us261613
New Member
Posts:4
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| 20 Feb 2011 02:15 PM |
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Hello all,
I recently had a 4 ton Carrier Geotherm put in. With outside temps at 25F or colder, my EWT=25F and LWT=19F and heat pump runs nearly constant. Frost even on the water lines going into unit.
My installer informs me the glycol system is protectected down to 10-15F and heat pump will protect itself by kicking off at EWT=20F. Working but system on alot & only running COP around 3.0 on performance charts. Would be at 4.0 with expected EWT=40F. I have a friend nearby with the same Carrier system but in a 5 ton unit with 5 vertical wells. His measured EWT with a cold night was 40F.
The original plan was to put in 6 loops -125' deep. Due to drilling issues, they could only go to 100' so they added 2 more loops or a total of 8. The hooked up 2 loops in series on 4 circuits each. I'm getting about 11 gpm through the heat pump so I have 2.75 gpm/circuit (11/4). I found on Carrier and Water Furnace manuals, both manufactures recommend over 3.8 gpm on a 3/4" poly line to keep Reynolds number >2500 for turbulent flow for 25% glycol line. At 2.8 gpm, I'm down to Re=1400. I believe this laminar flow is responsible for my EWT=25F.
So do I make the installer dig back up the header and re-plumb system? Also, what do we re-plump to? Putting 4 of the 100' wells in series gives me 800' effective length. Installer says with 2 Grundfos 26-116 pumps, they don't recommend more that 600' length circuits due to head pressure. This is pushing near the 60' head pressure on the dual pump curves at 10-11 gpm. Maybe I'd be better off, only using 6 of the 8 loops. Place 3 -100' loops in series to make 2 parallel circuits. Or place 2-100' loops in series to make 3 parallel circuits. Both would be reasonable head pressure and should both have turbulent flow.
Suggestions?
Thanks, Mark |
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decafdrinker
Basic Member
Posts:420
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| 20 Feb 2011 03:04 PM |
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I'll dive in (homeowner, learned a lot from this forums) and ask/suggest a few things...
1. How exactly did you measure the EWT and LWT?
2. How exactly did you measure the gpm through the system? Pressure across p/t ports? flow meters?
3. What is your "return" air temp (probably your room temperature) and your "supply" temp (EAT and LAT/DAT)?
4. What is your thermostat set at?
5. Where are you?
6. Is Aux heat on/off or have you ever noticed it going on?
7. (last one for now) What stage were you running/do you run most of the time?
I'll repeat I'm no expert, but everything I've read on here suggests that you're getting a 6F delta in your loop (25-19=6) which is very good, assuming your EAT/LAT rise is 20F or more. My delta is only about 4F.
If it's cold outside, it may indeed be that the HP runs most of the time. When the temp here gets below 25F outside, (Philadelphia, PA) my 4-ton Geo HP runs in stage 1 almost constantly, sometimes kicking into stage 2. House maintains at 69F. I have frost/ice on my lines coming in. I need to insulate more, but Geo loops can go down to 10/15F, hence the glycol mix.
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Looby
Basic Member
Posts:401
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| 20 Feb 2011 03:07 PM |
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Posted By us261613 on 20 Feb 2011 02:15 PM
So do I make the installer dig back up the header and
re-plumb system? Also, what do we re-plump to?
Why not just switch to methanol antifreeze? |
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| One measurement is worth a thousand expert opinions. |
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us261613
New Member
Posts:4
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| 20 Feb 2011 06:00 PM |
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Good questions:
1) Measured EWT=25F and LWT=19F with digital thermocouple place in screw access of water lines on both inlet & outlet of heat pump. Same way installer does.
2) Installer & I measured a 4 psi across the heat pump. FOr my model, according to manual thats about 11 gpm.
3) EAT = 69F, LAT=90F also measured with thermocouple.
4) Thermostat at 69F
5) St. Paul, MN
6) Aux heat does go on eventually when its about -5F outside and colder.
7) Most time in Stage 2 of heat pump
I am getting the 6 delta F out of the heat pump so its performing where it should. More concerned on performance of vertical loops. Its the first time my installer put in a 4 circuit system on a 4 ton system. I really think my heat transfer (low EWT) is due to low of flow rate. 11 gpm/4 = 2.74 gpm/circuit. Mfg. recommends 3.8 gpm or greater to have turbulent flow. I've seen on-line one can expect 3X heat transfer with turbulent flow.
