VAPOR COMPRESSION COOLING SYSTEM WITH IMPROVED ENERGY EFFICIENCY THROUGH ECONOMIZATION
A cooling system has a cooling circuit that includes an evaporator disposed in a cabinet, a condenser, a compressor, an electronic expansion valve and a liquid pump. a direct expansion mode and a pumped refrigerant economizer mode. When the cooling system is in the pumped refrigerant economizer mode, the controller controls a temperature of the refrigerant to a refrigerant temperature set point by regulating a speed of a fan of the condenser, controls a temperature of air in a room in which the cabinet is disposed to a room air temperature setpoint by regulating a speed of the liquid pump, and maintains a pressure differential across the liquid pump within a given range by regulating an open position of an electronic expansion valve.
1 . A cooling system, comprising:
a cabinet having an air inlet and an air outlet;
a cooling circuit that includes an evaporator disposed in the cabinet, a condenser, a compressor, an electronic expansion valve and a liquid pump;
the cooling system having a direct expansion mode wherein the compressor is on and compresses a refrigerant in a vapor phase to raise its pressure and thus its condensing temperature and refrigerant is circulated around the cooling circuit by the compressor and a pumped refrigerant economizer mode wherein the compressor is off and the liquid pump is on and pumps the refrigerant in a liquid phase and refrigerant is circulated around the cooling circuit by the liquid pump and without compressing the refrigerant in its vapor phase; and
a controller coupled to the liquid pump and the compressor that turns the compressor off and the liquid pump on to operate the cooling circuit in the economizer mode and turns the compressor on to operate the cooling circuit in the direct expansion mode;
wherein when the cooling system is in the pumped refrigerant economizer mode, the controller controls a temperature of the refrigerant to a refrigerant temperature set point by regulating a speed of a fan of the condenser, controls a temperature of air in a room in which the cabinet is disposed to a room air temperature setpoint by regulating a speed of the liquid pump, and maintains a pressure differential across the liquid pump within a given range by regulating an open position of the electronic expansion valve.
2 . The cooling system of claim 1 wherein the controller turns the liquid pump off when the cooling circuit is in the direct expansion mode.
3 . The cooling system of claim 1 including a bypass valve coupled around the compressor and through which the refrigerant flows to bypass the compressor when the cooling circuit is in the economizer mode and a liquid pump bypass valve coupled around the liquid pump and through which the refrigerant flows to bypass the liquid pump when the cooling circuit is in the direct expansion mode.
4 . The cooling system of claim 3 including a valve coupled to the outlet of the liquid pump, the control valve controlled by the controller to be closed when the cooling circuit is in the direct expansion mode and to be open when the cooling circuit is in the economizer mode.
5 . The cooling system of claim 3 including a variable flow discharge valve coupled to the outlet of the liquid pump, the variable flow discharge valve modulated by the controller to maintain a pressure differential across the liquid pump when the cooling circuit is in the economizer mode.
6 . The cooling system of claim 3 wherein the liquid pump is a variable speed pump and the controller modulates a speed of the liquid pump to control a flow rate of the refrigerant when the cooling circuit is in the economizer mode.
7 . The cooling system of claim 6 wherein the cooling circuit includes a bypass valve coupled around the electronic expansion valve and through which the refrigerant flows to bypass the electronic expansion valve when the cooling circuit is in the economizer mode, the bypass valve controlled by controller to be closed when the cooling circuit is in the direct expansion mode and open when the cooling circuit is in the economizer mode.
8 . The cooling system of claim 1 including a valve coupled around the condenser and controlled by the controller to mix a portion of the refrigerant flowing to an inlet of the condenser with refrigerant flowing from an outlet of the condenser.
9 . The cooling system of claim 8 including a pressure regulating valve coupled between the outlet of the condenser and an inlet of a receiver/surge tank and also between the outlet of the condenser and an inlet of the liquid pump.
10 . The cooling system of claim 9 including a three-way valve coupled between an outlet of the evaporator, an inlet of the compressor and an inlet of the condenser, the three-way valve controlled by the controller when the cooling circuit is in the direct expansion mode to provide refrigerant from the outlet of the evaporator to the inlet of the compressor and to block refrigerant flow from the outlet of the evaporator to the inlet of the condenser, and when the cooling circuit is in the economizer mode to provide refrigerant flow from the outlet of the evaporator to the inlet of the condenser and block refrigerant flow from the outlet of the evaporator to the inlet of the compressor.
