Data on this tab is partly taken from the NCM template and partly user-supplied. The rules are as follows.
The NCM activity specifies a minimum ventilation regime for the activity in terms of a flow rate and a profile. This appears as an air exchange of type Auxiliary Ventilation, taken from the NCM template. The NCM minimum ventilation regime applies to all heated and occupied rooms, whether air conditioned, mechanically ventilated or naturally ventilated.
Auxiliary ventilation assigned to the room by the user in other Views (via the room template or room-specific assignments) is automatically removed. This is to avoid a double-specification of minimum ventilation requirements.
Infiltration is also subject to a special treatment in VE Compliance, being derived from permeability and other parameters specified in the Building & System Data dialog.
Further guidance on ventilation settings in VE Compliance simulations is provided in Appendix A.
Infiltration
Infiltration is specified by parameters and methods set on the ‘Building Details’ tab of the Building & System Data dialog.
Fresh air requirement
This is the minimum level of ventilation (sourced from outside air) required by occupants.
Fresh air requirement is a function of occupancy and is typically calculated on the basis of 8 l/s/person. It applies all year round during the occupancy hours.
In the ‘real building’ (the model for non-compliance simulations, as presented in the Apache module and in the Room Template) the fresh air requirement should be set using either ‘System outside air supply’ (Room Data ‘System’ tab) or ‘Auxiliary ventilation’ (Room Data ‘Air Exchange’ tab).
Fresh air requirement applies to all types of conditioning (A/C, mech vent and nat vent). In the case of natural ventilation the implication is that it is achieved by window opening or trickle vents. Using MacroFlo for this is not recommended because of the complications this gives rise to in VE Compliance.
For Scotland Section 6 (2022), all user-specified settings for ‘System outside air supply’ and ‘Auxiliary ventilation’ are turned off and replaced by standard values and schedules appropriate to the relevant NCM activities and associated occupancy levels. Note that occupancy levels will in general be different in the ‘real’ and actual buildings, so the fresh air requirements will also be different.
Cooling ventilation
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.
