HVAC Experts--Heat Pump Control Wiring Question

[Matt Meiser]

We are installing a standby generator that has a feature to shed the load of the AC unit when demand is too high. There's a single contact in the transfer switch which they intend to have you use to break the Y wire to the compressor. We've got a single-stage Trane heat pump. Reviewing the thermostat manual and some online information, it looks like there's still just a Y wire to run the compressor and an O/B wire to switch the reversing valve. I'm assuming I can still just break the Y wire?

Related, what happens when the thermostat (Honeywall VisionPro IAQ if it matters) calls for heat using by turning on the heat pump but doesn't get any? Will it fail over to aux heat (i.e. nat. gas furnace here) automatically? I see some settings in the manual related to "droop control" which I assume are for this purpose. Here I'm not really concerned with comfort but with making sure the house doesn't freeze if we are away. If we are home, everyone in the house will be trained on how to put the thermostat in emergency heat mode if we are running on the generator.

[Scott T Smith]

We are installing a standby generator that has a feature to shed the load of the AC unit when demand is too high. There's a single contact in the transfer switch which they intend to have you use to break the Y wire to the compressor. We've got a single-stage Trane heat pump. Reviewing the thermostat manual and some online information, it looks like there's still just a Y wire to run the compressor and an O/B wire to switch the reversing valve. I'm assuming I can still just break the Y wire?

Related, what happens when the thermostat (Honeywall VisionPro IAQ if it matters) calls for heat using by turning on the heat pump but doesn't get any? Will it fail over to aux heat (i.e. nat. gas furnace here) automatically? I see some settings in the manual related to "droop control" which I assume are for this purpose. Here I'm not really concerned with comfort but with making sure the house doesn't freeze if we are away. If we are home, everyone in the house will be trained on how to put the thermostat in emergency heat mode if we are running on the generator.

Matt, what brand / model number transfer switch?

[George Skinner]

Yes, that would work. The house would be a couple of degrees cooler as most thermostats activate aux. heat when the temperature drops 2 degrees below the normal heat setting. The only downside is the aux. heat will turn back off when it regains the 2 degrees so will not be able to get the temperature up the the thermostat set point. This will keep the furnace fan running pretty much continuously until the house heats up on its own like on a Sunny day or until the transfer switch goes back to utility power.

[Matt Meiser]

Its a Generac RTSD100A3

Here's the manual, or at least one of them:
http://www.generac.com/genApps/Libraries/Manuals/ViewManual.aspx?ItemNbr=0J2119&modelnbr=RTSD100A3

[Matt Meiser]

George, that would be fine. Like I said we'd only be in that mode if we are away from home in the winter and there's a power failure, which I don't recall ever happening but it will sooner or later. If we're here we'll hit the button on the thermostat and just use gas. But most of our outages are during the spring and summer from thunderstorms, high winds, etc.

[Scott T Smith]

Matt, according to the manual you need "special connections" for a heat pump; the "Y" wire connection is for an air conditioner only.

[Matt Meiser]

Ah, I'm pretty sure that reads different than the copy I have--I've been reading it as special connections for a 2-stage heat pump and AC in mine--guessing they'd use double pole relay to break the trigger for both compressors.

[Matt Meiser]

Yes, that would work. The house would be a couple of degrees cooler as most thermostats activate aux. heat when the temperature drops 2 degrees below the normal heat setting. The only downside is the aux. heat will turn back off when it regains the 2 degrees so will not be able to get the temperature up the the thermostat set point. This will keep the furnace fan running pretty much continuously until the house heats up on its own like on a Sunny day or until the transfer switch goes back to utility power.

Thats how ours is set. There's also a 1 timeout if the heat pump isn't heating.