Bay Ridge Gardens—

Mixed-Humid Affordable 

Multifamily Housing Deep 

Energy Retrofit 

James Lyons, Mike Moore, Margo Thompson

Building America Partnership for Improved 

Residential Construction 

August 2013
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iii

Bay Ridge Gardens—Mixed-Humid Affordable Multifamily Housing 

Deep Energy 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, Mike Moore, Margo Thompson 

of the 

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

Cocoa, FL 32922 

NREL Technical Monitor: Stacey Rothgeb

Prepared under Subcontract No. KNDJ-0-40339-03

July 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...................................................................................................................................... 1

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

1.4 Project Partners................................................................................................................................ 3

1.5 Cost Effectiveness............................................................................................................................ 3

1.6 Tradeoffs and Other Benefits........................................................................................................... 4

1.6.1 Energy Savings Versus Implementation Costs................................................................... 4

1.6.2 Regulatory and Constructability Tradeoffs......................................................................... 4

1.6.3 Building Science “Risk Factors” ........................................................................................ 5

2 Research Questions ............................................................................................................................. 8

3 Retrofit Specifications ......................................................................................................................... 9

3.1 Selection and Cost Effectiveness of Final Deep Energy Retrofit Measures.................................... 9

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

Measures........................................................................................................................................ 12

3.3 Building Envelope Infiltration Reduction...................................................................................... 12

3.4 Duct Air Leakage Reduction ......................................................................................................... 16

3.5 Heating, Ventilation, and Air Conditioning Equipment Efficiency Upgrade................................ 19

4 Long-Term Monitoring Results and Utility Bill Analysis ................................................................ 22

4.1 Post-Retrofit Energy Savings in the Deep Energy Retrofit Units.................................................. 22

4.2 Energy Performance of the High Performance Hybrid Heat Pump and the 95 Annual Fuel 

Utilization Efficiency Gas Furnace................................................................................................ 24

5 Conclusions ........................................................................................................................................ 28

5.1 Developing a Deep Energy Retrofit Scope.................................................................................... 28

5.2 Energy Savings Realization Rate................................................................................................... 29

5.3 Implementation, Commissioning, and Testing of Efficiency Upgrade Measures ......................... 29

References................................................................................................................................................. 31
vi 

List of Figures

Figure 1. Aerial view of Bay Ridge development..................................................................................... 1

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

Figure 3. Polyethylene layer on inside face of concrete masonry unit (CMU) wall assembly............ 4

Figure 4. Exterior wall section showing limitted depth furring and polyethylene layer on inside 

face of CMUs......................................................................................................................................... 5

Figure 5. Air sealing opportunity at corners of duct boot where it meets ceiling drywall................ 13

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) 16

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

Figure 9. Pre-retrofit furnace and HVAC return plenum ....................................................................... 17

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. Pre- and post-retrofit energy use in DER Apartment 4 ....................................................... 23

Figure 13. Post-retrofit space heating energy use ................................................................................ 25

Figure 14. Heat pump versus furnace operation average indoor temperature and RH 

measurements .................................................................................................................................... 26

Unless otherwise noted, all figures were created by BA-PIRC.

List of Tables

Table 1. Summary of Rejected Upgrade Measures ................................................................................. 6

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

Table 3. Building Leakage: Blower Door Test Results.......................................................................... 14

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

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

Table 6. Average Indoor Winter/Summer Temperature and RH........................................................... 27

Unless otherwise noted, all tables were created by BA-PIRC.
vii 

Definitions

A/C Air conditioner

AFUE Annual fuel utilization efficiency

CFM Cubic feet per minute

CMU Concrete masonry unit

DER Deep energy retrofit

DOE U.S. Department of Energy

ERV Energy recovery or enthalpy recovery ventilator

ET Environmental tobacco smoke

GC General contractor

HERS Home Energy Rating System

HSPF Heating season performance factor

HVAC Heating, ventilation, and air conditioning

IAQ Indoor air quality

MEA Maryland Energy Association

MEEHA Multifamily Energy Efficiency and Housing Affordability 

Program 

MF Multifamily

PEG Patuxent Environmental Group

Realization Rate The ratio of actual energy savings to the predicted energy 

saving from the audit and modeling process

RH Relative humidity

SEER Seasonal energy efficiency ratio

SHGC Soar heat gain coefficient

SIR Savings to investment ratio

SPF Spray polyurethane foam 

Tenant-in-place 

remodel 

An approach to building renovation in which residents vacate 

their dwellings during the daytime and return at night. Basic 

dwelling functionality is restored and health/safety risks are 

addressed at the end of each workday.
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 research program. Such 

buildings represent great potential for energy savings, and the analysis of such projects provides 

valuable findings on efficiency measures, cost-effectiveness metrics, and risk factor mitigation 

strategies. 

The Bay Ridge energy retrofit project comprised 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 has been applied to the entire complex except for one 12-unit 

building, which underwent the DER scope as well as energy monitoring for a one-year postretrofit period. This report summarizes commissioning, short-term testing, utility bill data 

analysis, and results of on-site monitoring with a focus on the three-bedroom base scope and 

DER units. 

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

reductions of greater than 60% in the DER building; a hybrid heat pump system with a savings to 

investment ratio > 1 (relative to a high efficiency furnace) which also provides the resident with 

added incentive for energy savings; and duct leakage reductions of > 60% using an aerosolized 

duct sealing approach. 

