Simple Fan System
by S. Gabel and M. J. Brandemuehl
Revised for TRNSYS by N. Blair and R. Schwarz
This model was adapted strictly for use with the TRNSYS Program
by the Solar Energy Laboratory.
The algorithm calculates fan power and leaving air temperature and
humidity for a given flow rate and entering air conditions. The algorithm is
designed for use with system energy calculations for which the pressure rise
across the fan is constant. The assumption of constant fan pressure rise is
tantamount to assuming fixed supply air duct static pressure, which is common
in many standard HVAC systems. Fan design is characterized by the full load
power and volumetric airflow rate at a rating condition. Fan power consumption
at part-load is determined by an empirical relationship as a function of the
ratio of operating airflow to rated airflow. The coefficients for the empirical
fit are available for three methods of flow control: discharge dampers, inlet
vanes or variable speed drive. The pressure rise across the fan is not
calculated. The air temp. rise is calculated to account for shaft and motor
power input. Note that the algorithm will correctly calculate inlet air
conditions given outlet air conditions by specifying a negative airflow rate,
assuming that there is negligible change in air density across the fan.
Sample input and output included in source code.
Ref:A Toolkit for Secondary HVAC System Energy Calculations May 25, 1992
Joint Center for Energy Management Univ. of Colorado at Boulder