Installed WNDV049 Envision 4 ton the fall of 2008 with 2x700'x3/4" loops run to 1/4 acre pond 12' deep.  Loop total footage in pond is 1000' with 400' ground run to house at 7'.   We are are very satisfied with unit and have seen 50% saving on heat side verse propane.

Three weeks ago unit shut down with water flow fault.  After cycling unit it will run 3 or 4 days and fault again.  I checked temps with thermal imaging camera at the unit (temp probably not correct but spread should be close) ewt 31F and lwt 23F.   With 17% prop glycol solution it is border line.  I drilled hole in pond ice over field area and using under water thermometer I got a temp reading of 35%.  That is a 4 degree drop from the 39 degree temp that is normal for this area.   I don't know if that would be normal or not.  I think that the ponds volume could be border line also.  

I have the oppertunity to get the use of vertical drill with grouter for cost of fuel and material and considering 2x150'x3/4" tubed loops tied in with pond loops.  Would appreciate any and all input.   Thanks  

Makes sense, although you might want to compare the price to adding more horizontal loops or using your proposed vertical holes for open loop.

Why are you wanting to do that? Is your motivation to eliminate the faults or reduce your utility bills or what?

chas_1a - check your flow rate and pressures..
We have no hands on experience with GSHP, but from what we have learned your Delta sounds too high - pump working too hard - maybe one of your loops is plugged or impeller problems. What is the discharge pressure of your pump? [[about 20psi difference between suction and discharge for your head loss on your tubinge] I don't know the flow rate for your model, but most seem to need to be around 12 gal/min [3-4 gal/ton/min]. Hopefully you figure it out easily - since it has already run one winter without a problem, let us hope it is an easy fix. It will be interesting to hear what others with ACTUAL experience have to say :-)

31 EWT isn't out of bounds. I wonder if the system is set for no antifreeze, cutting out at 30F or so. With antifreeze, the cutout might be lowered to 15 F. I don't have in front of me a chart to determine what freeze protection is afforded by 17% PG. If the system is set to cut out at 15 F, I think I'd want freeze protection down to 5F or so, but I'll leave that to the northern pros.

I think the 8 deg waterside delta-T is about right as well.

Engineer,

Glad to see you respond - have gained alot of respect for your brain power after reading these forums.

Glad to know that the Delta T of 8 is fine - most of the responses we have seen listed on this forum are 3-5* range - the pdf files on the units led us to believe that the COP has a "sweet point" that has the gpm / water temp per ton. So that you aren't spending more on pumping than the unit can handle well or too little and making it run all the time. Is this wrong?

Wasn't trying to say the water temp was too cold. Just a reason why the it was kicking in on "flow problem"

We live in central NV - and plan to do a horizontal system - in the ground. We can't do a water based one - not enough water. Our well water is 165' down -expensive to pump! But did find the problem intriguing - Have so enjoyed reading the forums and learning all we can. We haven't studied that much on the types and % of anti-freeze yet, but i know we will have to allow for fairly cold water temps.

nevadarn

Based on your current loop design, sounds like you are manifoled in the house. Typical pond loops are installed in pond, headered, and ran back to house, for a 4-ton, probably 2 1.25" headers. Your sysetm as stated above should have a 12gpm flow. Best way to get 12gpm flow is thru 4-3/4" loops. This keeps turbulance numbers up and lowers pumping power as shown above. Not sure of the landscape between the home and the pond, and if the pond is big enough, but I'd recommend more loop in the pond if the pond is large enough to accomodate.

The other angle is to drill. We have tied vertical bore holes with a less than sufficent horizontal/pit system before. Your main concern here is how to balance flow thru differing length loops. If you drill, you will have (2) 1000' pipe runs, and (2) 300'+/- ft loop runs tied to the heat pump. If you can balance the flow thru each so that each loop sees 3gpm, you'll accomplish what you are trying to do. The problem will be that the vertical loops will flow too much water and the pond will have less flow due to pipe length. This can be corrected for with balancing valves in the house, I'm assuming this is the current location for headers, but is an expensive and complicated way to go.