The Bay Ridge DER was initially projected to achieve energy savings of approximately 52% 

compared to pre-retrofit conditions. Long-term analysis based on performance monitoring and 

utility bills revealed actual savings of about 43%. This savings level exceeds the current 

Building America goals for retrofits in mixed-humid climates of 30%. The long-term DER 

energy savings analysis focused on the three-bedroom unit, where occupancy was the most 

consistent across the pre- and post-retrofit periods. 

The energy savings realization rate of 83% (= 43%/52%) was affected partially by an 

overestimation of energy consumption in the pre-retrofit computer model that was not apparent 

until monitoring data became available; a likely overestimation of the effectiveness of energy 

feedback devices; a specification change in the energy recovery ventilator installed during the 

retrofit; and higher-than-anticipated wintertime thermostat settings during the post-retrofit 

period. The energy savings realization rate of 83% for this project tracks favorably with the 61% 

fuel realization rate cited by others as typical of affordable multifamily energy retrofit projects 

(Steven Winter Associates and HR&A Advisors 2012). This research notes that fuel savings are 

easier to predict in multifamily buildings compared to electricity savings, yet fuel savings still 

fall significantly short of 100% realization. The complex nature of buildings and systems that are 

present render it difficult to closely predict actual savings. As was the case with the Bay Ridge 

project, occupancy frequently does not remain consistent, thereby adding another level of 

uncertainty. 
ix

The findings of the Bay Ridge retrofit project are significant in that they illustrate that substantial 

energy savings can be realized through implementation of fairly straightforward retrofit 

measures that can occur during ongoing occupancy, that also provide comfort and durability 

benefits. The efficiency measures included only those that were not severely invasive and did not 

require displacement of occupants during construction. Sealing major (but accessible) building 

envelope air leakage sites, duct sealing, replacement of aging space conditioning and water 

heating equipment, windows, and attic insulation are relatively standard energy improvements 

that reduced monthly utility bills for both the building owner and the tenants, increased comfort 

for the occupants, and likely provided a safer indoor environment. 

Project findings are also significant in that they highlight opportunities to improve the energy 

savings realization rate in similar projects, including:

• Improving the characterization of pre-retrofit energy use via pre-retrofit monitoring and 

targeted diagnostics 

• Increased emphasis on educating residents on their impact on energy use and costs 

• Limiting or eliminating specification changes during construction 

• Applying increased conservatism on the energy impact of efficiency measures that are 

not readily quantified.

Additional findings include those energy efficiency measures that that showed promising energy 

savings but that were ultimately rejected due to “risk factors.” Risk factors covered various 

concerns, including occupant safety, potential unintended building failures, and possible 

regulatory/code issues. For instance, installing 1 in. of extruded polystyrene on the interior of the 

exterior walls would have provided a significant energy benefit. However, investigation of the 

wall assembly revealed a layer of polyethylene on the interior face of the masonry walls, 

presumably installed during initial construction as an air barrier. Hygrothermal analysis indicated 

potential risk of condensation and therefore, this measure was rejected. This research also reports 

on other rejected efficiency measures and the underlying reasons, which are valuable screening 

tools for similar projects.

 
1 

1 Problem Statement 

1.1 Introduction

Under this project, Newport Partners (as part of the BA-PIRC research team) evaluated the 

installation, measured performance, and cost 

effectiveness of efficiency upgrade measures 

for a tenant-in-place deep energy retrofit 

(DER) at the Bay Ridge multifamily (MF) 

development in Annapolis, Maryland. The 

design and construction phase of the Bay 

Ridge project was completed in August 

2012. This report summarizes system 

commissioning, short-term test results, 

utility bill data analysis, and analysis of realtime data collected over a one-year period 

after the retrofit was complete.

The Bay Ridge project comprised a “base 

scope” retrofit that was estimated to achieve a 

30%+ savings (relative to pre-retrofit) on 186 

apartments, and a “DER scope” which was

estimated to achieve 50% savings (relative to 

pre-retrofit) on a 12-unit building (Figure 1 and Figure 2). The base scope was applied to the 

entire apartment complex except for one 12-unit building, which underwent the DER scope. 

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

building, including improvements/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 build upon the current body 

of knowledge of MF retrofits. Toward this end, the 

research team has collected and generated data on the 

selection of measures, their estimated performance, 

their measured performance, and risk factors and their 

impact on potential measures. 

1.2 Background

DERs can provide 30% or greater energy savings, and 

are much easier to implement when a building is 

undergoing a “substantial” remodel, in which case 

contractors can have greater access to walls, ceilings, 

duct systems, etc. For projects like Bay Ridge that are 

not undergoing substantial remodels—which is more 

often the case—the selection of DER measures during a 

renovation must balance the energy savings of upgrade measures against the ability to 

Figure 2. Front view of three-story 

apartment building

Figure 1. Aerial view of Bay Ridge 

development
2 

realistically apply the measures with residents still occupying the building during at least 

some part of the day. Simultaneously, these upgrade measures must also be evaluated for 

their potential to trigger code/regulatory issues, exacerbate pre-existing risk factors in the 

building, and the ability of contractors to reliably and successfully apply them. 

The Bay Ridge DER research project builds upon this knowledge base by providing 

measured energy performance and cost data on a very common building type that underwent 

a moderate rehab.

1.3 Relevance to Building America’s Goals

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

research 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 mixedhumid 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 investigated a very common building type: a 1970s-era, three-story 

walk-up apartment building owned and operated by a major industry firm—Landex. 

Further, the renovation incorporated a retrofit model that property owners and 

affordable housing advocates support: tenant-in-place so the tenant may be 

inconvenienced for a short period of time but not displaced. 

