Short-Term Test Results: 

Multifamily Home Deep Energy 

Efficiency Retrofit

James Lyons 

BA-PIRC

January 2013
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iii

Short-Term Test Results: Multifamily Home Energy Efficiency Retrofit

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: 

James Lyons

Building America Partnership for Improved Residential Construction (BA-PIRC)

Cocoa, FL 32922

NREL Technical Monitor: Stacey Rothgeb

Prepared under Subcontract No. KNDJ-0-40339-00

January 2013
iv

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v

Contents

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

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

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

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

1 Problem Statement............................................................................................................................... 1

1.1 Introduction..........................................................................................................................1

1.2 Background..........................................................................................................................2

1.3 Relevance to Building America’s Goals..............................................................................2

1.4 Cost-Effectiveness ...............................................................................................................3

1.5 Tradeoffs and Other Benefits...............................................................................................3

1.5.1 Energy Savings versus Implementation Costs.........................................................3

1.5.2 Regulatory and Constructability Tradeoffs..............................................................4

1.5.3 Building Science “Risk Factors” .............................................................................4

2 Research Questions............................................................................................................................. 7

3 Retrofit Specifications ......................................................................................................................... 8

3.1 Selection and Cost-Effectiveness of Final DER Measures..................................................8

3.2 Implementation, Commissioning, and Short-Term Testing of Final DER Measures........12

3.2.1 Building Envelope Infiltration Reduction..............................................................12

3.2.2 Duct Air Leakage Reduction .................................................................................16

3.2.3 HVAC and Ventilation Equipment Efficiency Upgrade .......................................19

4 Conclusions ........................................................................................................................................ 22

4.1 Developing a DER Scope ..................................................................................................22

4.2 Implementation, Commissioning, and Testing of Efficiency Upgrade Measures.............23

4.3 Next Steps at Bay Ridge ....................................................................................................24

References................................................................................................................................................. 25
vi

List of Figures

Figure 1. Aerial view of Bay Ridge development; DER building outlined in red................................. 1

Figure 2. Front view of three-story apartment building .......................................................................... 1

Figure 3. Polyethylene layer on inside face of CMU wall assembly ...................................................... 4

Figure 4. Exterior wall section showing limitted depth furring and poly layer on inside face of 

CMUs...................................................................................................................................................... 5

Figure 5. Air sealing opportunity at corners of duct boot where it meets ceiling drywall ................ 12

Figure 6. Air sealing of duct register boot and an HVAC penetration................................................. 14

Figure 7. Floor plans for 3-bedroom and 2-bedroom apartments (same on all 3 floors) ................. 15

Figure 8. Supply trunk for third-floor apartment exposed to attic (pre-retrofit condition)................ 17

Figure 9. Pre-retrofit HVAC return plenum............................................................................................. 16

Figure 10. Diagram of duct bulkhead open to the attic space.............................................................. 18

Figure 11. Membrane application followed by SPF application to seal off top of duct bulkhead from 

attic ...................................................................................................................................................... 18

Figure 12. Energy end use reductions in the deep energy retrofit design ......................................... 23

Unless otherwise noted, all figures were created by Newport Partners, LLC.

List of Tables

Table 1. Summary of Rejected Upgrade Measures ................................................................................. 5

Table 2. Energy Efficiency Retrofit Measures........................................................................................ 10

Table 3. Building Leakage: Blower Door Test Results.......................................................................... 13

Table 4. Duct Leakage Test Results........................................................................................................ 17

Table 5. Energy Savings and Costs Analysis of Hybrid Heat Pump System...................................... 19

Unless otherwise noted, all tables were created by Newport Partners, LLC. 
vii

Definitions

AC Air conditioner

ACH50 Air changes per hour at 50 pascals

AFUE Annual fuel utilization efficiency

CFL Compact fluorescent lamp

cfm Cubic feet per minute

cfm25 Cubic feet per minute at 25 pascals

cfm50 Cubic feet per minute at 50 pascals

CMU Concrete masonry unit

DER Deep energy retrofit

ERV Energy recovery ventilator (or enthalpy recovery ventilator)

ETS Environmental tobacco smoke

HERS Home Energy Rating System

HSPF Heating seasonal performance factor

IAQ Indoor air quality

kBtu Thousand British thermal units

MMBtu Million British thermal units

MEA Maryland Energy Administration

Pa Pascal

RH Relative humidity

SEER Seasonal energy efficiency ratio

SHGC Solar heat gain coefficient

SIR Savings to investment ratio

SPF Spray polyurethane foam

W Watt
viii

Executive Summary

Multifamily deep energy retrofits (DERs) on relatively common building types are valuable 

research efforts for the U.S. Department of Energy’s Building America Program. Such buildings 

represent great potential for energy savings, while providing valuable research-generated 

efficiency measures, cost-effectiveness metrics, and risk factor strategies to the multifamily 

housing industry. The Bay Ridge project comprises a base scope retrofit with a goal of achieving 

>30% savings (relative to pre-retrofit), and a DER scope with a goal of 50% savings (relative to 

pre-retrofit). The base scope was applied to the entire complex, except for one 12-unit building 

that underwent the DER scope. The design and construction phase of the Bay Ridge project is 

now complete, and this report summarizes the commissioning, short-term testing, and analysis 

that occurred before, during, and just after the actual retrofit.

Findings from the implementation, commissioning, and short-term testing include air infiltration 

reductions of >60% in the DER building; a savings to investment ratio of >1 from the hybrid 

heat pump system (relative to a high efficiency furnace), which also gives the resident an added 

incentive for energy savings; and duct leakage reductions of >60% resulting from using an 

aerosolized duct sealing approach. Despite being a moderate rehab instead of a gut rehab, the 

Bay Ridge DER is currently projected to achieve energy savings ≥50% compared to pre-retrofit

levels, and the short-term testing supports this estimate. Long-term monitoring throughout 2012 

will evaluate actual performance.
1

1 Problem Statement 

1.1 Introduction

Under this project, Newport Partners (Newport; as 

part of the Building America Partnership for 

Improved Residential Construction research team) is 

evaluating the installation, measured performance, 

and cost effectiveness of efficiency upgrade 

measures for a tenant-in-place1 deep energy retrofit 

(DER) at the Bay Ridge multifamily development in 

Annapolis, Maryland. The design and construction 

phase of the Bay Ridge project is now complete, and 

this report summarizes the commissioning, shortterm testing, and analysis that occurred before, 

during, and just after the actual retrofit. 

The Bay Ridge project comprises a base scope 

retrofit that is estimated to achieve a >30% savings 

(relative to pre-retrofit) on 186 apartments, and a 

DER scope that is estimated to achieve 50% savings 

(relative to pre-retrofit) on a 12-unit building. The 

base scope was applied to the entire complex, except for one 12-unit building on which the DER 

scope approach was taken. 

A wide range of efficiency measures was applied to achieve this savings target for the DER 

building, including improvements and replacements of mechanical equipment and distribution 

systems, appliances, lighting and lighting controls, 

the building envelope, hot water conservation 

measures, and resident education. 

The results of this research will build on the current 

body of knowledge of retrofits, specifically deep 

retrofits in multifamily projects. Toward this end, the 

research team collected and generated data on the 

selection of measures, their estimated performance, 

their measured performance, their estimated and 

actual cost effectiveness, risk factors and their impact 

on potential measures, and the overall energy savings 

from two different retrofit packages applied to the 

same types of buildings in the complex. 

 1 Tenant-in-place refers to an approach to building renovation in which residents vacate their dwelling during the 

daytime, and return at night. Basic dwelling functionality is restored and health/safety risks are addressed at the end 

of each work day.

Figure 2. Front view of three-story 

apartment building

Figure 1. Aerial view of Bay Ridge 

development; DER building outlined in red
2

1.2 Background

DERs can result in >30% energy savings, and are much easier to implement when a building is 

undergoing a substantial remodel, in which contractors can have greater access to walls, ceilings, 

and duct systems. For projects like Bay Ridge that are not undergoing substantial remodels,

which are more common, the selection of DER measures during a renovation must balance the 

energy savings of upgrade measures against the ability to realistically apply the measures with 

residents still occupying the building (at least at night). Simultaneously, these upgrade measures 

must also be evaluated for their potential to trigger code/regulatory issues, exacerbate preexisting risk factors in the building, and affect the ability of contractors to reliably and 

successfully apply them. 

The Bay Ridge DER research project builds on this knowledge base by generating measured 

energy performance and cost data on a common building type that received a moderate rehab.

1.3 Relevance to Building America’s Goals

This research project is part of the U.S. Department of Energy’s Building America Program.

Overall, the goal of the Building America Program is to reduce home energy use by 30%–50% 

(compared to 2009 energy codes for new homes and pre-retrofit energy use for existing homes). 

Building America’s energy savings goals are particular to individual climate zones. The project 

site is located in Annapolis, Maryland, in a mixed-humid climate (climate zone 4A). As related 

to existing homes within mixed-humid climates, Building America has a goal of 30% energy 

savings from the pre-retrofit condition by 2013. 

The most important merits of the research at the Bay Ridge complex are as follows:

The project team is investigating a common building type: a 1970s-era, three-story walk-up 

apartment building owned and operated by a major industry firm. In addition, the renovation 

incorporates a retrofit model that property owners and affordable housing advocates support: 

tenant-in-place (in which the tenant might be inconvenienced for a short period of time but is not 

displaced). 

The research team is exploring risk factors and regulatory issues, and their roles in determining 

what efficiency measures might not be viable because they would jeopardize building 

performance, compromise occupant health, or trigger cascading regulatory requirements. Such 

risk factors are common and property owners need effective identification and mitigation 

strategies with which to navigate them.

Both building owners and energy efficiency program managers want to answer this question: 

How much energy did the project really save? Under this effort, the research team is validating 

estimated energy savings for two different retrofit scopes applied to the same building types with 

actual savings. The base scope retrofit is estimated at 30% savings and the DER scope is 

estimated at 50% energy savings. The research team deployed energy monitoring to evaluate 

post-retrofit performance characteristics.

Taken together, the components of this research will yield extremely valuable information to the 

U.S. Department of Energy and the multifamily building industry. This project will augment 

understanding of current capabilities in energy retrofits and remaining gaps.
3

1.4 Cost Effectiveness

Newport assessed and prioritized a wide range of potential efficiency measures, with the most 

effective and feasible measures combined into the DER scope. The following energy-related 

factors were assessed in the cost-effectiveness evaluation:

• Annual energy savings (modeled)

• Annual energy cost savings (modeled)

• Implementation costs (estimated)

• Cost effectiveness in the form of savings to investment ration (SIR; calculated).

Newport engineers and building analysts conducted energy modeling with REM/Rate to project 

the cost effectiveness of various measures on the basis of the SIR (highly relevant to multifamily

projects that receive weatherization funding) and other metrics. Building Energy Optimization 

software was also evaluated for this work, but was ultimately bypassed because of its lack of 

functionality in the following areas: modeling exterior wall orientations of varying construction 

type (e.g., common wall and exterior wall sharing the same orientation), and modeling hybrid (or 

dual fuel) heat pump systems. REM/Rate was also deemed acceptable for this project because, 

when the retrofit project also became a Building America research effort, energy upgrade 

analysis using REM/Rate had already been under way for more than 6 months under contract 

with the Maryland Energy Administration (MEA).

The modeling analysis generated a list of potential measures, but additional filters were applied 

to ensure that efficiency measures accounted for existing conditions and the project’s rehab 

model. These additional considerations were as follows:

• Compatibility with a tenant-in-place rehab model

• Compatibility with a rehab scope that did not include façade removal

• Sensitivity to creating cascading regulatory issues (e.g., exposing aluminum wiring as 

part of an air sealing and insulation efficiency measure)

• Avoidance of unintended consequences (e.g., creating hygrothermal problems or negative 

indoor air quality impacts).

