EP1262722A2

EP1262722A2 - A refrigeration plant

Info

Publication number: EP1262722A2
Application number: EP02445030A
Authority: EP
Inventors: Lennart Asteberg
Original assignee: Ingenjorsfirma Lennart Asteberg AB
Current assignee: INGENJOERSFIRMA LENNART ASTEBERG HANDELSBOLAG
Priority date: 2001-05-31
Filing date: 2002-03-11
Publication date: 2002-12-04
Also published as: EP1262722A3; SE517594C2; SE0101916D0; SE0101916L

Abstract

A refrigerant plant or system includes a refrigerant circuit (10) which comprises in series a first primary heat exchanger (11) with which heat is dumped into the environment, and a second primary heat exchanger (20) with which the heat delivered is reused for locality heating, for instance. The refrigerant is driven in opposite directions through the primary heat exchangers (11, 20). Secondary heat exchangers (31-33) are coupled between and in parallel with the primary heat exchangers (11, 20). Condenser units (51-53) belonging to at least one refrigerating machine (41-43) are cooled by the secondary heat exchangers (51-53). The rates of flow of refrigerant through the primary heat exchangers (11, 20) is controlled so that those refrigerating machines which shall satisfy heat recovery through the medium of a high temperature of condensation are selectively chosen.

Description

The invention relates to plant of the kind defined in the preamble of Claim 1.
The energy delivered by refrigerator condensers is often a heating source of interest with respect to heating processes and/or for property heating purposes (heating of apartment buildings or premises, tap water heating systems). This applies in particular to those refrigerating machines that are at work year-round. Examples of such refrigerators are refrigerators for food stores, industrial kitchens, refrigeration, cold-storage and freeze houses and also industrial processes. A heat recovery plant is often installed, when there is a need for such energy at a reasonable distance from the heat sources. One drawback with such heat recovery is that it is almost always necessary to recover the thermal energy at a temperature level which is higher than the temperature level of the ambient air; refrigerator condensers are normally cooled by ambient air. Consequently, it is often necessary to sacrifice some of the driving energy of the refrigerating machines, in order to raise the temperature level in respect of the energy available. The driving power increases with increasing jumps in temperature, i.e. an increase in the difference between the low temperature on the evaporator side and the high temperature on the condenser side of respective refrigerating machines. This results in an increase on the mechanical load on the compressor of said machine and therewith also in machine wear.
To summarise, there is a contrast between the recovery of heat and the possibility of allowing refrigerating machines to operate at the lowest possible condensation temperature.
Although it is feasible for the refrigeration circuits to be extended to the place where heat recovery is required, this would increase the amount of refrigerant required in the plant. In order to protect the environment, i.e. to reduce the amount of refrigerant that would be released into the environment should the refrigerant circuit be emptied accidentally, industry has striven for minimisation of the amount of refrigeration (e.g. Freon®, CFC, etc.) present in such machines, and has achieved its desire through the medium of rules and regulations and through legislation.
This desideratum can be satisfied in a heat recovery system of the kind indicated, by allowing the system circuit to transport surplus heat from the condensers of the refrigerating machines via an environmentally acceptable refrigerant or coolant, for instance by a glycol/water mixture. Such a refrigerant circuit will include a heat exchanger that delivers surplus heat to the ambient air, this type of system being designated an indirect system in the art. Earlier, it has been usual to pump the refrigerant directly into an outdoor air-cooled condenser for condensation, a so-called direct system.
A refrigerating plant will often consist of a plurality of refrigerating machines/refrigerating systems each having its own compressor, expansion valve, etc. On the other hand, the machines often share a common refrigerant circuit. This means that all refrigerating machines operate at the same temperature of condensation, since they are cooled by the circuit coolant. During the winter months, a system which lacks heat recovery can operate at a low coolant temperature of about 15°C, wherewith the machines will have a low driving energy requirement. Since such low coolant or refrigerant temperatures cannot readily permit premises to be heated (which often have a heating requirement of, e.g., 20°C), it is necessary to increase the temperature of the coolant to a higher level in order to be able to utilise the energy given-off by the condensers of such refrigerating machines. Normally, the temperature of the refrigerant circuit is increased and therewith the temperature of condensation of the refrigerating machines, up to temperatures of about 35°C or higher. A raise in the temperature of condensation by 20°C results in an increase in the driving energy of such machines by about 80%.
