This document summarizes a study on cold climate air source heat pumps in Minnesota homes. The study found that the heat pumps reduced propane consumption by 60-89% compared to propane furnaces and saved 19-35% on total heating costs. On average, the heat pumps met 84% of homes' heating loads. Preliminary results showed the heat pumps had coefficient of performance values between 1.5-3.5 and annual COPs of 1.4-1.8. While the heat pumps reduced energy costs, upfront installation costs averaging $15,000 were higher than incremental equipment costs compared to air conditioners. Further cost reductions and efficiency improvements are still needed for cold climate air source heat pumps.

1. Cold Climate Air Source Heat Pumps: Study
Update
Ben Schoenbauer, Senior Research Engineer
Better Buildings: Better Business Conference
March 2, 2017

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What We Do
• Energy Program Design & Delivery
• Engineering Services
• Lending Center
• Public Policy
• Research
• Education and Outreach

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Acknowledgements
• These projects are supported in part by grants from the
Minnesota Department of Commerce, Division of
Energy Resources through a Conservation Applied
Research and Development (CARD) program
• The heat pump project was also supported by Great
River Energy and the Electric Power Research Institute

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Learn about…
• The energy savings potential for ASHPs, as well as the
potential for offsetting the reliance on delivered fuels in areas
where natural gas is unavailable
• The differences in ASHP installed performance compared to
the manufacturer specified performance
• The applicability of both technologies to Minnesota’s housing
stock and the process that can be used to determine where
the best potential exists for each technology

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www.mncee.org
Cold Climate Air
Source Heat Pump
Field Assessment

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Agenda
• Cold Climate Air Source Heat Pump
• What is different?
• Opportunity
• Installation and operation
• Preliminary results
• Conclusions

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Cold Climate Air-Source Heat Pump?
• An ASHP uses a refrigerant system
involving a compressor, condenser, and
evaporator to absorb heat at one place and
release it at another.
• Delivery of both heating and cooling via
forced air distribution
• New generation systems can operate as low
as -13 °F
• ASHPs have the potential to deliver energy
and peak saving as well as reduce reliance
on delivered fuels.

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Opportunity
• Winter of 2013/2014 saw delivered fuel shortages in MN
• Delivered fuel expensive or unavailable
• Compensation with electric resistance space heaters
• Market:
• Delivered fuel are the primary space heating fuel for more than 40%
of homes in MN, IA, SD, ND (RECS, 2009)
• Over 25% of Midwest homes rely on fuels other than natural gas for
space heating (RECS, 2009)
• Over 47% of homes in the US rely on fuels other than natural gas for
space heating (RECS, 2009)

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• Primary Heating with LP1
• Metro, < 4%
• Outstate, up to 40%
• Primary Heat Sources2
• Utility gas, 67%
• Electricity, 16%
• LP, 10%
• Fuel Oil, 3%
• Wood, 3%
Source: Levenson-Faulk, Annie. 2015. “Propane Conversion Strategies: Energy Alternatives
for Minnesota Users of Propane Gas.” St. Paul, MN: Legislative Energy Commission
1 U.S. Census Bureau. American Community Survey 5-Year Estimates - 2009-2013
2 U.S. Census Bureau. American Community Survey 5-Year Estimates - 2010-2014
Opportunity - Minnesota

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Utilities and Rebates

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Study Overview
• Field Study
• 6 ccASHP in a variety of MN residences
• 3 installed for the 2015-2016 heating
season
• Monitor installed field performance of
ASHP and backup
• Incorporate into Conservation
Improvement Program (CIP)
• Climate zones 6 & 7

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Instrumentation
1 2 3
4
5
6 7
8 11
12
13
14
15
Power Measurements:
1) Outdoor unit
2) Indoor unit
3) Indoor fan
4) Reversing valve
Temperatures:
5) Supply Air
6) Return Air
7) Mechanical area ambient
8) Conditioned space
Additional:
9) Back up fuel consumption
10) Delivered air flow
11) NOAA data

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Installation
• Important Issues:
• Equipment
• Sizing
• Operation
• Integration with back-up systems

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Site Equipment
Site Number ASHP System ASHP Size ASHP Type Backup
1*
Carrier Infinity with Greenspeed
[25VNA048A003] 4 ton Ducted LP Cond. Furnace
2*
Bryant Extreme Heat Pump
[280ANV048] 4 ton Ducted LP Cond. Furnace
3*
Carrier Infinity with Greenspeed
[25VNA036A003] 3 ton Ducted LP 80% Furnace
4
Trane XV20i
[4TWV0036A] 3 ton Ducted LP Cond. Furnace
5
Mitsibishi Ductless Hyper Heat
[MUZ-FH18NAH] 1.5 ton Ductless Electric Resistance
6
Mitsibishi Ductless Hyper Heat
[MSZ-FH12NA]
1 ton
(2 units) Ductless Electric Resistance
* Installed during 2015-2016 heating season

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Manufacturer Specified Performance
NEEP | Cold Climate Heat Pump Specification

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Cold Climate Specification

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System Design: Sizing
The OAT for the systems
to switch to back up:
4 ton ~3 F
3 ton ~10 F
2 ton ~19F
Percentage of heating
load meet by ASHP:
4 ton ~ 86%,
3 ton ~ 77%
2 ton ~ 60%
3 °F
10 °F
19 °F
3 ton
4 ton
2 ton
House heating load
Targeted a maximum change-over temp of 10 F

