Cold 25F EWT

Hello all,
I recently had a 4 ton Carrier Geotherm put in. A recent check had my EWT=25F and LWT=19F after a cold night. Frost even on the lines.

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 onalot & only running COP around 3.0 on performance charts. Would be at 4.0 with expected EWT=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 manual, I need 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 assume 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

 

Mark,
You should have an op cost calc. from your installer somewhere that reflects average 3.5 to 4 COP. Sometimes you will get more than a 4 and obviously sometimes closer to 3.
In late winter we expect colder fields and certainly no one in my area designs for a 40* minimum EWT. Nor do I think your measured temperature after a long cold night is reflective of the actual deep ground temperature.
Sounds to me your installer has failed more by not discussing expectations than on the design side.
Good Luck,
Joe

 

EWT=25F

Joe,
Yes, I'm not expecting to always run at a COP=4. Certainly a 3.2-4 would be great.

However, I'm more concerned with the EWT=25F. My friend in the same climate has his EWT=40F on a 5 ton system. My carrier manual doesn't even list performance with EWT below 30F.

Today its 26F outside and my EWT=25F. THis doesn't seem right. WIth the earth at 45-50F, I attribute this to my low laminar flow rate of my installer mistakenly placing 4 parallel loops on my 4 ton system. With water only, I would likely have turbulent flow. But with higher viscosity glycol, with less than 3 gpm/circuit I have laminar flow & hence a poor mixing of water in the pipes and low heat transfer.

If they had installed only 3 circuits my flow rate would be up over 3.8 gpm and I'd expect my EWT to be at least in the mid to upper 30s??

Mark

 

I think you are off for the reynolds number, 2.75 gpm per 400 ft circuit should give you more than reynolds=1400. Usually, you only install 26-116 when you have to, they only give you 10% more ft of head than the 26-99, but consume 50% more electricity.
We run 4 ton systems with (4) 800 ft slinkies and (2) 26-99 all the time getting around 11 gpm, with reynolds above 2500.

I would take a step back and check if the load has been unusally high for 4 tons, or some of the loop might be air locked (check with your installer the purging) or (rare) a loop is shut off due to incorrect fusing supply and return together. None of it likely, given your 11 GPM, which is actually right on target. You effectively have (4) 400ft loops out there. I only have one loop running at 25FEWT out there. House is not fully insulated yet, but customer has already moved in, keeping inside temps 72-73 F, higher load causes longer run time, more BTUs extracted, deeper loop temps. Don't dig up your yard, it will not change much. Your loops indicate a higher load.

 

EST=25F

The Carrier manual has a table of Reynolds # for 25% Polyprop Glycol. For a 3/4" pipe it lists
2 GPM > Re=1271
3 GPM > Re=1919
So I think I'm laminar flow. Glycol has the higher viscosity. For water only, these numbers would be 5600 & 8400 respectively well in excess of 2500.

One member suggested switching to Methanol with lower viscosity would get met Re>2500. However, I don't know if its allowed in my area.

My house is only 25 yrs old. New windows and well insulated about 2800 sq. ft. so I think 4 ton load is appropriately sized. I am running <$3/day heating costs so not so bad. But still conerned with low loop temps.

Thanks

 

I was similarly surprised by the expectation of 40 EWT in St Paul this time of year. 30 would seem to be about right; a dip into the 20s not unexpected.

 

Lemme guess: The guy with 40F EWTs has an open loop system?

What's the undisturbed deep ground temperature in St. Paul?

 

Ground temp

I believe ground temp is around 45F here in MN.

I did do a test. With system off for 7 hrs - aux. heat on only, I then started Geotherm.
@t=0 min, EWT=39F
t=10 min, EWT=31F
t=30 min, EWT=28F

My co-worker used my same digital thermocouple (TC) on his newly installed 5 ton unit. I assume he put the TC into the PT valve far enough. However, don't know how long his unit was on before he did this measurement. He got an EWT=40F.

We did find 2 mismatched Grundofos pumps installed 1-99 & 1-116. Installer coming out today to put in matched 2-116s & reburp system for air. Assuming this might bring flow rates up and possible EWT up.

I'm kind of hearing from this forum, not to be to concerned with such a low EWT as long as it doesn't get low enough for system to kick out.

 

EWT=25, air in lines

Some new data to my issue, installer was out today with purge pump cart. It appears we have a large amount of air in loop field. The purge cart static water column would drop about 6 inches of water (>1 gal of water in a 7" dia.column) everytime we dead-headed the pump. With the 1.5 Hp pump, he could not get it to burp out.

