TECHNICAL NOTE MODELED ENERGY AND ECONOMIC PERFORMANCE ASSESSMENT OF A PORTLAND, ME. HOME WITH AN EXISTING OIL-FIRED NON-CONDENSING BOILER AND A TWO-HEAD MINI- SPLIT 38,000 BTU HEAT-PUMP OPERATING IN THREE MODES. JULY 2015 Dr. Thomas Butcher Brookhaven National Laboratory Building 526, P.O. Box 5000 Upton, L. I. NY 11719 Richard S. Sweeter, President EXERGY Partners Corp. 12020 Meadowville Court Herndon, Virginia 20170
Mini-Split Heat Pump Assessment There are several technical and economic assessments of the performance of cold ambient mini-split heat pumps versus oil heating systems with a wide variety of economic and operating assumptions. This brief modeling study was requested by Maine Energy Marketers Association who are seeking to understand how best to apply cold climate mini-split heat-pumps, particularly to existing oil heated homes. 2,500 ft 2 Ranch style home located in Portland, ME was modeled to develop a typical residential load profile for this location. This home is typical "code" construction. It has standard 2X4 stud wall construction, a basement and a peak roof with an R30 insulation level. The home does not use night setback. Setpoint is constant at 70 F for heating. A family of 4 is assumed and domestic hot water use is 63.4 gal/day which is the national average currently used in the DOE water heater test procedure. Table 1 presents the physical parameters used in the model. Table 1 - SUMMARY PARAMETERS Location - Portland, ME Size ft 2 2,500 Family Size - 4 Stories - 1 Envelop - Code compliant DHW Use gal/day 64.3 Setback F/F 70/70 Building Type Residential The three assessed operating modes are: 1. Oil-fired boiler heats the home 2. Oil-fired boiler heats the home in December, January and February and the heat-pump heats the home in all other conditions) 3. Heat-pump heats the home and when the heat-pump is capacity limited the oil-fired boiler supplements the heating. Usually this is accomplished by the heat-pump thermostats being set at a higher temperature that the oil-fired heating system. There are some technical concerns with the concept of operating the oil-fired boiler as a backup to a heat pump in the winter. An oil-fired central hydronic heating system has heat delivery units (baseboard radiators) in all rooms. The heat pump system may include a small number of heat delivery units (e.g. wall mounted cassettes). This may lead to reduced temperature uniformity in the home. Second, under very cold outdoor conditions and with some parts of the home not heated, the combination of cold rooms and potentially low circulation in the hydronic loop can lead to increased potential for frozen and broken pipes. Another consideration is the impact on oil-fired boiler efficiency. These systems have their highest efficiency under high load conditions. Extended operation under low load, heat-pump back-up service can lead to strong efficiency degradation for many systems currently installed. Page 2 of 6
Table 2 provides a summary of the economic results based on a 2.75 per gallon cost for heating oil and 15.5 /kwh residential electric cost. The results of this analysis show that adding heat pumps for heating purposes only is not economically viable. Table 2 - ECONOMICS Assume 38,000 Btu/h mmulti-split with two heads Cap Ex installed HP $8,000 Boiler Efficiency 86% Cost of HO $2.75 Cost of Electrictity /kwh $15.50 Boiler only energy cost $2,330 per year Base Simple payback Boiler Winter & HP Spring/Fall $2,169 per year 50 ye ars HP at capacity Boiler Back-up $2,046 per year 28 ye ars Loan amount Interest Total Avg annual interest 5% 10 year loan $8,000 $2,182 $10,182 $218.23 Boiler only energy cost plus interest $2,330 per year Base Boiler Winter & HP Spring/Fall energy cost plus interest $2,387 per year -139 ye ars HP at capacity Boiler Back-up energy cost plus interest $2,265 per year 123 ye ars Performance Model Brookhaven National Laboratory (BNL) developed an 8,760 hour model of the Maine home. BNL also develop a Heat Pump performance model based on data form the National Renewable Energy Laboratory s 1 cold climate heat pump test data. 1 Laboratory Test Report for Fujitsu 12RLS and Mitsubishi FE12NA Mini-Split Heat Pumps, Jon Winkler, Ph.D., September 2011 Page 3 of 6
Boiler only operation #2 oil HP electricity #2 oil back up Total Oil and Electric #2 Oil Source energy Btu Electricity Source with Oil bu Source Energy energy Btu Btu per year 117,328,629 0 0 117,328,629 127,888,206 0 kw per year 0 0 gallons 847 0 $ per gallon $2.75 $2.75 $/kwh $0.155 Boiler Only $/year $2,330 $0.00 $0 $2,330 BioBlend CO2/gal at 100 Year B0 Heating Oil @ 22.384 #/gallon B5 (3.8% reduction) 21.5334 #/gallon B20 (15.2% reduction) 18.9816 #/gallon B50 (38% reduction) 13,8781 #/gallon Boiler Only lb/yr CO2 Electricity lb/yr CO2 @ 0.722 #/kwh Total Lbs CO2 / year 18,962 0 18,962 18,242 0 18,242 16,080 0 16,080 12,876 0 12,876 Page 4 of 6
Boiler operating in winter (December, January and February) and Heat Pump Spring and Fall #2 oil Winter HP electricity Spring and Fall #2 oil back up Total Oil and Electric #2 Oil Source energy Btu Electricity Source with Oil bu Source Energy energy Btu Btu per year 86,609,715 9,759,885 287,245 96,369,600 94,404,590 29,677,124 kw per year 2,860 2,860 gallons 625 2 $ per gallon $2.75 $2.75 $/kwh $0.155 Boiler Winter HP Spring and Fall $/year $1,720 $443 $6 $2,169 Boiler Winter HP Spring and Fall BioBlend CO2/gal at 100 Year lb/yr CO2 Electricity lb/yr CO2 @ 0.722 #/kwh Total Lbs CO2 / year B0 Heating Oil @ 22.384 #/gallon B5 (3.8% reduction) 21.5334 #/gallon B20 (15.2% reduction) 18.9816 #/gallon B50 (38% reduction) 13,8781 #/gallon 14,044 2,065 16,109 13,510 2,065 15,576 11,909 2,065 13,975 9,537 2,065 11,602 Page 5 of 6
Heat Pump primary heating and Boiler Back-up when HP runs out of capacity #2 oil HP electricity #2 oil back up Total Oil and Electric #2 Oil Source energy Btu Electricity Source with Oil Btu Source Energy energy Btu Btu per year 0 35,015,052 22,955,428 35,015,052 0 127,684,159 kw per year 10,262 10,262 gallons 0 166 $ per gallon $2.75 $2.75 $/kwh $0.155 Heat Pump w Boiler Backup $/year $0 $1,591 $456 $2,046 Bioblend CO2/gal at 100 Year B0 Heating Oil @ 22.384 #/gallon B5 (3.8% reduction) 21.5334 #/gallon B20 (15.2% reduction) 18.9816 #/gallon B50 (38% reduction) 13,8781 #/gallon Heat Pump w Boiler Backup lb/yr CO2 Electricity lb/yr CO2 @ 0.722 #/kwh Total Lbs CO2 / year 3,710 7,409 11,119 3,569 7,409 10,978 3,146 7,409 10,555 2,519 7,409 9,929 Page 6 of 6