METHOD AND A SYSTEM FOR ESTIMATING LOSS OF REFRIGERANT CHARGE IN AN RVCS SYSTEM

Abstract

A level sensor is configured to provide a receiver level indicating an amount of the refrigerant present in the receiver and a level model provides a heat rejecting heat exchanger estimate indicating an amount of the refrigerant present in the heat rejecting heat exchanger based on a temperature of the refrigerant. From the sensor and the model, a loss of refrigerant from the RVCS system is estimated.

Claims

1. A method estimating the level of refrigerant charge in an RVCS system which comprises a refrigerant circulating in the loop between a low pressure side and a high pressure side, the low pressure side forming a volume for the refrigerant between an expansion valve and a suction side of a compressor and the high pressure side forming a volume for the refrigerant between a discharge side of the compressor and the expansion valve, the high pressure side comprising a heat rejecting heat exchanger and a receiver, and the low pressure side comprising an evaporator, the method comprising: providing a level sensor configured to provide a receiver level indicating an amount of the refrigerant present in the receiver; providing a level model configured to provide a heat rejecting heat exchanger estimate indicating an amount of the refrigerant present in the heat rejecting heat exchanger based on a parameter selected from a group of operating parameters which includes at least a temperature of the refrigerant; and estimating a loss of refrigerant from the RVCS system based on the receiver level and the heat rejecting heat exchanger estimate.

2. The method according to claim 1, for a RVCS system with a plurality of heat rejecting heat exchangers, the method comprising providing for each heat rejecting heat exchanger a specific level model configured to provide a heat rejecting heat exchanger estimate indicating an amount of the refrigerant present in a specific one of the heat rejecting heat exchangers.

3. The method according to claim 1, where the RVCS system is operated such that the refrigerant is distributed between the low pressure side and the high pressure side in a reproducibly manner prior to the estimation of the loss of refrigerant.

4. The method according to claim 1, comprising the step of making pump down by operating the compressor until the low pressure side contains no liquid refrigerant prior to the estimation of the loss of refrigerant.

5. The method according to claim 4, where the pump down comprises the step of preventing a flow of the refrigerant into the evaporator while simultaneously operating the compressor such that the refrigerant in the low pressure side is reduced to a reproducible amount prior to the estimation of the loss of refrigerant.

6. The method according to claim 1, further comprising the step of providing an alert to an operator based on the estimated loss of refrigerant.

7. The method according to claim 1, comprising providing a comparable system leak rate which specifies a loss of refrigerant from a reference system and comparing the estimated loss of refrigerant from the RVCS system to the comparable system leak rate.

8. The method according to claim 7, where the comparable system leak rate is an average value of the loss of refrigerant from the system over time.

9. The method according to claim 8, where the comparable system leak rate is a previously estimated loss of refrigerant from the RVCS system to determine an increase of leak rate over time.

10. The method according to claim 1, where the group of operating parameters consist of: a temperature of the refrigerant in the heat rejecting heat exchanger, a pressure in the heat rejecting heat exchanger, a suction pressure at the compressor, a temperature of a secondary fluid flowing through the heat rejecting heat exchanger, and a temperature at the evaporator.

11. The method according to claim 1, where the loss is estimated by comparing a total level with an expected level, where the total level constitutes a sum of the receiver level and the heat rejecting heat exchanger estimate.

12. The method according to claim 1, where the receiver level is provided in a specific unit, and where the level model provides estimation of a proportionality constant configured to convert an amount in the refrigerant in the heat rejecting heat exchanger to the specific unit.

13. The method according to claim 1, comprising a step of estimating an amount of refrigerant in a discharge line which connects the compressor and the condenser.

14. The method according to claim 1, where the loss of refrigerant from the RVCS system is estimated while the compressor is operated.

15. The method according to claim 1, further comprising the step of changing the level of the refrigerant charge in the RVCS system based on the estimated loss.

16. A controller for an RVCS system which comprises a compressor, a heat rejecting heat exchanger, a receiver, and an evaporator connected in a loop, and a refrigerant circulating in the loop, the controller comprising a processor operating on a set of instructions, and where the instructions are configured to execute the method according to claim 1.

17. An RVCS system comprising a controller according to claim 16.

18. The method according to claim 2, where the RVCS system is operated such that the refrigerant is distributed between the low pressure side and the high pressure side in a reproducibly manner prior to the estimation of the loss of refrigerant.

19. The method according to claim 2, comprising the step of making pump down by operating the compressor until the low pressure side contains no liquid refrigerant prior to the estimation of the loss of refrigerant.

20. The method according to claim 3, comprising the step of making pump down by operating the compressor until the low pressure side contains no liquid refrigerant prior to the estimation of the loss of refrigerant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In the following, the invention will be described in further details with reference to embodiments and with reference to the drawings in which:

[0048] FIG. 1 illustrates a system according to the invention;

[0049] FIG. 2 illustrates how the refrigerant may be distributed inside the components of the RVCS and how successively obtained samples lead to an estimates of the amount of refrigerant lost and of the rate at which refrigerant is lost;

[0050] FIG. 3 illustrates how the method could be implemented; and

[0051] FIG. 4 illustrates the basis of a model of a condenser.