• The project investigated “risk factors” and regulatory issues, and their roles in 

determining what efficiency measures may not be viable because they would 

jeopardize building performance or occupant health, or trigger cascading regulatory 

requirements. Such risk factors are common and need effective identification and 

mitigation strategies for property owners to navigate them.

• Building owners and energy efficiency program managers both want the answer to 

the question: “How much energy did the project really save?” Under this effort, the 

research team investigated actual energy savings achieved compared to estimated 

energy savings, for the DER retrofit scope. The DER scope was initially estimated to 

result in a 50% energy savings. 

Taken together, this research provides extremely valuable information to DOE and the MF 

building industry in understanding current capabilities in energy retrofits as well as 

remaining gaps. 

The Bay Ridge DER research also maps directly to Building America program goals as they 

were expressed in 2010–2011 work scope descriptions, including: 
3 

• “Developing the combination of retrofit measures for evaluation in individual test 

homes that will contribute to achieving 15-30% or more energy savings while also 

meeting safety, risk minimization, durability, reliability and cost requirements to be 

implemented on a broad basis.” 

• “Determining the simplest and most reliable measures to reduce energy use by a 

minimum of 15-30% and be scalable for application to large numbers of houses. 

Longer-term opportunities for “deep retrofits” yielding savings of 30-50% should 

also be considered.” 

• “Performing field evaluations of indoor air quality/ventilation strategies.” 

1.4 Project Partners

This Building America project originally started as a project supported by the state of 

Maryland through both the Maryland Energy Administration (MEA) and the Department of 

Housing and Community Development, under the Multifamily Energy Efficiency and 

Housing Affordability Program (MEEHA) program. The purpose of MEEHA is to promote 

energy efficiency and affordability in the state’s multifamily rental housing developments 

for low and moderate income households. Patuxent Environmental Group (PEG) was the 

lead auditor at Bay Ridge under the MEEHA phase of the project, while Newport Partners 

served as the energy consultant for the DER component, under contract to MEA. The owner 

of the Bay Ridge development, Landex, played a significant role in vetting and 

implementing efficiency measures. 

After the project was underway, it was brought into the DOE Building America program. 

The project’s inclusion in Building America leveraged the earlier efforts of the audit and 

DER consulting work, and provided additional resources for more analysis of the project 

results.

1.5 Cost Effectiveness

Newport Partners (“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 ratio (SIR) (calculated).

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

software to project the cost effectiveness of various measures on the basis of SIR, which is 

highly relevant to MF projects that receive weatherization funding) and other metrics. BeOpt 

software was also evaluated for this work, but was ultimately bypassed due to 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 
4 

modeling hybrid (or “dual fuel”) heat pump systems. REM/Rate was also deemed acceptable 

for this project because energy upgrade analysis using REM/Rate was already underway for 

more than six months, under contract with MEA, when the retrofit project also became a 

Building America research effort. 

While the modeling analysis provided a list of potential measures, additional “filters” were 

applied to ensure that efficiency measures accounted for existing conditions and the 

project’s moderate rehab model. These additional considerations were:

• Compatibility with a “tenant-in-place” rehab model (residents returned to the 

apartments in the evening for much of the retrofit project’s duration) 

• Compatibility with a rehab scope, which 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, 

negative indoor air quality [IAQ] impacts).

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

general contractor (GC), additional site inspections, hygrothermal modeling, and analysis of 

ventilation system options. 

1.6 Tradeoffs and Other Benefits

Several types of tradeoffs were evaluated in the development and selection of the efficiency 

measures. 

1.6.1 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 a SIR 

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

a SIR 

< 1 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 due to both the implementation cost and 

the SIR.

1.6.2 Regulatory and Constructability Tradeoffs

Given the tenant-in-place retrofit model being used at Bay 

Ridge, several measures under consideration were not 

selected due to complications with residents returning to 

their dwellings each night and 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 

Figure 3. Polyethylene layer on inside 

face of concrete masonry unit (CMU) 

wall assembly
5 

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-to-aluminum crimping 

retrofit approach because the aluminum wiring was otherwise not being exposed; however, 

if enough aluminum wiring was exposed, the authority would likely have required a full 

wiring replacement in the entire apartment. The crimping solution is an industry-recognized 

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, exposed nails, etc.

1.6.3 Building Science “Risk Factors”

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

assembly of uninsulated CMU with a layer of polyethylene 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 polyethylene if insulation were added to the inner side of this 

assembly. As a result, laminating R-5 XPS 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 4. Exterior wall section showing limitted depth furring and 

polyethylene layer on inside face of CMUs

Table 1 provides a concise summary of numerous measures which were considered during 

the DER scope development but ultimately rejected due to the factors discussed above. 

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

summary serves as a primer for important factors to consider.
6 

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 

insulation adhered to inside 

gypsum face of all exterior walls. 

1 in. rigid foam and sheetrock 

installed over existing wall 

surface. Extensions for windows, 

outlets, switches, etc.

