Vapour-compression heat pump system and method for operating a vapour-compression heat pump system
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Solution Overview
Problem
Two-stage air source heat pump systems face challenges in low-ambient temperatures, where defrosting the evaporator can compromise indoor comfort and require either rejecting heat from the superheated refrigerant vapour to an external fluid stream or recovering it within the cycle, increasing costs and complexity.
Innovation Solution
A vapour-compression heat pump system utilizing a thermal energy storage device with phase change material to store heat from the superheated refrigerant vapour stream, allowing for stable operation by providing heat for defrosting without cooling the indoor space and eliminating the need to reject heat externally, thus maintaining high coefficient of performance (COP).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reverse cycle defrosting is used to melt ice on the evaporator, then the evaporator can be defrosted, but indoor comfort conditions are compromised by cooling the indoor space
Solution Approach 1:
The system stores thermal energy in advance during heating operation by transferring heat from the superheated refrigerant vapour to the phase change material in the thermal energy storage device. This preliminary energy storage enables the defrosting operation to use stored heat rather than stealing heat from the indoor space, thus maintaining indoor comfort while enabling effective evaporator defrosting.
Solution Approach 2:
The thermal energy storage device with phase change material acts as an intermediary between the superheated refrigerant vapour and the evaporator. It stores heat from the refrigerant and releases it during defrosting, mediating the heat transfer process to avoid direct heat extraction from the indoor space that would occur in conventional reverse cycle defrosting.
2Temperature
If heat from the superheated refrigerant vapour is rejected to an external fluid stream, then the refrigerant can be cooled, but the COP of the cycle is limited
Solution Approach 1:
The system utilizes the phase change of the phase change material (from solid to liquid) to store thermal energy at a constant temperature. During heating operation, the phase change material absorbs heat from the superheated refrigerant vapour and undergoes phase transition, effectively cooling the refrigerant while storing the thermal energy for later use during defrosting operations.
Solution Approach 2:
Instead of discarding the heat from the superheated refrigerant vapour to an external fluid stream (which would limit COP), the system recovers this heat by transferring it to the phase change material in the thermal energy storage device. The stored heat is then recovered during defrosting operations, improving overall cycle efficiency and COP.
3Loss of energy
If heat from the superheated refrigerant vapour is recovered elsewhere within the cycle, then energy efficiency is improved, but system cost and complexity increase
Solution Approach 1:
The thermal energy storage device with phase change material serves multiple functions: it acts as a heat exchanger to cool the superheated refrigerant vapour during heating operation, and simultaneously serves as a heat source for evaporator defrosting. This multi-functionality enables energy recovery and improved efficiency without requiring separate, complex systems for each function.
Solution Approach 2:
The system uses its own superheated refrigerant vapour to charge the thermal energy storage device, and then uses the stored energy from the same system to perform defrosting. The heat pump system essentially serves itself by recycling its own waste heat through the phase change material, eliminating the need for external heat sources or complex interconnections with other systems.
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
The system ensures stable operation and maintains indoor comfort during defrosting while optimizing energy efficiency by using stored heat from the phase change material, reducing system complexity and costs.
Implementation Method 1
a thermal energy storage device which comprises a phase change material to receive and store heat from a superheated refrigerant vapour stream leaving the first compression stage
Implementation Method 2
a thermal energy storage device which comprises a phase change material to receive and store heat from a superheated refrigerant vapour stream
Implementation Method 3
the phase change material of the thermal energy storage device and the evaporator in a defrosting operation mode
Implementation Method 4
using stored heat from the phase change material
Data Source
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AI summary
A vapour-compression heat pump system and a method for operating a vapour-compression heat pump system is presented. The inventive system and method makes use of a thermal energy storage device which comprises a phase change material to receive and store heat from a superheated refrigerant vapour stream leaving the first compression stage, thereby also cooling the refrigerant close to its saturated vapour temperature, as desired. The system and method have the advantage that they allow a stable operation of the heat pump system. Furthermore, unlike prior art systems and methods, comfort conditions by cooling the indoor space during defrosting of the evaporator are not compromised and heat from the superheated refrigerant vapour exiting the first compression stage does not have to be rejected to an external fluid stream or recovered elsewhere within the cycle, i.e. the COP of the cycle is not limited and costs and complexity of the system and method are low.