Serenbe Nest Cottages

T. Butler, O. Curtis, E. Kim, S. Roberts, 

and R. Stephenson

NAHB Research Center

December 2012
NOTICE

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iii

Serenbe Nest Cottages

Prepared for:

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

Prepared by: 

T. Butler, O. Curtis, E. Kim, S. Roberts, R. Stephenson

Southface 

Energy Efficient Housing Research Partnership as part of the 

NAHB Research Center Industry Partnership

400 Prince George’s Boulevard

Upper Marlboro, MD 20774

NREL Technical Monitor: Stacey Rothgeb

Prepared under Subcontract No. KNDJ-0-40335-00

December 2012
iv

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v

Contents

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

List of Tables .............................................................................................................................................. vi

Definitions.................................................................................................................................................. vii

Executive Summary................................................................................................................................. viii

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

1.1 Background..........................................................................................................................1

1.2 Overview..............................................................................................................................1

1.3 Goals 2

2 Energy Efficient Solutions Package ................................................................................................... 3

2.1 Overview..............................................................................................................................3

2.2 Thermal Boundary ...............................................................................................................5

2.2.1 Foundation and Framing..........................................................................................5

2.2.2 Air Sealing and Insulation .......................................................................................6

2.2.3 Fenestration..............................................................................................................7

2.3 Systems................................................................................................................................7

2.3.1 HVAC ......................................................................................................................8

2.3.2 Plumbing..................................................................................................................9

2.3.3 Lighting and Appliances..........................................................................................9

2.4 Estimated Cost of Energy Efficiency Solution ..................................................................10

2.5 Measure Interactions..........................................................................................................10

3 Technical Pathway ............................................................................................................................. 11

3.1 Inputs to Building Energy Optimization Software ............................................................11

3.2 Energy Simulation Results.................................................................................................11

4 Experiment .......................................................................................................................................... 14

4.1 Test Plan.............................................................................................................................14

4.2 Research Questions............................................................................................................14

5 Short-Term Testing ............................................................................................................................ 17

5.1 Short-Term Characterization Testing ................................................................................17

6 Summary ............................................................................................................................................. 18
vi

List of Figures

Figure 1. Nest, lot nine................................................................................................................................ 1

Figure 2. Nest Cottage nine building envelope........................................................................................ 5

Figure 3. Foundation wall and framing, Nest Cottage nine .................................................................... 5

Figure 4. Air sealing detail at exterior basement wall corner, Nest Cottage nine................................ 6

Figure 5. Insulation at second floor and roof, Nest Cottage nine.......................................................... 7

Figure 6. Window specification, Nest Cottage nine ................................................................................ 7

Figure 7. CFIS system schematic © 2009 by Building Science Corporation; reprinted with 

permission............................................................................................................................................. 9

Figure 8. Source energy savings for Nest Cottage, lot nine over the B10 benchmark and the 

builder’s typical package................................................................................................................... 12

Figure 9. Annualized utility bill comparison for Nest Cottage, lot nine against B10 benchmark and 

the builder’s typical package ............................................................................................................ 13

Unless otherwise noted, all figures were created by Southface.

List of Tables

Table 1. Nest Cottage Building Specifications ........................................................................................ 4

Table 2. Research Measurements and Equipment................................................................................ 15

Table 3. Short-Term Equipment and Test Measurements .................................................................... 17

Unless otherwise noted, all tables were created by Southface.
vii

Definitions

ACH50

BA

BEopt

Air changes per hour at 50 Pa, infiltration measurement

Building America

Building Energy Optimization software

CFIS Central fan integrated supply, ventilation method

CFL Compact fluorescent lamp

CFM Cubic feet per minute, air flow volume measurement

CFM25 Air flow at 25 Pa, duct leakage measurement

CFM50 Air flow at 50 Pa, infiltration measurement

COP Coefficient of performance, heating efficiency

EER Energy efficiency ratio, cooling efficiency

EF Energy factor

GSHP Ground source heat pump

HSPF Heating seasonal performance factor, heating efficiency

HVAC

IECC

Heating, ventilation, and air conditioning

International Energy Conservation Code

LFL Linear fluorescent lamps

NCTH New construction test house 

SEER Seasonal energy efficiency ratio, cooling efficiency

SLA Specific leakage area, infiltration measurement
viii

Executive Summary

As part of the NAHB Research Center Industry Partnership, Southface partnered with Martin 

