Here’s one for the heat pump gurus:
I’m in a townhouse which has a 40 gallon natural gas powered water heater in the attic. Due to the location, nothing larger than a 40 gallon will fit (do have some spare height but no spare width). I just discovered rheem makes a 40 gallon model now (this must be recent? I checked a month or two ago and the smallest was 50). So physically, one could fit (lifting it into the attic is another matter...).
However, electrically the house can’t really support the 30A model, and the 15A one is tricky too. I have about 7 amps of spare capacity according to the load calcs- only 125A service, so I would have to bump the car charging speed down further to something like 24A, which I would rather not do. The 125A service cannot be upgraded without triggering an avalanche of utility upgrades costing tens of thousands of dollars. House is/was all gas appliances, we ripped out the furnace for mini splits, but stove/oven, dryer, and water heater are gas. The house originally had 60A service!
Anyway turns out the current water heater is about a year old. So I have time, obviously. But I have an upcoming project where a nice pathway from attic to garage is open, and the conduit run would be pretty inexpensive to do.
All my neighbors have upgraded to gas tankless. My wife and probably my kids will try to lean heavily to gas tankless when the time comes, but I guess I’ll run this conduit now, just in case. I just doubt a 40 gallon 15A rheem would cut it for a family of 4.
For fun I looked up solar thermal (we have space on the east facing roof for some collectors), but that kinda seems like a dying industry at least in the US residential market. I think we would be back to a 30A traditional electric hot water heater too, as backup.
Yep... you can invest $6k in a solar thermal system that will offset ~70% of your water heating with solar OR invest in a $1500 HPWH and add ~500w to a PV system increasing the cost ~$1500 to offset your water heating 100%. $6k for 70% or $3k for 100%?
Keep in mind that the 15A and 30A requirement is based on the resistance elements for backup heat. The compressor itself uses ~3A. There might be a way to disable the resistance elements. Depending on how long your showers are and how they're spaced I think a 40gal HPWH could probably work with a family of 4 in So. Cal.
Yeah, stay away from solar hot water. Only seems to make sense for heating pools these days. I kind of wonder if solar PV actually makes more sense here as well now that you have 20% efficient solar panels if you could use a heat pump. The size of the heat pump would probably need to be huge compared to the hot water heaters we're talking about.
Didn't realize there was
heat pumps for heating pools!:
One issue I think we're going to have to solve is how to avoid cost prohibitive panel upgrades. With the right demand response your typical house with ~100A service panel could easily handle all the electrification you'd need instead of the 200A panel that code requires since it basically assumes that you need to be able to handle every single appliance and device running at max load (ok, not quite, but pretty much).
In reality, most of the time you are running things at different times, and even if you did have everything running at once, if you could dial down the power for certain appliances or alter the timing, you could easily avoid panel upgrades.
Examples of high power devices that run intermittently and could be good opportunities for smart demand response:
EV Charging - Easiest one here
Dryer - same here, you'd probably be happen to extend run-time if needed
Heat pump water heater - just lock out the resistance elements at times
HVAC - Dial down the power
Oven - how often does this need to run at full power? Only when
Biggest issue with many of these is that they often pull high amounts of power for short periods of time - Oven and your typical single stage HVAC come to mind.
That said, I'm aware of two products that can allow you to add EV charging while sharing existing panel capacity (and to keep this on-topic, add/keep your heat pump water heater!):
DCC-9 and DCC-10 - Turns off EV circuit if main breaker exceeds 80% load. Biggest issue here is that abruptly turning off power is not ideal, IMO. Not sure what the long-term effects of doing this to an EV are.
Dryer Buddy - Basically lets you share your dryer outlet with your EVSE. Has automatic versions that automatically turn off the EVSE if the dryer is on.
I would love to see some sort of standard here with a centralized system that lets you set up priority of appliances and handles power sharing automatically. Also, instead of completely disabling appliances, instead dial down the max current. Think of how multiple Tesla HPWC handles sharing a circuit, but on steroids.
I guess the question is - can you build this cheaper than your typical service panel upgrade?
All of this kind of highlights how an integrated whole house heating/cooling system could probably get some big efficiency gains at least during certain parts of the year - Think Octovalve but for your house.
Of course once we have two Teslas and the third gen wall connector gets a software update, we can power share at might get a few more amps there.
