Impact of refrigerant undercharge and overcharge faults on building indoor conditions and HVAC system performance during cooling seasons: Field measurements

Faults in residential heating, ventilation, and air conditioning (HVAC) systems, often due to poor installation or gradual development, can significantly reduce system efficiency and lifespan, leading to 15-30% of total energy consumption being wasted. In newly installed air conditioners and heat pumps, refrigerant charge and airflow faults cause 20.7 TWh of wasted energy annually, equivalent to 9.6 million metric tons of CO2 emissions from U.S. single-family detached homes. Despite their impact, field test data on refrigerant overcharge and undercharge faults are limited. To address this gap, this study investigates how refrigerant undercharge and overcharge faults affect indoor comfort and HVAC system performance in residential buildings through field tests.

Oak Ridge National Laboratory’s (ORNL) Yarnell Station house, a two-story residential test facility was selected as the test building. This test facility is equipped with a 3-ton single-stage heat pump system with a Seasonal Energy Efficiency Ratio of 14 for cooling and a Heating Seasonal Performance Factor of 8.2 for heating efficiency. The installed HVAC system utilizes R-410A refrigerant.

We created a total of 12 scenarios, which included 2 baseline scenarios with no fault, 5 refrigerant undercharge fault scenarios ranging from 10% to 50% undercharge, and 5 refrigerant overcharge fault scenarios ranging from 5% to 25% overcharge, with each scenario being tested over a period of approximately seven days.

Data is collected at 1-minute and 1-hour intervals, including weather-related data (outdoor air temperature and relative humidity), building indoor condition-related data (indoor air temperature and relative humidity), and system-related data (supply and return air temperature, supply and return air relative humidity, supply air flow rate, suction pressure, energy consumption of each HVAC system component, and system runtime fraction).

By analyzing the field test data, we will provide a comprehensive analysis of how refrigerant undercharge and overcharge faults affect indoor conditions and HVAC system performance during the cooling season. We will identify which specific data points are affected by these faults. Based on this analysis, we will propose the essential sensors needed to detect refrigerant undercharge and overcharge faults.

To implement refrigerant faults into a building energy simulation model, it is crucial to understand how these faults impact HVAC system operations in actual building. This is the first step of our research, this paper will significantly contribute to our simulation-based future work, including simulation model calibration, comparisons between simulation results and field tests, and development of the fault detection and diagnosis algorithm.