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Heating, Ventilation, Air Conditioning and Refrigeration (HVAC/R)
What is the HVAC/R industry? Why is HVAC/R important? How bright is the future in the HVAC/R industry? What about heating? What is the HVAC/R industry? The HVAC/R industry manages indoor environments, designs, builds, installs, services, maintains, troubleshoots and repairs indoor comfort and cooling systems year-round. Why is HVAC/R important? Homes, office buildings, industrial plants, airplanes, cars and computer technology all rely on complex HVAC/R systems to create and maintain safe, healthy and comfortable living and working environments. Many industrial, medical, technical and commercial processes also depend on sophisticated heating, cooling air quality and ventilation systems. How bright is the future in the HVAC/R industry? As the population and economy grow, so does the demand for new residential, commercial, and industrial climate-control systems. People and businesses depend on their climate-control systems and must keep them in good working order, regardless of economic conditions. Heating and air-conditioning systems control the temperature, humidity, and the total air quality in residential, commercial, industrial, and other buildings. By providing a climate controlled environment, refrigeration systems make it possible to store and transport food, medicine, and other perishable items. Heating, air-conditioning, and refrigeration systems consist of many mechanical, electrical, and electronic components, such as motors, compressors, pumps, fans, ducts, pipes, thermostats, and switches. In central forced air heating systems, for example, a furnace heats air, which is then distributed through a system of metal or fiberglass ducts. Technicians maintain, diagnose, and correct problems throughout the entire system. To do this, they adjust system controls to recommended settings and test the performance of the system using special tools and test equipment. Technicians often specialize in either installation or maintenance and repair, although they are trained to do both. They also may specialize in doing heating work or air-conditioning or refrigeration work. Some specialize in one type of equipment—for example, hydronics (water-based heating systems), or commercial refrigeration. Technicians follow blueprints or other specifications to install oil, gas, electric, solid-fuel, and multiple-fuel heating systems and air-conditioning systems. After putting the equipment in place, they install fuel and water supply lines, air ducts and vents, pumps, and other components. They may connect electrical wiring and controls and check the unit for proper operation. To ensure the proper functioning of the system, furnace installers often use combustion test equipment, such as carbon dioxide testers, carbon monoxide testers, combustion analyzers, and oxygen testers. These tests ensure that the system will operate safely and at peak efficiency. After a furnace or air-conditioning unit has been installed, technicians often perform routine maintenance and repair work to keep the systems operating efficiently. They may adjust burners and blowers and check for leaks. If the system is not operating properly, technicians check the thermostat, burner nozzles, controls, or other parts to diagnose and correct the problem. Technicians also install and maintain heat pumps, which are similar to air conditioners but can be reversed so that they both heat and cool a home. Because of the added complexity, and the fact that they run both in summer and winter, these systems often require more maintenance and need to be replaced more frequently than traditional furnaces and air conditioners. During the summer, when heating systems are not being used, heating equipment technicians do maintenance work, such as replacing filters, ducts, and other parts of the system that may accumulate dust and impurities during the operating season. During the winter, air-conditioning mechanics inspect the systems and do required maintenance, such as overhauling compressors. Refrigeration mechanics install, service, and repair industrial and commercial refrigerating systems and a variety of refrigeration equipment. They follow blueprints, design specifications, and manufacturers' instructions to install motors, compressors, condensing units, evaporators, piping, and other components. They connect this equipment to the ductwork, refrigerant lines, and electrical power source. After making the connections, refrigerator mechanics charge the system with refrigerant, check it for proper operation and leaks, and program control systems. When air-conditioning and refrigeration technicians service equipment, they must use care to conserve, recover, and recycle the refrigerants used in air-conditioning and refrigeration systems. The release of these refrigerants can be harmful to the environment. Technicians conserve the refrigerant by making sure that there are no leaks in the system; they recover it by venting the refrigerant into proper cylinders; they recycle it for reuse with special filter-dryers; or they ensure that the refrigerant is