Correct HVAC multiplex setup

[mshaynes1992]

I have a couple of questions related to proper system setup and multiplexing.


1. Concerning floor SA and ceiling RA plenums serving multiple zones (all zones on a system), the ApHVAC user guide C (section 3.2.4) instructs the user to add those zones to their respective components on each multiplex layer (i.e. Supply plenum 1 serving zones 1-10 on each UFAD plenum component in the multiplex).

Is there any reason why this plenum component cant be placed outside, upstream of the multiplex layers in the system, and the return plenum placed downstream of the multiplex layers instead of the guide’s recommendations?

2. The same section in the ApHVAC user guide has an example showing a restroom receiving transfer air from an adjacent space, where the restroom is on the same layer as the zone supplying the TA, on a diverging branch immediately downstream of the space. The restroom is upstream of the exhaust fan on the same branch serving the restroom.

It was my understanding based on the transfer air loop default placement in the prototype VAV systems, that restrooms receiving transfer air are placed on their own multiplex layer in the normal zone component, and the transfer air/makeup air source/values are specified in the zone airflow settings dialogs. Which would be the correct way of modelling transfer air to a restroom for make-up, if all supply air to the space is from transfer air?

3. Finally, I have a system that is designed with OA/SA supplied to a handful of zones, and is the only source of SA for those zones, but also delivers SA to an IT equipment room to provide the ventilation air requirement. The majority of the IT equipment room’s cooling load is served by CRAC units though.

Is it possible or preferable to model the system under one modified prototype system, with additional components added to represent the CRAC units, or to model the system as two prototype systems – either completely independent of each other, or similar to prototype system 7i (multi-AHU system with common DOAS)?