An Encapsulated Crawlspace: Basic Engineering Calculations and Measurements

In An Encapsulated Crawlspace: Basic Engineering Calculations and Measurements, you'll learn ...

• Working equations from first principals for application to a crawlspace environment
• Measurements with calculations to examine performance of an encapsulated crawlspace
• Time-history measurements of temperature and relative humidity at several crawlspace locations
• Dew point and other parameter calculations from measured temperature and relative humidity

Overview

Credit: 4 PDH

Length: 28 pages

Students of this course will learn how to calculate and measure the parameters that affect moisture in an enclosed space, such as a crawlspace. The application is not limited to a crawlspace, although measurements taken by the author and calculations presented in the course are based on a particular residential encapsulated crawlspace.

The course begins with a very brief discussion of encapsulation of a crawlspace. Equations based on first principals are introduced along with the definition of terms. Numerous examples are given with graphical representations to support the development and application of the equations. The basic concepts on which this course is based should be familiar to all engineers or easy to grasp, particularly for mechanical and chemical engineers.

The starting point for developing a set of working equations includes an expression for the vapor pressure of water as a function of temperature, the definition of relative humidity, the ideal gas equation for air containing water vapor, the definition of partial pressure and a definition of dew point. The procedure for combining these expressions into a set of working equations is then presented. The working equations are used to calculate dew-point temperature, mass fraction of water vapor in air, specific volume of moist air, enthalpy of air/water vapor mixtures including water condensation, and other properties. Two sets of temperature and relative humidity measurements made over time and at several locations in an enclosed crawlspace are presented. These measurements are presented graphically and include the corresponding calculated dew-point temperatures. An EXCEL program listing is included that uses the working equations and provides a convenient way to combine the measured and calculated results.

A drawing of a functional encapsulated crawlspace is presented with the locations of the temperature and humidity sensors, and the location of the dehumidifier and its associated duct work. A photograph of the encapsulated crawlspace is also included. Measurements of temperature and relative humidity at several locations in the crawlspace are presented and used to determine dew point and other parameters of interest. Measurements of the wood moisture content at a number of locations around the sill plate and along one of the girders are given. These measurements are compared to an empirical correlation that relates wood equilibrium moisture content to relative humidity and temperature. The amount of electricity used by the crawlspace dehumidifier over time is also measured and briefly discussed.