Guidance on NCM HVAC System Type selection

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.

Sorting systems

The following table list includes the full SBEM description along with the assumptions made in SBEM concerning fixed and editable settings. These may help you to narrow down the most applicable system type to assign

• Cooling. Note all systems provide Heating, this cannot be removed but the activity heating setpoint may generate zero or minimal heat demand
• Ventilation can be Central (and mechanical), Local (either natural or Mechanical) or a mix of both.
• Pumps indicate if pumps (LTHW plus CHW for systems supplying cooling) are assumed for the system. Variable Speed indicates that this is an option for the type of system.
• Integral Fans. Some systems may include an integral fan