Frequently Asked Questions - Flow Control

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Frequently Asked Questions System and Valve Basics: 1. Q: What is good cooling coil performance? A: The temperature range is controlled within +/- F ( C) off the cooling coil at set point or below. Also, the coil delta T exceeds design, even at part load. 2. Q: What is delta T and why is it important? A: Delta T is the difference between the water return and supply temperature through a heating or cooling coil. All HVAC hydronics systems have a design delta T; however, this objective is rarely achieved at part load. Delta T is the single most effective indicator of system performance. The higher delta T, the less flow required to serve the load. 3. How fast will the leaving air temperature change when the coil flow rate varies?

A: A modulating pressure independent control valve does not allow a change in flow rate when the pressure differential across the valve changes. Flow only changes with a change in valve

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