Refrigerating Plant Control for Higher Evaporation Temperature
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Solution Overview
Problem
Existing refrigerating plants suffer from inefficiencies due to high superheating values at the evaporator outlet, leading to reduced heat exchange potential and increased energy consumption, particularly in dry expansion systems, and require excessive coolant fluid in flooded systems, impacting overall energy efficiency.
Innovation Solution
Implementing a refrigerating plant management method that includes a collecting receptacle to separate liquid and gaseous phases of coolant fluid, using a level sensor and electronic control to adjust the expansion valve, ensuring optimal wet saturated vapor conditions and minimizing liquid presence, combined with a regenerative heat exchanger to ensure only superheated steam reaches the compressor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thermostatic expansion valves are used to maintain superheating at the evaporator outlet, then liquid return to compressors is avoided, but heat exchange efficiency is reduced due to lower heat exchange coefficient of superheated steam and decreased temperature difference
Solution Approach 1:
The expansion valve is controlled dynamically based on real-time detection of evaporator outlet conditions. The valve opening degree is continuously adjusted according to the detected steam quality and temperature, allowing the system to transition from static superheating maintenance to dynamic optimization of heat exchange efficiency while preventing liquid return.
Solution Approach 2:
A feedback control system is implemented where the evaporator outlet conditions are continuously monitored and the expansion valve positioning is adjusted accordingly. The detected parameters (temperature, pressure, steam quality) feed back to the control unit which modifies the valve opening to optimize both heat exchange efficiency and compressor protection.
2Loss of energy
If liquid-recirculation (flooded) refrigerating plants are used to fully exploit evaporator heat exchange potential, then heat exchange efficiency is improved, but excessive coolant fluid is required due to high vacuum and wet saturated vapor conditions
Solution Approach 1:
The system changes the operating parameters of the evaporator by controlling the expansion valve to maintain optimal steam quality at the outlet. This allows the evaporator to operate closer to saturated conditions without requiring the excessive coolant fluid quantities needed in traditional flooded systems, achieving high heat exchange efficiency with reduced coolant inventory.
Solution Approach 2:
The patent replaces the mechanical liquid recirculation system of flooded plants with an electronically controlled expansion valve system. Instead of using a liquid separator and recirculation pump to maintain flooded conditions, the system uses electronic control to precisely regulate refrigerant flow, achieving similar heat exchange benefits without the complexity and excessive coolant requirements.
3Loss of energy
If the evaporator operates with wet saturated vapor to maximize heat exchange surface activity, then heat exchange potential is fully exploited, but liquid presence increases which may cause compressor damage
Solution Approach 1:
The feedback control system continuously monitors evaporator outlet steam quality and adjusts the expansion valve to maintain optimal conditions. When steam quality indicates approaching saturation, the system increases valve opening to prevent liquid carryover, while when conditions allow, it closes the valve to maximize heat exchange efficiency, dynamically balancing both objectives.
Solution Approach 2:
The system transitions from static expansion valve positioning to dynamic control based on real-time evaporator outlet conditions. The valve opening degree varies continuously to maintain the evaporator operating point at the optimal boundary between maximizing heat exchange efficiency and preventing liquid return to the compressor.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances energy efficiency by maximizing heat exchange, reducing coolant demand, and optimizing evaporation temperature, resulting in lower energy consumption and improved system performance.
Implementation Method 1
The coolant liquid coming from the condenser passing through the expansion valve expands adiabatically and cools down before entering the evaporator
Implementation Method 2
In the evaporator, the low-pressure coolant liquid absorbs heat from the environment, is transformed into superheated steam
Implementation Method 3
the low-pressure coolant liquid absorbs heat from the environment
Implementation Method 4
the coolant fluid, which is in a superheated steam state, is compressed at high pressure by the compressor and sent to the condenser, where it releases heat to the external environment, condensing in the form of high-pressure liquid
Implementation Method 5
releases heat to the external environment, condensing in the form of high-pressure liquid
Implementation Method 6
the liquid phase, and the gaseous phase of the saturated fluid separate, with the liquid phase that remains inside the collecting receptacle
Data Source
Figure 1
Figure 1a
Figure 2
AI summary
A method for managing a refrigerating plant consisting of one or more refrigerating units (22) supplied by a coolant fluid, comprising setting or detecting, for each refrigerating unit (22) of said one or more refrigerating units, a set temperature range within which each refrigerating unit (22) has to remain during operation of the plant; setting up, for each refrigerating unit (22) of said one or more refrigerating units, a respective control unit (23) configured to manage the operation of the refrigerating unit (22); setting up a central control unit (24) operationally connected to each refrigerating unit (22) of said one or more refrigerating units, and a central management unit (25) operationally connected to said central control unit (24); the method further comprises a first step that includes detecting, by said respective control unit (23), an operating temperature of each refrigerating unit (22) of said one or more refrigerating units, and verifying, by said central control unit (24), if said operating temperature is comprised in the set temperature range; a second step that includes increasing by a set amount an evaporation temperature of the coolant fluid in each refrigerating unit (22) of said one or more refrigerating units, by said central management unit (25), if the operating temperature of each refrigerating unit (22) is within said set range. A refrigerating plant comprising a coolant fluid, at least one compressor (1) a refrigerating unit (22) supplied with said coolant fluid, or several refrigerating units (22) supplied in parallel with said coolant fluid, in which each refrigerating unit (22) of said one or more refrigerating units comprises an evaporator (6) supplied with said coolant fluid through a respective expansion valve (5), in which each refrigerating unit (22) of said one or more refrigerating units is provided with a control unit (23) configured to detect parameters that define the work conditions of the refrigerating unit (22) and vary the work conditions of the refrigerating unit (22), in which each control unit (23) is operationally associated with a central control unit (24) configured to receive from each control unit (23) data relating to the work conditions of each refrigerating unit (22) of said one or more refrigerating units, and communicate the data to a central management unit (25), configured to regulate operating parameters of each refrigerating unit (22) on the basis of the data received from the central control unit (24).