High efficiency cooling system

1. A cooling system, comprising:

a cabinet having an air inlet and an air outlet;

an air moving unit disposed in the cabinet;

a plurality of separate cooling stages including an upstream cooling stage and a downstream cooling stage, at least the upstream cooling stage having a variable capacity cooling circuit;

each cooling stage including a cooling circuit having an evaporator, a condenser, a compressor and an expansion device;

at least the cooling circuit of the upstream cooling stage having a pumped refrigerant economizer mode and a direct expansion mode wherein each cooling circuit that has both the pumped refrigerant economizer mode and the direct expansion mode also has a liquid pump wherein when that cooling circuit is operated in the direct expansion mode a compressor of that cooling circuit is on and compresses a refrigerant in a vapor phase to raise the refrigerant pressure and thus the refrigerant condensing temperature and the refrigerant is circulated around the cooling circuit by the compressor of that cooling circuit and wherein when that cooling circuit is operated in the pumped refrigerant economizer mode the compressor of that cooling circuit is off and the liquid pump of that cooling circuit is on and pumps the refrigerant in a liquid phase and refrigerant is circulated around that cooling circuit by the liquid pump of that cooling circuit and without compressing the refrigerant in its vapor phase;

the evaporator of the cooling circuit of the upstream cooling stage and the evaporator of the cooling circuit of the downstream cooling stage arranged in the cabinet so that air to be cooled passes over the evaporator of the cooling circuit of the upstream cooling stage and the evaporator of the cooling circuit of the downstream cooling stage in serial fashion, first over the evaporator of the cooling circuit of the upstream cooling stage and then over the evaporator of the cooling circuit of the downstream cooling stage;

a controller that determines which of the cooling circuits to operate to provide cooling and for each of the cooling circuits to be operated to provide cooling that has both the pumped refrigerant economizer mode and direct expansion mode, determining whether to operate each such cooling circuit in the pumped refrigerant economizer mode or the direct expansion mode;

the controller operating each cooling circuit having both the pumped refrigerant economizer mode and the direct expansion mode in the pumped refrigerant economizer mode when an outside air temperature is low enough to provide sufficient heat rejection from the refrigerant flowing through the condenser to the outside air without compressing the refrigerant and when the outside air temperature is not low enough to provide such sufficient heat rejection operating that cooling circuit in the direct expansion mode;

the controller when a Call for Cooling first reaches a point where cooling is needed, operating the upstream cooling circuit to provide cooling and not operating the downstream cooling circuit to provide cooling and when the Call for Cooling has increased to a second point, additionally operating the downstream cooling circuit to provide cooling, wherein the cooling capacity at which the upstream cooling circuit is being operated to provide is less than the full cooling capacity of the upstream cooling circuit when the Call for Cooling reaches the second point;

wherein the compressor of each cooling circuit is a tandem compressor including a fixed capacity compressor and variable capacity digital scroll compressor, the controller controlling the fixed capacity compressor and variable capacity digital scroll compressor of each of the tandem compressors based on the Call for Cooling, which of a plurality of ranges that the Call for Cooling falls within and whether the Call for Cooling is ramping up or ramping down; and

wherein when there is an unmet Call for Dehumidification, the controller controls the tandem compressors based on the Call for Cooling and which of a plurality of dehumidification ranges that the Call for Cooling falls within including determining which of the variable capacity digital scroll compressors to ramp and controls the ramping of each variable capacity digital scroll compressor being ramped based on a the Call for Dehumidification and wherein control based on which of the plurality of dehumidification control ranges the Call for Cooling falls within and on the Call for Dehumidification takes precedence when there is an unmet Call for Dehumidification.

2. The cooling system of claim 1 wherein each expansion device is an electronic expansion valve, the controller when any of the cooling circuits are being operated in the direct expansion mode controlling the electronic expansion valve of that cooling circuit to control a suction superheat of the evaporator of that cooling circuit and the controller when any of the cooling circuits having both the pumped refrigerant economizer mode and the direct expansion mode is being operated in the pumped refrigerant economizer mode controlling the electronic expansion valve of that cooling circuit to maintain a minimum differential pressure across the liquid pump of that cooling circuit.

3. The cooling system of claim 1 wherein each of the condensers includes an electronically commutated fan, the controller varying the speed of the electronically commutated fan to maintain a temperature of the refrigerant leaving the condenser at a setpoint.

