jebs
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| 07/01/2009 8:34 AM |
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My 12 year old Geo unit is cooling poorly. A/C techs have not been able to figure out why. One of the grundfol circulator pumps seems extremely hot. Also my desuperheater is offloading significant heat into my water heater. The temp of the water coming out of the desuperheater is 130 degrees f. With the recovery unit enabled, it reduces the heat gain in my loop by 1 degree (inlet verses outlet). I realize that my loop temperature is high, but cannot figure out why. The last two cooling seasons I have had problems with the unit no keeping up. Also I am seeing a small amount of water loss in my loop. I have to re-charge it about once to twice a season. Anyone have any ideas, here is some data:
Equipment:
4 ton Addison unit
Water furnace flow center with 2 Grundfol circulators
6 – 60’ deep wells (720’ of loop, plus manifold run for a total loop length of 800 feet)
Water temp from loop: 108.0 degrees f
Water temp from unit to loop: 116.0 degrees f
Air temperature change delta T: 12 degrees (inlet verses outlet)
Circulator pump temperatures:
From loop: 95 degrees f
To loop: 165 degrees f
Could air in the loop or an un-purged circulator be causing the extreme heat in the circulator? Could the circulator itself be adding heat to the loop and causing the loop to not be able to offload the heat into the ground? My A/C contractor states that the pump temperature is not uncommon, hence I have not replaced it. |
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joe.ami
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| 07/01/2009 9:12 AM |
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Wow where to start.
Loop size would be smallish in my area, which I suspect would make it small in yours as well (generally would expect at least 150'/ton of utube or 1200'/pipe).
Loops shouldn't have to be refilled.
Might have a bad capacitor on the one pump.
What does your installer have to say about all this?
Good luck,
Joe |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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jebs
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Posts:7
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| 07/01/2009 9:28 AM |
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Joe,
Thanks for the reply.
My loop is actually longer than originally specified. The standard for loops in my area when installed (vertical wells) was 100 ft per ton. I am in North Florida. My loop consists of vertical wells packed with grout to aid in heat transfer. Each well is 60 foot deep. the system worked well for the first 8 years or so of operation. Just in the last few years have we begun to have problems. The installer has been out wice in the past month. First time the tech claimed dirty filters were the problem (I was not home so he was dealing with my wife, the tech was not familiar with Geothermal units). The second time they sent the actual installer of the system out. They spent 3 hours on-site and decided that the water recovery unit was plumbed wrong and that the loop was trying to cool my water down. nevermind that my water heater had been turned off for days. But with the recovery unit turned off, it made things worse, not better. Which is what you would expect. So I have little confidence in their troubleshooting an unusual problem. Heat rejection to the loop seems adequate. The Air temperature change seems about right given the high loop temperature. I have the option of switching to an open loop as I have a water well and a pont to discard into. I believe I will disconnect the ground loop and go open loop for a couple of weeks while my ground loop cools down. Since it seems that my loop is overwhelmed, maybe this will solve the issue.
jeb
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jebs
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| 07/01/2009 9:32 AM |
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| I forgot to add. The A/C contractor installed a new reversing valve at the end of the last cooling season. When they were on-site last, they said everything looked to be working within specs with the heat recovery unit turned off, but went crazy when it was turned on. Thus they blamed the recovery plumbing, and not the unit itself. I wonder if maybe when they replaced the reversing valve, they hooked something up wrong on the de-superheater |
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jebs
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Posts:7
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| 07/01/2009 9:51 AM |
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Joe,
You may be right about inadequate loop length. When the system was first put in, the loop was to short. One of the original well lops turned out to be plugged and the installer had to come back out and re-drill some additional wells. Thinking back to that disaster, it took several weeks on startup to determine the issues. My air handler was moving to much air which also contributed to the overload. Anyway, they came back added three more wells So I actually have 8 operational wells now instead of the 6. My total “pipe” length should be about 1050 feet, including the 100 or so feet the wells are from my house. Since this problem is somewhat new, the original length was probably adequate for the job. But since the wells are hooked up parallel, not in series, I wonder if one or two of the wells are plugged. This would certainly cause the overloaded ground loop.
