The report describes configurations of air-conditioner/heat pump systems that can meet regulations, codes, and standards' safety requirements using low GWP refrigerants, most notably ASHRAE Standard 15 and UL Standards 484 and 1995. It also looks at designs for safe use of refrigerants including hydrocarbons.
Purpose of the study
In order to assess the viability of using candidate low-GWP refrigerants in ducted residential air-conditioners and heat pumps, system configurations consistent with safety requirements and performance were assessed by AHRI. Features such as costs, technical risk, and suitability for the large replacement market were evaluated.
The AHRI study:
- Reviewed current US standards that guide the design of residential air-conditioning equipment.
- Evaluated and compared different system design configurations for the alternative refrigerants under consideration.
- Provided detailed descriptions of the best candidate system configuration for each of the alternative refrigerants under consideration, to serve as a starting point for future design investigations.
Propane equipment configuration
According to the report AHRI’s assessment is that a single-packaged, portable configuration of room air-conditioner would be the only configuration that would meet requirements of ASHRAE 15 and UL 484. Furthermore, to meet the charge requirements in the standards, the room air conditioner uses microchannel heat exchangers.
Specific design parameters for a hydrocarbon room air-conditioner:
- Cooling capacity: 0.34 RT
- Target efficiency: 11.0 EER
- Refrigerant charge: 150g
- Design Requirements: Charge minimisation, ignition prevention
- Charge Minimization Techniques: Microchannel Indoor Coil, Microchannel Outdoor Coil
- Ignition prevention techniques: Totally-enclosed air-over double-shafted motor, ignition-proof or enclosed electronics
Key Components for propane system:
- Compressor: R-290 Rotary Compressor. Several compressor manufacturers have developed rotary R-290 compressors whose efficiency is comparable to current R-410A systems. Gree Electric is using these compressors to achieve EERs of close to 12 in mini-split systems.
- Heat Exchangers: Microchannel Evaporator, Microchannel Condenser
- Expansion Device: 2 Capillary Tubes
- Additional Refrigerant Cycle Features: Reversing valve to reverse refrigerant flow for heat pumping. The reversing valve allows for the high-side and low-sides of the cycle to switch places.
- Unique Safety Features: Totally-enclosed air-over double-shafted motor. All electrical components should be ignition-proof, separated from the main chamber, or be located in an enclosure.
AHRI’s Low-GWP Alternative Refrigerants Evaluation Program
AHRI launched the low GWP Alternative Refrigerants Evaluation Program (AREP) to support industry’s research needs raised by the use of high GWP refrigerants. Since its launch the final test reports have been published for compressor calorimeter testing, system drop-in testing, soft-optimized system testing, and heat transfer testing of various refrigerants.