4. The cooling system of claim 1 wherein the condensers are air cooled condensers.

5. The cooling system of claim 1 wherein the condensers are water cooled condensers.

6. The cooling system of claim 1 wherein the air moving unit includes at least one electronically commutated fan, the controller increasing the speed of the electronically commutated fan as a cooling load on the cooling system increases and decreasing the speed of the electronically commutated fan as the cooling load decreases.

7. The cooling system of claim 1 wherein the controller first begins ramping the variable capacity digital scroll compressor of the upstream cooling circuit to provide cooling and when the Call for Cooling increases above a threshold, the controller also begins ramping the variable capacity digital scroll compressor of the cooling circuit of the downstream cooling stage in parallel with ramping the variable capacity digital scroll compressor of the upstream cooling circuit.

8. The cooling system of claim 1 wherein each cooling circuit has both the pumped refrigerant economizer mode and the direct expansion mode.

9. A cooling system, comprising:

a cabinet having an air inlet and an air outlet;

an air moving unit disposed in the cabinet;

a plurality of separate cooling stages including an upstream cooling stage and a downstream cooling stage, at least the upstream cooling stage having a variable capacity cooling circuit;

each cooling stage including a cooling circuit having an evaporator, a condenser, a compressor and an expansion device;

at least the cooling circuit of the upstream cooling stage having a pumped refrigerant economizer mode and a direct expansion mode wherein each cooling circuit that has both the pumped refrigerant economizer mode and the direct expansion mode also has a liquid pump wherein when that cooling circuit is operated in the direct expansion mode a compressor of that cooling circuit is on and compresses a refrigerant in a vapor phase to raise the refrigerant pressure and thus the refrigerant condensing temperature and the refrigerant is circulated around the cooling circuit by the compressor of that cooling circuit and wherein when that cooling circuit is operated in the pumped refrigerant economizer mode the compressor of that cooling circuit is off and the liquid pump of that cooling circuit is on and pumps the refrigerant in a liquid phase and refrigerant is circulated around that cooling circuit by the liquid pump of that cooling circuit and without compressing the refrigerant in its vapor phase;

the evaporator of the cooling circuit of the upstream cooling stage and the evaporator of the cooling circuit of the downstream cooling stage arranged in the cabinet so that air to be cooled passes over the evaporator of the cooling circuit of the upstream cooling stage and the evaporator of the cooling circuit of the downstream cooling stage in serial fashion, first over the evaporator of the cooling circuit of the upstream cooling stage and then over the evaporator of the cooling circuit of the downstream cooling stage;

a controller that determines which of the cooling circuits to operate to provide cooling and for each of the cooling circuits to be operated to provide cooling that has both the pumped refrigerant economizer mode and direct expansion mode, determining whether to operate each such cooling circuit in the pumped refrigerant economizer mode or the direct expansion mode;

the controller operating each cooling circuit having both the pumped refrigerant economizer mode and the direct expansion mode in the pumped refrigerant economizer mode when an outside air temperature is low enough to provide sufficient heat rejection from the refrigerant flowing through the condenser to the outside air without compressing the refrigerant and when the outside air temperature is not low enough to provide such sufficient heat rejection operating that cooling circuit in the direct expansion mode;

the controller when a Call for Cooling first reaches a point where cooling is needed, operating the upstream cooling circuit to provide cooling and not operating the downstream cooling circuit to provide cooling and when the Call for Cooling has increased to a second point, additionally operating the downstream cooling circuit to provide cooling, wherein the cooling capacity at which the upstream cooling circuit is being operated to provide is less than the full cooling capacity of the upstream cooling circuit when the Call for Cooling reaches the second point;

wherein the compressor of each cooling circuit is a tandem compressor including a fixed capacity compressor and variable capacity digital scroll compressor, the controller controlling the fixed capacity compressor and variable capacity digital scroll compressor of each of the tandem compressors based on the Call for Cooling, which of a plurality of ranges that the Call for Cooling falls within and whether the Call for Cooling is ramping up or ramping down;

wherein the controller selects which of a plurality of superheat control modes to use in operating the electronic expansion valve of each cooling circuit based on control parameters and a current operating status of each of the variable capacity digital scroll compressor and fixed capacity compressor of the tandem compressor of that cooling circuit; and

wherein the superheat control modes include a gated mode, a system mapping mode and a constant mode, wherein