Strong risk of winter season 

condensation within wall assembly, 

due to continuous layer of 

polyethylene vapor retarder within 

exterior wall assembly

Spray Foam Attic 

Insulation

Remove existing blown-in and 

batts; add 2 in. spray foam cap to 

floor of the attic; then re-apply 

blown-in to R-49 

Spot air sealing deemed more 

cost effective

Solar Electric- Array 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/cooling loads

Schedule delays for permitting; Site 

disturbance for loop

High Efficiency 

Furnace

95+ AFUEa furnace with 

electronically commutated motor 

blower motor (base scope used 

92.5 AFUE 2-stage furnace)

Hybrid Heat Pump system more 

cost effective in terms of SIR

Upgraded Windows U-0.29, SHGCb

-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 SEERc A/Cd (base 

scope: 15 SEER, 1.5 ton) 

Limited energy savings and SIR 

relative to base scope
7 

Energy Efficiency 

Retrofit Measure Description Primary Reason for Rejection

Auxiliary 

Dehumidification

Auxiliary dehumidification 

considered as an IAQ measure, 

given limited, anecdotal reports 

of high indoor RHe levels and 

anticipated lower post-retrofit 

infiltration levels

ERVf whole-dwelling ventilation 

selected instead for balanced 

ventilation (which helps to limit 

unit-to-unit air infiltration) and 

moderate 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 

a Annual fuel utilization efficiency

b Solar heat gain coefficient

c Seasonal energy efficiency ratio

d Air conditioner

e Relative humidity

f Energy recovery ventilator
8 

2 Research Questions

The key research questions for this project include: 

• What level of energy savings did the DER retrofit package achieve? Did the actual 

savings meet the estimated savings? 

• How did the hybrid heat pump performance compare to that of the high efficiency 

gas furnace?

• What do average indoor temperatures and RH indicate about occupant behavior? 

• What do the average summer RH measurements indicate regarding the ability of the 

cooling system and the whole-house mechanical ventilation system to manage indoor 

humidity?
9 

3 Retrofit Specifications 

3.1 Selection and Cost Effectiveness of Final Deep Energy Retrofit

Measures

To best understand the short-term test data, it is necessary to review the final selection of the 

DER scope efficiency measures. Newport’s chief initial role in the Bay Ridge project, while 

serving under contract to the MEA and prior to the project becoming 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 tasked 

with developing additional cost effective 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 hybrid heat pump in the DER instead of 

the gas furnace and A/C 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 we cost-effectively implement beyond the 

base scope measures to reach 50% savings? It is also important to note that the “50% 

savings” metric compares the DER scope to the pre-retrofit building condition. 

Given this background, Table 2 below 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%). Above this row, the Home Energy Rating System (HERS) Index values for all three 

building conditions is 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 (78 versus 75) 

but a much larger predicted 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 site energy usage, while the HERS Index is 

not impacted as significantly. 

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

base scope. Some of these measures show SIR > 1, while others do not. In order to pursue 

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 NAHB/Bank of 

America’s “Study of Life Expectancy of Home Components” Seiders et al. (2007) or 

estimated from industry data/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.
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 

SPFa: including all mechanical, 

electrical, and plumbing 

penetrations; top plates of interior 

walls; This work was in addition to 

the limited spot air sealing in the 

base scope.

0.5

Windows U-0.50 SHGC 0.40 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 runtime controls 

or damper); not ASHRAE 

62.2 compliant

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 W Same as base scope N/A

Duct Air Sealing

Supply trunk not sealed; 

3rd-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,b

92.5 AFUE 2-stage furnace back-up 

1.3
11 

Building System/ 

Component Pre-Retrofit Condition Base Scope DER Scope

DER Scope Measure SIR

(With Respect to Base 

Scope)

Space Cooling 10 SEER A/C unit 15 SEER, 1.5 ton (36/60 kBtu), 40°F transition temp; 

cooling: 15 SEER, 1.5 ton.

Domestic Water 

Heating

Central gas-fired storage, 

100 gal, 0.54 EF (serving 

12 dwellings)

100 gal,

95% thermal efficiency

Solar hot water with 3 flat panel 

collectors closed loop glycol; solar 

storage tank upstream of 100 gal,

95% thermal efficiency water heater

0.5

Lighting 100% Incandescents

100% compact fluorescent 

lamps for all permanent 

luminaires

In addition to 100% compact 

fluorescent lamps for permanent 

luminaires, supply resident with 

compact fluorescent lamps for all 

plug-in 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). 

A 10% savings rate was estimated 

based on available literature and 

plans to train the residents on how 

to operate the retrofitted dwelling 

efficiently, given by the property 

manager.

1.8

HERS Index 127 78 75 N/A

Predicted Energy 

Use Reduction 

(Relative to PreRetrofit)

35% 52%

a Spray polyurethane foam

b Heating season performance factor
12 

• 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 

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.

Initially, the pre-retrofit energy model was based on building audit data and diagnostic tests. 

When the energy use of this pre-retrofit model was compared with limited historical utility data 

for several apartments, it was within 5%–15% (depending on which apartment it was compared 

against). This was deemed acceptable given uncertain occupancy densities and behavior trends, 

and a well-documented audit of the pre-retrofit building condition. 

In subsequent analysis of post-retrofit utility bill and monitoring data, issues with the pre-retrofit 

model were identified that had the affect of over estimating pre-retrofit energy use, and thus, also 

over estimating energy savings. These issues are discussed below in Section 4 “Long Term 

Monitoring Results and Utility Bill Analysis.” 

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

over time (MEA policy).

• No assumed utility rate escalation. 

These factors were used in the following calculation of SIR:

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

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. 

3.3 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 very attractive (SIR ~5). 

The DER scope built upon 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, and plumbing MEP penetrations and the drywall/top plate 

joint of interior partitions. While 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. 
13 

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

In terms of implementation, the GC’s scope included detailed prescriptive requirements for air 

sealing which established what locations to seal, what sealing materials to apply, and how much 

sealant to apply. Additionally, the GC lead integrated coordination meetings among the trades, 

and conducted multiple on-site walk-thrus with the insulation contractor. Newport and PEG, the 

auditor for the base scope, also provided frequent on-site inspections.