DETAILED DESCRIPTION

[0052] It should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.

[0053] FIG. 1 illustrates a RVCS system 1 including a compressor 2 having a suction side 3 and a discharge side 4. A refrigerant circulates in a loop between a low pressure side 5 and a high pressure side 6 separated by the compressor and by the expansion valve(s) 7. The compressor could be a reciprocating compressor, a scroll compressor, a screw compressor or any other kind of compressor known for a RVCS system, or the compressor could be constituted by a rack including a plurality of serial or parallel coupled compressors.

[0054] The system includes an evaporator or a plurality of evaporators 8 which absorb thermal energy from the environment and evaporates the refrigerant. The system further includes a heat rejecting heat exchanger 9 which rejects thermal energy from the refrigerant to the surroundings.

[0055] The system further comprises a receiver 10 for storing the refrigerant. The receiver is sometimes referred to as a flash tank or simply a tank. The skilled person would realize that the system may contain any number of evaporators, heat rejecting heat exchangers, receivers, expansion valves, compressors, and the system may further contain a number of additional components, e.g. for preventing moist and freezing, for measuring temperatures and pressures or for controlling distribution of the refrigerant between different evaporators, heat rejecting heat exchangers, receivers, expansion valves, and compressors.

[0056] The system may operate in a subcritical or a transcritical cycle. The refrigerant leaves the pressure side of the compressor in a compressed and hot state. In the heat rejecting heat exchanger, the refrigerant is cooled down. It is common practice to refer to a heat rejecting heat exchanger as a condenser in subcritical operation, meaning that liquid is formed inside the heat rejecting heat exchanger, or as a gas cooler in supercritical operation, meaning that the refrigerant inside the gas cooler is in a supercritical state. The compressed refrigerant continues to the receiver which functions as a storage tank. From the receiver the refrigerant continues to the expansion valve where it expands. It then enters the evaporator where it evaporates.

[0057] A level sensor 11 is associated with the receiver and a controller 12. The sensor senses the level of refrigerant, e.g. in liquid form, which resides in the receiver and generates an L-signal indicative of the level. The signal is communicated to the controller.

[0058] The temperature sensor senses the temperature of refrigerant in the heat rejecting heat exchanger and generates a T-signal indicative of the temperature. The signal is communicated to the controller. Particularly, the temperature at the inlet (T.sub.0) and the outlet (T.sub.3) as well as the pressure could be determined. The temperatures at the internal boundaries (T.sub.1 and T.sub.2) may follow from the pressure and from a fluid model, c.f. also FIG. 4. Finally, the temperature of the secondary fluid (T-ambient) could be used. In a refrigeration system, this could be the temperature of air, water, brine or refrigerant which is applied for cooling the heat rejecting heat exchanger.

[0059] The controller contains a microprocessor and has data storage capability. The microprocessor operates on a set of instructions which includes a level model configured to provide a heat rejecting heat exchanger estimate indicating an amount of the refrigerant present in the heat rejecting heat exchanger based on the temperature of the refrigerant. The controller uses the model and the L-signal and the T-signal to provide an estimate of the level of refrigerant, and based on the level, the controller calculates a loss of refrigerant from the system.

[0060] The controller includes a communication interface configured to dispatch service indication when a limit value for the level of refrigerant is reached or when a limit value for the loss of refrigerant is reached. The communication interface may e.g. dispatch the service indication by internet, by SMS, by audible or readable alert signals etc. The service indication may include an estimated amount of refrigerant which is to be added during the announced service.

[0061] The communication interface further allows communication of an initial startup signal to the controller. The startup signal is entered when the RVCS is new, i.e. when a completely empty system is made and when it has just been filled with an exactly known amount of refrigerant. Upon receiving the startup signal, the controller uses the model and the L-signal and the T-signal to provide an estimate of the level of refrigerant. This estimate is marked as a zero-baseline estimate which is considered to represent a fully charged system.

[0062] The communication interface further allows the service personnel to communicate a service signal to the controller after repair work or service where the system is charged with additional refrigerant. Upon receiving the service signal, the controller uses the model and the L-signal and the T-signal to provide an estimate of the level of refrigerant. This estimate is marked as a service baseline estimate which is considered to represent an estimated fully charged system.

[0063] In one embodiment, the controller throughout the lifetime of the system compares estimates with the zero-baseline estimate and/or with the service baseline estimate when determining an estimate for the loss of refrigerant from the RVCS.

[0064] FIG. 3 illustrates functions of a system according to the invention and FIG. 4 illustrates the basis of a model of a condenser c.f. also previous description of the model

[00002]$\xi =\frac{.Math.\frac{\left(h_i-h_{i-1}\right)}{{\alpha }_i\left(\left(T_i+T_{i-1}\right)-2.Math.T_{\mathrm{amb}}\right)}.Math.\left({\zeta }_i.Math.{\rho }_g+\left(1-{\zeta }_i\right).Math.{\rho }_L\right)}{{\rho }_L.Math..Math.\frac{\left(h_i-h_{i-1}\right)}{{\alpha }_i\left(\left(T_i+T_{i-1}\right)-2.Math.T_{\mathrm{amb}}\right)}}.$

[0065] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.