No outdoor temp sensor on heatpump?

[broconne]

Basic Information
---------------
New construction
Cary, NC

I had a few options when building the house and went with a duel fuel hybrid system on the first floor and a variable speed heat pump on the second floor with electric strip backup.

The second floor system contains the following carrier equipment:
25hbb336a003
Fv4bnf003t00
Kfceh2901n09

Honeywell's VisionPRO 8000 thermostat.

I called the installer out to the house (there was a local builder involved and it was his sub that did all the hvac work) because I noticed that on neither of my stats were displaying the outdoor temperature.

He fixed the one downstairs and set the crossover point, at this point I started to question the installers quality - seems like a big miss since my furnace was coming on with every call for heat until he did this.

Then we went upstairs and he took the thermostat off the wall and there were no wires run for an outdoor temp sensor to the upstairs. He explained to me that with a variable speed HP you don't need an outdoor temp sensor that the system will just call for aux heat whenever it is needed and I don't need a crossover point. It seems to me that every time the system calls for heat it is using the aux heat too... This to me seems very inefficient and will end up being expensive..

Am I off base here? I figured I would have an outdoor temp sensor with this heat pump as well and it would run the heatpump until the temp dropped below a certain point and then it would use the aux electric heat?

[gary_g]

If the heat pump has back-up aux electric strips, no outdoor temp sensor, and a VIsionPro t-stat (I have this same set-up), the heat pump will run, and if it can't keep up, the t-stat will cycle the strips on and off as needed while the heat pump is running.

Take care.

[broconne]

Greg -
Thanks for the info. Would it be more efficient if I had an outdoor temp sensor? It doesn't seem to wait to see if it will get there or not.. It seems to turn on the strips almost immediately with the call for heat. Even if it is 50 degrees outside it will turn the strips on.. I am more interested in saving money on electricity than heating the second floor as quickly as possible.

[davefr]

If every call for heat results in strip heating comming on then there's a problem with the system. (Maybe just wiring or thermostat configuration)

Strip heating normally comes on when the thermostat detects that the HP is not getting up to temp fast enough or is there'as a big delta between room temp and thermostat setting.

An outdoor sensor will allow you to lock out the strip heating above a certain threshold but it sound like your system has problems. A HP system should do just fine without strip heating at a 50 degree outdoor ambient.

[broconne]

Well for example right now - it was 70 degrees inside and I set it 71. It ran without aux heat and got it to 71. Then I set it to 72 and it immediately turned on aux heat.

If there is a big differential and it is scheduled for example when it turns in the morning and the house has dropped 5 degrees.. I would rather it run just the HP to get it up those 5 degrees.. My understanding is that it is expensive (electricity wise) when the aux heat comes on... Is that something I can only make happen with an outdoor temp sensor and a lockout?

[beenthere]

Then you need an outdoor sensor, so you can lock out the aux until the heat pump reaches its balance point. If your going to use a setback like that.

[broconne]

Then you need an outdoor sensor, so you can lock out the aux until the heat pump reaches its balance point. If your going to use a setback like that.

Thanks - I can't tell, perhaps I am missing something, but is what I am suggesting a bad idea?

[beenthere]

The outdoor sensor is not a bad idea.
Setting a heat pump with electric aux heat back 5 degrees at night is.

PS: You could also have them enable adaptive recovery. That won't use the aux as much during recovery.

[davefr]

If there is a big differential and it is scheduled for example when it turns in the morning and the house has dropped 5 degrees.. I would rather it run just the HP to get it up those 5 degrees.. My understanding is that it is expensive (electricity wise) when the aux heat comes on... Is that something I can only make happen with an outdoor temp sensor and a lockout?

Yes, on the Vision Pro 8000 it's code 0360. You program it to lockout the strip heating based on outdoor ambient from your choice of settings. (40 degrees to 60 in 5 degree increments).

You obviously need the outdoor sensor to do this.

I still don't understand why your system is triggering strip heating at a 1 degree delta.

Have you read your Honeywell Thermostat manual?? If the installer forgot to give you one you can download it from Honeywell.

[broconne]

The outdoor sensor is not a bad idea.
Setting a heat pump with electric aux heat back 5 degrees at night is.

PS: You could also have them enable adaptive recovery. That won't use the aux as much during recovery.

Beenthere -
Thanks. Can you tell me why setting a heat pump back 5 degrees at night is a bad idea? Just trying to understand here.

[beenthere]

Because when it recovers. It uses the electric aux heat. Which cost more to operate, then what you saved.

As it gets colder out. The heat pump will take longer and longer to recover, by itself.
Meaning that it may have to start recovering at 1AM to get the temp up to set point by 6AM, if the aux is locked out.

[broconne]

Yes, on the Vision Pro 8000 it's code 0360. You program it to lockout the strip heating based on outdoor ambient from your choice of settings. (40 degrees to 60 in 5 degree increments).

You obviously need the outdoor sensor to do this.

I still don't understand why your system is triggering strip heating at a 1 degree delta.

Have you read your Honeywell Thermostat manual?? If the installer forgot to give you one you can download it from Honeywell.

