An In-Depth Look at Ground 

Source Heat Pumps and 

Other Electric Loads in Two 

GreenMax Homes

Srikanth Puttagunta and Carl Shapiro 

Consortium for Advanced Residential Buildings

April 2012 
ii

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iii

An In-Depth Look at Ground Source Heat Pumps and Other 

Electric Loads in Two GreenMax Homes

Prepared for: 

Building America

Building Technologies Program 

Office of Energy Efficiency and Renewable Energy 

U.S. Department of Energy 

Prepared by:

Srikanth Puttagunta and Carl Shapiro 

Steven Winter Associates, Inc.

of the 

Consortium for Advanced Residential Buildings (CARB) 

61 Washington Street 

Norwalk, CT 06854 

NREL Technical Monitor: Cheryn Engebrecht 

Prepared under Subcontract No. KNDJ-0-40342-00

April 2012 
iv

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v

Contents

List of Figures ............................................................................................................................................ vi

List of Tables ............................................................................................................................................. vii

Definitions................................................................................................................................................. viii

Executive Summary.................................................................................................................................... x

1 Introduction........................................................................................................................................... 1

1.1 Demonstration Homes .........................................................................................................1

1.2 Research Questions..............................................................................................................5

1.3 Expected Energy Savings Over Building America Benchmark ..........................................5

1.4 Partners ................................................................................................................................5

2 Energy Consumption Overview .......................................................................................................... 6

2.1 Energy Consumption Breakdown........................................................................................6

3 Ground Source Heat Pump.................................................................................................................. 9

3.1 Ground Source Heat Pump Efficiency Metrics .................................................................10

3.1.1 Heating Coefficient of Performance ......................................................................11

3.1.2 Domestic Hot Water Coefficient of Performance..................................................11

3.1.3 Cooling Energy Efficiency Ratio...........................................................................12

3.2 Ground Source Heat Pump Monitoring Results................................................................12

3.2.1 Space Conditioning................................................................................................13

3.2.2 Ground Conditions.................................................................................................16

3.2.3 Indoor Comfort ......................................................................................................17

3.2.4 Domestic Hot Water ..............................................................................................18

3.2.5 Desuperheater ........................................................................................................22

3.2.6 Drain Water Heat Recovery...................................................................................23

4 Photovoltaic System Performance ................................................................................................... 24

5 Lighting, Appliances, and Miscellaneous Electric Loads .............................................................. 26

5.1 Lighting..............................................................................................................................29

5.2 Appliances..........................................................................................................................31

5.3 Miscellaneous Electric Loads............................................................................................33

5.3.1 Standby Energy Use...............................................................................................34

6 Conclusions ........................................................................................................................................ 35

References................................................................................................................................................. 37
vi

List of Figures

Figure 1. GreenMax home in Black River Falls, Wisconsin.................................................................... 2

Figure 2. GreenMax home in Stoughton, Wisconsin............................................................................... 3

Figure 3. Site energy consumption by end use for Black River Falls home......................................... 7

Figure 4. Site energy consumption by end use for Stoughton home ................................................... 7

Figure 5. Site energy consumption by end use for average home in Midwest – East North Central. 7

Figure 6. Mean monthly site energy component breakdown and generation of Black River Falls 

home ...................................................................................................................................................... 8

Figure 7. Mean monthly site energy component breakdown and generation of Stoughton home .... 8

Figure 8. Black River Falls GSHP system................................................................................................. 9

Figure 9 Installation of ground loop at Stoughton residence .............................................................. 10

Figure 10. Measured versus literature COP of Black River Falls GSHP for space heating............... 14

Figure 11. Measured versus literature EER of Black River Falls GSHP for space cooling ............... 14

Figure 12. Measured versus literature COP of Stoughton GSHP for space heating ......................... 15

Figure 13. Measured versus literature EER of Stoughton GSHP for space cooling.......................... 15

Figure 14. Mean daily ground temperature of the Stoughton home ground source field loop ........ 16

Figure 15. Buffer tank and storage tank in Stoughton home ............................................................... 19

Figure 16. DWHR in Stoughton home..................................................................................................... 19

Figure 17. Schematic of GSHP/DHW systems at Black River Falls home .......................................... 19

Figure 18. Schematic of GSHP/DHW systems at Stoughton home ..................................................... 20

Figure 19. Measured versus literature COP of Black River Falls GSHP DHW mode ......................... 21

Figure 20. Measured versus literature COP of Stoughton DHW GSHP............................................... 21

Figure 21. Water heating component breakdown for Black River Falls home in January ................ 22

Figure 22. Stoughton PV system............................................................................................................. 24

Figure 23. Black River Falls PV system .................................................................................................. 24

Figure 24. Black River Falls LAMEL breakdown (kWh/yr) .................................................................... 27

Figure 25. Stoughton LAMEL breakdown (kWh/yr) ............................................................................... 28

Figure 26. Normalized hourly lighting profile comparison (Black River Falls)................................... 30

Figure 27. Hourly normalized energy use profile comparison for major appliances......................... 32

Figure 28. Monthly seasonal multipliers comparison for major appliances....................................... 32

Figure 29. Hourly normalized energy use profile comparison for MELs ............................................ 33

Figure 30. Monthly seasonal multipliers comparison for MELs .......................................................... 34

Unless otherwise noted, all figures were created by CARB.
vii

List of Tables

Table 1. Climate Information...................................................................................................................... 2

Table 2. Building Specifications for Test Homes .................................................................................... 4

Table 3. Source Energy Savings over BA B08 Benchmark .................................................................... 5

Table 4. Average Annual Energy Consumption and Generation by House.......................................... 6

Table 5. Rated Efficiencies of GSHP Models.......................................................................................... 10

Table 6. Measured Efficiency of GSHPs ................................................................................................. 12

Table 7. Rated Versus Measured System Efficiencies.......................................................................... 13

Table 8 Floor-to-Floor Temperature Variations (∆T = 2nd Floor – 1st Floor) ........................................ 18

Table 9. Water Heating Contribution by Source .................................................................................... 20

Table 10. PV System Performance Comparison to Modeled Values ................................................... 25

Table 11. Annual Lighting Electric Use Comparison at the Black River Falls Home (kWh/yr) ......... 29

Table 12. Yearly Major Appliance Electric Use Comparison (kWh/yr)................................................. 31

Table 13. Daily Standby Energy Use (Wh).............................................................................................. 34

Unless otherwise noted, all tables were created by CARB.
viii

Definitions

ACH50 Air changes per hour at a test pressure of 50 Pascal

ACHnatural Estimation of air changes per hour under natural operating conditions

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning 

Engineers

BA Building America 

BEopt Building Energy Optimization

Btu British thermal unit

CARB Consortium for Advanced Residential Buildings

CDD Cooling degree day

cfm Cubic feet per minute

cfm50 Cubic feet per minute at a test pressure of 50 Pascal

COP Coefficient of performance

DHW Domestic hot water

DOE U.S. Department of Energy 

DWHR Drain water heat recovery

EGUSA EnergyGauge USA

EER Energy efficiency ratio

ERV Energy recovery ventilator

FFA Finished floor area

FGB Fiberglass batt

gpm Gallons per minute

GSHP Ground source heat pump

HDD Heating degree day
ix

HSP House Simulation Protocol

HVAC Heating, ventilation, and air conditioning

ISO International Standards Organization

kWh Kilowatt-hour

LAMEL Lighting, appliances, and miscellaneous electric load

LED Light-emitting diode

MEL Miscellaneous electric load

NREL National Renewable Energy Laboratory 

PV Photovoltaic 

RECS Residential Energy Consumption Survey

SHGC Solar heat gain coefficient

W Watt

Wh Watt-hour
x

Executive Summary

The U.S. Department of Energy’s (DOE) Building America program continues to seek further 

confirmation of the true performance of homes and advanced mechanical systems through actual 

long-term field monitoring. Extensive monitoring of occupied homes provides valuable data that 

simply cannot be duplicated through laboratory tests and energy modeling.

Ground source heat pumps (GSHPs) are often touted as one of the most efficient, sustainable 

system choices for heating and cooling of homes. A DOE Energy Efficiency and Renewable 

Energy Web page, for example, claims that GSHPs have coefficients of performance (COPs) 

between 3.0 and 6.0 on winter design days:

Geothermal heat pumps (GHPs) use the constant temperature of the earth 

as the exchange medium instead of the outside air temperature. This 

allows the system to reach fairly high efficiencies (300%-600%) on the 

coldest of winter night (EERE 2011).

Although there is much anecdotal evidence, both supporting and detracting from GSHPs, few

data document in-situ performance of GSHPs in homes. As a result of market penetration to date, 

the Building America Program has a limited number of monitored sites that provide documented 

performance data.

