Carrier Corporation

Neil D Jenkins

Richard A Kolk

David M Martini

Darren S Sheehan

Anthony Brancato

An absorption chiller having a protection system for preventing the chilled water in the evaporator tubes from freezing in the event the water flow through the tubes closes down while the machine is running. A sensor in the evaporator heat exchanger is arranged to detect when the water flow through the heat exchanger tubes closes down and signals the machine controller. The controller, in turn, shuts down the machine and opens a valve in a feed line to the evaporator to deliver a high temperature working fluid from another section of the machine to the evaporator to maintain the temperature in the evaporator above that at which the water in the tubes freezes.

Absorptive chiller with evaporator protection

A feedforward control method for an absorption chiller includes determining the disturbance transfer function, determining the capacity valve transfer function, measuring the actual disturbance, and implementing the feedforward control function in a feedforward controller. The feedforward control function is represented by the ratio of the disturbance transfer function divided by the capacity valve transfer function. The disturbance transfer function and the capacity valve transfer function are measured by applying a known amplitude input perturbation to the disturbance or capacity valve and recording the resulting perturbation in the output leaving chilled water temp. The disturbance transfer function is then the ratio of the delta leaving chilled water temperature divided by the delta change in the disturbance. The capacity transfer function is the ratio of the delta leaving chilled water temperature divided by the delta change in the capacity valve.

Feedforward control for absorption chiller

In an absorption chiller system, a control input for the chiller is a heat source controlled by a capacity valve, which is in turn controlled by a PI controller. The controller is controlled by a non-linear control function. During operation, a disturbance in the system is measured. A signal error is defined as a setpoint for the leaving chilled water minus the disturbance. The non-linear control function is represented as C(s)&equals;K (1&plus;b&verbar;E&verbar;)&plus;K /s, where where K is the gain when said signal error is zero, &verbar;E&verbar; is the absolute value of the signal error, b is an adjustable constant, and K is an integral gain.

Absorption chiller control logic

A method of controlling the capacity of an absorption chiller by regulating the heat input to a generator in response to a selected one of two system variables. The first variable involves the measured chilled water temperature leaving the system evaporator and the second involves the calculated solution concentration that is being returned to the absorber. Data relating to each variable is sent to a selector where it is processed so that the data can be used to control the heat input to the generator. The temperature data is used to control the heat input during normal chiller operation, however, the selector changes over control to the concentrate related data when the solution concentration level approaches the solution crystallization limit.

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Collegeville, PA, United States of America

Neil D Jenkins