Heat pump short cycling

[Wiz02]

I have an American Standard heat pump and propane furnace for backup in my house.

When the propane furnace is running (installer has crossover from heat pump to backup at 40F) below 40, the furnace runs for what seems like enough time (5+ minutes) before cycling.

However, when in heat pump mode, the heat pump cycles after 1-2 minutes at most. No error codes in the control board display.

I changed the filter but no change in behavior as expected. Any ideas on what to check?

 

[BrandonV]

This is being done with the thermostat? What model?

 

[Wiz02]

This is being done with the thermostat? What model?

Honeywell t6 pro, which I wouldn't mind changing.

 

[BrandonV]

Honeywell t6 pro, which I wouldn't mind changing.

I'm no HVAC professional, but most of the Honeywell units I run into use the whole CPH setting. Basically it tries to learn how your unit cools/heats and then targets runtimes to match this in conjunction with the number of cycles per hour. The idea is to minimize the temperature swing you'd get with an older thermostat. Assuming everything is working correctly, changing this will either hold the system off longer (causing the temperature to drop) or keep it on longer and overshoot the temperature.

Look at page 8 here.

https://xrefs1.plumbersstock.com/product/6/4/640275_FcsP55.pdf

See what you have configured for 365, 366, 370, 371, 375, 378. You may want to drop the CPHs and experiment.

 

[Sumboodie]

I'm no HVAC professional, but most of the Honeywell units I run into use the whole CPH setting. Basically it tries to learn how your unit cools/heats and then targets runtimes to match this in conjunction with the number of cycles per hour. The idea is to minimize the temperature swing you'd get with an older thermostat. Assuming everything is working correctly, changing this will either hold the system off longer (causing the temperature to drop) or keep it on longer and overshoot the temperature.

Look at page 8 here.

https://xrefs1.plumbersstock.com/product/6/4/640275_FcsP55.pdf

See what you have configured for 365, 366, 370, 371, 375, 378. You may want to drop the CPHs and experiment.

I put a delay on make timer set to 10 mins on my T9 thermostat.

Sometimes would just walk by the thermostat and it would fire the boiler for a couple mins.
Constantly short cycling.

Honeywell tech support said it was working correct and the settings I had used where the longest "dwell" or whatever it's called.

Fine, I fixed the issue. T tstat has to call for heat for 10 mins before the timer allows it to kick on the heat. If it stops calling before 10 mins, timer resets.

 

[Wiz02]

I'm no HVAC professional, but most of the Honeywell units I run into use the whole CPH setting. Basically it tries to learn how your unit cools/heats and then targets runtimes to match this in conjunction with the number of cycles per hour. The idea is to minimize the temperature swing you'd get with an older thermostat. Assuming everything is working correctly, changing this will either hold the system off longer (causing the temperature to drop) or keep it on longer and overshoot the temperature.

Look at page 8 here.

https://xrefs1.plumbersstock.com/product/6/4/640275_FcsP55.pdf

See what you have configured for 365, 366, 370, 371, 375, 378. You may want to drop the CPHs and experiment.

Thanks Brandon, I had the manual, but of course it doesn't explain what to do with the settings. I will give it a try.

 

[Wiz02]

I put a b
delay on make timer set to 10 mins on my T9.

Sometimes would just walk by the thermostat and it would fire the boiler for a couple mins.
Constantly short cycling.

Honeywell tech support said it was working correct.

Fine, I fixed the issue. T tstat has to call for heat for 10 mins before the timer allows it to kick on the heat.

Where did you add the timer?

 

[Wiz02]

Thanks Brandon, I had the manual, but of course it doesn't explain what to do with the settings. I will give it a try.

So it seems that if the Honeywell thermostat is configured as a single stage, heating cycle rates are hidden. I will pull the heat pump documents and see check if it's a single or 2 stage system.

It doesn't sound like a good idea to configure the tstat to think it's a 2 stage heat pump if it's not. Thoughts?

Also, while it's dangerous to assume, given that there are heat cycle settings, I assume that the compressor cycle rate settings are for AC which works fine and I shouldn't mess with them. Do you agree?

 

[Sumboodie]

Where did you add the timer?

Between the t stat and boiler. Just cut into 1 of the 24v wires.

 

[BrandonV]

Also, while it's dangerous to assume, given that there are heat cycle settings, I assume that the compressor cycle rate settings are for AC which works fine and I shouldn't mess with them. Do you agree?

