Honeywell Heat/1Cool User Guide - Page 7

HEAT PUMP THERMOSTAT CROSS REFERENCE/SELECTION GUIDE Thermostat Descriptions and General Information This section describes some of the heat pump thermostats that Honeywell manufactures. Since heat pumps require thermostats with special features such as control of changeover valves, this section also explains some of the features and requirements unique to heat pump thermostat applications. Electromechanical Heat Pump Thermostats T841 Heat Pump Thermostats The T841 models control two-stage heat and one-stage cool in heat pump systems, using manual changeover. Heat anticipators are either adjustable or fixed; cooling anticipator is fixed. T841A models include up to three LED indicator lights; T841B models include up to two LED indicator lights. Provision for an outdoor reset to improve thermal performance is also available on select models. Y594 Combination Packs for Heat Pump Applications The Y594 Packs combine the appropriate T874 Multistage Thermostat and the Q674 Subbase for specific heat pump applications. Y594G models have automatic changeover; Y594R model has manual changeover. Heat anticipators are either adjustable or fixed; cooling anticipator is fixed. Accessories include tamper-resistant cover and locking lever assembly with thermometer, locking lever stops, outdoor thermistor, TG504 Key Lock® Cover, and the TG511 Versaguard™ Universal Thermostat Guard. Outdoor Reset Some heat pump thermostats apply outdoor reset to minimize the effect of the interstage differential. It takes more than a one-degree change in temperature to initiate the second stage of heating. Added to a certain amount of droop under high loads, there can be a fairly large offset between the setpoint temperature and the room temperature. To correct this difference, an outdoor thermistor is used. In warm weather, the outdoor thermistor has a very low resistance, permitting a large amount of current to flow in the heater. This reduces the call for second stage heating. In cool weather, the outdoor thermistor has a very high resistance, permitting a small amount of current to flow in the heater. When this happens, calls for second stage heating are more frequent. This helps reduce the difference between the setpoint temperature and the room temperature. Select one of the following T841 or Y594 models if a thermostat with outdoor reset capability is required: T841A1555 Y594G1161 Y594R1763 If an outdoor thermistor is not provided, use the Honeywell C815A Outdoor Thermistor, ordered separately. NOTE: All Honeywell electronic heat pump thermostats are droopless controls and do not require the use of outdoor reset. Electronic Non-programmable Heat Pump Thermostats T8411 Electronic Heat Pump Thermostats The T8411 models control two-stage heat and one-stage cool in heat pump systems, using manual changeover only. First stage heat anticipation is fixed; second stage heat anticipation is selectable at 3, 6, or 9 cph. Setpoints are permanently held in memory (no batteries required) and retained during power failures. Electronic thermostats provide droopless temperature control. 70-6627 • 5