Residential Heat Pump Water Heaters:HVAC Interaction Study

RTF HPWH SubcommitteeMay 14, 2015

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Today’s Agenda

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

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Introduction

• November 2014, RTF directed staff to develop a research plan to study the HVAC interaction effect induced by heat pump water heaters (HPWHs)

• April 2015, RTF accepted a research strategy for studying the HVAC interaction (or thermal coupling) parameter

• 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

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Sensitivity of Total HPWH Savings to HVAC Interaction Factor

HZ1 HZ2 HZ3 HZ1 HZ2 HZ3 HZ1 HZ2 HZ3Zonal Electric Resistance Electric Furnace Heat Pump

-

200

400

600

800

1,000

1,200

1,400

1,600

Tier 1, Interior

50%

75%

100%

Tota

l Ene

rgy

Savi

ngs (

Hot W

ater

+ H

eatin

g), k

Wh

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

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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?

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Question 1

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

Space Heater Portable A/C Unit HPWH

Uncertainty of Equipment Output/Performance Low High High

Cost to Setup and Run Experiment Low Medium High

Ability to Add Cooling Gain to Space (i.e. similar to that of a HPWH) No Somewhat Yes

Ability to Simulate the Magnitude of a HPWH's HVAC Interaction Effect Yes* Yes Yes

* If we can show experimental setup where heating gain produces symmetric HVAC interaction (i.e. as compared to cooling gain)

Equipment Used to Test HVAC Interaction / Thermal Coupling Effect

Equipment Characteristic

Space Heater Portable A/C Unit HPWH

Uncertainty of Equipment Output/Performance Low High High

9 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 0.5.

J F M A M J J A S O N D

Heating Energy Required

Energy from Internal Gains Gains that just

make you hotUseful gains Useful

10 Definition: Interaction Factor

• Interaction Factor = Thermal Coupling• HPWHs are a negative internal gain• HCƒ – 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: HCƒ differs from thermal utility which remains nearly unchanged regardless of a HPWHs thermal coupling

House Heating Loads and Gains

QLoad = UAΔT – QIntGains – Qsolar

QIntGains = QHeatGains + QHPWH

QHeatGains = QRefrig + QTV + QWii + QLights + …

0 2 4 6 8 10 12 14 16 18 20 22 24

UAΔT

QHeatGains

Hour of Day

QLo

ad

Qsolar

Symmetry in Positive and Negative Gains

QLoad = UAΔT – QIntGains – Qsolar

QIntGains = QHeatGains + QHPWH

QHeatGains = QRefrig + QTV + QWii + QLights + …

0 2 4 6 8 10 12 14 16 18 20 22 24

UAΔT

QHeatGains

Qsolar+1kW

-1kW

Hour of Day

QLo

ad

IntGain,i(+) = Decreased thermal load on HVAC from increased internal gains [kWh/day]

IntGain,i(-) = Increased thermal load on HVAC from decreased internal gains [kWh/day]

IntGain,i(+) = IntGain,i(-)

QIntGain,+ = (-1) * QIntGain,-

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.

0 2 4 6 8 10 12 14 16 18 20 22 24

UAΔT

QHeatGains

Qsolar

January

March

+1kW

-1kW

Hour of Day

QLo

ad

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

0 2 4 6 8 10 12 14 16 18 20 22 24

UAΔT

QHeatGains

Qsolar

March

+1kW

-1kW

Hour of Day

QLo

ad

Tin

• 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.

TSet Point

Qsolar

Controlling for Thermal Utility Complications Via Experimental Design

QLoad = UAΔT – QIntGains – Qsolar

QIntGains = QHeatGains + QHPWH

QHeatGains = QRefrig + QTV + QWii + QLights + …

QHPWH = QUAtank + Qcompressor (Qcompressor is negative)

0 2 4 6 8 10 12 14 16 18 20 22 24

UAΔT

QHeatGains

Test when the load is high

+1kW

-1kW

Hour of Day

QLo

ad

IntGain,i(+) = Decreased thermal load on HVAC from increased internal gains [kWh/day]

IntGain,i(-) = Increased thermal load on HVAC from decreased internal gains [kWh/day]

IntGain,i(+) = IntGain,i(-)

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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

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Question 2

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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

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Locations/Conditions of Test Cases (cont’d)

• 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

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Test Case Proposal

Test Case Description Test Location (on Floorplan)

Door Open or Closed?

Purpose of / Reason to Include Test Case

Water Heater Closet A N/A May be most disconnected area from the thermostatUtility Closet B N/A Most connected to the return ductLiving Room C N/A Probably the most connected area to the thermostatMaster Bath, Door Open D Open Highly buffered/disconnected from the thermostatMaster Bath, Door Closed D Closed Even more buffered from the thermostat

AB

CD

CAT recommends all test cases use the same HVAC system (central) for first phase of research.

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Test Case Proposal

• Thoughts from the subcommittee? • Does the subcommittee support this

proposal?

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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: