I have a 2 year old McQuay 2 ton unit. Last year my EAT and LAT were more than 20⁰F diffent and now they are only 7-10⁰ F different. Also, my EWT and LWT were about 8 degrees different and now they are 3 degrees different. I flushed the heat exchanger and that did not change anything. My field (vert. closed loop) is the same as last year and my flow rate is the same. It seems to me that everything is the same except the performance. Any thoughts or comments would be appreciated. Happy New Year!

Have you changed the air filter lately?

The fact that your heat extracted from your source water (given that the flow is the same) is significantly less points to your refrigerant circuit as a trouble source. Your heatpump is not taking enough heat out of the water, that is why your air temps are low, too.

Good point doc

Doc,

Thanks for your reply. Do you think that I have a freon leak (R410A) or some other problem?

I don't know. The first thing I would check is the refrigerant, which requires know how and some equipment, unfortunately nothing for a DIYfer. What is your EWT right now, and what is your return air?

What is the water pressure and GPM rate of flow.
Joe

My EWT is 48⁰ and return air is 68⁰. I have the thermostat set at 70 and it take a long time to reach the set point on the thermostat. Our outside temp is 40⁰ this morning. Again, thinks for your input!

I don't have a pressure gauge in line now but the fow rate is 6 gallons a minute. If the pressue reading is critical, I can put a gauge in the loop.

Thanks for your thoughts

We know system requires ~6GPM, but how do we know that's what we have? Among the things that can change water DT is GPM. DT dropping due to GPM would mean circulator speed went up which isn't likely, but now that we know you haven't checked in awhile......
Pressure may impact ability to remove heat as well. A closed loop system with very low pressure could see a significant drop in air side DT.
How is your EAT getting down to 48*? Do you dial down or are you losing that much head way?
joe

How are you verifying your flow rate? How did you flush your system, purge it and re pressurize without a pressure gauge? Is it non pressurized?

My system is a non-pressurized system so the only pressure I have is head pressure due to pipe/flow resistance. I think you misread one of the notes above. My EAT is not 48 - that was my EWT when Doc asked me after the unit had been running for a while. Thanks!

Got it. The GPM still matters. As does lack of air in the loop.
J

If you have a non pressurized flow center, and a McQuay HP, you probably did the install yourself. You can check how much the water level drops inside the canister of the flowcenter, when you take the lid of and the circulation pump turns on. It should not be more than 1-2 inches, otherwise you have too much air in the system. With the DIY kits, you should be able to turn off each loop to have the circulation pump purge out each loop. Fact is that your delta T on the source side is too low, with a one pump flowcenter (assuming this is what it is) with one 26-99 pump constant speed, it is unlikely that your flow is increased (doubled) compared to last season. With a non pressurized system, you unlikely have a vacuum lock in the loop. So your problem, unless we are missing something, is likely within your refrigerant circuit.

I like Docs thoughts as long as we verify loop delivery first.
Joe

Doc,

Your good! I did the install and have a two pump (26-99) flow center. I only use 1 pump at a time and alternate their use with a latch relay. I think I got most of the air out of my system as the water in the flowcenter only moves about 3/4 of an inch up or down when the system goes off or comes on. One last question: what do you think about some sort of buildup in the water/freon heat exchanger that is preventing the refrigerant from picking up heat from the water?Have you ever run across that? Thanks again--

Just curious, but what about the type of ground the loop is in? Could it be a grout shrinkage problem?

So it is unlikely you have too much air in, 0.75" drop sounds good. Why do you have a 2 pump flowcenter for a 2 ton loop? Usually 2 and 3 ton loopfields require only one 26-99 pump. Since the pumps are in series, you are pumping all the fluid through the passive impeller of the second pump, adding significant pressure drop to the loop system. That brings up another possible explanation for your low delta T, namely that for whatever reason you second pump is also on, significantly increasing flow and explaining your lower delta T on the source side. You need to verify that only one is running, best is to disconnect one temporarily.

Yes, anything within your heat exchanger which reduces the heat exchange can explain the symptoms. That is why everyone here keeps asking if the flow is the same! Please verify.

If your flow is the same as before, then it is unlikely that the issue is on the source side (loop) side of things. I would check refrigerant levels first. Verify amperage draw by the compressor and refrigerant temps.

While GPM remains a question, I'm in agreement with doc that this is probably a refrigeration problem, but don't know your background or qualifications with refrigerant and gauges. It's not rocket science and most brands have simple charts to use to check levels, but if you need refrigerant, do you have it? If you don't are you certified to buy it? Are you capable of finding the leak? If the answer to any of these questions is no then it's time to call for help.
Good Luck,
Joe