Derivation of walk-in cooler and freezer Performance Standard equations as they pertain to the ANSI/AHRI Standard 1250 and 1251

Abstract

The ANSI/AHRI (American National Standard Institute (ANSI)/ Air-Conditioning, Heating, and Refrigeration Institute (AHRI).) Standard 1250/1251 Performance Rating of Walk-In Coolers and Freezers strives to standardize refrigeration equipment performance rating. According to the Standard, refrigeration equipment is tested in a laboratory setting using a defined test method. An existing algorithm is used to calculate the Annual Walk-in Energy Factor (AWEF) which serves as a comparison of energy efficiency between equipment. In this work the algorithm was modified in an attempt to more closely approximate actual refrigeration system operation. To calculate the AWEF, a walk-in box load profile and a ratio of the equipment capacity to the refrigeration load are assumed by the Standard. An extensive literature review of ninety-eight articles was performed to address these assumptions. Information was categorized and analyzed for each load component, including lighting, occupancy, product, infiltration, conduction, and miscellaneous loads. Additional information was collected on refrigeration system design and operation. A model load profile was developed from which a revised AWEF algorithm was obtained. Simulations were performed on four walk-in refrigeration units to validate the revised calculation method. Raw results show improved correlation of compressor runtime, because a specific compressor runtime was targeted, reducing variation between hourly simulations and the 1250 calculation from -29.9% with the AHRI 1250 calculation (Becker et al. 2011) to 1.1% with the Proposed 1250 calculation. AWEF correlation between hourly simulations and the 1250 calculation degraded from -7.4% with the AHRI 1250 calculation (Becker et al. 2011) to 15.9% with the Proposed 1250 calculation. Plotting the results for the AWEF and compressor runtime correlation versus variation in the box load, between the hourly simulation and Proposed 1250 calculation results, revealed an issue with the compressor runtime calculation. At a box load variation of zero, the Proposed 1250 AWEF correlation is improved to -2.4%, and the Proposed 1250 compressor runtime correlation is degraded to -14.6%. If a specific compressor runtime had not been targeted, the AWEF correlation for each simulation set would have been improved. To summarize, the Proposed 1250 equations yield an improved AWEF calculation but do not accurately calculate the corresponding compressor runtime.