Load-based testing, Ratings Standard
The characterization of heating and cooling performance of HVAC&R equipment is required of all manufacturers for determining seasonal energy efficiency ratings. The current rating standards, e.g. AHRI Standard 210/240, CSA C656, determine seasonal energy efficiency (e.g., SEER) using a bin method along with data from steady-state tests at different operating conditions. These standards were originally developed for equipment with single or two-stage thermostat control, but have been incrementally updated to consider equipment with variable-speed compressors and fans. However, the equipment testing is performed using control overrides and doesn’t consider the interaction of the integrated controls with the equipment. As a result, the standard ratings don’t capture the full range of part-load operation and don’t necessarily reward manufacturers who have superior controllers. To address this issue, we have been working with the Canadian Standards Association (CSA) to develop and evaluate a load-based testing methodology for evaluating the seasonal performance of variable-capacity equipment. This new testing methodology could be applied to both variable-speed and staged equipment, enabling a more direct and fair comparison of their performance. The testing methodology involves emulating the response of a building’s sensible and latent loads to equipment controls by dynamically adjusting temperature and humidity setpoints of the psychrometric chamber reconditioning system. Convergence criteria have been developed to automate the overall testing methodology so that the equipment performance can be fully evaluated using short-term tests (e.g., 1 day). Ultimately, automated load-based testing could lead to a practical approach for capturing equipment performance models that could be used in energy simulation programs for determining more accurate and application specific performance ratings. This paper presents the overall methodology of load-based testing in addition to a discussion of some of the experimental results.