Daikin DCC048 SERIES Installation Instructions Manual

Contents

Daikin DCC048 SERIES Installation Instructions Manual Manual pdf 13 page image

13HEAT PUMP OPERATIONCOOLING C YCLEWhen the heat pump is in the cooling cycle, it operates exactly asa Summer Air Conditioner unit. In this mode, all the charts anddata for service that apply to summer air conditioning apply tothe heat pump. Most apply on the heating cycle except that “con-denser” becomes “evaporator”, “evaporator” becomes “con-denser”, “cooling” becomes “heating”.H EATING CYCLEThe heat pump operates in the heating cycle by redirecting refrig-erant flow through the refrigerant circuit external to the compres-sor. This is accomplished through the reversing valve. Hot dischargevapor from the compressor is directed to the indoor coil (evapora-tor on the cooling cycle) where the heat is removed, and the va-por condenses to liquid. It then goes through the expansion de-vice to the outdoor coil (condenser on the cooling cycle) wherethe liquid is evaporated, and the vapor goes to the compressor.When the solenoid valve coil is operated either from heating tocooling or vice versa, the piston in the reversing valve to the lowpressure (high pressure) reverse positions in the reversing valve.The following figures show a schematic of a heat pump on thecooling cycle and the heating cycle. In addition to a reversing valve,a heat pump is equipped with an expansion device and check valvefor the indoor coil, and similar equipment for the outdoor coil. Itis also provided with a defrost control system.The expansion devices are flowrator distributors and perform thesame function on the heating cycle as on the cooling cycle. Theflowrator distributors also act as check valves to allow for the re-verse of refrigerant flow.When the heat pump is on the heating cycle, the outdoor coil isfunctioning as an evaporator. The temperature of the refrigerantin the outdoor coil must be below the temperature of the outdoorair in order to extract heat from the air. Thus, the greater thedifference in the outdoor temperature and the outdoor coil tem-perature, the greater the heating capacity of the heat pump. Thisphenomenon is a characteristic of a heat pump. It is a good prac-tice to provide supplementary heat for all heat pump installationsin areas where the temperature drops below 45° F. It is also agood practice to provide sufficient supplementary heat to handlethe entire heating requirement should there be a component fail-ure of the heat pump, such as a compressor, or refrigerant leak,etc.Since the temperature of the refrigerant in the outdoor coil on theheating cycle is generally below freezing point, frost forms on thesurfaces of the outdoor coil under certain weather conditions oftemperature and relative humidity. Therefore, it is necessary toreverse the flow of the refrigerant to provide hot gas in the out-door coil to melt the frost accumulation. This is accomplished byreversing the heat pump to the cooling cycle. At the same time,the outdoor fan stops to hasten the temperature rise of the out-door coil and lessen the time required for defrosting. The indoorblower continues to run and the supplementary heaters are ener-gized.D EFROST C ONTROLDuring operation the power to the circuit board is controlled by atemperature sensor, which is clamped to a feeder tube enteringthe outdoor coil. Defrost timing periods of 30,60 and 90 minutesmay be selected by connecting the circuit board jumper to 30, 60and 90 respectively. Accumulation of time for the timing periodselected starts when the sensor closes (approximately 31° F), andwhen the wall thermostat calls for heat. At the end of the timingperiod, the unit’s defrost cycle will be initiated provided the sen-sor remains closed. When the sensor opens (approximately 75° F),the defrost cycle is terminated and the timing period is reset. Ifthe defrost cycle is not terminated due to the sensor tempera-ture, a ten minute override interrupts the unit’s defrost period.