dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
15
share rss forum feed


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

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

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.


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

2 edits
reply to pende_tim

redacted

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.



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

said by Lurch77:

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.

I am not forgetting it - that gives the theoretical COP of 1+.
However that heat is no more than the energy used by the compressor.


Hagar

join:2004-10-31
Sunnyvale, CA

I like the last two post I agree 100%.