Heat Pump with backup generator

[enigmapaul]

Hi all,

I have a Lennox 2.5 ton heat pump along with a CBX32M air handler. What i'd like to do is install a backup generator. A pretty large one (22KW) but not large enough to power the heating system with the electric backup heat which is 15KW in itself.

Can I just wire the compressor, and the air handler itself through the transfer panel to get basic heat/cooling without the electric backup heat? My theory being that it should be sufficient as long as its not very cold outside. if that happens, then we can add space heaters via plugin.

If that is possible, I think my problem is that the blower motor in the air handler is wired in with the electric backup elements. Is there a way to separate the blower and perhaps put it on the compressor circuit instead, so that I can power that through by transfer switch panel on a fairly modest ampacity circuit (about 15A for compressor and 1.7A for the blower)?

Thanks!

[The Daring Dufas]

I've setup systems like that in the past and the best way to do it is through the control system. The way I would do it is have a relay with normally closed contacts that will break the control circuit for the heating element contactor whenever the generator is running. It's not rocket surgery but you need to understand control circuits.

TDD

[Steve]

For a 2 1/2 ton heat pump, you don'g need 15kw strips in the first place. All you need is 10kw. Also remember that in heating mode you will have defrost cycles that will be running both the compressor and the strips at the same time.

FWIW, those plug it in the wall heaters average 5kw each. That defeats the purpose.

[The Daring Dufas]

Time for him to install gas logs and a propane tank. Of course, I wonder what fuel the generator is running on. I remember back in the middle of the last century when all electric homes in this area were considered to be the cleanest and most economical to heat. 8-)

TDD

[Stormin Mormon]

Sigh. More spam from Gmail.

[Stormin Mormon]

Where do I get a couple of those? The space heaters I've seen here run

1500 watts, and put out 5,200 BTU per hour.

[Stormin Mormon]

Clean electric. What a hoot. Just means that the pollution is some where else, in the power grid. Back in the seventies, my area got a nuclear power plant. Which is fine with me. They were talking about how clean the power is. Cleaner than coal, I'm sure. Just hope they figure out what to do with the radioactive stuff after it's used.

An example of non polluting clean power. Is to go to the woods and set up a gasoline generator, run a couple hundred feet of cord. The point of use has no pollution.

[danny burstein]

I saw one blowing over the wet floor at the airport. Of course it was using 277V.

Ah, can't find that one, but:

has lots of high output, portable units.

You _do_ have 440 service to your living room, right?

[Stormin Mormon]

Only via local step up transformer.

I wonder why anyone would make such a large filament heater. No fossil fuels avaialble, maybe?

[Greg O]

120 volt, 5,000 watt, plug in wall heaters? You running 120 volt, 50 amp circuits to run those heaters? Plug in heaters run 1500-1800 watts. Greg

[Steve]

My bad.

[Stormin Mormon]

Most of the space heaters I've seen sold, are 5,000 BTU.

[Greg O]

Which works out to about 1500 watt. Greg

[.p.jm.]

Don't confuse the boy.

Oops ! Too late ......

[The King]

The mormon school of hvac says one watt per btu. Don't you know nothing?

[enigmapaul]

[.p.jm.]

Simply interrupt the control side of the strip heat ( IOW the 24 VAC control to it ) with a small relay with a 120VAC coil, use a NO contact, and power that coil as 'always on' from a non-transferred circuit.

[The Daring Dufas]

Well duh! < me. It can be separated inside the unit without too much trouble. The darn heat strips and air handler will draw more than

65amps alone at 230VAC. The diagram I found online shows what would have to be split off. I would install a control relay to lockout the heat strips to prevent any possibility of power back feeding through the system via the electric heat relays when the main power goes out.

If you wanted to get a bit fancy, you can install a latching contactor of the type used in many transfer switches and lighting controls that will stay on until getting a signal from your transfer switch to open the circuit to the heat strips. You may have a more detailed wiring diagram that came with your unit than the one I found online. Of course, when splitting the power, pay attention to the phases and make darn sure BOTH power sources are disconnected when any work is done on the air handler.

TDD