosis (the hardening of arteries) and trigger heart attacks. Neurologically, carbon monoxide exposure will reduce hand to eye coordination, vigilance, and continuous performance. It can also affect time discrimination.
Ventilation is the name given to the process of changing air within a space or environment to help regulate temperature and/or remove any containments. Moisture, odours, smoke, heat, dust, airborne bacteria, carbon dioxide, the replenishment of oxygen or even improved airflow can all be controlled with ventilation. As a term ‘ventilation’ can include both the exchange of air within a space for outside air as well as the circulation of air within a building. Ventilation is probably the primary factor when it comes to maintaining acceptable indoor air quality in buildings and it includes both mechanical (or forced) and natural methods.
Mechanical or forced ventilation
Mechanical, or forced, ventilation is provided by apiece of mechanical equipment such as fan, large portable air conditioner or fan coil unit and used to help control overall air quality within an environment. Excess humidity, smells and various other contaminants are also often controlled using ventilation via dilution or replacement of the air with outside air. However, places with a high humidity level naturally you will need to use more to remove the excess moisture from the air as it enters the new environment. This process is called dehumidification.
Kitchens and bathrooms typically have ventilation fans or extractor fans to help control the typical smells and humidity associated with these environments. The most prominent factors to take into consideration when specifying an appropriate fan for such a space are the airflow rate (which is a function of the fan speed and exhaust vent size) and noise level (especially pertinent when being used in a domestic application). Direct drive fans tend to be the most suitable, low maintenance solution for the vast majority of applications.
Ceiling fans and table/floor fans, including man coolers and warehouse fans are generally a good, temporary way to increase circulation within a space to help alleviate stuffiness and increase the perception of reduced temperature by increasing evaporation of perspiration on the skin of anybody that might be in the environment. Because hot air rises, ceiling fans can also be used to help keep a space warmer in the winter as they circulate the warm stratified air from that accumulates towards the top of a room.
Natural ventilation is the ventilation of a building with outside air without using any mechanical method such as fans. It can be something as simple as opening windows, louvers or things called trickle vents when spaces are small and the application permits. After these very basic ways there are more complicated methods where warm air is allowed to rise up and escape high building via specialist vents to the outside, this is called stack effect. Because nature abhors a vacuum cool outside air is drawn into the building through low level vents. As natural ventilation uses almost no energy both maintenance and running cost are minimal, however they might not be suitable for all applications and care should be taken to ensure comfort. This is especially true of warm or humid climates, where maintaining comfortable working temperature using only natural ventilation might not be possible. In such area’s portable air conditioners and fixed air con units are used to supplement the natural ventilation system or as back up. Air-side economizers also use outside air to condition spaces, but do so using cooler 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 have 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.
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.
Natural ventilation is a key factor in helping to minimise the spread of airborne diseases and illnesses such as tuberculosis, the common cold, influenza and meningitis. Natural ventilation is the easiest and simplest form of HVAC as it requires little to no maintenance, is often free or at least inexpensive as can be provided by something as simple as opening doors, windows, or use of ceiling fans are all ways to increase natural ventilation and therefore reduce the risk of airborne contagion.
An air conditioning system, or portable air conditioner, provides cooling and, to some extent, humidity control for a single environment or even full building, depending on the system you’ve got. Buildings designed and built with integral air conditioning or HVAC systemswill usually also have sealed windows, this is because to maximise effectiveness climate control should be done within a sealed environment therefore open windows are counterproductive whenyou’re trying to maintain constant indoor air conditions. Where fresh, outside air is required itwill generally drawn into the system via a vent point which leads directly to the indoor heat exchanger section, creating positive air pressure. The return air to fresh air ratio or mix can usually be adjusted by the opening and/or closing of this vent. In most systems you should expect a typical fresh air intake of about 10%.
In order to satisfy the second law of thermodynamics conditioned air and a refrigeration effect are provided through the removal of heat rather than the addition of cool. This removal can be done through radiation, convection, or conduction. In an air conditioning unit the refrigeration conduction media will generally be a material such as water, air, ice, and/or specifically designed chemicals (which will normally have an alphanumeric industry name such as R22, R454C, R290 etc) are referred to as the‘refrigerant’. The refrigerant will used either as part of a heat pump system in where a compressor is utilised to drive a thermodynamic refrigeration cycle (this generally applies to the specifically designed chemicals), or a free cooling system which uses pumps to circulate a cool refrigerant (typically water or a glycol mix).
When installing an air conditioning system it is essential to ensure you have a correctly specified system. Under specified systems will result in inefficient usage and energy wastage.
