Innovative Energy Engineering



Doors

Doors allow persons, goods and vehicles to enter and exit the building. Their size, number and location are determined by function and egress requirements (code). Since doors are operating, they rely on seals that wear out, to prevent infiltration when the door is closed. When a door is open, infiltration is very high depending on wind and temperature difference. For design one can assume a velocity (often 0.25 m/s - 50 fpm). In addition doors have large thermal bridges. Because of this, the HVAC load due to doors is significant.

Frames and the doors have to be structurally stable they experience abuse. The required aluminum and steel should be thermally broken. Any glazing shall have a very low U-value. Air locks or vestibules can reduce infiltration. Keep in mind, even this top-of-the line door still has a U-value of 0.5 W/K-m² (0.29 Btu/°F-ft²). However, this is a great improvement compared to standard insulated doors that may have U-values of 1 W/K-m² (0.6 Btu/°F-ft²). In spaces designed for neutral pressure to outside, air curtain may reduce infiltration. the energy for the air curtain fans needs to be weighed against saved heating or cooling energy.

Infiltration through open Doors

For estimating infiltration through open doors, assume 0.25 m/s (50 fpm). Adjust for the % of time the door is open at the design time. Frequently used doors may be open half of the time during business hours, a side entrance may only be open for a minute every hour. This requires some judgement. Some designers just assume the space with doors to have an infiltration of 0.5 ACH, which does not account for different sized doors in relation to the volume of the space and the time a door may be open. Whichever method is chosen, it should take into account the actual opening size and the estimated time it is open.

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