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Thread: Setting Aux Heat by time of day?
01-17-2011, 02:10 PM #1Regular Guest
- Join Date
- Aug 2010
- Monroe County, PA
Setting Aux Heat by time of day?
Here in the PPL service area of Pennsylvania, the electric company has just instituted a new Time of Use (TOU) pricing policy - 6.108 cents off peak, 7.5 on peak (and that is supposed to include transmission charges too!) That makes the off peak price, even with resistance coils, about the same as oil and even lower than propane (there's no NG in our area). So it got me to thinking:
Since I've been b*tching so much here about defrost noises, why not just set the thermostat to Aux Heat overnight since rates are so low and keep the heat pump from coming on at all? Sure, it's a little more expensive than running the compressor, but at 6.1 cents / Kwh, it's not really more than what my oil-heat neighbors are paying. And aux heat is warmer and more comfortable to the skin in the bathroom when you get in the shower in the morning too.
I was really hoping to use the programmable feature of my Honeywell VisionPRO IAQ to accomplish this automatically, but alas, setting AUX HEAT is not one of the things you can control in the scheduling. I assume it's the same for all the other Heat Pump compatible thermostats out there (Although I'm all ears if anyone has any models that can).
- BTW - The house is pretty big and has 2 zones, each designed identically with a VisionPRO IAQ, Goodman MBVC1600 air handler and GSZC18 compressor. The house is quite well insulated - even at 9 degrees outside the HP alone has been able to keep the house at 70 degrees.
Are there any simple ways to force the system to use Aux Heat only from 10PM to 7AM?
The only thing I've been able to think of, and it seems overly complex, is:
Since I have a thermostat that can use an external sensor for set-point control, would it be possible to use the C7089 Outdoor Sensor (that can be added to the VisionPRO) to simulate the time-base aux heat use?
The approach would be use a small timer with an open/close circuit to in line with the wiring of the C7089 to the VisionPRO controller (I have to extend the connection anyway since the 5 foot lead on the sensor is not long enough). From 10PM to 7:30 AM the circuit would go open, creating infinite resistance (indicating colder than -40F). The rest of the time it would go closed, allowing the sensor to read normally. And of course, it would require entering a set point in the thermostat settings so the outdoor sensor would be incorporated into the calculations.
Alternately, since making the circuit go open might make the thermostat think the sensor was no longer connected, I may need to have it go through a resistor equal to the -30 or -40 temp would create. That's going to be much more difficult.
I really think using the outdoor sensor in this way, while imaginative, is probably not the best way to accomplish this.
I welcome suggestions for better ways to force Aux Heat only from 10PM to 7AM - whether they be for a specific alternate thermostat, a third-party timer my installer can add to the system, or well, whatever.