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

Residential Heat Pump Water Heaters
Heating System Interaction Factor
RTF HPWH Subcommittee
November 6, 2014
2
Presentation Outline
• Brief Recap from Last Meeting
• Heating System Interaction Factor
– Problem Statement
– Sensitivity
– Definitions
– Options
– Recommendation
3
Recap from Last Meeting (10/21)
• Presentation and notes from meeting can be found here
• 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.
4
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%
RTF Judgment
Required Ahead
5
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
Electric Storage Tank Water Heaters
Location
Overall
n
Basement
29%
240
Main House
44%
361
Garage
19%
155
Crawl
4%
31
Other
3%
27
Source: RBSA
Is the WH Space Location Conditioned?
Location
No
Yes
Basement
16%
84%
Main House
5%
95%
Garage
92%
8%
Crawl
86%
14%
Other
75%
25%
Overall
30%
70%
Conditioned Space Installation Heat Flows
Cool HPWH
Exhaust Air
Warm
House Air
Tank Heat Losses
• HVAC System Interaction = m*cp*ΔT + QUA
• Typical air Δ T at 68F entering air: ~15F
6
Ducted to Outside, Conditioned Space Heat
Flows
Cool HPWH
Exhaust Air
Added
Infiltration
Load
Warm
House Air
Tank Heat Losses
• HVAC System Interaction = m*cp*ΔT + QUA
• Δ T now depends on outside air T
• m now depends on added infiltration load
7
8
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
9
Sensitivity of Total Savings to Heating
Interaction Factor (%)
Total Energy Savings (Hot Water + Heating), kWh
1,600
Tier 1, Interior
1,400
1,200
Interaction
Factor
1,000
50%
800
75%
600
100%
400
200
HZ1
HZ2
HZ3
Zonal Electric Resistance
HZ1
HZ2
HZ3
Electric Furnace
HZ1
HZ2
Heat Pump
HZ3
10
Sensitivity of Total Savings to Heating
Interaction Factor (%)
Total Energy Savings (Hot Water + Heating), kWh
1,600
Tier 2, Interior (Non-Ducted)
1,400
1,200
Interaction
Factor
1,000
50%
800
75%
600
100%
400
200
HZ1
HZ2
HZ3
Zonal Electric Resistance
HZ1
HZ2
HZ3
Electric Furnace
HZ1
HZ2
Heat Pump
HZ3
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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 0.5.
Heating
Energy
Required
Energy from
Internal
Gains
Gains that just
make you hot
Useful gains
J
F
M
A
M
J
J
A
Useful
S
O
N
D
12
Definition: Interaction Factor
•
•
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
Note: HCƒ different from thermal utility which remains virtually unchanged
Added
Heating Load
HPWH
Fractional
Interaction
HPWH Full
Interaction
J
F
M
A
M
J
J
A
S
O
N
D
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Available Studies
• Field study of HPWH interaction factors was inconclusive
• What we know from PNNL Lab Homes Study1
– 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
1
PNNL. Impact of Ducting on Heat Pump Water Heater Space Conditioning Energy Use and
Comfort. July 2014.
14
PNNL Study – Water Heater Location
PNNL. Impact of Ducting on Heat Pump Water Heater Space Conditioning Energy Use and Comfort. July 2014.
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Heating System Interaction
Factors
•
•
•
RTF Judgment
Required Ahead
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.
II.
III.
2.
PNNL Lab Homes
More detailed assumptions, calculations
Large scale metering and/or billing analyses
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).
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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 HCƒ
– What if HCƒ is not 1 for main living area experiment?
17
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
18
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
19
Additional Research Options (III)
• Large scale field study
– Metering at 100-200 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
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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 U0
• 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
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Interaction Factor: Subcommittee
Recommendation to the RTF
Regarding interior installations and heating interaction
factor:
1.
2.
3.
4.
Recommend as a Proven UES with a heating system interaction
factor (HCƒ) of 75%;
Recommend as a Provisional UES with HCƒ = 75%, and direct staff to
scope a PNNL lab homes study for further heating system
interaction factor research;
Recommend as a Provisional UES with HCƒ = 75%, and direct staff to
scope a large-scale metering study for further heating system
interaction factor research; OR
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.
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Overall Subcommittee Recommendation
(To be filled out on the subcommittee call)
• Garage / unconditioned basement is Proven/
Active, as proposed.
• Interior _______________.
• Sunset Date: 1 year