A PUMP AND AN ENERGY RECOVERY APPARATUS FOR A REFRIGERATION SYSTEM

Field of the Invention

[1] The present invention relates to a pump and to an energy recovery apparatus incorporating the pump, both of which are particularly suitable for use in refrigeration systems.

Background and Prior Art

[2] Refrigeration systems having a compressor, a condenser, a metering device and an evaporator are well known. Such systems are designed to provide a desired cooling capacity at a specified ambient temperature, which in turn leads to specification of the compressor requirements. Thus compressors in refrigeration systems are specified to produce sufficient work to provide the cooling capacity at and below the specified maximum design temperature.

[3] The ambient temperature specified when designing refrigeration systems is well above the typical or average ambient temperature of the system in use: far less cooling capacity is required for much of the time the refrigeration system is operating. However, the power consumption of the compressor remains high in order to maintain adequate discharge pressure to push the refrigerant through the metering device, even on compressors with capacity control mechanisms.

[4] Variable speed compressors are used in some applications to enable adjustment of the compressor power consumption according to cooling requirements and thereby improve energy efficiency. The variable speed drives used in such compressors are expensive and are sensitive to heat and moisture.

[5] An alternative approach is shown in Figure 7 of US patent 7,658,082 in which a turbine S is provided between the compressor C and condenser 7 to recover energy from the system. While a portion of the work from the compressor C is recovered by the turbine S, the system of US patent 7,658,082 requires a pump P driven by a motor M2.

[6] Most refrigeration systems, however, simply use a compressor with a fixed work output, with the resulting waste of energy described above. Summary of the Invention

[7] In accordance with a first aspect of the invention there is provided a pump for a refrigeration system, comprising: first and second chambers each having a first inlet and an outlet; the first inlet of each chamber selectively being in fluid communication with an inlet line, the outlet of each chamber selectively being in fluid communication with an outlet line; first and second valve means for selectively placing the first and second chambers, respectively, in fluid communication with gas at a pressure comparable to pressure in the inlet line or with gas at a pressure comparable to pressure in the outlet line; pressure equalisation means to selectively equalise fluid pressure in the first and second chambers.

[8] Preferably, the pressure equalisation means comprises an equalisation valve selectively placing the first and second chambers in fluid communication with each other.

[9] Preferably, the pump further comprises a controller configured to actuate the first and second valve means and the equalisation valve.

[10]Preferably, the controller is operable between first, second and third states in which: in the first state the first valve means is actuated to place the first chamber in fluid communication with gas at a pressure comparable to pressure in the inlet line, and second valve means is actuated to place the second chamber in fluid communication with gas at a pressure comparable to pressure in the outlet line; in the second state first valve means is actuated to place the first chamber in fluid communication with gas at a pressure comparable to pressure in the outlet line, and second valve means is actuated to place the second chamber in fluid communication with gas at a pressure comparable to pressure in the inlet line; and in the third state the equalisation valve is actuated to equalise fluid pressure in the first and second chambers.

[ll]Preferably, the controller is operable to alternate between the first and second states and to enter the third state when transitioning from the first state to the second state. More preferably, the controller is further operable to enter the third state when transitioning from the second state to the first state.

[12]Preferably, a level sensor is provided in at least one chamber, the controller responsive to the or each level sensor in determining whether to change state

[13]ln accordance with a second aspect of the invention there is provided an energy recovery apparatus for a refrigeration system having a compressor, a condenser, a metering device and an evaporator, comprising: expander machinery provided between the compressor and the condenser; a pump according to the first aspect of the invention.

[14]Preferably, an output line from the condenser forms the inlet line.

[15]Preferably, first and second valve means are connected to an input of the condenser and to an output of the compressor, each valve means being actuatable to selectively place a respective chamber in fluid communication with the input of the condenser or the output of the compressor.

[16]Preferably, the outlet line is in fluid communication with an metering device provided at an input to the evaporator.

[17]ln accordance with a third aspect of the invention there is provided a refrigeration system comprising the energy recovery apparatus of the second aspect of the invention.

Brief Description of the Figures

[18]The invention will now be described with reference to the accompanying drawings, in which:

[19]Figure 1 is a pump according to an embodiment of the invention; [20]Figure 2 is a refrigeration system having an energy recovery system according to an embodiment of the invention;

[21]Figure 3 shows a bypass mode of the refrigeration system of Figure 2.

