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Heat pump and programmable Tstat savings

Posted by JMphoto (My Page) on
Mon, Dec 12, 11 at 13:40

We just built a new home and moved in during September. Our last house was oil/hot water baseboard, so the heat pump is new to us. In our old house I would program the heat to lower from 11pm until we came home from work the next day at 3pm. We have a Honeywell Pro 8000 programmable tstat on the new system, but it seems like some folks don't recommend setting the temp lower for heat pump like we used to, claiming the heat pumps take much longer to catch up and it ends up not saving as much. Would love to hear from some the HVAC experts on here. I currently have it set to 66 when we are home then drop to 62 when we are sleeping and away. We are in eastern PA about an hour north west of Philly.
Thanks


Follow-Up Postings:

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RE: Heat pump and programmable Tstat savings

JMphoto

Depending on your heating load and HP sizing, I don't recommend a setback more than 3 degrees. And auxiliary heat should be locked at around 32-35 degrees.

There is something about heat pumps, the use of auxiliary heat, setback, and false economy.

IMO


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RE: Heat pump and programmable Tstat savings

Thanks Tigerdunes. When you say the auxiliary heat should be locked at around 32-35 degrees, can you give me some info on that? Is that set or programmed somewhere? Our HVAC guy will be coming later this week just to do a system check since it is new and make sure everything is running OK.
What do you mean by your last comment [There is something about heat pumps, the use of auxiliary heat, setback, and false economy. ]?
Thanks


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RE: Heat pump and programmable Tstat savings

Most thermostats, if not all, will activate aux heat if the temperature difference (or demand) is more than 2*F. If you set a large setback, a thermostat that doesn't know any different will activate aux heat when the setback is complete. This will bring the house temperature up quicker but will use more power than perhaps leaving the temperature alone in the first place.

There are thermostats out there that have something called 'anticipation' or 'smart recovery' where the thermostat does not activate aux heat when coming out of a setback. It computes how much time it should take to get the temperature to the desire level and activates the hp early enough in order to be at the desired temperature at the end of the setback period. (It will do the same for cooling.)


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RE: Heat pump and programmable Tstat savings

Our Honeywell has what honeywell calls "Adaptive Intelligent Recovery" I know this sets the the system to come on earlier to start to warm the house, but I am not sure if that does prevent it from kicking in the aux heat. I had them disable the feature because it was coming on earlier than scheduled and I did not know anything about it, but now it sounds like I should have it turned on again?


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RE: Heat pump and programmable Tstat savings

I would think (although I have no Honeywell knowledge) that keeping the adaptive setting on would help prevent aux situations. I suspect your thermostat would do fine prevent aux anyway but the adaptive seems safer. Perhaps your HVAC people would know for sure.

People have different opinions but as long as you don't get into aux heat, then setbacks are helpful. The 3 degree rule is overly simplistic because if your system is oversized, that would be a different number - perhaps 6 degrees. Also with adaptive intelligent recovery, your system would probably fix things anyway. If your system takes 6 hours to get up 6 degrees than it would start 6 hours early - limiting the setback advantage but not eliminating it. You would be oversized if a/c dictated your sizing which is possible even in your climate if you had a great envelope and a lot of West windows.

Tigerdunes line was basically saying that over aggressive setbacks can be false economy - especially if aux heat kicks in. The aux heat setting probably doesn't apply to you - I think he was talking about NG backup.

Do you have geothermal or are you talking air source heat pumps?


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RE: Heat pump and programmable Tstat savings

Thanks for the great info. We have air source heat pump.


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RE: Heat pump and programmable Tstat savings

The "smart recovery" or "adaptive recovery" function on both a Lennox two-speed 16-SEER system in my previous house and the lower-end Carrier 1-speed 12-SEER system in my current house did not prevent the auxiliary from running toward the last few minutes of recovery. The room temp may been only 2F shy of the target, but the auxiliary would still trigger when the clock clicked-over to the target time. For that reason, I had an outdoor temp sensor option added in both cases to lock-out the auxiliary for avoiding unnecessary use of it. If another 20 to 30 mins of running without the auxiliary is needed to hit the target, fine by me.


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RE: Heat pump and programmable Tstat savings

To fully utilize any of the features here the stat needs to have an outdoor temp sensor. The adaptive recovery is only a guess unless the stat can 'see' the outdoor temp and over time calculate how much time is needed to ramp up the temp.

The 'lockouts' are only available with an outdoor sensor. You can set the stat so that under no circumstances will the strips come on above a certain set temp. I don't use setbacks as there is usually someone here 24/7 but my strip lockout is set at 35 degrees. Its 43 right now... The strips will NOT come on. I also have the heat pump 'locked out' at 0 degrees which it usually doesn't get below zero very often or for very long and I don't see much use to let the unit sit out there and run non stop in those temps.

