Evaporators

Close to the inlet, on a short straight run. Refrigerant leaves the valve as a mixture of liquid and vapor, and every elbow or long horizontal run between the valve and the unit gives the two phases a chance to separate. Once they arrive separated, the distribution device has nothing uniform to distribute.

The sign is superheat that hunts and will not settle, with an uneven temperature pattern across the pack.

No. More plates raise the evaporating temperature and help efficiency, but they also lower the refrigerant velocity in each channel. When the velocity is too low the vapor no longer carries the oil up and out of the unit, the oil collects in the channels, and capacity drifts down while the compressor runs short of oil.

The check is at minimum load, not design load. On a variable-capacity compressor or a staged system, the lowest stage is where an oversized evaporator gets into trouble. Give the capacity range as well as the full-load duty, so the plate count is chosen to work at both ends.

Every field of the designation. The prefix letter identifies the series, and with it the inlet distribution arrangement, so a B-series frame with the same plate size is not a substitute for a V-, F- or P-series evaporator. A trailing T is a different plate generation. The pressure class has to suit the refrigerant - M, for example, is fatigue tested for refrigerants such as R410A, up to 45 bar at 135 C.

If the system has been or will be converted to another refrigerant, say so, because a like-for-like unit is right for the original refrigerant only. Refrigerant Compatibility covers what changes, and the Model Number Guide decodes the nameplate.

Against the refrigerant. Counter-current piping gives the closest approach, which lets the unit evaporate at the highest temperature for a given leaving water temperature.

A reversible machine cannot have it both ways. When the cycle reverses, the refrigerant direction through the exchanger reverses while the water keeps going the same way, so the unit is counter-current in one mode and co-current in the other. Pipe it counter-current for the mode with the larger load or the tighter temperature requirement, and have the selection checked in both - a unit sized only as an evaporator can come up short as a condenser.

When refrigerant charge is the constraint. AsyMatrix plates form channels of two different volumes, and the hold-up volume can be up to 30 percent lower than a symmetric equivalent. With a flammable refrigerant such as R290, where the permitted charge limits what a machine can be, that reduction can decide whether a design is allowed at all.

Note the naming: AS in a model name means AsyMatrix, not All-Stainless. An AS frame is not copper free on that account, so it is not by itself the answer to an ammonia or pure water duty.