Can someone tell me how a desuperheater works and how it is tied into a geo thermal system ?

An energy saving device in a heat pump that, during the cooling cycle, recycles some of the waste heat from the house to heat domestic water.

Hi, Thanks, so this is a add on option or do they all come with it ? Now does it really heat the water so i would not need a water heater or do i still need a water heater during the heating cycle ?

It is an add on option that is a supplement only to your hot water heater

I thought it heated hot water during the heating season, so it only works in the summer while cooling?

If it heats the water in the heating mode, it's robbing the system of heat when it's needed to heat the house. The better setup is that it only runs in the cooling mode.

It can heat water when ever the heat pump runs, heating or cooling mode. While it is true that in heating mode some of the heat is pulled off to heat the water it is typically more efficient then any other way to heat water. In my case the geothermal is about 3.5 times cheaper then electric resistance or natural gas so I really like the option, just wish I had a larger pre-geo tank (only 40 gallons).

It is a small coaxial heat exchanger that intercepts the refrigerant at the hottest part of the loop - the compressor discharge. At that point the refrigerant is at a temperature higher than its saturation temperature. That is useful for domestic hot water. It is essentially free during cooling system (can actually slightly INCREASE EER) and relatively cheap during heating season as Brock notes.

Don't bother with it without also specifying a preheat tank, ideally sized at about a typical day's use of hot water.

how is the pre heat tank plumbed in? was thinking of purchasing new hot water heater then disconecting power from my old waterheater and using it for the pre heat tank because it has insulation, pressure limit valve, rated for potable water, etc. Is this a good idea? what about using an 'on demand' electric heater after pre heat tank?

Either method you describe will work. WF recommends inlet to desuper be connected to cold water inlet of preheat tank. Desuper outlet is connected to drain fitting on bottom of preheat tank. Natural convection causes warmer water to rise and stratify in preheat tank. Preheat tank hot water outlet goes to either tankless or conventional storage type water heater's cold water inlet.

My setup consists of two eighty gallon GE water heaters plumbed as described. Hourmeters on system indicate that desuper is saving 60-75% of electricity for water heating

Engineer how did you plumb the two, in series or parallel from the de super heater? I am seriously thinking of adding an 80 gallon tank, but toying with the idea of keeping the 40 gallon. I should have listened to them when they said get an 80 gallon to start but I had a 40 gallon electric sitting there doing nothing.

Why not use an in-direct water heater? Heats using a coil that receive hot water from a boiler or geo system. I have one that has a stainless steel tank and stainless steel coil. Has about 3" of EPS insulation.

Cost. Personally we did talk about the option and for a stainless steel tank with insulation and a coil I was quoted $2500+ instead I used and existing 40 gallon electric with decent insulation and the desuperheater was an addition $1000 or $1500 less. He also said the water would be hotter with the desuperheater then using the regular exchange.

Brock - preheat tank is in series with and upstream of regular domestic HW tank (or tankless unit)

Vermaraj - aside from cost, indirect water heater is typically designed to operate as an additional zone off an oil or gas-fired baseboard hot water heating system. Those systems operate with very hot water - 160 F or higher. An indirect water heater won't heat water without such a high temperature source, and geo won't provide that

My mistake, I thought you meant you had three tanks total, twin 80's in front of the "regular" 80. I was just trying to figure out if you did have twin tanks in front of your regular water heater (connected to the desuperheater). Would you connect the desuperheater inlet from the base (drain) of the second tank and the return or hot side of the desuperheater to the cold or inlet side on the first tank? Or should I not bother keeping the 40 if I get and 80?

I have just 2 80s. You could plumb the 40 and 80 for create the equivalent of a single 120. I'm not sure I'd bother keeping the 40 in the system unless both your hot water needs are high and your geo unit is 4 or more tons