The strips should be 'staged' also so only part of the set comes on if the heat pump is running and needs a boost. There is no need to be running full strip capacity with the heat pump operating. Also if you have the heat pump off or locked out the stat will start with one set and if the temp is not coming up fast enough the stat will activate the other portion also.

I have 15kw of heat strips staged at 10kw and 5kw. My first stage of strips is on the 10kw set to keep the air warm during defrost and if additional is needed the other 5 activates. My old system had 20kw staged 50/50.

These options when set up correctly can be the next best upgrade other than insulating and sealing which is always the number one payback.

I consider this type of setup a must for anyone who uses setbacks of any sort if you really want to save money in the long run.


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RE: Heat pump and programmable Tstat savings

Here is the product data manual for the Vision Pro 8000. I think you have a version of this thermostat.

As the other posters have stated, you need the optional outside temperature sensor installed and enabled in order to a good job of adaptive recovery and to lock out the emergency heat mode. This thermostat supports lock out temperaturs for both the heat pump and emergency heating. There is a minimum dead band of 5 degrees F between the two. It would be possible to set the lock outs so that the heat pump and back up heating would only operate within a 5 degree window of outside temperatures. I don't have experience with this so I don't know if this is the optimal set up for your situation.

I am a proponent of using set backs. I agree you need to be careful about the heat strips coming on frequently. The document does not indicate the algorithm when the emergency heat is enabled in conjunction with the heat pump.

I personally am not a fan of adaptive recovery. I disabled it for my thermostats.

Here is a link that might be useful: Honeywell Vision Pro 8000 Thermostat


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RE: Heat pump, setbacks, and false economy...

Large setbacks on HP systems are false economy if it takes hours to catch up with condenser running continuously and/or strip heat is included in the recovery mode. Not worth it especially if one considers the comfort factor as well.

IMO


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RE: Heat pump and programmable Tstat savings

FYI. The Honeywell VisionPro has a couple of relevant settings. One is the adaptive recovery (register 0530) that others have mentioned. There's also a register (0680) for how aggressively you want the heating system to operate to get to setpoint. This affects how quickly the stat calls additional heating stages. There's a similar register (0690) for cooling.

We run our dual-fuel system with daytime setbacks to 65F from 68/69F, adaptive recovery, and less-aggressive operation. The only downside is that it'll run forever (hours) to try to recover once we get into consistent temps in the 30's where we're just above the furnace lockout temperature.


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RE: Heat pump and programmable Tstat savings

See above post.

We run our dual-fuel system with daytime setbacks to 65F from 68/69F, adaptive recovery, and less-aggressive operation. The only downside is that it'll run forever (hours) to try to recover once we get into consistent temps in the 30's where we're just above the furnace lockout temperature.

Yep...

IMO


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RE: Heat pump and programmable Tstat savings

Not a downside if running constantly doesn't bother you.

Easily fixed by changing the furnace lockout. If the furnace is NG, then it probably would be worth changing it.

I am surprised that people find the same comfort temperature at night as they do during the day. I sleep at 62 and wake at 70. Quite a spread but that is done by not really heating the bedroom.

Agree to disagree. But I think we can all agree that it costs less to heat a house to 68 as compared to 72. We can probably all agree that using NG, the most aggressive setback you can handle saves the most money. If a setback forces you to use a more expensive heat (ie electric strips), then your savings are diminished possibly to zero and beyond.

The issue that seems to be the controversy is that if you setback but only use the heatpump to recover, the setback may not be beneficial. I would argue that it almost always is beneficial but I can imagine a rare situation where it wouldn't be helpful (mostly if it was trying to recover a setback in the morning when the outside temps were quite low and the COP was much worse than it would have been at midnight). This would definitely diminish the benefit and I would think that most of the time it would not diminish it to zero.

Even a properly sized heat pump should be able to recover nicely in the afternoon - at the heat of the day. It also is working with the best COP of the day. So I think daytime setbacks are really hard to argue with.


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RE: Heat pump and programmable Tstat savings

Thanks to all for the help. Since there is so much great info above and going back and forth, and some I don't understand since I am not an HVAC specialist and understand some terminology, can you guys help me recap what my best direction is? So it sounds like, if I keep the drop or setback to 3* max and set the thermostat to do a less aggressive recovery (as described above 0680) I should be OK. I have adaptive recovery turned off right now. My setback is simple, it goes to 62* at 11pm at night and stays there until 3pm when it comes up to 65* so its warmer when we come home.I figured 3pm would be easier than 6am outdoor temp wise. We not need to have it warm in the morning before work.


