11/30/2012

Optimize Your Air Handlers

Take the time to optimize your air handlers - the savings from year-round monitoring and control justify the effort.

By J.R. Howard

 
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    Dual-Duct Air Handlers
    In this dual-duct system in a 121,000-square-foot university facility, the dampers in the outside air duct and return air duct are controlled by the CO2 setpoint. The fan is controlled by the static pressure in the downstream ducts. The outside-air setpoint operates the valves to the preheat and precool coils. Only four water valves, two dampers, and the fan speed can be controlled in this system, but much can be done with them.
    Illustration Credit: QA Graphics
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    Continuous system monitoring provides a fault history and a view of performance over time, allowing you to develop a control strategy. The water meters graph reveals a stuck blowdown valve on a filter system without a meter.
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  • /Portals/1/images/Magazines/2012/1212/B_1212_AHU2.jpg

    Continuous system monitoring provides a fault history and a view of performance over time, allowing you to develop a control strategy. The boiler supply water plot shows that the boilers are cycling on and off too frequently.
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  • /Portals/1/images/Magazines/2012/1212/B_1212_AHU3.jpg

    Continuous system monitoring provides a fault history and a view of performance over time, allowing you to develop a control strategy. In the computer room air conditioner graph, the CRAC unit is cycling too often and may be oversized.
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  • /Portals/1/images/Magazines/2012/1212/B_1212_AHU4.jpg

    Continuous system monitoring provides a fault history and a view of performance over time, allowing you to develop a control strategy. The tower fan speed graph also shows short cycling. The control loop could be adjusted to match water temperature to fan speed.
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Some people make things happen, some watch what happens, and some wonder what happened.

If you want to create efficiencies in your air handling units (AHUs), keep on reading. A proactive approach to your air handlers can pay off with significant savings.

My facility, a 121,000-square-foot university building in Texas, was opened in 2005. It is equipped with dual-duct AHUs (see diagram). The dampers in the outside air duct and return air duct are controlled by the CO2 setpoint. The fan is controlled by the static pressure in the downstream ducts. The outside-air setpoint operates the valves to the preheat and precool coils. The hot deck setpoint and the cold deck setpoint operate, respectively, the water valves to the hot deck coil and the cold deck coil.

The dual-duct air handlers take 180 degree F. and 42 degree F. water and supply 100 degree F. hot air and 55 degree F. cool air through duct work to a terminal box. The terminal box adjusts the hot and cold dampers to provide sufficient air to reach a room thermostat setpoint.

The most sophisticated part of this facility’s system monitors the terminal box dampers, the room setpoint, and the room temperature. If the room damper exceeds 90%, then the controls lower the AHU supply temperature a few degrees. If this isn’t sufficient, then the AHU static pressure is increased.

Only four water valves, two dampers, and the fan speed can be controlled on the AHUs, but much can be done with them. My main strategy is to operate the system with the least energy while maintaining the warmest room at a maximum of 74 degrees F. The following suggestions assume that your system has digital controls with the ability to change setpoints based on demand and outside air temperature (OAT).


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Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.


Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.


When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.

Add highly responsive multi-zone comfort to any building project, in any climate. Our CITY MULTI H2i R2- and Y-Series VRF systems give you flexibility to fit the needs of any building. Enjoy 100% heating capacity at 0°F outdoor ambient, and 85% heating capacity at -13°F outdoor ambient.  For more information, log on to www.mitsubishipro.com

 
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