Description of Preferred Embodiments

[22]Figure 1 shows a pump 10 according to one embodiment of the invention, comprising first and second chambers 12a, 12b each having a respective first inlet 14a, 14b, first orifice 16a, 16b and outlet 18a, 18b.

[23]The first inlets 14a, 14b are selectively in fluid communication with an inlet line 20 via non-return valves 22a, 22b respectively, according to the relative pressure in the inlet line 20 and each chamber 12a, 12b.

[24]The outlets 18a, 18b are selectively in fluid communication with an outlet line 24 via non-return valves 26a, 26b respectively, according to the relative pressure in outlet line 24 and each chamber 12a and 12b.

[25]First valve means in the form of solenoid valves 30a, 32a are provided at the first orifice 16a. Valve 30a is actuatable to selectively place the chamber 12a in fluid communication with gas at a pressure P2, comparable to pressure in the outlet line 24. Valve 32a is actuatable to selectively place the chamber 12a in fluid communication with gas at a pressure PI, comparable to pressure in the inlet line 20. Pressure P2 is greater than pressure PI.

[26]Similarly, second valve means in the form of solenoid valves 30b, 32b are provided at the first orifice 16b. Valves 30b, 32b are actuatable to selectively place the chamber 12b in fluid communication with gas at a pressure, P2 or PI, respectively.

[27]Pressure equalisation means, in the form of solenoid valve 34 provided in a fluid path connecting the chambers 12a, 12b, selectively equalises fluid pressure in the chambers 12a, 12b when the valve 34 is actuated.

[28]The arrangement of valves and inlets is shown in the drawings for clarity. It should be appreciated that other arrangements and types of valves may be used without departing from the invention. For example, the valve 34 may connect the inlets 16a and 16b rather than have a separate connection. Similarly, valves 22a, 22b, 26a, 26b may be provided at the first inlet 14a, 14b between each chamber 12a, 12b and respective non-return valve 22a, 22b rather than at a separate orifice as shown in the drawings. The valves 22a, 22b, 26a, 26b are shown as non-return valves, however other suitable valves such as solenoid valves may also be used.

[29]The pump 10 is operated by a controller (not shown) which controls actuation of the valves 30a, 32a, 30b, 32b and 34 between a first state, second state and a third state as described below. The condition of each valve in each state is shown in table 1 below.

First state Second state Third state

Valve 30a Open Closed Closed

Valve 32a Closed Open Closed

Valve 30b Closed Open Closed

Valve 32b Open Closed Closed

Valve 34 Closed Closed Open

Table 1 [30]ln the first state, the chamber 12a at pressure P2 since valve 30a is open. Non-return valve 22a prevents liquid in the inlet line 20 flowing into the chamber 12a since pressure P2 is greater than pressure PI. With the chamber 12a at a similar pressure to outlet line 24, liquid in the chamber 12a can flow into the outlet line via valve 26a under the influence of gravity. The chamber 12b is at pressure PI since valve 32b is open. Non- return valve 26b prevents liquid in the chamber 12b flowing into the outlet line 24 since pressure PI is less than the pressure in the outlet line 24. With the chamber 12b at a similar pressure to inlet line 20, liquid in the inlet line 20 can flow into chamber 12b via valve 22b. The open valve 32b prevents air locks forming which would impede liquid flow into chamber 12b from the inlet line 20. [31]Thus, in the first state, chamber 12a is emptying into the outlet line 24 and chamber 12b is being filled from the inlet line 20. The second state is similar to the first state, with the open/closed condition of valves 30a, 32a, 30b, 32b reversed such that chamber 12b is emptying into the outlet line 24 and chamber 12a is being filled from the inlet line 20. [32]Operation of the pump 10 involves alternating between the first and second states, with transition from the first to the second state or vice versa occurring via the third state as described below.

[33]Level sensors (not shown) provided in the chambers 12a, 12b indicate to the controller when a change of state from the first or second states is needed. In one embodiment, in the first state, the controller is responsive to a level sensor in chamber 12b which indicates when that chamber has filled with liquid from the inlet line to a predetermined level. In the second state, the controller is responsive to a level sensor in chamber 12a which indicates when that chamber has filled with liquid from the inlet line to a predetermined level. Upon indication that a chamber has filled with liquid to a predetermined level, the controller changes state as described below. In an alternative embodiment, level sensors may be used which indicate when a chamber is nearly empty, or a combination of full and empty level sensors may be used. Alternatively to reduce cost and complexity a single level sensor may be used in only one chamber, one example of which is a level sensor providing 'full' and 'empty' signals to a controller.

