DRAFT – your comments are welcome.

3.2.4 Building Site Characteristics

Orientation

Applicability

All projects

Definition

The building orientation

Units

0-360 azimuth

Input Restrictions

As designed

Baseline Rules

The baseline building performance shall be generated by simulating the building with its actual orientation and again after rotating the entire building 90, 180, and 270 degrees, then averaging the results. The building shall be modeled so that it does not shade itself.

Exceptions:

a.   If it can be demonstrated to the satisfaction of the rating authority that the building orientation is dictated by site considerations.

b.   Buildings where the vertical fenestration area on each orientation varies by less than 5%.

NOTE: Exception ‘a’ would need a flag on the UI and if checked, it would need to be supported through documentation.

 

Shading of Building Site

Applicability

All projects

Definition

Shading of building fenestration, roofs, or walls by other structures, surrounding terrain, vegetation, and the building itself

Units

Data structure

Input Restrictions

The default is for the site to be unshaded. The user may input the necessary information to model shading of the building site by permanent objects or features likely to significantly reduce incident solar loads on the building site. “Permanent” here means likely to remain for the life of the building or likely to be replaced by objects that will produce similar shading over the life of the building.

All shading elements shall be modeled that have a height greater than their distance from the building and width facing the proposed design greater than one third of the building width. Smaller shading elements can be modeled at the discretion of the energy modeler.

Baseline Rules

The proposed and baseline building designs are modeled with identical assumptions regarding shading of the building site.

 

Local Terrain

Applicability

All projects

Definition

An indication of how the local terrain shields the building from the prevailing wind. Estimates of this effect are provided in the ASHRAE Handbook of Fundamentals.

Units

Choose from the following list

Description

Exponent (a)

Boundary layer thickness, d (m)

Flat, open country

0.14

270

Rough, wooded country, Suburbs

0.22

370

Towns and cities

0.33

460

Ocean

0.10

210

Urban, industrial, forest

0.22

370

Adjustments for local terrain should be made in accordance with the ASHRAE HOF.

Input Restrictions

The default is “Towns and cities”.  

Baseline Rules

The baseline building local terrain should be the same as the proposed design.