Heat Pump Rating

[lksmith]

This may be a hughly dumb question, but how do you rate the heat side of a heat pump? Is a 3 ton heat pump 36,000 BTU of cold air and 36,000 BTU of hot air? Or, do they come in different ratings for both cold and hot air? I've gotten so wrapped up in talking about the size of the back-up heat source (furnace) that I didn't even contemplate the size of the heat pump itself. Thanks in advance.

Larry Smith

[RoBoTeq]

The nominal capacity of the heating from a heat pump will be the same as the cooling but will diminish in capacity as the outdoor temperatures go down.

In all but the very southernmost states a heat pump system will require a supplemental back up heat source. The most common supplemental heat is electric resistance heaters but some systems utilize a fossil fuel furnace as the supplemental heat source.

For all intent and purposes, most heat pump systems are two stage heating consisting of the heat pump as the primary heat source and a supplemental heat source as the second stage.

[citywide service]

But then RoBo how do you explain the 14Seer pumps which give a higher heating capacity than cooling?

Example:

the ssz14's give a higher heating value than the cooling value; is this simply the nature of the 410a beast?


CW.

[turtle]

Originally posted by lksmith
This may be a hughly dumb question, but how do you rate the heat side of a heat pump? Is a 3 ton heat pump 36,000 BTU of cold air and 36,000 BTU of hot air? Or, do they come in different ratings for both cold and hot air? I've gotten so wrapped up in talking about the size of the back-up heat source (furnace) that I didn't even contemplate the size of the heat pump itself. Thanks in advance.

Larry Smith

This is Turtle.

Not all Heat pumps are rated the same on heating in heat pump mode. the cooling side is rated in SEER and the heating Rating is rated in COP and HSPF rating for the heating ability.

Pick the highest C.O.P. and the H.S.P.F. rated system that you can get.

So heating it is COP and HSPF rating /// then cooling is SEER rating.

TURTLE

[BaldLoonie]

It will vary. If you look at the full ratings of the SSZ14-036 most models will have same 47° heating output as they do cooling capacity. Could be that Goodman chooses to rate that way to make it simple. Of course, nobody is going to loose sleep over a BTU here & there.

In some brands, one could be higher, in other brands, one could be less. Rheem's RPNE R22 model tends to show 1000-1500 BTU higher heat than cool capacity. A glance at a York R410a machine showed the same with heating higher than cooling.

[drsmith012]

Originally posted by citywide service

But then RoBo how do you explain the 14Seer pumps which give a higher heating capacity than cooling?

Example:

the ssz14's give a higher heating value than the cooling value; is this simply the nature of the 410a beast?


CW.


Don' forget that it takes energy to compress the gas and make it hot. That energy is added to the hot gas by the compressor throught the act of compression, cooling of the motor and friction. Which is why heat pumps will always produce heat no matter how cold it gets (providing you never need a defrost cycle).

Cop (heating)= 1+(watts out/watts in) you can use watts, joules or BTUs, you will get the same number.
EER = BTU removed/watts. Over in Europe they use COP cooling which is COP(cooling)=watts removed/watts used. Notice no 1+.

As outdoor temp decreases so does capacity of the heat pump. But the inverse is also true for air conditing. As the outside temp increases the cooling capicity will decrease and because the higher ambiant temp the high side pressure increases which in turn increases the load on the compressor motor causing it to draw more power amking it run hotter.

[Edited by drsmith012 on 09-05-2006 at 02:54 PM]

[docholiday]

ALL heat pumps are rated at 47 degrees and 17 degrees. This is one of the challenges in designing heat pumps to make one that works with a smaller indoor coil, puts out similar heat and cool nominal values and actually works on top of all that.

You will find some where there is a few thousand btu differences, but that almost doesnt matter as you dont size heat pumps for the heating mode anyway. You size the auxiliary heat for the heating load and you find the balance point. If you oversize the HP in cooling just to get the heating side right, then you go through all of cooling mode suffereing because you cant seem to remove humidity.

[lksmith]

Thank you all for the input. At least the heating end of the heat pump is one thing I don't have to worry about.

Larry Smith