properly disposed of. Heating, air-conditioning, and refrigeration mechanics and installers are adept at using a variety of tools to work with refrigerant lines and air ducts, including hammers, wrenches, metal snips, electric drills, pipe cutters and benders, measurement gauges, and acetylene torches. They use voltmeters, thermometers, pressure gauges, manometers, and other testing devices to check airflow, refrigerant pressure, electrical circuits, burners, and other components. Heating, air-conditioning, and refrigeration mechanics and installers work in homes, retail establishments, hospitals, office buildings, and factories—anywhere there is climate-control equipment that needs to be installed, repaired, or serviced. They may be assigned to specific job sites at the beginning of each day or may be dispatched to a variety of locations if they are making service calls. Technicians may work outside in cold or hot weather, or in buildings that are uncomfortable because the air-conditioning or heating equipment is broken. In addition, technicians might work in awkward or cramped positions, and sometimes they are required to work in high places. Hazards include electrical shock, burns, muscle strains, and other injuries from handling heavy equipment. Appropriate safety equipment is necessary when handling refrigerants because contact can cause skin damage, frostbite, or blindness. When working in tight spaces, inhalation of refrigerant is a possible hazard. The majority of mechanics and installers work at least 40 hours per week. During peak seasons, they often work overtime or irregular hours. Boiler Heat Pump 
What about heating? Chilled water systems require a seperate source of heating. This would normally be in the form of a boiler and a hot water flow and return similiar to the chilled water system. It is possible to provide chilled water and hot water through the same set of pipes, (known as a manual or automatic changeover system) but these systems are more appropriate in offices when there is a clearly defined heating and cooling changeover season. An alternative is to use electrical resistance heating although the running costs are usually prohibitively high. Direct expansion equipment may utilize a heat pump which heats and cools through the same set of pipes. Frequently Used Terms Air conditioning equipment is referred to by abbreviated names and may be rather confusing to those not dealing with the equipment on a regular basis; here is a list of some of the most frequently used terms. Air to air heat pump Refers to totally packaged piece of equipment. The equipment contains one fan to be connected to ductwork to cool or heat the indoor atmosphere and one fan to reject (or reclaim) heat to the external atmosphere. Thes units may be positioned externally or they may be manufactured to be positioned internally (less usual). Air to air cooling unit As above but cooling only. Direct Expansion, DX or SPLIT equipment See under Direct Expansion. Air cooled chillers or air to water chillers Chillers which consist of condensers and compressors which are usually located externally and are air cooled. Chilled water is provided from these chillers. Air to water heat pumps As above except provided with a reversing valve and hot water as well as chilled water is provided. Water to water chillers As above except water is used to reject heat instead of air, the circuit rejecting the water is known as condenser water and is usually provided from a cooling tower. Water to water heat pump As above except unit provides hot water as well as chilled water. Defrost circuits As heat pumps extract heat from the external atmosphere even at very low temperatures it is inevitable the external coil freezes with ice. The coil therefore has to be warmed periodically in order to remove the ice, this is achieved by running the refrigeration circuit in reverse for a brief period of time. This cycle is referred to as the defrost cycle and therefore unlike a condensing unit (i.e. cooling only unit) heat pump units form water externally. Consideration has therefore to be given to the removal of the water formed, by the provision of an external tray or other device. Fan coil units and Air handling units These may be manufactured for the direct expansion market or for the hydraulic market. They generally consist of a filter, fan and a cooling and/or heating coil. The difference between a fan coil unit and an air handling unit has become increasingly blurred. A fan coil unit generally is a small unit quite often located in the conditioned environment, they may also be located above a false ceiling and connected to a very small amount of ductwork. Air handling units are generally always intended to be connected to distribution ductwork, and the fan is sized to facilitate this. Recently larger fan coil units have been manufactured as standard and have been designed to enable distribution ductwork to be connected, typically these larger fan coil units have fans capable of providing up to 150 Pascals static pressure (~0.6 inches water gauge). Heat Pump The outdoor unit associated with a direct expansion equipment incorporating a compressor, coil, reversing