Thermostat Help

HeatingHelp

This discussion was created from comments split from: Is there a thermostat that can control 2 heating systems?.

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@NJwoods, we've created a new discussion for you here to prevent confusion.

Thanks, @EdTheHeaterMan!

EdTheHeaterMan

Here is what I have come up with.

1. The Red area is in the attic
2. the Green area is outdoor.
3. The Gray area is the basement.
4. In the basement is a working 4 zone boiler system. I used a factory diagram to illustrate that system. There are no changes needed to make that system operate.
5. The thermostat wires from the boiler zines that match the Heat Pump Thermostat zones are pictured as brown thermostat wire from the basement to the thermostat location as a Red and a White wire.
6. Splice a new conductor from the boiler zone R and W wire to the air handler location. (I used the Purple and Brown of an 8 conductor thermostat wire. you can use a separate 2 conductor thermostat wire to do that)
7. W from the thermostat will call for heat from the Boiler only by way of a Heat Relay located in the air handler. The W will not connect to the heat pump at all.
8. This may allow both heating units to work simultaneously on some rare occasions, however there may also be some cold air blowing during defrost cycle.
9. If #8. causes a comfort issue, then connect W from the heat pump to W on the air handler to bring on AUX electric heat during defrost.)
10. The T675 remote bulb thermostat should be set at the lowest differential setting 3°F. and select the outdoor temperature that will best match your system. The higher the OD temperature the less Defrost cycles you will experience.

I will review this design again to see it there is a better solution. Anu comments from the HH Wallies are welcome.

This is the remote bulb thermostat to measure the outdoor temperature. You can use one for each heat pump. They get wired in or near the air handler. https://www.supplyhouse.com/Honeywell-T675A1565-Remote-bulb-Commercial-Temperature-Controller-0-F-to-100-F-20-ft-capillary-Copper-bulb-sensing-element.

NJwoods

Thank you so much for the help and moving this thread.

This solution seems like it makes sense to me and the issue of #8 is reasonable enough to live with.

One question/thought I have is that my heat pump does not have electric heat strips for backup/emergency heat. If I get the remote temperature controller, I see there is a setting 355 Balance Point (Compressor Lockout) and lets say I set it to 40*F, is there a way to wire my boiler up to the Aux/Emergency Heat and have this balance point call for the boiler zone heat? That might be what you are describing in #10.

The heat pump is Goodman Heat Pump GSZB403610 and Goodman Air Handler AMST36BU1400.

EdTheHeaterMan

@NJwoods said is there a way to wire my boiler up to the Aux/Emergency Heat and have this balance point call for the boiler zone heat?

YES

On your thermostat, in the programing section, you have to select the system type. if you select heat pump with Fossil Fuel backup, the compressor will stop and the boiler will start. there will be a time lag before the radiators heat up after the compressor stops. The time lag can be as much as 15 minutes, but will be at leadt 8 minutes.

that is because the sequence of operation of the boiler is this

1. heat pump reaches the point where backup heat is required. The compressor stops and W sends a signal to the zone valve in the basement.
2. the Taco 570 valve motor can take as long as 90 seconds from the call for heat, until the valve is completely open and the valve end switch starts the boiler.
3. The boiler pre-lighting sequence may be as long as 60 seconds with pre-purge ignitor operation, trial for ignition main valve opening and proof of flame. (if there is no proof of flame on the first try, then the pre-purge sequence starts all over again add another 60 seconds))
4. Now the main flame starts to heat up the cold water inside the boiler. that cna take several minutes to get hot enough water to to radiators. (once the flame is on the water does not instantly get to 160°. There is a slow to medium time lag there.
5. after all that time, you will start to get some heat from the radiators. This time lag is not always noticeable, and may not be a problem. Just be aware that it exists.

I can incorporate that into your wiring design, use the outdoor sensor feature of the thermostat and perhaps eliminate the T675A. I will need to read the thermostat specifications in detail to see if that id possible.

That's gonna be a Monday thing

EdTheHeaterMan

It appears that the thermostat TH6320WF2003 may be able to do everything you are asking. The trouble is that when you select ISU 200 = Heat Pump, ISU 205 = air to air, ISU 255 = Fossil Fuel, and ISU 335 = 40°F The fan in the air handler will continue to operate and blow cold air. That is because the thermostat assumes that the Aux Fossil Fuel heat is included in the duct system. With your system, the Fossil Fuel Aux is not included in the ducted system, therefor the fan needs to stop.

There needs to be an additional relay to stop the fan from operating when the compressor stops operating for heat below 40°F outdoor temperature. This is doable!

NJwoods

Thanks again Ed,

I think this is the exact problem that first happened when we tried to wire it up last year. Since it kept the fan on we were stumped and thought something was wrong, but not sure how to fix it.

It is no rush if this is a Monday thing, I'm swamped with the young kids on the weekend until they sleep so can't test too much anyways :).

EdTheHeaterMan

I have added a RIB relay to be installed in the AirHandler for the attic. It is a double poll relay. DPDT

I have removed the T675A thermostat and used a different relay. one set of contacts do the Zone Valve as usual, the other set of contacts disconnect the G or Fan wire at the same time. Purchase this relay https://www.supplyhouse.com/Functional-Devices-RIB2401D-Enclosed-Pilot-Relay-10-Amp-DPDT-w-24-VAC-DC-120-VAC-Coil?_br_psugg_q=rib+relayand wire it this way

By breaking the Green wire from the thermostat to the air handler with the NC contacts on the RIB relay the fan will not operate when the boiler is heating the zone. You still make the heat relay do the same thing with the zone valve using the COM and NO contacts on the RIB.

I did not make that change on the bottom air handler, but you can do the same thing there too.