Dodson Builders and the Serenbe community on the construction of a new test home in the 

suburbs of Atlanta, Georgia, in the mixed humid climate zone. The most recent subdivision 

within the Serenbe community, the Nest, will contain 15 small footprint cottage style homes, and 

Southface selected lot nine as the test home for this study. This Nest subdivision serves as a 

project showcase for both the builder partner and the Serenbe community as a whole. The 

planning and design incorporated into the Nest cottages will be implemented in each home 

within the subdivision. These homes meet Building America (BA) savings targets and serve as a 

basis of design for other homes Martin Dodson plans to build within the Serenbe community. 

Significant changes to the builder’s typical specifications include increased levels of wall and 

roof insulation using open cell spray foam insulation and the use of a ground source heat pump 

(GSHP) rather than a split system air conditioner and gas furnace.

As a BA test home, this home will be evaluated to detail whole-house energy use and HVAC 

efficiency. The main research priorities for this home include (1) determining the operational 

efficiency and energy consumption of the home’s HVAC system, with a focus on the additional 

system fan run time and load associated with the home’s central fan integrated ventilation 

supply, and (2) examining the cost effectiveness of certain high-profile energy upgrade 

measures, specifically a GSHP, and how these measures compare to projected energy savings 

and other potential energy upgrades.
1

1 Introduction

With the support of the DOE Building America (BA) Program, Southface partnered with Martin 

Dodson Builders to build a new construction test house (NCTH). The Serenbe community is 

located 32 miles southeast of Atlanta, Georgia, in mixed humid climate zone 3. A sustainable 

master planned community, Serenbe worked closely with the EarthCraft green building program 

to establish guidelines for development of the community and its structures. The most recent

subdivision within the Serenbe community, the Nest, will contain 15 small-footprint cottage style 

homes, and Southface selected lot nine as the test home for this study. All of the homes within 

the Nest subdivision meet the BA savings goals of using 30% less energy than comparable 

homes that meet the 2009 International Energy Conservation Code (IECC) and feature a ground 

source heat pump (GSHP) tied to a shared closed loop that exchanges heat with an adjacent lake. 

Figure 1. Nest, lot nine

1.1 Background

With technical support from Southface, the design team selected design elements, technologies, 

and construction methods that minimize cost increases while achieving substantial energy 

savings and maintaining whole-building performance metrics of durability, comfort, and suitable 

indoor air quality. The design is a test home in the mixed humid climate targeting BA and 

builder partner energy efficiency and cost goals that will ultimately develop into a commercially 

feasible energy efficiency solution package.

1.2 Overview

This single-family detached home, a two-story design over walkout basement, has 1,686 ft2 of 

conditioned floor area, excluding the unfinished basement, and was completed in 2011. The first 

floor has the kitchen, dining, and living areas as well as a bedroom and full bath. The second 

floor has two bedrooms and full baths as well as storage and mechanical spaces. Ceilings are 10 

feet at the first and second floors with portions of the second level including cathedral ceilings 
2

sloped to follow the roofline. The full height basement has an 8-ft ceiling height and includes 

both foundation and framed walls with a walkout at the rear of the home.

1.3 Goals

Specific goals for the Nest community as a whole and this NCTH in particular were established 

during the planning phase:

• Develop and implement a durable design that improved energy efficiency by at least 30% 

over a comparable house that meets the 2009 IECC.

• Create a tight thermal boundary to reduce air leakage and improve thermal performance.

• Design the HVAC system 100% in conditioned space for significant energy savings.

• Design a high performance GSHP HVAC system that ensures occupant comfort and 

minimizes costs by using common infrastructure.

• Develop a cost-effective design that could provide a basis for future home designs for 

Martin Dodson Builders and other homes in the Serenbe community.

