Trying to get a better handle on desuperheater performance, for my Climatemaster 3 ton unit. 

Does anyone know what the catalog performance  is based on as far as the assumed water side conditions? 

For example the climatemaster catalog has a column for HWC (hot water capacity), in kBTU's but doesn't list any conditions that  I can see.    I thought I remember reading 90 F EWT, but can't find anything ... I tried to check Waterfurnace, and Florida Heat Pump literature as well, but I'm not seeing it.

I remember 90 EWT in WF docs.

In round numbers figure about 10% of system nominal capacity, but it varies widely with EWT on load and source sides and somewhat with EAT. Higher thermostat setpoints, heating or cooling, increases DSH performance.

I was just trying to guestimate capacity on my desuperheater.  I'm assuming I'm getting somewhat more than the cataloged values, due to a better than average approach.  I'm guessing the desuperheater rarely has more than 6-8 hrs to work on the cold water in the buffer tank, before more cold is introduced as the hot water in the powered tank (GE HPWH) is being used.  So EWT to the desuper heater on average might be more in the range somewhere between 50 and 65.  

I was thinking one way to evaluate the "uprate factor" might be to take the ratio of the two different heat exchanger LMTD's (log mean temperature difference)... using say 60 EWT for the first case and 90 EWT for the second (with some reasonable delta T's and refrigerant side temepratures).    I'll just let you think I use that formula every day while I go dust off the PE Review Manual.... to try to find it.

Yes you can log EWT and LWT as well as hours of operation and GPM to figure performance, or go with the factory statede (about 10%) Curt mentioned.

You are correct that feeding water significantly cooler than 90 will raise heat transfer. However, the calculation is probably a bit more complex than the ratio you describe since the refrigerant's enthalpy varies with temperature and pressure. In addition, during times of cold buffer tank temps some refrigerant may condense in the DSH coil.

Another variable is Y1 vs Y2 operation if your CM is two stage. Y2 should produce considerably greater superheat.

Consider timing operation (I have hourmeters on Y1 and Y2) and monitoring buffer tank temps at high and low element ports (assuming your buffer tank is a typical storage electric water heater)

FYI - we did a desuperheater geothermal installation this winter 2012-13 with a preheat tank. We used a ThermoDrain drain water heat recovery unit to help preheat the incoming cold water to 73F instead of 47F when someone is taking a shower. We have a thermocouple reading the tank's temperature and during the winter months, it is anywhere between 100F and 125F. We added a pump and a delta T controller to the setup and when the tank has cold water in it and water is flowing down the drain pipe of the ThermoDrain. The cold water cycles through the coils of the ThermoDrain to heat up the water. This is great because now it captures the bathwater energy, diswasher energy etc....
The other nice thing is that the ThermoDrain manufactured by http://www.ecoinnovation.ca feeds the tank warm water that is preheated by shower water.
I bought my system from a local installer and the ThermoDrain was purchased on-line. http://www.ecoinnovation.ca
We went with a Waterfurnace, ThermoDrain as well as our variable speed pump Pentek in order to get the best combination.

One negative point I need to mention is that it costs a fortune in airfilters, they are hard to get a hold of and are costly.

Posted By Richard Bross on 15 Apr 2013 03:51 PM
One negative point I need to mention is that it costs a fortune in airfilters, they are hard to get a hold of and are costly.

We have the following washable electrostatic filter and love it.  I'm not affiliated with this company.

http://www.dustfree.com/products/air-filters/dust-fighter-95

We bought a custom size online to fit our Water Furnace.

Posted By Richard Bross on 15 Apr 2013 03:51 PM
We added a pump and a delta T controller to the setup and when the tank has cold water in it and water is flowing down the drain pipe of the ThermoDrain. The cold water cycles through the coils of the ThermoDrain to heat up the water. This is great because now it captures the bathwater energy, diswasher energy etc....

That makes for a nice setup.  Was your Thermodrain close to the hot water buffer?  What controller did you use? 

I have no easy place for adding one of these.   Need to destroy some walls to get it in.  I wish they made a long horizontal one so I could fit it easily in the basement.  I am guessing it would cost too much as it would need to very long as all the hot water is on the bottom of the drain pipe.