The vetting of potential measures against these factors involved extensive dialogue with the 

general contractor, additional site inspections, hygrothermal modeling, and analysis of 

ventilation system options.

1.5 Tradeoffs and Other Benefits

Several types of tradeoffs, described in the following subsections, were evaluated in the 

development and selection of the efficiency measures. 

1.5.1 Energy Savings versus Implementation Costs

The Newport research team conducted building energy modeling analysis along with cost 

estimating to compare energy cost savings versus implementation cost. Measures with an SIR >1 

generally passed this test, although this level is not a strict rule, and some measures with SIR <1 
4

were ultimately included in the DER scope. The magnitude of the implementation cost was also 

a consideration for marginal measures. For example, a solar electric array underwent initial 

screening but was not selected for further evaluation because of the implementation cost and the 

SIR.

1.5.2 Regulatory and Constructability Tradeoffs

Several measures under consideration were not selected because of complications with residents 

returning to their dwellings each night, in addition to underlying risk factors within the building. 

One example included potential air sealing measures. 

Invasive air sealing efforts near the rim joist, which would 

require opening up drywall bulkheads, were not selected 

because the project team felt that too much of the existing 

aluminum wiring in walls and ceilings would be exposed. 

The local regulatory authority approved a copper-toaluminum crimping retrofit approach because the 

aluminum wiring was otherwise not being exposed. If 

enough aluminum wiring was exposed, however, the 

authority would likely require a full wiring change in the 

entire apartment. The crimping solution is an industryrecognized approach to existing aluminum wiring, and 

represents a practical solution for moderate rehabs. A 

secondary concern with invasive air sealing was the ability 

to safeguard the apartment at night in a way that prevented 

residents from being exposed to open building cavities, energized wiring, and exposed nails, 

among potential hazards.

1.5.3 Building Science Risk Factors

Newport’s invasive investigations of the building revealed an exterior wall assembly of 

uninsulated CMUs with a layer of poly on the inner face of the block (see Figures 3 and 4). 

Hygrothermal analysis of this assembly showed significant risk of wintertime condensation on 

the inner face of this poly if insulation was added to the inner side of this assembly. As a result, 

laminating R-5 extruded polystyrene insulation to the existing drywall on exterior walls, which 

had been a cost-effective measure based on initial analysis, was rejected as a potential efficiency 

measure.

Figure 3. Polyethylene layer on inside 

face of concrete masonry unit (CMU) 

wall assembly
5

Figure 4. Exterior wall section showing limitted depth furring and 

poly layer on inside face of CMUs

Table 1 summarizes numerous measures that were considered during the DER scope 

development but ultimately rejected because of the factors discussed previously. Although the 

specific conditions of a given project dictate viable energy upgrade measures, this summary 

serves as a primer for important factors to consider.

Table 1. Summary of Rejected Upgrade Measures

Energy Efficiency 

Retrofit Measure Description Primary Reason for Rejection

Interior Insulation 

on Exterior Walls

R-5 continuous, interior, adhered to 

inside gypsum face of all exterior 

walls. One-inch rigid foam and 

sheetrock installed over existing 

wall surface. Extensions for 

windows, outlets, and switches

Strong risk of winter season 

condensation within wall assembly

because of continuous layer of poly 

vapor retarder within exterior wall 

assembly

Spray Foam Attic 

Insulation

Existing blown-in and batts

removed; 2-in. spray foam cap 

added to attic floor; reapplication of

blown-in to R-49

Spot air sealing deemed more cost 

effective

Solar ElectricArray

Multipanel photovoltaic array to 

generate electricity for all 12 

apartment units

Capital cost too great for DER 

budget

Ground-Source 

Heat Pump

Ground-source heat pump with 

central loop sized to meet building 

heating and cooling loads

Schedule delays for permitting; site 

disturbance for loop;
6

Energy Efficiency 

Retrofit Measure Description Primary Reason for Rejection

High Efficiency 

Furnace

95+ AFUE furnace 

with electronically commutated 

motor (base scope used 92.5-AFUE 

two-stage furnace)

Hybrid heat pump system more cost 

effective in terms of SIR

Upgraded 

Windows

U-0.29, SHGC-0.27 windows (base 

scope used U-0.35, SHGC-0.35 

units)

Limited energy savings (and SIR 

<1) relative to base scope, driven by 

relatively modest window area 

(14%–16% window to floor area 

ratio) and low design loads

Upgraded Cooling Utilize 16-SEER AC (base scope: 

15-SEER, 1.5 ton)

Limited energy savings and SIR 

relative to base scope

Auxiliary 

Dehumidification

Auxiliary dehumidification 

considered as an IAQ measure, 

given anecdotal reports of high 

indoor RH level and anticipated 

lower post-retrofit infiltration

ERV whole-dwelling ventilation 

selected instead for balanced 

ventilation and some amount of RH 

control

Venting Kitchen 

Range to Outdoors

IAQ upgrade for better kitchen 

ventilation

Construction team deemed too 

costly

Green Switch 

Switches and 

Outlets

Switch and outlet technology to 

allow residents to easily turn off 

electrical devices not in use with a 

remote switch

Reliance on regular, long-term 

resident intervention to realize 

energy savings

Notes: AFUE, annual fuel utilization efficiency; SHGC, solar heat gain coefficient; SEER, seasonal energy 

efficiency ratio; AC, air conditioner; IAQ, indoor air quality; ERV, energy recovery ventilator; RH, relative 

humidity
7

2 Research Questions

The key research questions for this DER project included: 

• Do two different specified >30% retrofit packages meet their respective energy savings 

targets based on post-retrofit analysis? If not, why? 

• What are the roles of different building system improvements in meeting energy savings 

targets? 

• How effective are different air sealing measures?

• What risk mitigation strategies are necessary to successfully implement these packages?
8

3 Retrofit Specifications 

3.1 Selection and Cost Effectiveness of Final Deep Energy Retrofit Measures

To best understand the short-term test data that follows, it is necessary to first review the final 

selection of DER scope efficiency measures. Newport’s chief initial role in the Bay Ridge 

project, while serving under contract to MEA and before the project became a Building America 

research project, was the development of the DER specifications. 

