Abstract
For the upcoming refrigerant transition from HFCs to minorly flammable HFO refrigerants (A2L), refrigerant charge reduction is important to mitigate the fire hazard. Microchannel heat exchangers (MHXs) are a mature technology, which is effective in reducing system charge while maintaining similar heat transfer performance. MHXs will be applied more widely when the new refrigerants are used. Prior studies of the A2L HFO blends were mostly focused on fin-and-tube coils (FTC). An in-depth study for an air conditioner (AC)/heat pump (HP) system using all microchannel heat exchangers is still lacking.
In FY19, a side-to-side comparison will be conducted between two residential split heat pumps, one using all FTCs and the other using all MHXs for drop-in investigation, to identify potential issues for future design. The two heat pumps have similar rated capacity, SEER, HSPF levels, similar fan, blower and compressor, but differ in heat exchangers. Both the HPs use two-stage compressors to facilitate investigating different refrigerant flow rates. We will drop-in HFO refrigerants (replacements for R-410A, e.g. R452B, R447B, R32, etc.). The experiments will reveal the potential of MHXs for charge reduction, and how the two systems using A2L refrigerants operate under standard SEER and HSPF rating conditions.
The two units were donated by our partner, i.e. Nortek Global HVAC, an industry leader in making heat pumps using all MHXs as well as FTCs. The units were shipped to ORNL this week, and the product design data were also shared for modeling the two units using HPDM.
