Appendix A. Ventilation in compliance simulations

This appendix provides guidance on the setting of ventilation in <VE> Compliance simulations.

 

Infiltration should normally be entered as an Infiltration air exchange (though occasionally it can be handled by MacroFlo). With the degree of air-tightness specified in the new Part L a value of 0.25 ach would be appropriate. Infiltration is carried across to <VE> Compliance for the actual building. An infiltration level of 0.25 ach is assumed for the notional building.

 

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 Apache View and in the Room Template) the fresh air requirement should be set using either ‘System outside air supply’ (Space Data ‘System’ tab) or ‘Auxiliary ventilation’ (Space 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 Part L2 (2010), 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.

 

Superimposed on the fresh air requirement it may be advantageous to add ventilation for cooling purposes (that is, when rooms get warm). There are 4 ways to do this:

5.       Using ‘Natural ventilation’ or ‘Infiltration’ air exchanges controlled by formula profiles.

6.       Using MacroFlo openings controlled by formula profiles. 

7.       Using the new ‘free cooling’ option.

8.       Using ApacheHVAC.

These mechanisms will apply in the same way in the ‘real’ and actual buildings.

Options 1 and 2 can be used in the usual way. However, it is important to bear in mind that whatever is specified here should not include the fresh air requirement – otherwise this will be assigned twice in the actual building. These mechanisms 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 (this is not spelt out in the notional building specification, but represents a reasonable assumption – without it the notional building would seriously overheat, which would tend to reduce its heating loads during subsequent hours). 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.