The base scope for the project was mostly finalized at the point when Newport was asked to 

develop cost-effective additional specifications for the DER scope. In accordance with MEA’s 

project goals, Newport used this base scope as the baseline for evaluating additional

improvements that would form the DER scope. DER measures that replaced or altered a system 

within the base scope (e.g., using a hybrid heat pump in the DER instead of the gas furnace and 

AC in the base scope) were evaluated on the basis of their marginal energy savings and marginal 

implementation costs relative to the base scope. This analysis approach essentially asked the 

question: What can be cost-effectively implemented beyond the base scope measures to reach 

50% savings? Note that the 50% savings metric compares the DER scope to the pre-retrofit

building condition. 

Given this background, Table 2 relates the energy systems of the pre-retrofit building condition, 

the base scope, and the DER scope. The last row of Table 2 also highlights the predicted 

(modeled) energy savings of the base scope design (35%) and the DER design (52%). Both of 

these levels exceed the project’s goal and meet or exceed Building America goals. Above this 

row, the Home Energy Rating System (HERS) index values for all three building conditions are 

also shown, with the base scope at 78 and the DER scope slightly better at 75. A primary reason 

for the relatively small spread in HERS index values (78 versus 75) but a much larger energy 

savings reduction (35% versus 52%) is that a significant portion of the heating load is “fuel 

switched” from gas (furnace) to electric (heat pump) in the DER. This shift significantly reduces 

heating energy usage; the HERS index is not affected as significantly.

Note that SIR values in Table 2 are only provided for DER measures that went beyond the base 

scope. Some of these measures show SIR >1; others do not. To reach the 50% savings level 

while also addressing ventilation and IAQ, MEA and the project team implemented some 

measures with SIR <1.

The following components made up the SIR calculation:

• Useful lifetime for measures was based on sources such as Seiders and colleagues (2007)

or estimated from industry data and experience.

• Implementation costs (equipment and labor) were based on quotes from the general 

contractor. In cases where a measure in the DER scope was replacing a system already 

included in the base scope, implementation cost was the net increase in cost for the DER 

measure.

• Estimated annual energy cost savings were based on REM/Rate modeling (with 

additional analysis as needed for some measures not characterized within REM), 

combined with utility prices of $0.12/kWh and $1.50/therm. In cases where a measure in 
9

the DER scope was replacing a system already in the base scope, annual energy cost 

savings were the net difference between the DER measure and the base scope measure.

• The pre-retrofit energy model was based on building audit data and diagnostic tests, and 

was compared with limited historical utility data and found to be within 15%. This was 

deemed acceptable given uncertain resident densities and behavior trends, along with a 

well-documented model of the pre-retrofit building condition.

• Life cycle energy savings were reduced by 15% to estimate degradation of performance 

over time (MEA policy).

• No utility escalation was assumed.

These factors were used in the following calculation of SIR:

SIR = (Useful Life * Annual Energy Cost Savings * 0.85) / Implementation Cost
10

Table 2. Energy Efficiency Retrofit Measures

Building System/ 

Component

Pre-Retrofit 

Condition Base Scope DER Scope

DER Scope Measure SIR

(with respect to Base 

Scope)

Attic Insulation R-19 R-49 with sealing of duct 

bulkhead Same as base scope N/A

Attic Air Sealing Leaky

Limited spot air-sealing from 

within the top floor units where 

leakage sites were accessible 

(e.g., bath fan housing) as part 

of overall unit air sealing

Air sealing of attic floor 

penetrations from attic side with 

SPF: including all mechanical 

electrical plumbing

penetrations; top plates of 

interior walls; work was in 

addition to the limited spot air

sealing in the base scope

0.5

Windows U-0.50 SHGC0.40 U-0.35 SHGC-0.35 Same as base scope N/A

Whole-House 

Mechanical 

Ventilation

None

Outside air duct in return air

plenum; (no run-time controls

or damper); not ASHRAE 

62.2acompliant

ERV (66 W; 61% Sensible 

Recovery Efficiency) to provide 

60 cfm continuous; ASHRAE 

62.2 compliant flow rates;

0.5

Bathroom 

Ventilation

Nominal 50 

cfm fan >6 

sones

110-cfm, 6-in. bath exhaust 

with integrated humiditysensing controls; 40 WSame as base scope N/A

Duct Air Sealing

Supply trunk 

not sealed; 

third-floor 

units located in 

open-top 

bulkhead

Aerosolized duct sealing 

applied; open-top duct 

bulkhead in attic sealed and

insulated

Same as base scope N/A

Space Heating 80% AFUE 

Gas Furnace

92.5-AFUE, 2-stage gas 

furnace (36/60 kBtu)

Hybrid Heat Pump: 8.50-HSPF, 

92.5-AFUE 2-stage furnace 

backup (36/60 kBtu), 40°F 

transition temp; cooling: 15 

1.3

Space Cooling 10 SEER AC 

Unit 15 SEER, 1.5 ton
11

Building System/ 

Component

Pre-Retrofit 

Condition Base Scope DER Scope

DER Scope Measure SIR

(with respect to Base 

Scope)

SEER, 1.5 ton

Domestic Water 

Heating

Central gasfired storage, 

100-gal, 0.54 

energy factor 

(serving 12 

dwellings)

100-gal,

95% thermal efficiency

Solar Hot Water with three flatpanel collectors, closed-loop 

glycol; solar storage tank 

upstream of 100 gal, 95% 

thermal efficiency water heater

0.5

Lighting 100% 

Incandescents

100% CFLs for all permanent 

luminaires

In addition to 100% CFL for 

permanent luminaires, supply 

resident with CFLs for all plugin fixtures

13.0

Refrigerator Non-ENERGY 

STAR ENERGY STAR ENERGY STAR N/A

Energy Feedback 

System None None

“Energy Dashboard” to educate 

residents on Electrical Usage 

(assuming 10% electrical savings

based in part on Parker et al.