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Operation
• Switchover set point:
• Ducted Systems: 10 degrees F
• Ductless Systems: -13 degrees F
• Controls:
• Ducted Systems: automated controls to bring up backup
• Ductless Systems: manual action by homeowner
• Interaction with back-up systems
• Ducted Systems: Integrated installs with shared controls
• Ductless Systems: Separate systems

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Furnace Integration – Keep or Replace?
• Issues:
• Air handler requires a multi-stage fan to achieve the full capability of
the ccASHPs
• Furnace and heat pump require integrated controls
• Proposed Solutions:
• New condensing furnace with control integration
• New 80% AFUE with multi-stage fan with control integration
• Retrofit existing system (future?)
• Plenum electric resistance heater

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Ductless

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Ductless: Install Location

22. Performance: Ducted Systems

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System Operation
• Heating system has 3 modes of operation
• ASHP heating
• Furnace heating
• Defrost
Outdoor Fan OFF
Refrigerant in reverse
Furnace ONDefrost

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ASHP and Furnace Cycle Efficiency, Site 2
• Without propane:
• COPs 1.5 to 3.5
• Furnace SS Efficiency
• 90% +
• Defrost reduces COP
to < 0.5
• ASHP lockout at 10 F

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System COP vs OAT

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System COP vs Furnace runtime

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ASHP Performance
• Rated COPs of
3.0-3.5 at 47 F
• COP observed
• 1.5-3.5 (site 1 & 2)
• 1-3.5 (site 3)

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Example: Capacity on a 17 ⁰F day
At 18:45
OAT = 15 F
House load = 15,300 Btu/hr
ASHP Output = 16,700 Btu/hr
ASHP Sup Temp = 89 F
Airflow = 734 CFM

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Meeting the Load

30. Performance: Ductless Systems

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Daily Performance

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Ductless with Backup

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Ducted v Ductless
• Heat pump only events have comparable COPs
• Ducted systems
• have larger capacities than single head ductless
• have larger airflows
• Ductless systems
• provided a smaller fraction of the homes energy (by design)
• operated at lower outdoor temperatures

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System Airflow

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Air Temperatures

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Energy Use Vs OAT Models

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Preliminary Results
• Compared to LP furnaces the ccASHPs
• Reduced between 40% and 65% of site energy consumption
• Reduced total heating costs 19% to 35%
• On average ccASHP met 84% of the homes heating loads
• Reduced propane consumption by around 60%, up to 89% at one site
• Compared to Electric Resistance Heat
• Provided more efficient space heating (COP of 1.6, compared to 1.0)
• Savings are largely dependent on usage and install location

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Conclusions
• Systems should sized for heating, typically results in 1-ton
larger system that if sized for cooling
• With proper sizing ccASHPs are capable of meeting the loads in
typical MN homes at or below 10 ⁰F outdoor temps.
• Preliminary results show ccASHP COPs of 1.5-3.5 and
annual system COPs between 1.4 and 1.8.

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Conclusions: LP
• ccASHPs will reduce delivered fuel consumption enough to
avoid costly winter refueling in most MN homes.
• 60% to 89% reduction
• Estimate annual usage of for a most homes should be under 375 gal

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Future Needs
• There is still room for improvement:
• Reduce unnecessary back-up heating
• Defrost?
• Lower change over point?
• Reduce upfront installation costs
• Systems with new furnaces cost $15,000
• New LP furnaces with modulating fans ~$5,500
• NREL database ccASHP only ~$7,000
• Costs are much higher than incremental equipment costs compared to
AC systems

41. Ben Schoenbauer:
bschoenbauer@mncee.org

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Policy Work

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Policy Analysis – Minnesota context
• Lack of structure for achieving delivered fuel savings from
ccASHPs for electric utilities
• The fuel switching concern – should not apply in these
scenarios
• Precedents: low income CIP
• New program suggestions
• Net BTU analysis
• Target homes that do not use utility natural gas

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Policy Analysis – Minnesota context
• Kushler, Marty. (2016). Analysis of the Policy Context and
Potential for an Air Source Heat Pump Pilot Program to be
Incorporated into Minnesota’s Energy Conservation Program
Structure for Cooperative Electric Utilities.
• mncee.org/heat_pumps

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ASHP Event w. Defrost

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Annual Energy Use and Costs
Baseline ccASHP Savings per Year
LP Use
(Gal) LP Cost
LP Use
(Gal) LP Cost
Elec. Use
(kWh)
Elec.
Cost Total Cost Cost [%]
Energy
(KBtu) Energy % Propane %
Site 1 1022 $1,320 372 $480 5,406 $649 $1,129
$191
[14%] 41,130 44% 64%
Site 2 928 $1,199 102 $131 5,978 $718 $849
$350
[29%] 55,338 65% 89%
Site 3 1123 $1,450 539 $696 4,051 $487 $1,183
$267
[18%] 39,606 39% 52%
• Payback? TBD! Still gathering data on the incremental cost of replacement
• Assumed costs: LP $1.29/gal, Electric $0.12/kWh