«May 2016 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States ...»
Heat Pump Water Heater
Ducting Strategies with
Encapsulated Attics in
Climate Zones 2 and 4
M. L. Sweet, A. Francisco, and S. G. Roberts
Partnership for Home Innovation
This report was prepared as an account of work sponsored by an agency of the United States
government. Neither the United States government nor any agency thereof, nor any of their employees,
subcontractors, or affiliated partners makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.
Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.
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U.S. Department of Commerce National Technical Information Service 5301 Shawnee Road Alexandria, VA 22312 NTIS http://www.ntis.gov Phone: 800.553.6847 or 703.605.6000 Fax: 703.605.6900 Email: email@example.com Heat Pump Water Heater Ducting Strategies with Encapsulated Attics in Zones 2 and 4
The National Renewable Energy Laboratory On behalf of the U.S. Department of Energy’s Building America Program Office of Energy Efficiency and Renewable Energy 15013 Denver West Parkway Golden, CO 80401 NREL Contract No. DE-AC36-08GO28308
M.L. Sweet, A. Francisco, and S.G. Robert
iii The work presented in this report does not represent performance of any product relative to regulated minimum efficiency requirements.
The laboratory and/or field sites used for this work are not certified rating test facilities. The conditions and methods under which products were characterized for this work differ from standard rating conditions, as described.
Because the methods and conditions differ, the reported results are not comparable to rated product performance and should only be used to estimate performance under the measured conditions.
iv Contents List of Figures
List of Tables
1 Project Overview
1.1 Problem Statement
1.3 Exhaust Duct Kit
1.4 Introduction to Project Sites
2.1 Research Questions
2.2 Modeling Results
2.3 Monitoring Approach
2.4 Monitoring Equipment
2.5 Monitoring Status
3 Performance Results
3.2 Uncertainty Analysis
3.3 Comparison of Set Point Temperatures
3.4 Combined Site Results
3.5 Effect of Duct Configurations in LaFayette
3.6 Impact on Encapsulated Attic Air Temperature and Humidity
3.7 Effect of Incoming Air Temperature
3.8 Error Induced by Measurement Instrumentation
3.9 LaFayette Survey Results
v List of Figures Figure 1. Exhaust duct kit supplied by A.O. Smith
Figure 2. Typical three-bedroom/two-bedroom duplex floor plan with red circles showing the locations of the HPWHs
Figure 3. Rendering of HPWH critical dimensions
Figure 4. Vertical intake transfer duct leads to a vent in the mechanical closet’s ceiling (left);
horizontal exhaust duct connected to 3-in. × 14-in. rectangular duct inside the wall cavity leading to the HPWH in closet (right)
Figure 5. Test home in Savannah, Georgia
Figure 6. HPWH in encapsulated attic (left); unducted exhaust with 10-ft duct attached (right).
...... 8 Figure 7. Site energy consumption of the typical two- and three-bedroom duplex units in LaFayette, Georgia
Figure 8. Site energy consumption of NCTH in Savannah, Georgia
Figure 9. Monitoring equipment installed on the air intake side of the heat pump
Figure 10. Changes in the HPWH operating mode and tank set point temperature can be seen in the raw data
Figure 11. Processed data of daily HPWH incoming and outgoing water temperatures depicting a change in tank set point temperature.
E1 includes period to the left of the first dashed line. E2 includes period to the right of the second dashed line.
Figure 12. Daily DHW use versus daily COP values for both set points at Savannah E
Figure 13. Bar plot of daily COP values for Savannah showing large deviations across the monitored period
Figure 14. Bar plots of daily COP values of all four units in LaFayette.
The bare areas indicate periods that did not meet all criteria to be considered valid data.
Figure 15. Scatter plot of daily DHW use versus COP for all five units
across the tank
Figure 17. Intake air wet bulb temperature and daily average COP
Figure 18. Intake ducting installation at Site A duct kit installed on the intake side with temperature/RH sensor attached to the grille (left); insulated 8-in.
flex duct connecting the duct to the attic (right)
Figure 19. Intake duct configuration at Site B.
Transfer grille in the ceiling before being removed (left); ducted intake grille and sealed exhaust relief vent (right)
Figure 20. Relief vent grille supplied with the duct kits (left); flexible adhesive strip supplied by A.
O. Smith to seal the relief vent (right)
Figure 21. Intake air temperature of Units A, B, and C over the periods T1 = 8/26/14–9/16/14 and T2 = 9/18/14–10/19/14.
Units A and B had ducted intakes during T2 and Unit C’s intake remained unducted for the entire period (+ indicate outliers).
Figure 22. Savannah E HPWH intake and exhaust temperatures and humidities
Figure 23. Savannah Unit E and F absolute humidities at the high center location of the attic and of the living space
Figure 24. Attic temperatures at five locations around the attic during the summer at Site A.
The circled area can be seen in zoom in Figure 25.
Figure 25. Zoomed section of Figure 24 showing attic temperature changes during HPWH operation
Figure 26. COP as a function of daily DHW consumption and intake air wet bulb temperature.
..... 31 Figure 27. Brass fittings housing the thermocouples measuring outlet (left); inlet water temperatures and flow rate before being insulated (right)
Figure 28. Images of an insulated water meter and thermocouple brass fittings at the LaFayette site; front grille/filter showing obvious signs of debris (right)
Figure 29. Effect of Badger Meter’s thermal mass on water temperature measurements.
............... 33 Figure 30. Histograms of daily average hot water temperatures measured leaving the tank during draw periods. Number of occurrences equals number of days.
Figure 31. Do you avoid taking consecutive showers to prevent running out of hot water?.
