Replies

1. Expert Member
   Akos | Oct 19, 2022 11:19am | #1

   Just to check, you current setup has two tanks. One on the de-superheater and a 2nd resistive tank in line to boost the temperature, you are looking to replace the 2nd tank with a HPWH.

   Realistically your operating cost is low enough (I get about $300/year) that any change until the tank fails has no ROI. When it does fail, a HPWH might be worth it if you can get a rebate, otherwise it is probably hard to justify.

   If the house has a basement and most of the showers drain through a single stack, a large drain water heat recovery pipe might be a better ROI.

2. 
   JeremyPepper | Oct 19, 2022 11:43am | #2

   So, first, thanks for the reply!

   In regards to your comment, we currently only have one tank. No storage tank. The desuperheater is hooked directly to the tank.

   For your follow-up suggestion. I’ve looked at that. We do have a basement. We have several drain lines. The primary drain would require us to cut out and replace drywall. Two secondary drains are very easy to access. As the kids get older one of them will likely split the load.

   My follow-on would be, money no object, any idea if adding the heat pump hot water heater would/wouldn’t lower our usage? If yes, by how much? The question is non-linear to me as I don’t have energy data from back before we had the desuperheater. We also have a new solar array and don’t truly know how much we will get out of it, but… as we plan to go electric with our next vehicle, it could become a cost/benefits analysis. If a heat pump water heater could eliminate, say, 1000 kWh/year of usage, that might allow 25% of an EV’s consumption to be supplied by our current array. Ergo, the reduction could theoretically power the EV so we were offsetting gasoline. Might change the ultimate outcome of the ROI calc. But… I don’t have a feel for how much we stand to benefit.

1. Expert Member
   Akos | Oct 24, 2022 10:40pm | #3

   I took a quick look at Bryant manual for the plumbing connections for a single tank. I think that diagram is wrong, you would want to use the bottom of the tank as input to the desuperheater and the output should go to the cold water inlet on the tank.

   Anyways, if you are using 100kWh/month, the desuperheater is working. I can't see why it would also not work with a HPWH. Since the desuperheater will be adding heat to the tank, there would be a bit less delta T for the HPWH, so I would expect a bit lower efficiency but should still be way better than a resistance tank.

   Since one of these HPWH are now running north of $2k, at least up here in the great white north, it is a pretty expensive way to save 60kWh to 70kWh /month. You are probably better off to add a panel or two to your array.

   "require us to cut out and replace drywall" I know this can seem like a big job, I used to be worried about having to do this. Cutting and patching drywall is simple and quick, a bit of care and quick setting mud means the whole thing can be done in a day. To make it much easier, you have to find the stud and cut along the middle of the stud with one of those oscillating multi tools. These saws tend to make a very clean cut and you can use the drywall piece just cut out to patch the hole. The hardest part is getting the paint to match, lot of times it is simpler to paint the whole wall section especially if the original paint has faded a bit.

2. 
   paul_wiedefeld | Oct 25, 2022 08:45am | #4

   How big is the current hot water heater? Increasing its size could allow the desuperheater to do more of the work.