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I have a Goodman model CPKJ36 heat pump that works in conjunction with a Janitrol propane furnace as the seconday heating system. A Goodman AFE 18-60 dual fuel board is used along with a Honeywell T8411R thermostat to control the heat pump and propane furnace. There are no resistance heating elements. The rating on the furnace indicates that it's a 100,000 btu unit with an output of 90,500 btu. I assume that this means a 90.5% efficiency.
The system does not have an outside thermostat at this time. The Honeywell T8411 thermostat is an earlier model and has a 5 degree differential between setpoint and room temperterature before calling for auxillary heat. New production units have a 2 degree differential. Setting the thermostat to emergency heat will always engage the propane furnace when heat is called.
My question is how to determine the optimum point for the system to switch from heat pump to propane furnace. My electric cost is .085 per KW and my propane costs are 1.49 per gallon.
Currently, the system will call for heat pump first, and if the heat pump is unable to meet the heating demand and the room temperature drops more than 5 degrees below setpoint, the propane furnace will begin operating. As soon as it brings the room temperature to within 5 degrees of setpoint, the propane furnace will shut down and the system will attempt to heat with the heat pump. This cycle will continue with the temperature of the room remaining 5-6 degrees below setpoint until I manually switch to emergency heat. If the outside temperature is above 25 degrees, the heat pump alone can usually meet the demand.
It would seem logical to install an outside thermostat to disable the compressor and redirect the stage one heating signal to the propane furnace, if the outside temperature fell below a certain level. I am certain that the optimum point to set this thermostat is related to the outside temperature, the efficience of the heat pump at lower temperatures, the cost of electricity, the cost of propane, and the efficiency of the propane furnace.
I would appreciate any comments that you may have about the above.
Thanks in advance.
The system does not have an outside thermostat at this time. The Honeywell T8411 thermostat is an earlier model and has a 5 degree differential between setpoint and room temperterature before calling for auxillary heat. New production units have a 2 degree differential. Setting the thermostat to emergency heat will always engage the propane furnace when heat is called.
My question is how to determine the optimum point for the system to switch from heat pump to propane furnace. My electric cost is .085 per KW and my propane costs are 1.49 per gallon.
Currently, the system will call for heat pump first, and if the heat pump is unable to meet the heating demand and the room temperature drops more than 5 degrees below setpoint, the propane furnace will begin operating. As soon as it brings the room temperature to within 5 degrees of setpoint, the propane furnace will shut down and the system will attempt to heat with the heat pump. This cycle will continue with the temperature of the room remaining 5-6 degrees below setpoint until I manually switch to emergency heat. If the outside temperature is above 25 degrees, the heat pump alone can usually meet the demand.
It would seem logical to install an outside thermostat to disable the compressor and redirect the stage one heating signal to the propane furnace, if the outside temperature fell below a certain level. I am certain that the optimum point to set this thermostat is related to the outside temperature, the efficience of the heat pump at lower temperatures, the cost of electricity, the cost of propane, and the efficiency of the propane furnace.
I would appreciate any comments that you may have about the above.
Thanks in advance.