Cold Climate Ductless Heat Pump for Residential Application
Air Source Heat Pump: Cold Climate Design vs. Electric Baseboard Heating
A variable speed ductless air source heat pump (see ID #300) specifically designed to operate at capacity without supplemental heat down to very low temperatures -- as low as -25F.
Item ID: 199
Technical Advisory Group: 2009 HVAC TAG (#2)
Since about 2006, low temperature heat pumps (LTHPs) have been a standard offering in the U.S. from many manufacturers, including several Asian manufacturers. They have tried different approaches, starting with more robust construction, to multiple compressors, to using an inverter to overspeed or run a compressor at speeds exceeding rated speed, to reclaiming heat. Some manufacturers still offer the multiple-compressor method of achieving heating capacity at low temperatures, while others have moved on to heat recovery, resulting in better efficiency.
Unlike standard heat pumps, the cold climate heat pump can provide efficient heating capacity even when it is very cold outside. This capacity allows the designer to eliminate the auxiliary electric backup heat typically found on or in conjunction with heat pump systems in many parts of the country. And even though the efficiency drops from AHRI-listed efficiencies at very cold temperatures, this technology still uses less energy than a conventional heat pump with electric resistance heat. Further, with the variable speed features of the compressor, fans, etc., a designer can select the equipment to meet the load at the cold temperature, knowing that it will modulate performance to meet the load year-round.
Low temperature heat pumps cut defrost time, provide higher efficiencies, have a quicker morning warm up, and have about 30% more heating capacity when compared to standard variable speed heat pumps at cold temperatures.
Baseline Description: Baseboard or Electric Forced Air Furnace heated homes
Baseline Energy Use: 5.9 kWh per year per square foot
The annual average electric space heat by home for Montana and Idaho is 8,437 and 8,629 kWh/year, respectively (Baylon, 2012 Pg 111). With a typical home being of 2,006 sf, the heating use is approximately 4.25 kWh/sf-year. (Note that electrically heated homes include those heated with baseboard heaters, air-source heat pumps, ground source heat pumps, and electric forced air furnaces).
Homes served by electric baseboard heating in the region have an EUI of 17.74 kBtuy/sf-year (or 5.19 kWh/sf-year). The "Residential Building Housing Stock Assessment: Metering Study" does not provide information showing the difference in electrical energy use for homes in Heating Zone #1 versus Zones #2 and #3, but this difference is given in Table #39 for gas forced air furnaces. This gas energy use ratio will be applied to regional homes with baseboard heating to yield an estimate of the annual baseboard heating EUI for homes in Heating Zones #2 and #3. The modified EUI is: 5.19 kWh/sf-year x (32.24/28.14) = 5.94 kWh/sf-year.
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 50%
Low and High Energy Savings: 15% to 70%
Energy Savings Reliability: 6 - Approved Measure
The estimate is for a climate that sees outside air temperatures below 20 degrees about 10% of the hours per year.
Per the Air-Conditioning, Heating and Refrigeration Institute (AHRI) this ET has Integrated Energy Efficiency Ratio's (IEER) in the high teens to mid twenty's. Existing equipment is in the low teens. Energy savings will depend on weather conditions for a given site. As the bulk of the energy used is for heating, a ductless heat pump COP of 3.5 is assumed (Daiken values range from 3.2 to 3.8). This would imply a heating and cooling energy savings of about 71%---given that the whole house electrical heating requirements are served by multiple ductless heat pump heads. But, ductless heat pumps typically are defined as a zonal heating source and are often installed with a single head and thus and do not serve the entire household. In fact, Baylon reports that a ductless heat pump typically provides only 45% to 80% of the space heating in residential DHP retrofits. (from Baylon, "Ductless Heat Pump Engineering Analysis", December, 2012).
With an initial heating load of 5.9 kWh/sf-year, and assuming an average savings of 71% applied to 70% of the heating load, we obtain a post-installation annual energy use of 2.95 kWh/sf-year with a savings of about 5,917 kWh/year with a DHP energy savings of 50%. This savings value will be used in this analysis.
