Better support for dedicated DHW boilers

[shorowit]

If a boiler is used for both space heating and water heating, the WaterHeatingSystem can be of type "space-heating boiler with storage tank" and can point to a HeatingSystem of type boiler. Within the HeatingSystem, one can specify AFUE, fuel type, heating capacity, type of boiler, etc. That's all good.

But if a WaterHeatingSystem is of type "dedicated boiler with storage tank", it's confusing to add the boiler under HVAC/HVACPlant/HeatingSystem (just to access all those properties) since it's not being used for space heating. Some of the needed properties (fuel type, heating capacity) are also available under WaterHeatingSystem but others (AFUE, boiler type) are not.

Perhaps the best non-breaking solution is to add a new DedicatedBoiler element under WaterHeatingSystem where additional boiler properties can be specified?

    <WaterHeatingSystem>
        <WaterHeaterType>dedicated boiler with storage tank</WaterHeaterType>
        <FuelType>natural gas</FuelType>
        <HeatingCapacity>60000</HeatingCapacity>
        ...
        <DedicatedBoiler>                      <!-- new element with children -->
            <AnnualHeatingEfficiency>
                <Units>AFUE</Units>
                <Value>0.8</Units>
            <AnnualHeatingEfficiency>
            <BoilerType>...</BoilerType>       <!-- Copy everything from https://hpxml.nrel.gov/datadictionary/3.0.0/Building/BuildingDetails/Systems/HVAC/HVACPlant/HeatingSystem/HeatingSystemType/Boiler>
        </DedicatedBoiler>

[RockyMtnBrian]

This is great as far as it goes... but one step further could be helpful for multifamily situations.

Some multifamily buildings have an array of dedicated boilers that heat water for a single storage tank. This setup provides redundancy for the hot water system, and allows for servicing/repairs/replacement of individual boilers without disrupting the system.

Ideally the storage tank could have the option of connecting to this array of boilers.