Development and evaluation of virtual refrigerant mass flow sensors for fault detection and diagnostics

•Three VRMF sensors are developed for estimating refrigerant mass flow rate.•Three VRMFs can estimate the mass flow rate with less than a 10% RMS error.•VRMF sensor can be used for on-line performance monitoring.•The differences between VRMF sensors can be used to isolate particular fault.

Refrigerant mass flow rate is an important measurement for monitoring equipment performance and enabling fault detection and diagnostics. This paper presents and evaluates three different virtual refrigerant mass flow (VRMF) sensors that use mathematical models to estimate flow rate using low cost measurements. The first model uses a compressor map that relates refrigerant flow rate to measurements of condensing and evaporating saturation temperature, and to compressor inlet temperature measurements. The second model uses an energy-balance method on the compressor that uses the compressor power consumption. The third model is developed using an empirical correlation for an electronic expansion valve (EEV) based on an orifice equation. The three VRMFs are shown to work well in estimating refrigerant mass flow rate for various systems under fault-free conditions with less than 5% RMS error. The combination of the three VRMFs can be utilized to detect and diagnose when the compressor and/or expansion device is not providing the expected flow.