Heat Pump Water Heater Defrost Control Without Reverse Cycle
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Heat pumps used for water heating face issues with frost accumulation on evaporator coils, leading to degraded performance and potential damage, especially when the coil temperature falls below freezing, and existing solutions like reverse cycle operation are counterproductive to water heating purposes.
Innovation Solution
A heat pump water heater system equipped with temperature and humidity sensors, a controller, and a fan that directs air across the evaporator coil after shutdown to melt frost, using a predetermined temperature and humidity threshold to determine when to activate the fan and deactivate the compressor, and optionally utilizing a heating element to enhance defrosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the heat pump operates in reverse cycle to melt frost on the evaporator coil, then frost accumulation is reduced, but the heat pump removes heat from the water being heated, reducing water heating efficiency
Solution Approach 1:
The system performs preliminary defrosting by activating the fan and heating element before the heat pump compressor starts operating. This ensures the evaporator coil is free of frost before water heating begins, preventing frost-related efficiency losses without requiring reverse cycle operation during heating.
Solution Approach 2:
The defrosting function is extracted from the heat pump cycle itself and implemented as a separate pre-processing step using the fan and heating element. This separates the defrosting operation from the water heating operation, allowing them to occur at different times and avoid conflicting thermal effects.
2Productivity
If the evaporator coil temperature falls below freezing to provide heated water, then water heating performance is improved, but frost and ice accumulate on the coil causing degraded performance and potential damage
Solution Approach 1:
The system applies preliminary anti-action by detecting conditions that would lead to frost accumulation (low ambient temperature combined with high humidity) and activating the heating element and fan before the heat pump operates. This preventive measure counteracts the potential frost formation before it can occur, allowing the evaporator coil to operate at optimal temperatures without frost damage.
Solution Approach 2:
The controller uses feedback from temperature and humidity sensors to dynamically control the heating element and fan operation. When sensors detect conditions favorable for frost formation (low temperature and high humidity), the controller activates the defrosting system, creating a closed-loop control that prevents frost accumulation while maintaining water heating performance.
3Power
If moisture in ambient air condenses on the colder evaporator coil, then heat transfer efficiency is improved, but the accumulated moisture eventually freezes forming frost and ice
Solution Approach 1:
The heating element acts as an intermediary that provides controlled heat to the evaporator coil and surrounding air. This intermediary heat source prevents moisture condensation from freezing by maintaining the coil temperature above freezing point during high-humidity conditions, while still allowing efficient heat transfer to occur during normal operation.
Solution Approach 2:
The system changes the temperature parameter of the evaporator coil dynamically based on ambient conditions. During high-humidity, low-temperature conditions, the heating element raises the coil temperature to prevent frost formation. During normal conditions, the coil temperature is allowed to drop for efficient heat transfer, demonstrating parameter adjustment to balance competing requirements.
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
Effectively reduces or eliminates frost accumulation on the evaporator coil by using ambient or heated air to melt frost after the heat pump is shut down, maintaining system performance and preventing damage, while not compromising water heating efficiency.
Implementation Method 1
output instructions for the fan to move air across the evaporator coil
Implementation Method 2
optionally utilizing a heating element to enhance defrosting
Implementation Method 3
one or more temperature sensors, and a controller. The controller can be configured to receive temperature data from the one or more temperature sensors
Implementation Method 4
The condenser coil can be in thermal communication with the water tank
Data Source
AI summary
A heat pump water heater can include a water tank and a refrigerant circuit that can be in fluid communication with an evaporator coil, a condenser coil, and a compressor. The heat pump water heater can include a fan configured to move air across the evaporator coil, a temperature sensor, and a controller. The controller can be configured to receive temperature data from the temperature sensor and, in response to the temperature data indicating a temperature less than a predetermined temperature threshold, output instructions for the compressor to deactivate and the fan to move air across the evaporator coil.