erphillips
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| 07/19/2009 8:20 AM |
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I have been concerned that my loop temps were running too high on my newly completed self installed system,
Original thread: http://greenbuildingtalk.com/Forums/tabid/53/forumid/13/tpage/1/view/Topic/postid/61325/Default.aspx
So I had a chance to have 5 200' wells drilled this week, They were solid limestone from top to bottom no ground water.
we installed 3/4" x 410' u-bend loops and grouted with BH-20.
In the first well I put 1-wire temperature sensors at 200', 150', 100', and at 5' depths. I fastened the sensors top the loop pipe.
The sensors were in for 3 days in the grouted wells before I finished piping the wells. I wanted to get a baseline temp
before using the loop. FYI temps are 200'= 63.6 150'= 64.5 100'= 65.6 and 5'= 66.8.
I piped the wells parallel with 1" x 3/4" x 1" fusion fittings and ran the 1" poly loop back to the mechanical room.
I also have 6 1" x 1000' horizontal loops @ 6' deep, all loops terminate in the mechanical room as 6 separate loops then header together for one in and one out from field.
I have 3 FHP units piped to 2 dual pump flow centers, the 5 ton on 1 and the 4 and 2 ton on the other one, check valves on the one serving 2 units, no check valves on the single.
The loop field is currently feeding both pump centers parallel IE: tee connection from loop to inlet of pumps and tee to loop from both pumps.
Now my question is how should I incorporate the well loop and the horizontal loop fields?
I see the options as:
Well's to the one of the flow centers, horizontal field to the other
or should I feed the horizontal loop first then the horizontal return through the wells ( Pre cooling the water before flowing into the wells )
I just want the lowest possible EWT for highest efficiency.
Any suggestions?
Thanks
Ed Phillips
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joe.ami
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| 07/19/2009 9:01 AM |
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Since you have the ability to do a variety of measurements, i suppose you could try both and see if one way performs better than another.
My gut reaction however would be to have them in paralell to cut length and friction loss. This is the main reason geo went from 1 pipe trenches to 2, 4, and 6.
Good luck,
Joe |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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erphillips
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Posts:19
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| 07/19/2009 10:43 AM |
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I though about connecting them in parallel I was concerned that the 1" Horizontal loops would have less friction loss than the 3/4" Vertical loops so little flow would go through the wells,
I suppose I could balance the flow with ball valves.
I will do some experimenting with various configurations.
Ed
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jonr
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| 07/19/2009 2:34 PM |
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You want the flow in each pipe to be proportional to the thermal capability of each loop - ie, each loop should be balanced to have the same return temperature. Parallel connections + valves will enable that; but too much parallelism will cause laminar flow.
The main reason to use multiple pipes (in horizontal and vertical loops) is to increase the pipe surface area for greater heat transfer. Larger pipe is the solution if just resistance is the concern.
From a thermal standpoint, I would use double U-tubes plus a high performance grout (> 1 Btu/hr-ft-°F) above the water level and sand or nothing below. They may be other factors to consider though. BH20 or similar (and PVC casings) are insulators.
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geodean
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| 07/19/2009 2:48 PM |
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| Try all of the options and let us know. It will be interesting to see the results. Since the horizontal has a higher ground temp, it might not add much benefit to the vertical. |
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Dewayne Dean
PalaceGeothermal.com
Why settle for 90% when you can have 400%
We heat and cool with dirt!
visit- http://welserver.com/WEL0114/- to see my system |
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erphillips
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Posts:19
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| 07/19/2009 8:39 PM |
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I wonder why Geo-Enterprises ( my supplier ) and my Well driller both recommended the BH20 for grouting. Geo-Enterprises is a large company that designs and supplies Geo projects all over the world.
Driller says he has used BH20 in hundreds of wells, Doesn't make sense with all the thermal enhanced grouts GeoPro has available to use one that has low thermal properties.
Ed |
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waterpirate
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| 07/21/2009 5:36 AM |
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Hi and welcome.
