Residential Heat Pump Water Heaters: HVAC Interaction Study RTF HPWH Subcommittee May 14, 2015

Today’s Agenda Brief recap and context for today’s meeting Present and discuss key questions Work towards subcommittee recommendation on both questions 2

Introduction November 2014, RTF directed staff to develop a research plan to study the HVAC interaction effect induced by heat pump water heaters (HPWHs) November 2014 April 2015, RTF accepted a research strategy for studying the HVAC interaction (or thermal coupling) parameter April 2015 NEEA has agreed to sponsor and fund (or co-fund) this research, but has asked the RTF subcommittee to weigh in on some of the final technical details of the PNNL Lab Homes study 3

Sensitivity of Total HPWH Savings to HVAC Interaction Factor 4 Interaction Factor +/- ~20%

Research Strategy: PNNL Lab Homes (from April 2015 RTF meeting) Research Goal – Observe the space conditioning energy interaction that results from the installation of a HPWH in interior spaces Data Collection – PNNL Lab Home Study: Test four install locations throughout home Use 1kW space heaters and operate on a schedule similar to HPWHs 5-10 days per location Analysis – Compute change in space heating requirement and HVAC interaction factor for each location – Observe range of results; depending on range, results may be combined (averaged) if within a narrow band, or results could point to needing additional measure identifiers

Key Questions for Today 1.What equipment should be used to induce the localized temperature change in the experiment home? 2.What locations and conditions should be tested in the experimental home? 6

Question 1 7

Equipment to Induce Temp Effect 8 What equipment should be used to induce the localized temperature change in the experiment home?

Definition: Thermal Utility Thermal Utility – Tells you if “waste heat” is useful or not – The ratio of useful internal heat gains to total gains that offset a heating requirement – 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

Definition: Interaction Factor Interaction Factor = Thermal Coupling 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 How much of the heat removed by the HPWH is realized as an internal gain/loss? Note: HC ƒ differs from thermal utility which remains nearly unchanged regardless of a HPWHs thermal coupling 10

House Heating Loads and Gains Q Load = UAΔT – Q IntGains – Q solar Q IntGains = Q HeatGains + Q HPWH Q HeatGains = Q Refrig + Q TV + Q Wii + Q Lights + … UAΔT Q HeatGains Hour of Day Q Load Q solar

Symmetry in Positive and Negative Gains Q Load = UAΔT – Q IntGains – Q solar Q IntGains = Q HeatGains + Q HPWH Q HeatGains = Q Refrig + Q TV + Q Wii + Q Lights + … UAΔT Q HeatGains Q solar +1kW -1kW Hour of Day Q Load Q IntGain,+ = (-1) * Q IntGain,-

Thermal Utility Complications in Measuring Thermal Coupling If thermal utility is not constant: thermal coupling can’t be measured positive and negative gains are not symmetric UAΔT Q HeatGains Q solar January March +1kW -1kW Hour of Day Q Load House floats off set point and the +1kW internal gains are no longer useful – their thermal utility changed. Moreover, the change in areas between the dashed March line and the red and blue lines is now different – the gains don’t have a symmetric utility Doh!

Complications: A More Nuanced View UAΔT Q HeatGains Q solar March +1kW -1kW Hour of Day Q Load T in House floats off set point. Load changes. Heat loss increases over that time period. Drywall stores heat. Sun goes away. Some, but not all heat returned to house as it “coasts” back to set point. T Set Point

Q solar Controlling for Thermal Utility Complications Via Experimental Design Q Load = UAΔT – Q IntGains – Q solar Q IntGains = Q HeatGains + Q HPWH Q HeatGains = Q Refrig + Q TV + Q Wii + Q Lights + … Q HPWH = Q UAtank + Q compressor (Q compressor is negative) UAΔT Q HeatGains Test when the load is high +1kW -1kW Hour of Day Q Load

Equipment to Induce Temp Effect What equipment should be used to induce the localized temperature change in the experiment home? CAT Proposal: space heater Least uncertainty in thermal output Easiest and cheapest to implement Produces symmetric HVAC effect if studied under the proper conditions A generic load that can represent other measures that interact with HVAC equipment 16

Question 2 17

What locations and conditions should be tested in the experiment home? Example Locations: BDRM-2, Master bath closet, near thermostat Example Conditions: door open or closed (if applicable), central/zonal heat Locations/Conditions of Test Cases 18

Locations/Conditions of Test Cases (cont’d) 19 Each test case will be run for a period of 5-10 days A minimum outdoor air temperature during test period should be required in order to ensure symmetry effect Test cases should represent a wide range of a space’s “connectedness” to the thermostat – E.g. space near thermostat should be highly connected – Spaces far away and/or highly buffered from thermostat will likely be less connected Test cases should be generic and test the expected range of HVAC interaction factors to the extent possible – E.g. a test case in the living room near the thermostat does not suggest HPWHs being installed in a living room, but rather attempts to place a “book end” on the factor of interest – Not all cases can be directly tested, e.g. a heated basement CAT proposes a phased approach to the research – First phase serves as proof of concept and may be sufficient on its own – Additional phases could be added to study additional scenarios – Additional reasons to phase research: peak season is only so long, other competing projects for PNNL Lab Homes

Test Case Proposal 20 Test Case DescriptionTest Location (on Floorplan) Door Open or Closed? Purpose of / Reason to Include Test Case Water Heater ClosetAN/AMay be most disconnected area from the thermostat Utility ClosetBN/AMost connected to the return duct Living RoomCN/AProbably the most connected area to the thermostat Master Bath, Door OpenDOpenHighly buffered/disconnected from the thermostat Master Bath, Door ClosedDClosedEven more buffered from the thermostat A B C D CAT recommends all test cases use the same HVAC system (central) for first phase of research.

Test Case Proposal Thoughts from the subcommittee? Does the subcommittee support this proposal? 21

Subcommittee Recommendation 1.What equipment should be used to induce the localized temperature change in the experiment home? Subcommittee recommendation: 2.What locations and conditions should be tested in the experimental home? Subcommittee recommendation: 22