Heat Recovery with HPWH
For two years I’ve been planning the house I broke ground on this week and in it, I’ve been planning on going radiant heat with an air to water heat pump and a tankless water heater since I loved the one at my last house.
However, I’m getting cold feet on the radiant due to the price tag that comes with it and I’m now debating about getting a Mr Cool air to air heat pump. I also saw another thread on here recently about a heat pump water heater which I had previously written off due to the enormous cost (>$2000). However, upon looking tonight I found out that NY gives a $2000 rebate which almost completely negates the cost and according to the Energy Star sticker the HPWH should use about $300 less in electricity per year.
My question, would it be worth getting a Doucette Heat Recovery Unit when a heat pump is already so efficient? Also I should probably not tack on this separate question but I will anyway: With inverter HVAC equipment do I still need a soft start device or are they capable of not flickering the lights on their own?
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I have a HPWH, I think it's great.
As for the heat recovery, the way they're typically plumbed is they go on the drain of the shower, and the cold water supply to the shower goes through the heat recovery. With your cold water warmed, you use less hot water to get the same mix temperature. This doesn't really affect the hot water heater. And while HPWH's are more efficient they're still going to be the second biggest user of energy in your house.
That said, I've never installed a heat recovery system or lived in a house with one. They seem like a great idea, yet it also seems like the manufacturers of them are constantly going out of business. So there must be a downside.
I received my first electric bill for our new 2000 sf structure that has a HPWH and a HP for heat. It was $60 for 8 days. If I can run $7-8 per day for heat and hot water, I'll be thrilled.
What about a drain water heat recovery pipe? Super reliable and adds capacity to the water heater for showers
Has anyone rerun the numbers on the drain water heat recovery devices when used with a HPWH? I wonder if they run into the same problem as solar water heaters as PV prices dropped...no longer cost effective.
In NY, I think they'll do really well still - the COP of a HPWH in NY isn't that high due to the heating needs. Plus it's like adding 10G of storage but with a longer lifespan compared to a heater.
Hot Gallons/Day 20
Delta T 70
Annual kwh output 1,249
COP 200%
Annual kwh input 625
DWHR % 50%
DWHR Savings 312
$/kwh $0.25
$ Savings/year $78.07
Good point that it'd be climate dependent.
I think this is the question the original poster is asking. Just googling, it seems that a heat recovery drain that recovers 50% of the heat is about $600. If you can install it as part of new construction the installation cost would be pretty minimal. I think that pays for itself even with a HPWH.
I think I've seen older posts from Dana Dorsett saying one of his favorite benefits to the drain water recovery was the extension of the usable capacity of your hot water. In that regard, it's sort of like insulating beyond code minimum. It's not just about cost recovery, but there is a convenience and comfort factor.
With that said... are there any options that work for slab on grade homes?
Other than putting the shower on the second floor?
Ha, sometimes people build single story homes.
If you look at this unit:
https://www.supplyhouse.com/ThermoDrain-TDH3500B-DR-PEX-52-1-Efficiency-3-x-50-x-3-4-Drain-Water-Heat-Recovery-2-Drain-Couplings-2-Installed-PEX-Fittings
The description says: "This unit may be installed horizontally with a reduced efficiency."
So you could put it under the slab. You'd probably want to insulate it from the ground. What I don't know is whether you'd want it to be accessible or whether you could just bury it and forget it.