Engineering Manual o.. - HVAC.Amickracing

CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONSFunctional principles:The primary side consists of the supply and return lines, plusnecessary pressure reducing, regulating, and safety equipment.Small Substation For Multiple Family BuildingsFigure 131 shows a typical direct heat transfer substation.This is self-regulating equipment which provides a givendifferential pressure, absolute pressure reducing, and safetyclose off functions.DISTRIBUTIONSUBSTATIONTCCONSUMERThe heat regulation unit (Fig. 130) provides the requiredtemperature by controlling the primary flow (A) or by mixingthe cooled return water with supply water (B). Differentconfigurations with two and three way valves can be used. Inthe flow control configuration a fixed speed circulating pumpincreases the pressure in the return line above the supply flowpressure. In the temperature control configuration either a jetpump or a three way valve is used.SUPPLY LINETHREE-WAYMIXING VALVEOR JET PUMPPSFTI01OUTSIDE AIRY11MY12TI31ROOMTIC13SSFCIRCULATINGPUMPRETURN LINECONTROL VALVEA) FLOW CONTROL B) TEMPERATURE CONTROLM11446Fig. 130. Two- And Three-Way ValveConfigurations for a Heat regulation Unit.Jet pumps use the effect of injection, making a mechanicalpump unnecessary, thereby, saving electrical energy. However,adapting and dimensioning jet pump applications to fit operatingconditions is difficult.Control loops used in a direct substation:– Supply flow temperature reset on outdoor air temperature.– Return temperature limit.– Time schedule functions.– Night setback and frost protection.TCPRFFig. 131. Small Direct Heat TransferSubstation for Multiple Family BuildingsSRFM11435Table 9. Description of Figure 131 Reference Points.ReferenceTI 01TI 31TIC 13Y 11Y 12ControllerDescriptionOutdoor air temperature sensorRoom temperatureSSF temperatureActuator control valve PSFCirculating pumpENGINEERING MANUAL OF AUTOMATIC CONTROL362