Similarly, there are few in-situ data about LAMELs (lighting, appliances, and miscellaneous 

electric loads) in residences. The TIAX U.S. Residential Information Technology Energy 

Consumption in 2005 and 2010 report is the most thorough information about items that make up 

LAMELs (Roth et al. 2006), but the use patterns are calculated based on equations and are not 

specifically monitored. Some studies, such as the Energy Information Agency Residential 

Energy Consumption Survey (EIA 2005), did homeowner surveys to estimate use patterns, but 

respondents may believe their uses are different than actual monitored data. 

The Consortium for Advanced Residential Buildings (CARB) partnered with WPPI Energy to 

answer key research questions about in-field performance of GSHPs and LAMELs through 

extensive field monitoring at two WPPI GreenMax demonstration homes in Wisconsin. CARB 

installed extensive monitoring equipment in each home to record the energy use of major 

equipment at 15-min intervals. Monitored loads include space conditioning, water heating, 

washer/dryer, microwave oven, coffee maker, range/stove, dishwasher, lighting, and plug loads.

CARB developed a monitoring protocol for GSHPs to effectively quantify the whole-system 

performance of these units, accounting for the ground loop pump, ductwork, and desuperheater. 

The National Renewable Energy Laboratory is revising this testing protocol into a formal 

document to be published next year.

These two test home evaluations provided valuable data about the true in-field performance of 

various building mechanical systems and LAMELs. This information, though a small sample set, 

validates the Building America House Simulation Protocol’s homeowner use patterns.
xi

The measured steady-state heating coefficient of performance (COP) for low- and high-stage 

operation of the Black River Falls GSHP system was 3.1, which is 31% and 23% less than the 

rated unit efficiency, respectively. The steady-state cooling energy efficiency ratio for the low 

stage was 18.1 and for the high stage was 15.9, which is 23% and 14% less than the rated unit 

efficiency, respectively.

The measured steady state heating COP for low and high stage operation of the Stoughton GSHP 

system was 2.7, which is 47% and 36% less than the rated unit efficiency, respectively. The 

steady-state cooling energy efficiency ratio for the low stage was 16.7, which is 44% less than 

the rated unit efficiency. This system rarely operated in high-stage cooling.

The water heating configurations varied significantly between the two homes. The measured 

COPs for water heating ranged from 1.5 to 3.0; impacts of the different system configurations 

are discussed more thoroughly in Section 3.2.4. The drain water heat recovery systems at these 

homes provided a passive 5%–10% contribution to water heating. 

Though the 2005 Residential Energy Consumption Survey data suggest that LAMELs are on 

average 26% of the overall electricity use in Midwest homes, both of these homes have higher 

percentages of LAMEL electricity consumption. The Black River Falls home is at 34% and the 

Stoughton home is at 41%. As the most efficient lighting and appliances available today have 

been installed in these homes, much of this electricity consumption falls under miscellaneous 

electric loads (MELs). For the Black River Falls home, MELs are roughly 17% (9% from outlets 

and 8% from other sources). For the Stoughton home, MELs are roughly 20% of the overall 

electricity use. As technology continues to inundate our lives, the entertainment center is 

becoming a larger energy hog. The Black River Falls home had roughly 12.4 % of its LAMELs 

electricity use or 4.2% of its overall electricity use attributed to the primary entertainment center.
1

1 Introduction

Through the U.S. Department of Energy’s (DOE) Building America (BA) program, the 

Consortium for Advanced Residential Buildings (CARB), led by Steven Winter Associates Inc., 

partnered with WPPI Energy to monitor the energy performance of two homes – designed to be 

net-zero energy – as part of WPPI’s GreenMax Homes Program in Wisconsin. These homes 

included advanced efficiency measures such as improved building envelopes, ground source heat 

pumps (GSHPs) for space conditioning and domestic hot water (DHW), desuperheaters, drain 

water heat recovery (DWHR), energy recovery ventilators (ERVs), and two-axis tracking 

photovoltaic (PV) systems. These demonstration homes have provided a wealth of information 

for the building community in terms of the science, effort, and cost of increasing the energy 

efficiency of the U.S. housing stock. Preliminary results for these houses were discussed in two 

previous reports (CARB 2010, Puttagunta 2010).

BA continues to seek further confirmation of the true performance of homes and advanced 

mechanical systems through long-term field monitoring. Extensive monitoring of occupied 

homes provides valuable data that cannot be duplicated through laboratory tests and energy 

modeling. CARB installed extensive monitoring equipment in each home to record the energy 

use of major equipment at 15-minute increments. Monitored loads include space conditioning, 

water heating, washer/dryer, microwave oven, coffee maker, range/stove, dishwasher, lighting, 

and plug loads. 

Energy monitoring enabled tracking of the energy performance of the house, and analysis of the 

energy consumption data gave an indication of how much energy was saved by the energy 

efficiency measures included in this project. Extensive monitoring of individual electricity loads 

allowed for comparisons against energy modeling software and the 2010 BA House Simulation 

Protocols (HSP). Comparison of these results includes the accuracy of the simulation software 

for predicting equipment energy use as well as the accuracy of the simulation protocols in 

modeling the magnitude and use patterns of lighting, appliances, and miscellaneous electric loads 

(LAMELs). Furthermore, extensive data collection allows for accurate and detailed analysis of 

the performance and efficiency of individual equipment. 

1.1 Demonstration Homes

Over the past two years, CARB partnered with WPPI Energy on two of its GreenMax 

Demonstration Projects in Wisconsin. These two homes were extensively monitored to evaluate

the performance of GSHPs, desuperheaters, dual-tracking PV systems, water heating systems, 

DWHR units, ERVs, and most electric loads (major appliances, lighting, and outlets, where 

possible) in the homes.

Approximately 150 miles apart, these test homes are located in the International Energy 

Conservation Code Cold Climate Zone 6A. Stoughton and Black River Falls have similar 

latitude, cooling degree days (CDDs), heating degree days (HDDs), and average rainfall, as 

shown in Table 1.
2

Table 1. Climate Information

House Climate Zone Latitude HDDs

(65°F base)

CDDs

(65°F base)

Average

Rainfall 

(in.)

Black River Falls Cold (6A) 42°N 7,755 426 34

Stoughton Cold (6A) 42°N 7,772 305 33

The first GreenMax project, a modernist home (Figure 1) located in Black River Falls, 

Wisconsin, was monitored between June 2009 and June 2011. Key features of this home include 

2 × 8 wall construction, exterior rigid insulation (R-5 above grade and R-10 below grade), a 

three-mode GSHP (heating, cooling, hot water), and a 5.76-kW dual-tracking solar PV system.

Daily and monthly data from this monitoring are available on WPPI’s GreenMax website (WPPI 

2011a).

Figure 1. GreenMax home in Black River Falls, Wisconsin

(image courtesy of WPPI Energy)

The second GreenMax project, a more traditional two-story colonial home (Figure 2) located in 

Stoughton, Wisconsin, was monitored between May 2010 and June 2011. During the design 

phase, CARB provided recommendations based on hourly energy simulations and a review of 

the building specifications and drawings. Most BA recommendations were geared toward 

durability and comfort, including adding a capillary break to the foundation assembly, adding an 
3

ERV, and designing efficient ductwork. The focus was on developing a cost-effective technology 

package that would achieve 50+% source-energy savings over typical mid-1990s construction

prior to the use of site generation (PV). Source energy is defined as the sum of the energy 

consumed at a residence and the energy required to extract, convert, and transmit that energy to 

the residence. Key features of this home include 2 × 6 advanced framed wall construction, two 

GSHPs (a water-to-air for space conditioning and a water-to-water for domestic water heating), 

exterior rigid insulation (R-5 above grade and R-10 below grade), and a 5.76-kW dual-tracking 

solar PV system. Daily and monthly data from this monitoring are available on WPPI’s 

GreenMax website (WPPI 2011b).

