Cantherm 520's can't keep up with the heat - in hot water

[theindel]

I've got two ground loop geothermal Cantherm 520's in Carlisle, MA. They provider heating, cooling and domestic hot water. I love that I don't have a combustion heating system, or noisy compressors outside. The Catherms are about 25 years old. I'm pretty sure I need to replace them, but with what? I'd prefer not to fall back to fossil fuel.

The units can't keep up with cooling when it gets above about 80 deg F. They super-heat the hot water tank, which then trips the pressure valve and blows about 35 gallons of scalding hot water onto the basement floor. I'm routinely having to reset hi-pressure on the upstairs unit, but strangely not on the downstairs unit. The downstairs unit is forced air, while the upstairs unit runs liquid to blowers on second and third floors. Lots and lots of windows in this house.

What would I replace these units with?

Can the grounds loops be re-used?

What are my options?

All suggestions welcome.

Regards,

Troy

[BaldLoonie]

Sounds like a modern GSHP system(s) are in order. Do these things tie into your water heater? That's not good, best way is for them to heat a preheat tank. If these kept up in the past, then sizing is likely right but they may be tired.

The ground loop is likely good though a smart geo guy should check flow, temps, etc. to rule out problems. If the loops are undersized, could be an issue too.

[theindel]

Both units tie into the domestic hot water tank, which blows the hot water onto the floor when it gets too hot. The upstairs unit (that gets the hi-pressure light) also ties into a separate smaller water tank (a heat sink?) which feeds an additional bedroom over the garage that was added 7 years ago over the garage. This confuses me because that little baby hot water tank (a heat sync?) seems to be storing cold water (both in/out pipes are cold).

I've only been in the house 2 years, so I don't know the whole story, but I suspect that the addition of the extra bedroom over the garage may have been too much load for the two Cantherms. The guy who designed the system is still around, and I think he is a genius and very nice, but I think he doesn't want to mess with it anymore.

[jtrammel]

You can get two new geothermal units of you want and yes you should be able to use same loop. For some reason your unit has high head pressure though. Could be internal to the unit, water flow, or a number of things. Get a pro in goes to give you an estimate and INSPECTION to determine your probl. Good luck wish you the best

[jtrammel]

No insulation on water lines in attic maybe

[beenthere]

Bet a good tech could find the problem with them and fix them.

[jtrammel]

Bet a good tech could find the problem with them and fix them.

Agreed

[theindel]

I've had a couple of different service companies in, but I'm not yet comfortable that they understand the problem, or what the right solution might be.

Thank you.

[beenthere]

Look for a company that specializes in geo's. What you describing sounds like a simple repair. Some older geo's don't have a good control system on the desuperheater, and can cause this when another problem occurs.