When the thermal energy is used to heat premises of some form or another, the requirement for recovered energy will vary from 0 and upwards. Because it is necessary to increase the energy input of all refrigerating machines connecting with the refrigerant circuit, merely to recover perhaps some few kilowatt hours, it may be that the increase in driving energy requirement for the compressors of the refrigerating machines will sometimes exceed the useful energy that can be recovered with the heat recovery circuit.
Accordingly, an object of the present invention is to provide plant with which the indicated drawback is eliminated either fully or partially.
This object is achieved with plant according to the invention.
The invention is defined in the accompanying Claim 1.
Embodiments of the inventive plant are defined in the accompanying dependent Claims.
Basically, the invention resides in coolant circuit that includes two primary heat exchangers with associated pumps which operate in opposite directions in the circuit, so as to form a circuit high-pressure side and a circuit low-pressure side.
A number of secondary heat exchangers are connected in parallel between the high and the low pressure sides, and are therewith connected at different distances from the primary heat exchangers. Each secondary heat exchanger cools a condenser belonging to a refrigerating or freezing machine through which a refrigerant flows. One primary heat exchanger dumps surplus heat into the environment (e.g. into the ambient air). The other primary heat exchanger delivers heat to a heat recovery circuit. The pump associated with said one primary heat exchanger is guided by the heat requirement of the heat recovering circuit. The pump which is associated with said other primary heat exchanger is controlled by a pressure difference sensor which senses the pressure between the high and the low pressure sides of the refrigerant circuit, such as to maintain a chosen pressure difference. Located on the outlet side of said other primary heat exchanger is a thermostat which maintains the refrigerant, or coolant, leaving said other primary heat exchanger at a chosen temperature level.
The refrigeration machines that are primarily intended to contribute heat to the heat recovery circuit are placed closest to the first primary heat exchanger in a given order. Those secondary heat exchangers that lie nearest the second primary heat exchanger will be kept at the chosen lower temperature level, since these heat exchangers receive refrigerant chiefly directly from the second primary heat exchanger, meaning that the corresponding refrigeration machines obtain a low temperature of condensation and a relatively higher efficiency.
It will be seen that the number of refrigeration machines that may operate at elevated temperatures of condensation will vary in accordance with the demand for recovered heat via the recovery circuit, and that the number of refrigeration machines that are utilised to satisfy the instant demand for recovered heat are therewith variable and self-adjusting. Alternatively, one single refrigeration machine may, of course, be utilised fundamentally for forming two or more heat sources which are coupled in series in the circulation circuit of the refrigeration machine via respective heat exchange units, and cooled at different temperature levels. These heat sources may include condenser units belonging to one single heat pump and, in addition, a hot gas cooler and/or a condensate supercooler, or combinations thereof. Certain types of heat pumps will also include a heat exchanger for cooling oil circulating in the compressor part of the heat pump. This oil cooler may also be used as a heat-exchange unit connected-up in the heat recovery circuit. This enables heat to be delivered from one single refrigeration machine to two or more secondary heat exchangers at different temperature levels. However, for the sake of simplicity, the invention will be described primarily with reference to the simple case in which each secondary heat exchanger delivers heat from an affiliated refrigeration machine via its condenser unit.
Because the rotational speed of the pump of the second primary heat exchanger is controlled by the pressure difference sensor, this pump will compensate for an increasing rate of flow through the first primary heat exchanger, by lowering its speed of rotation. By varying the speed of the pump of the second primary heat exchanger, it is possible to control continuously the distribution between recovered energy and energy dumped into the environment between 0-100%.
