Document 15DqoyqEbYqrNRbXLXDLgq94a

616 CHAPTER 34 1948 Guide - should be taken from the other portion of the double plenum chamber. In many in-, stances, separate zone heating and zone cooling coils are. employed, instead of mixing dampers. . '6. The control hook-up for a typical year 'round air conditioning system, including automatic. change-over from heating to cooling, is'indicated-in Fig. 1 and described as foljows: - Whenever the fan is started, solenoid air valve or relay E-l, actuated by the fan motor starter, opens minimum outdoor air damper D-l, places hygrostat H, in service, arid allows duct thermostats T-3 and T-4 to control the maximurn outdoor "air damper D-2 and the return air damper D-3. When the fans stop, E-l is de-energized, to close the outdoor air dampers and also to close humidifier valve V-4. Thermostat T-l positions steam valve V-3 on the reheater coil, to maintairi a constant space temperature. As the space temperature rises, T-l positions reheater valve V-3 , to a closed or to a minimum open position, as determined by low limit discharge ther-mostat T-5. Duct thermostat 1-6, in-the preheater, discharge, positions preheater coil valve V-l, to maintain a constant preheater discharge temperature. Automatic Control __________________ , .. 617 Remote-bulb thermostat T-2, with bulb located, in preheater discharge, operates valve V-3 on the preheater coil, to maintain a coristant preheater discharge teiriperature. On rising temperature," thermostat T-l, in the conditioned space, closes reheater "valve V-l and, through relay C-l, opens face damper D-2, for cooling;- On rising humidity in the conditioned space, hygrostat H closes humidifier!: valve V-2; and likewise,.through C-l may open face damper D-2.for dehumidification. For closer control,..the. face, and by-pass dampers should be .eliminated and cooling means continuously provided wheriever the outdoor dew-poirit rises above a predeter-. mined riiaximum. Reheatirig and humidifying may be required to provide the desired conditions.However, such a system will-be less economical in operation. PANEL HEATING CONTROL- : Automatic controls for radiant and convective heating differ some what due to :the thermal inertia characteristics; of the panel heating surface, and the increase in the mean radiant temperature within the space under increasing loads for. panel heating. On rising outdoor temperature, between-30 F and 65 F, duct thermostat T-3, located in the outdoor air intake, moves riiaximum outdoor air damper. D-2 toward the open position. At 65 F, outdoor, D-2 will be fully open and return air damper D 3 will be fully closed. ... As the outdoor air temperature rises above 65 F, duct thermostat T-3 positions V-5 in such a way as to by-pass low limit thermostat T-5, so that reheater coil valve V-3 is operated directly from thermostat T-l. As outdoor air temperature rises from 65 F to 75 F, duct thermostat T-4 gradually closes maximum outdoor air damper D-2 and opens return air damper D-3. Cooling thermostat T-2 positions cooling coil valve V-2, to admit more chilled water, as the space temperature rises. Hygrostat H positions humidifier valve V-4 to maintain the desired humidity in the conditioned space. 7. The arrangement of automatic control for a constant temperature and constant humidity air conditioning system, using 100 per cent outdoor air, is shown in Fig. 2, and the control description follows: Whenever the fan is running, relay or solenoid air valve E-l, actuated by the fan motor circuit, is energized, opens outdoor air damper D-l, and also permits hygrostat H, in the conditioned space, to control humidifier valve V-2. When the fan stops, E-l closes outdoor air damper D-l and humidifier valve V-2. Effect of Inertia of Panel : If a panel has considerable heat storage capacity (as compared with a convector or conventional radiator) it will continue to emit heat for some ;time after the room thermostat lias become satisfied and shut off the supply of heating medium. This Will cause uncomfortably warm con ditions to exist: in a space. Also,; there will be a considerable delay between the time'the thermostat calls for heat and the time heat is actually delivered to the space (because of the large part of the heat that must first be stored in the thermally "heavy" radiant surface). When ever inertia exists in the source of heat supply, uncomfortable cycling of space conditions will result unless means of anticipating load changes before they occur in the space, or means of setting the basic energy supply rate from load conditions, is provided. If a thermally heavy radiant surface is used the primary control should be actuated by outdoor temperature (load) to determine the basic tem perature of the heating medium supplied to the radiant surface. To