Commissioning and Envelope Leakage: Using HVAC Operating Strategies To Meet Design and Construction Challenges

David Sellers, Hannah Friedman, Larry Luskay, and Tudi Haasl, Portland Energy Conservation, Inc.

Keywords

Abstract

Successful HVAC design and efficient operation are inescapably linked to a “successful” building envelope design. From the HVAC system standpoint, a successful envelope must resist the transfer of heat and moisture and minimize the exchange of air across its boundary. While intuitive, these goals are often relegated to second place in favor of creating an aesthetically pleasing structure or making an architectural statement. The construction industry often presumes that if no water penetrates the building envelope, then the integrity of the system is satisfactory. But, scientific analysis and practical experience demonstrate that infiltration can lead to frozen pipes, condensation, and occupant discomfort.

This paper contains an overview and examples of design and construction issues that lead to envelope leakage problems. The discussion includes identification techniques used to locate and quantify the leakage, operational ramifications associated with the leakage, and solutions to mitigate the leakage using HVAC operating strategies. For two of the examples, a test was performed based on ASTM-E-779-99 (Standard Test Method for Determining Air Leakage Rate by Fan Pressurization) to quantify the leakage rate and assess its impact on building pressurization. The results of these tests and other field experiences indicate that achieving a completely airtight envelope is practically impossible. Thus, the architectural design and construction details targeted at providing an airtight envelope need to be supported by HVAC design and operating strategies that will mitigate the impact leakage that will inevitably occur.