VAV maximum and minimum airflow setting

[orator]

A space require supply air of 500l/s and its outdoor air requirement is 450l/s. If a VAV box is used for this space then maximum supply air setting of a VAV box is 500l/s and minimum airflow is set at 450l/s. How good is it to provide a VAV box with electric reheat coils in this case? The minimum airflow required to energize electric reheat coil is 450l/s in this case which is very close to 500l/s. please advice.

 

[cdxx139]

MAX = 500 l/s = 1060 CFM
MIN = 450 l/s = 950 CFM

You may have a high occupancy space? If so, add CO2 control. Then lower VAV MIN to meet heating load, or as low as 1/3 box max, whichever is greater.

knowledge is power

 

[orator]

Thanks cdxx139. Yes it is high occupancy space. I am not adding co2 control because the system is already provided with energy recovery heat pipe and co2 is not required in this case as per ashrae 90.1. Any suggestions..

 

[EnergyProfessional]

Adding zonal CO@ control like cdxx suggested likely is the only option you have. You may add a motion sensor to stop ventilation when room is unoccupied. but that doesn't hep you when only one person is in that room.

 

[Adnan86]

Cdxx /Energyprofessional, what if we schedule the occupancy (time when the zone is occupied) and switch off the ventilation for unoccupied time period. Is this correct according to Ashrae 62.1?

 

[EnergyProfessional]

scheduling is a good idea if you can predict occupancy, like in an office.
typically we add zonal motion sensor to bring the zones in a "standby" with wider deadband and no minimum flow. Because you can't predict when people leave their office, meeting room or come in later.

 

[317069]

if you are ok with running the electric heater at 450 l/s, what is the problem if it runs at 500 l/s.?
how would your control work in case VAV in minimum and your space does not need heating.?