Patent Application
20250216137
The present application claims the benefit of European Patent Application No. 23220368.7, filed Dec. 27, 2023, which is herein incorporated by reference in the entirety.
The present invention relates to a method and a device for controlling a refrigeration system with a plurality of chillers in an arrangement or network, which differ from one another in their performance characteristics with regard to the cooling capacity which can be provided, the electrical power consumed and the cooling water temperature.
The previous solutions for controlling a cascade/network with several chillers in an arrangement are not satisfactory. In particular, the previous solutions are difficult if refrigeration machines or chillers are combined in the arrangement and differ from each other in terms of design or type and have different respective performance characteristics, i.e., differ in terms of the cooling capacity/power that can be provided, the electrical power consumed and the cooling water temperature.
In embodiments, the invention relates in particular to a method for controlling a refrigeration system with a plurality of refrigerating machines/chillers in an arrangement or network, at least some of which differ from one another in terms of their performance characteristics with regard to the cooling capacity/power that can be provided, the electrical power consumed and the cooling water temperature. In embodiments, the method includes the steps of a) detecting a requested target cooling capacity and a current cooling water temperature; b) determining the available cooling capacity of the chillers in the arrangement/network on the basis of the respective performance characteristics and the determined current cooling water temperature; c) determining the possible combinations of chillers that can provide the required target cooling capacity; d) selecting, from the possible combinations of chillers and based on their respective performance characteristics, the combination that provides the highest overall efficiency; and e) operating the chillers of the selected combination.
By taking into account the respective performance characteristics of the available chillers and selecting or assembling a combination of several chillers within the arrangement/network with a view to maximizing the overall efficiency, the power consumption of the overall system can be reduced—with a specified target cooling capacity requested by a consumer—and, as a result, CO2 emissions and operating costs can be flexibly optimized. The provision of several chillers also provides a certain redundancy, so that even if individual chillers fail, e.g., due to maintenance or repair, a suitable combination of chillers can always be selected flexibly and automatically to meet a current performance requirement or demand.
Preferably, the method includes repeating steps c) to e) if the requested target cooling capacity or the detected current cooling water temperature changes. This allows the optimum combination of chillers within the system to be determined even if the required output or demand and/or relevant ambient conditions change.
Preferably, the operation of the chillers of the selected combination is controlled by adjusting the output of the respective chiller, preferably by adjusting the hot water mass flow that is supplied to the respective chiller. The hot water mass flow can preferably be controlled by activating the feed pump in the cold or hot water circuit of the respective chiller, whereby the output of the feed pump can preferably be modulated continuously or in stages, for example by controlling the rotational speed. The respective chiller regulates itself depending on the hot water flow supplied.
Preferably, during the step of selecting the combination of chillers to be operated in order to fulfill a performance requirement or demand, if several chillers with the same performance characteristics are present in the network, the combination with the chiller with the same performance characteristics is selected which has the lowest number of operating hours. This further boundary condition can achieve a uniform increase in the operating hours of the individual comparable chillers, which simplifies maintenance and monitoring of the overall system and reduces the risk of failure of individual chillers due to excessive wear.
Preferably, in the step of selecting the combination of chillers to be operated in order to meet a performance requirement or demand, the combination with the lowest number of chillers to be operated is selected. Reduced wear can also be achieved by this further boundary condition, which simplifies maintenance and monitoring of the overall system and reduces the risk of failure of individual chillers due to excessive wear of individual chillers. It should be noted that more powerful chillers are generally also designed for a longer service life and higher efficiency.
Preferably, the combination that requires the lowest number of machine starts is selected in the step of selecting the combination. Reduced wear can also be achieved through this additional boundary condition, which simplifies maintenance and monitoring of the overall system and reduces the risk of failure of individual chillers due to excessive wear. It should be noted that frequent starts lead to higher wear due to mechanical friction and alternating thermal loads.
Preferably, the process, in particular steps a) to e), is carried out centrally by a main chiller in the system, which controls the other chillers in the system as auxiliary or assist chillers. The main chiller can typically and preferably be the most powerful machine in the system, which also provides the largest proportion of the system's capacity due to its design and will therefore have the longest operating times, so that this machine will be used in the vast majority of combinations.
Preferably, the main chiller in the combination also controls peripheral devices of the refrigeration system, preferably a jointly used re-cooling device 4 (see
Preferably, the main chiller in the arrangement network also monitors malfunction in the chillers in the arrangement/network. The central monitoring of all chillers enables simplified maintenance and malfunctions that lead to the failure of a chiller can be taken into account directly when determining the chillers available for a current target cooling capacity.
In embodiments, the invention then also relates in particular to a device for controlling a refrigeration system with a plurality of refrigeration machines in an arrangement/network, which differ from one another in terms of their performance characteristics with regard to the cooling capacity or power that can be provided, the electrical power consumed and the cooling water temperature, the device being designed to carry out the method according to the invention. The device can be implemented as a component of a central control system and can be provided either directly at a control station of the system, for example at a main chiller, or via remote access at a remote position.
In the following, the invention is explained with reference to an embodiment shown in the figures, where:
The terms chiller, refrigeration machine, and cooling unit are used synonymously in the following for a self contained mechanical refrigeration generator or compressor refrigeration generator whose refrigerant-carrying components such as evaporator, compressor, condenser and expansion device are pre-assembled at the factory and form a closed refrigerant or cooling circuit-in contrast to a direct evaporator. The working medium of the chiller can be any refrigerant known in the state of the art, but preferably water-based refrigerants for environmental and regulatory reasons.
