Ground Source beats several Pros: Water remedy needed
I'm writing to find out if there is a valve available to reverse the direction of water (not refrigerant) flow in a ground-source heat pump. I am the son of the owner, an elderly lady whose late husband thought a ground-source heat pump to be wise. This is a bit involved, I regret the length of this post.
History: The unit in question is an old Climate Master 30,000 BTU which has had off and on trouble for years with cooling mode OK, in heating mode the low-pressure protect switch trips after the compressor has run for 10 to 30 seconds. In my absence, several AC techs have attempted to eliminate the fault, none succeeded. In one case I knew no good end would come when the tech disappeared then returned and asked, "Where's the outside unit?". At least once it was given the usual treatment, clean the evaporator, add some gas and collect $$$ to $$$. I don't think any measured the superheat and subcooling.
I was going to do just this today when the root cause finally dawned on me: The water is supplied by a well and controlled by a solenoid valve. It always flows through the coaxial heat exchanger in the same direction. The refrigerant reverses direction when changing from cool to heat. So the water flow is correct for cooling, the coolest incoming water in contact with liquid refrigerant exiting the coil. However, in heat mode the wrong way flow puts water already cold from supplying the latent heat of evaporation in contact with the cold gas exiting, which depresses the suction pressure.
I momentarily corrected the problem by greatly increasing the water flow but there seems to no part that I can find online, essentially a valve which will do for water what the valve inside the heat pump does for the refrigerant. That kind of valve is not suited for water, also the pressure differential would be inadequate to move the piston.
If anyone knows of an elegant solution to this problem, please share. I'm sure this problem is not unique and there's a better answer than four PVC ball valves.
Thank your for your attention,
Last edited by jpsmith1cm; 11-24-2012 at 09:02 AM.
water only flows one way on geo thermal heat pumps you need a tech that is familiar with your type of unit
I agree with the above. Research a competant tech/company that is familiar with geothermal add-nauseam. A correctly skilled tech will save you thousands in time, energy and comfort.
As above, water flow isn't reversed in a geo from one mode to the next. You have a problem, but changing water flow direction from one mode to the next isn't the answer.
I thank the three who responded to my post. You hit the nail on the head: the problem would have been resolved long ago had we a technician qualified on this design. Perhaps if I contact Climate Master they would give the name of the nearest authorized servicer. The elderly lady who owns it has had no luck asking for someone who understands heat pumps, not understanding or explaining the water-source or water-to-air aspect of it.
The other jaw of the vise is that I suspect most HVAC techs have no need learn how a coaxial heat exchanger works, as they rarely see them and when they do usually some familiar trouble in another component is present. In a heat-exchanger with perpendicular flow of one fluid to the other, which is what a regular outside condenser is, the direction of the flow is unimportant to close temperature approach of one fluid. This is also true in a coaxial unit if the water flow rate is so high that there is little temperature gradient, which is what I did by defeating the flow-regulator valve, allowing several times the 1.75 GPM normal rate.
Anyway, thanks for the use of the hall, I'll take up no more of your time. Shame on me for trying to get an engineering answer without paying an engineer.
Water flows in one direction for a geo thermal heat pump. Period. You have another issue. Please post more information. Model and serial number, Water temp, water pressure? You say you have a well pump, so I assume this is an open loop (pump and dump)?
Climate master had an issue with TXV's a few years back. Model and serial will tell me if your unit is included in the bad batch. A bad expansion valve could easily be causing the issue at hand.
if the unit is a pump and dump the coax is could be scaled up as the need descaled and flushed out every few years depending on the water hardness
Sorry no one wants to support your engineering solution, but.... The fact is you are barking up the wrong tree. Hooking up the circulator pumps with the flow going in the WRONG direction is prolly one of the most common install errors that are made. Of all the ones I have seen hooked up backwards, it made little if any differance on the performance of the unit. We switch them around if we are there with the equipment, if not we do not. The issue is allways something else, not flow direction. WSHP are simple things that do not need to be over thunk.
A broader view of this
Thank you very much to all who offered an opinion on this.
I likely should have said that the reason for going to all this trouble for a machine nearly 40 years old is that there is no desire to buy a new system now when two elderly persons in the home have been hospitalized and there is little excess cash.