Note: This is a deemed measure under the October 1, 2014 BPA "Energy Efficiency Implementation Manual". The deemed amount is $800 to $1200 per unit depending upon existing heating source (baseboard versus electric forced air furnace).
Energy Use of Emerging Technology:
3 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
This measure will only apply to homes in the colder climate zones, Heating Zones #2 and #3, with over 6000 heating degree days. For the technical potential for BPA, we can only count in the technical potential of those homes currently heated by electrical energy.
According to estimates in the Northwest Energy Efficiency Alliance's (NEEA's) 2011 Residential Building Stock Assessment (RBSA), 34.2% of single-family homes in the Northwest are heated with electricity but only 12.3% with electric baseboard heaters (Baylon, 2012). The Residential Building Stock Assessment also indicates (in a roundabout manner) that about 6.1% of the single-family homes in the region use electric forced air furnaces. As homes with electric forced air furnaces have a greater energy savings potential than do baseboard resistance heated homes, the baseline home square footage is increased by an additional 6.1% x (5,214/3,500) = 9.08% of the total single family home sf. Thus potential energy savings are equivalent to savings due to retrofitting 21.4% of the total housing stock.
We make the simplifying assumption that electrically-heated homes are the same average size as each category of home with all heating sources, so to get an estimate of square footage, we multiply the total square footage of homes times the percentage of homes that are electrically heated by baseboard electric heating and the adjusted number for electric forced air furnaces.
As this heat pump is optimized for cold climates, it is applicable in Heating Zones #2 and #3. The number of single-family households in these zones is 1,265,777 and with an average size of 2,006 sf, the cold climate square footage is taken as 2,539,144,650 sf ( Ecotope, 04/28/2014 Pg 12). Given that only 21.4% of these single-family homes are heated with resistance heat, the available square footage is approximately 543,377,814 sf . Note: this estimate likely overestimates the savings potential as space cooling loads in the Zone #2 and #3 areas likely means that most homes are heated and cooled with heat pumps (rather than employing resistance heat).
Regional Technical Potential:
1.60 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $4.75
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.01
Baseline Technology Unit Cost (Equipment Only): $0.01
Low temperature heat pumps cost about $2,500 to $3,500/ton. Standard variable capacity heat pumps cost about $1,500 to $3,000 per ton. Several sources suggest a price premium over standard efficiency heat pumps of $3,000 to $4,000 per installation (Navigant, for US DOE Building Technologies Program, 2012). This suggests a price premium of about $1.75/sf (cold climate premium) + $3.00/sf (for a 3-ton standard unit) = $4.75/sf.
Simple payback, new construction (years): 17.9
Simple payback, retrofit (years): 17.9
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
The savings are relative to the weather/climate. As the number of hours that heating is needed increases, the savings will also increase. In particular, as the number of hours that supplemental heat is required with other systems, the relative savings offered by the proposed technology also increase.
Low Temperature vs Standard graph: http://www.e3tnw.org/Documents/199_low%20temp%20vs%20standard%20graph.docx
Unlike the standard variable capacity heat pumps, the low temperature heat pump (LTHP) products can provide efficient heating capacity even when it is very cold outside (below 0 deg F). There are inherent losses in any mechanical process; for the refrigeration system, heat is wasted in the flash process at the outdoor coil. This heat can be recovered and diverted to prevent loss of operational capacity at low ambient temperatures. This allows the compressor to operate at higher speeds at low outdoor temperatures, thereby increasing the capacity. Carrier rates their GreenSpeed model line at 18--20 SEER and 12 to 13 HSPF (Navigant for US DOE Building Technologies Office).
Most manufacturers of variable capacity heat pumps offer low temperature heat pumps that can provide 100 % of rated heating capacity down to -8°F to -25°F. This is accomplished using an injection cooling circuit built into the outdoor unit, which actively cools the compressor to maintain the compressor discharge temperature as the ambient temperature falls.