[2008]). Estimated 10% savings 

rate based on literature and plans 

to train the residents on 

operating the retrofitted dwelling 

efficiently. Training to be given 

by the property manager

1.8

HERS Index 127 78 75 N/A

Predicted Energy 

Use Reduction 

(relative to PreRetrofit)

35% 52%

Notes: SPF, spray polyurethane foam; HSPF, heating seasonal performance factor; CFL, compact fluorescent lamp a ASHRAE (2010)
12

3.2 Implementation, Commissioning, and Short-Term Testing of Final Deep 

Energy Retrofit Measures

The following sections discuss key findings gained during the implementation, commissioning, 

and short-term testing of specific DER energy upgrade measures. Some building systems where 

the most salient findings will be gained from the long-term energy monitoring will be discussed 

in future reporting. 

3.2.1 Building Envelope Infiltration Reduction

Reducing natural infiltration was a primary strategy for the DER. The base scope included 

significant air sealing measures as they could be applied from within the apartment units (e.g.,

SPF around duct boot/drywall junction). Given typical pre-retrofit infiltration rates of 17 ACH50

(guarded) based on a sample of three representative buildings, the cost effectiveness of air 

sealing in the base scope was found to be attractive (SIR ~5). Figure 6 shows some typical air 

sealing locations.

Figure 5. Air sealing opportunity at corners of duct boot where it meets ceiling drywall

The DER scope built on this to also include additional air sealing in the attic. In the attics above 

the third-floor apartments, existing insulation was temporarily moved, and spray foam was 

applied to all mechanical electrical plumbing penetrations and the drywall/top plate joint of 

interior partitions. Although the implementation cost and estimated energy savings for this 

measure were more modest (SIR ~ 0.5), it was deemed as an acceptable step to further reduce air 

infiltration. 

In terms of implementation, the general contractor’s scope included detailed prescriptive 

requirements for air sealing that established what locations to seal, what sealing materials to 

apply, and how much sealant to apply. Additionally, the general contractor led integrated 

coordination meetings among the trades, and conducted multiple on-site walk-throughs with the 

insulation contractor. Newport and Patuxent Environmental Group (the auditor for the base 

scope) also conducted frequent on-site inspections.

Despite these efforts, the implementation of air sealing measures was inconsistent. This was 

partly the result of frequent turnover in the insulation contractor crew. The prescriptive nature of 

the air sealing requirements also had a role in this inconsistency, because workers would 
13

sometimes adopt the perspective of “What is the minimum step I have to apply at this location?” 

instead of “How can I reasonably achieve significant air sealing in conducting my work scope?”. 

As a result, Newport recommended that the property owners consider a performance-based air 

sealing approach for future projects. Such an approach would incorporate the following:

• Testing-in on a sample of units to establish a baseline

• Establishing a reasonable air infiltration reduction target (e.g., 30%–40% for moderate 

rehab). This target should be attainable, on average, with reasonable additions to 

contractor’s typical work scope

• Specifying best opportunities for reductions as guidance

• Implementing measures, and then testing-out.

Given the energy savings that are commonly attributed to air sealing in retrofits, validating these 

savings and linking contractor performance to tested reductions is a reasonable approach to 

consider.

Despite the inconsistency of the air sealing and a limited amount of rework, the average 

infiltration reduction in the DER units compared to the pre-retrofit condition was about 63%, as 

shown Table 3.

Table 3. Building Leakage: Blower Door Test Results

Max 

ACH50a

Min 

ACH50a

Average

ACH50a

Average ACH50

Reduction 

(compared to preretrofit condition)

Average 

ACH50 of 

Third-Floor 

Dwellings 

(n = 4)a

Ratio of 

Outdoor to 

“Total”

Leakageb

Pre-Retrofit 

Condition

19.4 14.8 17.1

Post-Retrofit 

Base Scope 

Dwellings 

(n = 18)

8.4 5.1 7.0 61% 7.3

(n = 6) 82%

Post-Retrofit 

DER 

Dwellings 

(n = 11)

8.3 5.2 6.4 63% 6.4

(n = 4) 81%

a Leakage to outdoors only, based on guarded blower door testing. This value was used in calculating energy savings 

from air sealing, not total (or unguarded) blower door leakage.

b Value determined by comparing guarded blower door results to unguarded blower door results

The additional attic air sealing efforts in the DER apartments also showed a marginal 

improvement relative to a tested sample of the base scope apartments, which had identical air 

sealing with the exception of work in the attic. The researchers predicted that the effectiveness of 
14

the attic air sealing would be most prominent in the third- (top-) floor apartments. This is 

illustrated in Table 3, which shows about a 12% leakage reduction in third-floor DER apartments 

(n = 4) compared to third-floor base scope apartments (n = 6).

Both guarded and unguarded blower door tests were performed. For the base scope and DER 

scope apartments, about 82% of all leakage through the apartment envelope was leakage to 

outdoors (as opposed to neighboring units). This ratio does not mirror the ratio of apartment 

envelope surface area, which is between conditioned space and outdoors and between 

conditioned space and neighboring units. Top-floor apartments have the highest percentage of 

envelope area between conditioned space and outdoors, at about 66% of their total shell area. 

Middle-floor apartments have the lowest percentage at about 24% (see floor plans in Figure 7). 

The surface area proportion, however, does not align with the measured distribution of air 

leakage in either case. This suggests that air leakage sites were not evenly distributed across the 

building envelope, with a greater concentration of leakage sites in the assemblies separating 

conditioned space from outdoor air. 

Figure 6. Air sealing of duct register boot and an HVAC penetration
15

Figure 7. Floor plans for three-bedroom and two-bedroom apartments (same on all three floors)

Referring to Figures 2 and 7, the guarded blower door tests were conducted on a stairwell basis. 

In other words, all six apartments accessed from a given stairwell and those that were 

“connected” through the shared mechanical room on each floor were simultaneously 

depressurized to –50 Pa and maintained at this level while a cfm50 reading was recorded for 

each. Arranging access for this level of testing, in addition to assembling enough technicians and 

equipment, was a significant effort. As a result, pre- and post-retrofit testing was conducted only 

on a sample of apartments and stairwells, as noted in Table 3.

