The present invention is directed towards a procedure for controlling a cooling system having the features of the first part of claim 1, and to such a cooling system having the features of the first part of claim 8.

A variety of principles of control are available to the person skilled in the art. One way is to adjust the temperature of the coolant in the equalization tank by controlling the run-time of the compressor. Another way is to adjust the outgoing temperature of the coolant by shunting at the equalization tank, see for example CH 265303, figure 2, or by bypassing the heat-sink, see for example US 5 743 102 A, which discloses the features of the preamble of claim 1.

Presently, there are no procedures for controlling the run-time of the compressor using the refrigeration requirements of the system, thus, one can not adjust the temperature in the coolant tank to meet the real cooling requirement.

It is not possible to adjust the evaporating temperature to the expansion valve since an expansion valve is constructed in such a manner as to provide an evaporation that in every operational case is as effective as possible. It is not constructed to regulate temperatures in evaporators. It is always the dimensioning of the evaporator as well as temperatures and flows on the secondary side of the evaporator, in combination with the capacity of the compressor, that determine the evaporating temperature. If, for example the expansion valve is closed in order to reduce the capacity the compressor can jam since high temperatures in the compressor, and if the valve is opened in order to, for example increase the capacity, fluid can be drawn into the compressor which, as a result, can cause serious damage in the compressor on valves, pistons, etc. One of the most important criteria in the dimensioning of refrigerating plants is to adjust the compressor, the expansion valve and the evaporator to each other in order to obtain optimal operational conditions at the so called point of operation.
By shunting out the correct temperature to the cooling objects does not give any true adjustment to the refrigeration load since the major part of the volume in the system is kept at a very low temperature, and the refrigerating unit is also working at low temperatures and thus with a low COP.

Known cooling systems for cooling food for example are dimensioned for the worst possible conditions. This means that the refrigerated display case is dimensioned for the greatest load of both customers- and goods in accordance to EN441. According to this standard, the refrigerated display cases are divided into different temperature classes depending upon the field of application. It has also been defined at which ambient temperature the cooling system is to be used. In Sweden the most common class is ISO2 which means that the ambient temperature is +22°C and that the relative humidity is 60%. Further, the refrigerating machines are dimensioned to provide the intended cooling effect even during hot summer days. Generally, the refrigerating machine will provide the intended cooling effect at an outdoor temperature of +27°C as well as ensure that highpressure release at considerably higher temperatures does not occur. Taken together, this result in that the cooling plant is heavily over-dimensioned for the most part of the year. The nominal power demand is usually about 70% of the installed effect. This heavy over-dimensioning results in serious drawbacks concerning efficiency and will be unnecessarily expensive for the storekeeper and for the customers.

Figures 1 and 1A of the present application schematically illustrate how the present-day, energy preserving, indirect cooling systems are structured.

The most common principle of regulation for a refrigerating machine is as follows:

• The compressors are capacity controlled so that the outgoing temperature of the coolant always is -8°C, independent of the incoming coolant.

To ensure a minimum flow over the evaporator of the refrigerating machine a two-circuit system with a fixed flow between the evaporator and an equalization tank is used. A pump P2 ensures this flow. The temperature in the refrigerated display cases is controlled by thermostats which open and close the valves V1-V3 respectively according to the requirement of the refrigerated display case.

To compensate for the increased or decreased flow requirement of the system pumps with multiple steps or speed controlled pumps P3 are used. A fixed pump P2 can also be used and so-called overflow valves which shunt the flow over the refrigerated display cases. These valves then uphold the pressure drop at a constant level in the machine regardless of the system load.

Figure 1 discloses a general temperature condition of a known system during normal operation. One can clearly see the drawbacks of letting the refrigerating machine work with a temperature of -8°C when the real need is just -6°C. This condition exists during the most part of the year.

The introduction of energy-saving measures is often followed by installing of night covers and blinds on the refrigerated display cases in order to reduce energy loss. In some cases the energy demand of the refrigerated display cases can be reduced by nearly 50%. As seen in figure 1A the temperature conditions in the system change but the refrigerating machines keep working with the same temperatures as before.

The reason for this is that there is no system on the market that allows an easy way of changing the temperature setting of the refrigerating machine to adjust it to requirements of the system. This operational condition is common during nights and during days when the store is closed. As is clearly seen, 80% of the annual time of operation the refrigerating machine works under extremely unfavourable conditions and thus not economically.

Therefore, the main object of the present invention is primarily, with simple measures and means, to effectively and safely solve said problem.

Said object is fulfilled by means of a procedure for controlling a cooling system as initially referred to and which has the features of the characterizing part of claim 1.

Known means for refrigerating control does not make it possible to achieve the desired control so that the temperature, in an effective and economical way, is set at a correct level.

