pandoraPremium
join:2001-06-01
Outland
kudos:1
1 edit | Could outside, warm inside It was cold outside last night, but warm inside my home. |
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| Re: At 7F outside heat pump maintained 73F indoors I assume its an air-to-air heatpump (outside unit looks like an AC unit)? What sort of Auxiliary heat do you have (electric, propane)? |
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pandoraPremium
join:2001-06-01
Outland
kudos:1
3 edits | redacted redacted |
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| Re: At 7F outside heat pump maintained 73F indoors Well it seems to be working. 
I had (have, thought the controls have been removed so it works as an AC unit only) an air-to-air heat pump, while it was well maintained it didn't seem to produce any comfortable amount of heat and ran for long periods of time. While I think the technology is good, especially with ground based systems, I just wasn't working for me. In my case aux heat was gas forced air and with high (getting even higher) electrical costs it made more sense to use gas, especially after the furnace was upgraded to one with much higher efficiency.
Thinking back, if it was zero out (32F) mine seemed to run 30min for every hour just to keep the house (2200sqft) at 20C (68F). During defrost it would switch on aux heat; it was the only time the house was comfortable. If I moved into an area without gas I would seriously look at the ground type systems they are much more efficient.
I am impressed with your results. |
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| reply to pandora
said by pandora:This thread to help maintain a record of my heat pump experience for others. We need to know the exact manufacturer, model no. etc. |
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pandoraPremium
join:2001-06-01
Outland
kudos:1
1 edit | redacted redacted |
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BobAccount deleted
join:2012-07-22
New Jersey Reviews:
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| reply to pandora
Re: At 7F outside heat pump maintained 73F indoors said by pandora:My estimate is 3,500 watts of electric resistive heat is about one U.S. BTU. 2 tons is about 7,000 watts of resistive electric. I'm not sure what (watt?  ) you're saying here.
1 Watt = 3.412 BTU/hr
1 Ton = 12000 BTU/hr = 3517 Watts
Did you mean to say "My estimate is 3,500 watts of electric resistive heat is about one U.S. BTU ton"? That would be correct. And it's not an estimate; it's the definition of the units. |
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| reply to Thane_Bitter
That is one of the things you need to accept up front: heat pumps do not have the same Delta T across the coils as a fossil fuel or resistance heater.
For an 18 SEER 4T Goodman, the Delta T at 47*, is 26*F. So if you have an a return air temp of 70* the best you will see at the registers is 96*. At an OAT of 10*, you are looking at a rated Delta T of 14* or an ideal air temp of 84* at the register. To some people, this is a cold wind, especially if the ducting is poor, and it induces drafts on occupants.
This assumes no losses in the ducting and the AHU is running at it's rated speed. Fan's can be slowed down and temperature rises can be increased slightly, at the cost of efficiency.
A fossil fuel/electric furnace will have discharge temps in the 115* range which feels "warm".
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The difference between genius and stupidity is that genius has its limits. |
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pandoraPremium
join:2001-06-01
Outland
kudos:1
1 edit | reply to Bob
redacted redacted |
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| reply to pandora
Re: At 7F outside heat pump maintained 73F indoors How are you disabling the supplemental heat? |
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redholm
join:2004-10-31
Sunnyvale, CA | reply to pende_tim
Good points on delta T.
Personally I want my HVAC system to be impossible to notice, ideally totally silent and no draft, it should just keep the temperature and air quality.
E.g. I do not want to notice air flows warm or cold. |
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BobAccount deleted
join:2012-07-22
New Jersey Reviews:
·Optimum Online
| reply to pandora
Re: Hostile?? Why? said by pandora:said by Bob:I'm not sure what (watt? ) you're saying here.
1 Watt = 3.412 BTU/hr
1 Ton = 12000 BTU/hr = 3517 Watts
Did you mean to say "My estimate is 3,500 watts of electric resistive heat is about one U.S. BTU ton"? That would be correct. And it's not an estimate; it's the definition of the units.
