Sizing Low and High Compression Stages of Reciprocating Compressor for Optimum Vapor Injection Performance in Economized Cycle

Vapor injection in conjunction with economized cycle is becoming more wide-spread as the unit efficiency requirements become more stringent and more difficult to meet with the new low-GWP refrigerants.   Economized cycle substantially boosts both efficiency and cooling/heating capacity.  A two-stage design is used in reciprocating compressors with vapor injected between the low and high compression stages. One of the most difficult tasks is to properly size the displacement of low and high pressure stages. This paper examines what controls this sizing to optimize vapor injected compressor performance with respect to operating conditions, refrigerant properties, and unit capacity and efficiency goals.