MechEng
you are right, but I have some points:
- How much percentage the VFD usually modulate of the nominal cfm?
- For the fresh air at normal operation, if the CO2 is under 600ppm (say 200ppm), what is the fresh air damper position would be (fully closed or partial open)?
- if all VAV boxes are 100% open,supply air fan in its nominal cfm (say 1000 cfm), return air fan modulate to keep a desired space pressure(say 900 cfm for sensor reading of 0.05" Wg),
fresh air (say 100 cfm), Co2 is under 600ppm,
Now,for some reason the Co2 became over 600ppm, how the control will respond to this situation to keep CO2 level.
- same question above, but the supply fan is not in its nominal cfm,I mean it will change either increase or decrease.
- VAV system is an instant CV system. I mean the CV unit give you 1000 cfm all the time, the VAV gives you 400, 500, ... up to 1000 cfm,depend on the conditions, but when it works on 500 cfm, it act like CV unit as long as there is no change in work conditions.
- if you have CV or VAV system with a return fan I don't think you will have an exhaust fan to kick on/off.