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pandora
Premium
join:2001-06-01
Outland
kudos:2

3 edits

1 recommendation

reply to Thane_Bitter

redacted

redacted



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

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.


laserfan

join:2005-01-14
Texas
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.

pandora
Premium
join:2001-06-01
Outland
kudos:2

1 edit

redacted

redacted


Bob4
Account deleted

join:2012-07-22
New Jersey
Reviews:
·Optimum Online
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.


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


pandora
Premium
join:2001-06-01
Outland
kudos:2

1 edit
reply to Bob4

redacted

redacted



BillRoland
Premium
join:2001-01-21
Ocala, FL
kudos:3
reply to pandora

Re: At 7F outside heat pump maintained 73F indoors

How are you disabling the supplemental heat?



Hagar

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.


Bob4
Account deleted

join:2012-07-22
New Jersey
Reviews:
·Optimum Online

2 recommendations

reply to pandora

Re: Hostile?? Why?

said by pandora:

said by Bob4:

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.


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast
reply to Hagar

Re: At 7F outside heat pump maintained 73F indoors

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.



pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast
reply to pandora

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.
--
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
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?



cowboyro
Premium
join:2000-10-11
Shelton, CT
Reviews:
·AT&T U-Verse

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.


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast
reply to pandora

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
--
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

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.



Hagar

join:2004-10-31
Sunnyvale, CA
reply to scooper

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.


pandora
Premium
join:2001-06-01
Outland
kudos:2

1 edit
reply to Bob4

redacted

redacted


pandora
Premium
join:2001-06-01
Outland
kudos:2
Reviews:
·ooma
·Google Voice
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reply to BillRoland

Re: At 7F outside heat pump maintained 73F indoors

said by BillRoland:

How are you disabling the supplemental heat?

I turned off the emergency heat breaker at the air handler. I wanted to be certain no other heat was arriving. The resistive module has a circuit breaker on it, when off, it can't heat up even if called.
--
Congress could mess up a one piece jigsaw puzzle.

pandora
Premium
join:2001-06-01
Outland
kudos:2

2 edits
reply to pende_tim

redacted

redacted


pandora
Premium
join:2001-06-01
Outland
kudos:2

2 edits
reply to pende_tim

redacted



cowboyro
Premium
join:2000-10-11
Shelton, CT
Reviews:
·AT&T U-Verse
reply to Hagar

Re: At 7F outside heat pump maintained 73F indoors

said by Hagar:

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.

So how do you heat the outside coils if you can't extract heat from inside? If the heat exchanger coils are cold it means they are not absorbing heat, if there is no heat absorbed there can be no heat output in the outdoor coils... so no defrost... food for thought...


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast

1 recommendation

I am with you on this. I have never in my (limited) experience seen a HP defrost without running the inside unit.

If it does not run inside, the outside unit will kick out on high head pressure.
--
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
reply to cowboyro

cowboyro,

How do you heat outside coils and how do you avoid cold air inside during defrost are two different questions.

There are two sources for heat to the outside coils. One is heat from inside the other is the heat that the compressor can generate. Both should be used to defrost the outside coils, since you want the defrost cycle to be as short as possible.

How to avoid inside temperature draft and discomfort during defrost is different problem. You will take some energy from the inside but how can you minimize/avoid and draft or discomfort. Stopping the inside fan is one of the smartest and easiest way. There is more to it but let’s keep it simple. The AUX heat does not help defrost it just remove the cold draft problem.

pende_tim

I only seen indoor unit fan on during defrost here in the USA. All units in northern Europe and Asia do not run the inside fan. The unit will not kick out on high pressure, the units are inverters (compressor is frequency modulated) so the compressor will slow down to avoid over pressure.



cowboyro
Premium
join:2000-10-11
Shelton, CT
Reviews:
·AT&T U-Verse

said by Hagar:

One is heat from inside the other is the heat that the compressor can generate.

The compressor (ideally) does not generate heat. Definitely not enough to melt the ice at 0F while the wind is blowing. In order to melt the ice you need to deliver copious amounts of heat into the coils. For that you need hot refrigerant - which can only be obtained by extracting heat from inside.

TomS

join:2008-01-21
Gloucester, MA

Wow, I guess we have been shown who's the boss here! I'm glad I didn't have any question or comment, until now, that is.



Hagar

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

Not a native speaker.

Not talking about the friction loss in the compressor but the heat that in the heat medium (refrigerant). That heat comes from two sources energy moved and energy input to the compressor.

Look at a heatpump heating and cooling specs. The heating specs have more BTU because the compressor work can generate heat which is useful for heating but not useful for cooling.



cowboyro
Premium
join:2000-10-11
Shelton, CT
Reviews:
·AT&T U-Verse

said by Hagar:

Not talking about the friction loss in the compressor but the heat that in the heat medium (refrigerant). That heat comes from two sources energy moved and energy input to the compressor.

Look at a heatpump heating and cooling specs. The heating specs have more BTU because the compressor work can generate heat which is useful for heating but not useful for cooling.

Conservation of energy - energy cannot be created or destroyed. At best you'll get in the "hot" side of the coils the energy fed to the compressor plus the energy absorbed at the cold point. If you're not absorbing energy at the cold point (which can *ONLY* be done by heating the coils) the best you can obtain at the hot point in theory is the energy fed to the compressor - for a COP of 1; in reality you'll have even less.
Heat pumps work by MOVING energy.


Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4

1 recommendation

You guys are forgetting heat of compression in your discussion. No, not enough to melt ice by itself in a heat pump system, but it is a significant source of heat in the refrigerant cycle.