valve and fan and provides heating and cooling. Condensing Unit As above but cools only and does not therefore incorporate a reversing valve. Condensor As above but does not incorporate compressor (which is then incorporated in the indoor unit). Low ambient controllers or head pressure controllers When equipment is required to provide cooling in cold weather the external unit will over condense i.e. will reject too much heat. To overcome this problem it is necessary to fit a low ambient controller also known as a head pressure controller. This device slows down the condenser fan or uses other methods to prevent over condensing.Some equipment has this fitted as standard others do not. What is the difference between Ventilation and Air Conditioning? Sometimes people confuse the meanings of air conditioning and ventilation. Air conditioning means that the air supply to an occupied space is brought to a required condition by cleaning, cooling, heating, drying, and humidifying. Ventilation implies fresh air supply, the removal of contaminants and heat, and air motion for cooling and freshening. In the majority of cases ventilation without air treatment will provide satisfactory air conditions. The essential requirement in ventilation is to replace contaminated and over-heated air with fresh outdoor air, and to counteract discomfort due to humidity. What rate of Ventilation is required? There are a number of factors to be considered, including: * Size of room or building * Number and type of occupants and their activities * Heat gains from equipment and solar radiation * Relative humidity * Outside air temperature and range of temperature * Calculation of air changes per hour for buildings or rooms according to particular characteristics and conditions prevailing The rate of ventilation can be worked out from these factors, though that is not always necessary. In many cases it is sufficient to follow recommended rates of air renewal for buildings of various types. One basis for estimating the rate of air renewal is the number of times an hour the air content of the building should be replaced with fresh air. The table Air Changes per Hour in the REFERENCE DATA section of this web provides recommended air changes per hour for various occupancies. What fan noise levels are acceptable? This varies according to a number of factors: (a) The occupancy of the area being ventilated; (b) The distance the fan is from the occupied zone (people) in the area; (c) Other background noise; (d) What acoustics exists in the area being ventilated. Sound is measured in decibels (dB) and the A-Weighting filter (dBA) is used to simulate what the human ear hears. If you refer to the NOISE DATA sheet in this website you will be able to compare sound level comparisons which are quoted at three metres from the fan without any acoustic barrier. Sound levels published in Pacific Fans product information are free field sound pressure levels at 3m. Do I need different VENTILATION considerations for the Office area and the Factory area? Yes, there are essentially two ways of ventilating a building: • Ventilation by displacement; • Ventilation by diffusion. Put simply, Ventilation by displacement is chiefly used to ventilate large industrial or commercial premises, while Ventilation by diffusion is the preferable method for supplying air to occupied zones such as offices and smaller premises. Ventilation by displacement when properly set supplies large volumes of good air at low velocity into the occupied area to displace the bad air. In using this method it is sometimes difficult to avoid some draught but mostly this is a minor consideration in the overall result. In this method, the supply fan/s should be positioned high to avoid draught and the airflow should be of sufficient volume to flow across the ceiling, or high space, for some distance before falling down to mix with the ambient air When bringing in cold air to an area, what factors should I take into consideration? There are a number of factors that must be considered: (a) Size of area ; (b) Position of fan/s (c) Obstacles in path of incoming air; (d) Where air inlets should be positioned. (1) The Supply Fan/s should be positioned high so that the air flow is directed along the ceiling (or high up if no ceiling). (2) It is also important that the air stream velocity is right to ensure the air stream flows through about 60% of the area depth before falling down to the occupied zone. Falling too early is less efficient. Larger Commercial Premises and Industrial Premises (1) The Supply Fans should best be positioned lower down at lower air velocity directly into the occupied zone The ventilation system must be set so that air which circulates to the occupied area is comfortable for the occupants of the area. Is it better to supply air through the ceiling or through the wall? Generally if is better to supply air from a ceiling diffuser rather than a wall diffuser. This is because the air from a ceiling diffuser spreads in all directions, and therefore takes less time to mix with the ambient air and to even out the temperature. |
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