Dave -
I am not sure why it is engaging the strips either.. The installer seemed to indicate that was "normal" even though I didn't think it was it seems like it confuses you as well. Yes, I did read the manual and the installer manual... Was not a lot of information about what should happen with a heat pump and electric strips.

[broconne]

Because when it recovers. It uses the electric aux heat. Which cost more to operate, then what you saved.

As it gets colder out. The heat pump will take longer and longer to recover, by itself.
Meaning that it may have to start recovering at 1AM to get the temp up to set point by 6AM, if the aux is locked out.

So, in general is it best to have no setback at all on a heatpump like this? Just keep it at a constant temperature? Or is a little setback better? With the average temperatures in this part of north carolina I was under the impression the heatpump would be efficient for most days.

[badtlc]

No setback helps insure that you use as little auxiliary heat as possible.

However, with the right controls, there is savings to be had by using a setback if it can recover w/out the use of aux heat.

[davefr]

Meaning that it may have to start recovering at 1AM to get the temp up to set point by 6AM, if the aux is locked out.

Beenthere,
It might start recovering at 1 am but it's not running from bedtime to 1 am. However it would without the setback.

Is there any way to optimize programmable thermostat settings based on daily schedule. When I'm home I like it at 66. But for night and daytime (approx. 16 hrs) I let it drop to 60 and then let it recover back to 66 late afternoon.

I'm totally guessing at these setback settings.

Is there any software or analysis that can tell you how much setback is optimal given the time your away from your home?

[davefr]

So, in general is it best to have no setback at all on a heatpump like this? Just keep it at a constant temperature? Or is a little setback better?

I'm sure it's a function of the duration of the setback.

If you're going to be gone for a few hours then I'm sure it's best to not do any setback. However if you're going to be gone for 16 hours then I'm sure some setback is optimal.

How much setback is appropriate given the duration that you're going to be away?

I'd like to see if there's a thermostat where all you tell it is your desired temperature while at home and then your schedule and it decides on the setback delta based on the duration of time you're gone and the outdoor conditions.

Maybe some of the high end Honeywell's do this?? I have no idea. I know on my older Chronotherm I have to tell it how much I'm willing to let the temp drop to when I'm gone. I'd rather have the thermostat optimize how far to let the setback go to given duration of my absense and outdoor conditions.

[badtlc]

From a pure energy standpoint, the larger setback is always going to save more energy no matter how long it takes to recover assuming one heating source. When you start talking aux. heat kicking in it is a different story.

[broconne]

Lots of information here.. I think I am taking away two key things.

1) My aux heat seems to come on too quickly.
2) My system would be more efficient if I could lock out the aux heat based on temperature.

That accurate? Anything big I am missing?

[beenthere]

The VP 8000. Is a 1° differential thermostat. So if you raise the temp 2°, the aux WILL come on.
Using an outdoor sensor. You can prevent it when outdoor temps are above the lockout temp.

Tell your builder.contractor that you want the outdoor sensor so you can use set back. And not have the aux heat coming on when its above balance point.

[beenthere]

Beenthere,
It might start recovering at 1 am but it's not running from bedtime to 1 am. However it would without the setback.

True. But, if it sets back at 10PM, and then has to start recovering at 1AM, you don't really save much.

Is there any way to optimize programmable thermostat settings based on daily schedule. When I'm home I like it at 66. But for night and daytime (approx. 16 hrs) I let it drop to 60 and then let it recover back to 66 late afternoon.

If you have gas heat, thats fine.

I'm totally guessing at these setback settings.

Is there any software or analysis that can tell you how much setback is optimal given the time your away from your home?

I tell people, 1° for every 2 hours they are gone from the house.
So if your gone for 8 hours, a 4° setback works well.

This is not for heat pumps. That don't have a way to lockout the aux heat. Or for heat pumps when the outdoor temp is below balance point.

[platchford]

Also keep in mind when using the program to setback temperature with the VP 8000 (and assuming adaptive intelligent recovery is on) that it takes at least a few days and maybe even a week or more for it to learn how early to start recovery. If it incorrectly predicts this then it will be forced to bring on the aux heat so as to have the proper set point at the proper time. That being said, after it has had a chance to learn the system it tends to be very good at avoiding using aux heat.

Regardless I would still get the OD sensor and have them lockout aux heat above 40 degrees or so. You certainly shouldn't need aux heat at 40 degrees if the system was sized properly.

[dan sw fl]

Lots of information here.. I think I am taking away two key things.

1) My aux heat seems to come on too quickly.
2) My system would be more efficient if I could lock out the aux heat based on temperature.

That accurate? Anything big I am missing?

Keep it simple. K.I.S.S.

No setback should be evaluated. You could well end up spending more with > 2'F set-back.
That 2'F maximum set-back might save 4% ($40 MAX Annual for Cary) with proper set-up.
Setback is a P.I.T.A. for heat pumps IMO.

Setback will N O T save you a significant amount.
Eat at home ONE night less per year instead of being a patron at that medium priced restaurant. Savings will proabably be double what setback will save you.

Sound simple? Simple Works!

