Yet another problem with my Hydro-Temp unit

I have now had a third compressor malfunction on my Hydro-Temp unit since we moved into our house July 1, 2011. Anyone who would like can reference my 2 previous posts from 8-31-11 and 11-14-11. In summary, we have a 6-ton Hydro-Temp unit that was installed shortly before we moved into a new construction home near Milwaukee on 7-1-11. We had two compressors fail on the first unit within the first 2 months. Our installer then replaced the unit in November. It did function this winter although I thought my heating bills were high. It made it through the summer and then just failed 3 days ago. It has been the 2-ton compressor that has failed all 3 times. This is a dual compressor unit with a 4-ton and 2-ton compressor. I haven't included any design details because I'm pessimistic about someone solving this problem via the forum, but let me know if you really want a crack at it. Clearly something is wrong. Does anyone have any suggestions about how to proceed? Know any experts near Milwaukee that can solve the problem? My installer is Interstate Heating and Cooling and they want to replace the compressor again -- brilliant!

 

Sorry to hear of another problem with your heatpump.

Having one that is the same brand myself, I know a bit about how they work.

All of the failures have been during cooling. These units during cooling will run the pump for DHW instead of the ground loop pump, until the DHW sensor is satisfied. Water flow between the DHW tank and heatpump needs to be of similar GPM as the ground loop. Of course this means we run 115* to 120* water through the heatpump to make cool air for a/c.

I would look first at the water flow for DHW re-heating, above mentioned function can be turned off, so ground loop operates all the time.

ChrisJ

 

Thanks, Chris, for the reply. Unlike you, I know very little about how they work, but what you say makes a lot of sense. In fact, of the three times this has happened now, our installer will turn off the DHW and the unit will run fine with just the 4-ton compressor alone. Obviously, this is less efficient for cooling and we have to use our backup electric water heater. Are you talking about the "Priority" switch for DHW toward the base of the unit or is the water flow for DHW re-heating a function that can be disabled with the installer's palm pilot application?

I did finally hear through my builder that the installer will be going back to the engineers at the distributor where the system was designed and request that they make a field visit and that they intend to find a solution. So, in fairness, it does look like they will try to do the right thing and solve this problem. I'm sure everyone is on the edge of their seats, so I'll let you all know what the final solution is to my puzzle.

Since you dared to take a crack at my problem, Chris, I'll reward you with some design data and I can probably muster up some entering and leaving air and water data if you are interested.

Loop field is composed of 8 vertical closed loops of 0.75 inch diameter PE pipe at 180 feet each for a bore length of 1440 feet.
Water heater is 120 gallons at 130*.
Heating Load: 109,363 Btu/Hr
Cooling Load: 75,488 Btu/Hr
Sensible Cooling: 72,664 Btu/Hr
Avg Internal Gains: 10,740 Btu/Hr
Annual Heating: 235.6 Million Btu
Annual Cooling: 33.9 Million Btu
Annual Water Heating: 21.5 Million Btu

I'm not sure what data is pertinent, so I just copied a bunch of it verbatim from my geodesigner system analysis. Any other opinions or help is greatly appreciated and thanks again to Chris.

 

That function is disabled by the palm pilot, I believe it's called the desuperheating mode.

120 gal at 130*F, from what I have learned 130* is a huge strain on the unit. 120 gal is quite large as well. I have a 55 gal tank set to 120*F.

It's always good to know what the EWT (entering water temp) and LWT (leaving water temp) is, to get an idea how the groung loop is performing.

Like I mentioned in your other thread, my installer called Hydro-temp directly when he was here and had a question.

Hopefully they can find an answer soon.

Chris

 

Entering and leaving temperatures

EWT = 56*
LWT = 67*
EAT = 70*
LAT = 52*

 

Yikes. That is a lot of really hot water.
130* is definately a lot of work on the compressors.
It will be interesting to hear what the experts have to say.
Every major manufacturer has long since dumped the 2 compressor design after many failures.
Good Luck.

