Geothermal residential system - frustrated

AngryPenguin

I am looking to buy a home with a geothermal system that uses the HBX ZON 0600 (zoning), HBX ECO-0550 ("the brains"), and the HBX THM600 (thermostat). It's a 5 ton geothermal unit that heats the home hydronically and cools the home using forced air (HSS air handler). This is a single buffer tank system.

As part of the inspection process, I had a licensed HVAC person who specializes in geothermal units but he wasn't quite familiar with the Geosmart compressor unit that was in the home.

I had one main thing to test. I wanted it to go from heating -> cooling, and even after waiting an hour, the THM600 (after requesting it to go to cool mode at, say 68F, it would auto bump it back to a 'low' of 72F), with scheduling off.

I'm probably overthinking this but this has me very concerned. I've read all of the manuals for the HBX units above.

Question: Is it 'normal' for it to take forever to switch from heat/cool for a single buffer tank system (even >1hour)? Anyone familiar this THM600 thermostat and why it appears I'm being 'locked' out of cooling things to a colder temp?

Thanks!

Hot_water_fan

Beyond this controls, which I’m not familiar with, yes it’ll take some time to switch over if there’s a buffer tank. Taking a tank from ~120F to ~40F is a lift: a 50G tank would tank 33,000 btus. Does an hour or so matter to you? 

GW

same--not familiar with that equipment, I just know the basics. Maybe someone set the min cool temp for 72?? If you paid him 'more' he coulda pulled the stat and jumped the wires. But not many hvac guys will do that on a home inspection, I would suspect

when you type: "Question: Is it 'normal' for it to take forever to switch from heat/cool for a single buffer tank system (even >1hour)? "
---are you saying the unit made a cooling call or did not? Seems like @Hot_water_fan thinks it came on but didn't have enough time to 'cool the tank'.

Hot_water_fan

That’s right @GW even if it did come on, there’s going to be a lag. 

GW

yes--seems like it never made a call tho

pecmsg

If the fluid is too hot it may not switch over until it cools. 

GW

you would think the contractor would have identified that the compressor went into cooling mode---seems like the stat was 'stuck'.

hot_rod

Do you have the manual for the heat pump? Maybe there is a time delay function to prevent quick change over from heat to cool

EBEBRATT-Ed

If you change over too quick you will easily overload the compressor with the heated water

I have been on many service calls on process chillers that went down for some problem and they did not want to stop there mfg process. By the time you get there the process water is 90-100 deg.

No compressor will take that. You have to get the water temp down to under 70 to get the compressor where it will stay on without tripping high head.

Unless glycol was involved, we would just feed city water in and drain water until the city water would cool the system enough to get it started.

yellowdog

There may also be lockout temps involved that will not allow it to goo into cool mode when the outdoor temp is too low.