Welcome to EnergyWise Roof Calculator
EnergyWise Roof Calculator Online is a Web-based application that provides a graphical
method of constructing roof assemblies to evaluate thermal performance and estimated
energy costs under normal operating conditions.
The information contained in this application is based in part on the provisions
contained in the American Society of Heating, Refrigerating and Air Conditioning
Engineers (ASHRAE) Fundamentals Handbook and ASHRAE Standard 90.1, "Energy Standard
for Buildings Except Low-rise Residential Buildings," versions 1999(2001), 2004
and 2007.
With ASHRAE 90.1, designers can demonstrate building envelope compliance using the
following methods:
Energy Cost Budget Method—Designers determine the "design energy cost"
and illustrate it does not exceed the "energy cost budget."
Prescriptive Method—Building components (e.g., envelope, HVAC, power,
lighting) have to meet the minimum requirements set forth in ASHRAE 90.1. Under
the prescriptive method, designers have two options:
Building Trade-off Option—The envelope performance factor of the "proposed"
building is less than or equal to the envelope performance factor of the "budget"
building.
Prescriptive Building Envelope Option—Roof assemblies shall meet a maximum
U-factor and minimum insulation R-value as specified in ASHRAE 90.1. This option
only can be used if the skylight fenestration area doesn't exceed 5 percent of the
gross roof area.
EnergyWise Roof Calculator Online is based on the Prescriptive Building Envelope
Option. For more specific details and information, refer to the appropriate version
of ASHRAE Standard 90.1. To purchase a copy, go to http://www.ashrae.org.
Because this application is intended to be a simplified guide, complex energy calculations,
such as solar heat gain and exterior shading considerations, have intentionally
not been included. For complex energy evaluation calculations, including evaluations
of the entire building envelope, building usage, or changes to heating and air-conditioning
equipment, consult the ASHRAE Fundamentals Handbook or an experienced mechanical
engineer.
This application determines "Annual Energy Cost" values which is useful when comparing
the energy costs and savings associated with various roof assemblies' designs. This
value should not be confused with the building owner's overall energy costs, which
in most instances will be somewhat larger than the "Annual Energy Cost" that is
attributable to the roof assembly only.
For a detailed financial analysis of the long-term costs and potential savings of
an energy-efficient roof system, consult an experienced accountant.