Independent U.S. study measuring CoP
Last Post 13 Aug 2012 09:29 AM by docjenser. 22 Replies.
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tex1User is Offline
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09 Jun 2012 02:35 PM
Out of curiosity, was there ever a U.S. study, measuring the CoP of randomly selected residential homes with (GSHP's)?
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16 Jul 2012 09:57 PM
Yes I think University of Wisconsin did one.
Time outUser is Offline
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19 Jul 2012 07:16 PM
... can you post the link. Thanks
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24 Jul 2012 04:29 PM
http://geothermaldigest.net/blog/2009/09/26/maine-based-foundation-tracking-geothermal-payback/
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24 Jul 2012 08:10 PM
That link appears to be concerned with a single university building, not randomly selected residential systems.
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01 Aug 2012 02:40 PM
There's a pretty-good ongoing Canadian study being run by Manitoba Hydro that would set appropriate performance expectations for US climate zone 7 (and the cold edge of zone 6), but I'm sure the geo-pros here aren't going to like the (sub-3 seasonal COP) average.

US studies use smaller sample sets, but whole-system seasonal COPS still tend to live in the mid 3s, under-performing the equipment's 4+ ratings by quite a bit.

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01 Aug 2012 08:08 PM
Posted By Dana1 on 01 Aug 2012 02:40 PM
There's a pretty-good ongoing Canadian study being run by Manitoba Hydro that would set appropriate performance expectations for US climate zone 7 (and the cold edge of zone 6), but I'm sure the geo-pros here aren't going to like the (sub-3 seasonal COP) average.

US studies use smaller sample sets, but whole-system seasonal COPS still tend to live in the mid 3s, under-performing the equipment's 4+ ratings by quite a bit.



The study might be good,but the execution of the design and installation might not be. As long as we compare apples and oranges and are uncertain about the design efficiency of the whole system, system performance will vary widely.
That is why the measured performance differs so widely. The seasonal COP differs between 1.8 and 3.5
Lets look at the worst system, #8, with a COP of 1.8, versus system # 9, the most efficient one. Both had a similar efficient rated unit (COP 3.8/3.9). So where is the difference of performance coming from? # 8 is a vertical loop, running at a weighted average of 32.8F, whereas the #9 running at a weighted average EWT of 38.8 degrees F, a whooping 6 degrees warmer. Min EWT of #8 is 24.1F, whereas the Min EWT of # 8 is 32.3F, which already tells a big part of the story: The vertical loop at #8 is way too short, whereas #9 is well sized. No wonder the compressor consumption per 10000 BTUs delivered is a whooping 50% higher in system #8 than in #9. In addition, the fan power used in #8 is 200% higher compared to system #9, which indicates very inefficient ductwork, which will also result in higher coil temperatures and consequently higher Amps drawn.
Circulation power for the ground loop: System # 8 uses 3 times as much power per BTU delivered than #9.
330 watts per 10000 BTUs delivered, that is about 1300 watts for a 4 ton, is crazy, we do the same with a 230 watt pump.
This study is pretty telling, since it shows a striking difference between a good and a badly designed system. Of course everything is averaged out in the results, and then the average COP is sub 3.0. Heatpumps were at least 2006 vintage or older, since they measured 2007 heating season, for sure older R-22 units, performing at a lower COP then todays R-410 units.

Perfect example why system design and installation is the most important factor for system performance, resulting in almost 100% difference in system performance despite similar efficient HP units!

www.buffalogeothermalheating.com
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02 Aug 2012 01:59 PM
"Perfect example why system design and installation is the most important factor for system performance, resulting in almost 100% difference in system performance despite similar efficient HP units! "

No kidding! A 100% delta in efficiency with nominally similar systems is a pretty huge design risk.

I don't imagine that the price paid by the homeowner was in any way related to the relative efficiency either. The fact that the survey-average COP was so abysmal means the industry is in pretty sorry shape regarding the average design-competence of the installers. Without independent verification of performance it's difficult to weed out hacks from those who do the math, and the client isn't likely to be able to tell the difference either before or after the contract is signed & system delivered as long as it's keeping up with the heating & cooling loads.

