VAV Diffuser & Dust

[MagicJS]

A collegue told me that if I want to use thermally powered VAV diffusers, I need to design special dust distribution system.

I thought dust accumulation is caused by dumping at low flow conditions by diffusers not designed for VAV. Is there a particular reason VAV diffusers worsen this condition? Also are there any other problems to consider when designing a VAV diffuser based system.

Thanks.

 

[lilliput1]

Check with your colleque. He may have said "duct" distribution, not "dust". Thermally powered diffusers must not see more than about 0.5"wg (verify from manufacturer - Thermafuser) because they can't close off at higher pressures. So air distribution is grouped in branches that is pressure controlled with a valve sensing the downstream pressure and holding it at the setpoint (below the 0.5' wg limit). Each branch feeds a group of thermally powered diffuser. Branch duct sizes and lengths are designed to allow operation within the 0.5"wg limit. Typically pneumatic operated bladder type air valves are used instead of butterfly type dampers, for less noise.