Speed control strategies for a condenser fan in a refrigeration system

1. A refrigeration system comprising:

a refrigeration circuit that includes at least a compressor, a condenser, an expansion valve and an evaporator;

a variable-speed condenser fan; and

a controller configured to, in a first mode of operation, monitor a current refrigeration demand of the refrigeration system and to set a speed of the condenser fan based on the current refrigeration demand of the refrigeration system,

wherein the controller is configured to:

monitor a set of current operating parameters of the refrigeration circuit that is indicative of the current refrigeration demand; and

set the condenser fan speed based on the set of current operating parameters,

wherein the controller is configured to set the speed of the condenser fan based on a predetermined model of system efficiency, which is a function of the set of current operating parameters and condenser fan speed,

wherein:

the controller is configured to set the speed of the condenser fan based on a predetermined relationship between the set of current operating parameters and a condenser fan speed at which system efficiency will be at its maximum for the set of current operating parameters; and

the predetermined relationship has been determined by performing a regression analysis using the predetermined model, and

wherein:

the predetermined relationship is in the form of a regression model, which is stored in a memory that is accessible by the controller; and

the controller is configured to:

input the set of current operating parameters into the regression model;

receive, as an output from the regression model, the condenser fan speed at which the system efficiency will be at its maximum for the set of current operating parameters; and

set the condenser fan to operate at a speed that is selected based on the condenser fan speed at which the system efficiency will be at its maximum for the set of current operating parameters.

2. A refrigeration system comprising:

a refrigeration circuit that includes at least a compressor, a condenser, an expansion valve and an evaporator;

a variable-speed condenser fan; and

a controller configured to, in a first mode of operation, monitor a current refrigeration demand of the refrigeration system and to set a speed of the condenser fan based on the current refrigeration demand of the refrigeration system,

wherein the controller is configured to:

monitor a set of current operating parameters of the refrigeration circuit that is indicative of the current refrigeration demand; and

set the condenser fan speed based on the set of current operating parameters,

wherein the controller is configured to set the speed of the condenser fan based on a predetermined model of system efficiency, which is a function of the set of current operating parameters and condenser fan speed,

wherein:

the controller is configured to set the speed of the condenser fan based on a predetermined relationship between the set of current operating parameters and a condenser fan speed at which system efficiency will be at its maximum for the set of current operating parameters; and

the predetermined relationship has been determined by performing a regression analysis using the predetermined model, and

wherein the predetermined relationship is in the form of a lookup table, which is stored in a memory that is accessible by the controller; and

the controller is configured to:

identify an entry in the lookup table that corresponds to the set of current operating parameters;

read from the entry data that is indicative of the condenser fan speed at which the system efficiency will be at its maximum for the set of current operating parameters; and

set the condenser fan to operate at a speed that is selected based on the condenser fan speed at which the system efficiency will be at its maximum for the set of current operating parameters.

3. The refrigeration system of claim 1 , wherein the controller is configured to set the speed of the condenser fan based on the predetermined model of system efficiency by:

performing an optimization algorithm using the predetermined model, to determine a condenser fan speed at which system efficiency will be at its maximum for the set of current operating parameters.

4. The refrigeration system of claim 3 , wherein performing the optimization algorithm comprises:

for each condenser fan speed of a group of predefined condenser fan speeds:

inputting the condenser fan speed in question and the set of current operating parameters into the predetermined model of system efficiency; and

receiving as output data from the predetermined model of system efficiency a refrigeration capacity value and a fuel or power consumption value; and

determining, based on the output data for the group of predefined condenser fan speeds, the predefined condenser fan speed for which the corresponding refrigeration capacity value and fuel or power consumption value yields the greatest system efficiency.

5. The refrigeration system of claim 1 , wherein:

the refrigeration system comprises a power source for supplying power to at least the controller and the condenser fan; and

the controller is configured to, in a second mode of operation:

determine, based on a current power consumption and a predefined maximum power capacity of the power source, an excess power capacity available from the power source;

determine a maximum speed at which the condenser fan can operate when utilizing the excess power capacity from the power source; and

set the condenser fan to operate at the determined maximum speed.

6. The refrigeration system of claim 1 , wherein the set of current operating parameters includes:

one or more of a compressor speed, a condenser air inlet temperature, an evaporator air inlet temperature, an evaporator fan speed and a throttling valve position; or

one or more of a compressor speed, a compressor suction pressure, a condenser discharge pressure and a throttling valve position.

7. The refrigeration system of claim 1 , wherein the controller is configured to:

monitor a first set of current operating parameters and a second set of current operating parameters different from the first set of current operating parameters, each of which is indicative of the current refrigeration demand; and

set the condenser fan speed based on the first set of current operating parameters interchangeably with the second set of current operating parameters.

8. The refrigeration system of claim 7 , wherein the controller is configured to:

set the condenser fan speed based on the first set of current operating parameters as a default in the first mode of operation, and to set the condenser fan speed based on the second set of current operating parameters if the controller detects a failure of one or more sensors for monitoring the first set of current operating parameters.

9. A refrigeration system comprising:

a refrigeration circuit that includes at least a compressor, a condenser, an expansion valve and an evaporator;

a variable-speed condenser fan; and

a controller configured to, in a first mode of operation:

monitor a set of current operating parameters of the refrigeration circuit that is indicative of a current refrigeration demand of the refrigeration system using a plurality of sensors;

perform an optimization algorithm using a predetermined model of system efficiency that is a function of the set of current operating parameters and condenser fan speed to determine a speed of the condenser fan at which system efficiency will be at its maximum for current values of the set of current operating parameters; and

set a speed of the condenser fan based on the determined speed of the condenser fan at which system efficiency will be at its maximum for the set of current operating parameters,

wherein performing the optimization algorithm comprises:

for each condenser fan speed of a group of predefined condenser fan speeds:

inputting the condenser fan speed in question and the set of current operating parameters into the predetermined model of system efficiency;

receiving as output data from the predetermined model of system efficiency a refrigeration capacity value and a fuel or power consumption value; and

determining, based on the output data for the group of predefined condenser fan speeds, the predefined condenser fan speed for which the corresponding refrigeration capacity value and fuel or power consumption value yields the greatest system efficiency.

10. The refrigeration system of claim 9 , wherein:

the controller is configured to set the speed of the condenser fan based on a predetermined relationship between the set of current operating parameters and a condenser fan speed at which system efficiency will be at its maximum for the set of current operating parameters; and

the predetermined relationship has been determined by performing a regression analysis using the predetermined model.

11. The refrigeration system of claim 10 , wherein:

the predetermined relationship is in the form of a regression model, which is stored in a memory that is accessible by the controller; and

the controller is configured to:

input the set of current operating parameters into the regression model;

receive, as an output from the regression model, the condenser fan speed at which the system efficiency will be at its maximum for the set of current operating parameters; and

set the condenser fan to operate at a speed that is selected based on the condenser fan speed at which the system efficiency will be at its maximum for the current parameters.