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View Full Version : COP - Where does it come from?

Jack2007
04-22-2008, 11:06 PM
Is the COP of a heat pump something that you need to calculate?

I have looked for the "COP" when researching heat pumps, but can not seem to find such a rating.
.

snewman24
04-23-2008, 12:02 AM
Is the COP of a heat pump something that you need to calculate?

I have looked for the "COP" when researching heat pumps, but can not seem to find such a rating.
.
COP is Coefficient of Performance

http://en.wikipedia.org/wiki/Heat_pump

air2spare
04-23-2008, 12:12 AM
you can calculate it

COP = SEER x .293

( if Im remembering me numbers correctly)

MrMcGoo
04-23-2008, 01:15 AM
Coefficient of performance is simple up to a point. If your COP is 4 (4 to 1), you put one kw into the condenser and out comes the equivalent of 4 kw of heat pumped into your air handler. This is a very neat trick indeed.

That's the simple part. The problem is the COP goes down as the outside temperature drops. So, at 47*F my COP is 4.06, but at 17*F it is 2.96. You get a COP from the manufacturer of your heat pump or ARI. The pair (heat pump and indoor coil) must be matched, or no numbers are available without major testing in a lab.

The moral to that story is to stay away from mismatched gear, it can cost way more than it saves.

Bill

snewman24
04-23-2008, 01:51 AM
Is the COP of a heat pump something that you need to calculate?

I have looked for the "COP" when researching heat pumps, but can not seem to find such a rating.
.

You're probably having trouble finding the COP for various heat pumps because it isn't as important as SEER and HSPF. SEER is an efficiency rating in cooling mode and HSPF is an efficiency rating in heating mode. See the following:

http://www1.eere.energy.gov/femp/pdfs/hp.pdf
http://www.energystar.gov/index.cfm?c=airsrc_heat.pr_as_heat_pumps

Twilly
04-23-2008, 05:14 AM
Twilli has often wonder that too about the cops, they just seem to be there when you least expect them......

beenthere
04-23-2008, 06:20 AM
On heat pumps, in heating mode, btu's divided by watts=COP.

Its a very usefull number.
On dual fuel systems, it helps you determine the financial balance point.
Knowing both teh thermo balance point and the financial balance point, you can determine at what temp its more economical to use the HP, or fossel fuel.

Twilly
04-23-2008, 07:46 AM
PA boys didn't like OBAMA

beenthere
04-23-2008, 07:52 AM
no comment.

gary_g
04-23-2008, 09:18 AM
You're probably having trouble finding the COP for various heat pumps because it isn't important as SEER and HSPF. SEER is an efficiency rating in cooling mode and HSPF is an efficiency rating in heating mode.

Wow. That is one of the most wrong statements that I have ever read on this site. COP is much more important than HSPF to a heat pump's performance in heating.

Take care.

gary_g
04-23-2008, 09:24 AM
Is the COP of a heat pump something that you need to calculate?

I have looked for the "COP" when researching heat pumps, but can not seem to find such a rating.
.

Goodman provides outstanding technical info on its website.

For my 3-ton 14 SEER Goodman heat pump:

Outdoor Temp ----------COP
65----------------------4.37
60----------------------4.22
55----------------------4.04
50----------------------3.86
45----------------------3.64
40----------------------3.45
35----------------------3.25
30----------------------2.98
25----------------------2.82
20----------------------2.65
17----------------------2.54
15----------------------2.46
10----------------------2.26
5-----------------------2.06
0-----------------------1.84
-5----------------------1.61
-10---------------------1.35

Hope this helps.

Take care

snewman24
04-23-2008, 05:32 PM
Wow. That is one of the most wrong statements that I have ever read on this site. COP is much more important than HSPF to a heat pump's performance in heating.
Take care.

Please back up your assertion and explain both ratings, and why you think COP is so much more important than HSPF in comparing different heat pumps for efficiency.

beenthere
04-23-2008, 06:58 PM
CHIPs, were does it come from. California highway Patrol, there s no I in there. :)

Jack2007
04-23-2008, 07:45 PM
Please back up your assertion and explain both ratings, and why you think COP is so much more important than HSPF in comparing different heat pumps for efficiency.
For me you are correct, the HSPF is most important when comparing heat pumps.

