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daddo said:
With heat pumps, it's best to set the temp you want and leave it alone.
we let our place cool down (I think down to 55 or 58) during the night and then start raising the temp back up about 15 minutes before we get up in the morning. Is that a bad thing to do with a heat pump?
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Mark
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fredhargis said:
That part (the outside temp) is different than the one I had (XL1200) and the geo I have now. The Trane had a thermostat in side the condenser housing that was adjustable to the cutover temp. Mine would cut ver to furnace only when the temp dropped below 30º. My current unit (Carrier) cuts over to the furnace when it hits 5º (also a gas furnace). It's interesting to see what your guy told you. The place I just bought has geo, but it's an older unit with no out side thermometer (that I'm aware of), I'll bet it works just as you described
I'm in the south so I forget things can be different up north. There are outdoor thermostats (sensors) that just prevent the aux heat from operating at a set temp, then there are ones that lock out the heat pump and allow the aux heat to work only, then as the temp keeps falling, allow even more aux heat to operate. Then there are outdoor sensors for certain thermostats to know what the temp and even humidity is and act accordingly. You can even place a sensor in each room of the home. I fought the regulations on heat strip sizing and had to go against the grain for elderly people in older homes. The smaller heat strips simply would not keep the home warm enough during unusually cold spells. Many elderly people require winter temps to be as much as 76*-78* @35%+ humidity to be comfortable (Systems aren't designed for those abnormal criteria). I oversize the strips and install a 7-9 minute time delay for the last 5 or 10kw strip to operate coupled with an outdoor thermostat to prevent it from working above 38*. This stopped the complaints. It would be easy to oversize the heat pump to maintain a higher temp, but then the complete system is oversized and will cause even more issues.
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meackerman said:
[blockquote]daddo said:
With heat pumps, it's best to set the temp you want and leave it alone.
we let our place cool down (I think down to 55 or 58) during the night and then start raising the temp back up about 15 minutes before we get up in the morning. Is that a bad thing to do with a heat pump?
[/blockquote] Mark it's not recommended with air source heat pumps due to the slower recovery they have. It's really bad in cold climates. I think it's more of a comfort issue than a "bad thing". That might be different in your part of the world (doesn't get as cold).
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daddo said:
[blockquote]Mr_Mike said:
Not yet a heat pump owner, but working on it.
Existing gas furnace has a dead band of something like 2 to 4 degrees.
Do you set up a heat pump thermostat to have a dead band of 1 degree?
Else, at a 1.5 degree differential, you would always have the strip heat cycle with the heat pump, at least for a while.
Dead band is the temp difference setting between heating and cooling settings on a thermostat set up in "auto" changeover mode. This prevents the system from cycling from heat to cooling at one set point. The 1.5 degree for aux heat is different and can also be different in some thermostats. There are "economy" settings where the thermostat will wait a default set determined amount of time before using the aux heat- be it another 1 or 2 degrees or in minutes. Then there is the "comfort" setting where comfort over rides energy savings and starts the aux heat at the 1.5 degrees regardless. Some thermostats "Intelligent recovery" where it records the running times and temperatures allowing it to already know how long it takes the home to warm up or cool down and will cycle the system earlier or later to maintain the set temp. In doing this, it may bring the heating cycle on sooner as to prevent the aux heat from being called for. Manually changing the temp set point on the thermostat prevents this option from working at that time. That, among other reasons is why a heat pump in heating mode is best set at one temp and not changed manually, unless of course you have a more effective way to recover like Thooks' gas furnace. But basically, the 1.5 degrees is the norm and isn't commonly a changeable feature.
[/blockquote] Thanks. "Dead band" is my term. I have no clue as to its proper use in HVAC.
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meackerman said:
[blockquote]daddo said:
With heat pumps, it's best to set the temp you want and leave it alone.
we let our place cool down (I think down to 55 or 58) during the night and then start raising the temp back up about 15 minutes before we get up in the morning. Is that a bad thing to do with a heat pump?
[/blockquote] It depends. If the outdoor temp is nearing the balance point of the system, no, it is not a good idea at all. The aux heat must run to recover and it costs you more to run it and you run the chance of icing up and calling for defrost cycles. During defrost, the cooling cycle is run along with the aux heat- not efficient. If you have a gas furnace for aux heating it isn't as big a deal- you just buy more gas and it recovers quickly. If it is not that cold outside, say above 48* and dry, it isn't too bad. The heat pump transfers the heat outside to the inside. The less heat outside, the less heat transferred until it gets to the point where the heat loss in the house is the same as the heat gained from the system, then it is only able to maintain whatever temp it is in the house, then the aux heat must work to bring the temp up further. Then, you hope the aux heat is sufficient enough to raise the temp in the house. If you have been doing that and it has worked fine for you and the system isn't overworking or your heating bills abnormally high, I'd say your ok.
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no aux heat strips in my heat pump. Previous owner that installed it didn't put them in for some reason.
installing them has been on the list of things to do, but its $700-800 to do so plus I have to run another electrical line cause the line it has is only 15 or 20 amps.
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Mark
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I found out that my thermostat has a Comfort/ Economy setting for the Aux heat strips. (It is buried in the installation programming mode.) In the comfort mode they kick in to raise the temperature faster. In the Eco mode it will try to use just the pump and only go to the Aux heat if it detects that the temp is not rising fast enough. It was set on comfort mode. I will try the economy setting and see if works OK for us or, if the temp is rising too slow, I'll go back to the original comfort setting.
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meackerman said:
[blockquote]daddo said:
With heat pumps, it's best to set the temp you want and leave it alone.
we let our place cool down (I think down to 55 or 58) during the night and then start raising the temp back up about 15 minutes before we get up in the morning. Is that a bad thing to do with a heat pump?
[/blockquote] It's not an efficient thing to do. Same goes with summer and cooling. Set the thermostat and forget it. Don't raise the temp while you are gone. Systems are sized to maintain temperature not for quick heating or cooling. I have heard people that turn their ac off when the leave in the morning and turn it on when they get home. Then they wonder why it never shuts off while they are home. It takes hours and hours to recover the air temp and the temp of the items in the house. In the end they done save any electricity and end up shortening the life of their compressor due to extremely long run times.
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seems its time to reprogram my thermostats...
Reality is that which, when you stop believing in it, doesn't go away. - Philip K. Dick
Mark
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meackerman said:
seems its time to reprogram my thermostats...
Also notice that all those programmable thermostats lost their energy star ratings. When the doe finally did real world testing they found that setback thermostats didn't save energy. They were originally going off of a computer model when they gave them the rating. There are a few of the test results online from doe and others showing the same results. I find it funny that nest is making a fortune off theirs but then the testing data isn't easily accessible to customers to inform them
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