I have two Waterfurnace water to water units (5 ton and 3.5 Ton).  They are configured to feed the same chilled water tank, but I have set the temperatures so that the 5 ton unit acts as a Primary, and the smaller unit only kicks in when the 5 ton can't keep up.  My DHW configuration is an electric Main tank and a separate Buffer tank, both are the same size.

My initial plans were to connect the DSH from the 5 Ton unit to the DHW Buffer tank in a manner consistent with a previous posting on this forum from "Bergy".  This posting called for a 1/2" line from DSH to the bottom of the Buffer tank, and a 1/2" line to DSH from above the 3/4" ball valve.  My geo-contractor is trying to talk me into hooking the 3.5 Ton DSH into the DHW Main tank as well.  He says this will reduce the dependence on electricity to keep the Main DHW tank at temperature.  It sounds somewhat logical, however I fear that it is more complicated than that.

To confuse matters more, I have a convection circulating loop installed in my hot water plumbing.  This is an insulated loop that returns to the bottom of my main DHW tank.  

Any thoughts on the best way to take advantage of the equipment I have installed?

I have a documented case where DSH directly to electric water heater actually raised the cost of hot water to the home.
The why was less consequential to me than solving the problem which I did with a buffer tank. The electric consumption by the water heater (individually metered) dropped to 1/2 it's pre DSH usage.
Good luck,
Joe

Don,

Both desuperheaters should be piped into the "Buffer tank". Both should have ball valves at the buffer tank where the lines come into and leave the tank. These are used for servicing the unit AND for throttling the flow to achieve the proper delta T through the desuperheater. Also, both lines need a check valve to prevent cycling water through the unit that's not running.

Bergy

Bergy,

Thanks for the reply.  Two questions:

1) Should the check valves be installed in the "To Desuperheater" line or the "From Desuperheater" line?


2) Is it okay that the hot water recirculating loop dump into the bottom of the Main Tank, or should I dump it into the Buffer Tank?  Basically, this loop is a continuation of the hot water line throughout the house, and then back down into the basement.  It is all insulated except for the last 15 feet.  The theory being that convection will cause the hot water to continously flow through the pipes, giving me instant hot water throughout the house.  A ball valve is included just prior to the Main Tank, so that I can control the flow rate or cut it off altogether.  BTW - this loop has not been tested yet.

1  Check valve from DSH or DSH out

2  Leave it connected to the main Tank

What Geotek said...

Bergy