Give us more detail on current install and operating perameters, EWT, LWT, PD across heat pump, pump pack currently being used, and there may be a better solution. Also, size of pond and depth is critical for deciding whether to drill or put more pipe in the pond.
Dan

Posted By engineer on 03 Mar 2010 09:32 PM
  With antifreeze, the cutout might be lowered to 15 F. I don't have in front of me a chart to determine what freeze protection is afforded by 17% PG. If the system is set to cut out at 15 F, I think I'd want freeze protection down to 5F or so, but I'll leave that to the northern pros.

I haven't seen anything definitive on needed freeze protection level.  If anyone has more information on this, please share it with us.

I can say that our closed horizontal loop is protected to 15f with antifreeze and we have the DIP switch set for 15f as well.  This (extremely cold) heating season, our lowest EWT was 37 and LWT was 32.  We don't need to go lower than 15f antifreeze protection based on actual loop temperatures.  With a new install, there is no such data.

How is freeze protection level calculated for a new install?  Are there any guidelines to follow?  If not, I assume it would depend on anticipated loop temperatures in extreme conditions (not 20 year averages) plus a safety margin?

When balancing multiple loops of any kind, just adjust the valves so that the return temperatures (not flows) are equal.

Why in the world would we add loops before making sure no other problems exist? We know it worked ok with existing loops last year.
What is the loop pressure?
Joe

Installed WNDV049 Envision 4 ton the fall of 2008 with 2x700'x3/4" loops run to 1/4 acre pond 12' deep.  Loop total footage in pond is 1000' with 400' ground run to house at 7'.


Those numbers don't add add up can you elaborate on length and size of pipe.
17% glycol is around 22F freeze protection, but that's a long pipe run.
I would get accurate temp readings in/out along with pressure drops.

I will try to clarify the loop length first:  I have 2 x 700' loops, 500' feet of each is in pond and 200' of each is in a 100' trench from pond to house.  Giving a total of 1000' in pond and 400' in the 100' trench.  The loops are 3/4" and are tied into a header 10' outside basement wall and the header is 1.25" and extends into the basement for 20' giving me a total of 60' of 1.25" for header system.

The unit came with 1 P/T port and 1 PSI/Temp gauge.    The gauge only goes down to 30 degrees and the needle  on the psi side is so wide, it covers at least 10 degrees.   I took the temp measurements with a thermal imaging camera and think that the actual temp would be colder.??   The gauge is showing 55psi on loop system as near as I can tell and goes down to 20-25 in warmer weather.   The Ewt was 31 deg and Lwt 23 deg.  I currently can't give you the pressure drop with set-up I now have.    I will install another P/T in spring and get a probe gauge. 

The flow center has 2 BGM-236 pumps.

With out the actual facts I realize everything is spectulation and I don't want to waste your time  I just think that I undersized my fields.  The unit had been doing a good job but with the electrical EM element coming on between 15 and 20 degrees and the ice I see on the brass 90 deg fittings at the unit makes me think that I undersized.

I guess my major concern was the about adding 2 verticals and not tearing up my front yard by putting another loop in a pond that might not have capacity to handle it. 

I thank all of you for your input  and time.

If 22 F freeze protection and 23 LWT are both true, it could be that a bit of slush is forming, drastically reducing flow and inducing the cut out.

IR thermometers really aren't accurate enough for loop lines. There are issues of focus spot size and emissivity to contend with.

I reiterate that 31 EWT is not in and of itself bad so long as the design contemplated such temperatures, and add that a bit of icing, especially on the leaving loop line is to be expected. Low 30s EWT results in LWT in 20s, and surfaces at temps in the 20s in warmer surroundings will ice up a bit. That's an inescapable function of thermodynamics and psychrometrics.

Agreed, you should add more glycol. It was only Feb and future LWTs could be even colder.

