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jonr
Senior Member
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| 22 Apr 2013 08:08 AM |
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It is very well established that designing a loop for EWT between 30F and 90F gives the best balance between upfront costs and operational costs. ...
I was trying to point out that one should not generalize, It is very well established that better EWT provides lower operational costs. What the best balance between upfront costs and operational costs is depends greatly on the individual circumstances (lots of things, but electricity costs would be one example) - don't generalize like this! |
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docjenser
Veteran Member
Posts:1400
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| 22 Apr 2013 12:03 PM |
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jonr, teach me here, what do you think loopfields should be designed for and how do you achieve that goal? |
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| www.buffalogeothermalheating.com |
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jonr
Senior Member
Posts:5341
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| 22 Apr 2013 12:29 PM |
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what do you think loopfields should be designed for and how do you achieve that goal? Generally :-), 1) the specific conditions and 2) by doing the math instead of generalizing. |
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docjenser
Veteran Member
Posts:1400
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| 22 Apr 2013 02:35 PM |
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So how do you do your math? What is the EWT range you design for? The specific conditions are only design parameters, but what do you want achieve, and how do you get there? |
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joe.ami
Veteran Member
Posts:4377
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| 23 Apr 2013 08:26 AM |
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The percent of loop it takes to raise average EWT only a couple of degrees tanks cost v benefit. This is fact not generalization. Anyone who plays with an op cost calculator can find out for themselves in minutes. A client I'm working on a proposal this morning for instance would need a full additional loop to raise there EWT just 2F. Cost approximately $1,650. Savings $26.00 yr at 8 cents a KWH. There is your well established lower operating cost.
If I want to bring minimum EWT to 35F on the same project, it would double the loopfield size at a cost of nearly $5,000 and save $66/yr on operation. Incidently an additional ton (larger geo) would cost half that and save $88/yr in operating cost. Of course if you are paying 20 cents a kwh it might be worth the extra ton but certainly not a few extra degrees of EWT.
Generally only someone new to geo or outside of the business thinks there's potential payback for designing higher EWTs. |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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jonr
Senior Member
Posts:5341
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| 23 Apr 2013 08:49 AM |
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So you are sticking with 30F and 90F as being the always correct numbers for min and max EWT? Generally, only sloppy designers believe that. |
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Palace Geothermal
Veteran Member
Posts:1609
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| 23 Apr 2013 08:56 AM |
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So you are sticking with 30F and 90F as being the always correct numbers for min and max EWT?
These numbers are the geo professional's accepted starting point for a loop design. |
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Dewayne Dean
<br>www.PalaceGeothermal.com<br>Why settle for 90% when you can have 400%<br>We heat and cool with dirt!<br>visit- http://welserver.com/WEL0114/- to see my system |
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jonr
Senior Member
Posts:5341
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| 23 Apr 2013 09:00 AM |
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Ah, starting point. As in, depending on conditions, you might change them (in either direction) to get a better balance of upfront costs vs operating cost? |
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joe.ami
Veteran Member
Posts:4377
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| 23 Apr 2013 09:02 AM |
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duplicate |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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joe.ami
Veteran Member
Posts:4377
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| 23 Apr 2013 10:27 AM |
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Posted By joe.ami on 23 Apr 2013 09:02 AM
I stick with best bang for my customers buck. Tell us about all your geo designs and satisfied customers jon.
We all see the fine point you are attempting to emphasize, but we already have too many geo shoppers here who think a little extra loop is good and worth paying for. Truth is it is very likely a waste of money. You know it's true.
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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jonr
Senior Member
Posts:5341
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| 23 Apr 2013 11:14 AM |
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stick with best bang for my customers buck...We all see the fine point Agreed, there are conditions/equipment where 25F min EWT is the best number. |
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docjenser
Veteran Member
Posts:1400
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| 23 Apr 2013 11:43 AM |
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Posted By jonr on 23 Apr 2013 08:49 AM
So you are sticking with 30F and 90F as being the always correct numbers for min and max EWT? Generally, only sloppy designers believe that.