Figure 2. GreenMax home in Stoughton, Wisconsin

The Stoughton home is likely a more applicable case study than the Black River Falls home, 

because the house and occupants (two adults, one newborn child, and one in-law) are a better

reflection of a typical U.S. household. Detailed building specifications for each home in addition 

to the descriptions above are shown in Table 2.
4

Table 2. Building Specifications for Test Homes

Specification Black River Falls Stoughton

Floor Area 2,352 4,638

Beds 3 5

Bathrooms 2 3.5

Occupants 2 4

Above-Grade 

Wall Assembly

2 × 8 stud walls @ 24-in. on center + R-27 

cavity insulation and R-5 rigid insulation on

exterior

2 × 6 wood framing @ 24-in. on center w/ 

hybrid cavity insulation (~1.1-in. R-6.5 

closed cell spray foam + R-19 blown 

fiberglass) and 1-in. R-5 extruded 

polystyrene foam on exterior 

Foundation 

Assembly

R-10 on exterior of foundation walls and under 

slab, 2 × 4 wood framing w/R-11 unfaced 

FGB**

1-in. R-5 rigid insulation on exterior with 

1-in. R-5 Tuff-n-Dry, 2 × 4 wood framing 

w/R-13 unfaced FGB, 2 in. of rigid foam 

under slab with 6-mil vapor barrier, 

capillary break for footing 

Ceiling 

Assembly R-50 flat ceiling R-50 loose fill fiberglass with 4 mil 

ceiling polyethylene, energy heel truss

Air Sealing

Air sealing package: spray foam rim/band, caulk 

framing, foam penetrations to exterior and 

through top/bottom plates

air sealing package: spray foam rim/band, 

caulk framing, foam penetrations to 

exterior and through top/bottom plates

Garage Walls

Interzonal wall (between garage and living 

space): R-27 cavity insulation with continuous 

air barrier

Interzonal wall (between garage and 

living space): R-21 fiberglass BIBS†††

system with continuous air barrier

Garage Ceiling R-50 flat ceiling R-19 FGB

Building 

Infiltration 700 cfm50/1.79 ACH50/0.09 ACHnatural 351 cfm50/0.52 ACH50/0.03 ACHnatural

Window 

Glazing

Anderson High Performance Low-E4 doubleglazed windows (U-0.29/SHGC***-21)Loewen Heat-Smart Plus 2 triple-glazed, 

low-e

2

, argon (U-0.19/SHGC-0.21)

Cooling System WaterFurnace Synergy 3-D SDV038 GSHP 

(18.5 EER†/4.0 COP)

WaterFurnace Envision NDV038 GSHP 

(20.1 EER/4.2 COP)

Heating 

System

WaterFurnace Synergy 3-D SDV038 GSHP 

(18.5 EER/4.0 COP)

WaterFurnace Envision NDV038 GSHP 

(20.1 EER/4.2 COP)

HVAC*

Controls Programmable thermostat 3-zone control, programmable thermostat

Ductwork Negligible leakage Negligible leakage

Whole-House 

Ventilation

Enerflow NRFLOE ERV (passive, no internal 

fans) RenewAire 90 cfm ERV 

Point-Source 

Ventilation

50–80 cfm fans for all bathrooms, kitchen 

exhaust hood ducted to outside

Panasonic WhisperGreen FV-05(08)VK1 

for all bathrooms, kitchen exhaust hood 

ducted to outside

Domestic 

Water Heating

WaterFurnace Synergy 3-D SDV038 GSHP (2.6

COP) and a Marathon MR105 electric resistance 

tank water heater

WaterFurnace Envision EW020 water-towater GSHP (2.8 COP)

PV 5.76 kW with dual axis tracking 5.76 kW with dual-axis tracking

Lighting 100% fluorescent or LED†† lighting 100% fluorescent or LED lighting

Appliances ENERGY STAR refrigerator, dishwasher, 

clothes washer

ENERGY STAR refrigerator, dishwasher, 

clothes washer

* Heating, ventilation, and air conditioning **Fiberglass batt *** Solar heat gain coefficient

† Energy efficiency ratio †† Light-emitting diode ††† Blow-in-basket system
5

1.2 Research Questions

The intent of evaluating various building mechanical systems and LAMELs in these two test 

homes was to obtain valuable information for consumers and builders about strategies to provide 

effective near-zero electrical homes. This information also was used to validate the BA HSP

homeowner use patterns. This research effort focused on answering the following research 

questions: 

• What is the installed system efficiency of these GSHPs? How do these differ from the 

units’ rated efficiencies? 

• How effective are GSHPs in providing domestic water heating? 

• Is DWHR effective in single-family homes and what are the major drivers in its 

performance? 

• What are the major contributors to LAMELs in these homes?

1.3 Expected Energy Savings Over Building America Benchmark

With highly efficient equipment and advanced building specifications, the GreenMax 

demonstration homes will show significant energy savings over a new home built to typical 

construction specifications. EnergyGauge USA v2.8.03 (EGUSA), an hourly energy simulation 

tool, was used to analyze the predicted cost savings over the BA Benchmark home. EGUSA was 

chosen over BEopt, the National Renewable Energy Laboratory’s (NREL) hourly simulation 

tool, because BEopt cannot yet model GSHPs. The 2008 BA Benchmark (Hendron 2008) was 

used because these homes were constructed before the most recent update to the benchmark. The 

B08 Benchmark is consistent with mid‐1990s standard building practice for a particular climate 

zone. These homes meet the BA goal of 50+% whole-house source energy savings, as shown in

Table 3.

Table 3. Source Energy Savings over BA B08 Benchmark

House

Annual Source Energy 

of B08 Benchmark

(MMBtu/year)

Annual Source Energy 

of Demonstration Home 

(MMBtu/year)

% Savings 

Over B08 

Benchmark

Black River Falls 400 151 62.3%

Stoughton 522 197 60.5%

1.4 Partners

WPPI Energy is a regional power company serving 51 customer-owned electric utilities that 

share resources and own generation facilities to provide electricity to more than 192,000 homes 

and businesses in Wisconsin, Upper Michigan, and Iowa.

WPPI Energy’s GreenMax Home initiative is designed to encourage the building or remodeling 

of homes that use reliable, sustainable energy systems. Program funding shares the incremental 

cost of building or remodeling a net zero energy home. The home designs and occupant lifestyles 

required to achieve net zero energy use must be replicable and appropriate for a mass market, 

community-based setting. 
6

2 Energy Consumption Overview

According to the 2000 Energy Center of Wisconsin’s “Energy and Housing in Wisconsin” study, 

Wisconsin homes using natural gas for heating, which represent approximately 70% of the 

state’s housing stock, use an average of 9,960 kWh of electricity and 1,026 therms of natural gas 

annually (Pigg and Nevius 2000). The average electricity use of all-electric homes, which 

represent less than 5% of the state’s housing stock, is 24,000 kWh annually.

The annualized energy usage of the two GreenMax demonstration homes, which are both allelectric (except for propane fireplaces in the Stoughton residence that are rarely used), was 

considerably less than the average Wisconsin energy use. The average annual electricity 

consumption and generation for both houses are shown in Table 4. Both houses consumed 

slightly more electricity than produced by the PV system; the homes were close to the net-zero 

energy goal. The total net electricity use for the Black River Falls and Stoughton homes were 

127 and 3,312 kWh, respectively. The Black River Falls and Stoughton houses consumed 62% 

and 41% less energy than the average all-electric Wisconsin house, respectively, when PV 

generation was ignored. 

Table 4. Average Annual Energy Consumption and Generation by House

House

Average Annual 

Electricity Consumption 

(kWh)

Average Annual 

Electricity Generation 

(kWh)

Net Electricity 

Use 

(kWh)

Black River Falls 9,280 9,143 127

Stoughton 14,204 10,892 3,312

The average annual electricity generation of the Black River Falls home was lower than 

anticipated because a malfunctioning inverter resulted in minimal PV generation in January and 

February 2011. The inverter was replaced in late February 2011, and generation totals have been 

comparable between the two sites since. If the inverter had not malfunctioned, annual generation 

is estimated at 9,973 kWh. In this scenario, the Black River Falls home would have been a net

producer of electricity with a net generation of 693 kWh/yr.

2.1 Energy Consumption Breakdown

The energy consumption of each home by end use is shown in Figure 3 and Figure 4. The largest 

energy consumers are the space conditioning and water heating GSHP systems. Appliances are 

the third-largest energy consumer followed by other electricity uses (such as lights, outlets, and 

other miscellaneous electric loads [MELs]). Energy consumption and generation for each home 

by month for the enitre monitoring peroid are shown in Figure 6 and Figure 7. 

During the summer months electricity generation was greater than electricity consumption

because of smaller space conditioning loads and more solar radiation. During the winter months, 

on the other hand, electricity consumption was greater than generation because of larger space 

heating loads and less solar radiation.
7

Figure 3. Site energy consumption by end 

use for Black River Falls home

The average site energy consumption by end 

use for an average home in the East North 

Central states (Wisconsin, Michigan, Ohio, 

Indiana, and Illinois) is shown in Figure 5

(EIA 2005). The results from the Stoughton 

home match end-use energy predictions: the

highly efficient building shell and 

mechanical equipment minimize heating, 

cooling, and DHW; this causes the LAMELs 

to consume a larger proportion of the total 

electric load. The Black River Falls home, 

however, does not show this trend, most 

likely because this home has only two 

occupants.