in the gated mode, each time the variable capacity digital scroll compressor of the tandem compressor of one of the cooling circuits unloads, the controller drives the electronic expansion valve of that cooling circuit from its current position down to a minimum open position until the that variable capacity digital compressor stops unloading and once that variable capacity digital scroll compressor stops unloading, the controller adjusts the position of that electronic expansion valve to achieve a desired superheat;

in the system mapping mode, each time that variable capacity digital scroll compressor unloads, the controller retaining that electronic expansion valve in its current position until that variable digital scroll compressor stops unloading and once that variable capacity digital compressor stops unloading, the controller adjusts the position of that electronic expansion valve to achieve a desired superheat; and

in the constant mode, the controller adjusts the position of that electronic expansion valve to achieve a desired superheat regardless of whether that variable capacity digital scroll compressor is unloading or loading.

10. A cooling system, comprising:

a cabinet having an air inlet and an air outlet;

an air moving unit disposed in the cabinet;

a plurality of separate cooling stages including an upstream cooling stage and a downstream cooling stage;

each of the plurality of separate cooling stage including a cooling circuit having an evaporator, a condenser, a tandem digital scroll compressor and an electronic expansion valve;

each tandem digital scroll compressor including a fixed capacity compressor and variable capacity digital scroll compressor;

at least the cooling circuit of the upstream cooling stage having a pumped refrigerant economizer mode and a direct expansion mode wherein each cooling circuit that has both the pumped refrigerant economizer mode and the direct expansion mode also has a liquid pump wherein when that cooling circuit is operated in the direct expansion mode the compressor is on and compresses a refrigerant in a vapor phase to raise the refrigerant pressure and thus the refrigerant condensing temperature and the refrigerant is circulated around the cooling circuit by the compressor and wherein when that cooling circuit is operated in the pumped refrigerant economizer mode the compressor of that cooling circuit is off and the liquid pump of that cooling circuit is on and pumps the refrigerant in a liquid phase and refrigerant is circulated around that cooling circuit by the liquid pump and without compressing the refrigerant in its vapor phase;

the evaporator of the cooling circuit of the upstream cooling stage and the evaporator of the cooling circuit of the downstream cooling stage arranged in the cabinet so that air to be cooled passes over the evaporator of the cooling circuit of the upstream cooling stage and the evaporator of the cooling circuit of the downstream cooling stage in serial fashion, first over the evaporator of the cooling circuit of the upstream cooling stage and then over the evaporator of the cooling circuit of the downstream cooling stage;

a controller that controls the operation of the cooling circuits and determining which of the cooling circuits to operate in a direct expansion mode to provide cooling based on a Call for Cooling and for each cooling circuit being operated in the direct expansion mode, the controller controlling the fixed compressor and variable capacity digital scroll compressor of the tandem digital scroll compressor of that cooling circuit based on the Call for Cooling, which of a plurality of ranges that the Call for Cooling falls within and whether the Call for Cooling is ramping up or ramping down;

the controller when any of the cooling circuits are being operated in the direct expansion mode controlling the electronic expansion valve of that cooling circuit to control a suction superheat of the evaporator of that cooling circuit and the controller when any of the cooling circuits having both the pumped refrigerant economizer mode and the direct expansion mode is being operated in the pumped refrigerant economizer mode controlling the expansion valve of that cooling circuit to maintain a minimum differential pressure across the liquid pump of that cooling circuit; and

wherein when there is an unmet Call for Dehumidification, the controller controls the tandem compressors based on the Call for Cooling and which of a plurality of dehumidification control ranges that the Call for Cooling falls including determining which of the variable capacity digital scroll compressors to ramp and controls the ramping of each variable capacity digital scroll compressor being ramped based on a the Call for Dehumidification and wherein control based on which of the plurality of dehumidification control ranges the Call for Cooling falls within and on the Call for Dehumidification takes precedence when there is an unmet Call for Dehumidification.

11. The cooling system of claim 10 wherein each of the condensers includes an electronically commutated fan, the controller varying the speed of the electronically commutated fan to maintain a temperature of the refrigerant leaving the condenser at a setpoint.

12. The cooling system of claim 10 wherein the condensers are air cooled condensers.

13. The cooling system of claim 10 wherein the condensers are water cooled condensers.

14. The cooling system of claim 13 wherein the air moving unit includes at least one electronically commutated fan, the controller increasing the speed of the electronically commutated fan as the Call for Cooling increases and decreasing the speed of the electronically commutated fan as the Call for Cooling decreases.