The 30F to 90F rule for loopfield design results in the best compromise between operating costs and upfront costs. If you have conditions that make the loop perform better (for example higher conductivity) you can make the loop smaller to save the customer money, but your goal to reach 30F remains the same. Is it detrimental to drop down to 28F? No.
The sometimes you cannot reach that goal, for example not enough room for the loop field. The same rule applies in heat dominated climate, you try to adjust the loopfield performance to get you within the 30F to 90F reach.
What you call sloppy, I call trying to establish the right balance between upfront costs and performance, which is the obligation of a designer.
Keep in mind that this discussion started with you saying that cramming pipe into a too small space does not work, and I objected to that. Cramming pipe into a small space can very well give you EWTs within the 30-90F range, it just depends on they are designed. However, since then are criticizing others but sidestep every question how you would do it better. You even went as far as calling others "sloppy".......not bad! |
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jonr
Senior Member
Posts:5341
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| 23 Apr 2013 02:56 PM |
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Keep in mind that this discussion started with you saying that cramming pipe into a too small space does not work, and I objected to that. I'll admit "small" was a vague addition to someone else's less than clear post. What's your claim - that you can use any space, no matter how small and still get a working or efficient loop? Hopefully not, and in that case we can both be right, for various definitions of "small". The 30F to 90F rule for loopfield design results in the best compromise As long as your are sticking with the exact numbers of 30F and 90F as always being "best", I can't help you. |
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docjenser
Veteran Member
Posts:1400
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| 23 Apr 2013 03:55 PM |
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I'll be happy to learn here, moving away from the 30-90F target if you help me to find a better target or way to design it. I keep asking you how you would do it better, how you would design better to find a better compromise between installation cost and operational costs in terms of loopfield design. But I have not heard anything productive yet. .....nothing....none....
What is the design target for your loops in term of EWT? |
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| www.buffalogeothermalheating.com |
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jonr
Senior Member
Posts:5341
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| 23 Apr 2013 04:57 PM |
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What is the design target for your loops in term of EWT?...I have not heard anything productive OK. There isn't a single number (that's really the point here). Joe answered this well with "best bang for my customers buck". I agree, you might not find this productive but a good answer would take a book (and no, I wouldn't be a good one to write it). how do you do your math? Usually, using software - (such as Ground Loop Design or GeoLink) and changing some of the parameters (like loop length and configuration). And of course incorporating lots of the specific data - electric costs, digging costs, borrowing costs, equipment, etc, etc. Preferably in a spreadsheet so that it is easy to look at changes. I keep asking you how you would do it better Other than using fixed values for min/max EWT, I have no idea how you are doing loopfield design. So if that is a broader question, it is unanswerable, even if I knew (which, depending on the issue, I might or, more likely, might not). Maybe that needs repeating - I don't have all the answers. In fact, being in the business, I'll bet that you have far more good answers than I do. But nobody is always right. |
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engineer
Veteran Member
Posts:2749
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| 23 Apr 2013 11:14 PM |
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FWIW, I think it was DeWayne (PalaceGeo) who suggests that closed loops be designed to generally deliver EWT 20*F + / - an area's deep undisturbed ground temperature. I like that - it has an attractive elegant simple symmetry, and it is more accommodating of local conditions than the hard-and-fast 30/90 guideline.
Unfortunately it is of little use to me here in Florida. Our deep ground temps run in the 70s. A closed loop system with EWT in the 90s will struggle to compete with conventional air source systems given that the average summer air temp here is 85 and design temps are 95 or less. In other words, even well-designed closed loop geo confers no significant advantage over air source systems away from the corrosive salt spray at the beach.
We are getting into open loop systems with reinjection, but pumping power has to be carefully considered so as not to squander open loop's potentially higher EER / COP
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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docjenser
Veteran Member
Posts:1400
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| 24 Apr 2013 09:49 AM |
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Posted By engineer on 23 Apr 2013 11:14 PM
FWIW, I think it was DeWayne (PalaceGeo) who suggests that closed loops be designed to generally deliver EWT 20*F + / - an area's deep undisturbed ground temperature. I like that - it has an attractive elegant simple symmetry, and it is more accommodating of local conditions than the hard-and-fast 30/90 guideline.
