Sorption heat pump and control method
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Solution Overview
Problem
Absorption heat pumps face operational issues due to low pressure differential between the high and low sides during start-up, leading to slow increase in heating or cooling capacity, especially when the hydronic fluid temperature is low, which can result in insufficient circulation rates and reduced system efficiency.
Innovation Solution
A method and system for controlling the flow rate of hydronic fluid entering the condenser in response to temperature measurements, reducing the flow rate when the temperature is below a predetermined value and for a predetermined time after activation, to maintain adequate pressure differential and enhance start-up efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the flow rate of hydronic fluid through the condenser is increased to improve heat transfer efficiency, then the heating or cooling capacity increases, but the pressure differential between high and low sides decreases, causing slow increase in capacity during start-up
Solution Approach 1:
The system dynamically adjusts the flow rate of hydronic fluid through the condenser based on operating conditions. During start-up, the flow rate is reduced to maintain adequate pressure differential, while during steady-state operation, the flow rate is increased to maximize heat transfer efficiency and capacity.
Solution Approach 2:
The control system anticipates the need for adequate pressure differential during start-up by pre-reducing the flow rate before capacity buildup occurs. This preliminary action prevents the pressure differential from dropping too low, ensuring proper fluid circulation from the beginning of operation.
2Reliability
If the flow rate of hydronic fluid is reduced during start-up to maintain pressure differential, then fluid circulation is improved, but the heat transfer efficiency and capacity increase slower
Solution Approach 1:
The system applies different flow rate strategies at different time periods: during the start-up period, flow rate is reduced to ensure reliable fluid circulation and pressure differential, while after start-up, flow rate is increased to maximize capacity. This periodic adjustment resolves the contradiction between reliable circulation and capacity development.
Solution Approach 2:
The flow rate is dynamically adjusted based on the operational phase of the system. The control system transitions from a circulation-optimized mode during start-up to a capacity-optimized mode during steady-state operation, allowing both reliability and productivity requirements to be met at different times.
3Loss of energy
If parallel flow configuration is used through condenser and absorber to maximize cycle efficiency, then efficiency is improved, but pressure differential control becomes more complex during start-up
Solution Approach 1:
The control system continuously monitors pressure differential and flow rate, using feedback to automatically adjust the hydronic fluid flow rate through the condenser. This closed-loop control maintains adequate pressure differential while preserving the parallel flow configuration for maximum efficiency, without requiring complex manual intervention.
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 ensures a sufficient pressure differential for proper fluid circulation, accelerates the increase in heating or cooling capacity, and maintains high efficiency by optimizing the flow configuration through the condenser and absorber, even at low initial hydronic fluid temperatures.
Implementation Method 1
The refrigerant vapor is condensed to a liquid in the condenser
Implementation Method 2
Absorbent weak in refrigerant exiting the desorber is also expanded to the low side pressure using a throttling valve or fixed restriction, and enters the absorber along with the low pressure refrigerant exiting the evaporator where the refrigerant vapor is absorbed into the absorbent
Implementation Method 3
A refrigerant is desorbed from an absorbent in the desorber at the high pressure using thermal energy from a suitable heat source
Implementation Method 4
The liquid refrigerant exiting the condenser is expanded to the low side pressure using a throttling valve or fixed restriction (or capillary tube) before entering the evaporator where it is vaporized by the low-grade energy source
Data Source
AI summary
A method operates an absorption heat pump system, specifically the flow of hydronic cooling fluid through the condenser during system start-ups, or when the cooling fluid temperature is low. To minimize the time for an absorption heat pump to reach full cooling or heating capacity, it is desirable for the high side pressure to increase as fast as possible, and the low side pressure to decrease as fast as possible. Since the high side pressure is a function of the temperature of the refrigerant exiting the condenser, if the condenser cooling fluid temperature is low, the corresponding high side pressure will be low, which may not permit adequate working fluid flow rates from the high pressure side of the system to the low pressure side.