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a0128958
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Posts:183
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| 08/06/2008 12:11 AM |
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Posted By Brock on 08/04/2008 11:55 PM
... what if you could run a circulation pump 24/7 and see what the temps are without the system dumping heat? It would be interesting to see the results.
Brock many thanks for the helpful comments. I agree with your pool example. It has to be correct, because
KBTU/hr = DeltaT * GPM * 0.5, assuming turbulent flow.
Your suggestion to do an experiment with the pumps is great! I'm going to think how I could run my pumps 24/7 for perhaps a couple of days. Right now they're wired to turn on with the GSHP's blower.
Does anyone know if Grundfos UP 26-116 pumps are designed to be run continuous duty?
Right now my (3) pumps are running 10 hrs per day each on avg. So I'd be adding an average of about 14 hrs each of run time. (And at 385 watts per pump, times 3 pumps, that's 1.2 KW. Times 14 hrs, that's 16 KWH of additional run time energy per day).
Thanks and best regards,
Bill
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a0128958
Registered Users
Posts:183
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| 08/06/2008 12:23 AM |
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Posted By Brock on 08/05/2008 12:03 AM
... do you set back the temps during the day or anytime? Or the loading we see in the charts due to sun/outside temps?
... (I think I am learning more then anyone else here).
Yes, all 4 tstats are on set back programs, as a function of time of day. Right now I use a 4 ° set back.
My residence has high cooling/heating load diversity - it has a lot of glass.
Thus, the KBTU/hr rates graphed here: http://welserver.com/WEL0043/EnteringWaterTemps.gif
are influenced by sun (time of day) and by variation of tstat set point temp.
For example, right now, only the bedrooms are calling for cooling, and are using just the 3 ton unit, with a Heat Rejection of 28 KBTU/hr.
I'm learning right with you. I'm exceptionally appreciative to those who are a lot smarter than me that have volunteered a little bit of their time to contribute.
Best regards,
Bill
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a0128958
Registered Users
Posts:183
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| 08/06/2008 12:30 AM |
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Posted By engineer on 08/05/2008 12:07 AM
... consider two scenarios in which I pick somewhat random numbers to illustrate - Say you run a 5 ton geo heat pump with 15 GPM and it has EWT of 85 and LWT (Leaving water temp) of 95. Suppose you can choose to pump it much much harder - say 30 GPM. With EWT of 85 LWT would be 90 (flow up by x2, so delta T down by x2). Of course the borehole field experiences the same 30 GPM so it takes the 90 F water and cools it back down only to 85.
In the 30 GPM scenario heat pump EER might be slightly increased by the LWT being 5 Deg F less, but that gain would be more than offset by all the extra pump power needed to go from 15 to 30 GPM. Note that in both scenarios EWT would be 85. Actually all the extra pump work would hit the loop field as extra heat, so EWT might even rise a couple tenths of a degree at 30 GPM.
... Your system may be slightly overpumped, based on actual verses suggested flows through your Envision units. However, you have larger 1" rather than 3/4" loop tubes which may well demand the extra flow to stay turbulent.
engineer, your example above is exceptionally well written. I think I've got it!
I didn't know that typical residential projects are done with 3/4" loop tubes. And since I have 1" pipe, I hadn't thought about the fact that maybe my higher flow rate may be needed to maintain turbulence. I assume this would be automatically handled by a loop design s/w package (i.e., making sure flow is high enough to maintain turbulence.)
Thanks,
Bill
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a0128958
Registered Users
Posts:183
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| 08/06/2008 12:42 AM |
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Posted By geodean on 08/05/2008 2:23
Other threads have mentioned that you are over pumping. If you have two units that equal 8 tons and you need 3 GPM / ton then 24 GPM would be just right.
The above thread says you are pumping 21 when both units are running. Where did the notion of overpumping come from?
On some of the commercial loop jobs that we do, they buy as much loop as they can justify and then run a fluid cooler at night to keep the loop temp down when the demand is high.
Dewayne, I've been trying to summarize to stay brief. 21 gpm was meant to be said just for the 5 ton unit alone.
Being more specific:
3 ton unit alone = 14 gpm (29 KBTU/hr at the moment)
5 ton unit alone = 21 (52 KBTU/hr at the moment)
3 & 5 ton units together = 11 + 19 = 30 gpm
The 14 and 21 gpm flows are 'off the charts' that WaterFurnace supplies.
I'm continuing to understand how the economics of the borehole field cost cause considerable implementation decisions that can deviate quite considerably from a theoretical design. Thanks for the above illustration.