The pressure of condensation of the individual refrigeration machines is controlled conventionally, internally in the refrigeration machine, by a self-acting valve, which regulates the flow rate of refrigerant to the condenser. The valve is controlled by the pressure of condensation of the condenser.
Alternatively, the pressure of condensation can be controlled by controlling the effective cooling surface area in the condenser. This is achieved on the refrigerant side ("the freon side") of the system. The thermostat located on the outlet side of the second primary heat exchanger controls the activation of the blowers (fans) that drive ambient air through the second primary heat exchanger to satisfy the refrigerating or cooling requirement.
The invention will now be described by way of example with reference to the accompanying drawings.
Fig. 1 is a schematic illustration of an inventive plant.
Fig. 2 is a schematic illustration of a variant of the plant shown in Fig. 1
The plant includes a circulation circuit 10, which contains a liquid, such as a glycol/water mixture. The circuit includes a first primary heat exchanger 11 which transfers heat from the circuit 10 to a heat recovery circuit 14 through which a fluid flows. The circuit 10 also includes a second primary heat exchanger 20, which delivers surplus heat to the environment, for instance to the ambient air.
The circuit 10 further includes a pump 12 (P2), which drives the refrigerant in the circuit 10 through the heat exchanger 11. The primary heat exchanger 20 has an associated pump 21 (P1), which drives the circuit refrigerant through the primary heat exchanger 20 in a chosen direction. The pumps 12, 21 operate in mutually opposite directions and therefore define therebetween a low pressure part 10a in the circuit 10. The remaining part 10b of the circuit receives flow from the two heat exchangers 11, 20 and forms the high pressure part of the circulation circuit 10. The heat exchangers 31, 32, 33 are connected in parallel between the circuit parts 10a, 10b and circuit refrigerant will flow therethrough due to the difference of pressure therebetween.
Secondary heat exchangers 31-33 are coupled at different distances along the circuit parts. The secondary heat exchanger 33 that lies nearest to the primary heat exchanger 11 receives refrigerant of high temperature that defines the temperature of condensation for the condenser 53. The secondary heat exchanger 32 next in line may possibly also receive from the heat primary exchanger 11 refrigerant of elevated temperature, and may possibly also receive a sub-flow of refrigerant from the primary heat exchanger 20, these sub-flows defining the temperature level on the condenser 52. The secondary heat exchanger 31 nearest the second primary heat exchanger 20 will normally be supplied with refrigerant having the temperature defined by the thermostat 23 that controls the blower 20.
The person skilled in this art will realise that the secondary heat exchangers 31-33, in this order, will be provided primarily with relatively cold refrigerant from the primary heat exchanger 20, and that the secondary heat exchangers 33-31 will primarily be supplied with relatively hot refrigerant from the primary heat exchanger 11, and that the refrigerant distribution from these two sources will be set automatically in relation to the demand/supply of heat via the circuit 14.
Located between the circuit parts 10a, 10b is a pressure difference sensor 22 (GP1) which controls the pump 21. Located on the outlet side of the primary heat exchanger 20 is a temperature sensor (GP3), which controls a blower (fan) 26 that regulates the rate of flow of the ambient air through the primary heat exchanger 20, so that the refrigerant output temperature from the primary heat exchanger 20 will be set to a pre-chosen value.
The pump 12 (P2) is controlled in keeping with the heat recovery requirement, wherewith the recovery circuit 14 may include a temperature sensor 13 (GT1) that controls the pump P2. A temperature sensor 16 (GT2) may be coupled between the pump 12 and the first primary heat exchanger 11 to limit the refrigerant temperature to said heat exchanger 11 in an upward direction, in those instances when there is no market for the heat delivered to the heat exchanger 11. It can be seen that refrigerant exiting from the primary heat exchanger 11 first flows through the secondary heat exchanger 33, which thus cools the condenser 53 at a temperature level which is normally relatively high (depending on the return temperature of the recovery circuit). This means that although the refrigerating machine (the heat pump) 43 will operate at a relatively high temperature of condensation, i.e. with a relatively low efficiency, it will, instead, contribute towards a relatively large quantity of thermal energy to the circuit 14. When not all of the refrigerant from the heat exchanger 11 is led through the heat exchanger 33, this refrigerant is forwarded in the low pressure part 10b to the heat exchanger 32, which, in this case, may also operate at a relatively high temperature in respect of its condenser 52, which, in turn, means that the refrigerating machine 42 (the heat pump) will operate with a relatively low efficiency (although contributing heat to the recovery circuit).