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

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

air sealing requirements also had a role in this inconsistency, as workers would 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 has recommended to the property owner a performance-based air sealing 

approach for future projects. Such an approach would incorporate: 

• 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 the 

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 in Table 3. 
14 

Table 3. Building Leakage: Blower Door Test Results

Maximum 

ACH50*

Minimum 

ACH50*

Average 

ACH50*

Average ACH50 

Reduction 

(Compared to 

Pre-Retrofit 

Condition)

Average 

ACH50 of 

3rd-Floor 

Dwellings 

(n = 4)*

Ratio of 

Outdoor to 

“Total” 

Leakage**

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%

* 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.

** 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 

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

illustrated above 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, both groups showed that 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 that is between conditioned space/outdoors and 

between conditioned space/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). 

In neither case does the surface area proportion align with the measured distribution of air 

leakage, however. This suggests that the distribution of air leakage sites was not evenly 

distributed across the building envelope, with a greater concentration of leakage sites in the 

assemblies separating conditioned space from outdoor air. 
15 

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

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 that were “connected” 

through the shared mechanical room on each floor, were simultaneously depressurized to –50 

Pascals and maintained at this level while a CFM50 reading was recorded for each. Arranging 

access for this level of testing, in addition to having enough technicians and equipment, was a 

very significant effort. Thus, only a sample of apartments and stairwells were tested pre- and 

post-retrofit as noted in Table 3.

In examining the lack of correlation 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 whether it was possible 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 which 

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), 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. Thus, 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). This points to the potential complicated nature of many MF buildings and the 

difficulties that can be encountered when performing energy audits, conducting and interpreting 

diagnostic test results, and implementing retrofit measures. It can be very easy to miss air 

leakage pathways to the outdoors and/or to other units in the building. 

Newport’s researchers separated out 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-
16 

to-unit leakage was occurring during the guarded tests for interior units—most likely across the 

firewall to the adjacent interior unit. However, the rough magnitude of the difference is 

reasonable given the costs and logistical challenges of guarded testing in this type of MF

building where depressurizing nine apartments would have been the ideal setup. Further, other 

factors such as more extensive leakage paths to outdoors may also have contributed to this 

difference.

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

3.4 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 vacuum to collect and expel dust, prior 

to aerosolized sealing. Duct cleaning prior to aerosolized duct sealing is recommended if the 

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

the old plywood plenums (see Figure 9 below), duct cleaning was part of the retrofit base scope 

for all apartments.

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 8). 
17 

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

The results of pre- and post-retrofit duct blaster testing are shown in Table 4. 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 9), were also replaced with sheet metal plenums.

Table 4. Duct Leakage Test Results

Total Duct Leakage 

(CFM@25 Pa)

Pre-Retrofit Condition 481

Post-Retrofit Base and 

DER Scope Dwellings 180 

% Reduction 63%

Figure 9. Pre-retrofit furnace and HVAC return plenum
18 

Insulating and air sealing the open-top bulkhead shown in Figures 8 (above) and 10 (below) 

involved a two-step process specified by the base scope auditor PEG. It involved (1) removing 

insulation from the bulkhead area and laying 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 below in Figure 11. This process proved to be 

effective when properly implemented; however, in some cases 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. 

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

Figure 11. 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 the 

third-floor apartments noted above in Table 3. 

3.5 Heating, Ventilation, and Air Conditioning Equipment Efficiency Upgrade 

The pre-retrofit heating, ventilation, and air conditioning (HVAC) systems were ~15-year-old 

furnaces and split system A/C units. Labeled efficiency levels were 80 AFUE and 10 SEER, 

respectively. The base retrofit scope upgraded these systems to a two-stage, 92.5 AFUE 

condensing furnace and a 15 SEER split A/C system. Given the mixed climate zone location 

(~4700 HDD; 17 F heating design temp) and the utility rates, Newport investigated hybrid 

heating options involving both electricity 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 changing from the base 

scope’s 92.5 AFUE, two-stage gas furnace with 15 SEER A/C to a hybrid heat pump (15 SEER, 

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

SIR of 1.3. Given that the base scope already utilized a 15 SEER split A/C 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 for electricity, which 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. 

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

Scope HVAC

Total Annual 

Heating 

Energy 

(MBtu) 

Total Annual 

Heating 

Energy Cost

(MBtu) 

Total 

Electric 

Cost

($/Resident)

Total 

Natural Gas 

Cost

($/Property 

Owner)

Base

92.5 AFUE, 36/60 

kBtu furnace

15 SEER, 1.5 ton 

A/C

30.4 $512 $20 $492

DER

15 SEER, 8.5 

HSPF 1.5 ton heat 

pump with 92.5 

AFUE 36/60 kBtu 

furnace

22.1 $401 $122 $279

DER Savings 

for Resident 8.3 $111 ($102)* $213
20 

While 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 

these added electricity costs 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 basis in retrofits, the issue of 

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

developments) is a key issue. 

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

whole-dwelling ventilation based on ASHRAE 62.2 rates. 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 runtime controls on the central air handling unit, 

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

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

(such as environmental tobacco smoke), balanced ventilation was preferred over supplyor exhaust-based. 

• Reports and observations of poor IAQ conditions (strong smoking odors) in the preretrofit buildings made a continuous system, located in the mechanical room, attractive. 

