Estimating Demand & Efficiency PDF

A summary report of recent studies highlights the increasing energy consumption of auxiliary equipment in building HVAC systems.¹ It was estimated that 1.5 quadrillion Btus (1.5 quads) were required to operate auxiliary equipment compared in 1995 to 1.85 quads for the primary space heating equipment and 1.87 quads for cooling. Supply, return and exhaust fan consumption was 83% of the total. Many of these studies used elaborate, hour-by-hour simulations to account for and predict auxiliary equipment energy consumption.²

Unfortunately, resources often are unavailable for conducting hour-by-hour analysis. If energy analysis is performed, it is often in the conceptual phase. Accurate energy analysis is best conducted after an initial detailed design is completed, several iterations that optimize cost vs. efficiency vs. space vs. comfort vs. code compliance are conducted, and the design is "value engineered" to meet the project budget. At this stage, energy efficiency may have a low priority and systems with high demand and energy requirements could result. A score sheet has been developed3 to quickly evaluate the impact of individual components on system demand (and efficiency) when detailed energy analysis is not possible.