We can now assume that refrigerant leaving the primary heat exchanger 20 has the temperature defined by the sensor 23 and passes through the secondary heat exchanger 31 which cools an associated condenser 51 at this temperature and gives the associated refrigeration machine (the heat pump) a relatively high efficiency.
The person skilled in this art will realise that the refrigeration machines 41-43 can operate at different temperatures of condensation, wherewith the heat supply to the heat recovery circuit 14 will consist of heat from those refrigeration machines 43, 42, 41 that lie, in turn, nearest the first primary heat exchanger. Because the pump P1 is controlled by a difference pressure transmitter 22, there is established a constant driven pressure to the secondary heat exchangers 31, 32, 33. This causes the pump 21 to slow down automatically when the pump 12 belonging to the first primary heat exchanger 11 begins to deliver a rate of flow that satisfies the heat requirement of the recovery circuit 14.
In accordance with the invention, those refrigeration machines 41, 42, 43 that lie nearest to the second primary heat exchanger or circuit cooler 20 that dumps heat into the ambient air can operate at a high efficiency, i.e. a relatively low temperature of condensation, to the extent in which heat delivered from the condensers 53, 52, 51 is not required for supplying heat to the recovery circuit. The rates of flow through the secondary heat exchangers 31, 32, 33 are self-setting and controlled by the pump 21 and its associated pressure difference sensor on the one hand, and by the pump P2 and the temperature sensor 13 of the recovery circuit on the other hand, wherewith the refrigeration machines 41-43 can operate at different temperatures of condensation for prioritising high efficiency in the case of certain refrigeration machines on the one hand, and a high heat emission from other refrigeration machines. It will be understood that the relative distances of respective secondary heat exchangers 31-33 from respective primary heat exchangers 11, 20 is significant in respect of the temperature level at which the corresponding condensers 51-53 can operate.
The invention thus provides a method of controlling the refrigerant in the circuit 10 so that only those refrigeration machines from which surplus heat can be utilised will work at high temperatures of condensation and therewith require relatively higher energy inputs. The distribution of energy to the heat recovery circuit and to the ambient air can be made continuous, i.e. smooth. The two pumps 12, 21 constitute a reserve one for the other, therewith enhancing the reliability of the plant in operation. Because the rates of flow through the secondary heat exchangers 31-33 are self-regulating, no separate control valves are required, which affords certain advantages since control valves normally cause drops in pressure that must be overcome with the aid of the pumps, i.e. with the pump driving energy.
A refrigerant circuit 10 includes a first primary heat exchanger 11, which delivers heat to a recovery circuit 14, and a second primary heat exchanger 20 which pumps heat into the ambient air. Each primary heat exchanger 11, 20 has an associated pump 12, 21 which pumps circuit liquid in opposite directions, so that the circuit will obtain a low pressure side 10a and high pressure side 10b, between which a number of secondary heat exchangers 31-33 are coupled in parallel at different distances apart. Each such parallel-coupled heat exchanger 31-33 cools a refrigerating machine 41-43 belonging to respective condensers 51-53. As an alternative (Fig. 2), one single refrigeration machine 41' can include a condenser unit which has three series-coupled units 51'-53' that function as a hot gas cooler, actually a condenser and condensate supercooler respectively, and are arranged in heat-exchange relationship with a respective secondary heat exchanger 31-33 at different temperature levels. Moreover, the refrigeration machine 41' may include an oil cooler 54', which forms a further secondary unit 34 in the heat recovery circuit. Fig. 2 also shows that the heat pump circuit may include a drying filter 55 and an inspection glass/?/56 for the refrigerant, between the condenser 32 and the supercooler 33.
The heat pump circuit also includes an evaporator 59 and an expansion valve 60. It will be understood that the heat exchangers 31-34 may be coupled in series, in temperature order, in the heat recovery circuit 10 (Fig. 1), possibly together with further units.
A pressure difference sensor 22 controls the pump 21 of the primary heat exchanger 20. The pump 12 of the heat exchanger 11 is controlled by the heat requirement of the recovery circuit 14. The refrigerating effect of the primary heat exchanger 20 is controlled by a thermostat 23 on the outlet side of said primary heat exchanger 20.

