RE: HVAC Systems - Zones

Shane Regan — Tue, 11 Apr 2017 14:44:09 GMT

Hi Matt,

I would firstly advise caution if you are intending to use Part L to determine if natural ventilation is required, as SBEM is not a design tool indicative of real-world conditions. (To see if natural ventilation is required you would need to use design tools such as CIBSE Gain, or if a more in-depth analysis of openable-windows is required then you would need to use Hevacomp Simulator).

In Part L, the mixed mode option would indeed be selected in the event of natural ventilation, however the final say on the HVAC type would need to come from your Assessor Scheme provider. The below info from the iSBEM manual may be of assistance with your selection:

HVAC system uses a mixed-mode cooling operation.
NB: “Mixed-mode” refers to a hybrid approach to space conditioning that uses a combination of
natural ventilation from operable windows, and mechanical systems that include air distribution
equipment and refrigeration equipment for cooling. A mixed-mode building integrates the use of
air-conditioning when and where it is necessary, with the use of natural ventilation whenever it is
feasible or desirable, to maximize comfort while reducing the energy use (compared to yearround
air conditioning).

I hope the above helps to clarify, if you need anything else please let us know.