November 15, 2013

Abstract: 

In this project, the post-retrofit results for 13 existing homes from the DER Pilot program were analyzed. Ten of these homes are single-family homes; two are two-family homes, and one is a three-family home. The information available for each home included pre- and post-retrofit blower door test results, a project description, reason for doing the project, and project cost information; and actual post-retrofit energy use information provided by the utility companies. The post-retrofit energy use for this project was for the 12-month period from August 2011 through July 2012 and for the 6-month period from January 2012 through July 2012. The post-retrofit performance and cost ranges provided by this research can provide concrete input for homeowners who are considering a DER.

Executive Summary

With the increasing demand for energy-efficient solutions for the existing housing stock, it is important to have demonstrated evidence that measures being implemented will in fact benefit the homeowner through a combination of energy savings, improved durability, and occupant comfort. Many of the deep energy retrofit (DER) performance data currently available are in terms of individual cases, often of nontypical homes or circumstances, and for many of these there has been insufficient post-retrofit time to adequately assess the actual performance results. The purpose of this research project is to use actual performance results for a diverse community of cold-climate retrofits to assess the effectiveness of a specific package of DER measures. Through the performance analysis of a group of post-retrofit homes, all of which have implemented the same DER measures and all of which have provided post-retrofit performance data for the same time period, a realistic range of post-retrofit performance results is demonstrated. By analyzing the post-retrofit data at the community level, the emphasis is shifted from the post-retrofit performance for the individual case to the post-retrofit performance achievable by using the DER measures package. Trends also begin to emerge about strategies that result in the best performance and how to make reasonable cost projections for a DER.

In 2009, National Grid started a DER pilot program that offered technical support and financial incentives to qualified Massachusetts homeowners who planned and successfully completed a retrofit that incorporated the performance requirements and goals of the National Grid DER measures package. This DER measures package, developed through collaboration with Building Science Corporation (BSC), includes specific thermal and airtightness goals for the enclosure components as well as health, safety, durability, and indoor air quality requirements. By providing measures that can be included with common renovation activities such as roof replacement, window replacement, re-siding, basement remediation, and remodeling, this DER measures package is expected to have widespread application for existing homes in the New England area. The post-retrofit performance and cost ranges provided by this research project can provide concrete input for homeowners who are considering a DER.

In this project, the post-retrofit results for 13 existing homes from the DER Pilot program were analyzed. Ten of these homes are single-family homes; two are two-family homes, and one is a three-family home. The information available for each home that was used in this analysis included pre- and post-retrofit blower door test results, a project description, reason for doing the project, and project cost information; and actual post-retrofit energy use information provided by the utility companies. The post-retrofit energy use for this project was for the 12-month period from August 2011 through July 2012 and for the 6-month period from January 2012 through  July 2012. 

The pre-retrofit energy use information available for the homes differed because in some cases, the home had been recently purchased but in other cases, the homeowner had been living in the home for many years. Where actual pre-retrofit energy use was not available, energy modeling using BEopt v1.3 was used to estimate the pre-retrofit energy use. The reduction of source energy use from the pre-retrofit homes to the post-retrofit ranged from 27%–75%. Well- maintained homes with the same owner for the pre- and post-retrofit and for which the DER was not combined with other major renovations ranged from 30%–45%. 

Total post-retrofit source energy use for the retrofits for the 12-month period ranged from 52– 217 MMBtu/yr and from 27–69 kBtu/ft2-yr. When normalized to account for weather conditions and divided by the number of households, all of these were below the Energy Information Administration Northeast average total source energy use per household of 174 MMBtu/yr of source energy and more than half were below 70% of that average total. Similarly, all but one retrofit were below the Northeast average of 67.5 total source kBtu/ft2-yr per home and many were below 50% of that average. Heating is the largest energy load in a cold climate and is most impacted by these DER measures. For the post-retrofit 12-month period, the actual source energy use for heating and cooling ranged from 8.5–27 kBtu/ft2-yr. 

The airtightness component in the DER package emphasized the need to identify the air control layer for each component of the enclosure and to plan continuous transitions between components. Using this approach nearly all of the homes were able to reach a post-retrofit airtightness result of 1.5 ACH50. The worst airtightness results occurred for the one home that did not include the basement in the conditioned space.