So yes, in some circumstances it might only have a general compressor CPH value. What is the value? Dropping it won't harm the AC bit at all. If anything you'll just extend the runtime. It's really a balance between comfort and efficiency.

 

[Wiz02]

So yes, in some circumstances it might only have a general compressor CPH value. What is the value? Dropping it won't harm the AC bit at all. If anything you'll just extend the runtime. It's really a balance between comfort and efficiency.

Good to know CPH is default value of 3.

 

[BrandonV]

Good to know CPH is default value of 3.

Yup. Sounds about right as the default. I have a different model Honeywell and 3 CPH in the summer (outside of the 110F+ days honestly was too short of a cycle for my liking).

I dropped it to 2 and I'm happy now with the AC & heat pump.

There is really zero harm in changing it and monitoring how it behaves. If you don't like what it's doing just revert it.

 

[Wiz02]

Between the t stat and boiler. Just cut into 1 of the 24v wires.

I think that I understand. You are basically saying if the timer is set to say 4 minutes, if the "turn on" request from the tstat goes on and off in less than 4 minutes, no turn on signal gets to the heat pump until the on time exceeds the delay.

If the compressor cycle per hour configuration change of the tstat doesn't work, I will give this a shot or buy a new tstat as I am not thrilled with the Honeywell if it can't handle something so basic.

 

[BrandonV]

If the compressor cycle per hour configuration change of the tstat doesn't work, I will give this a shot or buy a new tstat as I am not thrilled with the Honeywell if it can't handle something so basic.

If you choose a different thermostat, the professional White-Rodgers models are a great option.

Honestly, adjusting the CPH has made a huge difference for several people I've worked with who had Honeywells. While the thermostat may "overshoot" more now to compensate for fewer target cycles during the hour you'll get better runtimes.

Ultimately, it comes down to people preferring tighter temperature control, as opposed to the wider temperature swings seen with older thermostats.

 

[PoorUB]

Thanks Brandon, I had the manual, but of course it doesn't explain what to do with the settings. I will give it a try.

I have a 90+ furnace in my home and set the CPH to one and never noticed the difference in temperature in the home. Honeywell builds good thermostats, but IMO, they could loosen up the CPH or the temp differential a bit.

Often the CPH are "hidden" in the type of equipment selection. Higher CPH for high efficiency equipment, and lower CPH for low efficiency equipment. More CPH supposedly will give a more constant temperature range in the home, where a lower CPH you might notice the space getting cold before the heat come on. IMO, set it for one CPH and I bet when you walk by the thermostat it will always be right at set point.

 

[Sumboodie]

I think that I understand. You are basically saying if the timer is set to say 4 minutes, if the "turn on" request from the tstat goes on and off in less than 4 minutes, no turn on signal gets to the heat pump until the on time exceeds the delay.

If the compressor cycle per hour configuration change of the tstat doesn't work, I will give this a shot or buy a new tstat as I am not thrilled with the Honeywell if it can't handle something so basic.

Correct. The one I got is adjustable from a few seconds to 10 mins.

 

[Sumboodie]

I have a 90+ furnace in my home and set the CPH to one and never noticed the difference in temperature in the home. Honeywell builds good thermostats, but IMO, they could loosen up the CPH or the temp differential a bit.

Often the CPH are "hidden" in the type of equipment selection. Higher CPH for high efficiency equipment, and lower CPH for low efficiency equipment. More CPH supposedly will give a more constant temperature range in the home, where a lower CPH you might notice the space getting cold before the heat come on. IMO, set it for one CPH and I bet when you walk by the thermostat it will always be right at set point.

I wasted several hours of my time with their support over the course of a week or so.

A 5* temp swing would be plenty fine. Even 10* would be ok.

 

[Wiz02]

I wasted several hours of my time with their support over the course of a week or so.

A 5* temp swing would be plenty fine. Even 10* would be ok.

SWBO can feel a 1 degree Fahrenheit change and will say it's freezing if the temperature drops from 72 to 71 so I need to walk a fine line on the cycle per hour setting or external delay.

 

[Sumboodie]

SWBO can feel a 1 degree Fahrenheit change and will say it's freezing if the temperature drops from 72 to 71 so I need to walk a fine line on the cycle per hour setting or external delay.

I hardly notice if it's 60 or 65.