Best regards,
Bill |
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a0128958
Registered Users
Posts:183
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| 08/06/2008 12:54 AM |
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Posted By geodean on 08/05/2008 11:14 AM
... I have attached three hypothetical loop designs for your house. I used two cooling load values. One at 60,000 BTUH and one at 82,000 BTUH.
... for 82,000 you are short 800' of bore hole. This is assuming we want to keep you EWT below 90°.
If we let your EWT go to 100°, then your 2400' of bore hole can handle the 82,000 load. This is shown in the third attachement
... Hope this helps
Dewayne, these are going to help tremendously! Thanks!
The 82 KBTU/hr is both of my units running simultaneously, 1st stage only. I don't know what my cooling capacity is running 2nd stage - the units never need to run 2nd stage.
I don't start dumping 82 KBTU/hr of heat until about Noon (and causes EWT to rise a lot). From about 6 AM through Noon it's 30 or 52 KBTU/hr (and loop seems to be able to handle this rate, with not a lot of EWT rise). And starting at about 11 PM it stays around 30 KBTU/hr (giving loop EWT an opportunity to cool down for start of next day).
I'm going to need a little bit of time to digest the attachments. I was out all day today, so I got a late start tonight catching up here. I'll study the 82 KBTU/hr example particularly carefully - this is the rate at which my EWT rises with - and get back tomorrow (later today).
Many thanks!
Best regards,
Bill |
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Brock
Registered Users
Posts:203
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| 08/06/2008 3:31 AM |
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Would you need to run all three pumps, wouldn't just one of them circulate enough to give you good numbers?
What exactly is turbulent flow or turbulence, I have assumed it meant if there were multiple lines in parallel that there was enough flow to force it to move through all the lines rather then leaving one or more at a stand still. What happens on the loop end with 1/2 the flow, I understand the heat pump side. |
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Green Bay, WI. - geothermal heated indoor pool with a small solar setup |
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engineer
Registered Users
Posts:394
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| 08/06/2008 10:32 AM |
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Guys,
Help me understand what you hope to learn or accomplish by circulating loop water without a cooling load - I suppose it might have the beneficial effect of distributing heat better throughout the bore field, possibly slightly reducing EWT when loaded. What else did you have in mind?
Brock - for any given pipe size a certain minimum flow is needed to ensure turbulent flow - complete mixing of the fluid across the entire tube face - necessary for heat transfer between all the fluid and the tube walls. Below that minimum flow it is said to be laminar - fluid does not mix well and the fluid in the center of the tube does not transfer its heat to the pipe wall since it does not contact the pipe wall.
It is a goal of design to ensure turbulent flow in all parallel u-tubes in the bore field. This requires a minimum total flow as well as due care to ensure flow is well divided between the individual U-tubes. Design software should handle that. It is not enough to merely prevent a u-tube from being at a standstill - one must ensure all have the minimum flow to be turbulent.
Bill - I have no doubt that a pump able to run 10+ hours at a time can handle continuous duty. The Grundfos is likely rated for continuous pumping duty the only limit being fluid temp, and that limit should be on the name plate. Deadheading it, that is completely blocking either the inlet or outlet would be ill-advised, but aside from that you should be good to go. |
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Without data, you only have an opinion. |
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Brock
Registered Users
Posts:203
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| 08/06/2008 10:50 AM |
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The only reason I suggested running a pump continuously was to find out what the ground temp really is. Not that it would matter in the end because what matters are the number he already has when the unit is actually running.
Getting off topic a bit, but in our system we have two larger pumps that come on when the heat pump is on (heating the pool), then a single pump about half the size comes on when the forced air is calling for cooling (loop and air handler plumbed in parallel). If the heat pump is running it is obviously much cooler, but if the heat pump is off it just circulates the fluid from the field with the single smaller pump. I wouldn't imagine that smaller single pump could create turbulent flow, but even if I kick on the two larger pumps without the heat pump I don't see any change in the incoming loop temp or the temp in the air handler coil or the actual air temp out. |
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Green Bay, WI. - geothermal heated indoor pool with a small solar setup |
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a0128958
Registered Users
Posts:183
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| 08/06/2008 6:00 PM |
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Posted By geodean on 08/05/2008 11:14 AM
I have attached ... hypothetical loop designs for your house.
... For 82,000 you are short 800' of bore hole. This is assuming we want to keep you EWT below 90°.