As a group, the homes that used the “chainsaw” retrofit technique along with the air control layer, roof insulation, and wall insulation applied to the exterior had the best airtightness results and the lowest heating and cooling source energy use results. “Chainsaw” refers to a retrofit technique used at the intersection of the roof and wall whereby the existing rafter tails and rake overhangs are cut off and new overhangs are attached over the insulation at completion.

Projects included in this study implemented enclosure retrofit packages at an average cost of $18.62/ft2 of building enclosure. The unit cost for enclosure packages range from $9.99– $26.87/ft2 of building enclosure. For energy-related enclosure measures, the average unit cost is $13.13ft2 and the range is from $8.62–$22.20/ft2.

Total HVAC system costs ranged from slightly more than $10,000 to just less than $19,000 for projects that met the pilot program target by installing high efficiency heating and cooling equipment and distributed ventilation with heat or energy recovery. Some projects replaced only certain components of the heating, ventilation, and air conditioning (HVAC) systems as part of the DER project. For other projects, HVAC measures were limited to adding mechanical ventilation. The projects that installed new high efficiency heating equipment, cooling equipment, and distributed ventilation with heat or energy recovery report costs for combined HVAC measures ranging from just more than $10,000 to approximately $39,500.

Analysis of energy-related measure costs and project objectives resulted in a categorization of measures as follows: (1) measures pursued primarily for energy-related objectives; (2) measures pursued for a combination of energy-related and nonenergy-related objectives; and (3) measures pursued primarily in response to nonenergy-related objectives. On average for the projects in this study about half of the energy-related measure costs are assigned solely to energy-related objectives, and 20% of energy-related measure costs are assigned primarily to nonenergy-related objectives.

1 Introduction

Home retrofits have been targeted as an area of great potential for significant energy savings, employment opportunities, and market growth. However, the barriers to widespread adoption of comprehensive retrofit strategies remain high. Two such barriers are the lack of clear evidence that there is a substantial benefit to the average homeowner and perceptions relative to the high cost of a comprehensive energy retrofit. What is missing is evidence from a substantial sample of typical houses and homeowners demonstrating the benefits and indicating costs.

In this project, reported cost and measured performance data have been evaluated to assess the retrofit cost and the post-retrofit airtightness and energy use for a group of houses in Massachusetts which participated in a deep energy retrofit (DER) pilot program sponsored and administered by National Grid (National Grid 2011). By providing financial incentives and technical support to the participating projects, the National Grid DER Pilot program created an opportunity for a broad range of homeowners to undertake a DER project.

As participants in the DER pilot program, these retrofit projects all used the same set of retrofit targets, taken here as a “package of measures” for the measures to be implemented. This report assesses the effectiveness of the overall package of measures as well as the relationship between different implementation strategies used and measures of performance. This is accomplished by analyzing the full set of performance data for the group rather than looking at individual case studies, as has been done in past studies. This approach results in post-retrofit energy use and cost ranges based on the total community data that can be reasonably expected from use of the DER package. This is concrete evidence that can be used by homeowners to assess the potential benefit and cost of a DER.

The post-retrofit analysis of a community of retrofits in this research project is unique in that it incorporates all of the following: the community consists of a diverse group of New England home types as well as differing homeowner lifestyles and values, the DER package is comprehensive and advanced, the analysis is based on actual rather than modeled post-retrofit data and all energy use data are for the same time period, and the analysis is applied to the full community rather than to the individual cases.

The current research project shows that source energy savings from pre-retrofit to post-retrofit conditions ranging from 27%–75% can be achieved. But perhaps more importantly, it demonstrates that the DER retrofits can meet energy performance goals and benchmarks that apply to new home construction. 

Using this community of retrofits, the following research questions are addressed:

Does the DER measures package result in at least 30% actual source energy use reduction from the pre-retrofit conditions? A 30% reduction is the Building America (BA) program 2012 goal for existing homes in cold climates.

Are there discernible differences in energy use between the variations allowed within the DER measures package?

What post-retrofit airtightness has been achieved by the DER measures package?

Are there discernible differences in air leakage results between the variations allowed within the DER measures package?

What are the costs of the DER measures package?

Can the net cost of energy performance improvement be separated from the full DER measures package cost?

2 Background

DERs are beginning to be less unusual. It used to be that each time a DER was done, it would show up in a magazine article (for example, Pettit 2008; Joyce 2009). Unfortunately, it is still the case that much of this work is looked upon as experimental. Because of this, it has not been easy to measure the benefits except on a case-by-case basis, or to make the case that the measures needed for an effective retrofit are readily accessible to the average homeowner, since most homeowners are not comfortable experimenting on their houses. 

