Rochester Institute of Technology puts PICVs to the Test

Constant flow maintained at varied system pressures

In hydronic HVAC systems made up of traditional balancing and control valves, system pressure is affected every time a valve changes its position. When the system pressure changes, the flow through all of the valves reacts and causes the amount of heat transfer through each device to also change.

— Wednesday, May 27, 2015 By Timothy Vann, Engineering Team, RIT Facilities Management Services
Danfoss

Assuming that each device was at equilibrium to start, we can deduce that each device is now getting either too much or too little heat transfer. As a result, each device requests that their valve open or close to compensate for the change in flow induced by the change in system pressure.

Due to this chain reaction, HVAC systems with traditional valves can be inherently unstable, which leads to overflows and underflows at the terminal coils. In turn, this leads to wasted energy, suboptimal heat transfer, premature failure of equipment, and a less comfortable space for the building occupants.

At RIT, we wanted to investigate an alternate HVAC design that could improve the stability of our system. Our research suggested a relatively new technology called a pressure independent control valve (PICV), which is able to absorb system pressures to maintain a constant desired flow rate at all times. In theory, if a PICV functions properly, then changes in system pressure will not cause flow changes through the valves – thus solving the instability issues.

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