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RE: Heat pump and programmable Tstat savings

I would get an outdoor temp sensor installed so you can lock out the strips and have 'real adaptive' control. If you want to save money with a setback at least give your stat something real it can work with other than just a guess.

With no outdoor sensing... say there is a three day cold spell and it drops in the 20s and the stat starts temp recovery late and kicks in the strips because it started recovery an hour before the set time. The next few days it jumps up into the 50's and the stat starts recovery a few hours early..cause it is going off of averages.

With temp sensing it can calculate that with the outdoor temp at 50 it might start recovery an hour before the set time. At 20 degrees it can back up a few hours and gradually bring it up.

There are many in here that can help with settings to start with and how to change the settings to get the most for your money.

If you want to get the most out of setbacks you need to get the outdoor sensor. I think 20.00 on ebay or amazon will buy one. One other nice option is you can view the temp outside right at the stat.


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RE: Heat pump and programmable Tstat savings

Thanks Country. I will order one today. What is optimal placement on the house? Our front faces west.


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RE: Heat pump and programmable Tstat savings

I would advise against doing the setbacks with the heatpump.

Often time during the day when you might have the setback is the warmest part of the day. This is when your heatpump is able to get the most heat from the outdoor air. It is possible it uses less energy to maintain a house at 68 degrees fahrenheit with daytime highs in the upper 30's/low 40's then to do the setback with this same temperatures. When the heatpump runs to recover the temperature is often dropping.


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RE: Heat pump and programmable Tstat savings

Neo,

I don't follow the logic of your post. The OP stated he sets the temp at 66 when home, and 62 otherwise. Those are fairly low temperatures. A southern/western exposure on a sunny day may be able to maintain a temperature of 62 degrees. The heat pump may never come on while the sun is up.

The savings of a a set back will vary greatly form one house to another. You have to experiment to get the optimum benefit.


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RE: Heat pump and programmable Tstat savings

countryboymo- I never was really sure that the 'intelligent' part of the Honeywell Vision Pro was intelligent enough to take outdoor temperature into account. Maybe I'm wrong. Seems that would ideally require the stat to have some equipment-specific info (it doesn't) to optimize operation.

JMPhoto- ideally the outdoor sensor is near the heat pump so that it reflects that temperature. That said, our HP is on the S side, but it was easier to place the sensor under the eaves on the W side. As long as they aren't going to be radically different, either is fine. I'd try to keep it out of direct sun, though.

FYI, if your 3PM setback is coming on for you to get home at ~5PM, you ought to turn the adaptive recovery on. You're doing the same thing, and the stat will do a better job of it. You can still easily keep the setpoint for overnight and daytime at 62F as you stated.


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RE: Heat pump and programmable Tstat savings

All I'm trying to say is the heatpump may have to run a very long time in the early evening when the temperatures are colder outside to bring the inside of the house back up. The heatpump isn't good at bringing up temperatures to begin with. Even worse the outdoor air is likely colder and less heat will be extracted from the outdoor air. The heatpump running during the daytime would get more heat from the air because of the warmer temps. The cycles would be shorter and less often for this and because of heatgain from sunshine. I've tried this method. It is just better for me to keep the thermostat at the same temperature in my experience with setbacks and trying to recover with the heatpump.


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RE: Heat pump and programmable Tstat savings

I get it. What you are doing is using the mass of the house to store the heat during the day when the heat pump has an easier time to provide heat.


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RE: Heat pump and programmable Tstat savings

I don't get it. Where I live 3-5 pm is the warmest part of the day - perfect time to recover from setback.


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RE: Heat pump and programmable Tstat savings

My heat pump did in some cases run continuously for 4 to 5 hours to recover when I did a 10F heat setback during daytime (11 AM to 1 AM, 14 hrs), maybe long as to 8 AM in a few extreme situations if the indoor temp did drop the full 10F (auxiliary locked-out to 25F ambient) ... but it was blowing warm air the entire time and I was quite comfortable.


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RE: Heat pump and programmable Tstat savings

If its recovering from 3 to 5 pm that wouldn't be so bad. I wasn't coming home till 8:00pm. The recover from 6-8 was not nearly as good. I think a person should try and see what situations works best for them. The heatpump does produce more heat in-daytime warmer situations. I like the idea of running it when I'm getting the most COP.


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RE: Heat pump and programmable Tstat savings

I talked to someone from Honeywell a couple years ago after having issues with setup on my first visionpro 8000 series and was informed that the outdoor temp sensor would not only work for lockouts but would also be utilized for calculating recovery setback time. I could very well have been mis-informed also. I will have to research that.


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