No More Constant Speed Pressure Boosting Under ASHRAE 90.1 - 2010
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By Mark Bingham
“Constant speed pressure boosters are DEAD and GONE TO HEAVEN!”
That was the prevailing message recently from Chris Edmondson, CEO of JMP, as he briefed the folks here at about the upcoming mandatory changes under SECTION 10.4 of the new ASHRAE 90.1 – 2010.
Many of you know that Chris lives and breathes all things ASHRAE, so if he says constant speed pressure boosting will soon be a thing of the past, you might as well wave good-bye. We’re making preparations and so should you.
As of October 18, 2013, pressure boosters systems may no longer be controlled based on setpoints that are based on pump discharge pressures. Rather, they must be controlled based on demand, which typically means installing a pressure sensor at the “critical fixture” or the highest point in the system. In addition, this new standard, which has been adopted into commercial building codes, prohibits the use of pressure reducing devices to reduce the pressure of water supplied by booster system pumps. The only pressure reducing devices that will be allowed are those employed for safety per the 85 psi plumbing code limit.
The reason for the change is simple – energy savings. By basing the set point on the most remote fixture instead of the reading seen at the pump discharge, variable speed systems can and will achieve a much greater speed reduction. As an example, consider the system in the diagram below.
Changing the sensor location from the discharge header to the remote fixture allows for a pump speed reduction of 26% versus 10%! This savings translates into some pretty significant monetary savings for owners:
Pressure Booster System Control Strategy Operating Costs
Two constant speed pumps, 50/50 percent split $6,331/yr.
Two variable speed pumps, with local sensor located
at discharge header with 50/50 percent split $4873/yr.
Two variable speed pumps, with remote sensor located
at most critical fixture with 50/50 percent split $3205/yr.
*Based on 10 psi variable suction pressure and 20 psi friction head loss.
Not Loving the Idea Hardwiring a Distant Sensor? No Worries!
The energy savings produced from this mandate will be great, but one of two changes must occur in how we design and install these systems. Either a sensor will have to be installed at the top of the building and wired back to the booster controller OR an alternative logic that simulates remote monitoring must be used. One word of caution –it is typically not recommended to remote sense across a Building Automation System (BAS). The good news is that JMP’s Hyfab Division has alternative logic that accurately simulates remote monitoring without BAS involvement.
Hyfab is able to manufacture a pressure booster that will allow the system to be 90.1-2010 compliant without installing a pressure sensor at the critical fixture. Rather, the control logic resets the pressure booster setpoint based on measured demand (flow). This benefits the owner by providing additional energy savings at lower demand without the added cost of remote sensing.
Look for more information on this enhancement in the very near future!
If you want to see your states current adoption status visit www.energycodes.gov
