New York Geothermal Open loop System Lockout

Perfect Storm
I have a 5 ton Climate Master W2W open loop system. I get a lockout about once a season. It is a Code 4 (Water Coil Low Temperature Cut-Out Limit) Not a source side flow issue (15GPM @ 48 degrees). It's not a dirty coil.
I know what is causing it but I am not sure how to remedy it. It is the load EWT goes down to around 55 -60 degrees and the Source EWT is around 48. Based on the performance chart from Climate master the Load EWT is out of performance design. The load low temperature happens when the last heat call from 5 of 6 zones depletes most of the buffer tank hot water and it is satisfied before the heat pump can turn back on. Leaving the buffer tank return in the 70's. Then the basement slab zone comes on and dumps 50 degree water into the buffer tank. I have reduced the basement slab manifold water flow to about .2 gpm per loop which equals about 1 GPM for the 5 loops. The FP1 temp bulb plummets to around 27 degrees. (I verified this with another temp gauge) If it could run for another 3 minutes it would probably rise back up again. I thought about maybe mixing. I thought about keeping the buffer tank up to temp all the time not just when it calls. I thought about reducing the load side flow from 15 GPM to 10 for the first 8 -10 minutes of run time.
Any thoughts?

 

IMO the system shouldn't be so picky about low load side water temps and flows. I suspect a refrigerant charge or metering device problem (Thermostatic Expansion Valve), possibly also a refrigerant leak. Have a competent refrigeration tech measure source and load side refrigerant pressures and temperatures and calculate subcooling and superheat from those figures. Compare to manufacturer specification.

I don't know CM equipment but suspect that FP1 being at 27* it is similar to WaterFurnace freeze protection - measures temperature of refrigerant entering load side heat exchanger in heating mode. While the tech is there ask that they confirm FP1 sensor calibration. Off the top of my head it is a 10k thermistor; easy to measure.

Again, take this with a grain of salt since I don't service CM systems, but this feeels like a common loss of charge condition masquerading as a water side problem because the guys that write the manufacturer tech books can't imagine that their system can leak refrigerant...

 

A solenoid valve that takes too long to open when the system starts up can also cause this. Easy to tell if the system starts running without the well flow coming on. Usually the end switch is used to turn on the compressor/heat pump after the system is at full flow.

 

Thanks for the feedback. I had a geothermal tech check it out. They checked pressures, superheat / supercool. The TXV was replaced last year when it was in warranty. He said the same thing. I am trying to operate it outside it's intended parameters.

 

How old is your system?
It should have no issue with 48F source EWT and 50-60F Load water.

If that would cause issues domestic hot water generation in the northeast U.S. would not being possible with geo systems, which is not the case.
The W2W and the replaced TXV raises a flag.
Climate master has issues with some Coax heat exchanger linings loosening up and plugging up the TXV. Their fix was to replace the TXV. However, the Coax continued to loose some lining, and the TXV plugged up again and again.
We had multiple issues with W2W CM units, and had to replace a lot of them with other brands.

The 55-60F load water should not be an issue. We heat up 40F load water all the time, with W2W units.

 

This is an open loop system in case that makes a difference. If the JP1 was clipped this wouldn't be an issue with 48F Source EWT. When I look at the chart with those EWT (Source and Load) specs it is not recommended. (Grayed out)It is useable if you are in closed loop with antifreeze and JP1 clipped.

 

By the way, When I had my last lockout the Water Coil Low Temperature went down quickly to 27 degrees. I ended up flushing the COAX source side and got a lot of Iron Oxides. So I am sure it had a pretty large effect on thermal transfer. That helped quite a bit as it didn't drop as far and as quick.

 

not so sure if I follow you.

The only condition not recommended is very high entering load temps (130F ) when the source is 50F or above.

 

Sorry you were not able to follow. I was trying to keep it short. I made an error above. I meant JW3 clipped not JP1. I have no antifreeze in the system because it is open loop.

Can you teach me more about what you said above about high entering load temps "Only"?
Why does the chart provided by Climatemaster show a gray area when the Source & Load EWT's are too low? (Source <= 50F or Load <=60F) See attached chart
When my lockout happens, the entering source may be as low as 46 degrees with a LWT of 39-40F based on a 6.7F delta.
I have attached the Climatemaster Performance Data chart showing the gray area I am on the cusp of operating in.

