Choose your passive cooling method

In determining the appropriate method of passive cooling for a building, first we consider the two "C's"; comfort and climate.  Comfort is a combination of temperature and humidity, on the adapted psychrometric chart below, the blue lines represent dry bulb temperature and the red lines relative humidity. The blue shaded area is the ASHRAE comfort zone; between 68 and 80 degrees Fahrenheit and 20 to 80 percent humidity.

Below is a similar chart, but I have added the effective ranges for the common methods of passive cooling. We will use this chart to identify which method will work best for a given location.

Here we need to research local climate data in order to construct the hottest day of the year, this will be the design benchmark of the worst possible situation. For this we need to know the normal daily temperatures for the summer months, as well as the relative humidity throughout a typical summer day. I will use Bakersfield California as an example.Doing some web searching I can find that the daily information is thus:

We will use these numbers to graph a line representing the normal daily range of temperature and humidity for the location on our chart. Start with a point at the normal low temperature and the high humidity for each month. Place another point at the normal high temperature and the low humidity. Connect the dots for each month and you get something that looks like this.

The design condition (the solid dot on the chart) is from ASHRAE 1997 Handbook of Fundamentals. From the chart we can see that on a summer day in Bakersfield, high mass in combination with night ventilation could be an effective means of cooling a building. Evaporative cooling appears to meat the criteria, strictly speaking, however, the July and August proximity to its threshold makes it potentially less effective than High Mass/ Night Ventilation. So now, how do we figure how much mass we are going to need and how much of an effect will it have on our actual building? That lens is coming soon...