Abstract: A thermostatic expansion device for use in refrigeration systems includes a valve member adapted to control the flow of liquid refrigerant from a condenser to an evaporator of the refrigeration system. A pressure-responsive device is operatively connected to the valve member for responding to a differential pressure in the refrigeration system so as to open and close the valve member. A temperature-responsive device is operatively connected to the pressure-responsive device for responding to a temperature of the refrigerant at the outlet of the evaporator. A lead-lag compensation structure is connected to the pressure-responsive device for permitting a rapid movement of the valve member upon the occurrence of a sudden change either in the temperature of the refrigerant at the outlet of the evaporator or in the pressure at the inlet of the evaporator thereby maintaining a constant superheat at the outlet of the evaporator so as to effect stability of the refrigeration system.

Abstract: The control system of the invention regulates a centrifugal compressor having inlet guide vanes adjustable as one means for varying the compressor capacity. A variable speed motor is connected to drive the compressor, and provides another means for regulating the compressor capacity. The control system regulates the motor speed alone over one portion of the load variation curve, and regulates the motor speed jointly with the inlet guide vane opening over another portion of the load variation curve, to achieve the most energy-efficient operating condition while avoiding the surge condition. This optimum control path is realized by utilizing a signal which is a measure of the compressor head value. Compressor surge or instability is avoided by deriving a critical Mach number (speed indication) for any given operating condition, as a function of the compressor head and vane position, and preventing the motor speed from going below that Mach number under the specific operating conditions.

Abstract: A controlled space is maintained at a desired set point temperature by adjusting the evaporator boiling pressure in a refrigeration system, thereby controlling the evaporator capacity (namely, the amount of cooling imparted to the air supplied to the space) which is inversely proportional to the evaporator boiling pressure. When the space temperature tends to vary from the desired set point due, for example, to a changing heat load, the control system automatically changes the refrigerant flow through the evaporator to establish the evaporator boiling pressure (and hence the boiling temperature) at the control point required to cool the air sufficiently to maintain the controlled space at the desired temperature. More specifically, in response to a space temperature increase, the flow rate of the refrigerant increases to decrease the evaporator boiling pressure; and in response to a drop below the set point, the refrigerant flow decreases to increase the evaporator boiling pressure.