Pressure independent valves are becoming more widely used in variable volume HVAC hydronic systems. Are they worth the hype? Are the energy gains real?
The pressure independent valves can provide real savings in systems that have the low delta T syndrome, which seems to affect a lot of campus style centralized chilled water/hot water systems. The low delta T situation is mostly encountered during part load conditions and is manifested in excessive pumping. This over pumping consequently results in more than the ideal number of chillers/boilers and auxiliary equipment operating for the given loads.
Pressure independent valves (Belimo makes a pressure independent valve that actually maintains constant delta T across a coil) would help maintain a constant delta T at all load points which would show up in reduced pumping energy and in case of large cooling plants potentially reduced number of chillers/boilers and associated auxiliary equipment.
The savings from installing the pressure independent control valves will vary from one installation to another depending on how bad the delta T across the loads and buildings is. In addition, the savings will be affected by the efficiencies of the pumps (if they have VFDs or not?), chillers, boilers and cooling towers that will be affected by improving the delta T issues on site using these valves.
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