Superimposed on the fresh air requirement it may be advantageous to add ventilation for cooling purposes (that is, when rooms get warm). There are 3 valid ways to do this in VE Compliance.
1. Using ‘Natural ventilation’ air exchanges controlled by formula profiles.
2. Using the ‘free cooling’ option.
3. Using ApacheHVAC.
These mechanisms will apply in a similar way in the ‘real’ and actual buildings.
When natural ventilation (option 1) is used the air flows specified should be limited to the additional ventilation required for cooling.
Option 3 (free cooling) provides a simple way to introduce additional air for cooling purposes. The additional air will be brought in, subject to a given maximum (typically 5ach) and only if appropriate (ie outside temperature is less than inside) when the room temperature reaches the cooling set point. This applies whether or not there is air conditioning in the room. If there is no air conditioning, the free cooling represents an idealised form of natural ventilation, introducing just enough air to hold the room temperature at the set point. If there is air conditioning, the free cooling represents an idealised form of fresh air optimisation. The notional building assumes up to 5 ach of free cooling ventilation for naturally ventilated rooms Free cooling is recommended as a quick way to model natural ventilation, and for all types of simulation, not just VE Compliance runs.
Option 4 (ApacheHVAC) introduces additional complications in relation to fresh air requirement and should be undertaken only with considerable care. Ventilation profiles for the ApacheHVAC model must be set in such a way as to mimic the ventilation profiles in the standard NCM activities. The same also applies to plant operation profiles. These constraints mean that if this route is adopted it will almost certainly be necessary to create a special version of the ApacheHVAC system for the compliance simulation.
