Heat Pump Water Heater Support

[mdahlhausen]

Summary Add wrapped-condenser and pumped-condenser heat pump water heater object methods to openstudio-standards.

Background Heat pump water heaters (HPWHs) are a key technology for grid decarbonization. They are currently modeled in openstudio-standards by adjusting the part load efficiency curve for an electric mixed water heater object. This is substantially faster than using a stratified tank method that the residential teams uses to model small wrapped-condenser HPWHs. Small commercial establishments may use a residential-type wrapped-condenser HPWH, while larger establishments use a pumped-condenser HPWH placed outdoors.

Tasks

• [ ] Decide whether to keep the part load efficiency curve adjustment method, or use the stratified tank model
• [ ] Determine standard efficiencies to use for commercial type wrapped-condenser and pumped-condenser HPWHs
• [ ] Determine prevalence of wrapped-condenser and pumped-condenser variants
• [ ] Project future efficiency levels for HPWHs

If using the stratified tank method:

• [ ] update sizing method in openstudio-standards to scale HPWH (current hard-sized for single 80 gal tank)
• [ ] add separate methods for wrapped-condenser and pumped-condenser variants
• [ ] research performance curves for pumped condensers

Notes from 18 Oct 2018 meeting with residential team

• the residential team is considering speed-up methods for wrapped condenser modeling in EnergyPlus, perhaps using a TRNSYS modeling, with a goal to finish this work in 6-12 months ahead of the next major E+ release. They may use our approach of the part load efficiency curve.
• the full residential heat pump water heater measure allows the user to account for ducted units, in the case the water heater condenser exchanges air in a zone it is not physically located in
• a separate task is determine how to model losses from distribution systems for central HPWHs. BEOpt has some methods to handle re-circulation loops.
• performance rating methods for heat pump water heaters use UEF, which is similar to the old energy factor (EF) method, but uses a different draw profile
• 2nd generation heat pump water heaters are much more efficient than 1st generation
• Ben Larson and Jeff Robertson are the main points of contact

[mdahlhausen]

Added with #1420. Additional work would be to add different specifications for HPWHs of different sizes, and breakout larger sizes into a bank of HPWHs.