If we let your EWT go to 100°, then your 2400' of bore hole can handle the 82,000 load. This is shown in the third attachement
Since your units never run on second stage, I think your cooling load is closer to 60,000 than 82,000.
Hope this helps
Dewayne, this helps immensely! This is much appreciated!
I've been thinking for a while. I think I understand. Some key observations:
My GSHP system is, on average, at the moment, removing about 750 KBTU per day from my house. That's about 31 KBTU per hour on a 24 hour average.
My guess is this would be the Man J generated cooling load if I had a theoretically perfectly prepared Man J analysis that matched up to the exact existing conditions of my home.
On a 24 hour basis, at 31 KBTU/hr, it looks quite clear my 2400' of bore length, with 1" pipe / clay soil / std grouting, is quite sufficient. Certainly though, my EWT would vary considerably during the 24 hr day, due to time periods where the units' rate of heat rejection capacity is far greater than the soil's instantaneous ability to absorb the heat. In the afternoon / evening the soil gets 'overloaded,' and at night / early morning the soil 'recovers.'
In my case I have 8 tons of equipment, capable of operating on a fixed rate basis, in 1st stage, at either 30 (3 ton only), 52 (5 ton only), or 82 KBTU/hr (3 + 5 tons) heat removal rate.
When I operate at 30 KBTU/hr (3 ton only), my charts clearly show loop field capacity sufficient to not only absorb the heat but also to allow the soil to cool.
At 52 KBTU/hr (5 ton only), my charts clearly show loop field capacity still generally sufficient for the soil to absorb the heat without material EWT rise.
It's at 82 KBTU/hr (3 + 5 ton units) where my charts show heating of the soil faster than the heat can dissipate - i.e., EWT goes up.
Since your example is at 80 KBTU/hr with an EWT design constraint of 90°, it shows that I would need 3 more holes (890') to absorb this rate of HR *and* stay at or better than the EER associated with 90° EWT.
And if I instead use an EER design constraint associated with a max of 100° EWT, then I'm actually within 60' of bore length of being able to absorb the monsterous 82 KBTU/hr cooling rate all day long.
But 82 KBTU/hr all day long is almost 2 MBTU/day - far greater than my 3400 sf house can generate. Even in this 100+° heat right now, it's still 2.6 X what my house is currently generating.
My guess is my EWT is probably not going to get higher than 85° this summer. And noting that I have 2400 of bore length, with 1" pipe, etc., my guess is that if the s/w allowed you to work backward, my loop's cooling rate capacity is about 50 KBTU/hr on a continuous duty basis.
Enough to handle the 24 hour avg load of the home easily (31 KBTU/hr), and enough to handle the peak portion of the day where I'm pumping at 82 KBTU/hr without EWT rising above 85° versus my deep earth temp of 68°. All noting a direct relationship of EER to EWT.
Fascinating!
Now I understand why EWT 'appears' to be a function of outside avg temp, even though the loop is deep in the soil. It's not really directly correlated to outside temp.
It's because what is a function of outside avg temp is HR. And EWT is a function of how well the loop can absorb the heat (HR). And it's the loop's economical design that causes EWT to vary (and thus EER to vary).
Many thanks!
Best regards,
Bill |
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a0128958
Registered Users
Posts:183
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| 08/06/2008 6:11 PM |
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Posted By engineer on 08/06/2008 10:32 AM
... I have no doubt that a pump able to run 10+ hours at a time can handle continuous duty. The Grundfos is likely rated for continuous pumping duty ... you should be good to go.
Thanks.
Bill
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a0128958
Registered Users
Posts:183
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| 08/06/2008 6:22 PM |
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Posted By Brock on 08/06/2008 10:50 AM
The only reason I suggested running a pump continuously was to find out what the ground temp really is. Not that it would matter in the end because what matters are the number he already has when the unit is actually running.
I think it's an interesting learning opportunity. It's not obvious to me at the moment what to expect, beyond Brock's comment above.
And, the cost to do the experiment is low. At 14 hours of additional run time per day, for 1 pump (see next paragraph), times 385 watts, that's a cost of 5.4 KWH per day, which for me, @ $0.12/KWH, is 65 cents per day.
I'm only going to run 1 pump, as Brock suggests. This is easy to do, for a complete loop, as my 3 ton unit only has one pump associated with it.
I'll set up a second 50 hour chart, that structurally matches the EWT / HR chart I've been refering to ( http://welserver.com/WEL0043/EnteringWaterTemps.gif ), for easy comparison.