In examining the disconnect between building envelope surface area distribution (with 24%–

66% of total shell between living space and outdoors) and the measured leakage rates (with 

~82% of leakage to outdoors), the researchers examined the possibility that the guarded test was 

not completely guarded. This could occur if the guarded apartment was still in communication, 

via a floor assembly, wall assembly, or chase, to some other apartment that was not being 

simultaneously depressurized. The result would be an overestimate of the proportion of shell 

leakage to outdoors (as opposed to neighboring units). 

In reviewing the guarded blower door test results and protocol (which was established in the 

initial audit), the team found that it was possible that there was some communication from 

guarded apartments to unguarded apartments. This was a reality of the testing that required 

extensive equipment, staff, and full apartment access to all surrounding units. In the guarded 

blower door tests, tests were run by the stairwell. As a result, the interior units sandwiched 

between the stairwells had no guarding across the firewall assembly in the very middle of the 

building, which joined them to the neighboring interior units (e.g., the interior two-bedroom and 

three-bedroom units in the floor plan in Figure 7). 

Newport’s researchers separated guarded versus unguarded blower door results for the exterior 

apartments (those with three exterior walls plus the wall adjacent to the stairwell) versus the 

interior units. The results indicated that 79% of total leakage was to outdoors for the exterior 

units, versus 86% for interior units. This difference supports the concept that some unit-to-unit 

leakage was occurring during the guarded tests for interior units, most likely across the firewall 

to the adjacent interior unit. The rough magnitude of the difference, however, is reasonable given 

the costs and logistical challenges of guarded testing in this type of multifamily building where 
16

depressurizing nine apartments would have been the ideal setup. In addition, other factors such 

as more extensive leakage paths to outdoors might also have contributed to this difference.

3.2.2 Duct Air Leakage Reduction

The DER involved sealing the ducts with an aerosolized duct sealing system (also part of the 

base scope), which facilitated leakage reduction even though most ducts were inaccessible. All 

ducts were also cleaned using a brush-based system with a vacuum to collect and expel dust

before aerosolized sealing. Duct cleaning before aerosolized duct sealing is recommended if the 

ducts are extremely dirty. Because of this recommendation and the general conditions of the 

ducts and the old plywood plenums (see Figure 8), duct cleaning was part of the retrofit base 

scope for all apartments.

Figure 8. Pre-retrofit HVAC return plenum

The third-floor apartments were also targeted for duct leakage reduction and improved insulation 

through an additional measure: sealing the top side of a bulkhead that housed the supply trunk. 

This bulkhead was open to the attic space in terms of air movement, and had inconsistent levels 

of insulation (ranging from R-19 to no insulation) placed on top of the supply trunk (see 

Figure 9). 
17

Figure 9. Supply trunk for third-floor apartment exposed to attic (pre-retrofit condition)

Table 4 gives the results of pre- and post-retrofit duct blaster testing. Overall, the duct sealing 

efforts resulted in a significant reduction in total duct leakage (63%). The return plenums, 

originally constructed from plywood and in very poor condition—including signs of past water 

damage (Figure 8)—were also replaced with sheet metal plenums.

Table 4. Duct Leakage Test Results

Total Duct Leakage 

(cfm25)

Pre-Retrofit Condition 481

Post-Retrofit Base and DER Scope Dwellings 180

% Reduction 63%

Insulating and air sealing the open-top bulkhead shown in Figures 9 and 10 involved a two-step 

process specified by Patuxent Environmental Group (the base scope auditor ). It involved (1) 

removing insulation from the bulkhead area and putting down a membrane to serve as a 

substrate, and then (2) applying a layer of SPF to bond the membrane to the ceiling drywall as 

well as cap off the ends of the bulkhead. These two steps are shown in Figure 11. This process 

proved to be effective when properly implemented. In some cases, however, site inspections 

revealed that the insulation contractors would cover the top of the bulkhead with SPF but fail to 

block off the ends, which would still allow significant air leakage to the attic.
18

Figure 8. Diagram of duct bulkhead open to the attic space

Figure 9. Membrane application followed by SPF application to seal off 

top of duct bulkhead from attic
19

Sealing off this bulkhead also contributed to the whole-dwelling air leakage reductions for thirdfloor apartments noted in Table 3.

3.2.3 HVAC and Ventilation Equipment Efficiency Upgrade 

The pre-retrofit HVAC systems were ~15-year-old furnaces and split system AC units. Labeled 

efficiency levels were 80 AFUE and 10 SEER, respectively. The base retrofit scope upgraded 

these systems to a 2-stage, 92.5-AFUE condensing furnace and a 15-SEER split AC system. 

Given the mixed-climate zone location (~4,700 heating degree days; 17°F heating design temp) 

and the utility rates, Newport investigated hybrid heating options involving both electric and 

natural gas. A heat pump-only approach was ruled out early in the process because the electrical 

service to the units could not accommodate the required capacity for electric resistance backup 

heating.

The research team’s energy modeling and cost analysis concluded that changing from the base 

scope’s 92.5 AFUE, 2-stage gas furnace with 15 SEER AC to a hybrid heat pump (15 SEER, 

8.50 HSPF with 92.5 AFUE furnace backup) was a cost-effective, energy-saving measure with 

an SIR of 1.3. Given that the base scope already utilized a 15 SEER split AC system and a high 

efficiency furnace, the marginal cost to upgrade to the hybrid heat pump system was reasonable 

at $975.

Residents at the Bay Ridge development are responsible for paying their electric bills. Electricity 

is metered at the apartment level. Natural gas is paid for by the property management, and is 

metered at the building level. Therefore, the researchers conducted additional analysis to 

estimate the impact of shifting a portion of the space heating load and cost to the residents in the 

form of heat pump heating (see Table 5). 