• Develop a test and monitoring plan to determine the operational efficiency and energy 

consumption of the home’s HVAC system and examine the actual to projected energy 

savings and cost effectiveness of certain high-profile energy upgrade measures.

• Earn ENERGY STAR and EarthCraft house certification.

Southface plans to apply the lessons learned from this test home to future projects, and 

anticipates the findings will be particularly relevant to others in the mixed humid climate zone. 

These specific data will also provide additional documentation of in situ performance of GSHPs 

in homes to the BA Program. Given that 15 homes will be built within the Nest, Southface plans 

to apply the lessons learned from each home in subsequent homes. Utility data will be collected 

throughout the community to gain a better understanding of the effect of occupant behavior on 

overall energy consumption and the performance of the homes compared to modeled projections.

This report outlines the features of this individual test home, discusses construction and 

installation, and details short-term testing and monitoring.
3

2 Energy Efficient Solutions Package

2.1 Overview

The components included in these homes are used to improve the overall thermal performance of 

the building envelope, and bring mechanical components within conditioned space. These 

upgraded measures presented cost and energy tradeoffs to the project team, with the final 

measures chosen by the builder based on cost and constructability. The project team wished to 

improve on a base set of specifications that they have used on past residential projects. Table 1 

lists the building specifications for the home, as well as the base set of specifications and the BA

2010 benchmark specifications for reference.

The first step of this project was to detail the building envelope. The builder and Southface 

wanted to explore advanced options for using high R-value exterior walls that are not typically 

built in this climate zone. Initial specifications called for single 2 × 6 top and bottom plates with 

2 × 4 staggered studs at 16-in. o.c., but based on cost and implementation concerns, this plan was 

put aside in favor of a more conventional approach. Exterior insulated sheathing was also 

considered, but also not selected based on implementation concerns from the builder and 

feedback from the framing subcontractor. Final specifications called for a more conventional 

approach with a 2 × 6 wall assembly and full fill open cell spray foam insulation, resulting in a 

cavity insulation value of R-20. 

Next, the design team considered options for the HVAC system. Because space conditioning 

often represents the largest portion of residential energy consumption and has been a primary 

target for achieving substantial use reductions, it was a goal of this project to implement the most 

efficient system possible. Based on initial energy simulation studies and the partnership of an 

HVAC manufacturer, GSHPs were chosen to provide space conditioning. Because the Nest 

subdivision will include 15 homes when complete, the development partner from the Serenbe 

community saw the opportunity to reduce the installed cost of the GSHPs by using shared 

infrastructure. Instead of individual wells associated with the GSHPs for each home, the 

community features two separate loops tied to heat exchangers in the adjacent lake. Each loop 

serves multiple homes, seven homes on one loop and eight on the other, and includes a supply

and return line. Individual pump stations are installed in each home to move water through the 

loops.

With the reduced infrastructure and installation costs associated with the manufacturer 

partnership, GSHPs become a more cost-effective option. Southface has found however, that 

many projects choose to use GSHPs without evaluating other high efficiency alternatives, 

decisions that Southface believes are based on performance and cost perceptions not yet proven 

by real-world evaluation and monitoring. To further explore this issue, the primary system 

