Design and Construction of Refrigerant Charge Level Detecting Device in HVAC/R System with Microcontroller
Parvez Mahmud1, Shahjadi Hisan Farjana2
1M. A. Parvez Mahmud, Lecturer, Department of Mechatronics Engineering, World University of  Bangladesh, Dhaka, Bangladesh.
2Shahjadi Hisan Farjana, Lecturer, Department of Mechatronics Engineering, World University of  Bangladesh, Dhaka, Bangladesh.
Manuscript received on May 17, 2012. | Revised Manuscript received on June 22, 2012. | Manuscript published on June 30, 2012. | PP: 309-314 | Volume-1 Issue-5, June 2012. | Retrieval Number: E0526061512/2012©BEIESP

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Abstract: A charge level detecting device in residential and light commercial heating, ventilation, and air-conditioning (HVAC) systems and in refrigeration systems is used to detect the sufficiency of refrigerant or charge level whether it is proper or not. The most common problems affecting residential and commercial HVAC/R systems are slow refrigerant leaks, improper refrigerant charge and charging device. The usual methods for charge level detection are sight glass method and system high side and low side pressure measurement method. The limitation of sight glass method is it works only if a predictable amount of refrigerant remains in one part of system or constant flow of refrigerant is maintained throughout the system. Pressure of any HVAC/R system cannot be measured in a running system, and charge leaks occur in case of pressure method. Refrigerant charge level detecting device employs a method of determining if the refrigerant charge is within an acceptable range, including the steps of measuring the superheat and subcool temperatures at compressor inlet and condenser outlet. Actual superheat and actual subcooling values are calculated and these values are thus compared with target superheat and target subcool values in microcontroller device, thus obtained from manufacturers chart for particular type of refrigerant, which values depends on outdoor dry bulb temperature and indoor wet bulb temperature on system operating situation and shows the charge status result. The refrigerant charge indicator is based on the fact that when refrigerant starts to leak, the evaporator coil temperature starts to drop and the level of liquid sub cooling drops. An over charge in this system results in compressor flooding, damaging to the motor and mechanical components. Inadequate refrigerant charge can lead to increased power consumption, thus reducing system capacity and efficiency.
Keywords: Superheat, subcooling, refrigerant charge level, microcontroller.