Residential Heat Pump Water Heaters Heating System Interaction Factor RTF HPWH Subcommittee November 6, 2014

Presentation Outline Brief Recap from Last Meeting Heating System Interaction Factor – Problem Statement – Sensitivity – Definitions – Options – Recommendation 2

Recap from Last Meeting (10/21) Presentation and notes from meeting can be found herehere Summary of topics and direction from subcommittee: – Model calibration The subcommittee agreed that the HPWH model developed within SEEM was sufficiently calibrated for the purposes of estimating a UES. – How to treat the impending federal water heater standard The subcommittee agreed to assume the federal standard goes into effect now (instead of April 2015). They thought that the staff resources to develop multiple measure sets was not worth the effort and could be cumbersome for programs. – Whether to have an "any size" tank measure or separate small/large tank measures The subcommittee agreed that an "any size" measure based on the weighting of small and large tanks in the region was appropriate. A relatively short sunset date (~1 year) should be used to monitor market shifts in average tank size. – Valuing self-install labor at zero cost The subcommittee agreed to defer this discussion to the broader RTF, since it relates to the Guidelines and many measures in addition to HPWH. – HVAC interaction The subcommittee ran out of time and did not reach a recommendation. Subcommittee agreed to meet again to discuss this item. 3

Staff Highlighted Areas HVAC interaction factor (interior installs only) – Provisional measure assumed full HVAC interaction (100%); provisional research was inconclusive on this – Analysts believe average value likely falls between 50 and 100% – Should we use an assumption in this range OR pursue additional research? If we use an assumption, analysts suggest 75% 4 RTF Judgment Required Ahead

Heating System Interaction Applies only to interior ducted or non-ducted installations (i.e. garage and unconditioned basement installs are excluded from this discussion) Heat pump water heaters extract heat from the space where they are installed. Some of that heat energy is replaced by the heating system. We have observed that not every unit of energy removed from the air by the HPWH is replaced by the heating system 5 Electric Storage Tank Water Heaters LocationOveralln Basement29%240 Main House44%361 Garage19%155 Crawl4%31 Other3%27 Is the WH Space Location Conditioned? LocationNoYes Basement16%84% Main House5%95% Garage92%8% Crawl86%14% Other75%25% Overall30%70% Source: RBSA

6 HVAC System Interaction = m*c p *ΔT + Q UA Typical air Δ T at 68  F entering air: ~15  F Warm House Air Cool HPWH Exhaust Air Tank Heat Losses Conditioned Space Installation Heat Flows

7 HVAC System Interaction = m*c p *ΔT + Q UA Δ T now depends on outside air T m now depends on added infiltration load Warm House Air Cool HPWH Exhaust Air Tank Heat Losses Ducted to Outside, Conditioned Space Heat Flows Added Infiltration Load

Localized Cooling – Temperature Depression “Interior Ducted to Outside” (left) case exhausts air outside – no (or much less?) localized cooling so use as reference case “Interior Non-Ducted” (right) case shows lower average air temperatures – Approximately 8F colder across our study set 8

Sensitivity of Total Savings to Heating Interaction Factor (%) 9 Interaction Factor

Sensitivity of Total Savings to Heating Interaction Factor (%) 10 Interaction Factor

Definition: Thermal Utility Thermal Utility – The ratio of useful internal heat gains that offset a heating requirement to total gains – Example: Heating is required in a house for 6 months of the year Internal gains are 2,000 kWh/yr  Useful gains are 1,000 kWh/yr. Thermal utility is J F M A M J J A S O N D Heating Energy Required Energy from Internal Gains Gains that just make you hot Useful gainsUseful

Added Heating Load Definition: Interaction Factor HPWHs are a negative internal gain HC ƒ – heating and cooling interaction factor (0% - 100%) – What fraction of the maximum possible interaction is “seen” by the HVAC system? – Primary hypothesis for the value being less than 100%: HPWH is located in a space that’s somewhat coupled to the outside HPWH extracts heat and sometimes that heat comes directly from outside Note: HC ƒ different from thermal utility which remains virtually unchanged 12 J F M A M J J A S O N D HPWH Fractional Interaction HPWH Full Interaction

Available Studies Field study of HPWH interaction factors was inconclusive What we know from PNNL Lab Homes Study 1 – Interaction factor for interior HPWH installations ≈ 49% – Interaction factor for ducted HPWH installations ≈ 44% – Study looked at one installation of a HPWH in a closet next to an exterior wall 13 1 PNNL. Impact of Ducting on Heat Pump Water Heater Space Conditioning Energy Use and Comfort. July 2014.Impact of Ducting on Heat Pump Water Heater Space Conditioning Energy Use and Comfort

