Subcooling Bypass Control for Stable Heat Pump Heating Capacity
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Solution Overview
Problem
Conventional refrigeration cycle apparatuses fail to maximize enthalpy in the evaporator and reduce pressure loss in the low-pressure side refrigerant passage, leading to insufficient heating capacity when outside air temperatures are low, due to excessive refrigerant evaporation in the subcooling heat exchanger and increased compressor discharge temperature.
Innovation Solution
A refrigeration cycle apparatus with a bypass passage and expansion valve system that maintains the refrigerant at saturation temperature in the bypass passage and controls the degree of superheat at the evaporator outlet to prevent excessive refrigerant flow and maintain a desired dryness fraction, allowing for efficient heat exchange and reduced pressure loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the bypass expansion valve is controlled so that the degree of superheat at the outlet of the subcooling heat exchanger conforms to the target degree of superheat, then the refrigerant temperature is maintained, but the subcooling heat exchanger cannot operate to its maximum capability and enthalpy increase in the evaporator is not maximized
Solution Approach 1:
The invention changes the control parameter from maintaining target degree of superheat to maintaining saturation temperature at the subcooling heat exchanger outlet. This parameter change allows the subcooling heat exchanger to operate at maximum capability, maximizing enthalpy increase in the evaporator and improving heating capacity while preventing refrigerant superheating
Solution Approach 2:
The invention implements feedback control by using a temperature sensor to detect the actual temperature of refrigerant at the subcooling heat exchanger outlet and comparing it with the saturation temperature calculated from compressor suction pressure. The bypass expansion valve is adjusted based on this feedback to maintain saturation temperature, ensuring optimal heat exchange efficiency
2Temperature
If the refrigerant is superheated in the bypass passage, then the refrigerant temperature increases, but the specific volume of refrigerant increases, circulating amount reduces, and compressor discharge temperature increases
Solution Approach 1:
The invention applies preliminary anti-action by preventing refrigerant superheating in the bypass passage through saturation temperature control at the subcooling heat exchanger outlet. This preemptive measure avoids the subsequent harmful effects of increased specific volume, reduced circulating amount, and elevated compressor discharge temperature that would occur if superheating were allowed
3Productivity
If the rotation speed of the compressor is increased to provide sufficient heating capacity at low outside air temperature, then the heating capacity increases, but the discharge temperature increases and compressor reliability decreases
Solution Approach 1:
The invention changes the refrigerant state parameter from superheated to saturated at the subcooling heat exchanger outlet, which prevents excessive discharge temperature rise when compressor rotation speed is increased. This allows the compressor to operate at higher speeds for sufficient heating capacity while maintaining reliability through controlled discharge temperature
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 configuration maximizes enthalpy in the evaporator, reduces pressure loss, and allows for a sufficient heating capacity by maintaining the refrigerant in a desired state, enabling higher compressor rotation speeds and efficient heating performance even at low outside air temperatures.
Implementation Method 1
the heat exchange between the main flow refrigerant and the bypass flow refrigerant
Implementation Method 2
a subcooling heat exchanger is provided in a refrigerant circuit downstream of a condenser and an expanded refrigerant is made to flow into the subcooling heat exchanger so that the refrigerant that has flowed out of the condenser is subcooled
Implementation Method 3
an evaporator 115 that are connected circularly
Implementation Method 4
a compressor 111
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A refrigeration cycle apparatus 1A includes: a refrigerant circuit 2 provided with a subcooling heat exchanger 23; a bypass passage 3 extending through the subcooling heat exchanger 23; and a controller 4 for controlling a main expansion means 24 in the refrigerant circuit 2 and a bypass expansion means 31 in the bypass passage 3. The bypass expansion means 31 is controlled so that a bypass side outlet temperature conforms to a saturation temperature at a pressure of a refrigerant to be drawn into a compressor 21, and a degree of superheat at an outlet of an evaporator 25 calculated based on an evaporator outlet temperature is equal to or lower than a predetermined degree of superheat.