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indamental Series Item : Choosing the Best HVAC System filet//cl/windows/TEMP/0,2637,16287,OO.ht Types Of HVAC Systems There are four basic types of HVAC systems used in commercial buildings. They are and water, all-water, and unitary. Watersystems are also called hydronic systems. F the term used for heating and cooling with liquids. All-air-)ype systems provide heated or cooled air to the conditioned space through a system. The basic types of all-air duct systems are: single-zone, multizone, dual or c terminal reheat, .constant air volume, variable air volume (VAV), and combination sy: the typical system, cooling and heating is accomplished by the mixed air (a combina' return and outside air) passing over a refrigerant coil (cooling) or a heat exchanger The basic air-water system (also called air-hydronic) is a central system similar to the system with chilled water coils instead of refrigerant coils for cooling (with an air-cool condenser) and hot water coils for heating. A variation of this system is the water-air (hydronic-air) system with refrigerant coils for cooling and awater-cooled condenser All-water (all-hydronic) systems accomplish space cooling by circulating chilled Ovate central refrigeration system through cooling tails in air handling units (also called ter or fan-coil units). The units are located in the building's conditioned spaces. Heating is accomplished by circulating hot water through the same (cooling/heating) through a separate heating coil. When one coil is used for cooling only, heating only, and cooling at various times, atwo-pipe water distribution system is used. When twc used, one for heating and one forcooling, a four--pipe water distribution system is us may also be accomplished using electricity or steam. Straight water heating system commonly use convectors, baseboard radiation, fin tube radiation, standard fan-coil unit heaters. zs Unitary Systems A unitary system is an air-conditioning unit that provides all or part of the air-conditioi functions. The components, fan(s), filter(s), controls, and the cooling apparatus (refri refrigerant piping, compressor(s), and condenser) are all factory-assembled into an i package. Components, are matched and assembled at the factory to achieve specific performance objectives in accordance with industry-established increments of capac cfm of air per ton of refrigeration). These performance objectives are set by trade as that have developed standards by which manufacturers may test and rate their equiF These performance parameters and standards allow for the manufacture of quality-c factory-tested systems. Types of unitary systems include window-mounted air conditioners and heat pumps, through-the-wall air conditioners and heat pumps, packaged terminal air conditioner pumps, packaged units, and rooftop units. Unitary systems are used in a wide range of applications and may or may not be use central systems. Cooling capacity can range from fractional tonnage for window-type 100 tons of refrigeration or more for packaged units. A unitary system that uses the i system as the primary heating source is a heat pump. Commercial-grade unitary sys called packaged units. Some packaged units also have heating apparatus (e.g., nat~ heat exchanger, electric elements, steam or hot water coils) and humidifiers. A pack designed to be placed on the roof is called a rooftop unit. Packaged Units Packaged units are used in almost all types of building applications, especially in apl where performance requirements are less demanding, and relatively low initial cost simplified installation are important. Applications include hotels, manufacturing planl~ facilities, motels, multi-occupancy dwellings, nursing homes, office buildings, school: centers, and other buildings with limited life or limited income potential. Wowever, pay units are also used in applications where dedicated, high pertormance levels are req as computer rooms and laboratories.