Constant volume ventilation system

[Explorer]

Hi everyone!!

I am having a doubt on IES and was wandering whether anybody can provide help.

I need to model an office which uses a constant volume ventilation system. The air is supplied from the floor at about 18 C and extracted from the ceiling. My idea was to model the system as "Constant Volume System (fixed fresh air rate)”, which will be fed by a LTHW gas fired boiler. The cooling/ventilation system will be the modelled as "Centralised balanced A/C" with heat recovery.

My doubt is whether this system is representative? Does it assumes that air will be supplied from the ceiling? And at which temperature?

Any advice will be more than appreciated.

[Nick]

Hey, I haven't done any underfloor applications myself, though I know the people at IES have. The example I saw involved using some of the CFD tools to model the under floor velocities and stratification, from an energy balance standpoint I'm not sure if there is a difference between ceiling diffusers and underfloor air distribution in the apache dynamic sim, that is without running a Macro or Micro flow and linking the results to the simulation. But I would be interested to hear how this is done if someone would like to chime in!

[Complex Potential]

I am assuming you are talking about a compliance model, in which case...

A constant volume system should only be applied for true air conditioning where the room is being held to a cooling setpoint, the central air rates have been sized on the peak cooling load and the off coil temperature can drop sufficiently to deal with it when needed. If all you are doing is providing the air at 18C at a lower rate (min fresh air perhaps?) then I would argue that a constant volume system is inappropriate and will penalise you heavily on the aux energy side.

If it is basically min fresh air you should probably model it as a heating only radiators and mechanical ventilation since the NCM modelling guide stipulates that fresh air should be modelled as being brought in at outside condition.

CP