Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
2000-05-04
2001-08-21
Buiz, Michael Powell (Department: 3744)
Refrigeration
Automatic control
Refrigeration producer
C062S179000, C062S203000
Reexamination Certificate
active
06276152
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to chillers providing a chilled fluid such as water for use in air conditioning, refrigeration and the like. More particularly, the present invention is directed to the control of a variable flow chilled water system and represents an improvement in chiller capacity control.
A chiller is a device providing a chilled fluid. For many years it was considered necessary that chillers be constant flow devices. Articles such as “Why Must Chillers be Constant Flow Devices?”, the Trane Engineering Newsletter, Volume 9, Number 1, January-February 1980 cite reliable heat transfer from a temperature control and instability in the control system as reasons supporting the premise that chillers must be constant flow devices.
In recent years this has changed and variable flow chilled water systems have begun to be implemented. An article “Don't Ignore Variable Flow” by James P. Waltz was published in the July 1997 issue of Contracting Business (pages 133-144) discussing basic variable flow chilled water systems. On the final page of the article, the author recognizes the ongoing problems in controlling variable flow chilled water systems. Problems are cited regarding minimum flow control, incorrect speed control, and insufficient cooling or flow capacity.
Many of these problems result from a chiller system which cannot compensate for simultaneous changes in the capacity of one or more chillers and in the flow rate of the chilled water being provided to the air handlers.
SUMMARY OF THE INVENTION
It is an object, feature and advantage of the present invention to solve the problems of the prior art systems.
It is an object, feature and advantage of the present invention to provide a variable flow chilled water system with controls that compensate for changes in chiller capacity and chilled water flow rate simultaneously.
It is an object, feature and advantage of the present invention to provide a controlled method for a chiller capacity control which automatically adjusts chiller capacity control to reject disturbances caused by variable flows in chilled water while maintaining control stability at low water flow rates.
It is a further object, feature and advantage of the present invention to accomplish this while adjusting chiller capacity to compensate for changes in the load.
It is an object, feature and advantage of the present invention to predict load changes and adjust the chiller capacity before the leaving water temperature of the chiller is affected by load changes and to adjust the chiller capacity before the leaving water temperature of the chiller is affected.
It is an object, feature and advantage of the present invention to improve chiller efficiency as water flow rates are reduced.
The present invention provides a method of controlling chiller capacity in a chiller system. The method comprises the steps of: measuring entering the fluid temperature of a fluid entering a heat exchanger; measuring the fluid temperature of the fluid leaving the heat exchanger; determining a desired leaving fluid temperature; establishing chiller capacity as a function of the difference between leaving fluid temperature and the desired leaving fluid temperature; and adjusting the determined chiller capacity as a function of the difference between entering fluid temperature and the desired leaving fluid temperature.
The present invention also provides a chiller system including a chilled fluid loop where the temperature of the fluid is controlled by varying the capacity of a chiller. The system comprises a variable capacity chiller including an evaporator; a chilled fluid loop in heat transfer relation with the evaporator; a sensor measuring the leaving fluid temperature of the evaporator; and a sensor measuring the entering fluid temperature of the evaporator. The chiller system also comprises a mechanism for providing a desired leaving fluid temperature; a pump controlling the rate of fluid flow in the fluid loop; and a controller operably controlling the chiller capacity in response to changes in the variable flow rate of the pump. The controller is connected to the setpoint mechanism and the entering and leaving fluid temperature sensors. The controller includes a feedback loop controlling chiller capacity in response to leaving fluid temperature and a feed forward loop controlling chiller capacity in response to entering fluid temperature.
The present invention further provides a method of controlling chiller capacity and chilled water flow rate in the chiller system. The method comprises the steps of: determining a leaving water temperature of chiller water leaving an evaporator; determining an entering water temperature of chilled water entering the evaporator; controlling the speed of a variable flow pump as a function of the leaving water temperature; controlling the capacity of a chiller system, operably connected to the evaporator and providing a heat sink, as a function of the entering water temperature and as a function of the leaving water temperature.
REFERENCES:
patent: 3710852 (1973-01-01), Porter
patent: 4269034 (1981-05-01), Rzechula
patent: 4274264 (1981-06-01), Andres
patent: 4483152 (1984-11-01), Bitondo
patent: 4589060 (1986-05-01), Zinsmeyer
patent: 5201648 (1993-04-01), Lakowski
patent: 5347821 (1994-09-01), Oltman et al.
patent: 5355691 (1994-10-01), Sullivan et al.
patent: 5396782 (1995-03-01), Ley et al.
patent: 5419146 (1995-05-01), Sibik et al.
patent: 5553997 (1996-09-01), Goshaw et al.
patent: 5561599 (1996-10-01), Lu
patent: 5600960 (1997-02-01), Schwedler et al.
patent: 5611211 (1997-03-01), Whipple, III
patent: 5632154 (1997-05-01), Sibik et al.
patent: 5669225 (1997-09-01), Beaverson et al.
patent: 5946926 (1999-09-01), Hartman
patent: 5950443 (1999-09-01), Meyer et al.
“Why Must Chillers Be Constant Flow Devices?”, Jan.-Feb., 1980, vol. 9, No. 1, Trane Engineer's Newsletter.
“Don't Ignore Variable Flow”, by James P. Waltz, Jul., 1997, Contracting Business.
American Standard International Inc.
Beres William J.
Buiz Michael Powell
Jiang Chen-Wen
O'Driscoll William
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