Knowledgebase
Guidance on NCM HVAC System Type selection
Posted by Andrew Bairstow on 02-Jul-21 09:16 PM
Guidance on NCM HVAC System Type selection

The following represents the official definitions and advice on how to select the most appropriate HVAC of the 26 HVAC system types handled by SBEM and DSM. There are four overall categories covering heating, cooling and mechanical ventilation. Note that cooling only systems are not available.

The System type selected in the General sub-tab automatically brings with it some assumptions. For example, whether mechanical ventilation is an integral part of the system and the degree of local time and temperature control that is (or can be) provided. The majority of system types used in UK buildings can be found in the system type drop-down box. However, there are a few systems which require further guidance, such as:

VRF with natural ventilation - Select 'Split or multi-split system with natural ventilation', and then adjust the efficiencies in the Heating and Cooling sub-tabs to values suitable for the VRF.

Chilled Ceilings

If 'Chilled ceiling' is selected, the default assumption is that there is displacement ventilation.

Chilled ceiling with no mechanical ventilation - select 'Chilled ceilings or passive chilled beams and displacement ventilation', and then set the specific fan power to zero.

Chilled ceiling with mixing ventilation - select 'Chilled ceilings or passive chilled beams and displacement ventilation', and then use twice the actual specific fan power in  order to capture the effect of the higher ventilation rate.

Mixed Air/Destratification
If your HVAC system is a high velocity forced-convection warm air heater, which does the job of mixing the air in the zone similar to destratification fans, then you can model this in iSBEM by first selecting the appropriate HVAC system type (flued or unflued) and then ticking the box related to destratification fans in the zones served by that system. You will then need to justify this to Building Control using the necessary documentation for your system's functions.