Thanks for input. |
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dgbair
New Member
Posts:54
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| 20 Feb 2011 06:23 PM |
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What Looby said.... A antifreeze switch should get you around a 1000 point gain on the Reynolds number..... (I didn't run your exact numbers) |
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us261613
New Member
Posts:4
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| 20 Feb 2011 06:25 PM |
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THe suggestion on switching to Methanol is a great suggestion. This would get me to likely the turbulent flow I need.
I'll run past my installer again but I believe he told me glycol only is allowed for closed loop systems in my area.
Thanks for the suggestion though. I'll check again on the legality of using Methanol. ANy long term drawback on using Methanol?
Thanks! |
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geome
Advanced Member
Posts:987
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| 20 Feb 2011 06:32 PM |
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For what its worth - per Wikipedia on 2/20/2022:
"Methanol is readily biodegradable in both aerobic (oxygen present) and anaerobic (oxygen absent) environments. Methanol will not persist in the environment. The "half-life" for methanol in groundwater is just one to seven days, while many common gasoline components have half-lives in the hundreds of days (such as benzene at 10–730 days). Since methanol is miscible with water and biodegradable, methanol is unlikely to accumulate in groundwater, surface water, air or soil." |
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| Homeowner with WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon. |
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jonr
Senior Member
Posts:5341
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| 20 Feb 2011 07:44 PM |
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I've seen on-line one can expect 3X heat transfer with turbulent flow. No, you won't see anything even close to that difference on the loop system. 30% maybe (it's been while since I checked). |
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Looby
Basic Member
Posts:401
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| 20 Feb 2011 08:56 PM |
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Posted By jonr on 20 Feb 2011 07:44 PM
No, you won't see anything even close to that difference...
... 30% maybe (it's been while since I checked).
Sounds like a genuine imitation 'definite maybe.' Nothin' more valuable than a
citation-free WAG from a net.SelfAppointedXpurt who hasn't checked in a while.
...worth every penny! ...or NOT,
Looby |
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| One measurement is worth a thousand expert opinions. |
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joe.ami
Veteran Member
Posts:4377
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| 20 Feb 2011 08:59 PM |
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Laminar flow may not be the industry supported standard but it can work fine as DOC is indicating elsewhere.
His study indicates that greater pumping watts to create turbulent flow may not pay great dividends.
j |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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waterpirate
Basic Member
Posts:467
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| 21 Feb 2011 06:21 AM |
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What was the install date for your system? Everything you have posted is good info as far as performance of your unit. I would not sweat the flow rate, however I do support a switch to methanol as the easiest way to increase the flow to what you want.
We see abnormal loop temps on systems that went directly to cooling in last years heatwave, and directly into heating in this years hard freeze temps. You may see improved loop temps when the loop temp is given the opportunity to swing back the other way. It is all about data collection over time to really dial in your system.
Eric |
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| Eric Sackett<br>www.weberwelldrilling.com<br >Visit our Geothermal Resource Center! |
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joe.ami
Veteran Member
Posts:4377
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| 21 Feb 2011 10:07 AM |
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Ya know US 26, I'd like you to verify your thermometer first in a glass of ice water.
Second you need to understand that more ground loop will seldom cause ill save possible extra pumping power. You are suggesting that it would be beneficial to reduce the size of your loop field by 25%. This shows a misunderstanding of all the forces at play.
Your preoccupation with Reynolds number shows a very myopic course of study.
I'm not trying to pick on you, but you are ignoring answers that don't agree with your mindset.
joe |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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Looby
Basic Member
Posts:401
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| 21 Feb 2011 02:56 PM |
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Posted By us261613 on 20 Feb 2011 06:00 PM
I've seen on-line one can expect 3X heat transfer with turbulent flow.