BTW: R410A systems aren't inherently more efficient than R22- if anything R22 has a (very) slight edge in comparably designed & optimized systems. Advances in HP efficiency over time have nothing to do with the changeover from R22 to R410A, but since R410A units are newer, they have the benefit of the overall trend in design improvement. But clearly, even the very best of HP efficiency can be brought to it's knees by gross errors of the system designer.
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05 Aug 2012 01:27 PM
Just found this Link to share; http://www.toolbase.org/Technology-Inventory/HVAC/geothermal-heat-pumps#code
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05 Aug 2012 04:00 PM
I did not meant to imply that R410A is that much more efficient than R-22 inherently, but simply that they are more modern vintage.
I also looked a bit closer at the study from Manitoba.

Some of the compressor consumption measured indicates very inefficient working conditions for the compressor (over 600 watts per 10000 btus), and also very high parasitic losses for circulation pumps and and fans. If we use single constant speed speed circulation pumps on 2-6 ton heatpumps (Grundfos 26-99), we see circulation pump power between 40-60 watts for 10000 btus, depending on the size of the heatpump, and a similar amount for the ECM fan with well designed and sized ductwork. Usually we see around 700 watts total for 10000 btus delivered.

If the circulation power and fan power would be around 50 watts each, some the systems measured would run around the 700 watts/10000 BTU mark and indeed surpass surpass the published COP for 2nd stage operation at 32F. In the study they sometimes make the blower work efficient, sometimes the circulation pumps, and sometimes the compressor, but never all 3 together. The reason why they can surpass the published COP is the fact that the seasonal EWT from a well designed loopfield is around 38F (as they show here in the study), usually resulting in a COP performance increase around 7-8% above published specs. If they keep the blower and circulation consumption down, they are off setting the parasitic loses of the blower and the circulation pumps.
That way a system COP above 4.0 should be easy to achieve in forced air applications. But obviously many installer or designer struggle with this.
www.buffalogeothermalheating.com
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06 Aug 2012 06:09 AM
I guess I'm having trouble with the implication that 38* EWT is "good design". If we were to suggest that, then wouldn't 40* be better or 50?
The industry standard at or around 30*-90* is due to the fact of extremely rapidly diminishing returns with the amount of loop it takes to raise minimum EWT 8* particularly with vertical loops (depending on drilling costs).

Of course the cost of electricity and severity of local weather all matter in design, but I would argue in my area (heating dominated with average 8 cent/kwh electricity) someone who designed for 38* EWT was a hack who cost his customers at least three thousand dollars to save them less than $100/yr in electricity because he has so little design knowledge.

Same with flow centers or anything. Higher COPs and lower pumping costs matter most where electricity costs a lot. Responsible design is a combination of cost v benefit not just lowest operating cost.
Joe Hardin
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06 Aug 2012 07:18 AM
There are a lot of people who are willing to pay somewhat more to be "greener", even if it doesn't have a good ROI based on our subsidized energy prices. Ie, it's not always about $.
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06 Aug 2012 08:43 AM
Posted By jonr on 06 Aug 2012 07:18 AM
There are a lot of people who are willing to pay somewhat more to be "greener", even if it doesn't have a good ROI based on our subsidized energy prices. Ie, it's not always about $.

So because "it's not always about $" are you suggesting my points are not valid?
 
Sometimes it is about money.

Every responsible design considers money.

"Greener" might be spending the extra thousands on PV.
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
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07 Aug 2012 03:02 AM
I think you have a good loopdesign in heat dominated climate if your EWT does not drop below 30-32 F. Minimal EWT of 30F usually means an AVERAGE SEASONAL COP of 38F. Of course is higher better, but as discussed before you have diminishing returns on your investment. The whole point here was that the units are rated at 32F, and if you have a higher seasonal COP the unit itself runs at a higher than advertised COP. Averaged over the season!


The circulations pumps are easy. You simply design you loopfield to run on a single 26-99 and not dual pumps or 26-116s. Save tons of operational costs...
www.buffalogeothermalheating.com
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08 Aug 2012 12:49 AM
Posted By docjenser on 07 Aug 2012 03:02 AM
...The circulations pumps are easy. You simply design you loopfield to run on a single 26-99 and not dual pumps or 26-116s. Save tons of operational costs...

Wish I had known this when my system  was installed.  Instead, my WaterFurnace Envision 2-stage variable speed 3 ton geothermal unit runs on a 26-116, requiring 385 watts.  And my 5 ton unit runs on 2 of these 26-116 pumps configured in a push pull setup, requiring 770 watts just for pumping.