No. I stated my working estimate for watts to tons is 3500 watts is about a ton. Being off 17 watts over many thousands of watts is meaningless and within any margin of error for the various devices, generators, and delivery systems my home uses. Why the demonstration of hostility?? Read my message again. You said that 3500 W = 1 BTU. I simply asked for clarification, because that couldn't be correct. (I'm not talking about the 17 W. I'm an engineer, and know all about rounding, estimates, et al.)
As far as hostility is concerned, take a look in the mirror. |
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| reply to pandora
Re: At 7F outside heat pump maintained 73F indoors I wonder if you can buy a heat pump that can be powered by PoE. |
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Not meaning to steal the thread....
That is one of the reasons we put a HP in our new house to replace the builders propane furnace.
When the gas furnace came on, it blew very hot air for 5-10 minutes then shut off. Room went back to 70* room temp when the jet engine blast stopped, and we felt cold. Repeat this 2-3 times an hour and we were really uncomfortable.
With the HP, I never can tell when it runs, and the room always just feels the same temperature. One night just after the install, I was sitting there and after an hour of so was marveling at how well the house held the heat since the HP had not come on, then I looked at the thermostat, and the unit was running.
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The difference between genius and stupidity is that genius has its limits. |
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Did you do the Manual J on the house yourself or did the HVAC guys do that as part of building up the proposal?
Just out of curiosity, what were your design conditions and the resulting heat loss and gain? Did they estimate a balance point? You must have a huge load to support 2x 48,000 BTUH systems.
I am also surprised that with the unit only putting out 25 MBh @7*F it was able to hold the house. Your balance point must be very low.
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The difference between genius and stupidity is that genius has its limits. |
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redholm
join:2004-10-31
Sunnyvale, CA Reviews:
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| reply to pende_tim
You and Pandora seem to have well designed HVAC system and good experience with your heatpumps. Thanks for sharing your experience.
I do not understand why HP are not more popular in the US and why the common perception is that they are no good? |
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| said by redholm:I do not understand why HP are not more popular in the US and why the common perception is that they are no good?
There is a widespread misconception that "heat pumps don't work in cold climates".
Actually undersized head pumps don't work well in cold climates. The "upstairs" system of my home gets to even cycle at 10F. |
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scooper
join:2000-07-11
Youngsville, NC
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| reply to redholm
said by redholm:You and Pandora seem to have well designed HVAC system and good experience with your heatpumps. Thanks for sharing your experience.
I do not understand why HP are not more popular in the US and why the common perception is that they are no good?
They're pretty popular below the Mason Dixon Line. Maybe the issue was people weren't getting properly designed systems installed, or not using them correctly / false expectations.
I have no complaints with mine either, but since I grew up out on the Great Plains, what really got us motivated were two months of $400 resistive heating months in a row - that's why we installed the propane furnace as backup. |
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said by pandora:said by Thane_Bitter:I assume its an air-to-air heatpump (outside unit looks like an AC unit)? What sort of Auxiliary heat do you have (electric, propane)?
Other forum members assured me, I'd have cold air blowing in when the heat pumps were defrosting freezing my family. So far, none of the dire predictions have occurred. Do you use the AUX heat when defrosting? That will of course make a huge difference in the register temp.
What is your defrost timer set for? 30 or 60 minutes?
I assume you are not using the 4 wire communicating system between the HP and the AHU since you are not using the Goodman branded thermostat?
Tim
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The difference between genius and stupidity is that genius has its limits. |
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redholm
join:2004-10-31
Sunnyvale, CA Reviews:
·AT&T U-Verse
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| I hope there is not a defrost timer, a modern heatpump should not have a defrost timer it should sense when defrost is needed. The defrost cycle is a surprisingly complex problem to optimize but doing better than a timer is not hard.
Also the HP should not need an AUX heater to avoid cold air during defrost. A modern heatpump should turn of the indoor fan. If you open up the inside unit and measure the coils temperature it might show 10-15 Fahrenheit but you should not feel any cold air.
E.g. if you have a defrost timer or feel cold air (without AUX heat) replace your heatpump with a better one. |
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