Just curious but I want to compare some of my numbers of
actual btuh net output
actual cop at full load
actual eer

Again not looking for manufacturer specs but actual installed performance
you can include ground temps or manufacturer

Just as a point of reference I have a system with btuh at 75k ( 5 ton ) cop well over 4.5 and eer at 17.8
I'm confident in my calcs and measurements but Im well above manufacturer specs and Im curious if this is common

Hard to precisely calc COP in field without accurate air flow and wattage measurements

and dont you guys take those measurements at start up ?

Maybe not I was forced to for a power company rebate, but now Im wondering how common my numbers are

I don't believe COP requires air flow measurement.

I believe fundamental numbers needed are EWT, LWT, presence or not of antifreeze, GPM derived from delta pressure across heat exchanger, and GSHP power consumption not including pumps.

I believe COP can then be calcultated:

COP = ((EWT - LWT) * GPM * 500 * (antifreeze factor) + (Watts * 3.42)) / (Watts * 3.42)

For example, assuming no antifreeze, for a 3 ton WaterFurnace Enviosion GSHP running in 1st stage:

COP = ((60.0 - 54.2) * 8.0 * 500 * 1) + (1470 * 3.42)) / (1.470 * 3.42) = 5.6

Hope this helps.

Best regards,

Bill

I calculate COP the same way. 500 is for straight water, 480 is with 20% methanol for antifreeze.

Ok, I really want to find out what my system is doing COP wise. I have never known how to get a real GPM number; I just have what he told me it was. Fortunately I do have P&T ports all over the place, although no P&T sensors are they universal?

I am confused though, how is the GPM the delta across the heat exchanger? Wouldn't every heat exchanger be slightly different?

Also where does the size of the heat pump come in or is that part of the watts consumed?

OK, I'll concede that with a solid GPM value and water temps one can calc Btuh output, and a clamp meter will give unit amps. I hadn't had a required 2nd cup of coffee when I penned that this AM.

I believe I've read that if ESP is within limits the ECM blower will flow CFM within 5 % of setpoint

Anybody know an approximate power factor for a typical geo unit?

ARI Standards account for air flow, loop pump and blower power requirements, compressor's energy use, and a lot more factors in determining COP. If one is not picky, coefficient of performance for heating, as its name implies is the total energy output divided by total energy input. Use the same units, e.g., btus out / btus in or KWH out / KWH in.
Regards, Masoud

Ok, that went over my head, but I did throw Bill's calculation above from in excel and it seems to work. If anyone wants to see it, here it is.

Since my system is water to water couldn't I do that on both sides? As long as I knew the water temps and GPM, the power would remain the same. I am learning a lot and becoming more dangerous…

This assumes that all the compressor heat ends up in the house (was it this forum we had this discussion recently or another one?) This is valid if your heat pump is in conditioned space, but if it is like mine and is in an unheated basement some of the compressor heat is lost. The loss is generally small, but if you're looking for high precision it might be necessary to take that into account.

Absolutely - that's how I do it and you can see how much compressor heat is being lost to your utility room.

Also, you asked about figuring flow by pressure drop - you are right, the curve is unique to every heat exchanger. Most manufacturers will provide a table of flow vs pressure drop. This method assumes your heat exchanger is flowing as it did when new with no scale, etc.

One thing to keep in mind for those of us with water-water units is that the pump(s) on the hydronic side is not accounted for in the ARI standards. For most units this should be fairly insignificant but if you have a heat pump like mine with a huge pressure drop across the hydronic side heat exchanger you can easily use several hundred watts of pump power.

Also, I can't speak for every manufacturer, but many of the specifications I've seen do not include loop pump power in their power or COP figures. They are included in the ARI ratings as you say, but in the additional tables of output, cop, etc vs temperature frequently only the compressor power is included.

Fortunately my heat pump is in a conditioned space, good for times when we want heat (9 months a year), not so good in summer when I am trying to cool. Although in summer I dump heat in the indoor pool and dump the cool in to the house so I am using both sides of the heat pump in summer.

Keep in mind COP isn't a single point unless you determine a seasonal average. It varies widely with loop temp hydrionic or air flow flow and temp, etc. Maybe some open loop systems maintain a nearly constant COP throughout the year, but for most climates the COP at the start of the heating season will be much higher than the average of the whole season (sorry if I'm stating the obvious).

I need to generate an updated version, but here is a plot of COP vs hydronic and loop temp for part of last year's season. This is strictly hydronic btus divided by compressor power, so it does not include the heat lost from the cabinet to my basement. I think that's less than 1000btu/hr, though. I'll also throw in a plot of COP vs. time (this one does include both loop and hydronic pump power). In my case the output is reasonably close to the rating, but the compressor power consumption is consistently 10-15% higher than spec.

For my unit, the COP changes gradually over the season due to loop temperatures, but it changes significantly day-day depending on the weather since my hydronic temps are controlled based on outside temp.

One other thing - you need pretty accurate measurements to determine COP accurately. An error of 1 degree either way on the temperatures can have a huge effect. My measured COPs probably have a 10% error band or so.

 

Yes, I believe this is correct.  Thus, for a current technology ECM blower that's operating within it's normal operating range, you should be able to determine a close approximation to Heat of Extraction from the air side instead of the water side (CFM * TD * 1.08).  Eliminates need for pressure guage and water flow chart.

Best regards,

Bill

OK, my real time COP performance data is shown below, for my WaterFurnace Envision 2-stage variable speed GSHP units (5 and 3 ton).  This is fresh data, for about the past 12 hours.

In this case, the units are running exclusively in 1st stage.

Lack of data during certain time periods does not mean unit(s) was/were not running.  Since I can measure COP only when one unit is running (i.e., not both simultaneously), there are some gaps in the data.  And this morning there were few times only one was running such that the 3 ton COP numbers are 'fringe' numbers.  (My WEL instrumentation system does some unusual things at the beginning and end of cycles).

Overall, it looks like my 5 ton unit is running near 5.0 COP in 1st stage, and my 3 ton unit is running near 3.4 in 1st stage.

The power portion of the measurement is without the water loop pumps.  I backed out 385 watts/pump.

This has been an interesting and good learning thread.  Thanks to everyone for the contributions.

Best regards,

Bill

here is the COP on my unit



The flat lines are when the unit is not runnig




http://welserver.com/WEL0114/COPdays.gif


http://i45.photobucket.com/albums/f58/dewdean/ScreenHunter_21-1.jpg

Dewayne, I'm impressed with your WEL design implementation skills!  What you show above is one of the few real-time COP monitors that I've seen implemented using a WEL.  Nice job!

And nice job using the WEL's sampling function - sure keep the data cleaned up nicely.

I had to do my 'real time' COP analysis 'off-line' because I don't have enough remaining WEL 'device slots' to implement the calculation and because I don't have a dedicated watt meter per each GSHP unit.

Did you remember to subtract out about 385 watts / pump motor?.

Best regards,

Bill

Bill,

Thanks to your excellent tutoring, I am getting my WEL figured out. I did not subtract out the the 385 watts. Not sure of the reasoning for doing it. I figure that it needs to be factored in to get a true COP.