PNNL Study – Water Heater Location PNNL. Impact of Ducting on Heat Pump Water Heater Space Conditioning Energy Use and Comfort. July 2014.Impact of Ducting on Heat Pump Water Heater Space Conditioning Energy Use and Comfort 14

Heating System Interaction Factors Houses are not single zones (no surprise) The HPWH install zone can thermally “decouple” to varying degrees from thermostated part of house What to do on interaction factor? 1.Consider more research to further explore this value. Options: I.PNNL Lab Homes II.More detailed assumptions, calculations III.Large scale metering and/or billing analyses 2.Assume a value. If a value is assumed: Assume same value for ducted and unducted installs – (When you don’t know something, make the simplest estimate) Assume same value for zonal and central heating systems – Across PNW, about half of interior, electric water heater installs are in zonal houses and half are in centrally heated houses Analyst proposal is to use 75%. – The PNNL study looked at a particular installation (next to an exterior wall) which is likely to yield a lower than average value. – The PNNL study did not consider occupant interaction (i.e. the possibility of raising the house’s t-stat setting to overcome a cold zone caused by the HPWH). 15 RTF Judgment Required Ahead

Additional Research Options (I) PNNL Lab Homes Study – Install 1kW space heaters in four different locations within lab homes. Main living area near thermostat Master bathroom (a distant zone) Kitchen ??? Bedroom ??? – Operate heaters on a schedule similar to HPWHs. – Observe change in space heating requirement Experimental period: 5-10 days per location – Cost: < $100,000 (?) – Outcomes & Caveats Results from four locations could help bound the value for HC ƒ – What if HC ƒ is not 1 for main living area experiment? 16

Additional Research Options (IIa) Temperature-depression correlation study – Use existing data from both PNNL lab homes and HPWH field studies – Lab homes show a known temperature depression and a known heating interaction Associate an X degree temperature difference with a Y amount of interaction for lab homes Scale field study homes accordingly – Required assumptions Temperature difference is a surrogate for interaction Zero temperature difference = 100% interaction Both scale linearly – Are the results generalizable? We have only ~15 cases in the field study to use – Are the required assumptions reasonable? Analysts say no 17

Additional Research Options (IIb) Caution: No option guaranteed to add more certainty than we have now Hand calculations – Balance heat flow in to HPWH zone from interior with heat flow to exterior and heat extracted by HPWH – To solve, need to assume or know: Conductance & Area between house and HPWH zone Air temperature in house and HPWH zone Conductance & Area between HPWH zone and outside Rate of heat removal from air in HPWH zone Mass of air in HPWH zone Informed modeling – Use a multi-zone heat transfer model Requires making the exact same assumptions as for the hand calculations – Potentially integrate with whole-house simulations to test against Delphi panel – Assemble national experts on HPWHs Combinations of the above 18

Additional Research Options (III) Large scale field study – Metering at sites using a flip-flop protocol Random / representative sample Half year in ER only mode Half year in heat pump mode Measure heating system, outdoor temperature, & DHW energy on a daily basis Cost: $500,000 to $1,000,000 ? – Potentially applicable to other heating & cooling interaction measures (lighting, appliances, etc) – Need caution in study design because signal here is relatively small 19

Other Notes Phase I SEEM Calibration implemented – Of minor importance (only impacts space heating interaction) – For simplicity, used a full insulation retrofit package to set the building U 0 Phase II SEEM Calibration implemented – Non-utility fuel accounted for Water heater scavenges some heat from the wood stove so we don’t see an electric grid penalty but we do need to buy more wood Cooling interaction ignored as of this time – ~30-50kWh/yr 20

Interaction Factor: Subcommittee Recommendation to the RTF Regarding interior installations and heating interaction factor: 1.Recommend as a Proven UES with a heating system interaction factor (HC ƒ ) of 75%; 2.Recommend as a Provisional UES with HC ƒ = 75%, and direct staff to scope a PNNL lab homes study for further heating system interaction factor research; 3.Recommend as a Provisional UES with HC ƒ = 75%, and direct staff to scope a large-scale metering study for further heating system interaction factor research; OR 4.Recommend ________________________________________ Christian, Adam, and Ben recommend option 2 above. Reason: Less costly research may bound the interaction factor to an acceptable degree, thereby not requiring further, more costly research. If this turns out not to be the case, further, more costly research may be pursued at that time. 21

Overall Subcommittee Recommendation (To be filled out on the subcommittee call) Garage / unconditioned basement is Proven/ Active, as proposed. Interior _______________. Sunset Date: 1 year 22