Minimum outside air on VAV

[remp]

Hello,

Does anyone have a genuine control strategy to control and maintain minimum outside air on a VAV system?

Thanks!

 

[urgross]

Having a separate minimum outside air and variable air louver seems to have worked best for me, and is a lot easier on TAB contractors.

 

[SAK9]

Use a dedicated injection fan

 

[willard3]

A dedicated injection fan.

 

[EnergyProfessional]

you can use OA reset with a CO2 sensor in return.
Even better would be to use an ERV for ventilation, that would equal the above injection fan.

 

[317069]

Consult the rooftop manufacturer, they have the best knowledge of their product and product control.

 

[BronYrAur]

Are you asking about ensuring the minimum OA gets into the air handler, or that the min OA reaches each individual space served by a VAV box?

 

[Ziggypump]

The ventilation calculations have a very good hold on this question. 62MZCalc, while a little difficult to initially understand, does a fabulous job in illustrating the amount of outside air at the design condition. And the International codes follow the same path, with differing equations to a point.

My main question would be, can you supply 30% of air to the space for heating (see ASHRAE 90.1) and still maintain the minimum outside air required?

 

[lilliput1]

Have the VAV return fan track the VAV supply air fan with constant differential equal to the minimum OA CFM. You need airflow measuring station at the supply & at the return. Consider Air Monitor airflow measuring stations at each fan inlet.

 

[Drazen]

Calculation is more important and more complex than control strategy. You have to size VAV units to both provide cooling and fresh air in all conditions, including minimum load conditions.

 

[GMcD]

There was similar information discussed and referenced in this discussion:

http://www.eng-tips.com/viewthread.cfm?qid=408480