Development of a new model for investigation of the performance of carbon dioxide as a refrigerant for residential air conditioners
Abstract
This study presents the development, validation and application of a new model for simulating the performance of residential air-to-air CO 2 air conditioners and heat pumps. Validation of the model has been accomplished using recent experimental data for a gas cooler and evaporator, each tested as stand-alone components, as well as CO2 system data. Heat exchanger capacities were predicted within the bounds of experimental error. Compressor power consumption and system COP were within 5%. Air pressure drop was predicted within 30%. Refrigerant pressure drop was overpredicted by a factor of 1.0–2.5. Using alternate friction factor correlations and removing minor loss coefficients failed to isolate the source of the error, but analysis of the experimental techniques provided possible explanations. Case studies simulating an R-410A system in both cooling and heating modes were conducted. The maximum simulated cooling COP of 3.01 is 76% of the value of a high-efficiency R-410A air-conditioner and the maximum simulated EER of 9.8 is 90% of the value of a mid-efficiency R-22 air-conditioner. The maximum simulated heating COP of 3.47 is 94% of the value of a mid-efficiency R-410A heat pump and 105% of the value of a mid-efficiency R-22 heat pump. Improving compressor overall efficiency by 0.1 across the board has the largest impacts on EER (cooling) and HPF (heating), resulting in performance gains of between 26–30% (cooling) and 13% (heating) over the base system cases. Increasing fin density by 25% raises cooling COP but lowers EER (COP is defined here as the useful heat transfer divided by compressor power consumption only, with no fan power). However, the ratio of fin pitch to louver pitch for the simulated heat exchangers was outside the range tested during development of the air-side friction factor correlation used here. In heating mode the increase in fin density was performance-neutral. Increasing airflow rates by 100 cfm (0.047 m3/s) per ton increased HPF in heating mode, but was performance-neutral in cooling mode. Increasing heat exchanger volumes at constant face area by 20% raised performance slightly.
Degree
Ph.D.
Advisors
Groll, Purdue University.
Subject Area
Mechanical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.