As to the advantages of thermally enhanced grout in the field, you are splitting hairs. The product tests well in the lab under controlled parameters and you birth the efficiancy numbers that you think are better.
In the field:
It mixes poorly
It does not hold the sand in suspension
You do not get lab quality results
You may in fact wind up with a grout that performs at a lower number than standard grout.
The real purpose of the grout is to seal the borehole against contamination first, and add conductivity second.
Many of the grouts on the market have a sliding scale in regard to solids content that is accomplished simply by the addition of more or less make up water. This gives you a better grout that performs properly to meet both jobs.
Eric Sackett
weberwelldrilling.com |
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Eric Sackett
WeberWellDrilling.com |
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erphillips
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Posts:19
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| 07/22/2009 9:33 PM |
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Results so far:
Heat pumps out to Horizontal Loop Field header, Return from Horizontal Loop to well inlet header, Return from wells to heat pumps = Caused Reduced flow to about 18 gpm, EWT 78 deg LWT 88 deg with 1-5 ton and 1- 4 ton unit running. ( Don't like the flow rate! )
Horizontal and Vertical loop's teed together with a full port ball valve on the horizontal to balance flow I set Vertical flow to 13 GPM and the total flow was at 28 GPM 2 Units running EWT is 72 deg LWT is 82 deg. ( Seems like the best setup )
I have a Flow meter inline with the Vertical Loop and a flow meter on the return from both loops together so I assume the flow is 15 GPM through the Horizontal Loop with the above setup.
If I operate 1 flow center at 15 GPM with no call for AC from any heat pump for 12 hours my loop temp goes to 68 deg ( I believe I am getting some loop temp rise from residual heat in the horizontal loop field from running it for several weeks at high temps )
Not sure of the well temps right now as I don't have my WEL connected full time yet.
Ed
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erphillips
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Posts:19
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| 07/22/2009 9:37 PM |
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One last question should I add any antifreeze and if so what type? Everything is below frost line but If I need to add antifreeze I want to do it now while I still have the Purge cart.
How Much antifreeze ? 6000 Feet of 1" HDPE and 2050 Feet of 3/4" HDPE plus about 200 feet of misc 1" piping to & from Vertical loops and to units.
Thanks
Ed |
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jonr
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| 07/22/2009 9:58 PM |
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Are the return temps from the verticals and the horizontals the same? That is the key to thermal balance.
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geodean
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| 07/22/2009 11:03 PM |
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Posted By erphillips on 07/22/2009 9:37 PM
One last question should I add any antifreeze and if so what type? Everything is below frost line but If I need to add antifreeze I want to do it now while I still have the Purge cart.
How Much antifreeze ? 6000 Feet of 1" HDPE and 2050 Feet of 3/4" HDPE plus about 200 feet of misc 1" piping to & from Vertical loops and to units.
Thanks
Ed If you are in a heating dominated climate, then you need antifreeze with freeze protection to 20 degrees.
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Dewayne Dean
PalaceGeothermal.com
Why settle for 90% when you can have 400%
We heat and cool with dirt!
visit- http://welserver.com/WEL0114/- to see my system |
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erphillips
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Posts:19
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| 07/22/2009 11:17 PM |
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No Return temps are not the same now, The Horizontal field is returning at about 80 deg with a LWT of 88 I believe it will balance out better in a couple of months when the Horizontal field temp stabilizes, I had high loop ( 90's ) temps for a month or so with only the Horizontal field connected that is why I added the wells. I think the ground temperature will go down and allow better thermal balance but I added a lot of heat to my field and it is pretty much solid limestone so the temps seem to change slowly.
Right now I am after lower EWT more then thermal balance from both loops, so I have the flow adjusted to lower the EWT as the wells provide colder return temps.
That may not be what I should want but that is what I am going after right now. I am mixing a little cold with a little warm to get a good flow rate and water temps that keep my EER up.