[34]The controller enters the third state when transitioning from the first state to the second state or vice versa. In the third state, the valves 30a, 32a, 30b, 32b are all closed and the valve 34 is open to place the chambers 12a, 12b in fluid communication with one another. This has the effect of equalising the pressure in the chambers 12a, 12b. Prior to pressure equalisation, one chamber is at pressure PI and the other at pressure P2; the resulting pressure will be at an intermediate pressure between these two pressures. Pressure equalisation occurs quickly so the controller is configured to enter the third state for a brief period. It is preferred that the period is chosen to match the required system mass flow rate.

[35]Without the third state, when changing from first to second state or vice versa one chamber at pressure PI would be connected to gas at pressure P2 and the other chamber at pressure P2 would be connected to gas at pressure PI. With the third state, both chambers are equalised to an intermediate pressure before being connected to gas at another pressure according to the next state. This reduces the amount of work required to have both chambers at the operating pressure of the new state. Gas may flow into or out of each chamber depending on whether the intermediate pressure is higher or lower than the gas to which each chamber is then connected.

[36]The controller may be a programmable logic controller (PLC), microcontroller with valve interface circuits, or other suitable form.

[37]Figure 2 shows a refrigeration system 100 with like reference numerals used to denote like parts to those shown in Figure 1. The refrigeration system 100 includes a compressor 104, a condenser 106, a metering device 108 and an evaporator 110 provided in a fluid circuit.

[38] efrigeration systems are designed to provide heat rejection up to a maximum operating ambient temperature which is typically far higher than the average operating temperature. In the UK, for example, refrigeration systems are designed to operate at ambient temperatures up to 36°C, while the average maximum temperate across a year is in the range of 8.5-ll°C. When a fixed capacity compressor is used, the fan speed of the condenser 106 is typically adjusted based on ambient temperature to prevent ice forming on the evaporator 110. Thus the compressor 104 is operating at full power while the fan speed of the condenser 106 is reduced. Since the power consumption of the condenser fan is typically much less than the compressor, fixed capacity refrigeration systems have relatively constant power consumption when operating irrespective of ambient conditions.

[39] In the refrigeration system 100, however, expander machinery 112 is provided between the compressor 104 and the condenser 106. The expander machinery 112 converts a portion of the work output of the compressor 104 into electricity, reducing the net power consumption of the refrigeration system 100 when the ambient conditions are below the maximum operating ambient temperature. One example of suitable expander machinery is a turbo-expander, however other suitable devices converting work into electricity may be used.

[40]A pump 10 of the type shown in Figure 1 is provided between the condenser 106 and metering device 108 with the inlet line 20 connected to the condenser 106 and the outlet line 24 connected to metering device 108. The pump 10 and expander machinery 112 form an energy recovery system of the refrigeration system 100. Use of the pump 10 avoids need to use motorised pump, increasing the benefit of expander machinery 112.

[41]Valves 30a, 30b of the pump 10 are connected to the compressor 104's output which provides gas at pressure P2. Valves 32a, 32b are connected to the expander machinery 112's output which provides gas at pressure PI.

[42]When the ambient temperature is below a threshold value, the expander machinery 112 and pump 10 are operated. Expander machinery 112's output is at a lower pressure than compressor 104's output - for example the pressures may be 7 bar and 12 bar, respectively. Without pump 10, the pressure entering metering device 108 would be at the expander machinery 112's output pressure, which would likely lead to collapse of the fluid circuit due to low pressure. Pump 10 operates as described above in relation to figure 1 such that pressure in the outlet line 24 is comparable to the pressure at the compressor 104's output.

[43]The refrigeration system 100 includes bypass valves 114, 116 which provide bypass lines for the expander machinery 112 and pump 10, respectively. When the ambient temperature exceeds the threshold value, as determined by a temperature sensor (not shown) in the embodiment, the controller opens bypass valves 114, 116, turns off the expander machinery 112 and places the pump 10 in the third state.

[44]This enables the full output of the compressor 104 to be used when ambient temperatures are above the threshold value, when operation of the expander machinery would remove too much work from the fluid circuit for the refrigeration system to correctly operate. When the turbine 112 is bypassed, output pressure from the compressor 104 is sufficient to drive the fluid circuit, so pump 10 is also bypassed. Bypass valves 114, 116 also provide a failsafe mode in the event of failure of either turbine 112 or pump 10, ensuring refrigeration continues.

[45] Modifications and variations such as would be apparent to a skilled addressee are within the scope of the invention, which is defined by the following claims.