DRAFT – your comments are welcome.

3.3.5 Infiltration

Infiltration Method

Applicability

All projects

Definition

Energy simulation programs have a variety of methods for modeling uncontrolled air leakage or infiltration.

  • Some procedures use the effective leakage area which is generally applicable for small residential scale buildings.
  • The component leakage method requires the user to specify the average leakage through the building envelope per unit area (ft²). The component leakage area is applied to gross area of exterior walls, roofs, and exposed floors, but slabs on grade and interior partitions are excluded.
  • Other methods such as air changes per hour (ACH) require the specification of a maximum rate, which is modified by a schedule

Units

List: effective leakage area, component leakage, air changes per hour, or other method supported by the energy analysis software.

Input Restrictions

The default method is the component leakage method; however, there are no restrictions on other reasonable methods.

Baseline Rules

The infiltration method used for the baseline building shall be the same as that used for the proposed design. 

 

Infiltration Data

Applicability

All projects

Definition

Information needed to characterize the infiltration rate in buildings. The required information will depend on the infiltration method selected above. For the effective leakage area method, typical inputs are leakage per exterior surface area in ft² or other suitable units and information to indicate the height of the building and how shielded the site is from wind pressures. The air-changes per hour (ACH) method requires an estimate of the ACH and a schedule which modifies the ACH for various periods during the year. Similar data would be specified for the leakage per component area method. Only zones with exterior wall area are assumed to be subject to infiltration.

Units

A data structure is required to define the effective leakage area model, while a single numeric value can define the ACH or the leakage per area of exterior envelope method.

Input Restrictions

Any reasonable inputs may be specified, consistent with the chosen infiltration modeling method. Acceptable ranges for inputs should be defined for each method supported by rating software. Default is 0.38 cfm/ft² of exterior wall. 

Baseline Rules

The infiltration data for the baseline building shall be the same as the proposed design unless the proposed design employs specific measures that go beyond the mandatory measures specified by the baseline standard. When credit is taken for reductions in infiltration (see above), test results or research reports shall be provided that document and support the inputs used for the baseline building and the proposed design.

 

Infiltration Schedule

Applicability

When an infiltration method is used that requires the specification of a schedule

Definition

With the ACH method and other methods (see above), it may be necessary to specify a schedule that modifies the infiltration rate for each hour or time step of the simulation. Typically the schedule is either on or off, but can also be fractional.

Units

Data structure: schedule, fractional

Input Restrictions

The default infiltration schedule is 1.0 (100% of specified infiltration rate for periods of time when the fans serving the thermal block are not operating and a 0.25 for periods of time when the fans are operating. This is based on the assumption that when the fan system is on, the pressure of the interior space above the pressure of the exterior infiltration of outside air is reduced.  When the fan system is off, interior pressure drops below exterior pressure and infiltration increases.

Baseline Rules

The infiltration schedule for the baseline building shall be the same as the proposed design.