Figure 6 and Figure 7 show the data 

provided in Figure 3 and Figure 4, 

respectively, in an average monthly bar 

chart format. The solar PV generation is also 

provided for each month.

Figure 4. Site energy consumption by end 

use for Stoughton home

Figure 5. Site energy consumption by end 

use for average home in Midwest – East 

North Central 

(EIA 2005)

It is clear from these figures that space heating is the dominant source of energy consumption. 

Unfortunately, the peak for the space conditioning (winter dominant) is the exact opposite of the 

solar PV generation (summer dominant), so net metering is critical to achieving energy neutrality 

over the course of the year. It is also evident that besides the space conditioning energy 

consumption, the energy consumption of the other components is fairly varied for the Black 

River Falls home versus the more uniform monthly consumption pattern of the Stoughton home.

Heating

54%

Cooling

4%

DHW

8%

Appliances

14%

Lights

3%

Outlets

9%

Misc

8%

Heating

35%

Cooling

7%

DHW

17%

Appliances

16%

Lighting, 

Misc.

23%

Ventilation

2%

Heating

52%

Cooling

4%

DHW

18%

LAMELs

26%

LAMELs

34%

LAMELs

41%
8

Figure 6. Mean monthly site energy component breakdown and generation of Black River Falls 

home

Figure 7. Mean monthly site energy component breakdown and generation of Stoughton home

0

200

400

600

800

1,000

1,200

1,400

1,600

Electricity [kWh]

Heating Cooling DHW Appliances Lighting Outlets Misc. PV

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800 Electricity [kWh]

Heating Cooling DHW Appliances Ventilation Lighting, Misc. PV
9

3 Ground Source Heat Pump

A GSHP system was installed in both houses to supply space heating, space cooling, and DHW. 

Each system uses a horizontal closed, pressurized, slinky ground loop consisting of two trenches 

at a depth of 8 ft. Environol 1000 solution (21.4% ethanol) is circulated between the ground coils 

and the GSHPs, which are located in the unfinished portions of the basements. Although these 

systems are very similar, there are some differences.

The Black River Falls home has two 300-ft trenches at a depth of 8 ft and separated by 8 ft. A

triple-mode GSHP (WaterFurnace Synergy 3-D 3-ton dual speed heat pump) provides space 

heating, space cooling, and DHW from the same unit. A desuperheater runs directly to the 

electric water heater. A passive ERV, which has no internal fans and uses the air handler to move 

air through it, was connected to the central duct system, but this has been replaced with a typical 

heat recovery ventilator with internal fans (currently not interlocked with the GSHP air handler 

fan).

Figure 8. Black River Falls GSHP system

The Stoughton system has two 110-ft trenches at a depth of 8 ft and separated by 15 ft. Two 

separate GSHPs provide space conditioning (WaterFurnace Envision 3-ton dual-speed heat 

pump) and DHW (WaterFurnace ESeries 2-ton). A desuperheater runs from the Envision to a 50-

gal preheat storage tank. The ESeries runs to an 80-gal primary tank. There is no auxiliary water 

heating source. 

CARB contacted both HVAC contractors that installed these two systems, but they did not have 

a clear explanation about why the Black River Falls ground loop field is larger than the 

Stoughton installation. The Stoughton home has a larger building load and an additional GSHP 

for water heating, so we would anticipate a larger ground loop field for this site.
10

Figure 9 Installation of ground loop at Stoughton residence

(image courtesy of WPPI Energy)

These GSHP systems have EER ratings greater than 18 and COPs greater than 4.0. The

International Standards Organization (ISO)/Air-Conditioning and Refrigeration Institute-rated 

efficiencies of the GHSP models installed in these homes are shown in Table 5.

Table 5. Rated Efficiencies of GSHP Models

GSHP Model 

Number House Low Stage High Stage

EER COP EER COP

WaterFurnace Synergy 

3-D heat pump SDV038 Black River Falls 23.7 4.5 18.5 4.0

WaterFurnace Envision 

3-ton dual speed NDV038 Stoughton 30.0 5.1 20.1 4.2

WaterFurnace ESeries 

2-ton EW020H Stoughton N/A N/A N/A 2.8

3.1 Ground Source Heat Pump Efficiency Metrics

GSHPs are rated in accordance with American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE)/ISO 13256-1. Ratings are performed at an entering water 

temperature of 77°F in cooling mode and 32°F in heating mode. In terms of the indoor rating 

conditions, units are tested at an indoor air temperature of 80.6°F dry bulb and 66.2°F wet bulb

(46% relative humidity) in cooling mode and 68°F dry bulb and 59°F wet bulb (58% relative 

humidity) in heating mode.

As with other equipment ratings, GSHP ratings apply only to the manufacturer’s unit and not to 

the entire space conditioning system. Installed efficiencies are always below the rated 

efficiencies. According to ASHRAE/ISO 13256-1, the “effective power input” used in the 

calculation of COP/EER should include the compressor, the water pump, the air handler fan, and 

all associated controls. However, fan power used in the calculation of a unit’s COP/EER does 
11

not include flow resistance from ducts, nor does pump power include the resistance of the ground 

loop. The rationale for this is that the design of the duct system and ground loop is unknown to 

the manufacturer and this rating method allows for apples-to-apples equipment comparisons. 

One additional result, however, is that literature COP and EER values are substantially higher 

than the efficiencies of installed systems.

CARB developed a monitoring protocol for GSHPs to effectively quantify the whole-system 

performance of these units, accounting for the ground loop pump, ductwork, and desuperheater.

NREL is revising our testing protocol into a formal document to be published next year. System 

efficiency has been defined for this project using Equations (1) and (2). The efficiency of the 

heating and DHW systems are defined by the COP, which is the dimensionless ratio of useful 

heating energy output by the system to the net energy input to the system.

[dimensionless] net energy input

useful heating energy COP = (1)

The efficiency of the cooling system is defined by the EER, which is also the ratio of the useful 

cooling energy output by the system to the net energy input to the system, but is defined by the 

units Btu/Wh.

[Btu/Wh] net energy input

useful cooling energy EER = (2)

3.1.1 Heating Coefficient of Performance

The COP of the entire heating system (not just the heat pump unit) is

, ( ) 3.413 /

( ) 3.413 /

,

,

W W W W Btu Wh

Q W W W Btu Wh

COP

comp fan pump DSH pump

h fan comp DSH pump

h

+ + + ×

+ + + × = (3)

where

COPh = coefficient of performance of the complete heating system 

[dimensionless],

Qh = useful heat extracted from ground loop [Btu],

Wcomp = energy consumed by the compressor [Wh],

Wfan = energy consumed by the fan [Wh],

Wpump = energy consumed by the ground-loop pump [Wh], and

WDSH,pump = energy consumed by desuperheater pump [Wh].

3.1.2 Domestic Hot Water Coefficient of Performance

The COP of the DHW is

, ( ) 3.413 / W W W 2 Btu Wh

Q COP

comp pump pump

h

DHW

+ + × =

−

(4)
12

where

Wpump-2 = energy consumed by the DHW pump [Wh].

3.1.3 Cooling Energy Efficiency Ratio

The EER of the cooling system is

, ( ) 3.413 /

comp fan pump DSH , pump

c DSH fan comp

W W W W

Q Q W W Btu Wh

EER

+ + +

+ − + × = (5)

where

EER = energy efficiency ratio [Btu/Wh],

Qc = heat dumped to ground loop [Btu],

Wcomp = energy consumed by the compressor [Wh],

Wfan = energy consumed by the fan [Wh],

Wpump = energy consumed by the ground-loop pump [Wh],

QDSH = heat transferred to DWH by desuperheater [Btu], and

WDSH,pump = energy consumed by the desuperheater circulator [Wh].

3.2 Ground Source Heat Pump Monitoring Results

The overall heating COP and cooling EER were measured at both houses over the entire 

monitoring period. This accounts for all energy use of the GSHP regardless of whether the 

system was supplying conditioned air. The efficiency values also included all standby electricity

use. In addition, the steady-state efficiencies were calculated for each house and system, where 

steady-state is defined as the system being in operation for a full 15-min logging interval. The 

overall and steady-state efficiencies are shown in Table 6. 