investigation in this home includes researching the HVAC system.
4

Table 1. Nest Cottage Building Specifications

Measure B10 Benchmark Base Specification Nest Cottage

Foundation Sealed Crawlspace Basement Basement

Foundation Insulation R-5 R-10 R-10

Wall Construction 2 × 4 2 × 4 2 × 6

Wall Insulation R-13 R-13 R-20

Ceiling Construction Vented Attic Vented Attic Cathedral Attic

Ceiling Insulation R-30 R-30 R-26

Window Ratings U-0.40, SHGC-0.30 U-0.35, SHGC-0.31 U-0.35, SHGC-0.31

Infiltration SLA = .00036 ELR < 0.40 ACH50 < 5

Heating Efficiency 7.7 HSPF 92 AFUE 5.5 COP

Cooling Efficiency 13 SEER 13 SEER 16 EER

Supply Duct Location 65% crawlspace, 35% 

conditioned space

50% conditioned space, 

50% basement

50% conditioned space, 

50% basement

Return Duct Location 100% crawlspace 50% conditioned space, 

50% basement

50% conditioned space, 

50% basement

Duct Leakage 15% total < 5% to outside < 5% to outside

Ventilation Exhaust 100% 

ASHRAE 62.2

Central fan integrated 

supply, 100% ASHRAE 

62.2

Central fan integrated 

supply, 100% ASHRAE 

62.2

Hot Water Efficiency 0.86 EF, electric 0.59 EF, gas storage 0.67 EF, gas storage

Lighting

66% incandescent,

21% CFL,

13% LFL

66% incandescent,

21% CFL,

13% LFL

20% incandescent,

80% CFL

Appliances Benchmark ENERGY STAR ENERGY STAR
5

2.2 Thermal Boundary

The thermal boundary for this home includes the insulated basement walls, exterior walls, and 

full cathedral ceiling. This design achieves the goal of bringing all HVAC equipment and 

distribution within the conditioned envelope.

Figure 2. Nest Cottage nine building envelope

2.2.1 Foundation and Framing

The home is built on a poured concrete foundation wall at the front of the home that drops off to 

follow grade moving toward the rear of the home. The home has 2 × 6 exterior walls, a 

conventionally framed roof assembly, and engineered floor joists.

Figure 3. Foundation wall and framing, Nest Cottage nine

Legend

Above-grade exterior walls and roofline

Below-grade basement walls
6

2.2.2 Air Sealing and Insulation

A single contractor completed air sealing measures and insulation installation as a package, 

following the standard air sealing and insulation requirements of the EarthCraft and ENERGY 

STAR programs. Caulk and expanding foam were used for air sealing in the following areas:

• Penetrations through top and bottom plates

• Bottom plate to subfloor 

• Penetrations through band 

• Penetrations through subfloor 

• Window and door rough openings 

• Gaps in exterior sheathing 

• Exterior wall penetrations

• Penetrations through insulated ceilings

• Wall/ceiling penetrations through drywall in attached garage.

Figure 4 shows air sealing details at an exterior basement wall corner, including the caulk to seal 

the bottom plate to the basement slab and the expanding foam to seal seam and gaps in the 

exterior sheathing. Also note the two stud corner, which allows for more complete insulation fill. 

Figure 4. Air sealing detail at exterior basement wall corner, Nest Cottage nine

Open cell spray foam was used for insulation in all areas, providing additional resistance to air 

infiltration. Insulation specifications included an R-10 exterior drainage mat at the foundation 

walls, full fill of the exterior 2× 6 wall cavities with open cell spray foam insulation resulting in 

R-19, and 7 inches of foam applied to the roof deck resulting in R-26. The exposed insulation in 

the attic space required a spray-applied ignition barrier. This full fill approach represents a major 

change from typical building practices in this climate zone, where open cell spray foam is 

typically applied to a depth of 3.5 inches, resulting in a cavity insulation value of R-13. The first 

home built in the subdivision received these typical levels of insulation installation because of

communication problems between the builder and insulation subcontractor. This error was
7

corrected on subsequent homes, with additional installation guidance provided by the insulation 

manufacturer. Given the high humidity of the local climate, the moisture performance of this 

assembly remains unknown and a topic for future research efforts.

Figure 5. Insulation at second floor and roof, Nest Cottage nine

2.2.3 Fenestration

The home features high performance glazing with low solar heat gain coefficient, U-0.35, 

SHGC-0.31 throughout.

Figure 6. Window specification, Nest Cottage nine

2.3 Systems

The primary system investigation in this home includes researching the HVAC system. Regarded 

as one of the most efficient system choices, GSHPs incorporate complex components and 
8

extensive infrastructures to reduce the effect of fluctuating ambient conditions for heat exchange, 

and rely on sophisticated controls strategies to extract efficiency out of part-load conditions. 

