EN12831 Ventilation Calculation
See source code for a reference implementation of the EN12831 ventilation calculation.
Estimated air permeability rate calculated from minimum ventilation rates table 1.7 CIBSE DHDG.
| Room | Volume (m3) | External Envelope Area (m2) |
Room Temp (°C) | Minimum air change rates Nmin (h-1) |
Air Terminal Device (ATD) m3/hr |
Ventilation Heat Loss *Room* |
Ventilation Heat Loss *Zone* |
Ventilation Heat Loss *Room* No Min |
Ventilation Heat Loss *Zone* No Min |
|---|---|---|---|---|---|---|---|---|---|
| {{ room.name }} | {{ room.vent_heat_loss | number(0) }} W ({{ room.qv_room / room.volume | number(2)}}) | {{ room.vent_heat_loss_zone | number(0) }} W ({{room.qv_zone / room.volume | number(2)}}) | {{ room.vent_heat_loss_nl | number(0) }} W ({{room.qv_room_nl / room.volume | number(2)}}) | {{ room.vent_heat_loss_zone_nl | number(0) }} W ({{room.qv_zone_nl / room.volume | number(2)}}) | |||||
| Total | {{ zone.volume | number(1) }} m3 | {{ zone.envelope_area | number(1) }} m2 | {{ zone.qv_ATD_design_z | number(0) }} m3/h | {{ zone.vent_heat_loss_rooms | number(0) }} W ({{zone.qv_rooms / zone.volume | number(2)}}) | {{ zone.vent_heat_loss | number(0) }} W ({{zone.qv_zone / zone.volume | number(2)}}) | {{ zone.vent_heat_loss_rooms_nl | number(0) }} W ({{100*(1-zone.vent_heat_loss_rooms_nl / zone.vent_heat_loss_rooms) | number(2)}}%) | {{ zone.vent_heat_loss_nl | number(0) }} W ({{100*(1-zone.vent_heat_loss_nl / zone.vent_heat_loss) | number(2)}}%) |
Minimum air change rates: The MCS heat load calculator sets the minimum air change rates to values found in the CIBSE DHDG Table 3.8. Carefully studying the equations in the standard suggests this is the wrong approach. These minimum air change rates appear designed to be used as a floor for air change rates in very air-tight buildings, for normal buildings the equations that derive ventilation heat loss from the air-permeability value produce suitable results without the need for artificially high limits.
External envelope areas: The example calculation given here is a mid-terrace house, the external envelope areas do not include the party wall areas with the neighboring properties. This is consistent with how party walls are treated in the MCS heat load calculator and EN 12831 definition 6.3.3.6 but is inconsistent with the CIBSE TM23 and ISO 9972 definition of envelope area. How this is treated may change in future.
The blower door test for the example property above came to 8.4 m3/h.m2 @ 50 Pa, but this was calculated for an envelope area that included party walls (240 m2). This air-permeability rate entered above represents the same volume flow 8.4 m3/h.m2 x 240 m2 = 2016 m3/hr, but this is now divided by the smaller envelope area without the party walls of 133 m2. This results in a revised air-permeability value of 15.2 m3/h.m2.
Building vs room heat loss: Note that EN 12831-1:2017 calculates a different heat loss for rooms individually as compared to the zone as a whole. Rooms facing the wind will have cold air pushed into them. This air would then move, pre-warmed, to adjoining rooms on the other side of the building, resulting in higher heating requirements for wind-facing rooms than those on the leeward side. The latter halving reflects an averaging out of these effects across the entire building.