 

[PoorUB]

SWBO can feel a 1 degree Fahrenheit change and will say it's freezing if the temperature drops from 72 to 71 so I need to walk a fine line on the cycle per hour setting or external delay.

My wife is the same way. It took me years to get her to stop moving the thermostat 5 degrees. First she was cold, adjust the stat, now she is warm, turn it down and start the process over. Now she will bump it one degree unless she is freezing, then she will bump it two degrees.

I doubt you will notice any difference is you set the CPH to one.

 

[Bert_]

I have a 90+ furnace in my home and set the CPH to one and never noticed the difference in temperature in the home. Honeywell builds good thermostats, but IMO, they could loosen up the CPH or the temp differential a bit.

Often the CPH are "hidden" in the type of equipment selection. Higher CPH for high efficiency equipment, and lower CPH for low efficiency equipment. More CPH supposedly will give a more constant temperature range in the home, where a lower CPH you might notice the space getting cold before the heat come on. IMO, set it for one CPH and I bet when you walk by the thermostat it will always be right at set point.

I spent some time messing with this back when I still had a digital thermostat, a Honeywell.

The cycles per hour setting seems to be more of a suggestion and not necessarily what it will actually do. I had mine set to one and it almost always ran multiple times per hour.

Other brands use a temp differential adjustment which I think is better.

 

[Wiz02]

I spent some time messing with this back when I still had a digital thermostat, a Honeywell.

The cycles per hour setting seems to be more of a suggestion and not necessarily what it will actually do. I had mine set to one and it almost always ran multiple times per hour.

Other brands use a temp differential adjustment which I think is better.

The fact that other brands use the actual input (temperature) to control the output (temperature) is why I said that I would have no problem changing thermostats.

I haven't started looking for a new tstat yet, but I will if I am not happy with the CPH setting change.

I will see if there is a thread here as well as check out @BrandonV suggestion of pro White-Rodger's.

 

[BrandonV]

Other brands use a temp differential adjustment which I think is better.

Not super popular with professionals but the closest thing I've seen to an old school thermostat is the digital Lux brands. You can configure them to act like an old mercury T-stat would behave.

 

[Bert_]

Not super popular with professionals but the closest thing I've seen to an old school thermostat is the digital Lux brands. You can configure them to act like an old mercury T-stat would behave.

Looks very similar to the pro1 iaq thermostats I can get. Honestly I kind of like them.

My solution in my house was to just put in a mercury thermostat.

 

[danski0224]

It doesn't sound like a good idea to configure the tstat to think it's a 2 stage heat pump if it's not. Thoughts?

It may not control properly.

Also, while it's dangerous to assume, given that there are heat cycle settings, I assume that the compressor cycle rate settings are for AC which works fine and I shouldn't mess with them.

On a Honeywell Prestige 2.0 thermostat, Heating (gas), heating (heat pump) and cooling all have separately adjustable cycles per hour settings. I know because I have set them.

 

[danski0224]

However, when in heat pump mode, the heat pump cycles after 1-2 minutes at most.

I would confirm that there is no longer a call for heating when the heat pump is appearing to turn off.

 

[Wiz02]

It may not control properly.

On a Honeywell Prestige 2.0 thermostat, Heating (gas), heating (heat pump) and cooling all have separately adjustable cycles per hour settings. I know because I have set them.

Thanks for the information. I have a T6 Pro and I believe that selecting a single stage HP configuration hides the cycles per hour (CPH) options with the T6.

I agree that setting the tstat configuration to 2 stage for a single stage hp isn't a smart idea.

Since we are in a relatively cold snap for this area, the propane furnace is supplying all the heat, so messing with HP/Compressor CPH settings won't accomplish anything until it warms up outside enough to crossover to using the HP.

I will play with the settings when it's warmer and report back.

 

[Wiz02]

I would confirm that there is no longer a call for heating when the heat pump is appearing to turn off.

If control board display on the heater / ac (not the tstat) is displaying, "idle" is that a good enough sign that the tstat isn't calling for heat?

 

[danski0224]

Probably

 

[Wiz02]

Probably

I can check voltages it's not a big deal, but I will do it tomorrow unless I work on adding shut off valves for the new sink.

I find messing with plumbing fixtures in cold weather is asking for trouble but a new sink and counter top will be here in a few days so I need to cut off the stubs and add shut offs beforehand.