A testing standard allows for comparison between manufacturers and models of equipment. The testing agency for refrigeration equipment is AHRI. AHRI tests and documents the efficiency of equipment under a given set of conditions, and is similar to UL testing for equipment safety. For variable refrigerant flow (VRF) equipment, the AHRI standard is #1230, and can be understood in depth by reading http://www.ahrinet.org/App_Content/ahri/files/standards%20pdfs/AHRI%20standards%20pdfs/1230.pdf.
At standard AHRI rating conditions, residential products can operate with a Heating Seasonal Performance Factor (HSPF) as high as 10.6. Heat pumps with this kind of heating performance at low ambient conditions can eliminate or substantially reduce the need for auxiliary heat in most of the U.S.
Low temperature heat pumps cut defrost time, provide higher COP at cold temperatures, have a quicker morning warm up, and have about 30% more heating capacity when compared to standard variable speed heat pumps at cold temperatures. Unfortunately, these advantages do not always contribute to energy savings. A BPA-sponsored field test of Hallowell cold-climate heat pumps found that they were not superior to a standard air-source heat pump. Coefficients of performance for a unit installed in McCall, Idahowere well below industry standards. A unit installed in Portland, OR performed with a Heating Seasonal Performance Factor (HSPF) of about 7, which is slightly above the pre-2006 federal minimum standard for air-source heat pumps. Poor performance is explained by product design, faulty outdoor temperature sensors, and sizing of equipment relative to heating load.
Most ductless mini-split heat pumps do not come standard with auxiliary heat. The standard practice for retrofitting with ductless heat pumps where zonal electric resistance heat such as baseboards are available is to leave that heating system in place as backup heat for when the compression heat is not viable. For new construction, alternative heat would have to be provided for especially cold conditions.
This technology is available from a few manufacturers at this time. There are more than a few installations where, in the past, the engineer would have had electric strip backup heat in each indoor unit, but these units are performing well without backup heat. Some examples include two churches in the Spokane area, neither of which has auxiliary heat: Christ the King Lutheran Church in Coeur D'Alene has been running for almost a year and Calvary Chapel in North Spokane recently started.
End User Drawbacks:
If the temperature drops below a certain point, this equipment will turn itself off so backup heat may still be required for climates where the outside air temperature can drop below this cutout temperature. This minimum temperature varies by manufacturer, from about -8⁰F to -25⁰F. Therefore, in climates where the outside temperature can drop below the minimum rated temperature for the unit, it would be prudent to include the electric heat backup.
This technology uses less energy to heat a building when outdoor temperatures are below about 35⁰F; however, that savings comes with a 20 to 30% premium on equipment cost.
Operations and Maintenance Costs:
No information available.
Both technologies have an effective life of 15-20 years.
Ground-source heat pumps offer similar efficiencies but at a much higher first cost. Standard ductless mini-split heat pumps along with backup heating – especially as a retrofit where backup heating is already in place – is also an option.
Reference and Citations:
Baylon, et. al.,
2011 Residential Building Stock Assessment: Single-Family Characteristics and Energy Use
Northwest Energy Efficiency Alliance & Ecotope
Ductless Heat Pump Impact & Process Evaluation: Billing Analysis Report
EnergyExperts Q & A
Washington State University Extension Energy Program
Air-Source Heat Pumps
U.S. Department of Energy
Cold Climate Heat Pump Projects at Purdue University & the Living Lab at the new Herrick Labs Building
Purdue University/Herrick Labs
Development of a High Performance Air Source Heat Pump for the US Market
Oak Ridge National Laboratory
Cold Climates Heat Pump Design Optimization
U.S. Department of Energy
Preliminary Market Assessment for Cold Climate Heat Pumps
Sentech, Inc/Oak Ridge National Laboratory
Cold Climate Heat Pump shows promise, but manufacturing delayed
Residential Building Stock Assessment: Metering Study
Northwest Energy Efficiency Alliance