[dan sw fl]

Do you have THAT itch, you JUST HAVE TO scratch?

Set the t-stat at 69'F instead of 74'F for the month of January to save $11.

Turn the t-stat to 79'F in the Summer instead of 76'F to save that $40 per year.

[davefr]

Keep it simple. K.I.S.S.

No setback should be evaluated. You could well end up spending more with > 2'F set-back.
That 2'F maximum set-back might save 4% ($40 MAX Annual for Cary) with proper set-up.
Setback is a P.I.T.A. for heat pumps IMO.

Setback will N O T save you a significant amount.


I disagree. From the time I go to bed until I return from work the following day is nearly 20 hours during the workweek.

Are you really saying that there's no gain in a setback?? This makes absolutely no logical sense.

I will agree that setback shoudn't be used for short durations.

[badtlc]

I disagree. From the time I go to bed until I return from work the following day is nearly 20 hours during the workweek.

Are you really saying that there's no gain in a setback?? This makes absolutely no logical sense.

I will agree that setback shoudn't be used for short durations.

The ONLY time a setback doesn't save money is when Auxiliary heat is used to recover. If you can recover w/out using Aux, it does save money.

[davefr]

The ONLY time a setback doesn't save money is when Auxiliary heat is used to recover.


I would be willing to bet my 20 hr setback from 66 degrees to 60 degrees saves money even if strip heating is used during the recovery.

If my HP duty cycle is reduced significantly for 19.5 hrs, then 30 minutes of recovery using strip heating becomes almost negligable. (even at 3-5X the power consumption) It also saves wear and tearn on the HP.

Where am I wrong??

I just don't know where to choose the optimal setback temp. Beenthere suggests 1 degree per every 2 hrs. Dropping down from 66 to 56 seems a bit too much but maybe I'll try it.

I'd like to see some more intelligence built into thermostats. Enter the rate your paying for power and a couple other parameters and let it choose the most economical setback temp. Thermostats are designed to efficiently provide the temp you want for various parts of your day. Temp isn't important when you're away. The "away" time should have an option to maximize energy savings and let temp float to where the thermostat decides within certain limits. With outdoor sensors the thermostats could calculate the rate of heat loss and adjust accordingly. It would also be nice to give them wireless internet so you could remote control/monitor your home from anywhere.
(ex: If my return to home will be delayed let me delay recovery by overriding the themostat from my office internet connection)

[Bubbleheadski]

Heat pumps work better and faster the warmer it is.... in heat mode. SO the colder it is outside the harder it has to work.... so the little bit the aux heat has to come on when its 40 out wont take forever if you set it back 5 degrees. At 40 degrees outside you should probably be getting 25 degrees of heat from the heatpump. If you have a 10kw strip heat, add on another 25-30 degrees. Your house will heat up quickly. And electric heat is more efficient than the LP or Natural gas the dual fuel system is using. (for the same amount of time.)

[beenthere]

Heat pumps work better and faster the warmer it is.... in heat mode. SO the colder it is outside the harder it has to work.... so the little bit the aux heat has to come on when its 40 out wont take forever if you set it back 5 degrees. At 40 degrees outside you should probably be getting 25 degrees of heat from the heatpump. If you have a 10kw strip heat, add on another 25-30 degrees. Your house will heat up quickly. And electric heat is more efficient than the LP or Natural gas the dual fuel system is using. (for the same amount of time.)

But, often, NG and LP, are cheaper to use then electric strip heat, due to fuel and electric rates.
Not always though.

[dan sw fl]

I disagree. From the time I go to bed until I return from work the following day is nearly 20 hours during the workweek.

Are you really saying that there's no gain in a setback?? This makes absolutely no logical sense.

I will agree that setback shoudn't be used for short durations.

That would more properly be referred to as a 4-hour set-UP.

OR just leave it at 60'F _ 24/7, YOU WILL BE FINE.

[dan sw fl]

Are you really saying that there's no gain in a setback?? This makes absolutely no logical sense.

I DISAGREE that Everyone reads well!

My statement applies to a very specific location where I know that the annual heating bill is 'not large'.

If the heating bill is $500 / year and you have a sizable setback
you'll save ~10% or $50.

READ S I G N I F I C A N T ! !! !!!

Is $50 a significant annual savings?
To some, it might be, to me , NO.

I'll carpool and save more than $70 per Month!

Someone in Oregon is going to save a lot more than someone in Cary, NC.
Your heating season is 2 to 3 times as long.

[dan sw fl]

I would be willing to bet my 20 hr setback from 66 degrees to 60 degrees saves money even if strip heating is used during the recovery.

1
Where am I wrong??

2
I'd like to see some more intelligence built into thermostats.

1
Determine your Oregon temperature bin data and equipment performance
so you can assess your heating cost in a thermal / economic model.

2
If thermostats get any more intelligence,
they'll easily pass the intelligence of MANY humans!

[davefr]

OR just leave it at 60'F _ 24/7, YOU WILL BE FINE.

Good idea but my wife complains when her feet stick to the cold floor.


If thermostats get any more intelligence,
they'll easily pass the intelligence of MANY humans!

That's not hard to do!