Infiltration

Data in the infiltration form is used to specify unintentional air flows over the building envelope without having to visit each zone. The Leak area and Given additional in/exfiltration parameters of each zone are by default linked with the global Infiltration data.

Two basic methods of infiltration modeling are supported by IDA ICE: given (equal) in- and exfiltration flows and, alternatively, flows based on leak sizes, fan pressure, wind pressure and thermal buoyancy effects. The latter is default.

When wind driven flow (the latter) has been selected, leaks are automatically introduced in each external wall of each zone (not in floors or roofs). The combined sizes of all these leaks is given here as a single flow/pressure point. This data is then distributed to each zone according the Zone Distribution method, by default according to total wetted External surface area (with Overall internal Envelope area definition). However, note that the unit for leakage is different in the zone form, where leakage is instead specified in terms of Equivalent Leakage Area at 4 Pa.

It is possible to break the link to the global infiltration data from a zone and give another leakage area locally (just type in the input field). It is also possible to set the Leak area of the zone to a very small number and instead introduce "manual" leaks in specific places on the walls of the zone. Note, however, that it is not permitted to set leakage to zero. Completely air tight zones will yield a singular system matrix and the problem cannot be solved.

When instead fixed flows are specified, constant envelope air flows to and from each zone are introduced. However, small envelope "natural ventilation" leaks are also introduced to absorb pressure differences because of for example imbalances in mechanical supply and return flows.

A common problem when fixed flows are used in combination with unbalanced mechanical ventilation is that pressure difference over the envelope becomes unrealistically large. A warning for this is then issued during the simulation and the remedy is to specify larger leak areas in zones with unbalanced mechanical ventilation.