Water-Air Heat Pump High Pressure Lockout

[exzavior7]

We have 3 WAHP's running to cool/heat our building. The whole building is about 3 years old. We had some problems over the winter with one of heat pumps (6-ton Trane GEHE) locking out on high pressure, the fan would continue to run and compressore would shut down, particularly when OA temps dropped below -10F. After checking airflow (appears normal), checking waterflow (appears normal when the heat pump is actually working), and inlet/outlet water temps were fine (37F at the lowest outlet, and system has 35% glycol). The strainer was full of flux, tons of flux. I was concerned with all the excess flux that the heat exchanger might be gummed/plugged up. But the heat pumped worked when OA temps were above -10F, in fact the compressor would kick back on automatically when the OA temps rose above -10F.

All of that is to say, I kept coming to the conclusion that the heat pump was really locking out because of too low MA temp from the OA being so cold. While the other smaller heat pumps worked great all the time (they have very minimal OA). My math calc'd a MA temp of around 52F entering the bad heat pump when the OA temp was at -10F. Which made sense if there's a low-limit lock-out on these heat pumps (<55F). Unfortunately for me but great for the clients using the building, we didn't have a another -10F day/week for the rest of the winter, so everything worked again and I wasn't able to test my theory and close the OA off to that heat pump.

Now its the hot summer (99F yesterday) and that same heat pump is locking out on high pressure. I haven't been around to know all of the details (still getting the details for the maintenance worker there), but I do know its high pressure lock out. Water temps are good (not too hot, 52F). Airflow is good. The fan continues to run while the compressor is shut down. I do not know if/when it starts back up, if it ever does, I don't know yet.

Any ideas to why the heat pump is locking out on high pressure at the extreme end of the temps? I have more that enough capacity in my bore field to handle the peak loads of heating and cooling.

Is it just a coincendence that it locks out during these peak temps? Bad pressure switch? Plugged heat exchanger? Over charged refrigerant (I'm least familiar over charge symptoms)? All these problems coincide with the high pressure lock out in both heating and cooling seasons, but I'm just not sure where to go right now. Thanks -

 

[Compositepro]

A high compressor pressure is due to lack of condenser cooling capacity of a plugged expansion valve. Since you see the problem at temp. extremes, it seems you do not have enough condenser capacity. Probably due to inadequate flow due to plugging and high outside air temp.

 

[Drazen]

undercharged refrigerant? when there is no enough refrigerant, compressor is going to its peaks trying to reach capacity.

 

[MTES93]

Probably hi/lo mixed air temps. They (heat pumps) can be picky. If my memory serves, the refrigerant circuit more or less balances itself out around the source/sink temps and resulting pressures (these heat pumps have limited staging I assume). So the lower the indoor coil EAT temp in heating (its a condenser coil) the lower the entire circuit gets pulled down. So you are probably going off on low suction pressure (but you said high pressure??).... In cooling mode, the indoor coil is an evaporator, the hotter the air is the higher the pressure it is on the condenser side... so you are probably going off on high pressure limit.... These are probably extended range heat pumps being they are on a geothermal field, but that extends the water/brine loop temperature operating range, not the air temp and the air temps should be w/in a range recommended by the mfgr.... Been awhile since I played w/ a refrigerant circuit but I think I have most of it right or at least close.... Some of the other posts maybe able to elaborate on this...

This is an over simplified view but we (Helena) have had similar issues w/ other mfgr's heat pumps in a similar installation, these were going off on low pressure w/ low OSA temps resulting in a low mixed air temp. Anything you can do w/ the ERU or vent unit to increase temp in winter, doubt if you have cooling on the unit do you? Can you put some or all of the air into the room directly w/ out impacting residents too much? Sound like you can't.

Have you checked w/ Jon at Trane regarding the min/max temps?

Agreed, the flux (I know who the contractor is) is not good and this has happened numerous times on past jobs w/ them.

Take care CH!

 

[EnergyProfessional]

First off, you need to drain and flush the glycol system. the flux you found is everywhere else in the HX etc. this should have been done....

Flushing with clear water, detergent, and clear water again.

All the above advice is correct, but you may face in addition limited glycol flow and HP HX fouling diminishing heat transfer.