So I have myself 2@2 ton waterfurnace geothermal systems sharing one well field (4@250ft). One combined system includes a desuperheater for my downstairs (living area, kitchen, etc) while the other is a split system without a desuperheater for the upstairs (bedrooms). My hot water system is 2 tanks in series...the first for preheating with the desuperheater with the second for actual heating. Well...one thing that bothers me is that for about 1/4 of the year I only run the upstairs system. 1/2 the time I run both, while the final 1/4 i don't run anything. And most of my hw usage occurs when the upstairs is occupied and the upstairs system is operating. I wonder if installing a second desuperheater on the upstairs system would be worth it. This should increase hw generation for 3/4 of the year. And it would better match demand with generation. Any thoughts or experience out there? I'm more curious than anything right now.

You could purchase an after market dsh, and it would probably pay, but you would need your original installer on board to keep the warranties in tact. Depending on their mark-up, your savings may barely justify expense.

# of people (full time residents) is an important arbiter of hot water usage, cost and payback

Most Certainly! We have 2 adults and 2 infants. Hot water usage has significantly increased with the daily bathtime and having to run the dishwasher . In addition, somehow our laundry has doubled (I still can't fathom how folks so little go through so much clothing!) I'll look into the aftermarket DSH. Any suggestions on a MFR?

FYI, I just came across some other forums talking about the Turbotec Enviro-Pak DSH. Very cool. There were some other MFRs too (Bard, etc).

I'd just need to figure out how it would be installed in addition to my other DSH. Would I need some check valves to insure flow doesn't go back towards the other DSH (or vice versa)?

My geothermal installer owes me for numerous references, so maybe I can figure something out here...

BTW. I just looked at my runtime numbers thanks to my Ecobee thermostats. Last year, my upstairs unit (without the DSH) ran ~2.2x longer than my downstairs unit (with the DSH). The actual numbers show the upstairs unit accounts for 68.6% of the total cooling runtime while during the swing Spring months accounting for over 75% of the total runtime. Now i just need to figure out how much one of these things costs...

You might want to take a peak at those geospring air source water heaters. They can be had for as little as $700 before federal and state rebates. And they don't care about shoulder seasons.

"BTW. I just looked at my runtime numbers thanks to my Ecobee thermostats. Last year, my upstairs unit (without the DSH) ran ~2.2x longer than my downstairs unit (with the DSH). The actual numbers show the upstairs unit accounts for 68.6% of the total cooling runtime while during the swing Spring months accounting for over 75% of the total runtime."

Hold on Tommyj, runtimes are determined by overall load for which DSH is only a small fraction. While runtime indicates spare capacity, the comparison to downstairs unit means little without discussion of other loads.

I already have a Geospring ASHP. It operates in series with my DSH pre-heat tank.

Hey joe.ami...I'm not sure what you're getting at. I'm not comparing any operating loads of the system with or without my DSH. I'm just making the point that my A/C upstairs runs 2x more than my downstairs unit. And when it comes to utilizing a DSH to create hot water, for two of the same sized systems, then a system that runs longer will generate more HW than the other. Given that my goal here is to take advantage of the A/C reject heat and produce HW from it via a DSH, then doesn't it make sense to look at install a second DSH on my upstairs unit given that it runs 2.2x longer? Am I missing something?

FYI, I looked into the Turbotec enviro-pak. Those units are about $400 without installation. Talking to my HVAC contractor, given that I've provided a number of referrals and allowed folks to even come over to my place to view my system (which led to sales), they offered to replace my upstairs hydro unit (Envision Series) with a new one (Series 5) that includes a DSH. I would only have to pitch in on the labor to the tune of $1k. Given that one of those units typically goes for $7-8k, I'm thinking this is a pretty good deal. And since I'm replacing the system with an new upgraded system, I do believe that I may be able to get a federal and state tax credit for it upgrade. Not bad, eh?