Variable Flow Controller
by T.B. Jekel
This controller determines either the optimum fraction of flow to
be sent through the coil, or the fraction given a constant coil outlet
temperature when subject to changing loads was developed. A curve fit of
the saturation line on the psychrometric chart (enthalpy and humidity
ratio), the space set-point temperature and humidity, and the SHR are used
with Newton's method to predict the saturation temperature at which the
load line intersects the saturation line. The optimum fraction of flow
rate through the coil is calculated using the saturation temperature and
humidity ratio (coil outlet state), set-point temperature and humidity
ratio, and the circulation flow rate of air through the system. The inputs
to the controller are the space set-point temperature, humidity ratio, and
enthalpy, the space load and sensible heat ratio, and the circulation flow
rate. Also, if the performance with a constant coil operating temperature
is desired, the outlet coil temperature must be input, and if the optimum
performance is desired, the convergence tolerance used in Newton's method
must be input. The coil outlet state was assumed to be saturated at the
outlet temperature because in order to take into account the bypass
fraction, the inlet state of the A/C coil is needed and this significantly
complicates the calculations. Output from the controller is the fraction
of the total flow that should be sent through the coil and the temperature
of the outlet air from the air-conditioner coil.
REF: T.B. Jekel "Modeling of Ice-Storage Systems"
Masters Thesis 1991 University of Wisconsin at Madison