Best regards,
Bill |
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geodean
Registered Users
Posts:590
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| 08/06/2008 8:15 PM |
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Posted By a0128958 on 08/06/2008 6:00 PM
Some key observations:
My GSHP system is, on average, at the moment, removing about 750 KBTU per day from my house. That's about 31 KBTU per hour on a 24 hour average.
My guess is this would be the Man J generated cooling load if I had a theoretically perfectly prepared Man J analysis that matched up to the exact existing conditions of my home.
A Manual J calculation figures peak load not average daily load.
This has been a fascinating thread. I think we have learned a lot. I know that I have.
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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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a0128958
Registered Users
Posts:183
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| 08/07/2008 12:38 AM |
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Posted By Brock on 08/06/2008 10:50 AM
... I suggested running a pump continuously ... to find out what the ground temp really is...
OK, the experiment is about 4 hours old. One pump is running 7x24, circulating water through the loop and the 3 ton coax heat exchanger.
My initial observation is that it simply makes it easier to obtain real-time temperature measurement of the ground.
Magnified 5 hour chart: http://welserver.com/WEL0043/EnteringWaterTempsFiltered4.gif
50 hour chart showing before and after: http://welserver.com/WEL0043/EnteringWaterTemps.gif
It's the blue line. Since the 3T pump is running 7x24, sample process has been removed.
Best regards,
Bill |
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geodean
Registered Users
Posts:590
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| 08/07/2008 12:59 AM |
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Posted By Brock on 08/06/2008 10:50 AM The only reason I suggested running a pump continuously was to find out what the ground temp really is.
The loop temp is going to be constantly fluctuating as the heat is absorbed by the surrounding ground and more heat is dumped into the loop when the heatpumps are cooling.
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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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Brock
Registered Users
Posts:203
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| 08/07/2008 1:50 PM |
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| Very interesting to see what the loop is doing. Did it make any difference in EWT? I wouldn't think it wouldn't be very noticeable, if any, but as engineer suggests maybe it would distribute heat better throughout the field. Maybe if there was one sweet spot with close proximity to flowing ground water who knows. I would guess outside temps and heating load might swing that more than one of the pumps running 24x7. |
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Green Bay, WI. - geothermal heated indoor pool with a small solar setup |
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a0128958
Registered Users
Posts:183
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| 08/07/2008 1:58 PM |
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Posted By geodean on 08/07/2008 12:59 AM
The loop temp is going to be constantly fluctuating as the heat is absorbed by the surrounding ground and more heat is dumped into the loop when the heatpumps are cooling.
Absolutely.
I think I've seen enough to put the pump back to normal.
See below charts for summary on how my 8 hole, 300' deep each, 1" HDPE pipe, damp clay soil borehole field is performing in Dallas area 68°F deep earth, at 3 distinct Heat of Rejection (HR) dumping rates (30, 52, 82 KBTU/hr), in the month of Aug. with outside air temp highs in 100+° range and average temp at 90°.
My key conclusions are:
1. My loop field's steady state heat absorption capability (i.e., without short or long term soil temperature rise) is about 50 KBTU/hr.
2. My Entering Water Temp (EWT) varies by about 7° during a 24 hour day. If I had smaller GSHP units, capable of lower HR rates, this 'swing' would be less.
3. Running pumps continuously doesn't provide any material HVAC benefit, but it does make it easier to measure earth temps.
4. Since there are time periods where I put into my loop field more than 50 KBTU/hr, my soil temp has been rising over the course of the summer. I estimate it's at 75° right now, 7° above the Dallas area 68° deep earth temp.
5. My standard issue Grundfos pumps indeed require about 320 watts each.
Best regards,
Bill |
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Brock
Registered Users
Posts:203
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| 08/07/2008 2:15 PM |
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| Bill what are you collecting all the data with? |
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Green Bay, WI. - geothermal heated indoor pool with a small solar setup |
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a0128958
Registered Users
Posts:183
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Brock
Registered Users
Posts:203
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| 08/07/2008 5:09 PM |
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| Dang, if I buy one and my wife complains, I am giving her your email address ;) |
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Green Bay, WI. - geothermal heated indoor pool with a small solar setup |
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John in the OC
Registered Users
Posts:54
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| 08/07/2008 6:45 PM |
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NuBee Here:
What should one expect to pay for a turn key for a unit (4000SF home in moderate California climate? and how long to get a return in $?
Can they work as a sole source of Heat & A/C? Who's the best with the longested, cleanest history in selling these?
Thanks |
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