Project Report


Comments on
Voluntary Home Energy Rating Systems Guidelines
Docket Number EE-RM-95-202
Buildings Division, EE-432


Peport Prepared for: Conservation Services Group
Report Dated: October 29, 1995
By: John Proctor, Proctor Engineering Group, Boston, MA

Introduction

Goals

In order to evaluate the Proposed Voluntary Home Energy Rating System Guidelines it was first necessary to determine the goals of the Guidelines. As we interpret the existing information there is a primary goal and a number of subsidiary goals:

The primary goal is to improve the energy efficiency of residential buildings with attendant benefits to the economy, environment, consumers, and nation.

Secondary goals include;

Principles

In order to accomplish the goals of the rating system there are basic principles to move us in that direction. We would summarize those principles as:

Discussion

In order to be effective the guidelines must set a standard that, if followed, will meet the primary goal -- to improve the energy efficiency of residential buildings.

The guidelines propose a rating scale based on a Reference Home (RH). The Rated Home will be classified by how much energy it will consume for space conditioning and water heating compared to the Reference Home. The selection of the RH characteristics is therefore critical. The Reference Home must be sufficiently better than both the new and existing housing stock to provide upward pressure on building efficiency. In other words a building that ranks "Four Stars" (the level of the RH) should be recognizable as an energy efficient building. This will help meet Principle One - Incentive to Higher Efficiency. The classification of the Rated Home relative to the RH must be sufficiently valid and accurate that lenders, consumers, and others can depend on the rating to properly inform them of how this building is likely to perform. For this reason the parameters that effect space conditioning and water consumption must be determined above some minimum level of accuracy. This will help meet Principle Two -- Ratings Actually Represent Performance.

An outgrowth of the need for validity is the question of accuracy. It is important that large differences in validity and accuracy between various components of the system cannot exist. If large differences in validity and accuracy are allowed into the system Principle Three - Maintain the Primary Goal is violated. Large inaccuracies may increase sales of individual technologies, but if the tradeoffs between technologies are made with inaccurate and invalid numbers, the primary goal will not be accomplished. The use of default assumptions must be carefully scrutinized to avoid these inaccuracies.

Reference Home

A Reference Home is an energy efficient home. Proctor Engineering Group recommends that the RH be a home that has building elements that are in the top quartile to decile of existing energy efficient homes. At a minimum this means that building elements of the Reference Home would fit above the top 10% of new construction.

Two items in the Reference Home definition need correction. These are air leakage rates and distribution system efficiency.

Seasonal Air Exchange Rate

Section 437.103 Paragraph a 15 sets a seasonal air exchange rate for the Reference Home at 0.65 air changes per hour (ACH). Existing energy efficient structures already have air exchange rates of less than 0.20 (see Table A in the full report. Ordering instructions listed below)

While existing structures have measured seasonal air exchange rates of 0.20 or less, Proctor Engineering Group recommends 0.35 ACH because it is an ASHRAE consensus standard. 0.35 ACH is a reasonable value for the Reference Home (it represents the efficiency limit without some form of mechanical ventilation).

How would a Reference Home air exchange rate of .35 compare to the air exchange rates in energy efficient homes and new construction?

The discussion in the NOPR supporting a Reference Home seasonal air exchange rate (page 37954) confuses the RH air change rate with a default air exchange rate for a rated home. A rated home could have an air exchange rate anywhere from near 0 ACH (using a heat recovery ventilator or air purification) to 2 or more ACH. The primary effect of setting the air exchange rate too high for the Reference Home is that it makes a "Four Star" rating too easy and reduces the incentive for improvement.

We recommend that Section 437.103 Paragraph (a) (15) be revised to read: "A seasonal average air leakage rate of 0.35 air changes per hour;"

This would provide a Reference Home leakage rate in the top quartile to decile of efficiency for current new construction.

Seasonal Distribution Efficiency

Section 437.103 Paragraph a 13 Table 3 sets the distribution efficiency for the Reference Home with a forced air system with ducts outside the conditioned space at .72. Current new construction (which has notoriously leaky ducts) averages .72 according to the Treidler study. Studies in California, Nevada, and Arizona have shown that distribution system efficiencies above .90 are attainable without extreme measures (See Table B in the full report. Ordering instructions are listed below.)

Proctor Engineering Group recommends that the seasonal distribution efficiency for the Reference Home be .90 for ducts outside the conditioned space. This is still less efficient than the .95 goal set by the Association of State Energy and Technology Transfer Institutions (ASERTI) along with EPRI and GRI (ASERTI, 1992). Field measured distribution efficiencies for standard leaky duct construction show distribution efficiencies as high as .82. Easily achievable levels of duct tightness have shown efficiencies above .90.