Table 6. Measured Efficiency of GSHPs

Black River Falls Stoughton

Overall Steady-State Overall Steady-State

Heating COP 2.7 3.1 2.6 2.7

DHW COP – 1.9 1.4 2.0

Cooling EER 17.5 17.0 15.0 16.7

As shown in Table 6, when the system was running at steady-state, it has a better heating COP 

performance. These systems are sized for the dominant heating load, and therefore oversized in 

terms of cooling capacity (even at part-load capacity), resulting in system short-cycling during 

the cooling season. Short-cycling refers to short run times of the HVAC unit. Starting and 

stopping equipment at short periods can be detrimental to machine life and drastically minimize 

the latent capacity of the unit. As there were fewer steady-state operations (as defined for this 

evaluation) during the cooling cycle and those were primarily at peak conditions (full-stage 

operation and highest ground loop entering temperatures), the steady-state cooling EER ended up 

slightly lower than the overall EER.
13

3.2.1 Space Conditioning

The measured monthly system COP is lower than the rated COP from the engineering data (see 

Table 7), because the rated COP does not account for the external piping resistance (the ground 

loop pump energy), fan energy is measured with no blower external static pressure (or no 

ductwork), and the desuperheater pump energy is not included. Table 7 shows the performance 

difference between the rated efficiencies and the efficiency of the system as installed. The values 

below show the steady-state efficiency. Based on the discrepancy between the rated and 

measured efficiencies, the overall efficiencies of these GSHP systems are not significantly higher 

than alternative space conditioning methods, especially compared to the new inverter driven 

compressor air-source heat pumps available in the market.

Table 7. Rated Versus Measured System Efficiencies

ISO/ARI Rated Heat 

Pump Efficiency

(COP/EER)

Measured Steady State 

Efficiency

(COP/EER)

Performance 

Difference

(COP%/EER%)

Low Stage High Stage Low Stage High Stage Low Stage High Stage

Black River Falls 4.5/23.7 4.0/18.5 3.1/18.1 3.1/15.9 31%/23% 23%/14%

Stoughton 5.1/30.0 4.2/20.1 2.7/16.7 2.7/– 47%/44% 36%/na

This difference between the rated efficiency of a heat pump unit and the in-field system 

efficiency is important when performing energy modeling to estimate home performance. The 

rated equipment COP entered into common modeling tools is often taken as the effective COP of 

the modeled system. Some software programs have been corrected to include ground loop pump 

power. The manufacturers are not to blame, because they can rate only the portion of the product 

that they manufacture; therefore, designers and contractors need to acknowledge the difference 

between rated efficiency and system efficiency.

The average monthly measured COP/EER of the Black River Falls system and the manufacturerlisted COP/EER for the heat pump only are shown in Figure 10 and Figure 11, respectively. The 

Black River Falls system uses a single-speed ground loop pump that is operating at roughly 7.4

gpm. The manufacturer’s ratings in the figures are based on ground loop flow rates of 7 gpm for 

high stage and an interpolated 7 gpm for low stage (manufacturer data provided performance 

ratings at 6 gpm and 8 gpm).
14

Figure 10. Measured versus literature COP of Black River Falls GSHP for space heating 

Figure 11. Measured versus literature EER of Black River Falls GSHP for space cooling

The average monthly measured COP/EER of the Stoughton system and the manufacturer-listed 

COP/EER for the heat pump only are shown in Figure 12 and Figure 13, respectively. The 

Stoughton system uses a single-speed ground loop pump that is operating at roughly 9.1 gpm. 

The manufacturer’s curves displayed are based on ground loop flow rates of 9 gpm for high stage 

and 8 gpm for low stage, which is the highest flow rate the manufacturer lists for low-stage 

operation.
15

Figure 12. Measured versus literature COP of Stoughton GSHP for space heating

Figure 13. Measured versus literature EER of Stoughton GSHP for space cooling

For both systems, the average COP on high speed (or full-load capacity) is similar to when on 

low speed, despite the efficiencies indicated on the manufacturers’ specification sheets. 

Depending on the incoming fluid temperature, there may be a benefit from low-stage operation, 

but nothing comparable to the advertised benefit from the manufacturers’ data. This is likely due 
16

partially to the use of single-speed ground loop pumps for dual-stage compressors and partly due 

to the rating test procedure.

Interestingly, because of how these systems have been installed and configured, the Synergy 3D 

GSHP is actually performing better in heating mode (higher COP) than the Envision GSHP,

which has a higher rated COP. The Envision GSHP installed at the Stoughton House is being 

penalized by higher pump energy needed for that design. This system has two GSHPs connected 

to a single ground loop, and both ground loop pumps run regardless of operation mode.

Even though these two systems are horizontal slinky at a depth of 8 ft, the incoming ground loop 

temperature for the Black River Falls shows a large temperature range over the course of the year 

(30°–80°F for the Black River Falls system versus 35°–70°F for the Stoughton system). Though 

not verified (as we were unable to install loop field temperature sensors at the Black River Falls 

installation), it is our theory that this is due to the Black Rive Falls home being located at the top 

of a slope, about 45 ft above the water, so one side of the ground loop field is exposed to the 

slope so it will be more adversely affected by ambient air temperatures than the Stoughton 

system.

3.2.2 Ground Conditions

As both of these installations are horizontal ground loop configurations, the efficiencies were

affected more by outdoor conditions (see Figure 14) than a vertical field loop would have been. 

The incoming fluid temperature from a vertical field loop would be more consistent throughout 

the year, as deeper ground temperatures vary less than ground temperatures 8 ft below grade. A 

vertical loop would have likely maintained roughly a 50°F temperature year round, which would 

have resulted in steady state COPs closer to 3.6 for Black River Falls and 3.0 for Stoughton. 

Figure 14. Mean daily ground temperature of the Stoughton home ground source field loop
17

3.2.3 Indoor Comfort

Both homes were monitored to ensure that the GSHP was able to maintain the indoor 

temperature at desirable levels all year round. The Black River Falls home is a single-zone 

system; the Stoughton home has three zones.

During the summer, the indoor temperature of the Black River Falls home’s main level was 

fairly consistently controlled at 75°F and never exceeded 78.5°F. In the winter, the indoor 

temperature was maintained at 68°–70°F and never dropped below 65°F. 

Over the summer, the Black River Falls homeowners expressed concern about what they 

perceived to be high relative humidity in their home. According to CARB’s monitoring, there 

were periods during the 2009 summer when the relative humidity spiked to 67%, but on average 

it was 55% for the summer months. This is at the upper end of the desirable humidity levels. 

The sensible cooling load of this home is fairly small, so there is not a continuous call for 

cooling by the GSHP. This is the sole method of mechanical dehumidification designed into this 

home. The heat pump system is not required to run for extensive periods of time to address the 

sensible load, and therefore it is not able to adequately control the building’s latent load. The use 

of a whole-house dehumidifier during the summer might be warranted to compensate for the 

minimal operation of the GSHP in cooling mode.

In addition, the Black River Falls homeowners open the windows and rear sliding doors in the 

summer to promote natural ventilation and cooling when outdoor conditions are suitable. The 

ERV was set up to provide whole-house mechanical ventilation without consideration for natural 

ventilation. The homeowners decided to turn off the ERV during the summer and found the 

home to be comfortable and the home was able to maintain relative humidity below 60%.

CARB evaluated the HVAC design of the Stoughton home to ensure that it was rightsized, was 

optimized for efficiency, and would be able to maintain indoor comfort. Each floor (basement, 

first floor, and second floor) has its own zone. Comfort guidelines are provided in ACCA’s

Manual RS (ACCA 1997). The guide specifies comfort to be the ability to maintain an average 

floor-to-floor temperature difference of 2°F or less and a maximum floor-to-floor temperature

difference of 4°F or less. Table 8 shows the monthly temperature variations between the first and 

second floors. Comparison to the basement was not made as the basement zone rarely called for 

cooling. The average temperature differential criteria are met for every month monitored. The 

maximum temperature differential criteria are nearly met. The few instances in which the 

maximum and minimum temperature differences exceeded 4°F were typically for less than 30 

min.
18

Table 8 Floor-to-Floor Temperature Variations (∆T = 2nd Floor – 1st Floor)

Month

Maximum ∆T 

Between 1st and 2nd 

Floors

Minimum ∆T 

Between 1st and

2nd Floors

Average ∆T 

Between 1st and

2nd Floors

May 2010 1.8°F –2.0°F –0.4°F

June 2010 1.4°F –1.6°F –0.2°F

July 2010 1.8°F –2.0°F –0.1°F

August 2010 2.0°F –1.7°F –0.3°F

September 2010 1.4°F –2.3°F –0.9°F

October 2010 1.2°F –2.6°F –1.0°F

November 2010 –0.1°F –3.6°F –1.3°F

December 2010 –0.2°F –4.6°F –1.8°F

January 2011 –0.1°F –3.6°F –1.7°F

February 2011 –0.1°F –4.3°F –1.9°F

March 2011 4.4°F –4.3°F 1.7°F

April 2011 3.7°F –4.9°F –2.0°F

May 2011 2.5°F –3.4°F –1.1°F

June 2011 0.7°F –2.8°F –0.9°F

Average 1.5°F –3.1°F –0.9°F

3.2.4 Domestic Hot Water

According to the 2000 Energy Center of Wisconsin’s “Energy and Housing in Wisconsin” Study, 

28% of homes have electric water heaters, and on average these homes use 3,250 kWh/yr to heat 

domestic water (Pigg and Nevius 2000). The Black River Falls and Stoughton homes used 775 

and 2,159 kWh/yr of electricity annually to heat domestic water, respectively, which is a 76% 

and 34% reduction over a typical Wisconsin home.

