Victor Olgyay, in his book Design With Climate (1963), lays out a clear analytic procedure to guide the decisions necessary to create comfortable and energy efficient houses. The procedure begins with information about the range of temperature that humans consider comfortable.
This is followed by a discussion of heat gains and losses. People gain heat from metabolism, through conduction and convection, through their skin from the air temperature, and from everything around them that is warmer than their skin radiating energy toward them. People lose heat by conduction and convection through their skin to the air temperature, to all the materials that surround them that are cooler than their skin radiating energy away from them, and by evaporation of moisture off of their skin. Comfort ranges for various groups of people versus effective temperature can be experimentally determined (Figure 12.1). The effective temperature is calculated using a complicated equation that includes air temperature, humidity, mean radiant temperature, and air motion (Olgyay 1963, 14–18).
Victor Olgyay combined the information contained in the effective temperature into a chart of temperature versus humidity with overlays for mean radiant temperature, air speed, and added moisture in the air. He called the chart the bioclimatic chart (Figure 12.2). The bioclimatic chart transforms a complex equation for the effective temperature into an easy to read chart (Olgyay 1963, 19–22).
The cigar shaped area in the center of the bioclimatic chart represents the comfort range where most people would be thermally comfortable in the shade with light clothes on. This comfort range is roughly between 70 and 80 degrees Fahrenheit, and from about 20 to 75 percent relative humidity. If the air temperature is below this range an increase in the mean radiant temperature will provide the sensation of thermal comfort. If the air temperature is above the comfort range an addition of air motion can cause a cooling sensation by evaporating moisture off a person’s skin. If the air temperature is above the comfort range and the humidity is very low, the addition of moisture into the air can actually lower the air temperature at the expense of raising the relative humidity. Note that the comfortable temperature range gets narrower as the humidity level rises from 50 to 80 percent. This happens because, as humidity increases, it is more difficult for people to cool their skin via the evaporation of sweat.
FIGURE 12.1 Effective temperature comfort ranges for men and women in different cities demonstrates that there is a range of comfortable temperatures.
Source: Olgyay, Victor. Design With Climate. Copyright 1963: Princeton University Press. 1991 renewed PUP. Reprinted by permission of Princeton University Press.
Brown and DeKay in their book Sun, Wind, and Light (2001) provide a version of the bioclimatic chart that relates areas of the bioclimatic chart to passive solar strategies for heating and cooling a building. This form of the bioclimatic chart is easier to use in a design environment (Brown and Dekay 2001, 54–55).
The National Oceanic and Atmospheric Administration (NOAA) measures and publishes weather data for numerous locations around the United States. Using the monthly maximum and minimum temperature and the maximum and minimum relative humidity, the local weather conditions can be plotted on the bioclimatic chart. To do this it is necessary to understand the relationship between temperature and humidity on a typical day.
FIGURE 12.2 The bioclimatic chart maps human comfort in relation to temperature, humidity, mean radiant temperature, and wind speed.
Source: Olgyay, Victor. Design With Climate. Copyright 1963: Princeton University Press. 1991 renewed PUP. Reprinted by permission of Princeton University Press.