Which compressor type does not require a crankcase heater to prevent refrigerant migration?

The correct answer is scroll compressors. Scroll compressors utilize a particular design where two spiral-shaped elements compress the refrigerant. This design allows for minimal refrigerant pooling in the crankcase, significantly reducing the risk of refrigerant migration when the system is off. Consequently, scroll compressors do not typically require a crankcase heater to prevent refrigerant from accumulating in the oil, which is a critical concern in systems with other compressor types, especially during prolonged shutdowns.

In contrast, reciprocal and rotary compressors generally have more significant potential for refrigerant migration when the system is not running. These designs can cause refrigerant to condense and settle in the crankcase, necessitating the use of crankcase heaters to keep the refrigerant in a gaseous state, thus preventing it from migrating and diluting the compressor oil. Centrifugal compressors are also more complex and often utilized in larger commercial applications, where refrigerant migration can be a concern, leading to similar considerations for crankcase heating.