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Author Topic: 1 thermostat for heat pump and outdoor wood boiler  (Read 157 times)

morfem

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1 thermostat for heat pump and outdoor wood boiler
« on: November 29, 2017, 07:31:56 AM »

I have seen this mentioned in some of the older threads but wanted to start a new one in case someone else is looking to do the same thing.

My house is currently heated with a heat pump and Backup electric strip heat in the plenum that comes on automatically if the heat pump cannot keep up.

I have looked for thermostats that would allow me to have the wood burner be the primary heat source and the heat pump as second and electric strip heat as third with no luck.

I came across an old post from Schoppy and he basically did what I am looking to do by using an aquastat.

If the water coming in the house form the OWB is hot then a call for heat from the thermostat would start the secondary loop circulator and the blower in the air handler. If the water is cold and a call for heat then it would send the signal to the heat pump and blower to start just like it is currently wired today.

Am I missing anything with this?

All the solid colored wires and the dashed yellow line shows how the thermostat is currently wired. The proposed (yellow) wiring goes to an aquastat to direct the signal to either the circulator or the heat pump.

I do not think I need to do anything with the (reversing) O/B terminals.....?
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E Yoder

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Re: 1 thermostat for heat pump and outdoor wood boiler
« Reply #1 on: November 29, 2017, 05:02:40 PM »

You've got the basic idea.
Circulator will need a relay so 24 v. can start the 120v. circulator.
We use a Ranco temp control to trip a DPDT relay that breaks the compressor and strip when the water temp is above the set point on the ranco. Basically the same thing. The way you have it you won't want to bump the temp up too fast and trip the strip heat.
If you run the wood furnace for domestic water in the summer you'll need a switch to shut the aquastat off so the compressor can run for AC.
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NaturallyAspirated

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Re: 1 thermostat for heat pump and outdoor wood boiler
« Reply #2 on: November 29, 2017, 08:27:19 PM »

 You can use a Nest for three stages of heat if you wish.  There other three stage thermostats out there as well.
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morfem

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Re: 1 thermostat for heat pump and outdoor wood boiler
« Reply #3 on: November 30, 2017, 07:35:28 AM »

Thanks E Yoder. I like the idea of the Ranco Temp control. I did not think about the problem of bumping up the temp to fast and the emergency heat kicking in. I changed  the relay to a DPDT. I'm not planning to run it in the summer so at this point I wouldn't need a switch.
New drawing attached.

Naturally aspirated with the nest thermostat can I have the first stage of heat be the outdoor wood boiler? I currently have a 4 heat 2 cool White Rogers (1F95EZ-0671) thermostat and was told by tech support that the heat pump had to the first stage of heat. Is there a work around for that with the nest?

Thanks for the input.
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Re: 1 thermostat for heat pump and outdoor wood boiler
« Reply #4 on: November 30, 2017, 07:55:57 AM »

Thanks E Yoder. I like the idea of the Ranco Temp control. I did not think about the problem of bumping up the temp to fast and the emergency heat kicking in. I changed  the relay to a DPDT. I'm not planning to run it in the summer so at this point I wouldn't need a switch.
New drawing attached.

Naturally aspirated with the nest thermostat can I have the first stage of heat be the outdoor wood boiler? I currently have a 4 heat 2 cool White Rogers (1F95EZ-0671) thermostat and was told by tech support that the heat pump had to the first stage of heat. Is there a work around for that with the nest?

Thanks for the input.
You can hook it up anyway you wish, however there are certain handicaps (that all multistage thermostats will have I imagine).  Things such as temp deltas before stages kick on, runtime deltas before lower stages kick on, ect.

So far no one has seem to locate a perfect thermostat that has all the flexibility to configure every setting. 
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E Yoder

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Re: 1 thermostat for heat pump and outdoor wood boiler
« Reply #5 on: November 30, 2017, 11:31:55 AM »

One other thought, if your air handler is a variable unit you'll have to break the yellow wire after the air handler as it goes out to the outside unit. On some variables it'll only run low speed fan unless the Y gets a signal.
If you have a fixed speed never mind this.
Ranco will need to be run on C1 as you're "cooling" the outdoor furnace with the air handler.
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morfem

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Re: 1 thermostat for heat pump and outdoor wood boiler
« Reply #6 on: November 30, 2017, 01:20:51 PM »

The air handler does have a variable speed blower. Drawing changed.

Would I also need to break the brown wire for the emergency heat after the block for the same reason?

Thanks
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E Yoder

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Re: 1 thermostat for heat pump and outdoor wood boiler
« Reply #7 on: November 30, 2017, 04:30:27 PM »

No, break emergency heat before the air handler or it'll come on.
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Re: 1 thermostat for heat pump and outdoor wood boiler
« Reply #8 on: November 30, 2017, 05:25:15 PM »

By variable I'm referring to a variable, not one with two or three fixed speed options.
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morfem

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Re: 1 thermostat for heat pump and outdoor wood boiler
« Reply #9 on: December 11, 2017, 11:14:19 AM »

E Yoder is there a particular way that you attach the sensor from the Ranco to the pipes? I have it zip tied and electrical taped to the pipe but it is reading about 25-30 degrees lower than the temp of the pipe.

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E Yoder

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Re: 1 thermostat for heat pump and outdoor wood boiler
« Reply #10 on: December 11, 2017, 12:27:29 PM »

I tape on with metal foil tape (maximum contact) and wrap with micro bubble insulation, seal off with foil tape on the ends of the insulation. It usually reads within 5 degrees.
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