Allow schedules to be used for water heater deadbands

[jmaguire1]

General Summary

For both mixed and stratified water heaters, the deadband can only be specified as a number. Allowing for a schedule to be used instead would make it easier to model certain types of load shifting events for residential electric water heaters.

Detailed Description

For residential water heaters, CTA-2045 specifies what commands can be sent to a water heater. "Basic Load Add", supported by all versions of the standard, doesn't change the setpoint temperature of the water heater but reduces the deadband to try to force the tank to "top off" without any overheating that may present a safety risk for occupants. "Advanced Load Add" is only supported in "B" versions of the standard and water heaters supporting this command must include an integrated tempering valve, which is less common. I usually use a brief, slight increase in setpoint temperature to fake a "Basic Load Add", but it'd be a lot more straightforward to model if the deadband could be scheduled. That would also mean it could be actuated if someone wants to simulate a controller (like a home energy management system) that might send Basic Load Add signals.

Possible Implementation

No response

[joseph-robertson]

In the case of WaterHeater:Mixed, for example, we would replace the "Deadband Temperature Difference" field with something like "Deadband Temperature Schedule Name" (similar to "Setpoint Temperature Schedule Name")? A constant schedule could then be used for backward compatibility.

Seems a lot like #7360.

[jmaguire1]

That was my idea for this one, yes. Super relevant to this is #11403 (which calls out this issue as one of the use cases). Just changing this to use a schedule and then most users use a Schedule:Constant would resolve my issue here, but there are other examples of where it'd be nice to allow either a number or a schedule, where the number is treated as a Schedule:Constant.