first by VFd i suppose you mean a fan with a VFd. the outside air flow rate is controlled by two signals, one from the outside air temperature sensor, and one from the indoor air quality, in the applications where the air changes per hour for the fresh air is to be maintained, then these two signals are treated somehow in the DDC, and the output signals is sent to motorized volume dampers which will control the fresh air flow.
This exactly what called economizer !!
but i want to ask something!! why do you want to keep a constant fresh air flow while the supply air is varying due to the partial load ?!?
i think you dont have to maintain the fresh air quantity !!! all you need is to keep the fresh air flow to the supply air flow ratio constant.
sure with a minimum fresh air quantity needed for comfort operation
شكرا رائد على الرد,
ردى على سؤالك: المالك فى هذا المشروع مهتم بمعدل تغيير الهواء النقى , اضافة الى ذلك الا ترى انه من المفروض المحافظة على كمية الهواء النقى الداخل للمنطقة خصوصا ان تصميم كمية الفريش للماكينة يعتبر اقل كمية هواء فريش فقط حتى يقلل الاحمال
it was client requirement to maintain the air change ( fresh air ACH ) ,in addition to that
dont you think we should maintain the fresh air quantity as we have already designed the AHU for the least allowable fresh
air ( as per 62.1)
so for example if we are in winter and the AHU is at part load ( lets say 30 %) the fresh air introduced to the space will by less than one third of that value the space is designed to