In terms of humidity removal, after consulting with maintenance staff, Newport’s researchers 

determined that controlling indoor summertime RH (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. 

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

research team noted these findings: 

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

transition temperature. 

• Due to miscommunications from the GC 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 longterm energy monitoring system in December 2011. Due to the mild winter, there were 

limited 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 furnace 

assumes 100% of the heating load. 

• After two or three sub-40°F nights without furnace operation, Newport alerted the GC 

and HVAC contractor that the furnace was still not operating when it should. The 
21 

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

also learned that the outdoor temperature sensor relies on wireless communication to 

communicate with the unit, and that this wireless sensor is battery powered. While 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 a backup heat source. It is recommended that a reminder be 

posted on the equipment to replace the battery as part of the annual maintenance protocol. 

DER apartment residents were provided with limited education on the hybrid heat pump system. 

The property manager did provide a basic overview of the features of the DER apartments to 

residents. However, the session 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). While the 

residents now have an aligned incentive for heating energy conservation (modest set points; 

keeping windows closed), there appeared to be some reluctance to highlight the fact that 

residents now pay for part of their own heating. 

This challenge is likely common in MF developments where fuel switching occurs, and the end 

result can be lost energy savings.
22 

4 Long-Term Monitoring Results and Utility Bill Analysis

Once the retrofits were complete monitoring equipment was installed in two base scope 

apartments and two DER apartments. All four apartments faced the same cardinal direction and 

were located on the third floor of the buildings; two apartments were two-bedroom units (713 ft2) 

and two were three-bedroom units (909 ft2). Occupancy was not equivalent across units of the 

same size, and in some cases, it was also not consistent in the pre- and post-retrofit periods in the 

same unit despite efforts to obtain apartments with the same residents. Thus, resident-neutral 

comparisons of pre- and post-retrofit energy use and of post-retrofit energy use in the base scope 

versus DER apartments are difficult to make. The variability in occupancy was not controllable, 

and thus the monitoring plan was developed based on the best available information at the time. 

Monitoring including the following data: 

• Indoor and outdoor temperature and RH

• Hybrid heat pump runtime and natural gas consumption 

• Heat pump blower and compressor electricity consumption 

• Gas furnace runtime and natural gas consumption 

• Apartment-level hot water consumption. 

Newport used the data collected over an 11-month period along with utility billing data to 

answer the following questions: 

• What energy savings did the DER units show compared to the pre-retrofit condition? Did 

the actual savings meet the estimated savings?

• How did the energy performance of the high efficiency hybrid heat pump compare to the 

95 AFUE furnace? 

• What do the average summer and winter indoor temperatures measurements indicate 

regarding occupant preference and behavior? 

• What do the average summer RH measurements indicate regarding the ability of the 

cooling system and the whole-house mechanical ventilation system to manage indoor 

humidity?

4.1 Post-Retrofit Energy Savings in the Deep Energy Retrofit Units

Apartment 4, a three-bedroom, 909-ft2 unit in the DER apartment building, offered the best 

opportunity for pre- and post-comparison due to the fact that it had the greatest consistency in 

occupancy as well as the greatest availability of utility bill history. (Generally, utility bill 

availability was inconsistent due to frequent resident turnover, along with the need to obtain 

resident permission to access bills.) Therefore, the comparison of pre- and post-retrofit energy 

use concentrated on Unit 4. Figure 12 below illustrates the total pre- and post-retrofit energy use 

of Apartment 4 as a function of average monthly temperature.
23 

Figure 12. Pre- and post-retrofit energy use in DER Apartment 4

The savings in total energy use resulting from the DER measures was 43% relative to the preretrofit condition. The percentage savings was calculated by:

1. Regressing pre- and post-retrofit monthly energy use as a function of monthly average 

outdoor temperature. 

2. Applying the resulting equations for each period to an annual set of average monthly 

temperatures based on a 30-year dataset from the National Oceanic and Atmospheric 

Administration. 

3. Summing the monthly energy consumption values to achieve annual totals 

4. Calculating the percent savings. 

The 43% reduction in pre- versus post-retrofit energy savings is lower than the original 

projection of 52% energy savings which was based on modeling in REMRate. However, the 43% 

realized energy savings do exceed the Building America goals for the mixed-humid climate. 
24 

One key reason for the initial, higher estimate of energy savings (52%) was an overestimate of 

pre-retrofit energy use in the REMRate model, specifically for water heating and space heating. 

The REM model initially assumed a volume of hot water consumption that was approximately 

10% greater than that revealed in the post-retrofit monitored data. In addition, pre-retrofit space 

heating energy use was perhaps exaggerated due to an overly conservative derating of equipment 

performance based on age and an assumed maintenance factor. Actual combustion efficiency test 

results were not available from the initial energy audit performed prior to the project’s inclusion 

in Building America. 

Another likely overestimation in the energy savings calculation was an assumed 10% electrical 

energy savings resulting from the energy dashboard system in each DER apartment (Table 2). A 

study released after this initial estimate arrived at an average electricity savings of 3.8% based on 

nine pilot programs (Foster and Mazur-Stommen 2012). In the case of the Bay Ridge occupants, 

it is unknown to what extent they actually paid attention to the energy dashboards. Relatively 

high winter indoor temperatures and low summer indoor temperatures observed in the postretrofit data indicated that these devices did not encourage occupants to moderate thermostat set 

points. 