At its most basic a refrigeration cycle comprises four essential elements to provide cooling:
- A refrigerant. This will begin the cycle in a gaseous state. A compressor will then pump the refrigerant gas up to a high pressure and temperature.
- During the next phase of the process the gas enters a form of heat exchanger, generally known as the condensing coil or condenser. At this point it will lose energy (in the form of heat) to the outside and so will cool. As it cools it will condense into its liquid state.
- Some type of expansion valve or capillary will regulate the refrigerant liquid flow to ensure the proper rate.
- Finally, the liquid refrigerant is returned to another heat exchanger where to evaporate, hence the heat exchanger on this side of the system is often called the evaporating coil or evaporator. As the liquid refrigerant evaporates it absorbs energy (again in the form of heat) from the inside air, returns to the compressor, and repeats the cycle. During this type process heat is absorbed from the indoor air and transferred outdoors, which leads to the cooling of the environment.
Where an air conditioning system is used somewhere with a variable climate there will probablybe a reversing valve fitted. These are devices that switch the system from heating to cooling as and when required. 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.
One of the most attractive attributes to free cooling systems is the potential to offer very high efficiencies, which when combined with some sort of seasonal thermal energy storage method allows them to use the cold of winter for summer air conditioning. Commonly used mediums for such storage can be deep aquifers or naturally occurring underground rock masses which arethen accessed using a number of small-diameter, heat-exchanger-equipped boreholes. Systems with small storages can be hybrid, using free cooling at the start of the warmer season before switching to a heat pump to further chill the circulation coming from the storage later in the season. These heat pumps are 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.
Another feature on some systems is something called the “economiser mode” or alternatively the “free-cooling mode”. When in this mode the control system open the outside air damper to the optimum distance whilst simultaneously closing the return air damper to the most effective distance, which has the effect of causing fresh, outside air to be supplied to the system. When the outside air is cooler than required the system will allow the demand to be met without using the mechanical supply of cooling (typically chilled water or a direct expansion “DX” unit), thereby saving energy. The control system of a free cooling system can monitor the temperature of the outside air vs. return air or compare the enthalpy of the air, which is often done in high humidity climates and it causes more of an issue. In both cases, the outside air must be less energetic than the return air for the system to enter the economiser mode.
Packaged vs. split system
In the United States a fixed, central, “all-air” air-conditioning system (more frequently called packaged systems) with combined outdoor condenser/evaporator units are usually installed in residences, offices, and public buildings during construction, however because they require a network of large air ducts throughout the building they are very difficult to retrofit (install in a building that was not designed to receive it). Where an air conditioning system is required post construction then a ductless minisplit system can be used instead. Outside of North America, packaged systems are usually only fitted in applications involving large indoor space such as stadiums, theatres or exhibition halls.
One of the most popular alternatives to packaged systems is to use separate indoor and outdoor coils in split systems. Such systems are the preferred method across the world, with the exception of North America where split systems are more often used in domestic applications. They are however gaining popularity in smaller commercial buildings. Split systems are a really good option for small buildings where complicated duct work just isn’t an option the space conditioning efficiency is of prime concern. Amongst the benefits of ductless air conditioning systems are ease of installation, no duct work, control for different environments and flexibility of control plus quiet operation. The duct work in a packaged system can account for a large loss in efficiency, as it can be directly responsible for up to 30% of the total system energy consumption. Used correctly minisplit systems can be an effective part of an energy efficiency strategy as there are none of the losses associated with ducting.
In a split system, the condenser is sited remotely, usually on an outside wall, while the evaporator is installed in the area that needs cooling. The two sides of the system are then connected using copper refrigeration pipes. The evaporator section is commonly referred to as ‘the indoor unit’, will normally be mounted on a wall or suspended from a ceiling and feature oscillating ventsto ensure an even distribution of cooling.Where a false ceiling is used other indoor units mount inside the ceiling void and allow short lengths of duct handle air from the indoor unit to several vents or diffusers placed around the room or rooms
Whilst on the one hand split systems offer greater efficiency and a smaller footprint than packaged systems. On the other hand, package systems tend to be slightly quieter indoors as the fan is located outside.
The process of dehumidification (removing moisture from the air) in an air conditioning system is done by the evaporator. Since the evaporator is usually cooler than the ambient air and below the dew point, any moisture within the air therefore condenses on the coil tubes. This moisture then runs down the coil fins and is collected in a drip tray that sits below the coil, where it is removed via either some sort of condensate collection device (a bucket) or a condensate pump.
