Am the victim of an installation gone bad and am trying to rectify the problems. The system was plumbed to one 60 gal tank which supplied DHW and radiant floor heating throught a heat exchanger. There was no electrical hook up to the tank and the DSH was also plumbed to the same tank. The system (I was told) would produce a water temperature of 125, enough for both domestic and radiant floor needs. All from one 4 ton Hydron Module model ww48. the question is, when I replumb this unit,would 3, 40 gal Marathon tanks be correct? One tank as a buffer for the radiant floor, one as a buffer for DHW and one wired for DHW. Also does the circulation pump between the buffer tank and heat pump run all the time or only when the heat pump is running?

1) Three tanks would be the best setup.  They don't need to be Marathon unless you have a lot of money to throw at this project.

2) The circ pump only needs to run while the heat pump is running.

I don't know about sizing, but if larger size tanks would be of benefit to you, Marathons tend to be less expensive on a per gallon basis the larger the tanks get. What I'm trying to say that the incremental cost for a larger Marathons may be less than you think, (but still expensive). We love our single 85 gallon unit.

This excerpt is from another forum:
...NJ, Sussex Power and Light, which sells them at great prices to anyone who wants them. My 85 gallon tank cost $818 which was the best price I could find anywhere and shipping wasn't bad at $65...

We paid more than this for our tank. Also, electric Co-Ops sometimes have good or discounted, prices to its members.

I hope your DHW is isolated from radiant water.

Ian

With water to water geo my best (in terms of comfort and efficiency) heat only system would include (based on the assumption that a heat load calc was done and the 4 ton Hydron Module was properly sized to 100% load at  minimum EWT's)-

1- 60 gal buffer tank for radiant only controlled by outdoor reset

1- 60 gal indirect water heater zoned w/1 hour timed priority and adjustable differential aquastat for DHW preheat.

1- 60 gal (or larger if you need) electric DHW tank powered to finish what the geo doesn't handle

Each tank is performing a different function and should be selected with those functions in mind.

Flow rates require special attention to ensure proper and efficient function. The lower the temps you can run the greater the efficiency. Properly sized pumps and piping make this possible. Geo loves radiant.

Unless you have excess capacity with your unit I would skip hooking up the desuperheater in a heating only system. The DSH will reduce capacity to heat and we have provided for geo DHW.

What make and model tank do you have now? Maybe it can be reused.

I agree with engineer. DHW and heat loop water should never touch.

I have a Rheem Professional 612 with a capacity of 270 liters, that was the only tank in the system. It was connected to both the DHW and the radiant floor and was not connected to the power grid, ie; stand a lone. The heat loop and the DSH were both plumbed into the same tank. A taco 13 pump circulated the water between the two continuesly regardless of weather the unit was running or not. I can only assume that everything was sized properly. FYI... there are 4 vertical bores holes 150ft into solid rock with 3/4 pipe filled with grout. With this we were trying to heat a 2000 sq ft home constructed entirely using ICF's and R50 in the attic

I have little on the heat exchanger, no paper work. I tell you that it is made by FlatPlate and is 5" x 12" x 1" in size. It is installed between the buffer tank and the radiant floor distribution, making the radiant side completely separate from the rest of the setup.

Something like this?

Flatplate 5x12 heat exchanger

That pretty much discribes it.

Ian

I haven't forgotten about you. I will reply when I get the time.

To avoid throwing good money after bad you need to start with answers to basic questions such as heat load, radiant loop capacity etc. plumbing it right will still not make it work if you aren't sized correctly.
Good Luck,
Joe

I like to think I'm not throwing good money into a sinkhole. The system ran for 5 years with few problems, the odd lockout happened once or twice a year, tx valve replaced 3 times , freon leak from a cracked pipe, contacts burned twice, the third time set fire to the wiring within the unit. All this I blame on the installers lack of competence and knowledge. But the fact that the system did supply heat when it was working leads me to believe some of this setup is right ie: the ground loop, and that replummbing the system correctly should solve the major problems.

Ian, you titled the thread "bad installation" and now concede system "ran with few problems for 5 years". The other problems you mention are not necessarily the installers fault either (i.e. bad txv, burnt contacts, cracked pipe).
Your emotion in the situation (and I'm not blaming you for being upset), is clouding the information you are offering.
May I suggest a deep breath and a start from the top listing service history?
joe