Engineering Manual o.. - HVAC.Amickracing

CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONSTable 13. Description of Figure 142 Controls.ReferenceDescriptionDDCControllerQIR 02 Cold water meteringQIR 15 Flow meter (heat meter)TI 01Outdoor air temperatureTI 11PSF temperatureTI 14PRF temperature (heat meter)TIC 13 PRF temperatureTIC 22 SSF temperatureTIC 31 Loading circuit temperatureTIC 32 HW storage tank temperatureTZA+ 21 High temperature limit (SSF)Y 12Control valve primary flowY 23Circulating pump (SSF)Y 24Circulating pump (SSF)Y 33Circulating pumpY 34Charging pump (HW storage tank)2. DHW temperature control: Valve Y 12 in conjunction withTC 32 maintains the HW storage tank water temperature.Thermostat TIC 32 supplies the HW storage tank loadingcycle start point. During the loading cycle, SSF waterheats HEX 2, other loads are switched off, and the pumpsY 24, Y 34 load the HW storage tank. Temperature sensorTIC 31 turns loading operation off.3. DHW Circulating pump control: Circulating pump Y 33is time schedule controlled to maintain the DHWtemperature at the end of the line.Functional DiagramVariations of temperatures based on a heat surface factor(HSF) of radiators in a building (equivalent to a building heatcurve variation) ranging from 0.8 to 1.6 (Fig. 143).SSF SETPOINT TEMPERATURE (F)15814012210486ADJUSTABLE RANGE OFSSF SETPOINTTEMPERATURE CURVESHSF = 1.6HSF = 0.8Control Strategies1. Secondary Supply Flow (SSF) temperature control:Modulating normally-closed Valve Y 12 in the primarysupply flow (PSF) and TIC 22 control the SSFtemperature. The SSF setpoint is reset based on outdoorair temperature (Fig. 143). If the primary return flow(PRF) exceeds the TI 14 temperature limit, the SSF 1temperature reset schedule is adjusted to a lowertemperature schedule. If the SSF temperature exceedsthe high limit setpoint of hard wired thermostat (TZA+21), power to valve Y 12 is shut off closing the valve.5 12 19 27 34 41 48 55 63 70OUTSIDE AIR TEMPERATURE (F)M11442Fig. 143. SSF Temperature Reset Range.HYBRID BUILDING SUBSTATIONCombination Jet Pump and Heat Exchanger.The Heating System is mainly used in Eastern Europe or theCIS and consists of a Hydro-elevator Mixing Valve (jet pump).Hydro-elevators are mostly uncontrolled devices, mixing thebuilding return water with supply water according to the hydromechanicalconfiguration in the valve and requires no pumpfor heating water circulation in the building heating system(Fig. 144).ENGINEERING MANUAL OF AUTOMATIC CONTROL371