.......... 35 vi Figure 32. How often, if ever, do you experience a shortage of hot water while showering or bathing?
Figure 33. How often, if ever, do you experience a shortage of hot water while using the kitchen sink?
Figure 34. I am satisfied with the supply of hot water in my home.
Figure 35. Do you hear noise from the mechanical equipment behind the locked doors in your home?
Figure 36. How often do you hear the operation of mechanical equipment behind the locked doors in your home?
Figure 37. Does the noise disturb your daily activities? If yes, please explain.
Unless otherwise noted, all figures were created by Partnership for Home Innovation.
vii List of Tables Table 1. BEoptE+2.3 Inputs for Three Water Heater Types
Table 2. Model Site Energy Consumption (kWh/yr) and Change from an ERSWH to HPWH.
Negative Values Indicate a Net Gain from ERSWH.
Table 3. Monitoring Equipment and Purpose
Table 4. Timeline of Monitoring Equipment and Dwelling Occupancy Activity.
Units A, B, C, and D Are in Lafayette and Units E and F Are in Savannah.
Table 5. Number of Monitored Days, Number of Occupants, and Average Daily DHW Use for Each Monitored Site
Table 6. Uncertainty for Example Daily Values
Table 7. Unit E Time Frames of Differing Tank Set Points
Table 8. Summary of All Monitored HPWH Daily Average Variables Used To Compute Daily Average COP
Table 9. Date Ranges of Each Site and the Duct Configuration AppliedSite
Table 10. Average Intake and Exhaust Air Temperatures and Absolute Humidities, Measured In Grains per Pound, across the Heat Pump during Operation
Table 11. Statistics of Number of Occurrences of Short DHW Draw Durations
Unless otherwise noted, all tables were created by Partnership for Home Innovation.
ix Executive Summary This study focused on the performance of heat pump water heaters (HPWHs) with several duct configurations and their effects on whole-building heating, cooling, and moisture loads. A.O.
Smith 60-gal Voltex (PHPT-60) HPWHs were included in the final designs at two project sites as an energy-conservation measure. The HPWHs were ducted to or installed within spray-foamencapsulated attics. A.O. Smith has been involved since the early stages of both projects, and its research and development team has provided insight and critical details.
The New Construction Test Homes (NCTHs) at both sites were completed in the beginning of 2013; however, they were not occupied until early 2014. The U.S. Department of Energy’s Building America research team Partnership for Home Innovation partnered with Southface Energy Institute, the LaFayette Housing Authority, and the Housing Department of the City of Savannah to design energy-efficient, affordable housing for this study. LaFayette, Georgia, is situated in the northwestern corner of the state, approximately 30 miles due south of Chattanooga, Tennessee, in the mixed-humid climate (International Energy Conservation Code Climate Zone 4A). The LaFayette site consists of 30 units in 15 duplexes; each has an HPWH installed in the mechanical closet with exhaust ducts to the encapsulated attic and a transfer grille that allows supply air to enter the closet from the attic. The transfer grille and exhaust duct provide sufficient air volume to prevent the cooled air from recirculating.
For this study, the team monitored four NCTH units in two adjacent duplexes, each of which consisted of a two-bedroom unit (1,040 ft2) and a three-bedroom unit (1,245 ft2). Two singlefamily, one-story homes (~1,160 ft2) in Savannah, Georgia, were monitored. Savannah is located on the northern Georgia coast about 15 miles from the Atlantic Ocean in International Energy Conservation Code Climate Zone 2. The HPWH is installed in a spray-foam-encapsulated attic wherein a 10-ft exhaust duct terminates. The exhaust duct was installed to determine its impact on HPWH performance and to prevent cooled air from recirculating. The house adjacent to the test home is of similar size, dimension, and construction, and the encapsulated attic includes an A.O. Smith electric resistance storage water heater (ERSWH). Attic temperature and relative humidity in this neighboring home were also monitored.
Building Energy Optimization E+2.3 models were constructed for the three-bedroom and twobedroom units of the typical duplexes in LaFayette and for the NCTH in Savannah. Duplex units in LaFayette have variable-speed, split-system, air-source heat pumps with a seasonal energyefficiency ratio of 14 and a heating season performance factor rating of 8. The NCTH and neighboring unit in Savannah have ground-source heat pumps with a seasonal energy-efficiency ratio of 18.2 and a coefficient of performance of 3.7. Ducts for every monitored site are located in the encapsulated attics. Site energy use was analyzed for domestic hot water (DHW); cooling;
heating; and a heating, ventilating, and air-conditioning (HVAC) fan/pump in each NCTH.
DHW site energy consumption decreased significantly for the two- and three-bedroom units in LaFayette and the NCTH in Savannah by 1,287 kWh/yr (57%), 1,512 kWh/yr (56%), and 1,536 kWh/yr (62%), respectively, compared to an ERSWH. The cooling site energy consumption of the three models decreased slightly by 59 kWh/yr (10%), 70 kWh/yr (9%), and 97 kWh/yr (11%), respectively, which indicates that the cooling energy consumption decreased because the HPWH could cool and dehumidify air. The heating site energy consumption increased by 123 kWh/yr (11%), 147 kWh/yr (11%), and 88 kWh/yr (11%), respectively, to compensate for the x HPWH cooling air during the heating season. The models indicate that annual total home savings for an HPWH compared to an ERSWH was 1,222 kWh (28%), 1,436 kWh (27%), and 1,568 kWh (37%), respectively, which indicates an increase in savings with increased DHW consumption (because larger dwellings consume more DHW).
Ducted HPWH performance agreed with previous field studies of ducted and unducted HPWHs.