Efficiency and Building Envelope
OTHER PARTS OF THIS ARTICLEPt. 1: This PagePt. 2: ASHRAE 90.1 Add Building EnvelopePt. 3: Efficiency Metrics for Windows, Walls and Roofs
American society is obsessed with measurement: Superbowl viewership rates, year-to-date flux of the Dow Jones, the body mass index of celebrities.
Ideally, facility executives are equally obsessed with their own metrics: occupancy rates, office churn and energy consumption. For the latter, it is relatively simple to take stock of the performance of systems within a building. But how does one apply efficiency metrics to the building envelope? How does one measure performance?
The short answer is that there is no short answer. It requires a bit of common sense, some knowledge of existing standards, and awareness of how best to apply both for accurate measurements. A careful reading of current ratings is also essential.
Ultimately, building performance is about two controllable factors: the systems within the building, and the efficiency of the envelope. Much focus is given to the efficiency of building systems such as lighting, heating, and cooling, but often little attention is paid to the envelope. Generally, if the envelope keeps the rain out and the heat — or cool — in, the performance is deemed acceptable, even when that’s clearly not the case.
When building a new facility, facility executives can request engineering firms to construct a software-based envelope model that calculates the cost of energy against HVAC system performance, building load requirements, construction materials and myriad other considerations.
Based upon the model requirements, facility executives should be able to make informed decisions about what R-values, U-values, window, wall and roofing specs are needed to meet targeted envelope performance.
Facility executives in existing buildings can model envelope performance, as well, and there’s plenty of help out there, says André Desjarlais, program manager for the Oak Ridge National Laboratory’s (ORNL) Building Envelope program.
“There’s a whole family of experts to assess the quality of the building envelope itself,” he says.
But in the absence of the budget to hire a team of consultants, Desjarlais recommends retrieving the original building schematics.
“Get access to the construction drawings of the building,” he says. “Look hard at the building envelope and know what you’ve got.”
Building schematics are only the starting point. A bit more historical digging is required for an accurate metric of any building’s envelope performance. For example, facility executives should also research the applicable energy codes and standards at the time of a building’s construction. Any deviation from original design intent, change orders, and remodeling or retrofits should be accounted for as well.
With such documentation, facility executives will have a good indication of the levels of R-values in the roof and walls. Taking this information, plus the performance values of modern windows, will provide a rudimentary but accurate picture of envelope performance.