11 . The cooling system of claim 1 including a valve coupled between an outlet of the evaporator, an inlet of the compressor and an inlet of the condenser, wherein the valve has a first position where it provides refrigerant flow through the valve from the outlet of the evaporator to the inlet of the compressor and blocks refrigerant flow through the valve from the outlet of the evaporator to the inlet of the condenser, and a second position where it provides refrigerant flow through the valve from the outlet of the evaporator to the inlet of the condenser and blocks refrigerant flow through the valve from the outlet of the evaporator to the inlet of the compressor, the valve controlled by the controller to be in its first position when the cooling circuit is in the direct expansion mode and in its second position when the cooling circuit is in the economizer mode.
12 . The cooling system of claim 1 including a variable capacity valve coupled between an inlet of the condenser and an inlet of a receiver/surge tank, an outlet of the condenser coupled to an inlet of the liquid pump, the variable capacity valve modulated by the controller to modulate a pressure of the receiver/surge tank to force liquid from the receiver/surge tank to the liquid pump.
13 . The cooling system of claim 1 including a pressure regulating valve coupled between the outlet of the condenser and an inlet of a receiver/surge tank, a variable capacity valve coupled between an inlet of the condenser and the inlet of the receiver/surge tank, the receiver/surge tank having an outlet coupled to an inlet of the liquid pump wherein refrigerant flowing to the inlet of the liquid pump preferentially flows through the receiver/surge tank and then to the inlet of the liquid pump or flows around the receiver/surge tank to the inlet of the liquid pumps.
14 . The cooling system of claim 1 including a pressure regulating valve coupled between the outlet of the condenser and an inlet of a receiver/surge tank, the receiver/surge tank having an outlet coupled to an inlet of the liquid pump wherein all the refrigerant flowing to the inlet of the liquid pump first flows through the receiver/surge tank and then to the inlet of the liquid pump.
15 . The cooling system of claim 3 including a suction line accumulator coupled between the outlet of the evaporator and the inlet of the compressor, the compressor bypass valve coupled around both the suction line accumulator and the compressor, wherein when the cooling circuit is in the direct expansion mode, the refrigerant flows from the outlet of the evaporator through the suction line accumulator to the inlet of the compressor and wherein when the cooling circuit is in the economize mode, the refrigerant flows from the outlet of the evaporator through the compressor bypass valve to flow around the suction line accumulator and the compressor.
16 . The cooling system of claim 1 including a suction line heat exchanger having a first heat exchange path coupled between an outlet of the liquid pump and an inlet of the electronic expansion valve and a second heat exchange path coupled between an outlet of the evaporator and an inlet of the compressor, a bypass valve coupled around the first heat exchange path of the suction line heat exchanger and the electronic expansion valve, the bypass valve controlled by the controller to be closed when the cooling circuit is in the direction expansion mode and open when the cooling circuit is in the economizer mode to bypass the suction line heat exchanger and the electronic expansion valve.
17 . The cooling system of claim 1 wherein the liquid pump free wheels when it is off and refrigerant flows through the free wheeling liquid pump when the cooling circuit is in the direct expansion mode.
18 . The cooling system of claim 3 including a compressor inlet solenoid valve coupled between the inlet of the compressor and an outlet of the evaporator, the compressor bypass valve coupled around both the compressor and the compressor inlet solenoid valve, the compressor inlet solenoid valve controlled by the controller to be open when the cooling circuit is in the direct expansion mode and controlled by the controller to be closed when the cooling circuit is in the economizer mode.
19 . The cooling system of claim 1 and including a plurality of cooling circuits with each cooling circuit included in one of a plurality of cooling stages including an upstream cooling stage and a downstream cooling stage wherein the evaporator of the cooling circuit of the upstream cooling stage (upstream evaporator) and the evaporator of the cooling circuit of the downstream cooling stage (downstream evaporator) are arranged in the cabinet so that air to be cooled passes over them in serial fashion, first over the upstream evaporator and then over the downstream evaporators;
the cooling circuit of each cooling stage having a direct expansion mode wherein the compressor of that cooling circuit is on and the refrigerant is circulated around the cooling circuit by the compressor of that cooling circuit and a pumped refrigerant economizer mode wherein the compressor of that cooling circuit is off and the liquid pump of that cooling circuit is on and the refrigerant is circulated around the cooling circuit by the liquid pump of that cooling circuit.
20 . The cooling system of claim 18 wherein when one of the upstream and downstream cooling stages can be in the economizer mode and the other must be in direct expansion mode, the controller operates the cooling circuit of the upstream cooling stage in the economizer mode turning liquid pump of that cooling circuit on and the compressor of that circuit off and operates the downstream cooling stage in in the direct expansion mode turning the compressor of the downstream cooling circuit on.
