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Laboratory Exhaust Fan Bypass Air for Stack Velocity

asked 6 years ago

updated 6 years ago

I am wondering how I might model a common laboratory exhaust fan system in EnergyPlus and or OpenStudio. The term exhaust fan generally means a fan dedicated to a thermal zone or a system and it exhausts air from those components, maintaining a mass balance etc.

In large laboratories, an exhaust fan might actually only exhaust some of the buildings airflow and makeup or bypass and blend in outside air. The goals of the exhaust fan system is to maintain a minimum effluent discharge velocity or plume height. Therefore the fan system has a minimum volumetric flow (cfm) must pass through the fan. To maintain this minimum cfm, a bypass air damper is provided with the exhaust fan system to bleed unconditioned air to mix with the reduced lab exhaust volume. This allows the exhaust fan to maintain the desired discharge velocity.

My question is how I could even go about doing this in an energy model. I have a fairly good understanding of how the air-node networks and systems in energyplus are setup and I cannot seem to think of a way this could be done, outside of creating a completely DEDICATED zone and system to the exhaust fan system.

This article has a great example image of what I described here as well: http://www.greenheck.com/library/arti...

Any input would be much appreciated. Thanks.

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answered 6 years ago

If I am following correctly, the bypass air only affects the exhaust fan power consumption; it has no impact on the zones and/or system. I would use an EMS program with a sensor on the exhaust fan inlet node volume flow rate and an actuator on the exhaust fan "Fan Pressure Rise". Since the fan power is proportional to the pressure rise, then the EMS program can adjust that anytime that the node flow rate is below the minimum.

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Asked: 6 years ago

Seen: 530 times

Last updated: Jul 19 '18