One member actually pointed to a possible cause, scale in the waterside of the coax condenser. This is a distinct possibility. I tend to set aside, but not eliminate, this possiblility as I cleaned the coax with a descaling agent from Nalco two years ago and the flow is unrestricted and cleaning made little difference. Also scale would cause high head pressure in cool.
I think I can point to what it isn't. The air coil is clean and has good flow over the entire surface. The blower motor died a while back and I took out the wheel and scrubbed every blade, got all of 35 years dirt out of the wheel and housing before reassembling. (Complaint about "It's too loud now!") I think we can say for sure it isn't undercharged, several techs have added gas, if anything it maybe overcharged now. The symptoms aren't those of a compressor fault. It isn't a TXV, it's a capillary system. Hard to say if having a guage set connected 8 to 10 times over the years got enough air, dirt and water in to cause trouble.
Anyway, my thoughts about the heat exchanger were based on some experience I had with steam plants, thanks to the Navy. Here the water plumbing has some problems, sometimes water hammer when the system shuts down, so next weekend I am going to temporarily replumb it with opposite flow. If I then have good heat and poor cool, that would confirm my expectation that this water coil behaves somewhat like a steam condenser cooled by seawater.
Thanks again, may you have many quick and easy calls today.
Originally Posted by waterpirate
AC4AQ, I too have had experience with Navy steam plants. Mine was gained while in the Navy Nuclear Propulsion program. That was years ago, 1979-1985, just prior to my entering the HVAC field, where I have spent 27 years in the commercial side of it. I lurk here in this forum, and residential forums, just out of curiosity, and the chance to learn. That knowledge and experience gained in the Navy has helped me over the years, but I would never use it over what I have learned in this field. Just as getting one small part of a heat transfer equation will definately give a wrong answer, assuming that different applications will respond similarily can be misleading. Especially when there may be unknown, therefore unaccounted for, differences. You are fortunate to have some of the more knowledgeable and experienced professionals here, who volunteer their services, helping you. You would do very well to heed their advice. I believe especially about calling someone who is experienced with your system.
Originally Posted by AC4AQ
I suspect that is the answer right from the start has been to find someone with the proper qualification on this equipment. So far, we've yet to find her/him.
Since I last wrote, I found a valve which will accomplish the task of reversing the direction of the water flow in the coaxial heat exchanger and it did provide some meager but noticeable results. Not good enough to correct the problem though.
In cooling mode, reversing the water flow (discharge at capillary end) caused the head pressure to rise from about 190 psig to about 215, and a slight rise in the suction. In heating mode, with correct flow (discharge at caillary end) when the compressor starts the suction pressure steadily sinks for about 25 seconds until the low-pressure switch trips. After the unit restarts, the suction pressure again drops, but may stabilize at aroung 40 psig, then it gradually rises. When the system reaches stability, the suction pressure is around 62 psig, with a head pressure of around 205. With reversed water flow (as it was originally), the suction pressure sinks more rapidly and stabilizes at 55 psig. No temp reading yet on suction line to compressor, but not very cold. Also gas hisses loudly in heat mode only, not sure which line is noisy.
I hope I hit upon the means to find the right tech for the job, as the diagnosis seems to be difficulty. I'm hoping I can find a tech I can communicate with in advance, who will analyze the data and be able to say, "the reversing valve is sticking in heat mode" or some such thing and come with the wherewithal to do the job right the first time.
Thanks to those who have shared their knowledge. If you ever need advice on high-powered audio amplifiers from QSC, Crown Audio, etc, I'll be glad to reciprocate.
Originally Posted by Nuclrchiller
please check your e-mail.
I'm a former Navy snipe (conventional 1200 psi steam propulsion), I still work around steam boilers and centrifugal chillers on a daily basis, yet I still would consult with a sharp geothermal tech before diving into the thing myself, thinking my snipe days should carry me through. Just as I would expect the geothermal tech to ask me questions about a Carrier 19XR chiller, since I'm around that machine all the time (even then I defer the heavy matters to a tech who is also a former snipe, knows 19XRs like the back of his hand, and very trustworthy).
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.