Research and testing have documented efficacies that are double a standard efficiency 

conventional air-to-air system, but this comes at more than twice the initial cost. When this cost 

premium is considered, along with the lowered space conditioning loads of high performance 

homes and the capabilities of the typical HVAC contractor to size, install, and commission a 

GSHP, the question of cost effectiveness becomes a major issue in the choice of this technology 

over high efficiency conventional systems or emerging technologies such as variable refrigerant 

flow split systems. Currently, the market has demonstrated that the high price, technological 

complexity, available tax incentives, and acoustic and aesthetic benefits of GSHPs from the 

elimination of exterior condensers have given the system cachet in the high-end residential 

market, similar to marquee kitchen appliances and luxury automobiles.

2.3.1 HVAC

The GSHPs included in this project present an opportunity to evaluate the cost effectiveness and 

in-field efficiency of this technology in a lake loop application. The GSHPs used in these homes 

are rated at 16 energy efficiency ratio (EER) and 5.5 coefficient of performance (COP) at full 

load and 18.6 EER and 6.3 COP at part load for water loop applications per AHRI/ISO 13256-1

(Air-Conditioning, Heating, and Refrigeration Institute, 1998). Southface has found that many 

projects, including the Nest development, choose to use GSHPs without evaluating other high 

efficiency alternatives and believe that these decisions are based on performance and cost 

perceptions that have not been proven by field evaluation. Collecting installation and operating 

costs in this project will allow for improved decision making on future projects. Southface plans 

to follow the Advanced Systems Research Draft GSHP monitoring guidelines.

Meeting ASHRAE 62.2 ventilation rates introduces another tradeoff choice to builders in the 

mixed humid climate zone. Builders want to meet the air flow requirements in the most costeffective manner, while choosing a system that mitigates the added costs and latent loads that are 

introduced by ventilation air in this climate. The most popular ventilation strategy in the local 

market is the central fan integrated supply (CFIS). This strategy consists of a ducted outside air 

intake connected directly to the return plenum of the central HVAC system. The negative 

pressure of the return pulls ventilation air through the intake, and the air is distributed throughout 

the home using the blower and ductwork of the central system. The intake duct includes a 

mechanical damper equipped with a ventilation timer, allowing variable amounts of outside air to 

be introduced into the central system. This timer ensures adequate ventilation on mild days when 

the central system is not calling for heating or cooling by opening the damper and calling on the 

central fan to run.
9

Figure 7. CFIS system schematic

© 2009 by Building Science Corporation; reprinted with permission

Monitoring the additional system runtime linked to the CFIS controller, as well as the 

temperature and relative humidity of the incoming air stream, will produce more data on the 

energy costs and effectiveness of this ventilation approach. Southface hopes to build on the past 

BA Program ventilation studies conducted by the Building Science Corporation and the 

Consortium for Advanced Residential Buildings teams focusing on the additional heating, 

cooling, and fan energy consumption associated with this ventilation strategy (Building Science 

Corporation, 2009) (Constortium for Advanced Residential Buildings, Steven Winter Associates, 

Inc., 2010)

2.3.2 Plumbing

A 0.67 energy factor (EF) gas storage water heater provides water heating for the home. All 

plumbing is located within the home’s thermal boundary.

2.3.3 Lighting and Appliances

The home includes a lighting package with a mix of 80% CFL and 20% incandescent bulbs, as 

well as ENERGY STAR kitchen and laundry appliances.
10

2.4 Estimated Cost of Energy Efficiency Solution

Southface is still working with the project partners to collect detailed cost data regarding the 

upgraded envelope measures and HVAC systems, including the shared loop infrastructure, 

GSHPs, and ventilation controllers used by the project. These data will be incorporated into the 

long-term monitoring report in 2012 to answer research questions regarding the cost

effectiveness of these upgraded measures and to address gaps in the current NREL cost database.

