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  1. #1

    Optimal Use of Heat Pump

    We moved into our house about 6 months ago and the heat pump recently died. Since we were running on aux heat and a bit overwhelmed with such a big expense we got a few quotes and had a new pump installed right away. Luckily, I did have time to do some research and hopefully made a decent decision.

    That all said, I am still anxious to see how the new heat pump works out. There are certainly many horror stories online and I hope we never become one of them. I am also worried we won't see any monetary benefits from the change - that's the only potential upside to laying out such a big expense.

    My question is, how many we get the most out of our new system as far as reducing our utility bills? For example, I read somewhere that turning down the heat too much at night can be counter-productive as the aux heat may have to kick in to get back up to higher temps at waking time?? I know heat pumps have their own little quirks so I want to try and run ours as efficiently as possible so any advice is greatly appreciated.

    Background: We replaced a Carrier FV4ANF003/38YXA042 (3.5 ton, 10+ years old) with a Carrier 25HPA6/FE4 (4 ton) with Infinity Thermostat with a 10 yr parts&labor warranty. We live in Southeastern PA.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    34,095
    There is such a temp as the thermal balance point. That's where the temperature loss of the house meets the output of the heat pump. At that point, the heat pump will run constantly to MAINTAIN the set temp. That often is in the 20s. So if you want the heat pump to WARM the house up after a setback without strip heat help, you better be above that balance point. The higher above it, the more recovery. Most stats try to avoid using strips but when you get close to or below the balance point, it is IMPOSSIBLE. You can experiment a bit and see how your system does with a few degree night setback. Watch in the morning and if you see the stat bringing on the backup, better not do a setback at that outdoor temp.

    In my house, with gas backup, it won't run above 20 out. So if I do a setback with the temp in the 20s, there is no recovery. The pump runs constantly but not raising the temp. In the 30s I can setback a couple degrees and warmup in about an hour. In the 40s out, warmup is rather fast.

  3. #3
    Join Date
    Nov 2008
    Location
    California
    Posts
    145
    Not sure if your thermostat allows you to adjust the temp bands that trigger aux heat. If it's like mine, then any 2-degree variance that can't be made up soon enough will trigger high stage or aux heat (depending on your equipment and the use of adaptive recovery.) One way to have your setback and still avoid aux heat is to stage your recovery. Meaning, set a target temp no more than two degrees above setback, followed one or two hours later by another two degrees of recovery. If your unit is capable of handling that in the time allotted, then you'll have a four degree recovery without using aux heat.

    Aside from any savings achieved, running your heat pump less overnight is a good way to avoid noisy defrost cycles at times when you're trying to get some shuteye.

  4. #4
    Join Date
    Aug 2010
    Location
    White House TN
    Posts
    113

    Your on the right track

    The whole setback at night is a huge mistake in my book with a heat pump the best thing you can do is find a comfortable temp and leave it alone the programmable thermastats are great if your out of town alot but not much good for day to day. Your house will have alot to do with the recovery rate as well if it is insulated very well you my be able to play with it some but you will not see much of a savings on your electric bill.

  5. #5
    We do setback at night because we like it much cooler to sleep in (65 degrees) versus 69-70 degrees when we get out of bed. During the winter, we cannot sleep with warm temperatures. We could open windows but that would be counter-productive.

    We do something similar in the summer (temperatures adjusted accordingly) with a decrease in temperature at night and a warmup in the morning.

    We recently replaced our systems with hybrid systems - the balance point is about 40 degrees OAT as far as cost of gas versus efficiency of our heat pump. Backup is not a problem with such a system because today natural gas is cheap in our area. Electricity is 13 cents a KW after all the distro charges are added.

    Most newer thermostats attempt to keep the aux heat off, but may turn it on if they realize they are not keeping up (even within a degree). This was costing us a fortune when we had electric strips as aux heat backup. The setback was costing us potentially $2-3 dollars a day.

  6. #6
    Join Date
    Nov 2008
    Location
    California
    Posts
    145
    Quote Originally Posted by charlesw615 View Post
    programmable thermastats are great if your out of town alot but not much good for day to day.
    Since energy savings from setbacks depend on local utility rates, the capacity of the HP relative to the heat load, climate, what T-stat you have, etc., etc., I can appreciate those folks who just want to set it and forget it. That's really the only thing one can do if your HP is not capable of bringing the temp back up in a reasonable time frame. However, the OP has a 4 ton unit, so he may be able to benefit from using the setback approach.

    As for programmable T-stats being not much good day to day, that's a bit of an overstatement IMHO.

  7. #7
    Join Date
    Feb 2004
    Location
    Pacific NW
    Posts
    567
    how ma_y we get the most out of our new system

    If your Poco has a low nightime rate, it may even pay to INCREASE the tsat setting at night (e.g about 70% or less of the daytime rate)

    In what part of the country do you live?

    Here is what I do at my own house (PNW), where I have an air-air Rheem plus a custom GSHP. My outdoor tstat puts control of house temp to the Rheem when it is above about 45F outside, run the GSHP below that.
    NO aux resistance heat at all. I even removed the coils to improve (very slightly) airflow, and live with a very occasional blast of cold air for high humidity days when the outdoor coil needs to defrost if outdoor temp over 45F.

    Many HPs have a separate circuit breaker (CB) for the aux heat, if yours does, try simply switching the aux heat CB off and see if you can tolerate the cold air blast during a defrost cycle. If no CB, ask you installer for his opinion on this option for your area. I'm in Seattle area, figured it saved me about 8% on electric bill when I was only running the Rheem, before installing the GSHP.

  8. #8
    Join Date
    Jul 2008
    Posts
    551
    to get the most, you need a quality programmable t-stat that allows you to lockout the aux heat strips and has good, predictive recovery programming. Then....

    1) Find out what setbacks you want to use.
    2) Find out how low the outside temp can get before you can no longer recover from the setbacks.
    3) Find out the thermal balance point at which the heat pump can't maintain (hopefully lower than #2).
    4) lockout aux heat until about 5 degrees above the thermal balance point.

    The rest is up to you staying on top of things. Use the setbacks when the temperature is warm enough. When it isn't, just press hold on the t-stat to maintain temps until the temps get warm enough again.


    It gets slightly more complicated if you have NG aux heat.

  9. #9
    Wow guys, thanks for all the input. This is a bit more complicated than I anticipated though.

    We have the Infinity Tstat which I understand to have it's own controlling behavior, but the manual that came with it doesn't give me much info. I need to see if I can figure out if and how to control the aux set point it sounds like. All I did find was that the Infinity starts the recovery 90 minutes prior to the wake time. Other than waking up at 4:30 am, I'll have to get creative.

    At this point I think we'll have to wait till next winter to really get a feel for the system as things are starting to warm up weather-wise. Heating is our bigger expense here in PA.

    The Infinity Tstat sounded cool when we were getting quotes, I just wish that all the data it is collecting could be outputted to the user.

  10. #10
    This is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary, or ask questions of the OP here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

    Further infractions may result in loss of posting privileges.
    Last edited by beenthere; 01-27-2013 at 12:09 PM. Reason: Non Pro * Member

  11. #11
    Join Date
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    67,928
    Imsuchanovice, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

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