At the right price, more loop makes sense from an efficiency standpoint alone.

"Why in the world would we add loops before making sure no other problems exist? We know it worked ok with existing loops last year.
What is the loop pressure?
Joe"

DID THIS SYSTEM WORK WITHOUT LOCK-OUTS OR NOT THE FIRST YEAR?!!!!!! (2nd time I ask) It seems you indicated it did.
If that is so then I ask again, why add loops until we determine what is wrong?
Adding loops may have an efficiency benefit and mask or solve current symptoms for awhile, but you still outta fix the problem.
j

Posted By joe.ami on 05 Mar 2010 08:57 AM
"Why in the world would we add loops before making sure no other problems exist? We know it worked ok with existing loops last year.
What is the loop pressure?
Joe"

DID THIS SYSTEM WORK WITHOUT LOCK-OUTS OR NOT THE FIRST YEAR?!!!!!! (2nd time I ask) It seems you indicated it did.
If that is so then I ask again, why add loops until we determine what is wrong?
Adding loops may have an efficiency benefit and mask or solve current symptoms for awhile, but you still outta fix the problem.
j

I have not had any problems with system until the first flow fault 3 weeks ago.   I understand that I could have problem unrelated to loop size.  I have an opportunity to add vertical fields at material and fuel cost only.  I need to shut system down to install reliable measuring system and my thinking was to add the fields at the same time.   Spring is just around the corner and I wanted to wait for warmer weather before shutting unit down.  Thanks again for your time and input.

Posted By engineer on 04 Mar 2010 10:49 PM
If 22 F freeze protection and 23 LWT are both true, it could be that a bit of slush is forming, drastically reducing flow and inducing the cut out.

IR thermometers really aren't accurate enough for loop lines. There are issues of focus spot size and emissivity to contend with.

I reiterate that 31 EWT is not in and of itself bad so long as the design contemplated such temperatures, and add that a bit of icing, especially on the leaving loop line is to be expected. Low 30s EWT results in LWT in 20s, and surfaces at temps in the 20s in warmer surroundings will ice up a bit. That's an inescapable function of thermodynamics and psychrometrics.

I understand the emissivity issue with IR measurement and agree that there is high probability of slush.  I really don't want to shut unit down in cold weather but it would probably be best to do so and get my protection down to 15deg at least.   Thank you.

I have 2 x 700' loops, 500' feet of each is in pond and 200' of each is in a 100' trench from pond to house.  Giving a total of 1000' in pond and 400' in the 100' trench.  The loops are 3/4" and are tied into a header 10' outside basement wall and the header is 1.25" and extends into the basement for 20' giving me a total of 60' of 1.25" for header system.


I'm showing around 80ft/hd @ recommend 12GPM with glycol for that loop.
If you do add to the loop you will have to do some serious re-piping to get proper flow, or you will be wasting you time if not your money. 

just my 2 cents

Posted By geotek on 05 Mar 2010 02:14 PM
I'm showing around 80ft/hd @ recommend 12GPM with glycol for that loop.
If you do add to the loop you will have to do some serious re-piping to get
proper flow, you will be wasting you time if not your money. 

Yep, I concur. P-glycol, low temperatures, and long runs of 3/4" pipe
could be part of the problem. Adding more p-glycol will reduce your
GPM and LWT even further.

Have you considered switching to methanol antifreeze? It has much
less pressure drop for any given level of freeze protection, (e.g., 20%
methanol gives the same 15F protection as 30% p-glycol). Methanol
also has better heat transfer (due to higher Reynolds# and increased
turbulence).

Your system has a total volume of about 50 US gal. -- so, switching
antifreeze types should not be terribly expensive.

That said, I strongly agree with joe.ami's advice to thoroughly diagnose
the problem before attempting to "fix" it.

Looby

So you are thinking about adding loops just cause you can?
I guess if you want to.....
Measure the LWTemp before you decide there is slush there.
Your proposed methods of attacking the problem may simply muddy the water.
Loop pressure wasssss....?