Table 5. Energy Savings and Costs Analysis of Hybrid Heat Pump System

Scope HVAC

Total Annual 

Heating 

Energy 

(MMBtu)

Total Annual 

Heating 

Energy Cost

($)

Total 

Electric 

Cost

($, resident)

Total 

Natural Gas 

Cost

($, property 

owner)

Base

92.5 AFUE, 36/60 

kBtu furnace; 15 

SEER, 1.5 ton AC

30.4 512 20 492

DER

15 SEER, 8.5 

HSPF 1.5 ton heat 

pump w/ 92.5 

AFUE, 36/60 kBtu 

furnace

22.1 401 122 279

DER 

Savings for 

Resident or 

Property 

Owner

8.3 111 (102) 213
20

Although the shift from furnace-only heating (base scope) to the hybrid heat pump was estimated 

to result in added electricity costs of $102, the measure was deemed acceptable because even 

with this added electric cost for heating, the DER residents gained a net heating energy cost 

savings of about $100/year when compared to the pre-retrofit building condition. When 

considering the application of hybrid heating systems on a larger scope in retrofits, increased 

utility payments (and the potential impact on allowable rents in affordable housing 

developments) are a key consideration. 

Along with the shift to combined heat pump/furnace space heating, the researchers integrated

whole-dwelling ventilation based on ASHRAE 62.2 rates (ASHRAE 2010). Key factors that lead 

to the specification of an ERV included the following. 

• The base scope system, which was a 3-in. outside air duct routed into the return air 

plenum with no motorized damper or run-time controls on the central air-handling unit, 

was deemed insufficient by the research team in terms of energy performance and IAQ. 

• Because of frequently cited IAQ concerns caused by apartment-to-apartment air leakage 

(such as environmental tobacco smoke [ETS]), balanced ventilation was preferred over 

supply- or exhaust-based. 

• Reports and observations of poor IAQ conditions (strong ETS odors) in the pre-retrofit 

buildings made a continuous system, located in the mechanical room, attractive.

• In terms of humidity removal, after consulting with maintenance staff members, 

Newport’s researchers determined that controlling indoor RH in the summertime (via the 

ERV’s ability to reduce the moisture load in incoming fresh air) was more critical than 

specifying a system based on pre-supposed high indoor winter RH levels (which would 

have indicated a heat recovery ventilator).

• Also, given the reported and observed IAQ in several apartments, an airflow rate of 60 

cfm was specified. This rate is at least 25% higher than the minimum flow rated 

permitted under ASHRAE 62.2 (ASHRAE 2010). 

During the implementation and commissioning of the HVAC and ERV systems, Newport’s 

research team noted several findings.

• The hybrid heat pump systems did not cycle into furnace operation at the agreed-on 

transition temperature. 

• Because of miscommunications from the general contractor to the HVAC contractor, the 

HVAC contractor did not initially install the correct thermostat for the hybrid heat pump 

system. After this was corrected, Newport closely monitored the hybrid heat pump 

system using the long-term energy monitoring system in December 2011. Because the 

winter was mild, there were few nights with ambient temperatures <40°F, which was the 

transition temperature for the system. Below this temperature the heat pump is cycled off 

and the furnaces assumes 100% of the heating load. 

• After two or three <40°F nights without furnace operation, Newport alerted the general 

contractor and HVAC contractor that the furnace was not operating when it should. The 

underlying problem was that the thermostats were not wired correctly to the furnace. The 
21

research team also learned that the outdoor temperature sensor relies on a wireless, 

battery-powered sensor to communicate with the unit. Although this wireless sensor did 

not cause the initial problem, battery change-outs will be a long-term maintenance issue. 

If furnace operation fails in this system because the system does not sense outdoor 

temperature, the resident will pay for 100% of space heating and will rely on a heat pump 

without backup heat.

DER apartment residents were given limited education on the hybrid heat pump system. The 

property manager did offer residents a basic overview of the features of the DER apartments. 

The session, however, was poorly attended and it is unclear how much information was given on 

the hybrid heat pump (e.g., who pays for the different operating modes). Although the residents

now have an aligned incentive for heating energy conservation (e.g., modest set points and

keeping windows closed), there appears to be some reluctance to highlight that residents now 

pay for part of their own heating. 

This challenge is likely common in multifamily developments where fuel switching occurs, and 

the end result can be lost energy savings.
22

4 Conclusions

The DER project at Bay Ridge has yielded numerous findings related to the selection of the DER 

scope; the ability to achieve >50% energy savings; and the implementation, commissioning, and 

short-term testing of efficiency upgrade measures. And because the building type at Bay Ridge is 

quite common, many of these findings will also apply to other multifamily retrofit projects. Key 

conclusions are noted in the following sections.

4.1 Developing a DER Scope

When evaluating potential energy upgrades to include in a retrofit of this type, several types of 

trade-offs must be considered. The most obvious is the balance between energy savings and 

implementation cost. This decision should also factor in the expected life cycle of an upgrade 

measure. The SIR is a widely recognized metric for addressing these factors. An efficiency 

upgrade with an SIR >1 is generally considered a good efficiency investment that will pay for 

itself over the course of its life cycle. Several of the DER measures had SIRs >1, with the 

exceptions of attic insulation, whole-dwelling ventilation, and the solar hot water system. Note 

that these values were developed conservatively; energy savings estimates were conservative and 

made relative to the base rehab scope. In addition, a 15% performance degradation factor was 

applied to all measures.

Beyond the question of energy savings versus implementation cost, several other critical tradeoffs must be considered in developing a retrofit work scope. These factors can greatly affect the 

cost, complexity, and effectiveness of energy upgrades, and include the following:

• Regulatory tradeoffs. Within this project, the presence of aluminum wiring in the 

building was addressed through an industry-recognized copper-aluminum crimping 

system. If a large amount of aluminum wiring were to be exposed, however (e.g., as part 

of an air sealing effort), the local regulatory authority would require a more extensive 

replacement of the aluminum wiring. Other types of potential regulatory issues that could 

be triggered by an energy upgrade measure include fire safety (especially in multifamily

units), combustion safety, and even environmental impacts (e.g., related to ground source 

heat pump loop installation).

• Constructability tradeoffs. In this project, the residents returned to the apartments at 

night, which required the dwelling to be safe and habitable at the end of each work day. 