 

Seeing 56*F EWT tells me that the unit hardly ever runs with the ground loop circulating. That means the heatpump is cooling while using 125*-130* fluid, just like having a very overheated ground loop. That has to be very hard on the compressor/compressors.

Do you need 120gal of DHW?

I have not run my system with the desuperheater funtion off. I would have to read the manual and see if it says what happens. Probably would have to stop cooling, reversing valve would switch and water heating would continue until aqaustat is satisfied.

I went to Hydro-Temps website recently, they are putting variable speed Bristol compressors in new models.

Chris

 

A lot of hot water?

I just take what they give me. I am not a compulsive bather with a fear of germs, but apparently my installer thought I should have a 120 gallon tank for a family of 5. My Geodesigner System Analysis used 130* as the hot water setpoint and also assumed 70 gallons for daily hot water use. I'm not sure why there is such discrepancy in the size of the hot water tanks between the design and the final installation -- maybe that is the problem. I did decrease the setpoint to 120* after installation, but my wife complained so I had to turn it back up.

Can you explain this system to me, Chris? Why does the desuperheater function use the DHW flow loop for cooling? So the air in my home transfers heat to the compressor/refrigerant loop which then transfers the heat to the DHW loop instead of transferring heat to the ground loop. Is that right? What does this have to do with the EWT?

 

Let me start by saying I am not a pro on this forum, I am a homeowner with a 4-ton Hydro-Temp system, I don't know very much about refrigeration. I know what I know from following the posts on this and other forums.

Our heatpumps are what is refered to as Hybrid units, can heat air and water. Other manufacturers' hybrid units can not heat (or cool) air at the same time as water, they work on priority or shared priority(so many minutes then switch). Hydro-temp has a patent for their units to do at the same time.

Now this is where my knowlege gets a little light, the refrigeration area. When the compressor is running it is making heat and cold.

"What does this have to do with the EWT?" With a traditional water to air heatpump the ground loop is slowly warmed up through out the summer during cooling, 70*,80* or even 90* EWT. Yours being 56* means what you said, "So the air in my home transfers heat to the compressor/refrigerant loop which then transfers the heat to the DHW loop instead of transferring heat to the ground loop", is basicly right.

When the a/c shuts off, meaning the thermostat is satisfied, but your hotwater tank is less then 130*, the ground loop pump turns on, reversing valve switches and heat is taken from the ground loop, keeping your EWT lower.

I don't know if all that helps. Chris

 

Can they state with a fair degree of certainty that the compressor has in fact failed?

I have heard that more than half of reportedly dead compressors are in fact not operational owing to external wiring or control errors. Properly wired, they spring, phoenix-like from supposed ashes.

What is the failure mode(s)? Possibilities include internal short or open winding, mechanical seizure, or breech of hermetic case. Has it been the same each time?

Compressors rarely die of natural causes, most are murdered by a gross fault in their operating situation - such as a high voltage electrical fault, loss of refrigerant charge, or liquid refrigerant inhalation.

Replacing the compressor without determining and fixing the operating issue is a nearly surefire way to become a serial compressor killer.

It is possible that the high discharge temperatures pressures and associated high currents needed to produce 130* domestic hot water is killing these compressors, but heat pump water heaters are able to perform that task with ease.

If while producing hot water compressor current is above nameplate rating, that would be clue of a design flaw or operational problem. Any tech able to fog a mirror ought to be able to make that measurement and determine cause of death.

 

Compressor

Thanks for the replies so far. The new compressor will be installed this Wednesday and I am told that an engineer from the supplier that designed our system will come along to troubleshoot once the compressor is installed. I'll try to get some more information about why the compressors are failing.

I'll ask about: 1. compressor current during DHW heating, 2. the size of the DHW tank, 3. the DHW temperature of 130*, and 4. the cause of previous compressor failures. Did I get this right and/or does anyone have more suggestions?

 

Are you paying to fix this thing or is this all under warranty? Lord I hope not. 3 compressors in a year!
With a tax credit available I'd have to think about something different.
No one wants to bring up the elephant in the room (replacement) but what is your serious long term expectation for this pc of $#!.....oops I mean equipment? Maybe your installer is tired enough of fixing it he'll put in a different brand at cost (minus tax credits you could get one literally below cost!).

