Is this desuperheater + buffer tank plumbed correctly?

by **taco_mel** » Thu Nov 05, 2009 8:42 pm

Our desuperheater was activated today for the first time and as thrilled as I was to feel the pipe getting warm, I did wonder if this plumbing job was correct. (The heating contractor has done numerous installs but this was the first buffer tank he'd connected. There was a diagram for a buffer tank published in the manual for the unit -- a Carrier badged Tranquility 27.)

Attached is a sketch of the connections. Specifically I am curious that the hot water from the geo unit seems to mix with the cold water supply, and there is no kind of shutoff or valve there. So my question is -- is this the optimal plumbing? Should there be a fancier connection than just the "T" where the water supply meets the DHW output?

by **urthbuoy** » Thu Nov 05, 2009 9:42 pm

As you've shown it, the flow is backwards. The t in the cold line is the dsh "in line". The out from dsh leads to the t in the drain valve. Nothing fancier than a T is required, but you can include a check valve to stop cycling when the unit isn't running and an air valve is commonly used on a high point.

by **GeoXNE** » Fri Nov 06, 2009 5:23 am

taco_mel

Your setup is the ClimateMaster preferred piping method for a Double Tank Installation With the exception of several shutoff valves that enable power flushing through the HWG exchanger. Check it out here pages 16 thru 18-
http://www.climatemaster.com/downloads/97B0045N03.pdf

Originally common practice was to not draw water from the bottom of the tank to prevent clogging the HWG exchanger with tank sediment. However this method has some disadvantages.
-doesn't send coolest water to HWG for efficiency
-goes against natural flow setup of tank forcing removal of heat trap nipples on some tanks (Allowing possible ghost flow and increased standby losses)

The ClimateMaster method with valves allows power purge flushing of HWG and tank individually to remove entrapped air and sediment.

by **taco_mel** » Fri Nov 06, 2009 6:29 am

As per the install manual, they have set it up by the book. (Including the shut off valves which I didn't draw.) I was not aware of the flushing setup and this did indeed look backwards when I compared it to many of the diagrams I have seen here on this forum -- thanks to you both for helping me learn something today!

by **teetech** » Fri Nov 06, 2009 7:24 am

-doesn't send coolest water to HWG for efficiency
-goes against natural flow setup of tank forcing removal of heat trap nipples on some tanks (Allowing possible ghost flow and increased standby losses)

GeoXNE
I'm not sure I understand your statement. Are you talking about the Climatemaster drawing above?

by **GeoXNE** » Fri Nov 06, 2009 7:51 am

teetech

Those comments refer to the reverse flow suggested by urthbuoy and some manufacturers.

I have done it both ways and prefer the ClimateMaster method (as drawn in taco_mels diagram with addition of valves and in the ClimateMaster IOM link provided above).

by **jrh** » Fri Nov 06, 2009 8:09 am

I agree with urthbuoy, the flow is backwards. With this setup you will be sending heat into your cold water pipes, and drawing sediment into your HX

by **GeoXNE** » Fri Nov 06, 2009 9:41 am

jrh

Using the ClimateMaster method, when the HWG(desuperheater) pump is on there is lower pressure at the DHW in (in this case the bottom of the tank at the teed drain). Because of this the DHW out will flow down the tank cold water dip tube only. The hottest water stays at the top of the tank where you want it available for use. The coolest water goes to the HWG for best heat transfer efficiency.

The ability to quickly purge air and sediment out of the HWG loop and tank with the flip of a couple valves is a great advantage. The need to flush the HWG becomes another maintenance item but is very easy with this setup and should be a matter of course as is flushing the HW tank.

by **teetech** » Fri Nov 06, 2009 10:56 am

I see your point GeoXNE.
In the old days a coaxial fitting was used at the bottom of the tank for both in and out DSH lines. Sediment would collect (who flushes their water heater anyway) and plug the fittings causing pump failure and plugged coax. The extra valve would be an easy way flush the fitting. I liked the old coaxial fitting except for the sediment problem. It eliminates having to circulate backwards through the dip tube.

I wonder how many installers are removing those heat trap nipples.