Adobe and Latent Heat;

A Critical Connection

John J. Morony

Biology Department

Southwest Texas Junior College

Del Rio, TX 78840

P O Box 421627

Del Rio, TX 78842

Abstract

A series of ongoing experiments provide evidence supporting the opinion that ìAdobe is warmer in the winter and cooler in the summerî. Two modules were constructed, one each of adobe and cinderblock. Both have 8 inch walls and same internal dimension with roofs and floor of the same material. With an outdoor ambient temperature of 98† F, interior temperatures were 90† for adobe and 103† for the cinderblock. Why the13† difference? The adobe module lost 8† by way of latent heat of vaporization in accord with known properties of soil; the cinderblock gained 5† due to simple heat conduction.

Adobe is soil and remains soil after incorporation into a building and thus adobe is subject to the thermal dynamics of soil. A reverse effect occurs when adobe takes on moisture when humidity is high and temperature are low. During cold weather data loggers for temperature and moisture were placed in each of the modules over a total of ten days. During each diurnal cycle the lowest and highest temperatures were restricted to the cinderblock.

Simple experiments are provided to illustrate the thermal properties of adobe (i.e., soil). Phase change from liquid water to vapor, or the reverse, will result in a very high latent heat that serves to lower or raise the temperature of adobe.

Clay, the binder for adobe, is hygroscopic and moisture content varies with changes in moisture availability. Such variations preclude adobe being assigned a specific heat capacity as is the case with conventional building material.

One cannot restrict evaluation of adobe to the parameters of sensible heat, as does the building industry, and ignore known principles of soil science especially as concerns the role of latent heat. Experimentation by the author provides strong evidence that as a construction material adobe blocks keep a building warmer in the winter and cooler in the summer than cinder block. The explanation for this phenomenon lies in the role of latent heat, not sensible heat ñ a critical distinction.

(Word count 331)