The airflow rate is lowered by reducing duct leakage. The cooling power is lowered by reducing the amount of waste heat from the fan. The savings are achieved without compromising thermal comfort or indoor air quality.

SAV also reduces noise from mechanical equipment. Since the pressure and flow are lower, there is less hiss from dampers and diffusers, and less fan rumble.

Because of the problems with traditional static pressure reset methods, most VAV systems use constant pressure control. Constant pressure control wastes energy because the duct pressure is always higher than necessary. The following table compares the benefits of SAV with InCITe™ to those of constant pressure control and traditional methods of resetting static pressure.

The following figure shows an example of how much energy you could save. SAV reduces the average power consumption by 0.23 W/sqft. This is comparable to the energy savings from a lighting retrofit. The cost-savings from SAV are $0.1/sqft/year at $0.1/kW-h and 4500 run-time hours per year for Oakland, CA. The amount that you will save depends on your utility rate, operating schedule, weather, and current operating pressure.

Requirements

SAV is applicable to all VAV air-handling systems. It can be applied to systems with pneumatic controls, legacy digital controls, or modern direct digital controls (DDC). SAV and InCITe both require a sensor that can measure fan flow rate. Federspiel Controls can provide one if your system doesn’t already have one.

Case Studies

Making a green building greener

SAV with InCITe™ was implemented at 1111 Franklin Street in Oakland, CA. The building is owned by the University of California and is occupied by the UC Office of the President. The building has 8 occupied floors with 200,000 square feet of office space. The building is conditioned by a single built-up VAV air-handling unit with two parallel supply fans. Each supply fan has a 100 hp motor and each is designed to supply 83,000 CFM at design conditions.

The building has pneumatic terminal controls. This fact makes it impossible to implement static pressure reset strategies that use terminal damper position for feedback.

Prior to implementing SAV with InCITe™, 1111 Franklin received an Energy Star building label for its low energy use. Nevertheless, SAV with InCITe™ is able to reduce fan energy use at UCOP by 0.43 kW-h/sqft/year, and natural gas consumption by 0.05 therms/sqft/year, making an already green building even greener. Natural gas savings are achieved because the pneumatic terminal controls revert to a minimum position when heating, so the supply flow rate, and therefore the amount of re-heat, is reduced by SAV with InCITe™.

County of Alameda

SAV with InCITe™ was implemented at 1401 Lakeside Plaza, which is owned and operated by the County of Alameda California. The building has 12 floors with 146,000 square feet of office space occupied by County employees from several agencies. Floors 2-12 are conditioned by packaged VAV air-handling units, one on each floor.

The County had been trying for nine years to reduce the speed and energy consumption of the VAV fans in the building. At one point they implemented a static pressure reset strategy that tried to keep the most-open terminal damper at 95% open. That strategy failed (it ran the fan at 100% speed all the time) because there was always at least one VAV box that did not respond correctly to pressure changes. Faulty VAV box operation is not uncommon, but it doesn’t prevent SAV with InCITe™ from working correctly.

The following figure shows the supply duct static pressure before and after SAV with InCITe™ was implemented. On average the pressure was reduced by 34%. Average fan speeds were reduced by 21%. The projected annual cost savings is $14,500/year.