Infiltration Heat Loss Building

Reference data and engineering information about infiltration heat loss building for hvac systems applications.

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Overview

Engineering reference data for Infiltration Heat Loss Building in HVAC systems.

Key Formulas

Sensible Heat

$Q = \dot{m} c_p \Delta T$

Heat causing temperature change.

Latent Heat

$Q = \dot{m} h_{fg} \Delta\omega$

Heat causing moisture change.

COP (Cooling)

$COP = Q_c / W$

Coefficient of performance.

Variables

Symbol	Description	Unit
$Q$	Heat transfer	W
$\dot{m}$	Mass flow rate	kg/s
$c_p$	Specific heat of air	J/(kg·K)
$\Delta T$	Temperature difference	K

Infiltration Rates by Wall Construction

The following table provides measured infiltration rates through various wall types at different wind velocities. These rates are critical for estimating the volume of unconditioned air entering a building through cracks and gaps in the building envelope.

5 rows

Infiltration rates through various wall constructions based on exterior wind velocity.
Wall Type	Infiltration Rate @ 5 mph(ft³/ft crack·hr)	Infiltration Rate @ 10 mph(ft³/ft crack·hr)	Infiltration Rate @ 15 mph(ft³/ft crack·hr)	Infiltration Rate @ 20 mph(ft³/ft crack·hr)	Infiltration Rate @ 25 mph(ft³/ft crack·hr)	Infiltration Rate @ 30 mph(ft³/ft crack·hr)
Frame Wall with lath & plaster or wallboard	0.03	0.07	0.13	0.18	0.23	0.26
Brick Wall, 8 1/2" plain	2	4	8	12	19	23
Brick Wall, 8 1/2" plain with plaster or wallboard	0.02	0.04	0.07	0.11	0.16	0.24
Brick Wall, 13" plain	1	4	7	12	16	21
Brick Wall, 13" plain with plaster or wallboard	0.01	0.01	0.03	0.04	0.07	0.1

Source: engineeringtoolbox.com

Key Formula for Infiltration Heat Loss

The total infiltration heat loss ( $Q_{inf}$ ) for a building can be estimated using the air change method. This formula links the infiltration air volume to the sensible heating load.

$Q_{inf} = 1.08 \times CFM \times \Delta T$

Where:

$Q_{inf}$ is the infiltration heat loss (Btu/hr).
$CFM$ is the infiltration airflow rate in cubic feet per minute.
$\Delta T$ is the temperature difference between inside and outside air (°F).
$1.08$ is the volumetric heat capacity of air (Btu·min/ft³·hr·°F).

The $CFM$ can be determined from building infiltration rates and air change data, such as the values provided in the table above.

Building Types and Infiltration Characteristics

Infiltration rates and their impact on heat loss vary significantly based on building type and use. Common building categories referenced in infiltration analysis include:

Offices, apartments, hotels
Entrance halls and vestibules
Industrial buildings
Houses
Public buildings

Each category has different exposure levels (e.g., frequency of door operation, construction standards) that influence the overall infiltration air change rate.

Key Definitions

Air Change Rate: A measure of the volume of air added to a space divided by the volume of the space per unit of time, often expressed in air changes per hour (ACH). It is used to estimate total infiltration.
Infiltration Rate: The volumetric flow rate of outdoor air entering a building through unintentional leakage paths (cracks, joints, etc.) in the building envelope, often measured in cubic feet per minute (CFM) or cubic feet per hour per linear foot of crack.