A commercial dehumidifier is an air-conditioner-like device that helps controls the humidity, or at least excess moisture, of a room or building. They will often be used in basements which have a higher relative humidity because of their lower temperature and also because they are normally below ground and therefore suffer from a propensity for damp floors and walls. In food retailing establishments such as supermarkets, large open chilled display cabinets act as highly effective dehumidifiers. As a opposed to a dehumidifier, a humidifier increases the humidity of a building.
Most modern air conditioning systems, even small window package units, are usually equipped with air filters. Generally manufactured from a lightweight gauze-like material they be regularly replaced, washed or cleaned using a vacuum cleaner to avoid airflow restriction, reduction in performance and in the worst cases catastrophic failure. As an example, if you imagine a building in a high dust environment, such as a joinery, or a home with furry pets, these environments will require more regular filters changes than places with much cleaner environments. It should be noted dirty filters contribute to a lower heat exchange rate, meaning reduced efficiency and energy wastage, shortened equipment life, and higher electricity bills; another effect of inhibited air flow is iced-out evaporator coils, which can completely stop air flow. Additionally with reversing heat pumps, very dirty or blocked filters could potentially cause overheating during a heating cycle, and can result in damage to the system or even fire.
As an air conditioner moves heat between the evaporator and condensor coils, it is imperative both are be kept clean. In addition to replacing or cleaning 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 damage 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.
With greater running costs and greater awareness of environmental issues manufacturers of HVAC equipment have been making efforts to increase the efficiency of their equipment. Although originally a result of rising energy costs, it has more recently been driven by efforts to reduce the environmental impact of such equipment. In additional, improvements to the HVAC system efficiency might also help increase occupant health and have a positive effect on productivity.In the US, the EPA has imposed tighter restrictions over the years. There are several methods for making HVAC systems more efficient.
Historically, water heating was seen as the most efficient way to provide heating throughout an entire building and as such was standard in much of the world. These days though forced air systems that can also double for air conditioning during the warmer months and are more popular in the United States.
Forced air systems are widely used in churches, schools and high-end residences, and do enjoy some benefits:
- Better air conditioning effects
- Energy savings of up to 15-20%
- Even conditioning
One drawback however is the installation cost, which is marginally higher than a traditional fixed HVAC system.
The energy efficiency of a central heating system can be improved with the introduction of independently controls for each are or zone within the building. This allows users to switch heat on and off, and thermostatically control it only in the places where it’s needed rather than heating an entire building, similar in a way to non-central heating systems. Where water heating systems as used the thermostats control zone valves, whereas in forced air systems they control zone dampers inside the vents that selectively increase or decrease the flow of air to suit requirement. In this case, the control system is very critical to maintaining a proper temperature.
Forecasting is another method of controlling building heating by calculating demand for heating energy that should be supplied to the building in each time unit.
Ground source heat pump
Ground source heat pumps, also known as geothermal heat pumps, are very similar to ordinary air sourced heat pumps, but rather transferring heat to or from the air they rely on the stable, even temperature of the earth to provide heating and cooling. As many regions experience large seasonal swings in temperature they would need very large-capacity heating and cooling plant to maintain year round comfortable environments. Alternatively, a conventional heat pump system used to heat a building in somewhere like Montana’s regularly see’s bitterly low temperatures ( even hitting −57 °C) or to cool a building in Death Valley, one of the hottest places on Earth would demand an enormous amount of energy due to the extreme difference between manageable temperature required inside and the extreme outside air temperatures. Whereas not far below the earth’s surface the ground remains at a relatively constant temperature. By utilising this huge source of relatively moderate temperature, the required capacity of a heating or cooling system can often be dramatically reduced. Although ground temperatures vary according to latitude, at 1.8 m underground, temperatures generally only range from 7 to 24 °C.
One example of a geothermal heat pump using a body of water as an effective heat sink is the system in place at the Trump International Hotel and Tower in Chicago, Illinois. As the building is situated on the Chicago River it has easy access to a large HVAC resource and therefore uses cold river water by pumping it into a recirculating cooling system, where heat exchangers transfer heat from the building into the water, and then the now-warmed water is pumped back into the Chicago River.
So, while the initial installation and set up costs might be slightly higher than regular heat pumps, geothermal heat pumps can produce markedly lower energy bills – up to 30 to 40 percent lower, according to estimates from the US Environmental Protection Agency.
Geothermal heat pumps also provide higher efficiency than air source heat pumps. Some models show as much as 70% saving when compared to electric resistance heaters.
Ventilation energy recovery
Energy recovery systems can use 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 to the incoming outside fresh air.