 

Joe, this 3rd compressor is on ilikegeo's second complete unit!

When I had a problem with my unit, just a sensor, my installer called the manufacturer directly. Maybe have the distributer get the manufacturer involved.

Chris

 

maybe get the manufacturer involved. maybe get a new manufacturer or repairman. this is outrageous.

 

Just thought the manufacturer's engineer could help troubleshoot, distributor may not be as familiar with these pc's of $#!... they are a bit of a different animal.

Three yrs ago when we were building our house I admit I didn't do enough research. Wanted to do radiant and air, Hydro-temp units did both and 100% DHW, seemed like the perfect unit. If I knew then what I know now, I would have gone a different route.

Chris

 

I am now cautiously optimistic after installation of the new compressor followed by the troubleshooting performed by both the technician from the installer and the engineer from the distributor. The whole process took about 8 hours so I can't say they didn't spend enough time on the issue. They found one thing that could explain the problem: there was a large amount of sediment (presumably iron) coating a filter screen in the DHW waterline (DHW out) going from the Hydro-Temp unit to the DHW tank. They discovered this because there was a significant pressure gradient across this line (about 10 times expected). Upon further inspection, the screen was found to clogged with iron sediment. The engineer believes this may have been there since the installation of the first unit.

Reasons why this makes sense:
1. Increased pressures caused by an obstruction to flow in the DHW out line (from the unit) would make the compressors work harder to supply DHW -- is that right?
2. When the other compressors have failed, I have always been able to operate the unit with a single compressor for heating or A/C only. In all of these instances I have used the backup electric water heater instead of the Hydro-Temp unit to produce DHW.
3. Slow build-up of iron or some other sediment would explain why this unit seemed to operate without any problems from November until August before blowing another compressor.

Reasons why this does not make sense:
1. It would be difficult to explain all 3 compressor failures with this one problem. If this screen was the problem all along, then the second unit should have failed soon after installation in November. I don't recall that they flushed this line of debris, but maybe they did as part of the installation of the second Hydro-Temp unit.
2. I suppose there could be two separate explanations (e.g. bad unit first, dirty screen second), but that seems too coincidental. Does lightning strike the same place twice? Rarely.
3. Any others? Or I guess time will tell….

I had my well water tested prior to move-in, but the testing did not reveal a need for an iron filter. Having said that, we've already had iron stains on the side of our house from a leaking hose bib and I've noticed some small iron rings on the toilets. I think I'll have my water retested and strongly consider an iron filter to prevent any more clogged filter screens.

I did ask about the 3 compressors that were already killed-off. The engineer stated that there is no way to tell from the dead compressors what caused them to fail. He also did not think that the size or temperature of the DHW tank had anything to do with the failures and they apparently did test the electrical current the compressor was drawing during DHW heating.

 

"If this screen was the problem all along, then the second unit should have failed soon after installation in November."

During heating season the ground loop is circulating while making DHW, radiant water and warm air, it's not until cooling season when the ground loop shuts off and the DHW loop is acting as the ground loop, it was probably the lack of water flow in the DHW loop that killed the compressors. I would think there should be some kind of low flow shut down sensor.

Chris

 

Chris, it looks like the way my system is configured, that there must be a flow loop between the Hydro-Temp unit and the DHW tank even during heating season. I don't know how to attach photos here, but I'll send you some if you don't mind. And, btw, I didn't forget about your request for some pictures of my radiant heat configuration. I know that was a long time ago, but I'll send them to you now. Better late than never.

 

Yes there is flow between Unit and DHW tank in heating, but the ground loop is also circulating, taking heat out of the groung to make hot water. 2 pumps running, one is probably a bronze pump(DHW), like one in picture, the other is a black one(ground loop), mine is under the auto-purge tank.

Somehow Hydro-temp units can make cool air and hot water at the same time, while shutting down the ground loop. I think other hybrid units have to stop and change modes.

Chris

 

I hope this takes care of your troubles.