The BA program has been working to overcome these two obstacles. There are several other BA groups doing research to evaluate the performance effectiveness of cold climate home retrofit approaches at the community scale. Among these are the Consortium for Advanced Residential Buildings’ (CARB) role in the Retrofit NYC Block by Block project (Eisenberg et al. 2012) and in the recently completed retrofit of the Chamberlain Heights duplex and quad affordable housing complex (Donnelly and Mahle 2012) as well as the Partnership for Advanced Residential Retrofits (PARR) team’s work in the Chicagoland project development of energy efficiency retrofit packages for typical houses in the Chicago area (Spanier et al. 2012). 

These research projects have the potential to provide a significant set of post-retrofit performance data using utility bills and other testing to evaluate the energy use level achieved and achievable by fairly comprehensive retrofit measures packages. However, the current reports have only limited results available, if any, and thus results are presented in terms of prediction models rather than actual performance data. In this current research project, BSC is making use of a year of post-retrofit utility bills and performance data for retrofit projects and uses this actual performance information to evaluate achievable performance levels for the DER retrofit measure package. The projects evaluated in this current report represent fewer than one third of the total number of National Grid DER Pilot projects for which similar post-retrofit data will soon be available. However, this evaluation of the early projects is deemed important to both establish methodologies of evaluation and to begin to meet the need for measured performance data. In subsequent a research effort already underway, the performance results for the full set of National Grid DER Pilot projects will be evaluated.

The CARB and PARR research projects adopt the approach that the retrofit measures packages be tailored for particular house types—e.g., ranch house, NYC row house, triple-decker. BSC has found that each retrofit project has its own set of unique constraints that are based not so much on house type and age as its history and existing conditions. Therefore, tailoring retrofit measure packages to specific house types may not be necessary. In the results described in the current report, a single DER retrofit measures package has been applied to a variety of housing types, as well as significantly different ages and existing conditions. The evaluation of post- retrofit performance suggests that the post-retrofit performance is impacted more by the specific implementation methods selected for measures package than by the house characteristics.

Other previous work related to high performance retrofit has focused on individual components or measures. For example, in one recent BA project, BSC worked with a weatherization program to evaluate and develop plans for inclusion of roof or attic insulation in the weatherization program (Neuhauser 2012). The current study evaluates the impact of a comprehensive measures package. 

BSC has also worked on several projects using individual retrofits from the National Grid DER pilot program. In one project, BSC performed a case by case evaluation of the implementation of the DER measures for five of the DER pilot program participants (Neuhauser 2011). In a second project, BSC looked at the pre- and post-retrofit performance data for seven DER projects, four of which were early participants in the DER pilot program (Osser et al. 2012). 

All of these earlier research projects dealt with the individual projects—either in terms of how the DER measures were implemented or the post-retrofit performance that they achieved individually. None of them compared and analyzed the performance data as a group. Now that additional projects have been completed in the National Grid DER pilot program, there are enough data available to warrant the analysis of all of these projects as a community of retrofits rather than as individual cases. The number of completed projects is large enough that the impact of the retrofit measures as a package can be analyzed and trends from the available data about these projects begin to emerge. Using this approach, the emphasis is shifted from the post-retrofit performance for the individual case to the post-retrofit performance achievable by using the DER package. On the other hand, the number of houses involved is not so large that the results of the analysis are limited to statistical assessments. So when a particular project falls out of the performance range for the majority of the community, the details for that project can be further analyzed to explain the discrepancy.

3 The National Grid Deep Energy Retrofit Pilot

3.1 Measures and Targets

The National Grid DER pilot program was established in 2009. The DER homes included in this report are all of those that successfully completed the National Grid DER pilot program and were occupied by January 2012. Participants in the DER pilot program are required to meet health, safety, and indoor air quality guidelines; specific thermal targets for each enclosure component (e.g., roof, above-grade walls); an overall airtightness target; minimum efficiency of mechanical equipment; water management; and durability requirements. While there are not specific instructions for how these targets are to be met, all implementation plans are reviewed for sound building science before the project is accepted into the pilot program and field verification of each completed measure is required in order to receive the financial incentives. In addition, all project teams are to include a qualified contractor or design consultant with previous DER experience and approval by National Grid. . .

Download the complete report here.