Air Conditioning Energy
The capabilities of vapor compression refrigeration cycles are limited by thermodynamics. This is the most commonly used form of cooling in portable air conditioners, air conditioning systems and heat pump devices and they way they move heat rather than convert it from one form of energy to another, so the usual thermal efficiencies do not appropriately describe the performance of these devices. While Coefficient-of-Performance (COP) is used to measure performance, it is a dimensionless measure has not been universally adopted. Instead something called the Energy Efficiency Ratio (EER) is used to represent the performance of many HVAC systems. Furthermore, to more accurately characterise the performance of air conditioning equipment over a typical cooling season an adjusted version of the EER, the Seasonal Energy Efficiency Ratio (SEER), or in Europe the ESEER, can be used. Unlike the EER, which is based on a constant outdoor temperature of 35°C (95°F), SEER ratings are based on seasonal temperature averages instead. The current industry minimum SEER rating is 14 SEER and engineers have highlighted areas where the efficiency of the existing cooling plant could be improved. One example is better fan blade design and manufacture.The most economical process of fan blade manufacture is to stamp them out of sheet metal, however this does tend to compromise aerodynamic efficiency.Instead, a well-designed blade, well engineered blade can reduce electrical power required to move the air by up to 33%.
Demand controlled kitchen ventilation
Demand controlled kitchen ventilation (DCKV) is a form of HVAC that utilises a building controls approach to monitor and adjust the volume of exhaust and supply air within a commercial kitchen in real time response to the actual cooking loads. Traditional commercial kitchen ventilation systems operate in a simple on/off way, so they’re either at 100% fan speed or 0% irrespective of the actual requirement and as such are not as efficient as they could be, DCKV technology changes that to provide significant fan energy and conditioned air savings. By using smart sensing technology in this way, both the exhaust and supply fans can be adjusted to capitalize on the affinity laws for motor energy savings, reduce makeup air heating and cooling energy and thereby increasing safety whilst also reducing ambient kitchen noise levels.
Air filtration and cleaning
Air cleaning and filtration removes unwanted, unpleasant or even potentially hazardous particles, contaminants, vapours and gases from the air within an environment. The filtered, cleaned air then is used for heating, ventilation and air conditioning of that environment. Air cleaning and filtration should be taken in account when protecting the environments within buildings.
Clean air delivery rate and filter performance
The clean air delivery rate is the volume of clean air an air cleaner provides to a room or space. To determine the CADR, the amount of airflow in a space should be taken into account. For example, an air cleaner with a flow rate of 100 cfm (cubic feet per minute) and an efficiency of 50% has a CADR of 50 cfm. In addition to CADR, filtration performance is an essential part of maintaining a desirable indoor environment. Filter performance depends on the size of the particle or fibre, the filter packing density and depth as well as the air flow rate.
HVAC industry and standards
The HVAC industry spans the globe, with staff trained for everything from operation and maintenance, system design and construction, equipment manufacturing and sales, to education and research. Although historically self-regulated by HVAC equipment manufacturers of HVAC equipment regulations and standards organizations such as HARDI, ASHRAE, SMACNA, ACCA, Uniform Mechanical Code, International Mechanical Code, and AMCA have been established to support the industry and encourage high standards and achievement.
The starting point in carrying out an estimate both for cooling and heating should consider both the exterior climate and desired interior conditions. However, before beginning the heat load calculation, the fresh air requirements for each area should be accurately ascertained, as pressurisation is also a key consideration.
ISO 16813:2006 is a significant ISO building environment standards that stes out the general principles of building environment design, an important part of which is the provision of a healthy indoor environment for any occupants, as well as the need to maintain the environment for future generations. It also promotes collaboration among the stakeholders and parties usually involved in building and environmental design for the sake of greater sustainability. In the United States ISO16813 applies to both new construction and the retrofit of existing buildings
The building environmental design standard aims to:
- 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.
The Chartered Institution of Building Services Engineers is the body that covers the essential Service (systems architecture) that allow buildings to operate. It includes the electro-technical, 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 essential for measurements, planning and theory. In addition most employers also require a degree in a relevant 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 gain an Honours Degree and a master’s degree in a relevant engineering subject.
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 North America
In the United States, HVAC engineers generally are members of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), EPA Universal CFC certified (for installation and service of CFC 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 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, is held in conjunction with each winter 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 most general of four volumes of the ASHRAE Handbook is Fundamentals; it includes heating and cooling calculations. Each volume of the ASHRAE Handbook is updated every four years. 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.
HVAC professionals 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. HVAC techs who have been trained can also be certified in areas such as air conditioning, heat pumps, gas heating, and commercial refrigeration represents 2%-3% of the GDP.
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