Delta T Coil Control Valve for Chiller Systems

The goal of this project is to determine and validate energy savings for a typical retrofit for two delta T valves in an HVAC chiller system. Delta T is the difference between the water supply and return temperature across a cooling coil. When downstream cooling coils have a low delta T, it can result in increased pumping costs for the chilled water distribution system. The assessment will look at two different pressure independent valves to control flow through coils: 1) a valve with embedded flow sensor couple with supply and return water sensors to optimize coil performance and communication with a BAS system, 2) a mechanical valve that maintains a constant differential pressure and flow across the controlled surface. The project will investigate the market potential and utility program perspective by surveying customers who might be a target market for this technology and identifying gaps and barriers.

This report provides a summary of the results of measurement of energy-smart pressure independent control valves used in a chiller system at a university. The concept of the use of these type of valves is to reduce pumping and chilled water production energy by measuring the actual energy output in British thermal units (BTUs) of each of the coils and adjusting the temperature difference across the coil to a more efficient operating value. This project entails measurement and verification at two buildings on campus, the Student Health Center and Welch Hall, an instructional building comprised mostly of administration offices. The project involves the installation and testing of six (6) chilled water valves in two buildings on a university campus. Three were installed on air handling units (AHUs) in the Student Health Center and three were installed Welch Hall. In general, the coil ratings and settings (temp, etc.) varied across all six AHUs. Each AHU served several spaces with a Variable Air Volume (VAV) system. The two buildings are served from a main central plant (CP) that provides chilled water to most of the campus. Both buildings that were converted with energy control valves are served from a main CP. The basic premise of this technology is to optimize the chilled water flow through the coil by limiting the flow when load is reduced or satisfied. Typically, a pressure-dependent valve will “overcool” the space as the temperature nears the set point by maintaining a maximum flow through the coil even though there are less BTUs supplied or required by the space. The new technology provides for sensing of flow, supply temperature, and return temperature across the coil, thereby providing a full recognition of the BTU output of the coil. When the space requires less cooling, the flow is reduced and the temperature difference is increased until the space requires additional cooling. This “higher Delta T” optimizes the BTU output of the coil to the space requirements. For this installation and testing, the smart energy valve was capable of being set in three separate modes: Pressure Dependent (PD), Pressure Independent (PI), and Smart Energy Mode (SMV). Under a condition where the building was at full load and at design day conditions, all three valves would essentially operate in the same position (fully open). Where the valves differ is operations at other load conditions that can vary depending on time of day and season.