Perhaps I should have been more specific in my original post. I started thinking about the "COP" in another thread when considering the cost of fuel and if it would be practical for me, in the Philadelphia PA. area, to use a heat pump.

My fuel costs, (most recent, although they seem to go up each day)

1 million btu's of heat from PROPANE at \$3.15/gallon, 80% efficient furnace:
(1,000,000 / 91,000) x 3.15 / .8 = \$43.27

1 million btus of heat from fuel OIL at \$3.56/gallon, 80% efficient furnace (1,000,000 / 139,000) x 3.56 / .8 = \$32.02

Electricity at 16 cents per KW-HR, outdoor temp = 35F (COP = 3)(heat pump) (1,000,000 / 3413) x .16 / 3 =\$15.63

Electricity at 16 cents per KW-HR, outdoor temp = 35F (COP = 1.7)(heat pump) (1,000,000 / 3413) x .16 / 1.7
= \$27.58
So I started looking for the "COP" to see if I should consider a heat pump. Some were using a "COP" of 3, others 1.7 or 2.5.
WarmAir.com uses 1.7.

So far oil and heat pump do not seem that far apart depending on the "COP".

For my area the stats are;
896 Cooling Degree Days -- 5383 Heating DD, -lowest average temp=30*, highest avrg temp=75* -- actual lowest temp=18*, actual highest temp=87*
.

Jack2007
04-23-2008, 07:53 PM
Goodman provides outstanding technical info on its website.

For my 3-ton 14 SEER Goodman heat pump:

Outdoor Temp ----------COP
65----------------------4.37
60----------------------4.22
55----------------------4.04
50----------------------3.86
45----------------------3.64
40----------------------3.45
35----------------------3.25
30----------------------2.98
25----------------------2.82
20----------------------2.65
17----------------------2.54
15----------------------2.46
10----------------------2.26
5-----------------------2.06
0-----------------------1.84
-5----------------------1.61
-10---------------------1.35

Hope this helps.

Take care
Thanks. If they are reasonably in the ballpark for most 14 seer units, I can make a better decision.
.

snewman24
04-23-2008, 09:25 PM
For me you are correct, the HSPF is most important when comparing heat pumps.

Perhaps I should have been more specific in my original post. I started thinking about the "COP" in another thread when considering the cost of fuel and if it would be practical for me, in the Philadelphia PA. area, to use a heat pump.

My fuel costs, (most recent, although they seem to go up each day)

So I started looking for the "COP" to see if I should consider a heat pump. Some were using a "COP" of 3, others 1.7 or 2.5.
WarmAir.com uses 1.7.

So far oil and heat pump do not seem that far apart depending on the "COP".

For my area the stats are;
896 Cooling Degree Days -- 5383 Heating DD, -lowest average temp=30*, highest avrg temp=75* -- actual lowest temp=18*, actual highest temp=87*
.

From the table you can see that COP is always changing as the outdoor temperature is changing. That's why they use Heating Seasonal Performance Factor. It's basically a seasonal average of COP so it's much more meaningful.
Try the following site which uses HSPF to calculate possible savings:

http://www.hvacopcost.com/

Jack2007
04-23-2008, 10:15 PM
From the table you can see that COP is always changing as the outdoor temperature is changing. That's why they use Heating Seasonal Performance Factor. It's basically a seasonal average of COP so it's much more meaningful.
Try the following site which uses HSPF to calculate possible savings:

http://www.hvacopcost.com/
Thanks.
If only I save HALF what that calculation says I will, I'll be a very happy camper.
.

Andy Schoen
04-23-2008, 10:30 PM
So far oil and heat pump do not seem that far apart depending on the "COP".

Sigh! COP of a properly functioning heat pump within its design range will always be significantly greater than a gas or oil furnace.

COP is strictly a ratio of output versus input energy or power. Fuel costs are not relevant in the COP calculation.