Another contributing factor was a lower-than-actual energy use estimate for the ERV. The 

specified ERV was not installed after initial approval, due to product availability delays for the 

HVAC contractor. As a result, the energy consumption for the whole-dwelling ventilation system 

more than doubled, and added an additional 1 MBtu/yr in energy consumption beyond the 

originally specified ERV. 

Finally, a recent study by Steven Winter Associates and HR&A Advisors (2012) cited actual fuel 

savings realization rates substantially lower than initial projections in affordable MF building 

energy retrofits. Whereas savings between 25% and 50% were originally predicted, actual fuel 

savings proved to be only between 10% and 40%. The fuel savings realization rate was 61% with 

a 90% confidence level ± 14%. This savings realization rate is for space and water heating only. 

The study notes that electricity savings in MF buildings are even more difficult to predict. Thus, 

the total energy savings realization rate of 83% (= 43/52) for the Bay Ridge project compares 

favorably with these findings. Because MF buildings (and occupant behavior) are complex with 

multiple factors impacting one another, empirical studies and modeling do not always prove fully 

reliable, despite being critical inputs to the audit and retrofit process. The authors of the 

aforementioned study recommended “capping” overly optimistic predictions to maintain more 

conservative projections and improve realization rates. 

4.2 Energy Performance of the High Performance Hybrid Heat Pump and the 

95 Annual Fuel Utilization Efficiency Gas Furnace

As discussed previously, the 92.5 AFUE two-stage furnace that was installed as part of the base 

scope energy package was upgraded to a hybrid heat pump for the DER scope due to the 

estimated SIR of 1.3 relative to the base scope. Like the mechanical equipment in the base scope 

units, the backup furnace that was part of the hybrid system had an AFUE of 92.5. The heat 

pump, however, had ratings of 8.5 HSPF in heating mode and 15 SEER in cooling mode. When 
25 

correctly commissioned, the system was set to transition to furnace operation at an outdoor 

temperature of 40oF. 

Figure 13 shows the daily energy consumption of each of the systems as a function of indooroutdoor temperature difference over a three-month winter period from January through March. 

Figure 13. Post-retrofit space heating energy use

The measured data do show that the DER Apartment 4 consumed 17.6% less energy for space 

heating than did the base scope apartment (17) over the three-month period (6.69 MBtu versus 

8.12 MBtu). However, potential complicating factors that could influence these results include 

different mechanical ventilation systems (see Table 2); differences in window operation; 

differences in ventilation fan use; differences in envelope tightness (although blower door testing 

across several base scope and DER units showed similar average results); and duct tightness 

(results on these specific units were not available from the audit contractor). 

The chart in Figure 13 also indicates some interesting trends. Under warmer outdoor temperature 

conditions, e.g., lower indoor-outdoor temperature difference, the energy consumption of the two 

systems converges. This makes sense because calls for heat will be more intermittent and 

runtimes are likely to be shorter, dampening out compromising equipment and operating 

efficiencies. As outdoor temperatures become colder and demand increases, the energy 

consumption of the two systems begins to diverge, indicating possible differences in furnace 
26 

versus heat pump operation and performance. Then as outdoor temperatures get very cold ≥ 40oF 

temperature differential—energy consumption again converges as both units are operating under 

the natural gas furnace, which has similar AFUE ratings. 

The BA-PIRC team also reviewed the data to characterize heat pump operation versus furnace 

operation over a three-month period of space heating. The controls were set such that the furnace 

would assume all heating operation when the outdoor temperature dropped below 40oF . Supply 

plenum average temperatures generally remained between 85o– 95oF under heat pump operation. 

Figure 14 shows heat pump versus furnace operation as a function of outdoor temperature 

difference. The gas furnace satisfied the majority of the space heating demand constituting 76% 

of the space heating energy. The reason for the furnace operation during a period with 

temperatures in the upper 50s and low 60s is uncertain. 

Figure 14. Heat pump versus furnace operation average 

indoor temperature and RH measurements 

Temperature and RH sensors were placed near the ceiling in the living rooms of all four 

apartments, post-retrofit. Table 6 below shows the average winter and summer indoor 

temperatures and the average indoor RH in each of the apartments. 
27 

Table 6. Average Indoor Winter/Summer Temperature and RH

Unit

Average 

Temperature 

December–February

(°F)

Average 

Temperature 

June–August 

(°F)

Average RH 

June–August

(%)

Apartment 4 75.6 75.7 58.7

Apartment 4-2 77.6 74.7 58.5

Apartment 17 75.9 76.1 56.5

Apartment 17-2 77.2 69.3 63.8

Heating season indoor temperatures indicate fairly high heating system thermostat set points, 

even in the DER apartments (4 and 4-2) where the tenants shifted from not paying for any 

portion of their heating (pre-retrofit gas furnace) to paying a substantial portion of their space 

heating energy costs (post-retrofit hybrid heat pump system where residents paid for electricity). 

Hourly data for at least one of the apartments also show some winter indoor temperatures > 80oF. 

This indicates that the seasonal averages likely mask even higher intermittent set points for the 

system. 

The summer season indoor average temperatures indicate that at least one apartment (17-2) had 

an extremely low thermostat set point. In addition, the average indoor RH in this apartment 

during the June through August period was clearly the highest at almost 64%. At least part of this 

difference can be attributed to the whole-dwelling ventilation system in the base scope 

apartments. This ventilation system (specified by an outside consultant who was not part of the 

BA-PIRC research team) was simply an outside air duct routed into the return plenum with no 

control logic or damper. Thus, in unit 17F, a very low cooling thermostat set point would result 

in greater A/C system runtime and consequently, a greater latent load introduced from the 

outdoor ventilation air. 