The DHW systems in each home consists of a GSHP system, a desuperheater, and a DWHR

system. The Black River Falls home has auxiliary electric backup; the Stoughton Home relies 

solely on a dedicated water-to-water GSHP. The 50-gal preheat tanks in both homes (see Figure 

16) are fed by the main water line, which runs through DWHR units (see Figure 16) to capture 

some of the energy from hot water running down the drain. The preheat tank is connected to the 

space conditioning GSHP desuperheater via an internal heat exchanger. Schematic diagrams 

outlining the location of these systems are shown in Figure 17 and Figure 18.
19 

Figure 17. Schematic of GSHP/DHW systems at Black River Falls home 

Figure 16. DWHR in 

Stoughton home

Figure 15. Buffer tank and storage 

tank in Stoughton home
20

Figure 18. Schematic of GSHP/DHW systems at Stoughton home 

Table 9 shows the calculated energy supplied by these additional sources and their overall 

contribution to the water heating. Standby heat losses of the storage tanks are not included. The 

Stoughton home uses significantly more energy for water heating (more energy was supplied,

even though it has been monitored for roughly half the time period). This is anticipated with the 

higher occupancy of this home (three adults and a baby at the Stoughton home versus only two 

adults at the Black River Falls home).

Table 9. Water Heating Contribution by Source

Water Heating 

Source

Black River Falls Stoughton

Average Annual 

Energy Supplied 

(MMBtu)

DHW 

Contribution

Average Annual 

Energy Supplied

(kBtu)

DHW 

Contribution

Desuperheater 5,751 61.6% 5,541 32.5%

DHW GSHP 1,397 15% 9,654 56.6%

DWHR 530 5.7% 1,863 10.9%

Electric Water 

Heater Auxiliary 1,652 17.7% – –

Total 9,330 17,058

The average monthly measured COP of the Black River Falls and Stoughton DHW GSHP 

systems and the manufacturer-listed COP for those heat pumps only are shown in Figure 19 and 

Figure 20, respectively.
21

Figure 19. Measured versus literature COP of Black River Falls GSHP DHW mode

Figure 20. Measured versus literature COP of Stoughton DHW GSHP

Once again, the Synergy 3D GSHP is actually performing better in DHW mode (COP) than the

system with higher rated efficiency, the dedicated Envision EW GSHP. The DHW COP for both 

systems is consistently lower than the rated performance. Regardless, the DHW mode is an

efficient method to heat water compared to standard electric resistance water heating methods. In 

comparison to the recent heat pump water heaters that are on the market, the Stoughton system 
22

has a similar performance range and the Black River Falls system is slightly better (though it has 

an auxiliary electric resistance water heater to meet demand loads).

3.2.5 Desuperheater

A desuperheater is a secondary heat exchanger that captures some waste heat from the GSHP 

refrigerant line prior to rejecting to the ground. Typical operation of a desuperheater provides 

water preheating during cooling mode operation, but during heating mode, it “robs” potential 

heating capacity from the space conditioning. A reversing valve or smarter control logic 

(available in some newer GSHP models) is needed to avoid the space heating penalty, if this is of 

concern.

In the Black River Falls home, the desuperheater was directly plumbed to the water heater that 

has independent controls set to maintain DHW temperature at roughly 110°F. In January, an 

on/off switch was installed on the desuperheater pump in case it needed to be shut off to 

optimize whole-house system performance (the homeowners have decided to not use the on/off 

switch seasonally). CARB recommends that the desuperheater be piped to a preheat tank (as was 

done at the Stoughton Home) and not directly to the auxiliary electric resistance water heater. 

This recommended configuration will allow for the maximum usable heat transfer from the 

desuperheater.

Figure 21 shows the daily heating contribution of the various components (electric water heater, 

DWHR, desuperheater, and buffer tank, which is directly supplied by the GSHP DHW mode) 

that heat water for the Chambers’ home. Daily hot water use is also shown on the second y-axis.

As noted in Figure 21, not all heat is delivered to the DHW as there are standby losses and an ondemand recirculation loop.

Figure 21. Water heating component breakdown for Black River Falls home in January

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

(10)

0 

10 

20 

30 

40 

50 

60 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Daily Hot Water Usage [gallons]

Daily Heat Delivered [kBtu]

 

Water Heater Drain Water Heat Recovery Desuperheater Buffer Tank Hot Water Usage

Not all heat is delivered to domestic hot water as there are 

standby losses and a on-demand recirculation loop, but 

this chart provides a breakdown of source contribution.
23

In general, the desuperheater was acting as anticipated, essentially robbing heating capacity from 

the space conditioning to provide water heating during heating/DHW mode. During the coldest 

winter months, there is minimal operation of the electric resistance water heater. 

When there was no demand for hot water and the GSHP was providing space heating (see the 

first three days of January), the desuperheater had a negative impact to water heating. As a result, 

the desuperheater was robbing heat from the water heater and increasing the heating capacity 

(the return temperature from the desuperheater loop was higher than the supply temperature 

during heating). Without any water demand, the primary tank temperature was not losing heat 

except for standby loss. At some point, the tank temperature was hot enough that the energy 

provided by the desuperheater was not useful and the desuperheater return temperature was 

actually returning hotter than it was leaving the GSHP. When there are draws for hot water, the 

tank temperature drops (from the cold incoming water) and the desuperheater once again is able 

to provide useful energy.

3.2.6 Drain Water Heat Recovery

The DWHR device in each home is a heat exchanger on the central waste drain that captures 

some heat from the hot water that goes down the drain and uses this energy to preheat cold water 

coming into the water heater.

The Black River Falls home used a R3-30 (3 pipes, 30 in. long) Power Pipe DWHR, which the 

manufacturer claims has a 32.9% heat exchange effectiveness at equal flow of 2.5 gpm. The 

Stoughton home used a R3-72 (3 pipes, 72 in. long) Power Pipe DWHR, which the manufacturer 

claims has a 58.5% heat exchange effectiveness at equal flow of 2.5 gpm.

As previously shown in Table 9, the Black River Falls and Stoughton DWHR units provided 

5.7% and 10.9% of the overall water heating needed for these homes, respectively. The 

manufacturer advertises up to 35% hot water savings, but the performance of these units is

heavily correlated to shower use. In addition, with the use of low flow showerheads and faucets, 

the 2.5 gpm equal flow conditions were not typically found in these homes. The homeowner’s

hot water draw patterns and use determine whether this technology is applicable to single-family 

residential projects.
24

4 Photovoltaic System Performance

Each home uses a 5.76-kW solar PV system to harness the power of the sun. These systems 

consist of two pole-mounted 2.88-kW arrays of solar PV panels. The arrays are supported by 

dual-axis tracking systems that enable each to tilt and move, following the sun’s position to 

convert as much sunlight as possible during the course of a day and season. These tracking 

systems can produce as much as 30% more energy than a fixed-position system. 

Figure 22. Stoughton PV system Figure 23. Black River Falls PV system

The actual PV generation tracked fairly consistent with the anticipated PV generation based on 

solar energy modeling. NREL PVWatts calculator was used to estimate the yearly solar energy 

output, assuming a direct current to alternating current derate factor of 0.83. Typical 

Meteorological Year 2 files for Black River Falls and Stoughton are not available, so less 

accurate 40-km monthly grid cell data published by NREL were used for each city. These data, 

which are based on measurements from 1961 to 1990, provide “monthly average daily total solar 

resource information on grid cells of approximately 40 km by 40 km” (NREL 2011). The results 

of the modeled PV generation versus actual generation are shown in Table 10. As previously 

mentioned in Section 2, the overall electricity generation of the Black River Falls home was 

lower than anticipated because a malfunctioning inverter resulted in minimal PV generation in 

January and February 2011.

