WINDOW 5.2 is a publicly available computer program for calculating
total window thermal performance indices (i.e. U-values, solar heat
gain coefficients, shading coefficients, and visible transmittances).
WINDOW 5.2 provides a versatile heat transfer analysis method consistent
with the updated rating procedure developed by the National Fenestration
Rating Council (NFRC) that is consistent with the ISO 15099 standard.
The program can be used to design and develop new products, to assist
educators in teaching heat transfer through windows, and to help
public officials in developing building energy codes
THERM-Two-Dimensional Building Heat-Transfer
THERM is a state-of-the-art, Microsoft WindowsT-based computer
program developed at Lawrence Berkeley National Laboratory (LBNL)
for use by building component manufacturers, engineers, educators,
students, architects, and others interested in heat transfer. Using
THERM, you can model two-dimensional heat-transfer effects in building
components such as windows, walls, foundations, roofs, and doors;
appliances; and other products where thermal bridges are of concern.
THERM's heat-transfer analysis allows you to evaluate a product's
energy efficiency and local temperature patterns, which may relate
directly to problems with condensation, moisture damage, and structural
THERM's two-dimensional conduction heat-transfer analysis is based
on the finite-element method, which can model the complicated geometries
of building products
THERM is a module of the WINDOW+5 program under development by
LBNL. WINDOW+5 is the next generation of the WINDOW software series
and is being developed for the Microsoft WindowsT operating environment.
THERM's results can be used with WINDOW's center-of-glass optical
and thermal models to determine total window product U-factors and
Solar Heat Gain Coefficients. These values can be used, in turn,
with the RESFEN program, which calculates total annual energy requirements
in typical residences throughout the United States.
Optics5.2 allows the user to view and modify glazing data in many
new and powerful ways. Optical and radiative properties of glazing
materials are primary inputs for determination of energy performance
in buildings. Properties of composite systems such as flexible films
applied to rigid glazing and laminated glazing can be predicted
from measurements on isolated components in air or other gas. Properties
of a series of structures can be generated from those of a base
structure. For example, the measured properties of a coated or uncoated
substrate can be extended to a range of available substrate thickness
without the need to measure each thickness. Similarly, a coating
type could be transferred by calculation to any other substrate.
Today's energy-efficient windows can dramatically lower the heating
and cooling costs associated with windows while increasing occupant
comfort and minimizing window surface condensation problems. However,
consumers are often confused about how to pick the most efficient
window for a residence. Product information typically offers window
properties: U-factors or R-values, Solar Heat Gain Coefficients or
Shading Coefficients, and air leakage rates. However, the relative
importance of these properties depends on site- and building-specific
conditions. Furthermore, these properties are based on static evaluation
conditions that are very different from the real situation a window
will be used in.
A computer tool such as RESFEN can help consumers and builders
pick the most energy-efficient and cost-effective window for a given
application, whether it is a new home, an addition, or a window
replacement. It calculates heating and cooling energy use and associated
costs as well as peak heating and cooling demand for specific window
products. Users define a specific "scenario" by specifying
house type (single-story or two-story), geographic location, orientation,
electricity and gas cost, and building configuration details (such
as wall, floor, and HVAC system type). Users also specify size,
shading, and thermal properties of the window they wish to investigate.
The thermal properties that RESFEN requires are: U-factor, Solar
Heat Gain Coefficient, and air leakage rate. RESFEN calculates the
energy and cost implications of the window compared to an insulated
wall. The relative energy and cost impacts of two different windows
can be compared.
Online Glass performance Calculator