Therefore, a further object of the present invention is to find a system that can solve the above stated problem. The object is also fulfilled by means of a cooling system as initially referred to having the characterizing features of claim 8.

Referring to the appended drawings, a preferred embodiment of the invention will be described. In the drawings:

• Figure 1 and figure 1A illustrate known solutions for controlling the cooling system for refrigerated display cases, and
• Figure 2 and figure 3 illustrate control systems according to the present invention during normal operation and during night conditions, respectively.

According to the present invention a pipe 1, for supplying coolant, is connected to a present pump 2 arranged to pump coolant through said pipe 1, through the refrigerating unit and where 3 indicates its evaporator. A similar system 4 which is arranged to allow a variable flow, comprising means 5 for sensing the temperature difference between the incoming and outgoing coolant, and to use this obtained value as input to the capacity controlling of the present refrigerating machine. A pump 2 of said refrigerating machine includes a speed regulator 8 which affects the value of the outgoing temperature of the coolant. In the example disclosed the refrigerated display cases are in the drawings assigned the numbers 18-20.

Said pipe 1 supply coolant to and divert coolant away from said refrigerated display cases 18-20.

One method for controlling refrigerating machines and the temperature of their coolants with a system, which is carried out according to what has been stated above, comprises adjustment of the outgoing temperature of the present refrigerating unit to the real demand for refrigeration, and thereby creating a cooling system 4 that works with a dynamic temperature of the coolant. Thus, the system 4 is coupled as a one-circuit system with a variable flow rate through the refrigerating unit.

By using the temperature difference between incoming and outgoing coolant as input to the capacity controlling of the refrigerating machine, and allowing the speed regulator 8 of the pump 2 to affect this value, the desired effect can easily be obtained.

When the valves in the system are beginning to close, the flow in the system decreases and the pump adjusts its capacity by decreasing its speed. With a decreased flow through the evaporator, the temperature difference between incoming and outgoing coolant increase. The capacity controlling of the refrigerating system then decreases the speed of the compressor in order to maintain the temperature difference. This means that the outgoing temperature will increase and the evaporating temperature rises. Concurrently with the rise of the temperature of the system the valves will begin to open again and the pump will increase its capacity until balance is achieved.

The refrigerating machine cannot run at full effect until the pump runs at full capacity and this condition can only be achieved when all the valves are open.

In order to guarantee the quality of, for example groceries in the intended refrigerated display cases, restrictions regarding the highest and lowest temperature of the coolant can be introduced.

By use of the present system solution many problems are solved and for the system many advantages are provided: A simpler system solution provides a simpler and less expensive installation, e.g. the cost for equipment in the store can be reduced by around SEK 100.000. Reduced energy loss in the piping system. Heavily increased COP. Very high energy saving potential. Can be applied to basically all new and already existing systems. Higher food quality through a more even temperature. The risk of freezing of sensitive groceries is eliminated.

The refrigerating compressor 9 is connected to yet another line circuit 10. The numbers 11-13 denote a plurality of control valves within the system 4 and which are connected to the line circuit 1 which in said pump 2 functions, as well as connects, the refrigerated display cases 18-20.

The numbers 14, 15 denote two pressure sensors while two temperature sensors are denoted by the numbers 16, 17, and which are a part of said line circuit 1.

Thus, the temperature difference between the incoming and the outgoing coolant is used as signal input to the capacity controlling of the refrigerating machine and the speed regulator of the pump 2 thereby affects this said value.

The flow in the system is set to decrease when, for example the valves 11-13 in system 4 are beginning to close, whereby the pump 2 adjusts its capacity by decreasing its speed.

By decreasing the flow through the evaporator 3, the temperature difference between the incoming and outgoing coolant increases.

The speed of the compressor can be reduced by said capacity controlling in the refrigerating machine in order to maintain the difference in temperature between the incoming and outgoing coolant and thereby obtain an increase of the outgoing temperature and also an increase of the evaporation temperature.

In order to optimise the condition between the evaporating temperature and the temperature of the coolant, a pressure- and temperature sensor 50 in the evaporating circuit 10 can in some cases be used which gives a signal to the system's capacity control. A further circuit 25 leads from a condenser 27 to a coolant cooler 26 of, for example a known type, and a pump 6 is connected to said circuit 25. A speed regulator 7 is arranged to be able to affect the value of the heat-carrier and said pump 6.

The invention is not limited to the above described nor to the disclosed embodiment in the appended drawings. Modifications are possible, especially regarding the character of the different parts, or by the use of similar technology without departing from the scope of the invention such as defined in the claims. The invention can be applied to any refrigerating application and thus not exclusively to refrigerated display cases for groceries as exemplified above.