Claims

A refrigeration plant comprising a refrigerant circuit (10) which is filled with refrigerant and which includes a first primary heat exchanger (11) with an associated first pump (12) for driving refrigerant through the first primary heat exchanger (11), at least two secondary heat exchangers (31-33) which are coupled in parallel over the conducting parts (10a, 10b) of the circuit (10), said parts connecting with the first primary heat exchanger (11), wherein the secondary heat exchangers are adapted to cool a respective heat emitting unit (51-53, 51'-53') through which refrigerant flows and which is affiliated with at least one refrigerating machine (41'; 41-43), such as a refrigerator or freezer, wherein the first primary heat exchanger (11) is in heat-exchange relationship with a heat recovery circuit (14) for cooling said circuit, characterised in that the refrigerant circuit (10) includes a second primary heat exchanger (20) through which heat from the refrigerant is delivered to the environment, preferably the ambient air; in that the secondary heat exchangers (31-33) are coupled in the circuit (10) between the first primary heat exchanger (11) and the second primary heat exchanger (20); in that the second primary heat exchanger (20) has an affiliated pump (21) which drives refrigerant in a predetermined direction through said second primary heat exchanger (20); in that the first primary heat exchanger (11) has an affiliated pump (12) which is adapted to drive refrigerant in a predetermined direction through said first primary heat exchanger (11); in that the pumps are adapted to drive fluid through the circuit (10) in mutually opposite directions, so that the circuit will obtain a low pressure side from which refrigerant is pumped by the pump, and a high pressure side to which refrigerant is pumped by the pump; in that the pump (21) of the second primary heat exchanger is controlled by a pressure difference sensor (22) which senses the difference in pressure between the low pressure side (10a) of the circuit (10) and the high pressure side (10b) of said circuit; and in that the pump (12) of the first primary heat exchanger (11) is controlled in keeping with the heat requirement of the recovery circuit (14).
Plant according to Claim 1, characterised in that the secondary heat exchangers (31-33) whose affiliated heat emitting units (51-53; 51'-53') shall primarily deliver heat to the heat recovery circuit are located nearest the first primary heat exchanger in a given order.
Plant according to Claim 1 or 2, characterised in that the speed of the pump (21) affiliated with the second primary heat exchanger (2) are regulated substantially continuously, or smoothly, by the pressure difference sensor (22).
Plant according to any one of Claims 1-3, characterised in that the refrigerating machines (41-43) are adapted to internally control the pressure of condensation with the aid of self-acting valves which control the rate of flow of refrigerant to the condensers, wherein the valves are adapted to be controlled by the pressure of condensation of the refrigerating machines.
Plant according to any one of Claims 1-3, characterised in that the refrigerating machines (41-43) are adapted to control the pressure of condensation by control of effective refrigerating surface area in the condensers (41-53) of said machines on the refrigerant side thereof.
Plant according to any one of Claims 1-5, characterised in that the secondary heat exchangers (31-34) are adapted to receive heat from a respective refrigerating machine via a condenser unit, hot gas cooler, condenser supercooler and/or compressor oil cooler included in respective refrigerating machines.
Plant according to any one of Claims 1-5, characterised in that at least two of the secondary heat exchangers are adapted for cooling at different temperature levels.