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Thane_Bitter
Inquire within
Premium
join:2005-01-20
Reviews:
·Bell Sympatico
reply to pandora

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.


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast
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".
--
The difference between genius and stupidity is that genius has its limits.


Hagar

join:2004-10-31
Sunnyvale, CA
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.


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast
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.
--
The difference between genius and stupidity is that genius has its limits.


Hagar

join:2004-10-31
Sunnyvale, CA
Reviews:
·T-Mobile US
·AT&T U-Verse
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?


cowboyro
Premium
join:2000-10-11
Shelton, CT
said by Hagar:

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.

scooper

join:2000-07-11
Youngsville, NC
kudos:2
reply to Hagar
said by Hagar:

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.


Hagar

join:2004-10-31
Sunnyvale, CA
Maybe I am biased since I live in California. Electricity here is very expensive compared to gas that even with a COP of 4 you would not save money.

Heatpumps are not common which is sad since we have the perfect climate for them.