Unfortunately it is of little use to me here in Florida. Our deep ground temps run in the 70s. A closed loop system with EWT in the 90s will struggle to compete with conventional air source systems given that the average summer air temp here is 85 and design temps are 95 or less. In other words, even well-designed closed loop geo confers no significant advantage over air source systems away from the corrosive salt spray at the beach.
We are getting into open loop systems with reinjection, but pumping power has to be carefully considered so as not to squander open loop's potentially higher EER / COP
Lets do the math here and look at heat dominated climate. Buffalo, NY, 50F ground, +/- 20F you are down to 30F in the winter (summer is irrelevant, but we get up to 65F loop temps). Then you have Florida, 70F ground, +20F would mean 90F loop temp in summer (here heating is irrelevant). So you are back to 30/90F wether you are in Florida or in Buffalo.
Now lets take a place in the middle, 60F ground, following the +/- 20F concept would mean you are doing 40F/80F designs. NOw I would argue that you are then wasting the customers money, and you should make the loops smaller, to add 10F on each end, since the operational benefit is not that much greater between 30 and 40F, and from 80 to 90F. Plus 90% of the time the temp would be between 40F and 80F anyway. So where ever you are in the U.S. you are back to 30/90 as a design goal.
Are you always dead on? No. Each house behaves different, some have more solar gain, others do not. Some owner suddenly dials up the thermostat more. So in reality we see our loops run between 28 and 32F in the winter, so 30F +/- 2. Why would I design for anything else? Designing something for 35F EWT would almost increase the loopfield costs by 50%, designing down to 25F would touch some safety margins I would be uncomfortable with. However you twist it, there is a good reason to shoot for 30/90. |
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joe.ami
Veteran Member
Posts:4377
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| 24 Apr 2013 10:13 AM |
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"If I want to bring minimum EWT to 35F on the same project, it would double the loopfield size at a cost of nearly $5,000 and save $66/yr on operation. Incidently an additional ton (larger geo) would cost half that and save $88/yr in operating cost. Of course if you are paying 20 cents a kwh it might be worth the extra ton but certainly not a few extra degrees of EWT."
Lest we forget, more tonnage (with enough loop to support it) might be cheaper than elevating EWT just 5F. |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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jonr
Senior Member
Posts:5341
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| 24 Apr 2013 10:45 AM |
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A good summary here, where they write "blanket recommendations to limit the entering water temperature to a specific value (such as 90°F [32C]) may result in borefields that are significantly oversized. "
http://www.ornl.gov/~webworks/cppr/y2001/pres/111249.pdf
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docjenser
Veteran Member
Posts:1400
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| 24 Apr 2013 08:00 PM |
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Posted By jonr on 24 Apr 2013 10:45 AM
A good summary here, where they write "blanket recommendations to limit the entering water temperature to a specific value (such as 90°F [32C]) may result in borefields that are significantly oversized. "
http://www.ornl.gov/~webworks/cppr/y2001/pres/111249.pdf
While the quote you are giving is directly our of the document, it misrepresents what was actually studied and what the actual data in the document shows.
The study was a software simulation, whereas the designers had designed a loopfield for a certain cooling load in the southern US. However, the conclusion was that their loads on the loop was to high for 3 reasons.
1) they did not account for the desuperheater
2) they assumed that the performance of the heatpump is 5% less than advertised
3) they assumed a thermostat setting of 72F when in reality thermostat settings of 75F in cooling mode should be accounted for
By correcting those loads they calculate the maximum EWT to be 88.9F instead of 95F. They also mention that if the loopfield would have been designed for 90F instead of 95F, the corrected EWT would have been 83.9, resulting in much higher borehole costs than needed, but solely to incorrect load numbers.
They also state that lowering the EWT brings only marginal operational cost savings, which do not justify the increased loopfield costs, a point we all agree here. Nothing else was in the article.
BTW, Geolink, the software you were mentioning, uses default numbers of 30/90 to size loopfields. I don't use GLD, but Looplink also uses 30/90. |
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