That's in the right ballpark. Here's a handy-dandy online calculator
that gives p-drop, Reynolds number, and heat transfer coefficient
for any pipe diameter, flow rate, and brine type of your choice.
http://www.engineeringpage.com/calculators/thermal/inside_tube_coefficient.html
...the web knows all,
Looby |
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| One measurement is worth a thousand expert opinions. |
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us261613
New Member
Posts:4
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| 21 Feb 2011 11:49 PM |
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THe system was installed in late December. COld outside temps. Had to use electric heat blankets to thaw top soil.
Perhaps outside tube thermal conductivity will improve as soil has a chance to settle around loops and moisture fill back in around wells? Somewhat sandy/clay ground. |
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docjenser
Veteran Member
Posts:1400
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| 22 Feb 2011 01:25 AM |
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Posted By Looby on 21 Feb 2011 02:56 PM
Posted By us261613 on 20 Feb 2011 06:00 PM
I've seen on-line one can expect 3X heat transfer with turbulent flow.
That's in the right ballpark. Here's a handy-dandy online calculator
that gives p-drop, Reynolds number, and heat transfer coefficient
for any pipe diameter, flow rate, and brine type of your choice.
http://www.engineeringpage.com/calculators/thermal/inside_tube_coefficient.html
...the web knows all,
Looby
Originally Posted by docjenser
How much heat transfer does one loose if the reynolds #
drops from lets say 2500 down to 1500?
About 16%
Code:
Heat transfer coefficient (W/m^2-°C) versus Reynolds Number
On edit: The table below is for 1" ID pipe. Larger pipe has lower
heat transfer coefficients -- but about the same % differences.
Re U
---- ---
600 195
800 228
1000 245
1200 260
1400 274
1500 280
1600 286
1800 298
2000 308
2200 318
2400 327
2500 332
2600 336
2800 344
3000 352
4000 387
5000 417
you confuse me now, did't you just post that bringing down the reynolds # from 2500 down o 1500 reduces the heat transfer by 16%. Now it is x3? please clarify |
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| www.buffalogeothermalheating.com |
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docjenser
Veteran Member
Posts:1400
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| 22 Feb 2011 01:32 AM |
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Posted By us261613 on 21 Feb 2011 11:49 PM
THe system was installed in late December. COld outside temps. Had to use electric heat blankets to thaw top soil.
Perhaps outside tube thermal conductivity will improve as soil has a chance to settle around loops and moisture fill back in around wells? Somewhat sandy/clay ground.
Usually vertical loops (in contrast to horizontal ones), which have been grouted, do not need much settling. A/C season will help, yes. |
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| www.buffalogeothermalheating.com |
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Looby
Basic Member
Posts:401
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| 22 Feb 2011 02:09 AM |
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Posted By docjenser on 22 Feb 2011 01:25 AM
you confuse me now, did't you just post that bringing down the reynolds #
from 2500 down o 1500 reduces the heat transfer by 16%. Now it is x3?
please clarify
Sources were cited/linked in both posts. At least one is in error,
_OR_ I flubbed the data entry. It happens. You shoulda checked
the math before investing big $$$ in the results.
If/when you have better information to offer, feel free to contribute.
BTW, still watin' for an explanation of why every geo manufacturer
and every geo-design manual/program wastes so much time, ink,
and effort worrying about Reynolds numbers & turbulence?
...guess they just didn't "get the word" yet, huh?
Looby |
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| One measurement is worth a thousand expert opinions. |
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jonr
Senior Member
Posts:5341
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| 22 Feb 2011 05:21 PM |
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A geothermal loop is a system with many pieces restricting heat flow; there is far more to it than just heat transfer from across the pipe wall. 16% (as a percent of the total) is reasonable, 3x is an indicator of myopic thinking by someone who knows just enough to confuse some people.
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Looby
Basic Member
Posts:401
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| 22 Feb 2011 05:47 PM |
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Posted By jonr on 22 Feb 2011 05:21 PM
...there is far more to it than just heat transfer from across the pipe wall.
Wasn't discussing heat transfer across the pipe wall, (k)einstein.
Please try to keep up.
... myopic thinking by someone who knows just enough to confuse some people
Versus someone clueless enough to confuse himself?
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| One measurement is worth a thousand expert opinions. |
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joe.ami
Veteran Member
Posts:4377
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| 22 Feb 2011 09:24 PM |
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probably not worth worrying about testing the thermometer either..... |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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