Heat Pump Water Heaters and Residential Engineering Departments

A few weeks ago the US Department of Energy finalized efficiency requirements for residential electric tank water heaters. The efficiency requirement was last updated in 2010 and is supposed to be revisited every 6 years, but was not done during the 2016-2020 Presidential term. The new requirement will take effect in 2029, and should result in substantially more effort to make heat pumps the default choice for electric homes. The regulation does not mandate heat pumps specifically but most manufacturers will decide that heat pumps, a proven technology, are the most sensible way to increase the efficiency of their product line.

The push by manufacturers is important because water heaters are frequently replaced with little time for the end user to investigate alternatives because the old unit has already failed. We replaced the water heater in our home in 2021, moving from a gas appliance to electric. We had enough time to find an installer in our area familiar with heat pump installation — emeraldECO, in our case — but not everyone will have that amount of time to make a decision.

Having manufacturers make heat pump water heaters be the default means that contractors will need to train their crews to be ready to install heat pump water heaters, or risk losing business. They have to be prepared to explain the technology to their customers, and to help navigate available in incentives and rebates for the devices. It is a way to incentivize the entire supply chain from manufacturer to distributor to contractor to end-user.

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Revisiting an earlier topic: a more sophisticated product installed in the residence brings more complexity in operating the infrastructure. Our heat pump water heater has a Wi-fi connection. It can notify us of faults... and has. It has signaled a blocked overflow pipe as a problem, but following up showed no blockage and no sign of a problem. The design of infrastructure for residential use has to take into account that the property owner won't be knowledgeable about its operation. There won't be an engineering department.

Residences as Utility Infrastructure

The universal first troubleshooting step is to reboot. No matter what the product is, no matter what the problem is, try turning it off and back on &emdash; which is how I found myself figuring out how to reboot a solar inverter. It turns out to be difficult to power cycle something which makes its own power.

When we added solar panels to the roof in 2019 we chose a SolarEdge inverter with an integrated vehicle charger, expecting to never acquire another gasoline car. We have been happily using the SolarEdge inverter to charge the EV we subsequently acquired.

Happily charging until Saturday, that is. I boggled plugging in the car, quickly pulling the plug out and back in without fully intending to. The inverter beeped and the car's indicator lit when first plugged in, then turned off and didn't come on again. There it sat, neither charging nor disengaging no matter what I did. Left a few hours, it just sat there not charging. Plugging it in again the next morning did not change anything.

So: time to reboot the inverter.

Getting an inverter to fully reboot requires cutting power from every source that sneaky thing might use:

1. Turn the switch to disconnect from the photovoltaics.
2. Turn off the breaker where the inverter connects to the house electrical panel.
3. Pull the shutoff switch to disconnect from the grid completely. This would have powered off the whole house were there no batteries.
4. Wait for capacitance in the inverter to drain and all of its LEDs to turn off, then another 60 seconds.

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Commercial buildings have long been responsible for substantial utility infrastructure, from boilers to electrical transformers to, sometimes, subway connections and underground steam tunnels. Residences have typically hosted much less infrastructure, and the equipment has been gradually refined so as to be simple for the homeowner. Ground fault breakers, electric starters for pilot lights, and so on have all been developed to minimize the need for a residence to have to deal with odd failures or dangerous conditions.

The clean energy transition is moving more infrastructure into residences which might once have been exclusively the domain of a service provider. Very few homes have a private gasoline station, but many will have private chargers. Very few homes have generators supplying their electricity, but many will have solar and virtual power plants using residential batteries in unison are already here.

The design of infrastructure for residential use has to take into account that the property owner won't be knowledgeable about its operation. There won't be an engineering department, there won't be anyone paying attention to it. I have on the whole been happy with the inverter and the Powerwell it connects to, but there is more to be done to handle odd cases like this.