 

I don't have the full manual in front of me, but I believe that grey area on that chart just shows where you are at risk of ice formation in your source coax heat exchanger. Given your source and load temperatures and source flow of 15 GPM, you are not in the grey area of that table. If you only had source flow of ~7.5 GPM, then you would be in the grey area. Under this very low source flow condition, the heat exchanger would be extracting much more heat from the source water and potentially dropping the temperature to the point of freezing. But your source flow is more than sufficient to prevent this.

 

If your open-loop source water is coating the inside of your coax heat exchanger with mineral build up, that is negatively affecting heat transfer from the cold refrigerant to the warmer source water. That will cause the refrigerant temperature on the source side to drop and potentially cause the low temperature lock-out. You may need to perform more frequent or more thorough cleaning of the source side heat exchanger.

Have you had your source water tested? Does it meet CM specs for water quality?

 

"Operation not recommended are the black marked areas where you make 130F water"

If you have 15 gpm, your delta T is around 5F, meaning you have 48F going in on the source side and 43F going out back to the ground (or being discharged). The grey area is only about the source to be protected from freezing, not the load. This is not the compressor envelope.

You should be easily able to expose your heatpump to 35F load water when your source is 48F and the have 15 gpm flow.

 

Code 4 is ice risk formation in the coax on the source side.
If I look at the chart and look at column for EWT source. It shows everything below 50F EWT is gray. Regardless of Source flow. So wouldn't that stand to reason that I am operating in the gray with 45F EWT?

 

You are correct I need to do more cleaning. I didn't do it this year. I did have the water tested. It did meet CM specs. The fouling I am getting when I clean it looks like iron oxide. My water test was <.05 PPM and the spec is <.2ppm

Here is the part that I seem to fail to understand from previous replies.
Once you look at the chart column for source side EWT. It lists rows for 40F EWT and 50F EWT (Source)
All of the rows in the 40F EWT source are grayed out. Doesn't that mean I am at risk of Coax freeze like it says in the manual if I got below 40F LWT Source. This is the area that I think I get in trouble with sometimes. My well water temp drops to the 45 - 46F. Which is usually end of heating season. (I might need to bleed off more GPM) I know the load temp is mostly irrelevant but it does exasperate the problem when I am on the bubble.

 

So you have an open well? The heat exchanger in open systems usually freezes at around 38F LWT, which is not where you want to be, 39-40 F LWT does not freeze (yet). So if you have 40F EWT, it is tough to stay above 38F LWT, you must have way to much flow. Or if you have 50F and only 7.5 gpm, you might get close to 38F also, which is why that row is still "grey". With more flow at 50F EWT you are getting above 40F LWT and out of the danger of freezing, which is why the rows with higher flow rates are not grey anymore.

 

Thanks. Makes more sense.

 

Chris makes a good point...check to see that water flow is quickly established when compressor cycles on; ideally a few seconds before.

 

I experienced a similar problem 8-10 years ago with (2) different units that was quite similar. These were both water to air wf units. It had to be the right conditions as you said, the perfect storm. Conditions were open loop, desuperheater with a preheat tank, and EWT to the desuperheater of 55 degrees or less. Unit would run just fine until I flipped the desuperheater on and the inrush of cold water would drop the temperature of the line at the fp thermistor below the 30 degree trip point. 1st unit was solved by slowing flow across desuperheater with partially closed valve and 2nd unit was changed to a closed loop so there was no longer an issue. Lockout conditions/temps were the same whether I had 8 or 15 gpm source flow (3,4 ton units). I think you may be on the right track with keeping tank up to temp all the time. Not sure how your controlling it..

 

One more note. 2nd stage coming on under those conditions would drop the line temp from just above the trip point of 30 degrees to 27-28 causing the lockout.

 

I guess I am scratching my head a bit what could bring your Fp1 temp down to 27-28F. If you have 45-50F EWT, and enough flow, I would think the DSH is too small to drop the FP1 by 2-3 degrees. I would question that the FP1 thermistor is accurate, or that you don't have the flow you think you had.
When the heat exchanger freezes, it does so gradually, from the outside in. The pressure drop goes up due to the smaller lumen, indicating higher flow, which is not the case. Ice form and acts as an insulator, your FP1 temp goes down, and triggers the fault. But Wisconsin has around 48-50F EWT, so does NY.
Ice formation in the coax can fool you....happened to me before.