Of course, fuel costs are relevant when it comes to deciding on your air condition system or furnace.

There's enough misinformation about COP in this thread that I'm going to have a beer. :(

snewman24
04-23-2008, 11:37 PM
Sigh! COP of a properly functioning heat pump within its design range will always be significantly greater than a gas or oil furnace.

COP is strictly a ratio of output versus input energy or power. Fuel costs are not relevant in the COP calculation.

Of course, fuel costs are relevant when it comes to deciding on your air condition system or furnace.

There's enough misinformation about COP in this thread that I'm going to have a beer. :(

Hey Andy
Before you get intoxicated (just kidding) please correct the misinformation....

gary_g
04-24-2008, 02:43 PM
Please back up your assertion and explain both ratings, and why you think COP is so much more important than HSPF in comparing different heat pumps for efficiency.

COP = output heat (or cooling) / input work. Same units (btu/hr), dimensionless. COP varies with outdoor temperature. It provides a snapshot look at efficiency by dividing btu's produced versus energy consumed. It is a straight-forward calculation.

HSPF = Total space heating required during the space heating season in btu's / total electrical energy consumed during the same season in watt-hours.

The problem with HSPF (as well as SEER) is that it is a "seasonal" number. It is a complex calculation filled with summations, averages, assumptions and data tables. The HSPF calc (along with the SEER calc) is different for the various condenser/air handle combinations: single speed compressor, dual speed compressor, dual compressor, fixed speed air handler fan, and v-s air handler fan. HSPF is typically stated for Region IV which has 2250 heating load hours. Region IV HSPF calculation ranges from -8F outdoor temp (.1% of the value of the calc) to 62 F (13.2% of the value of the calc), and it is separated in "bin" temps of 5 degree increments (each bin temp has its own weight% in the value of the HSPF calculation).

If you live in Regions I, II, III, V, or VI, the HSPF will be calculated differently and another HSPF will be obtained. However, only the Region IV HSPF is stated by the manufacturer per ARI.

HSPF is just a way for the consumer to compare the efficiency of heat pump systems in the heating mode, but it is an artificial number that is determined by the weight% of the various bin temperatures used in the calculation.

If you have some time, check out ARI Standard 210/240, Performance Rating of Unitary Air Conditioning and and Air Source Heat Pump Equipment. Pages 90 to 105 for HSPF, pages 82 to 90 for SEER. It will change the way you think about these 2 performance factors.

I apoligize for the rudeness of my initial reply, but when you said that "COP isn't as important as SEER or HSPF", I just about fell off my chair.

Take care.

snewman24
04-24-2008, 02:56 PM
I apoligize for the rudeness of my initial reply, but when you said that "COP isn't as important as SEER or HSPF", I just about fell off my chair.
Take care.

You have to realize the context of the OP's question. He's a homeowner asking the question in the residential (non-pro) forum. I assumed he was asking about COP because he was trying to compare the various heat pumps against each other. The industry uses the HSPF as the best way for a consumer to do that. That's why they post the SEER & HSPF ratings so prominently. A table or curve of COP values at various temperatures would mean nothing to them. You're not talking to an exclusive group of refrigeration engineers here.

beenthere
04-24-2008, 03:55 PM
Gary G. is also just a home owner.

snewman24
04-24-2008, 04:03 PM
Gary G. is also just a home owner.

Uummmm.......just a homeowner who happens to be a mechanical engineer according to his profile..........

beenthere
04-24-2008, 04:15 PM
So you never meet a M.E. that says it has to work the way he said. Even though it can't.

He read the ARI testing standards a couple months ago, and now advises people how to select their equipment from that one paper.

gary_g
04-24-2008, 04:16 PM
Uummmm.......just a homeowner who happens to be a mechanical engineer according to his profile..........

Actually, I am a midget porn star. The mech engr is just a cover.

beenthere
04-24-2008, 04:17 PM
Personally.
I use COP for all operating cost comparisons between duel fuel, heat pumps with electric aux. When the graph says the HP alone can't maintain temp, HSPF doesn't count much.

beenthere
04-24-2008, 04:18 PM
Actually, I am a midget porn star. The mech engr is just a cover.
Some of them make more then us. :)

gary_g
04-24-2008, 04:23 PM
He read the ARI testing standards a couple months ago, and now advises people how to select their equipment from that one paper.

