We've installed a number of geothermal (ground source) heat pumps in new homes. I like the desuperheater option for meeting some of the home's hot water heating needs.

I'm not a tax professional, and I didn't stay at a Holiday Inn Express last night, but I suggest you look at the after-tax cost of the desuperheater. Currently there's a 26% federal tax credit provided you place the new system in service by year end. Next year it drops to 22% Assuming a 26% credit, the actual cost is .74 x $1,200 = $888.

The average cost to produce hot water in a home in the U.S. based on $.10/kWh is $440/yr. Depending on your climate zone, I'd estimate the desuperheater would reduce that by roughly half or $220/yr. At that level you'd recover the incremental cost of the desuperheater in around 4 years, assuming no increase in energy cost and ignoring the time value of money. If it only reduces the cost of hot water heating by a third, you'd recover your incremental investment in about six years, again assuming no increase in energy cost and ignoring the time value of money.

I consider the desuperheater a good incremental investment which will be even more attractive as energy costs increase.

The Energy Tax Credit applies to the price of your entire system.

My understanding of the tax credit is that it applies to the cost of the entire system.

The OP is evaluating the return on an incremental investment. The tax credit applies to the incremental investment and so it's the after-tax incremental investment which needs to be considered in the analysis.

I guess I missed the word "incremental" in the question.

As I understand the DSH does not make hot water on demand and the hot water is a bonus, and harvested waste heat only when the unit is running in heat or cool mode. Water furnace states up to 50% savings, but depends on run time, season, inlet water temperature, demand for hot water and storage tanks sizes and insulating quality. Good storage tanks can go days and only lose a degree so it matters.

You've had a system for 26 years and know how much it runs so you're the best source to answer your question. If you'll rarely use it in the spring, summer or fall the savings will be negligible, and where most of the savings are derived. If your house is well insulated and efficient the geo system will run less in the heating season giving less hot water savings. For me I don't believe one could save me more than 20% to 25%, but even using Tim's generic calculations it would save me $100 a year so payback would come in 12 years and quicker than a tankless hot water heaters.

I do know finding one who knows much about Geothermal and DSH on this site would be lower than seeing a UFO, so I'm posting a link to browse. It's dedicated to geo topics and you could lurk or join and submit your own questions to the community. I'm a member but mostly lurk because there are so many more who can answer questions better than I could.

geoexchange.

A good friend has a ground source heat pump system with desuperheater equipment included at his large vacation house in a somewhat remote area. There's no natural gas, fuel sources are electricity and propane.

He's told me that during months when the HVAC system is used for cooling, the desuperheater provides a useful boost for hot water production. Not so much during heating months.

I think the thing is, the heat is available anyway, whether used for domestic hot water or "pumped" back into the ground. It's a by-product of cooling, just as is the hot air that blows out of the top of a regular AC compressor. Use it or not. As to the right configuration and tanks, rely on your HVAC contractor, not anonymous comments on the internet.

The only option for extracting heat via desuperheating is when the compressor is running. It's certainly not an on-demand hot water heater.

It might be counter intuitive, but systems such as geothermal heat pumps provide the best return on investment when installed in homes with poorly performing thermal envelopes--i.e., homes that use lots of energy for heating and cooling. If a home is well insulated, has good quality windows and doors, and low air infiltration, the incremental cost of a geothermal system may not be a sensible investment. In running the numbers for my clients in our coastal VA climate (zone 4), I've only been able to demonstrate a reasonable return on incremental investment for a geothermal system when Uncle Sam kicks in via a tax credit. If the OP has a really energy efficient thermal envelope they'll be well served to consider alternatives to a geothermal system.

@outpaientzero, your stated payback time fails to consider the tax credit on the initial investment. If your savings is $100/yr simple payback time (which ignores the time value of money) would be 8.8 years not 12 years.

I can't offer much in the way of cost-recovery advice. For us, we had geo-thermal (an older no-frills unit) in our previous house, and when designing the post-fire replacement, there was no question about going geothermal again. Since options here for heating would be propane or electric, plus a heat-pump for cooling, I didn't even bother with the math. We have a WF 5 (open loop) with the DSH option (2-tank).

I put some temperature probes on the water lines to/from the WF and to/from the DSH tank. We're deep into cooling season, and here are some temperature numbers that you may find useful or interesting:

During a cooling cycle, the water from the well is about 10C, and water to the discharge well is 16 to 19C. The temperature of the water to the DSH is around 30C. So for us, the DSH preheats the hot water tank by about 20C. The second electric tank is then set to heat to 55C to supply the house (all numbers rounded). So by my very rough estimates, the DSH reduces the workload (and thus cost) of heating my water to nearly half. Exactly how that translates into dollars savings isn't really as easy to determine. But since we've already made the investment, and we plan to live here pretty much forever, it's one of those things I prefer not to get concerned over. :-)

Where do you live?

Provide as much detail about your ground loop as you possibly can.

SR

Consider a hybrid electric heat pump, which would provide the least operating costs for hot water and decouple your hot water from your HVAC. The hardware cost of that is ~$1500 and comes with potential tax credits of its own.

Jake, isn't it the same proposition no matter what primary mechanism is used for domestic hot water? If the incoming water can be reasonably and economically prewarmed with existing heat that would otherwise go unused, there's a benefit.

Thank you everyone for all your input. We have to know later this week what we want since I guess it take 2 months to get. I would prefer to have it installed when it isn't terribly hot..

I think we're going to go with the desuperheater again. With climate change rearing its head, I think we'll have lots more super hot summers, so it will help with the desuperheater............if we don't lose electricity a lot too. With the Federal tax credit, the price of the DSH pales in comparison to the new unit. To fsq4cw: Not sure the ID of the tube is, but the length is probably something like 300-450 ft.(??)

WaterFurnace sold out to a different company and couldn't tell me for sure, but the HVAC guy was able to figure it out. I'm in Central Indiana. I've always been really impressed with the company we use, but lots has changed in 26 years and especially with Covid, etc., so I'm hoping they're as good as they've always been. Our rural REMC used to always replace our water heater for free, But there's been unbelievable "growth and development" in this county, and I don't think they do that anymore. If I have anymore questions about this, I'll know where to come. Thanks all!

@catherinet (5IN),

Are the desuperheater and associated components on your existing system 26 years old? If not, how long was their useful life?

Hi Charles. Everything was new, but we did have to replace the compressor. I forget how long that lasted, but it happened shortly after the warranty ran out. :( That was pretty much the only problem we had with it all those years, and it is still doing fine........except in winter if it stays extremely cold out, but we had old door and window issues until recently, so that was probably the problem. Our HVAC guy always said he preferred to err on the small side, so that it dehumidifies as much as possible in the summers.........and it has done great with that. The only reason we're replacing it soon is because we don't want it to quit working in summer or winter and surprising us., plus they apparently don't make parts for this model any more.

@catherinet (5IN),

Thanks for the information. The oldest geothermal systems we've installed are around 16 years +/- old and I'm trying to get a sense of their life expectancy. I'm not sure they will live to age 26, but if they do, that will be one heck of a return on investment.

Hi again. Like I said, I don't know if replacing the compressor early on gave it a longer life, but I also purchased the twice yearly service plan and had that done routinely. The HVAC guy told me that lots of people don't maintain them for years and years, and of course they have bigger problems. I also took pretty good care of the filter. It would be fun to see how long this one could potentially last, but would be a bummer to have it break down and not be repairable at a really inconvenient time.

Don't forget your Entergy Tax Credit.

Yes! Thanks jrb! That will definitely help!