Although the Stoughton home is significantly larger in floor area and volume, both homes were 

designed with the same PV generation capacity with a goal of being net zero. Post analysis by 

CARB determined that the Stoughton PV system was undersized based on the anticipated annual 

energy consumption of that home provided by the original rater.
25

Table 10. PV System Performance Comparison to Modeled Values

Month

Black River Falls Stoughton

Predicted 

Solar 

Radiation 

(kWh/m2-day)

Predicted 

AC 

Energy 

(kWh)

Actual 

AC 

Energy 

(kWh)*

Predicted 

Solar 

Radiation 

(kWh/m2-day)

Predicted 

AC 

Energy 

(kWh)

Actual 

AC 

Energy 

(kWh)

January 4.14 654 437 3.72 590 627

February 5.48 753 493 5.02 710 699

March 5.97 901 962 5.35 810 742

April 7.08 983 850 6.77 953 1,010

May 7.94 1,117 737 7.55 1,071 1,218

June 8.34 1,100 982 8.22 1,082 1,098

July 8.28 1,119 1,127 7.96 1,067 1,259

August 7.59 1,032 1,082 7.2 976 1,229

September 6.33 849 850 6.11 820 962

October 5.06 724 657 4.67 668 1,074

November 3.32 484 558 3.07 435 651

December 3.56 550 407 3.29 512 322

Year 6.09 10,266 9,143 5.75 9,694 10,892

* Average electricity generation over the two years of field monitoring.
26

5 Lighting, Appliances, and Miscellaneous Electric Loads

LAMELs are often grouped together as the remaining contributors to the total home electricity

demand after space heating, space cooling, DHW, and ventilation. LAMELs are heavily 

dependent on occupant use, and several studies have attempted to measure the use patterns and 

quantity of LAMEL electricity use. Unfortunately, these studies cannot replace the high-quality 

data obtained through extensive monitoring. The TIAX U.S. Residential Information Technology 

Energy Consumption in the 2005 and 2010 Report is the most thorough information on items 

that make up LAMELs (Roth et al. 2006), but the usage patterns are calculated based on 

equations and not specifically monitored. Some studies, such as RECS (EIA 2005), estimate use 

patterns through surveys, but respondents may believe their uses are different than actual 

monitored data. 

The BA HSP, part of the Benchmark, stipulate the quantity of yearly energy use from LAMELs 

as well as the use patterns for these loads based on various other studies. The B10 HSP includes 

appliances that are in compliance with “the federal appliance standards in effect as of January 1, 

2010, and lighting characteristics and miscellaneous electric loads most common in 2010”

(Hendron and Engebrecth 2010). The two houses evaluated here, however, were constructed 

with all ENERGY STAR appliances and high-efficacy lighting. Therefore, these houses should 

show savings over the B10 Benchmark in lighting and appliances, but not necessarily in MELs,

which are more difficult to predict and control. Unfortunately, a completely direct comparison 

between the BA HSP and the two test homes cannot be made because component loads in the 

test homes were not disaggregated in the same manner as the BA HSP. 

The measured component load breakdowns of the Black River Falls and Stoughton LAMELs are 

shown in Figure 24 and Figure 25, respectively. The major categories are appliances, lights, and 

MELs. MELs have a subcategory of Outlets and Other MELs. A more detailed breakdown of 

those categories is provided by end load where data are available with the lighter shade of the 

primary categories.

In the Black River Falls home, the lighting in the master suite and the outlets in the living room 

were the major sources of electricity use for these two major components. The outlets in the 

living room comprise the home entertainment center, so it is not surprising that this represents 

more than half the outlet loads. 

The major appliances account for approximately 40% of the electricity consumption in the two 

test homes outside of heating, cooling, and hot water. These are all top-of-the-line units 

(ENERGY STAR labeled, if available), so little can currently be done from a technology 

standpoint to reduce this use. The same is true of the lighting, which is nearly all compact 

fluorescent or LED lighting. Essentially, the homeowners would need to alter their behavior to 

see a significant reduction in the lighting and appliance portion of their LAMELs consumption.
27

Figure 24. Black River Falls LAMEL breakdown (kWh/yr)

Lighter shades are subcomponents of darker shades of the same color.

1,462

100

71

167

147

112

306

558

310

99

138

17

17

39

1,601

848

391

30

37

35

34

98

200

23

753

Appliances:

 Dishwasher:

 Oven:

 Induction Cooktop:

 Coffee Maker:

 Clothes Washer:

 Clothes Dryer:

 Refrigerator:

Lights:

 Living / Kitchen / Dining:

 Master Suite:

 Basement:

 Garage / Stairway:

 Outside:

MELs

Outlets:

 Living Room:

 Kitchen:

 Dining Room:

 Master / Hall / Guest:

 Common Bath:

 Office:

 Garage:

 Outside:

Other MELs:
28

Figure 25. Stoughton LAMEL breakdown (kWh/yr)

Lighter shades are subcomponents of darker shades of the same color.

2,598

202

336

870

858

84

247

3,336

1

4

81

36

15

102

100

0

361

326

2,309

Major Appliances

Induction Cooktop

Oven

Clothes Dryer

Refrigerator & Island

Outlets

Garbage Disposal &

Dishwasher

Clothes Washer

Lighting and MELs

Whirlpool Tub

Shower Steamer

Microwave Oven

Clothes Washer

Wine Cooler

Kitchen Outlets

Septic System

Sump Pump

Well Water Pump

Water Softener &

RenewAire ERV

Lighting and Other MELs
29

5.1 Lighting

In the BA HSP, the lighting loads are separated into four categories: interior hard-wired lighting, 

interior plug-in lighting, garage lighting, and exterior lighting. The yearly electricity

consumption and lighting profiles can be defined using two methods. The more complicated 

Option 2 calculates the yearly loads and hourly load profile based on a room-by-room 

calculation. The simpler Option 1, which is the basis for comparison in this report and the 

method implemented in BEopt, defines the yearly loads as a function of finished floor area 

(FFA) or garage area, which is measured in square feet, as shown in Equations (6) through (9).

These equations are meant to approximate a house with a lighting breakdown of 66% 

incandescent, 21% compact fluorescent, and 13% T-8 linear fluorescent. 

Interior hard-wired lighting = 0.8 × (FFA × 0.542 + 334) kWh/yr (6)

Interior plug-in lighting = 0.2 × (FFA × 0.542 + 334) kWh/yr (7)

Garage lighting = Garage Area × 0.08 + 8 kWh/yr (8)

Exterior lighting = FFA × 0.145 kWh/yr (9)

The lighting electricity consumption for the Black River Falls home was measured individually 

for interior hard-wired lighting, garage lighting, and exterior lighting. The interior plug-in 

lighting is included in the outlet electricity consumption because outlet loads could not be 

separated by end use. The categorization of plug-in lighting is similar to other categorizations, 

where plug-in lighting is considered a miscellaneous electric load. Unfortunately, the lighting 

electricity consumption could not be monitored separately in the Stoughton home because the 

electrical panel was installed and configured prior to CARB’s input on how to zone the breakers. 

A comparison of the yearly lighting electricity use between the Black River Falls home and the 

BA HSP values for a similarly sized home is shown in Table 11. The Black River Falls home 

shows a tremendous savings in lighting energy over the BA HSP. These savings are mostly due 

to the installation of high-efficiency lamps, but may have been influenced by differing use 

patterns at the home than predicted by the protocols.

Table 11. Annual Lighting Electric Use Comparison at the Black River Falls Home (kWh/yr)

Appliance BA HSP Black River Falls

Interior Hard-Wired 1,287 271

Interior Plug-in 321 N/A

Garage 52 17

Exterior 341 39

In the HSP, lighting use over the course of the year is determined using normalized hourly 

lighting profiles for each month of the year. These profiles are defined in the BA Analysis 

Spreadsheet for Option 1. A comparison between the stipulated profiles and the measured load 

profiles of the Black River Falls home is shown in Figure 26. The profiles show remarkable 

correlations, but the morning lighting loads are somewhat underestimated.
30

Figure 26. Normalized hourly lighting profile comparison (Black River Falls)

Although the lighting schedules in the HSP do not correct for geographic differences in the 

amount of light over the course of the day or year, the geography of the home does not seem to 

be a factor in the discrepancy between the HSP and the Black River Falls lighting profiles. 

Located in a northern climate, these homes experience less sunlight in the winter and more 

12AM 6AM 12PM 6PM 12AM

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February

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October

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November

Black River Falls Home BA Simulation Protocols

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December
31

sunlight in the summer than the average American home. However, there is no clear pattern 

between morning lighting intensity and month of the year in the Black River Falls home.

Instead, the discrepancy may be due to the residents waking up earlier than the “average” 

American approximated by the protocol. The Black River Falls home sees a peak in lighting 

energy during the 6:00 a.m. hour, whereas the HSP profiles predicts a peak during the 7:00 a.m. 

hour. This suggests that the HSP expects residents to wake up during the 7:00 a.m. hour , but the 

Black River Falls residents wake up during the 6:00 a.m. hour. There is more light during the 

7:00 a.m. hour, so the residents use more energy during the morning because they start the day

earlier.

