Document dn9y4OnrJ7NM8y3qNB0yBEkmq

220 KENNETH E. ROBINSON Unit heaters are very popular since they will provide large quantities of h<j at a reasonable cost. They are usually mounted between the lower trusses sf the roof, where space is easily available. Large units with coils and blower$ indirect fired furnaces are also used extensively and may likewise be inbus? in the upper section of the plant. These units can be controlled automatic^ and, if properly sized and located, can also, be used to bring in all or part outli air in winter and summer. '4 One of the difficulties with units located between the trusses is that wHl recirculation is used the warm air at the ceiling is drawn through the uiji Figure 5. An application of radiant heat un -a'partially'upenedi uninsulated''building^ o heat source is used. heated to a greater temperature, and discharged with a high velocity;, attempt to force it to the floor. This results in a hot blast over anyon --immediaterareat-while-peraons-a-few-feet-away-mayrberuroldcTfTp^' plant-generate any smoke and fumes that normally rise-to. the-upper's' the building, these are also forced down toward the occupied area. Units used to supply heated outside air to replace that disi exhauit....fan.S.,.ai:e.u.sually dnstalled.,in,,the_same....way...and .cause-theplaints from the occupants. In winter, it may A desirable to introduce a: than room temperature to control the heat generated by the operation '? discussion of make-up air on page 225). -?'> w ' AIR CONDITIONING 221 3. Controls f ^Sr*% AiJIi fl i_ -Vvf?t)i p'd of supplying heat requires some form of automatic controls One method is to use an outdoor thermostat to control the IgUlates the input to the heater. Such a system should include a IptnQfche building to maintain proper building temperatures when gMISPklaons are not running. Air-supply units that provide tempered llllfQUj'd have both a room thermostat and a thermostat in the duct pSt^mperature at all times. Otherwise the room control might be m&i sigffijorocess'heat and allow untempered air to be delivered. *91& s*;eam system should have some method of assuring that 'supplied to the coil wheheyer.'the'temperature of the out- ^^^prlpzing, tq heat the air supply systems ^^Spfh'St tire full ste'aih capacity, is provided whenever the outside below 40 F., which prevents freezing but may., cause over- J^rapl^CThis can be prevented if the valves on both the preheat and face and bypass dampers are modulatedXby the control ^^pfeihlso special controls to place on the discharge? side of the coil "||lp|if if the air temperature drops below the control- setting. |j|p|aye been frozen because'the condensate did hot . drain away to the belief of many persons, there is no such thing as a ,_.,MSS'i>etter name is a steam distributing coil, which will freeze if ^ySfeotected. *<Wmi B. REMOVING HEAT FROM A SPACE ^chapter concerns itself only with the problem of removing heat from peopling) to provide suitable environment for employees, not for process ^nuilfibe remembered-that cooling is accomplished by removing heat jion!|n"d that it is more difficult to remove than to add B.t.u.'s.6 ^sl|||Sproach to any cooling problem is to tryXto eliminate heat at its efyon. Often this can be done by changing the.'operation; for example, pjotibn heating rather than direct-fired furnaces for certain forging ..KEKernext step might well be that of isolation--the*'operation is .djj^^afate building or a given section of the main building where it ^l||fepd"trb'atdd"Str'al"separ'8te'probTemt:iOix^eSt!,eMdlywlhr`ge;``hot Jpften -more practical to supply small confined area's with cool air jp*8f the operators than to try to cool the entire area. above-mentioned approaches are fairly well' 'ffnHefstood'. The &l|mteoncernsdarge =areas- where-some-heat--is-generat&*throughout, aMgejlmachine shops. When large numbers of people are employed, even -IV yrj'on.. cooling load, Heating, Ventilating, Air Conditioning Guide, 1965. American failing and Air-Conditioning Engineers, New York, 1955. y$.