The evaporator and condenser are typically designed as heat exchangers in the chiller and have the task of absorbing heat from the refrigerant or cooling circuit and later transferring it to another system via pipes/conduits, whereby the two processes take place with material separation. The heat dissipation from the condenser can be water-cooled via a recooling device in a separate coolant circuit or air-cooled. Optionally, the chillers can have a so-called free cooling function, in which the heat from the cold water is transferred directly to the outside air-possibly using the recooling device-if its temperature is low enough. The refrigerant or cooling circuit remains switched off and the electricity consumption, which is mainly caused by the compressor, is reduced, so that electricity consumption can be reduced and CO2 savings can be achieved.
Every refrigeration machine of a certain type is known to have a typical performance diagram consisting of the cooling capacity that can be provided, the electrical power consumed and the cooling water temperature. Such an exemplary performance diagram is shown in
It should be noted that the performance diagram for a chiller without a by-pass valve is limited in terms of cooling capacity/power and electrical power in that such a chiller can only be controlled in a partial range of, for example, 30% to 100% and cannot be reduced to 0% output power. Accordingly, the cooling water temperature output by such a chiller is also limited.
The efficiency of the chiller (COP, EER or energy efficiency ratio) can be determined from the ratio of the cooling capacity/power to the electrical compressor power consumed. A high ratio stands for low power consumption combined with high cooling capacity. In principle, the efficiency ratio decreases as the difference between the cooling and ambient temperature increases. Therefore, each refrigeration machine can be operated at its maximum efficiency at a different output.
The cooling capacity required for the design of a refrigeration system for an object can be covered either with a single device or with a so-called cascade or network. The latter consists of a plurality of chillers that are switched on and off as required. While this solution requires more space, in practice it often ensures greater efficiency because the operating times can be optimized by designing the refrigeration system in individual performance levels. The individual refrigeration machines or chillers operate for longer periods in the optimum performance range, they consume less and are also subject to less wear and tear, which occurs at high cycle rates (frequent start-up and shut-down).
The object of the invention is therefore to provide a method and a device for controlling a refrigeration system with a plurality of refrigerating machines or chillers in an arrangement or network, which differ from one another in terms of their performance characteristics with regard to the cooling capacity/power that can be provided, the electrical power consumed and the cooling water temperature, with which a higher overall efficiency and service life of the refrigeration system can be achieved.
As a solution, the invention proposes a method for controlling a refrigeration system with a plurality of refrigerating machines/chillers according to claim 1 and a device for controlling a refrigeration system with a plurality of refrigerating machines/chillers according to claim 11. Preferred embodiments are defined in the respective dependent claims.
The method according to the invention for controlling a refrigeration system 1 with several chillers 2, 3a to 3e in an arrangement or network, at least some of which differ from one another in terms of their performance characteristics with regard to the cooling capacity or power that can be provided, the electrical power consumed and the cooling water temperature, is described below using the network shown in
First, a consumer requests a target or demand cooling capacity from the system and this request is detected by the main chiller. The main chiller then determines which possible combinations of chillers in the network, including itself, can provide the requested target cooling capacity. The main chiller then determines the cooling water temperature of the respective chiller. With this information, the respective 3-dimensional performance diagram can be reduced to a 2-dimensional performance diagram with absorbed electrical power and delivered cooling power on the basis of the respective performance characteristics (see
The above procedure for selecting an optimum combination of available chillers is repeated if the requested target cooling capacity or the detected current cooling water temperature changes.
After selecting the optimum combination of chillers for a requested target cooling capacity or cooling water temperature, the main chiller controls the associated auxiliary or assist chillers and itself (and switches off any machines that are not required or can be switched to standby mode with minimum or 0% capacity.
For this purpose, the main chiller adjusts the output of the respective chiller, preferably by adjusting the hot water mass flow rate supplied to the respective chiller, whereby the hot water mass flow rate supplied to the respective chiller can be adjusted by controlling a feed pump 5 in a respective hot water circuit 6 (see
Communication between the main chiller and the auxiliary or assist chillers, the consumer and any peripheral devices in the system preferably takes place via the Modbus communication protocol (MODBUS TCP).
In addition to the basic determination of the possible combinations of chillers in the network that can practically provide a requested target cooling capacity at a given cooling water temperature, the main chiller can also take other boundary conditions into account when selecting the chillers that are ultimately controlled for operation. These boundary conditions can include the selection of the chiller with the lowest number of operating hours in a combination of several chillers with the same performance characteristics, i.e. chillers of the same design, are present in the system. Furthermore, these boundary conditions can prioritize a selection of the combination that has the lowest number of chillers to be operated. Finally, these boundary conditions can prioritize a selection of the combination that requires the lowest number of machine starts. Which of these boundary conditions is then given priority must be determined in advance.
The central control of the system by the main chiller also offers the possibility of detecting faults or malfunctions in all chillers in the system. The central monitoring of all chillers enables simplified maintenance and faults or malfunctions that lead to the failure of a chiller can be taken into account immediately when determining the chillers available for a current target cooling capacity. For example, in the event of a fault or failure, a replacement chiller of suitable capacity can be switched on without any relevant time delay or a new selection can be determined if this is not possible.
Furthermore, the operating capacity utilization of all machines in the network can be monitored and the activation and deactivation or selection of the chillers can be carried out with a view to achieving uniform operating hour utilization of at least comparable machines.
Finally, the central monitoring of all chillers in the network enables a central visualization of the most important machine data of the arrangement or network.
It should be noted that the chiller acting as the central control unit (the main chiller) does not necessarily have to be the one with the highest capacity.
It should also be noted that the steps for selecting the optimum combination of chillers do not necessarily have to be carried out in the specified order.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23220368.7 | Dec 2023 | EP | regional |