Lots of good info but very heavy math.

I was surprised to see how SEER is actually calculated. Now that I understand the calc, I can sort thru the smoke and mirrors of high SEER numbers.

snewman24
04-24-2008, 04:28 PM

Lots of good info but very heavy math.

I was surprised to see how SEER is actually calculated. Now that I understand the calc, I can sort thru the smoke and mirrors of high SEER numbers.

So what is the alternative Gary G. method for selecting the best heat pump for a given climate region?

Andy Schoen
04-24-2008, 08:30 PM
Using COP if fine if you are willing to do some amount of math and willing to look up the normal ambient temperatures for your area. HSPF rating generally works fine if you don't want to do the math, and your ambients do not remain below 17&#176;F for extended periods of time. ;)

beenthere
04-25-2008, 12:35 AM
Enter your weather conditions once in the templete. Them just enter the HP's BTU's and COP at those conditions when the HP won't maintain temp in the house.

If I had to do it by hand, I'd use HSPF. :)

gary_g
04-25-2008, 08:17 AM
So what is the alternative Gary G. method for selecting the best heat pump for a given climate region?

For cooling, especially for climates with hot summers, EER is the number I would look at. SEER is for mild summer climates. The SEER calc gets the majority of its value (66%) from the 3 lowest outdoor temps (67, 72, 77F). The lowest temperature, 67F, accounts for 21% of the value of the SEER calc. Who runs their central a/c system when its 67F outside? In hot climates, EER dictates operating costs. Yes, I know that EER does not include factors for cycling, partial loading, etc. The rated versus actual cooling btu's must also be taken into account. A 3-ton rated system should put out 36,000 btu cooling, not 33,000 btu's.

For heating, the rated versus actual btu's at 47F are important. Again, 3 tons of rated heating btu's should be 36,000 btu. This is more important in heating than in cooling. The output btu at 17F should also be considered if it is a cold climate. The btu ratings at 47F and 17F are ARI published numbers. For heating efficiency, Region IV HSPF is the only ARI published information.

Take care.

beenthere
04-25-2008, 08:56 AM
The actual BTU output has no bearing on the EER of a unit. Any more then it does on the SEER.
Obviously it needs to be looked at when sizing a unit for the structures load.

For your area, how many cooling hours do you have at 1/3, 2/3 and at full capacity of your unit.

Do a operating cost comparison for your house, using SEER. And then one using EER.
You'll find EER is unrealistic.

I was around 30 years ago when the EER to SEER rating was being pushed.
It was and still is part propganda. Many of us didn't like it. But after you do some comparisons, you'll see why its better to use SEER then EER for most of this country.

You tell people how to choose units based on EER. But yet you don't offer to do any operating cost comparisons. If you really think EER is the proper rating to use.
Do some operating comparisons and post them.

Walk the walk. Don't just talk.

gary_g
04-25-2008, 11:38 AM
You tell people how to choose units based on EER. But yet you don't offer to do any operating cost comparisons.

I inform people that EER determines true operating costs on hot summer days. I offer them this info because most homeowners only hear about SEER and how it is the the equivalent to the MPG rating on a vehicle. Most of the time my statements read something like "Whichever SEER system you get, make sure get a 12 EER minimum". Do you disagree with that?

I have done cost comparisons for different heating fuels as you have seen in the past. I do not do operating cost comparisons for SEER. I personally think the SEER calc is B/S. This opinion was formed after I actually read ARI 210/240. Do you think the salesmen who are pushing high SEER systems do the operating cost comparisons for homeowners? I'll answer for you - no, they don't. Homeowners are lucky to get a Manual J, let alone some calc that states how much they'll save (or not save) by purchasing high SEER equipment over the life of said equipment. As Mr Bill pointed out, most salesmen push high SEER systems because they make more \$\$ from the sale.

