When AHU systems are used to extract stale air from the building, a controlled proportion of this air may be recirculated to avoid having to condition all supplied air. Alternatively, heating or cooling may be provided by electric heating elements or direct expansion refrigeration units built into the air handler. Air Handling Units can also be used to supply fresh air for ventilation and to extract stale air.įor heating or cooling, AHU coils may be connected to central plant such as boilers or chillers, receiving hot or chilled water for heat exchange with the incoming air. Supply air passing through the AHU is filtered and is either heated or cooled, depending on the specified duty and the ambient weather conditions. Alternatively, an AHU can be open to the space it serves. In most cases, AHUs are connected to air distribution ductwork. From the evaporator, the low pressure water vapour passes to the absorber where it re-combines and dilutes the concentrated lithium bromide solution, so that the cycle can be repeated.Ībsorption chillers typically require a hot water temperature of 70-95 degC to produce chilled water at around 7 degC.Īir handling units (AHUs) are used to supply and circulate air around a building, or to extract stale air as part of a building’s heating, ventilating and air conditioning (HVAC) system.Įssentially, an Air Handling Unit system comprises a large insulated metal box that contains a fan, heating and/or cooling elements, filters, sound attenuators and dampers. This generates chilled water that is then distributed to the cooling system. This condensed water is then transferred to a lower pressure evaporator, where it evaporates and absorbs heat from water in adjacent cooling coils.
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In the condenser, the water vapour from the generator condenses under high pressure. The water vapour is transported to the condenser and the lithium bromide is transported to the absorber. In the generator a dilute lithium bromide solution is heated, causing water to evaporate off – resulting in water vapour and a concentrated lithium bromide solution. As the absorption cycle proceeds, these two fluids are separated and combined, as follows: The basic absorption cycle employs two fluids, a refrigerant (typically water) and an absorbent (typically lithium bromide). They are often used in conjunction with combined heat and power (CHP) making use of the surplus heat from CHP engines in summer to provide cooling.Īn absorption chiller consists of a generator, a condenser, an evaporator and an absorber. Absorption chillers use heat energy to generate chilled water that can be used for air conditioning or process cooling applications.