28 FEBRUARY 2003
It is often useful to calculate the behavior of the proposed system at "most
common" conditions and assess these calculations in addition to the traditional peak
design calculations. This will help ensure that the selected equipment and controls are
capable of modulation and control at all points of operation rather than simply at
DATA SET PAGE 4: PSYCHROMETRIC DISPLAY OF DESIGN VALUES.
Figure 2-4 is an example of Data Set Page 4, a psychometric display of the site's
Similar to Data Set Page 3, this chart depicts the saturation curve (when
RH = 100%) along with peak design values. The design values are calculated as in the
table on Data Set Page 1 (Figure 2-1), but this chart shows their relationships
graphically, depicting their position relative to each other and relative to the saturation
Above and to the left of the saturation curve, RH would be greater than
100% (not possible). The area below and to the right of the curve (including the points
on the curve itself) represent the area where RH is less than or equal to
100%, and thus where all observations occur. Note that since the humidity ratio is a
function of pressure, and pressure varies with elevation, different sites will have
different saturation curves.
The dry bulb temperature is the horizontal coordinate on this scatter plot,
and the humidity ratio is the vertical coordinate. Peak design values are depicted by the
red square (1.0% Temperature [dry bulb]), the green circle (1.0% Humidity Ratio), and
the blue diamond (99% Temperature [dry bulb]).
The table below the chart shows the exact values of 99% dry bulb
temperature, 1.0% humidity ratio, and 1.0% dry bulb temperature, along with calculated
values of enthalpy, mean coincident wet bulb temperature, and humidity ratio (as
applicable). The value of enthalpy coincident to each temperature/humidity ratio is
created using the psychrometric functions provided by the Linric Company, Bedford,
New Hampshire. The dry bulb temperature and humidity ratio are used to calculate
enthalpy using the Linric algorithms.