Importance of Refrigerant Line Sizing by Nick Fisher

Importance of Refrigerant Line Sizing

At Carlson & Stewart Refrigeration, Inc. we strive to design and install superior commercial and industrial refrigeration systems. One of the key components to delivering on this is correctly sizing the refrigerant lines for each refrigeration system. Improperly designed line sets can cause the refrigeration system to struggle to keep up with the system’s demand and may result in additional maintenance work down the line.

I have been trained to design the line sets for refrigeration systems with many factors in mind including minimizing temperature difference and pressure drop as well as ensuring adequate and proper oil return to the compressor from the evaporator.
Line sizing is a balancing act between refrigerant velocity and temperature and pressure deltas. In general, the larger the line size is, the lower the temperature and pressure deltas will be but, that usually will result in a lower refrigerant velocity. That lower refrigerant velocity will reduce the effectiveness of the vapor refrigerant to “push” the oil through the evaporator and back to the compressor. A good rule of thumb I have been taught is to design for minimal temperature and pressure deltas while maintaining at least 750 ft/min in horizontal suction line runs and 1,500 ft/min in vertical suction line runs, also referred to as a riser.

In general, a suction line riser is needed whenever the flow of refrigerant in a suction line must go vertical, usually to pipe in the ceiling between the evaporator location and the compressor or condensing unit location. Sometimes, the riser line size is smaller than the rest of the suction line size. This is to reduce the temperature and pressure deltas while also maintaining the necessary refrigerant velocity to ensure adequate oil return from the evaporator.

It is always best practice to install a p-trap at the base of the suction riser. This is to ensure that no oil from the system will back-feed into the evaporator. If oil does back-feed into the evaporator, often it will settle in the evaporator and coat the tubing throughout the coil. This will cause a decrease in heat transfer throughout the evaporator and could ultimately result in the system not keeping up with the demands of the space that it was specifically designed to cool.

Carlson & Stewart Refrigeration, Inc. will properly design and install the line sets for the refrigeration equipment for each space to ensure the maximum capacity and efficiency can be achieved and maintained.

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