Method for controlling water-heating system, and water-heating system
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Solution Overview
Problem
In hot water supply systems using heat pump hot water suppliers with CO2 refrigerant, high inflow water temperatures due to unadjusted water flow rates and temperatures lead to inefficient operation and scale buildup in heat exchangers, causing performance deterioration.
Innovation Solution
A control method that adjusts the water flow rate and temperature into the heat pump hot water supplier by using sensors to detect flow rates and temperatures in the system, controlling a circulation pump to maintain optimal inflow conditions, thereby keeping the inflow water temperature low and improving heat pump performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If water is heated by heat pump hot water supplier and discharged at high temperature directly, then hot water supply is achieved, but scale is generated in heat exchanger and water circuit is clogged
Solution Approach 1:
A circulation pump is introduced as an intermediary device to control water circulation between the hot water storage tank and heat pump hot water supplier. The pump enables precise control of water flow rate, ensuring that heated water circulates back to the storage tank rather than being discharged directly, thereby preventing scale generation while maintaining hot water supply capability
Solution Approach 2:
The system performs preliminary heating of water in the hot water storage tank using the heat pump hot water supplier, then circulates the pre-heated water back to the tank. This preliminary action allows the system to maintain hot water availability without continuously discharging high-temperature water that causes scale formation
2Ease of operation
If water flow rate into heat pump hot water supplier is not adjusted according to load, then system operation is simple, but inflow water temperature becomes high and performance deteriorates
Solution Approach 1:
The system incorporates a flow rate detection device that continuously monitors water flow rate into the heat pump hot water supplier and provides feedback to the control unit. The control unit adjusts the circulation pump operation based on this feedback to maintain optimal flow rate, ensuring high heat pump performance while keeping the system easy to operate through automatic control
Solution Approach 2:
The system performs self-adjustment of water flow rate based on detected load conditions. The control unit automatically regulates the circulation pump to maintain optimal inflow water temperature and flow rate without requiring manual intervention, combining ease of operation with maintained performance
3Productivity
If hot water is stored in hot water storage tank and used directly, then low temperature water can be supplied to heat pump, but inflow water temperature may become high depending on tank and heat exchanger selections
Solution Approach 1:
The system replaces reliance on passive thermal stratification in the storage tank with active mechanical control using a circulation pump. The pump actively manages water circulation to ensure low-temperature water is consistently supplied to the heat pump, providing reliable temperature control independent of tank and heat exchanger design variations
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 the operational efficiency of the heat pump hot water supplier by maintaining low inflow water temperatures, preventing scale buildup, and ensuring efficient energy use in hot water supply systems.
Implementation Method 1
a circulation pump provided in a circulation-side circuit
Implementation Method 2
heat is exchanged between hot water heated by the heat pump hot water supplier and cold water on the site side using a heat exchanger
Implementation Method 3
water supplied to the heat pump hot water supplier... to exchange heat with refrigerant in the heat pump hot water supplier
Data Source
Figure 1
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AI summary
In a heat pump hot water supplier system of an indirect heat exchange type for indirectly heating on-site low temperature water with water quality such as in Europe (hard water), the temperature of water flowing into the heat pump hot water supplier may become high depending on selections in on-site construction. In this case, in a heat pump hot water supplier utilizing CO2 refrigerant, unit inflow water temperature rises, so that inefficient operation is continued. In a system in which an on-site water inflow pipe and a hot water storage tank-side water inflow pipe are provided with flow rate sensors, and low temperature water on the site side exchanges heat with high temperature water in the hot water storage tank to indirectly supply high temperature water, to lower the temperature of the hot water storage tank water inflow pipe to generate low temperature water, and then cause it to flow into the hot water storage tank to lower inflow water temperature into the heat pump hot water supplier to improve the operation performance, the output of the circulation pump is adjusted so that the water flow rate of the hot water storage tank-side water inflow pipe becomes equal to the water flow rate of the on-site water inflow pipe, thereby enabling high efficiency.