Load shedding a heat pump

[jbslade82]

We had a whole house standby generator installed. It has some isolation relays built into the automatic transfer switch (Generac 200amp ATS). These are 24 volt wiring meant to break a connection on an A/C unit when the generator is stressed. I believe this is doable on our pool heat pump. I'm just not sure what connection to break. Temp sensor? Compressor?

 

[JamesW]

Remote switch.

 

[wgipe]

I installed a Generac 22kw unit last summer. I have a gas heater on the pool (so no load issue there), but have a heat pump on the house. For the house heat pump, I had to order a $70 relay that was typically used by utility companies to shed a/c loads in times of peak demand in places like AZ and CA. In my case, it’s a normally closed contactor, and you have to configure the transfer switch accordingly (you can configure for either normally-open or normally-closed). I then ran 2-conductor thermostat wire to the heat pump and connected that to the new contactor. When the transfer switch kicks over to generator power, it waits 5 minutes, then kicks in the heat pump. It is a huge unit, and I’ve never had any sort of issue with it handling the whole house load.

in your case, the remote switch contacts may well be all you need, but I would call the manufacturer and ask. I’m glad I did, as they required that $70 contactor or it would void the warranty on the heat pump.

Just food for thought. Good luck - will be a fun little project.

 

[JamesW]

Verify with the manufacturer that the remote switch will work as the cutoff.

 

[Bama Rambler]

I installed a Generac 22kw unit last summer. I have a gas heater on the pool (so no load issue there), but have a heat pump on the house. For the house heat pump, I had to order a $70 relay that was typically used by utility companies to shed a/c loads in times of peak demand in places like AZ and CA.

Can you tell us what the relay does, or give us a make and model?
I would think that it has some delay capability to keep the compressor from restarting too soon.

 

[wgipe]

Can you tell us what the relay does, or give us a make and model?
I would think that it has some delay capability to keep the compressor from restarting too soon.

See attached for the schematic as well as the invoice, which should give you everything you need. I should clarify that this load shedding relay was installed on the heat pump side as specified by AirEase, the manufacturer of the heat pump - then that relay was wired to the a/c relay inside the transfer switch. My understanding is that it does exactly what you suggest - since installing the relay, when power is restored, the thermostat shows a "waiting" countdown for several (3? - can't remember) minutes and then tries to fire. So the sequence goes as follows:

1.) Utility power lost
2.) Generator fires and stabilizes
3.) Transfer switch kicks over to generator power
4.) Generac relay in transfer switch waits 5 minutes, then engages its relay (either opens or closes, depending on the need of the unit you are controlling)
5.) Heat pump initiates its internal wait sequence (I think 3 minutes in my case - all may not have this)
6.) Heat pump kicks on as normal.

When utility power is restored:

1.) Utility power restored for more than 60 seconds.
2.) Transfer switch returns to utility power
3.) Generator cools down and stops
4.) Thermostat initiates wait sequence
5.) Everything is back to normal.

Hope this helps - feel free to ask anything else - happy to try to help in any way I can.

Wes

 

[Bama Rambler]

That's a DPDT relay. They're using it to interface the control circuit so you're not supplying power from a secondary source.