I think with the lower deep earth temps my verticals will always provide a little lower return temps, I do have good thermal balance on my separate loop fields IE all 6 horizontal loops are balanced to give the same return temps and the vertical loops don't have valves to balance them but all are the exact same length and read the same temp on all returns using a clamp on K type meter probe, I measured each after several hours of run time and waited for the meter to stabilize to take the readings. My verticals are connected in the ditch to 1 x 1 x 3/4 tee's then to the mechanical room as 1 pair of lines, the Horizontals all run the the mechanical room as individual 1000' loops.
Ed |
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erphillips
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| 07/22/2009 11:26 PM |
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geodean
I am in The Tulsa, OK area I believe my avarage Heating Degree days are 3078 and my average cooling degree days are 2150 http://apps1.eere.energy.gov/states/residential.cfm/state=ok
Would that be considered heating dominated?
Thanks
Ed |
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joe.ami
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| 07/23/2009 7:14 AM |
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Posted By erphillips on 07/22/2009 9:37 PM
One last question should I add any antifreeze and if so what type? Everything is below frost line but If I need to add antifreeze I want to do it now while I still have the Purge cart.
Thanks
Ed
Sounds like you are heating dominated.
Below the frost line is good, but not necessarily enough. Remember we will be taking heat out of the water you are circulating. While it sounds like you have enough tube to keep it above freezing, consider the modest cost of antifreeze vs the price of a new coaxial heat exchanger if damaged by freezing.
j
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jonr
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| 07/23/2009 7:22 AM |
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> Right now I am after lower EWT more then thermal balance from both loops, so I have the flow adjusted to lower the EWT as the wells provide colder return temps.
This is the point - balanced temperatures should give you the lowest EWT/LWT. But I agree, it is a moving target and it will take awhile to stabilize.
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jonr
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| 07/23/2009 7:41 AM |
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This will calculate your pipe volumes:
http://www.hydro-temp.com/help/drawings/Loop_Volume_Calculator.xls
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engineer
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| 07/23/2009 8:39 AM |
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Not a loop specialist but I think that in this special case one would NOT strive for equal return temps - loop fields have completely different characteristics.
Then again, I liked the idea of leaving water going to the horizontal field first and then the vertical, but that didn't give you lowest EWT, so my intuition is off.
Joe suggested paralleling everything for max flow + minimum friction. My concern there is that flow may drop into the laminar range in some paths, reducing heat transfer, but again, I'm not a loop specialist.
I can envision an undesirable result of the horizontal field ADDING heat to the vertical field in certain situations, although maybe that wouldn't be bad since it would aid in the horizontal field's recovery. In fact, you seemed to describe that happening when you 'mixed' temperatures by running pump through both without cooling load.
As an engineer often tempted to over-complicate things I have in mind the possibility of using the vertical loop all the time but find a way to use the horizontal field only when needed, such as via a valve controlled by a leaving water temp sensor.
At any rate, try different options and let us know.
As for freeze protection, should a system be freeze protected down to a temp a few degrees below the units' freeze protection cut out temperature (15 in the case of my WaterFurnace), or is 20 sufficient?
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Without data, you only have an opinion. |
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joe.ami
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| 07/25/2009 8:57 AM |
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Posted By engineer on 07/23/2009 8:39 AM
As for freeze protection, should a system be freeze protected down to a temp a few degrees below the units' freeze protection cut out temperature (15 in the case of my WaterFurnace), or is 20 sufficient?
Does WF ask for 15* freeze protection?
The other pertinant question is how temp is monitored and where.....thermistor on EW or LW.....low pressure switch etc.
I don't know every manufacturer's design, but the 6 or so I know want 20* protection.
As far as mixing the loop fields, as long as both are fully engaged (unimpeded) they will combine to create a result (in this case lower summer EWT) wether in paralell or series. Wouldn't they?
j |
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Geothermal; Savings Underfoot |
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jonr
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| 07/25/2009 9:20 AM |
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My understanding (from the manual) is that WF has a switch that specifically allows closed loop without antifreeze. No idea if this would cause cutouts in your case.
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