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jonr
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Posts:330
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| 07/01/2009 10:15 AM |
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Can you get access to your manifold to check in/out temps of each loop? That will tell you which ones are working.
Do you keep static pressure on your loops?
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jebs
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Posts:7
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| 07/01/2009 10:28 AM |
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| Unfortunately, the manifold for my loop is burined in my backyard. I may have to bite the bullet and dig it up anyway to check the temps on each loop. I do not have any static pressure numbers on my loops, no devices installed to get them. |
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jebs
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Posts:7
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| 07/01/2009 10:30 AM |
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| Must spell check.....burined should have been buried |
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Bergy
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Posts:114
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| 07/01/2009 11:05 AM |
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Some important information needed...
We need to know the loop pressure "in" and the loop pressure "out". Your manuals should have a pressure drop table in them. The pressure differential (delta P) and entering water temp will show how many GPM are flowing through your unit. ANY service tech, worth a dime, knows you do not put refrigerant gauges on the system UNLESS the water side analysis shows a problem.
If you have to "juice" your loop several times a year you have a problem that needs to be addressed. You may have air in the loops and should have them power purged.
It sounds as if pump #2 has a bad capacitor or the impeller is seized. 165* is NOT the normal running temp for the circulator.
Bergy
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jebs
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| 07/01/2009 11:25 AM |
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Bergy,
Thanks for the reply. I will have to check the pressure. I think the loop pressure "out" line from the unit to the flow center is about 35 psi, but will need to check both and verify. I will see about getting a new cap for that pump and replace it I agree that having to "juice" the loop is an obvious problem. but since the "leak" is so small it has not been a huge issue (or maybe it is). The system probably could stand to be purged, but the temperature gain into the loop makes it appear that the the loop is circulating okay (no noise from the circulators indicating air is present). But it would seem that a little air in parallel loops could cause flow problems. |
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joe.ami
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| 07/01/2009 3:22 PM |
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What were the credentials of the original installer? Did you check references?
Find a local drilling expert on the International Ground Source Heat Pump Association (IGSHPA) web-site and verify well depth. Generally when we speak of verticals, we would say 150'/ton meaning 300' of pipe.
I still suspect you are short looped. Further the leak and constant addition of make-up water could have loops locked out as well (BTW paralell would be the common install style).
DO NOT dig up your back-yard yet until absence of air and proper loop size is verified.
It is not lost on me that your system worked for the first many years, but wether it worked efficiently is a different question.
You may have been marginal to begin with and well undersized now.
You should probably get a different pro on site.
j |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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jonr
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| 07/01/2009 4:28 PM |
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> But it would seem that a little air in parallel loops could cause flow problems.
Correct, it can disable some of the loops.
If you don't keep static pressure in the loop you can get cavitation in the pump and leaks can let air in.
From CM:
perform final flush and pressurize the loop to a static
pressure of 50-75 psi -517 kPa] (winter) or 35-40 psi
-276 kPa] (summer). After pressurization, be sure to
loosen the plug at the end of the Grundfos loop pump
motor(s) to allow trapped air to be discharged and to insure
the motor housing has been flooded.
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engineer
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| 07/01/2009 5:56 PM |
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I agree that loop length seems small. We do a 250' well for each ton here in Jax FL area owing to high ground temps and long cooling season.
The 8 degree delta T across water side implies decent flow, but having inlet water at 108 F is a problem. It is almost certainly reducing the capacity of your unit and causing it to consume excessive power and operate at very high pressures. That's hard on the compressor and other components.
If it once worked much better (lower EWT, higher airside delta T) then I suspect one or more loops may be airlocked out - that is not seeing any flow, concentrating all the heat in the remaining flowing loops.
The 165 deg pump is a problem as well - I'm not sure it is related.
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Without data, you only have an opinion. |
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a0128958
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Posts:451
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| 07/01/2009 10:01 PM |
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Posted By engineer on 07/01/2009 5:56 PM
I agree that loop length seems small. We do a 250' well for each ton here in Jax FL area owing to high ground temps and long cooling season. ...
And here is Dallas it's generally 300' wells per ton.
Best regards,
Bill
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Real time energy monitoring system at:
http://welserver.com/WEL0043/ |
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