This ruled out the possibility of some energy upgrade measures because of

constructability—the contractors simply could not complete the work scope within these 

parameters. Residency issues, as well as scheduling constraints, might rule out some 

measures.

• Building science risk factors. This is a broad category of pitfalls to keep in mind when 

evaluating different energy upgrade measures, covering thermal and moisture 

considerations along with other factors such as radon and combustion safety. In this 

project, the presence of poly sheeting within the exterior wall assembly posed a 

significant condensation risk if interior insulation had been added.
23

Despite these challenges in specifying workable efficiency upgrade measures, the Bay Ridge 

DER is estimated to achieve a 52% reduction in energy use compared to the pre-retrofit building. 

The measures used to achieve this reduction are listed in Table 2. Figure 12 shows the 

distribution of these savings across energy end uses.

Figure 10. Energy end use reductions in the DER design

4.2 Implementation, Commissioning, and Testing of Efficiency Upgrade 

Measures

Air sealing in a tenant-in-place retrofit model where the envelope assemblies generally could not 

be opened up was constrained. Despite this limitation, significant infiltration reductions (63%) 

were realized by applying an “inside-out” air sealing strategy that reestablished the drywall as 

the unit’s air barrier. Caulk and spray foam sealant were used at most leakage locations 

accessible from within the apartments during construction. These locations included HVAC 

boot/drywall joints; floor/wall intersections; framing joints around windows; around wiring and 

plumbing penetrations through drywall or framing; behind shower/tub inserts; and around fan 

housings. Establishing performance-based air sealing agreements with contractors was also 

identified as a method to help ensure acceptable results and streamline the training and 

implementation process. 

Air sealing from the attic space also proved to be effective in the DER building. This measure 

involved removing the existing insulation, applying spray foam at all penetrations as well as 

drywall/wall top plate joints, and then reinsulating the attic space (R-49). This work can be 

scheduled separately from the work inside the apartments. Ideally, it should be scheduled for 

cooler periods of the year, which improves the installation quality and worker safety.

HERS: 127

Total Annual Energy: 100.9 MMBtu

Cooling: 

6.2

6%

Heating: 

60.9

61%

Water 

Heating: 

17.4

17%

Lights and 

Appliances: 

16.4

16%

PRE-Retrofit

(MMBtu/yr)

HERS: 75

Total Annual Energy: 47.8 MMBtu

Cooling: 

3.7

8%

Heating: 

22.1

46%

Water 

Heating: 

8.4

18%

Lights and 

Appliances 

13.6

28%

DER Scope

(MMBtu/yr)
24

Duct leakage reduction with aerosolized duct sealant also proved effective (63% reduction), 

especially given that most ducts were inaccessible. Aerosolized duct sealing, though, should not 

necessarily be the only measure applied to improve thermal distribution system performance. In 

this project, the ducts for the top-floor apartments were indeed accessible, and in need of 

remediation because they were located in a bulkhead left open to the attic space above. Methods 

to correct this type of assembly must both air seal and insulate the location where the ducts are 

located, which favors the use of spray foam and a resilient backer material. Again, work quality 

and worker safety are enhanced if this fairly detail-oriented work can be performed during cooler 

periods.

HVAC systems offer the largest energy savings opportunity in multifamily retrofits where the 

envelope cannot be substantially changed. A dual fuel heat pump system optimized energy 

performance at Bay Ridge, and was cost effective because the marginal cost above a furnace and 

AC system was reasonable (~$975/system) compared to energy savings. The use of a dual fuel 

system presents several opportunities and challenges. First, if natural gas is master-metered for 

the building but residents pay their own electric bills, switching to dual fuel heat pumps shifts a 

significant amount of heating load (and cost) to the resident. This offers an opportunity to align 

conservation incentives, because the person setting the thermostat also pays for some of the 

heating cost. To take advantage of this opportunity, however, resident education is needed. 

Commissioning of dual fuel heat pump systems is also crucial to ensure proper operation and to 

optimize the transition temperature. Transition temperatures can be set by rule of thumb, or 

calculated more precisely to minimize either energy usage or energy cost.

Whole-dwelling ventilation in a multifamily DER is an important consideration when significant 

envelope air sealing is also specified. Balanced ventilation was specified in the Bay Ridge DER 

to avoid ventilation-induced unit-to-unit air movement and the migration of odors and ETS. 

These ERV units were superior to the base scope ventilation system in terms of air flow and 

energy efficiency; however, quantifying the resulting IAQ benefits to justify the cost difference 

can be challenging. This does not, though, diminish the importance of whole-dwelling 

ventilation, especially in a DER project.

4.3 Next Steps at Bay Ridge

The research team specified, installed, and commissioned a long-term energy monitoring system 

in two DER apartments and two base scope apartments. This system will measure wholedwelling energy usage; dual fuel heat pump run time, energy use, and efficiency; indoor and 

outdoor temperature and RH; hot water consumption; and window state (open or closed). These 

data will allow further analysis of the actual energy performance of the two DER apartments and 

the two base scope apartments. Electric utility bills for each of these four apartments are also 

being collected and will be used to complement the data acquisition system data. Pre-retrofit 

utility bill histories for the apartments are not available because the pre-retrofit residents have 

moved and the accounts are in their names. All monitoring will continue into January 2013. Final

analysis and reporting to update this report will take place in April 2013.
25

5 References

ASHRAE (2010). Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential 

Buildings. ANSI/ASHRAE Standard 62.2-2010. Atlanta, GA: ASHRAE. Accessed November 

27, 2012: http://www.ashrae.org/standards-research--technology/standards--guidelines (available 

for purchase).

Parker, D., Hoak, D, and Cummings J. (2008). Pilot Evaluation of Energy Savings from 

Residential Energy Demand Feedback Devices. FSEC-CR-1742-08. Cocoa, FL: Florida Solar 

Energy Center.

Seiders, D. et al. (2007). National Association of Home Builders/Bank of America Home Equity 

Study of Life Expectancy of Home Components.
DOE/GO-102013-3796 ▪ January 2013

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