Initially, the programmable thermostats were set at 68o

F and 75oF, respectively, for winter and 

summer months when the retrofit was completed and the occupants were given some instruction 

how to use them. Likewise, they were introduced to the “energy dashboards” and shown how 

they could use these devices to monitor their energy consumption relative to certain actions such 

as raising and lowering thermostat temperatures. However, from the measured average indoor 

temperatures and RH levels, it is apparent that more effective resident education could result in 

greater energy savings in any of the post-retrofit apartments.
28 

5 Conclusions

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

DER scope; the ability of the retrofit to achieve more than 30% energy savings and possibly as 

high as 50% savings; and the implementation, commissioning, short-term testing, and long-term 

monitoring of the efficiency upgrade measures. Because the building type at Bay Ridge is quite 

common in many parts of the country, many of these findings will also apply to other MF retrofit 

projects. Key conclusions are noted below. 

5.1 Developing a Deep Energy Retrofit Scope

In the evaluation of potential energy upgrades to include in a retrofit of this type, several types of 

tradeoffs 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 value > 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, although 

lower SIR measures such as whole-dwelling ventilation were also included in the DER scope, 

given the importance of adequate ventilation in post-retrofit, air-sealed apartments. It is 

important to note that SIR values in this program were developed in a very conservative manner: 

energy savings estimates were made relative to the base rehab scope, plus a 15% performance 

degradation factor was applied to all measures.

Beyond the question of energy savings versus implementation cost, there are several other 

critical tradeoffs to consider in developing a retrofit work scope. These factors can greatly affect 

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

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

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

system. However, if a large amount of aluminum wiring were to be exposed—as part of 

an air sealing effort, for example—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 

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

heat pump loop installation). 

• Constructability tradeoffs. Within this project the residents returned to the apartments 

at night for most of the project, which required the dwelling to be safe and habitable at 

the end of each workday. This ruled out the possibility of some energy upgrade measures 

due to constructability—the contractors simply could not complete the work scope within 

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

measures in this way. 

• Building science “risk factors.” This is a broad category of “pitfalls” to be aware of 

when evaluating different energy upgrade measures, covering thermal and moisture 

considerations, along with other factors such as radon and combustion safety. Within this 
29 

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

significant condensation risk if interior insulation were added. 

5.2 Energy Savings Realization Rate

The Bay Ridge DER achieved a 43% energy use reduction compared to the pre-retrofit building 

by incorporating efficiency measures mostly with SIR values > 1 compared to the base scope. 

Compared to the initial savings estimate of a 52% reduction, the validated energy savings 

represent a realization rate of 83%. Relative to other affordable MF retrofit projects, this is a 

favorable result. Opportunities to improve the realization rate further include:

• Improving the characterization of pre-retrofit energy use via pre-retrofit monitoring and 

targeted diagnostics 

• Increased emphasis on educating residents on their impact on energy use and costs 

• Limiting or eliminating specification changes during construction 

• Applying increased conservatism on the energy impact of efficiency measures that are 

not readily quantified. 

5.3 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, very significant infiltration reductions 

(63%) were realized by applying an “inside-out” air sealing strategy that re-established 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, including 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 re-insulating the attic space (R-49). This work can be 

scheduled separately from the work inside the apartments, and ideally should be scheduled for 

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

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

especially given that most ducts were inaccessible. However, aerosolized duct sealing should not 

necessarily be the only measure applied to improve conditioned air distribution system 

performance. In this project, the ducts for the top-floor apartments were 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 area where the ducts 

are located. This favors the use of spray foam and a resilient backer material. Again, work 
30 

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 MF retrofits where the envelope 

cannot be substantially changed. A hybrid heat pump system optimized energy performance at 

Bay Ridge, and was cost effective because the marginal cost above a furnace and A/C system 

was reasonable (~$975/system) compared to energy savings. The use of a hybrid system presents 

several opportunities and challenges. First, if natural gas is master metered for the building but 

residents pay their own electricity bills, switching to dual fuel heat pumps shifts a portion of the 

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. As seen in Table 6 

above, it appeared that all of the apartments had fairly high thermostat set points during the 

winter. With increased education regarding potential cost savings on monthly utility bills, 

residents might be more inclined to lower their thermostat settings. Commissioning of hybrid 

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 an MF 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, energy 

efficiency, and maintaining reasonable average indoor humidity levels. However, quantifying the 

resulting IAQ benefits to justify the cost difference can be challenging. Even so, this does not 

diminish the importance of whole-dwelling ventilation especially in a DER project. 
31 

References 

Foster, B. and Mazur-Stommen, S. (2012). Results from Recent Real-Time Feedback Studies. 

Report Number B112. American Council for an Energy-Efficient Economy. 

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

Energy Demand Feedback Devices. FSEC-CR-1742-08, Florida Solar Energy Center for U.S. 

Department of Energy, January 2008.

Seiders, D.; Ahluwalia, G.; Melman, S.; Quint, R.; Chaluvadi, A.; Liang, M.; Silverberg, A.; 

Bechler, C. (2007). National Association of Home Builders/Bank of America Home Equity 

Study of Life Expectancy of Home Components. 

Steven Winter Associates and HR&A Advisors. (2012). Recognizing the Benefits of Energy 

Efficiency in Multifamily Underwriting. Deutsche Bank Americas and Living Cities. 
 

DOE/GO-102013-3957 ▪ August 2013

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