scope:

INTRODUCTION

Heating and cooling energy consumption measurements are critical for operations, controls, and fault detections of HVAC systems. In large commercial HVAC systems, the chilled water system may include multiple chillers and a thermal storage tank. Either the chillers or the storage tank will load and unload based on the system cooling load or consumption rate (McQuiston et al. 2005). The energy consumption is closely related to HVAC system operations. Fault or inefficient operations will lead to energy consumption levels 15% - 30% greater than optimal (Friedman et al. 2007). A simplified tool was developed to detect HVAC system faults by measuring heating and cooling energy consumption at the whole building level and calculating energy consumption deviation from the prediction (Friedman et al. 2007).

Generally water flow has to be measured in order to determine energy consumption in either chilled water systems or hot water systems. The water flow measurements are critical to develop heating and cooling energy meters.

The water flow measurement shares the same principle as the air flow measurement. The flow rate is often determined by measuring pressure difference across an orifice, nozzle or venturi tube (ASHRAE 2001). However, valves, dampers, bends and fittings upstream from the flow devices can cause errors. Long, straight pipe or duct should be installed upstream and downstream the flow devices, to assure fully developed flow for the proper measurements. These conditions are hard to be satisfied in actual systems. Meanwhile, for existing systems, extremely high installation and retrofit cost may make it impossible to install a new flow meter.