Document N2VmyEodDyLEvDyxqjBXneNGR

Heating Ventilating Air Conditioning Guide 1939 Unit Heaters. Ventilators. Air Conditioning. Cooling Units On vacuum or open vented systems the return from each unit should h a urine, with which the use of heated air in rapid circulation with fitted with a large capacity trap to discharge the water of condensatio f rm distribution is of particular advantage. They may be used for and with a thermostatic air valve for eliminating the air, of with a heavy1 duty trap for handling both the condensation and the air, provided th UrU ture absorption, such as fog removal in dye-houses, or for the pre01f. 0f condensation on ceilings or other cold surfaces of buildings in air finally can be eliminated at some other point in the return system 6 orocess moisture is given off. When such conditions are severe, it For high pressure systems the same kind of traps may be used as with ecessary that the heaters draw air from outside in enough volume to vacuum systems, except that they must be constructed for the pressure **rovide a rapid air change and that they operate in conjunction with ! used. If the air is to be eliminated at the return header of the unit a high pressure air valve can be used; otherwise the air may be passed with ntilators or fans for exhausting the moisture-laden air. (See discussion ^condensation in Chapter 7). I the condensate through the high-pressure return trap, with some danger 1 of return pipe corrosion and the problem of its elimination at some other UNIT VENTILATORS7 point in the system. Unit ventilators while designed primarily for ventilation must incor OTHER TYPES OF UNITS porate controlled heating. A typical unit ventilator is illustrated in Fig. All Electric The foregoing discussion relates generally to units in which steam or hot water is used as the heating medium. Electric unit heaters are ap plied where electric power is abundant and cheap and where other forms of fuel are scarce and expensive. The low first cost, easy control, and inexpensive installation of this type of heating have also accounted for many other installations in which electricity has conveniently provided heat for short periods of time. (See Chapter 40). Direct Fired A recent development in gas burning equipment is the direct-fired industrial unit heater. These heaters are of the warm-air type and are equipped with fans which cause the air to pass over the heating surfaces at a fairly high velocity and then direct the warm air in to the space to be heated. As is the case with the steam-fed unit heaters, the gas-fired appliances may be used for heating stores, shops, and warehouses. They usually are suspended in the space to be heated and in most instances leave the entire floor and wall area free for commercial use. Partial or complete automatic control also may be secured on appliances of this type. This type of heater is often used for temporary heat, during building construction or where the installation of a steam or hot water plant is for some reason not justified. For permanent installations, it is usually advisable to provide an exhaust duct from the gas-fired unit heaters to remove products of combustion from the occupied space. While this is not necessary in large open industrial plants, in smaller closed^ rooms, it becomes essential. Turbine Driven Where high pressure steam is available it is sometimes used to drive a steam turbine direct-connected to the unit heater.. The exhaust from this turbine, reduced in pressure, is then passed into the heating coil where it is condensed and returned to the boiler. Fig. 8. Typical Unit Ventilator Showing One of Many Arrangements of Dampers and Heating Coils 8. They usually consist of a semi-decorative cabinet containing the following necessary or optional parts: ' 1. Outside air inlet. 2. Inlet damper for closing the opening to the outside air inlet when the unit is not in use. 3. Adhesive or dry type filters for cleaning the air (optional). 4. A heating element usually of special design and intended for low pressure steam. 5. Motor and fan assembly. ' 6; Mixing chamber where warm and cold air streams are brought together. (No "firing chamber is normally provided where sectional type convectors are used). 7. Outdoor air inlet and recirculating air mixing damper (optional). - 8. Discharge grille or diffuser. 9. Temperature control arrangement. INDUSTRIAL USES In addition to their prime function of heating buildings, unit heaters may be adapted to a number of industrial processes, such as drying 440 The primary functions of a unit ventilator are: fA roof vmtilntnr For information on roof ventilators, see 441