5.2 Appliances

In the BA HSP, major appliance loads are defined as the electricity and gas loads from the 

refrigerator, clothes washer, clothes dryer, dishwasher, and oven/range. The annual electricity

loads are defined as a function of the number of bedrooms (Nbr). The forumlas for these loads in 

all-electric homes in kWh/yr are shown in Equations (10) through (14).

Clothes Washer = 38.8 + 12.9 × Nbr kWh/yr (10)

Dishwasher = 87.6 + 29.2 × Nbr kWh/yr (11)

Refrigerator = 434 kWh/yr (12)

Clothes Dryer = 538.2 + 179.4 × Nbr kWh/yr (13)

Oven/Range = 250 + 83 × Nbr kWh/yr (14)

A comparison between the yearly major appliance electricity use of the HSP Benchmark and the 

Black River Falls and Stoughton homes is shown in Table 12. These homes use less energy than 

the BA HSP predicts because of high-efficiency appliances. Use patterns may also be a factor, 

but the impact on use is not easily determined.

Table 12. Yearly Major Appliance Electric Use Comparison (kWh/yr)

Appliance BA HSP

(3-BR)

Black 

River Falls

BA HSP

(5 BR) Stoughton

Clothes Washer 77.5 112 103.3 247

Dishwasher 175.2 100 233.6 84

Refrigerator 434 558 434 N/A

Clothes Dryer 1,076.4 306 1,435.2 870

Range/Oven 499 238 665 538

Unlike lighting, The BA HSP defines the use of major appliances and MELs by an hourly 

normalized energy use profile and a monthly seasonal multiplier. The BA HSP hourly and 

monthly profiles are compared to the equivalent profiles measured at the two test homes in 

Figure 27 and Figure 28. Again, the BA HSP hourly and monthly profiles show remarkable 

correlations to the measured loads at the two test homes.
32

Figure 27. Hourly normalized energy use profile comparison for major appliances

Figure 28. Monthly seasonal multipliers comparison for major appliances1

 1 There are no data for July and August for the clothes dryer at the Stoughton Home. Data are shown as a dotted line. 

The Stoughton refrigerator could not be isolated as it included the kitchen island outlets on the same breaker.

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Clothes Washer

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Dishwasher

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Refrigerator

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Clothes Dryer 

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Range/Oven

Black River Falls Home

Stoughton Home

BA Simulation Protocols

Jan Apr Jul Oct Jan

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Clothes Washer

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Dishwasher

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Refrigerator

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Clothes Dryer

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Range/Oven

Black River Falls Home

Stoughton Home

BA Simulation Protocols
33

5.3 Miscellaneous Electric Loads

The BA HSP hourly and monthly profiles for selected MELs are compared to the equivalent 

profiles measured at the two test homes in Figure 29 and Figure 30, respectively. Only some 

MELs were monitored directly in the test homes. Therefore, these graphs are selective and 

exclude many of the measured MELs in the HSP. Furthermore, the plug-in lighting energy is 

included in the total MEL numbers for the Black River Falls home, which may explain the 

discrepancy between the BA HSP profile and the measured values. Again, the BA HSP hourly 

and monthly profiles show remarkable accuracy to the measured loads at the two test homes.

For the Black River Falls and Stoughton homes, the cooking appliances are considered to be the 

sum of the electricity measured at the kitchen outlets, range hood, coffee maker, and microwave. 

At the Black River Falls home, the microwave is measured on the same breaker as the oven and 

is not included in the cooking appliances. The MEL refrigerator is the sum of the electricity 

measured at the wine cooler and the beer refrigerator. The total MELs cannot be graphed for the 

Stoughton home because the lighting and MELs are measured as a combined value.

Figure 29. Hourly normalized energy use profile comparison for MELs

12AM 6AM 12PM 6PM 12AM

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All MELs

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Cooking Appliances

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Refrigerator

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Home Entertainment

Black River Falls Home

Stoughton Home

BA Simulation Protocols
34

Figure 30. Monthly seasonal multipliers comparison for MELs

5.3.1 Standby Energy Use

During July 2009 the homeowners at the Black River Falls home were not home, which provided 

an opportunity to measure the standby energy use. Although the homeowners at the Stoughton 

home were not out of town during a similar period of time, there are days throughout the year 

that provide an opportunity to determine standby energy use. The Black River Falls and 

Stoughton homes have a daily standby energy use of 412 and 375 Wh/day, respectively, when 

looking at the dishwasher, oven, cooktop, coffee maker, clothes washer, clothes dryer, and 

microwave. Assuming an electricity rate of $0.10/kWh this standby energy amounts to an 

additional $15.03/yr and $13.69/yr, respectively, for the appliances. 

Table 13. Daily Standby Energy Use (Wh)

Appliance Black River Falls Stoughton

Dishwasher 37 25

Oven 5 155

Cooktop 190 27

Coffee Maker 155 –

Clothes Washer 25 35

Clothes Dryer 0 0

Microwave N/A 133

In terms of the lighting and outlets, the only consistent standby energy use was from the garage 

outlets at the Black River Falls home. This circuit breaker averages 133 Wh/day (roughly 5 W) 

when there was no home occupancy. After some investigation, it was determined that the home 

security system is wired into the garage electrical circuit.

Jan Apr Jul Oct Jan

0

0.5

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1.5

2

All MELs

Jan Apr Jul Oct Jan

0

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Cooking Appliances

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Refrigerator

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1.5

2

Home Entertainment

Black River Falls Home

Stoughton Home

BA Simulation Protocols
35

6 Conclusions

These two test home evaluations provided valuable data about the true in-field performance of 

various building mechanical systems and LAMELs. In addition, this information, though a small 

sample set, helps to validate the BA HSP homeowner use patterns. Answers to the other research 

questions are:

• What is the installed system efficiency of these GSHPs? How do these differ from the 

units’ rated efficiency? 

The steady-state heating COP for low and high stage operation of the Black River Falls 

GSHP system was 3.1, which is 31% and 23% less than the rated unit efficiency, 

respectively. The steady-state cooling EER for the low stage was 18.1 and for the high stage 

was 15.9, which is 23% and 14% less than the rated unit’s efficiency, respectively.

The steady-state heating COP for low and high stage operation of the Stoughton GSHP 

system was 2.7, which is 47% and 36% less than the rated unit efficiency, respectively. The 

steady-state cooling EER for the low stage was 16.7, which is 44% less than the rated unit 

efficiency. This system rarely operated in high-stage cooling mode.

The differences between the rated and measured system efficiencies are caused in large part 

by the ground loop and desuperheater pump energy in the efficiency calculations and the 

added fan power from the inclusion of a full duct system connected to the GSHP. These

items are not accounted for (or not fully accounted for) in the rated unit efficiencies.

• How effective are GSHPs in providing DHW? 

These two variations in GSHP water heating (three-mode GSHP and dedicated DHW GSHP) 

provided COPs of 1.5–3.0. Though highly efficient, heat pump water heaters can provide 

water heating efficiencies of 1.5–2.5 at a significantly lower first cost. In the case of the 

Black River Falls GSHP, this third mode was just an add-on benefit to the space conditioning 

system. For the Stoughton home, the inclusion of a dedicated GSHP just for water heating 

was not cost effective and resulted in greater ground loop pumping being associated with the 

space conditioning GSHP.

• Is DWHR effective in single-family homes? What are the major drivers in its 

performance? 

For the more standard length DWHR unit (72-in. unit at the Stoughton home), a 10% DHW

saving is good for a passive system. As overall water use is not high at these homes, the cost 

benefit of this system is minimal. These units are largely dependent on shower use, so the 

systems will likely have greater benefits in multifamily housing.

• What are the major contributors to LAMELs in these homes?

Though the 2005 RECS data suggest that LAMELs are on average 26% of the overall 

electricity use in Midwest homes, both of these homes have higher percentages of LAMEL 
36

electricity consumption. The Black River Falls home is at 34% and the Stoughton home is at 

41%. As the most efficient lighting and appliances available today have been installed in 

these homes, much of this electricity consumption falls under MELs. For the Black River 

Falls home, MELs account for roughly 17% of total electricity use (9% from outlets and 8% 

from other sources). For the Stoughton home, MELs are roughly 20% of the overall 

electricity use.

As technology continues to inundate our lives, the entertainment center is becoming a larger 

energy hog. The Black River Falls home had roughly 12.4% of its LAMELs electricity use or 

4.2% of its overall electricity use attributed to the primary entertainment center.

One component that is likely overlooked in the design process is the well pump and the 

associated water treatment/softening systems used when city water is not readily available. 

For the Stoughton home, these components accounted for 12.6% of the LAMEL electricity

use. 
37

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WPPI Energy. (2011a). “Black River Falls: Energy Data.” www.greenmaxhome.com/projects/

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DOE/GO-102012-3532 ▪ April 2012

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