ASME Hydropneumatic Tanks Play An Important Role in Pressure Booster Systems
/By Chris Edmondson
“Do I really need a hydro-pneumatic tank on my variable speed pressure booster?”
It’s a question many engineers will ask, particularly after ASHRAE 90.1 – 2010 takes effect in commercial building codes as early as October of this year. As discussed in an earlier blog on variable speed pressure boosting, the new ASHRAE standard no longer permits pressure reducing devices to reduce the pressure of water supplied by booster system pumps. This essentially puts an end to constant speed pressure boosting, which brings variable speed to the forefront. But since the whole point of variable speed pumping is to more accurately align demand with supply, why would hydro-pneumatic tank still be required?
The answer is simple: Hydro-pneumatic tanks are necessary to keep variable speed booster pumps from short cycling.
How Hydro-pneumatic Tanks Save Energy and Increase Equipment Life
Hydro-pneumatic tank are primarily used in a domestic water system for draw down purposes when the pressure boost system is off on no-flow shutdown. Otherwise the pump(s) would cycle on and off every time someone flushed a toilet or got a glass of water at 3AM in the morning. This type of short cycling wastes a lot of energy and shortens equipment life, particularly in buildings with distinct demand patterns like hotels.
Hydropneumatic tanks (ASME and non-ASME) hold water and air under pressure. The compressed air creates a cushion that can absorb or apply pressure as needed to provide efficient water supply under low demand conditions without the operation of the pressure booster pumps.
It is a misnomer that variable speed booster systems can operate effectively without a hydropneumatic tank. Invariably, short cycling will occur without this low-cost pressurization strategy in place. And as you will hear us say over and over again, the most efficient pump is the pump that doesn’t run.
Stay tuned for more on sizing and placement of hydro-pneumatic tanks within a variable speed pressure booster system. And if you just can’t wait, check out our Variable Speed Pressure Booster video, which covers hydropneumatic tank sizing and placement.