You yourself have stated that "High SEER is more for comfort than energy savings".

beenthere
04-25-2008, 12:22 PM
Depending on weather or not, a jump from 14 SEER to 15 SEER means that the 15 SEER equipment is going to be 2 stage equipment will determine if I give EER a lot of cosideration or not. I'd rater have a 11.5 EER and 15 SEER 2 stage over a 12 EER 14 SEER single stage.

You push EER, only for areas that don't even see 90*, let alone 95*.

I have never seen you do an operating cost comparison for anybody between 2 heat pumps, or A/C's of different EER's, and post the results.

Baltimore Maryland, Your design is only 91*F. If you eliminate temps under 75*F as need ing A/C.
Your OD operating ambients are 73.3&#37; of the time between 75 and 85*, and only 26.7% of the time between 85 and 105*. Meaning SEER will give a better operating cost comparison.

With most newer thermostats using CPH instead of a cooling anticipator. Many A/C's with a CPH setting of 3 are cycling off and on at a regular enough interval, that SEER is a better representation of operating cost difference even at higher OD ambients.

At what OD temp does your HP, run an on cycle of 45 minutes straight in cooling mode.
At what OD temp does your HP, run an on cycle of 30 minutes straight in cooling mode.
At what OD temp does your HP, run an on cycle of 15 minutes straight in cooling mode.

beenthere
04-25-2008, 12:26 PM
Yes, high SEER 2 stage equipment is more for comfort then savings. The cost increase of the equipment makes monetary ROI either too long, or not at all possible during the reasonable life span of the equipment many times.

Does that mean its not worht it to have the added comfort, and operating cost savings?

gary_g
04-25-2008, 02:35 PM
Baltimore Maryland, Your design is only 91*F. If you eliminate temps under 75*F as need ing A/C.
Your OD operating ambients are 73.3% of the time between 75 and 85*, and only 26.7% of the time between 85 and 105*. Meaning SEER will give a better operating cost comparison.

If you eliminate outdoor temps under 75F, you have eliminated the temperatures at which 66% of the value of the SEER is calculated. A 16 SEER system is no longer 16 SEER when the lower temps are removed. The temperature bin requirements, by definition of the SEER calculation, are 67F to 102F in 5 degree increments.

Here are the bin temps and the weight% of these bin temps in the SEER calc (with a v-s motor in the air handler):

Temp------Weight% in SEER calc
67----------21.4
72----------23.1
77----------21.6
82----------16.1
87----------10.4
92----------5.2
97----------1.8
102---------.4

Total = 100%

It is obvious from the above that the SEER calc is geared towards lower outdoor temps.

With the exception of v-s compressor systems, high SEER systems obtain their high SEER number by using a dual-speed or dual compressor, and being able to run on low speed at the lower outdoor temp ranges of the SEER calc (which also carry the most weight in the calc). Once a high SEER system kicks into 2nd stage, EER becomes the operating cost factor, especially at higher outdoor temps.

It hasn't been stated that EER changes with temperature, only the 95F calculation is published by the ARI.

From Goodman's Expanded Cooling Data for my 3-ton, 14 SEER heat pump:

Outdoor temp-------EER
115-----------------9.92
105-----------------11.1
95------------------12.1
85------------------13
75------------------14.1
65------------------15.5

As outdoor temps drop, more btu's are produced with less condenser amp draw = lower operating costs while the system is running, regardless of SEER.

gary_g
04-25-2008, 02:37 PM
Does that mean its not worht it to have the added comfort, and operating cost savings?

That depends on the purchasing budget of the homeowner. In most homes, a single speed compressor works just fine.

beenthere
04-25-2008, 03:47 PM
The elimination of the temps below 75*F, was to show you, how little time is spent at the higher temps as a percentage that you keep stressing. If I include the temps down to 65. Then, only 12.54&#37; of the time is your area between 85 and 105*, with the other 87.54% of the cooling season between 65 and 85*.
Most of this country has a very small amount of time at the 95*F conditions you keep wanting to refer to, when you look at the entire cooling season.

A single stage system will work in any home. That is not the point.

You still haven't answered my run time question.