2.5 Measure Interactions

These upgraded measures present cost and energy tradeoffs to the project team, with the final 

measures chosen by the owners based on cost. Many of the energy efficiency features 

incorporated into the home design are new to the design team and trade contractors and require a 

learning curve that will subsequently be evaluated for success and opportunities for improvement 

as the testing results emerge. Based on the changes from the initial project specifications that 

took place during construction, knowledge gaps with trade subcontractors and product suppliers 

continue to present barriers to implementing high performance housing in this market. Given the 

learning curve, detailed construction documents, scopes of work, and builder oversight are 

necessary to implement measures that are unfamiliar for trade subcontractors.
11

3 Technical Pathway

3.1 Inputs to Building Energy Optimization Software

Because design and construction began in 2009, initial energy simulations were completed using 

Energy Gauge software and the 2008 BA benchmark. Southface has since completed energy 

simulations and cost tradeoff analysis using the Building Energy Optimization (BEopt) tool 

demonstrate that the home meets the current BA goals of 30% above the B10 BA benchmark. 

The finalized building specifications for the Serenbe Nest cottages residence were compared to a 

base set of specifications that the project team has used on past projects of similar scope (see 

Table 1). 

Several assumptions were made for this comparison based on gaps in the available BEopt inputs. 

At this time BEopt does not have an option to include the GSHP used in this project. In lieu of 

this option, the most efficient air-source heat pump from the BEopt options library was chosen 

for the simulation, 18 SEER, 9.2 HSPF, and 0.95 EF, respectively. It is anticipated that the added 

efficiency of this option would increase the source energy and utility bill savings above the 

estimated levels listed in the results section. 

Southface plans to update the simulation models on the release of updated versions of BEopt that 

include input options for GSHPs. The long-term monitoring data gathered will also allow for 

additional refinement of modeling results, and give a true picture of the home’s total energy 

consumption.

3.2 Energy Simulation Results

The Nest Cottage, lot nine test home is projected to save 30.1% over the BA B10 benchmark. 

Optimization studies for the project were not completed given that construction specifications 

had been finalized before the introduction of the BEopt tool. Figure 8 graphically depicts the 

simulation results.
12

Figure 8. Source energy savings for Nest Cottage, lot nine over the B10 benchmark and the 

builder’s typical package 

The preliminary annual cost savings are estimated to be more than $417 per year compared to the 

B10 benchmark. Figure 9 depicts components of the savings.
13

Figure 9. Annualized utility bill comparison for Nest Cottage, lot nine 

against B10 benchmark and the builder’s typical package
14

4 Experiment

4.1 Test Plan

A detailed short-term testing and long-term monitoring plan was presented in Southface’s test 

plan for the Nest Cottages, focusing on whole-house performance. The primary thrust of the 

investigation for this home will include whole-house performance, with a detailed evaluation of 

the GSHP (e.g., performance against rated efficiency values, previous studies, and the modeled 

consumption of high performance conventional systems). Test results will produce data to 

address the question of real versus perceived value.

4.2 Research Questions

Using this new construction test house for testing and evaluation is critical to answering the 

following research questions:

• Is the measured energy use for heating and cooling consistent with modeled estimates 

given similar ambient weather conditions?

• How do the efficiency, capacity, and operation costs of the GSHPs compare to AHRI

ratings and manufacturer’s published data?

• What is the additional fan energy, heating, and cooling consumption associated with the 

central fan integrated ventilation system?

• How does the cost effectiveness of certain high-profile energy upgrade measures, 

specifically a GSHP, compare to projected energy savings and other potential energy 

upgrades?

To answer these questions, the following research measurements were made or equipment 

installed:
15

Table 2. Research Measurements and Equipment

Parameter of Interest Test Method Purpose

House Infiltration Rate Blower door test and diagnostic evaluation • At construction completion, provide overall infiltration rate 

and locate remaining major leakage paths.

HVAC Duct Tightness 

and Overall Duct System 

Performance

Duct leakage test; air handler and diffuser 

flow rates; room pressure differentials (air 

handler running, doors closed); total external 

static pressure

• At construction completion, characterize overall air 

delivery system.

Ventilation System 

Performance

Balometer and hot wire anemometer 

measurements

• At construction completion, measure supply ventilation air 

flow rate and exhaust fan flow rates. Measure house 

depressurization during exhaust fan operation.

Whole-House Electric Energy transducer and recording devices • Record whole-house electricity use.

• Identify a demand profile.

