Adding second source of Aux/Emergency Heat


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Old 02-09-21, 09:16 AM
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Adding second source of Aux/Emergency Heat

Hi,
I have an American Standard Platinum 19 heat pump and air handler with electric heat strip backup. Recently I installed a hydronic heating coil with gas boiler as a backup heat source during longer power outages and connected the circulation pump relay to the Aux port 24v relay/supply on my Honeywell interface module. Ive been testing with the breakers on the heat strips off and the system seems to work fine when calling for Aux heat (its pretty cold right now) the hydronic system does a good job of boosting heat output and covering for the heat pump when cycling. Im considering using this as my permanent solution for aux heat as the cost is likely lower and it keeps the system running. Only small thing is that when I switch to emergency heat it says waiting for equipment for a few minutes but then flips on the aux relay and works as normal.
My question is if there are any settings in the Honeywell around how it uses aux heat that I would want to change? For instance at what outside temp does it start using aux heat or how it integrates it into the overall operation of the heat pump?

Any thoughts would be greatly appreciated.
AC
 
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Old 02-10-21, 03:43 PM
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You didn't leave any specs or model numbers for what you're using.
Thermostat model number.

Most thermostats trigger the AUX heat when the room temperature drops 3 or more degrees below the set temperature. The only thing the outside temperature would control is when the heat pump shuts down.
 
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Old 02-12-21, 10:25 AM
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Hi Pete
My thermostat is a THX9421 using an IAQ board. The air handler is an American Standard with I believe a 5 ton heat pump, its the platinum series and just a few years old. Ive been running the system in emergency heat mode with the heat strip breakers turned off and its working really well, I am guessing its significantly more efficient than my heat strips/heat pump considering its below 30 here the last few days.

If I find this is much more efficient than the heat pump/strips are there settings to shut the heat pump down when it gets too cold and just work of the aux/emergency heat which in my case would be this hydronic fed heat exchanger?

Thank you
Arthur
 
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Old 02-19-21, 08:11 PM
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Last edited by AllanJ; 02-19-21 at 08:23 PM. Reason: Too many "what ifs" I did not want to second guess and write in additional paragraphs to cover here ..
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Old 02-20-21, 09:46 AM
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Ive been running the system in emergency heat mode with the heat strip breakers turned off and its working really well, I am guessing its significantly more efficient than my heat strips/heat pump
So just like my GEO thermal system you dont run in Aux, or in my case it's called Emergency mode. It will automatically switch to that mode when the unit can not keep up with the temp demand.

Switching to Aux/Emergency mode will bypasses the heat pump and use Aux heat 100% like if the heat pump died, but the fact that your running in Aux mode with breaker off and the system is working normally indicates that feature has been disabled.

Don't overthink, it's a backup feature, it wont come on except for those rare occasions when it's really needed and even then it's probably cheaper than letting the heat pump run constantly trying to make heat!
 
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Old 02-20-21, 10:12 AM
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A heat pump with backup electric AND hydronic heating is treated a little differently.
That stat can and will do anything you want but it is not easy to program.
There are many steps to consider.

In heat pump mode it shows two aux heat sources available.
The second aux source gives you an option to run with or without the heat pump.

You could also go into dual fuel programming and set the stat to use the hydronic as backup aux heat.
In dual fuel mode..... the aux heat does not run with the heat pump.

Many options but the programming needs to be worked thru.
Honeywell installation/programming manual for IAG (pdf)
 
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Old 02-20-21, 06:35 PM
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Is there any disadvantage to just leaving my current setup where I知 using the same aux signal to trigger the hydronic system as the heat strips but leave the heat strip breaker off? Seems to be working fine, still just using it on emergency mode to get an idea of cost and test the system. Based on 10 plus days I知 at 60 bucks in gas so figure 200 for the month which is absolutely much lower than my heat pump plus strips in 30-40 weather.

I ordered the wired temp sensor and am going to install it and configure the lock out to 40 degrees but might play around with it to see what痴 most efficient. I realized my wireless one went missing when the siding was redone.

The big question in my mind is should I change the aux heat type to hydronic or does it even matter?

I did read through the manual, it sounds like hydronic is supported and treated like electric in that it can run in parallel. More curious if there are differences in when it calls the fan and or how much cfm it pushes based on heat type. Basically is there tuning to do?

thanks!
 
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Old 02-26-21, 03:38 PM
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It's probably your heat strips that drive the cost way up.

You should use the hydronic coil as aux instead, and set the thermostat to lock out the heatpump (via an outdoor temp sensor) when the hydronic coil is cheaper.

This can be calculated - need heatpump model and utility rates.

Aux heat type shouldn't be changed -> hydronic is different from hydronic coil.
 
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Old 02-27-21, 05:19 AM
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Thanks! I now have the temp sensor installed and the lockout set to 40 for now. If you could help with calculating that would be great.

It痴 an American Standard Platinum 4A6H7060A1000BA. Utility rate is .1139

One interesting thing I知 noticing which may have nothing to do with the cost, in 40 degree weather the heat output of the heat pump is about 85, as measured by a manual gauge I installed in the duct above the air handler, the hydronic system output is 105. I知 not sure how accurate the gauge is but the relative difference is interesting.

thank you for your help!
Art
 
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Old 03-05-21, 06:08 PM
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hydronic is different from hydronic coil
Is it really useful to have both hydronic radiators along the walls and hydronic coils in the heat pump/air conditioning duct system?

If your nominal heat is heat pump and you are retrofitting hydronic to take the place of the electric strips for aux heat then you would have only the coils in the duct, If you are retrofitting the heat pump to the house with hydronic radiators then the thermostat would simply switch on the boiler when it calls for aux heat,

So you would never need to have two different alternatives, hydronic and hydronic coil, when programming the thermostat.
 
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Old 03-06-21, 05:46 AM
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Yes, what I have is a hydronic coil i believe, a dedicated loop that goes to a air/water heat exchanger mounted inline with the air handler/duct system.

Is there any difference to how the thermostat operates between hydronic coil and electric heat strips, I知 still set to electric as the backup heat source but it seems to be working fine.
 
 

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