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Heat Pump Water Heaters: Interior, Ducted Installations

Heat Pump Water Heaters: Interior, Ducted Installations. Presentation to the Regional Technical Forum December 13, 2011. Ben Larson, Ecotope ben@ecotope.com. Background. In October 2011, Provisional UES approved for heat pump water heater (HPWH) for:

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Heat Pump Water Heaters: Interior, Ducted Installations

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  1. Heat Pump Water Heaters: Interior, Ducted Installations Presentation to the Regional Technical Forum December 13, 2011 Ben Larson, Ecotope ben@ecotope.com

  2. Background • In October 2011, Provisional UES approved for heat pump water heater (HPWH) for: • Northern Climate Specification Tier 1 • Buffer space installs • Interior (non-ducted installs) • Northern Climate Spec Tier 2 • Buffer space installs • Northern Climate Spec Tier 2 Interior Installations require exhaust ducting • Left as “TBD” in October • Today’s presentation covers ongoing analysis

  3. Overview • Equipment airflows and installation • Analysis method • Analysis output and findings • Discussion and continued research

  4. Equipment Exhaust Airflows • Flow range of interest: 350cfm to 150cfm • Flow measurements in lab: • Static pressure variation created with damper at duct outlet • Different models have different fans and flow characteristics • Field airflows will depend on specifics of each installation • 4” duct, 10 feet long with 3 elbows at 160 cfm creates 0.72” static pressure

  5. Analysis Inputs • Used the same assumptions as with earlier HPWH analysis • 45 gallons per day of hot water • water temperature rise: 72.5F • results in a little less than 4 hrs per day of runtime for indoor temperatures ranging from ~64F – 78F • house characteristics the same • tightness: 7ach50 • ducts: sealed • 4 HVAC system types • baseline tank EF: 0.92 (50 gallon size)

  6. Analysis Updates • Using updated version of SEEM which allows direct infiltration modeling in combination with exhaust airflows • HPWH exhaust air ducted outside • Water heater runs based on draw schedule • Water heater COP varies as indoor temperature changes • Ex: higher inside T in summertime for houses without cooling gives better performance than wintertime situations

  7. Interior installation temperature range.

  8. DHW Energy Use Only – No HVAC System Interactions • Baseline DHW Energy Use: ~3100 kWh/yr • Measure DHW Energy Use: 1130-1280 kWh/yr • varies because indoor temperature varies with season and climate • DHW Energy Only Savings: 1820-1970 kWh/yr • Houses without cooling have higher summer temperatures and therefore better water heater performance so more savings • HPWH Interior Install Annual COP: 2.3-2.5

  9. Overall Savings Estimates • Impact on house heating + cooling system depends on climate, exhaust airflow, and HVAC system type • Combining DHW energy savings with heating + cooling impact produces the overall energy savings estimate • 5 scenarios in 5 climates considered on next slide: • Interior non-ducted (0 cfm flow to outside) • 4 levels of exhaust ducting to outside • 150, 200, 250, and 300 cfm

  10. Heating System Interaction • CFM is airflow ducted to outside (“0” corresponds to no ducting) • Negative values are a heating system debit

  11. Cooling System Interaction • None for houses without cooling system (Zonal Resistance and Electric Furnace) • Cooling savings for ducted installations nearly negligible but not so for nonducted ones • CFM is airflow ducted to outside (“0” corresponds to no ducting) • Positive values are a cooling system benefit

  12. Analysis Outputs: Savings Estimates DHW Savings Combined with Heat+Cool Interaction

  13. Analysis Caveats • Caution:as yet, analysis does not include performance variation of HPWH with airflow • Performance at lower airflows could be expected to decrease but what is the critical airflow where performance drops significantly? • Space heating heat pump sizing • Analysis used constant size for both measure and base • Ducted HPWHs sometimes increased house load enough to trigger auxiliary resistance heat which shows as a nonlinear response in the heating interaction • Especially relevant for 250-300cfm flows and coldest climates

  14. Measured Airflow Variation Effects • NEEA lab testing of ATI66 at 40F ambient found a decrease in COP of 10% for an airflow decrease from 338 to 177cfm • BPA HPWH lab evaluation observed Voltex compressor performance for 3 flow scenarios at 67F ambient temperature • Full flow: 475 cfm • ⅓ filter area blocked: 372 cfm • ⅔ filter area blocked: 284 cfm  Small changes in performance

  15. Analysis Discussion • Space heating impact (and therefore overall savings) is highly dependent on amount of exhaust airflow • Also, climate dependence due to increased infiltration rate: more outside air at lower temperatures increases heating load • Is there a optimized airflow which might reduce HPWH performance but at the same time provide a minimal space heating impact?

  16. Continued Research – Next Steps • Field Measurements: • NEEA project with 10-15 ducted, indoor installations will measure airflow as installed • Project will also provide incremental install cost estimates • Lab Measurements: • Plans to measure AirGenerate compressor performance at 200cfm and 150cfm at 67F ambient air. • Installation Specification: • Is it desirable to write a spec to limit airflow upon installation? • Analysis for houses with Ductless Heat Pumps • Where is the HPWH? Is it heated by the DHP or the resistance heating system?

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