Space Conditioning 

Equipment

Energy transducers

• Compressor

• Air handler fan

• Supp. heat

• Loop pump

Temperature/RH sensors

• Supply plenum

• Return plenum

Temperature/flow sensors

• Ground loop supply

• Ground loop return

• Document the operation of the HVAC system relative to 

interior setpoints and exterior ambient drivers.

• Document the real time efficiency of the HVAC system.

• Document the added run time attributed to the CFIS 

ventilation system.

Indoor Environment

• Temperature/ RH sensors

• 1 sensor in each HVAC zone (1 on each 

floor)

• 1 sensor located in supply duct for each 

zone supply

• 1 sensor in basement

• 1 sensor outside

• Analyze the operation of the HVAC system relative to 

interior and exterior temperature and humidity drives.

Other TBD • Additional short-term tests or monitoring devices may be 

added based on ongoing measured data inspections, and/or 

field performance reported by builder staff or consumers.
16

Short-term tests are detailed in the following section. Long-term monitoring will be detailed in a 

future report after at least one year of monitored data has been collected.
17

5 Short-Term Testing

5.1 Short-Term Characterization Testing

Table 3 outlines the short-term measurement parameters and equipment used to obtain accurate 

and reliable measurements.

Table 3. Short-Term Equipment and Test Measurements

Measurement Equipment Test Measurements

Infiltration Rate Blower door apparatus 950 CFM50, 2.9 ACH50

Duct Loss Duct Blaster apparatus1

160 CFM25, 11.9% of conditioned 

floor area total leakage;

0 CFM25, 0% of conditioned floor 

area leakage to the outside

Air Handler Flow 

Rate Trueflow grid2 1,040 CFM

1. Energy Conservatory Duct Blaster System

2. Energy Conservatory TrueFlow Air Handler Flow Meter

The short-term characterization testing results outlined in Table 4 include infiltration and duct 

leakage. The testing results show that the project met two of its primary goals—creating a tight 

thermal boundary to reduce air leakage and improving the thermal performance of the HVAC 

system by placing the air handler and ductwork 100% within conditioned space—with an 

infiltration rate of 2.9 ACH50 (950 CFM50) and duct loss to the outside of 0% of floor area served 

(0 CFM25). Air handler and duct flow rates continue to be gathered as part of the ongoing 

systems commissioning and startup of the long-term monitoring sensors.

Long-term monitoring will include sensors that record electric load and consumption,

temperature, relative humidity, and fluid flow. The sensors in the home’s mechanical room 

monitor electricity draw and the operation of the space conditioning and hot water equipment; 

they are hard wired for power and data logging. Temperature and relative humidity sensors 

located in the home’s conditioned space, basement, and outdoors are equipped with a long-lived 

battery-fueled wireless transmitter that communicates with the main data logger in the 

mechanical room. A receiver/modem in the home receives and uploads data at preprogrammed 

intervals to a central server via an internet connection.
18

6 Summary

The design and implementation goals for this test house have been achieved. The home is 

projected to reach the 30% savings goal, a high performance thermal boundary that reduces air 

infiltration and brings mechanical equipment within conditioned space has been constructed, and 

the home will serve as a showcase and example for future development in the Serenbe 

community. With monitoring efforts planned to start in December 2012, Southface plans to focus 

on (1) determining the operational efficiency and energy consumption of the home’s HVAC 

system, with a focus on the additional system fan run time associated with homes central fan 

integrated ventilation supply; and (2) examining the cost effectiveness of certain high profile 

energy upgrade measures, specifically a GSHP. Next steps include the following:

• Finalize collection of detailed cost data regarding the upgraded envelope measures and 

HVAC systems, including the shared loop infrastructure, GSHPs, and ventilation controllers 

used by the project, and prepare a detailed payback analysis.

• Prepare a long-term monitoring report based on at least one year’s performance data.
19

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Standard 13256-1 Water-to-Air and Brine-to-Air Heat Pumps — Testing and Rating for 

Performance. Arlington, VA: Air-Conditioning, Heating, and Refrigeration Institute.

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Ventilation Systems for All Climates. Sommerville, MA: Building Science Corporation.

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least 50% wastepaper, including 10% post-consumer waste.