Best regards,

Bill
Energy reduction & monitoring</br>
American Energy Efficiencies, Inc - Dallas, TX <A
href="http://www.americaneei.com">
(www.americaneei.com)</A></br>
Example monitoring system: <A href="http://www.welserver.com/WEL0043"> www.welserver.com/WEL0043</A>
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08 Aug 2012 02:22 PM
... can you post the "Electric Utility" in your area? (average 8c/kwh)
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08 Aug 2012 11:40 PM
Posted By Bill Neukranz on 08 Aug 2012 12:49 AM
Posted By docjenser on 07 Aug 2012 03:02 AM
...The circulations pumps are easy. You simply design you loopfield to run on a single 26-99 and not dual pumps or 26-116s. Save tons of operational costs...

Wish I had known this when my system  was installed.  Instead, my WaterFurnace Envision 2-stage variable speed 3 ton geothermal unit runs on a 26-116, requiring 385 watts.  And my 5 ton unit runs on 2 of these 26-116 pumps configured in a push pull setup, requiring 770 watts just for pumping.

Best regards,

Bill


That is 1155 total! That is crazy. Do a pressure drop calculation, with 3000 hours average run time, a new pump setup might pay for itself very quickly.Or tell me your setup, I can run the numbers for you.
www.buffalogeothermalheating.com
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09 Aug 2012 01:33 AM
Posted By Time out on 08 Aug 2012 02:22 PM
... can you post the "Electric Utility" in your area? (average 8c/kwh)
In the Dallas area, it's a deregulated market.  Many (many) Retail Electric Providers (REPs) compete to sell at the residential retail level.  These REPs are separate from the Transmission (regulated) companies, and are separate from the actual generating companies (also0 regulated).

I use TXU as my REP.  ONCOR is my transmission company, and Luminat is my generating company.

For 2011, I used 19,714 kWh from the grid at an average advertised rate of 9.9 cents.  I used 7993 kWh from my solar PV system at a cost of 6.9 cents.  Net electricity used was 27,707 kWh at a rate of 9.1 cents.  This is about 76 kWh/day, and an average monthly cost of $211.

I also used 40 MCF of natural gas for cooking, drying clothes and hot water heating, at $39/mo.  Add in the NG usage into a total energy sum, the result is about 108 kWh/day usage, at a rate of 7.6 cents, resulting in monthly payments of $250.

This year, 2012 YTD, gas and electric rates have fallen.

On a 12 month rolling avg basis, my advertised grid rate is down to 9.1 cents.  If you reside in the north Texas area, and your grid rate isn't in the low 9 cents, on a full 12 month average basis, then you're paying too much and it's time to change REPs.  Again, I use TXU (Market Edge program).

So far this year the rate I'm paying for what I use from my solar PV system is about 6.0 cents.  Thus my the net rate for kWh purchased from both sources (grid and solar) is currently at 8.4 cents.  This is the "average 8 cents".

Add in natural gas consumption that's currently at about $32/mo, and I'm down to about 7.2 cents/kWh for the past 12 months for total energy consumption (electricity + NG) at the moment.

Probably more information than you wanted, but, I wanted to illustrate 3 things:
1. If you live in an area where you have to shop around for an REP, you have to spend some time finding good rates (again I use TXU Market Edge).
2. Putting in a solar PV system on a lease basis is a 'no brainer' if adequate incentives are available.
3. If you have access to NG, putting as much as you can on it (including clothes drying) probably will be less expensive than using electricity for the same purpose.

Best regards,

Bill



Energy reduction & monitoring</br>
American Energy Efficiencies, Inc - Dallas, TX <A
href="http://www.americaneei.com">
(www.americaneei.com)</A></br>
Example monitoring system: <A href="http://www.welserver.com/WEL0043"> www.welserver.com/WEL0043</A>
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09 Aug 2012 01:43 AM
Posted By docjenser on 08 Aug 2012 11:40 PM


That is 1155 total! That is crazy. Do a pressure drop calculation, with 3000 hours average run time, a new pump setup might pay for itself very quickly.Or tell me your setup, I can run the numbers for you.
Thanks.  I'll respond with the information tomorrow.

Each of the 3 pumps may be easy to replace, as shut off valves are installed on each side of each pump.  See picture.

Running the numbers for me would be much appreciated.  Many thanks.

Best regards,

Bill
Energy reduction & monitoring</br>
American Energy Efficiencies, Inc - Dallas, TX <A
href="http://www.americaneei.com">
(www.americaneei.com)</A></br>
Example monitoring system: <A href="http://www.welserver.com/WEL0043"> www.welserver.com/WEL0043</A>
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10 Aug 2012 02:40 AM
Need your piping layout, length, diameter etc. Also heatpump type and model
www.buffalogeothermalheating.com
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