21 . The cooling system of claim 1 wherein the controller has a refrigerant temperature feedback control loop for controlling the temperature of the refrigerant by regulating the speed of the condenser fan, the refrigerant temperature feedback control loop having an output at which a condenser fan speed control signal is output and having as inputs the refrigerant temperature setpoint and a feedback signal which is actual temperature of the refrigerant, a room air temperature feedback control loop for controlling the temperature of the air in the room in which the cabinet is disposed by regulating the speed of the liquid pump, the room air temperature feedback control loop having an output at which a liquid pump speed control signal is output and having as inputs the room air temperature setpoint and a feedback signal which is an actual temperature of room air, and a liquid pump pressure differential control feedback loop having an output at which an electronic expansion valve position signal is output and having as inputs the given range and a feedback signal which is a pressure differential across the liquid pump, wherein the control loops have different magnitudes of response times.
22 . The cooling system of claim 21 wherein the controller has a separate controller for each of the feedback control loops.
23 . The cooling system of claim 23 wherein the refrigerant temperature set point is a fixed set point, the room air temperature set point is a user input setpoint that the user inputs into the controller, and the given range is a fixed range.
24 . The cooling system of claim 23 wherein the refrigerant temperature control loop also includes as an input an output of a feed forward controller, the feed forward controller having as inputs the liquid pump speed control and the electronic expansion valve position signal.
25 . A cooling system, comprising:
a cabinet having an air inlet and an air outlet;
a cooling circuit that includes a direct expansion refrigeration cooling circuit including an evaporator disposed in the cabinet, a condenser, a compressor and an expansion device wherein the condenser is at an elevation higher than the evaporator;
the cooling circuit having a direct expansion mode wherein the compressor is on and compresses a refrigerant in a vapor phase to raise its pressure and thus its condensing temperature and refrigerant is circulated around the cooling circuit by the compressor and an economizer mode wherein the compressor is off and a liquid column of refrigerant at an inlet of the evaporator induces a thermo-siphon effect causing refrigerant to circulate around the cooling circuit and without compressing the refrigerant in its vapor phase; and
a controller coupled to the compressor that turns the compressor off to operate the cooling circuit in the economizer mode and turns the compressor on to operate the cooling circuit in the direct expansion mode.
26 . A cooling system, comprising:
a cabinet having an air inlet and an air outlet;
a cooling circuit that includes an includes an evaporator disposed in the cabinet, a condenser, a compressor, a liquid/vapor separator tank and a liquid pump;
the cooling circuit having a mode wherein the compressor and liquid pump are both on with the liquid pump pumping refrigerant through the evaporator with the refrigerant leaving the evaporator circulated to an inlet of the liquid/vapor separator tank and not to an inlet of the condenser, and the compressor compressing refrigerant circulating to an inlet of the compressor from an outlet of the liquid/vapor separator tank to raise its pressure and thus its condensing temperature with refrigerant leaving the compressor circulated to the inlet of the condenser, and a pumped refrigerant economizer mode wherein the liquid pump is on and the compressor is off and bypassed, the liquid pump pumping refrigerant in a liquid phase through the evaporator with the refrigerant leaving the evaporator circulated to the inlet of the condenser and not to the inlet of the liquid/vapor separator tank and wherein refrigerant circulates without compression of the refrigerant in its vapor phase.
27 . A cooling system, comprising:
a cabinet having an air inlet and an air outlet;
a direct expansion cooling circuit having an evaporator disposed in the cabinet, a condenser, a compressor and an expansion device;
a pumped cooling fluid cooling circuit having an evaporator disposed in the cabinet, a condenser, a liquid pump and an electronic expansion valve;
the cooling circuit having a direct expansion mode wherein the direct expansion cooling circuit is operating to provide cooling and a pumped cooling fluid economizer mode wherein the direct expansion cooling circuit is not operating to provide cooling and the pumped cooling fluid cooling circuit is operating to provide cooling;
a controller coupled to the liquid pump and the compressor that turns the compressor off and the liquid pump on to operate the cooling circuit in the economizer mode and turns the compressor on to operate the cooling circuit in the direct expansion mode;
wherein when the cooling system is in the economizer mode, the controller controls a temperature of the refrigerant to a refrigerant temperature set point by regulating a speed of a fan of the condenser of the pumped cooling fluid cooling circuit, controls a temperature of air in a room in which the cabinet is disposed to a room air temperature setpoint by regulating a speed of the liquid pump, and maintains a pressure differential across the liquid pump within a given range by regulating an open position of the electronic expansion valve.
28 . The cooling system in claim 27 wherein when the cooling system is in the direct expansion mode, the pumped cooling fluid cooling circuit is also operated to provide cooling.