Advanced Building Simulation

Simulation and uncertainty: weather predictions 61
typical weather data for simulation processes. The modeling methods introduced are
also not intended to forecast weather conditions of the type we are accustomed to
seeing on television. Rather, the model described here is intended to provide a likely
sequence of hourly weather parameters when such data are not available from any
measured source. Only statistical parameters need be available. Parameters that are
not of particular interest to building thermal loads (such as rain, snow, pollen count,
and visibility) will not be addressed. Parameters that are included in the modeling are
dry-bulb temperature, humidity (dew-point temperature), solar radiation, wind
speed, and barometric pressure.
Specifically, the modeling addresses the following parameters.
Sun–earth variables (daily):
Solar declination angle
Variation in the solar constant
Equation of time
Time of sunrise and sunset
Solar/site-related data (hourly):
Sun’s altitude and azimuth angles
Direct normal radiation
Solar radiation on horizontal surface (direct, diffuse, and total)
Sky data (daily):
Atmospheric extinction coefficient
Cloud cover fraction
Temperature data (hourly):
Dry-bulb
Dew-point
Relative humidity (from dry-bulb and dew-point temperatures)
Barometric pressure (hourly)
Wind speed (hourly)
Several statistical methodologies have been investigated for generating weather data
for thermal simulations in buildings (e.g. Adelard et al. 1999). The models and procedures
illustrated in this chapter will demonstrate but one approach developed by
the author (Degelman 1970, 1976, 1997).
3.2 Benefits of building simulation
Two systems that have strong interrelationships and that affect a major portion of
a building’s cost are the thermal envelope (roof and walls) and the air-conditioning
system. Minimizing the cost of a wall or roof system by cutting back on insulation
material is not usually the proper approach to use in minimizing the total cost of a
building. If wall and roof constructions are minimal, the heat gains and heat losses
will be larger throughout the life of a building, and the operating costs will be larger.
Experience shows that it is preferable to use more expensive wall and roof systems
to attain better insulation values, which in turn results in a savings over the life cycle
of the building.