HPWH additional fields

[shorowit]

Some way to describe:

• 120V products (could apply to other appliances like dryers, cooking range, etc. too)
• Shared vs dedicated circuit
• Tempering valve (integrated vs separate, temperature, etc.)
• ???

[jmaguire1]

There's been a few offerings of low power appliances that can run on 120V for the residential market, as a way to electrify without requiring a panel upgrade. Currently, there's three products types of products I'm aware of that have 120V offerings (or will soon):

• Clothes dryers
• Cooking ranges
• Heat pump water heaters

I'm currently tackling 120V HPWH modeling for OS-HPXML, and trying to think of the best way to designate this in HPXML. I think the safest thing would be an explicit 120V/240V element associated with the HPWH object. You could try to infer this from things like the element/HP capacity, but that seems a lot less straightforward than directly identifying the power draw.

To make things a little more complicated, there's also "shared" and "dedicated" circuit versions of 120V HPWHs on the market, at least from one manufacturer. My understanding is per NEC to be "shared" max power draw has to be < 900 W (half of a 15A 120V circuit), which limits how quickly you can reheat the tank. Lab testing shows this matters a lot in terms of recovery time, so it probably makes sense to install a dedicated circuit version if you have the capacity (which is probably the minority of homes).

To deal with that, maybe we have an optional "shared"/"dedicated" option if it is 120V, with the default being shared if not provided? Shared is more what people think of when they think of 120V appliances, but the extra recovery could be a big deal and so if I were looking to do this and had the panel capacity, I'd probably opt for a dedicated circuit version.

The one other thing we'll want to deal with as part of modeling 120V HPWHs is that they frequently overheat (to 140F) and include a mixing valve with a separate setpoint (125F by default). I see HPXML has a "HasMixingValve" element along with "HotWaterTemperature", but is there any way to set the mixing valve temperature? We could default it to 125F, but my understanding is users can actually change the mixing valve temperature, which is closer to what they get out of the tap, rather than the setpoint temperature to boost the energy stored and make a cold shower less likely. Is it worth adding a mixing valve setpoint if a mixing valve is specified, rather than just saying one exists and assuming it's setpoint?