He's coming back tomorrow with a larger pump cart. See if this will get the air out of loop field. Likely cause of low EWT.

 

Any air in a closed loop system is bad. Get it gone.

 

Could indicate a kinked loop, but yeah wanna make sure air is out.
j

 

air in loop field

We've tried with a 1.5 HP water pump to get the air out of loop field. We're still getting about 1 gallon drop of column when dead headed.

Beginning to think there is a kink in loop and may have to dig up header in Spring.

 

did he try reversing?

Maybe this will help?
http://forum.geoexchange.org/geothermal-loops/4514-purge-cart-reversing.html

 

Purge reversal

dgbair,
Thanks for the good suggestion on reverse purging. We did try this but did not seem to help.

I'm concerned with the volume of their purge cart and my 4 parallel loop system. They did not have flowmeter to know water rate we were pushing. Should probably be up over 20 gpm with 4 circuit system with glycol. In hind-sight, hould have timed water flow into 5 gal. bucket to determine rate.

They may come back with a different/larger pump cart system before we resort to digging up header system in Spring.

 

Loop Temperature

This thread seems to be dealing with my concern. When i initially lined up for my system i was of the understanding that the ground temperature at loop depth would be about 60F which I assumed is what my incoming loop temperatyre would be. On the initial startup my loop temperature was about 55F in and 52F out and the system seemed to be keeping the 2200 sq ft. house comfortable at 70F. After a cold snap of -38C for a few nights the system is no longer able to get the house up to 70F. Today was relatively mild -7C and the house temp fell back to 68F with the 3 ton pump running continously.

This thread talks about EWT ( I assume this is Entering Water Temp) of 30F. My current EWT is 32F and as I said it is not able to maintain the house at a temperature of 70F. My thought is that my loop is very cold but this thread suggests otherwise.

What should I be expecting and is there other things I should be looking at.

My pump is a 3 Ton ClimateMaster Tranquility 27 with horizontal ground loops at 10" My EWT is currently 32F and leaving at 29F. Any info will be appreciated. Thanks

 

Bob

Where are you at?

That would be a pretty common loop temperature around here (Interior BC, Canada) at this time of year.

 

Loop Temperature

Thanks UrthBuoy. I am in Saskatchewan approx. 100KM NE of Saskatoon. I am surprised at the fact that is a normal loop temp. Given that I am wondering what might account for the sudden loss of ability to keep the house warm. Granted the basement is unheated & the slab is not poured but the walls are all ICF and the basement opening is covered over with foam insulation.

I did expect that the system would work a bit harder then normal to compensate for the unfinished basement and I was quite satisfied with the way the system was performing given the situation. Ultimately I expect the system will bring the house up to temp and cycle very little.

FYI, the house is a 2100 sq. ft. bungalo with 4" of medium density foam (WallTite) in the walls and 5" of foam sprayed over the entire roof deck. The basement walls are 2.5" ICF blocks filled with 6" of concrete.

Is it possible that my loss of heating ability is simply due to the unheated, no-slab basement? Yesterday the temperature was back to -6 pr so but the performance is not the same as prior to the sub 30 weather. Any more ideas? Thanks.

Bob

 

Loop Temperature

Thanks for the reply UrthBuoy. I replied this AM but obviously screwed it up; I don't see my post.

Anyways, I am about 100KM North of Saskatoon located in the South Saskatchewan River valley. I expect, if anything, our ground temperatures are lower then yours so it sounds like I should be in the ballpark when it comes to loop temp. So now I need to figure out why my performance went downhill after the cold snap. Perhaps it really is due to the fact my basement is unheated and no slab.. The entire system was designed around the finished basement which is to be heated by another 4 Ton water-water unit. What I find curious is that the vendor did tell me that the basement system would not contribute anything to the upstairs heat and the basement is fairly well isolated from the upstairs. If you can think of anything else I can look at it would be appreciated otherwise I guess I better hurry and finish my basement. Thanks.

Bob

 

So how were the loops tied- in?
From what I read you have 8 loops total. (800')
Tied-in them together for a total of 4-200' loops.
Then from that point how are the loops tied-into header?

It's going to take you a while to purge. Your trying to force air down into the ground 100' then back up and back down another 100', all at the same time your running water through 2 other pairs of loops.

What kinda flush cart are they using? Homemade or professional built?