We recommend that Section 437.103 Paragraph (a) (13) Table 3 be revised to show: .90 distribution efficiency for heating and cooling with ducts outside the conditioned space. Basement specification should be similarly revised.

Rated Building

Section 437.104 Paragraph e allows determination of air leakage and duct leakage values based either on (1) diagnostic test data or (2) on observations. Proven, effective, and inexpensive measurements of house leakage and duct leakage are available and should be used.

Air Leakage

The Department has invited comments on the possible range of error that can occur with estimated air leakage or with diagnostic testing and an infiltration model. An experienced and well trained rater cannot make reasonable estimates of air leakage. Proctor Engineering Group has worked in this field since 1979 and we have worked closely with both researchers and practitioners across the United States.

We have attempted to estimate the leakage of homes before we measured that leakage, we have known some of the best practitioners in the country try to estimate leakage in advance of measuring it. We have never seen anyone capable of performing this task. We know of no study that has shown that even the most experienced person can accurately estimate the leakage rate of a single family building. On the other hand there are volumes of studies that show that using the proper diagnostic tools (a blower door) trained personnel can actually measure the leakage of a building in a short time period.

EPRI has studied the correlation between actual infiltration rates and infiltration rates modeled based on blower door testing and both the LBL and the AIM models (Palmiter and Bond, 1994) This study showed that both models tracked the base infiltration well.

Distribution Efficiency

Distribution Efficiency is at least as critical as air infiltration rates . Numerous field studies have found that many ducted distribution systems are very inefficient. . Since it is not uncommon for the distribution efficiency of a ducted system to be less than .50, this single measurement may be the most important measurement in the rating system. Many of the duct problems are hidden from view and so non destructive testing is necessary. There are duct test machines that determine the amount of duct leakage. These machines are easy to use, not very expensive and have been proven to be effective in measuring duct leakage.

We recommend that Section 437.104 Paragraph (e) be revised to read: "For existing homes, the determination of air leakage and duct leakage set forth as building elements 10 and 11 in Table 5 are determined by on-site diagnostic test data." Delete Paragraphs e1, e2, e2i, and e2ii.

Defaults

The purpose of the rating system is to rate buildings, not to rate assumptions. The most detrimental assumption is that the rated home is more efficient than it is. A common way of making that error is assigning default values based on the average home . If the default is average, half of the buildings will be overrated and opportunities for improvement will be lost.

Section 437.104 Paragraph e 2 i allows for a default value of 0.67 air changes to be used as the air leakage rate. This would overrate at least half of the homes.

Section 437.104 Paragraph e 2 ii allows for a yet undetermined default value to be used as the duct leakage rate. This leaves open the possibility that more than half of the homes will be overrated.

Section 437.107 a allows for a projected rating for to-be-built homes. This makes it likely that homes will actually perform below their rating.

Air Leakage

We have recommended that the raters utilize a blower door to determine the leakage of the home.

However, if the final rule allows a default air leakage that leakage rate should represent the bottom end of the housing stock. If it allows anything else it will overrate buildings and reduce the incentive for energy efficiency. Based on the known values of air leakage listed in Table A, we recommend that if a default value is used for air leakage that it be set at 2.0 ACH.

We recommend that if Section 437.104 Paragraph (e) (2) (I) is not deleted, it should be revised to read: "for air leakage 2.0 air changes per hour shall be used unless the rater has tested the air leakage of the home."

Duct Leakage We have recommended that the raters utilize a duct leakage test to determine the distribution efficiency of the home.

However, if the final rule allows a default distribution efficiency that leakage rate should represent the lower end of the housing stock. If it allows anything else it will overrate buildings and reduce the incentive for energy efficiency. Based on the known values of distribution efficiency listed in Table B, we recommend that if any default value for distribution system leakage above .45 needs to be justified by a duct leakage test.

If a higher default is used, it will create an additional and unwarranted advantage to ducted systems vs. distributed systems (e.g., heat pumps over eletctric baseboard).

We recommend that if Section 437.104 Paragraph (e) (2) (ii) is not deleted, it should be revised to read: "for ducted systems with ducts outside the conditioned space, the default distribution efficiency shall be .45 unless the rater has tested the duct leakage of the home. Projected Ratings

Since experience in California and other states has shown that houses are often built less efficient than the plans indicate, it is necessary to distinguish between a rating based on plans and defaults and a rating based on the actual home.

We recommend that Section 437.107 be changed by adding a Paragraph (c) as follows: "The projected rating must be clearly labeled as 'PROJECTED'. It also must contain a notice that the projected rating is based on a review of the plans and that no inspection has taken place to ensure that the house is built to meet the projected level of efficiency."

Training, Certification, and Quality Assurance

The Department has invited comment on these areas. Having worked in this field since 1979 and investigated a wide variety of training, certification, and quality assurance approaches, we make the following recommendations:

REFERENCES

Also see Program Design


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