A heat pump system
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Solution Overview
Problem
Air-source heat pump systems experience a significant drop in heating capacity and coefficient of performance (COP) as ambient external air temperature falls, and they require defrosting methods that consume electrical power without providing heat to the building, leading to reduced efficiency and the need for backup heating sources.
Innovation Solution
A heat pump system that directs residual thermal energy from the condenser to defrost the evaporator while using stored thermal energy from a thermal energy storage means to maintain heating to the building during defrosting, eliminating the need for backup heaters and improving COP.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional defrosting methods (reverse cycling, hot-gas bypass, or electrical heating) are used, then the evaporator can be defrosted, but electrical power is consumed without providing heat to the building, reducing overall system efficiency and COP
Solution Approach 1:
The system uses itself to defrost the evaporator by redirecting hot refrigerant gas from the compressor directly to the evaporator through a bypass conduit, eliminating the need for external electrical heating or reverse cycling. The hot gas from the compressor provides the necessary heat to melt frost and ice on the evaporator coils.
Solution Approach 2:
A bypass conduit acts as an intermediary pathway, allowing hot refrigerant gas to travel directly from the compressor to the evaporator without passing through the condenser and expansion device. This intermediary channel enables the defrosting function while maintaining continuous heating operation.
2Reliability
If reverse cycling method is used to defrost evaporator, then ice is melted, but heat is extracted from the condenser causing reduction in building interior temperature and requiring backup heating
Solution Approach 1:
The bypass conduit serves as an intermediary that allows hot refrigerant gas to reach the evaporator directly from the compressor, bypassing the condenser. This prevents heat extraction from the condenser and maintains building interior temperature while still achieving evaporator defrosting.
Solution Approach 2:
The defrosting function is extracted from the main refrigeration cycle by creating a separate bypass pathway. This allows the defrosting operation to occur independently without disrupting the normal heating function through the condenser.
3Reliability
If hot-gas bypass method is used to defrost evaporator, then ice is melted, but none of the heat is supplied to the building's central heating system, reducing overall COP
Solution Approach 1:
The system maintains multi-functionality by allowing the refrigerant circuit to simultaneously perform both heating (through the condenser) and defrosting (through the bypass conduit to the evaporator). The compressor's hot gas serves dual purposes: maintaining heating operation and defrosting the evaporator.
Solution Approach 2:
The bypass conduit enables continuous useful action by allowing hot refrigerant gas to continuously flow to the evaporator for defrosting while the main circuit continues to provide heating to the building. This eliminates interruptions in heat supply during defrosting operations.
4Reliability
If electrical heater is used to defrost evaporator, then frost and ice are melted, but additional electrical power is consumed and ASHP unit must be switched off interrupting heat supply
Solution Approach 1:
The system uses its own compressor-generated hot refrigerant gas to defrost the evaporator, eliminating the need for external electrical heaters. This self-service approach maintains system operation and heat supply continuity during defrosting.
Solution Approach 2:
The bypass conduit enables continuous heat supply to the building during defrosting operations. The ASHP unit remains operational throughout the defrosting process, with the compressor continuously providing both heating and defrosting functions simultaneously.
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 allows for continuous heating during defrosting, enhancing the system's efficiency and reducing operating costs by maintaining heat supply and increasing the coefficient of performance (COP) of the heat pump system.
Implementation Method 1
directing stored thermal energy from a thermal energy storage means to the condenser in order to heat the interior of a building during the defrosting operation
Implementation Method 2
direct residual thermal energy from a condenser to defrost an evaporator
Implementation Method 3
melt the ice that has accumulated in the evaporator
Implementation Method 4
vaporised refrigerant being compressed to form a hot vapour
Implementation Method 5
The flow of liquid refrigerant then proceeds to the expansion valve where it expands, thereby reducing pressure and temperature
Data Source
AI summary
A heat pump system for controlling the internal temperature of a building. The system comprises a compressor, a first heat exchanger, an expansion device and a second heat exchanger which are fluidly coupled together by a flow of refrigerant to define a refrigerant circuit, and a thermal energy storage means which is thermally couplable to the refrigerant circuit to exchange thermal energy with the refrigerant. The heat pump system is configured to be operable in a normal heating mode and in a defrosting mode. In the normal heating mode, thermal energy is transferred from the second heat exchanger into the refrigerant and transferred from the refrigerant by the first heat exchanger to heat the building. In the defrosting mode thermal energy is transferred from the thermal energy storage means into the refrigerant and transferred from the refrigerant by the first heat exchanger to heat the building and by the second heat exchanger to defrost the second heat exchanger. The heat pump system comprises a switching assembly which is configured to switch between the normal heating and defrosting modes, and wherein the switching assembly is configured, when operating the heat pump system in the defrosting mode, to direct refrigerant exiting the first heat exchanger to flow through the second heat exchanger to cause residual heat in the refrigerant to defrost the second heat exchanger.