Hygrothermal Property Measurements

Introduction
The program for Hygrothermal Property Measurements seeks to measure the properties of moisture transfer through laboratory research. The data obtained will help us to understand the combined moisture and thermal transfer, thus enabling us to develop strategies for proper moisture control in buildings.

Issues
Moisture transfer through building envelopes affects more than the energy efficiency of the building. It also influences the building’s durability and indoor air quality, and the health and safety of the occupants. Moisture damage to the exterior envelopes of numerous buildings has been widely publicized in the past few years. Moisture control is key to the development of both energy efficient and durable buildings. Proper moisture control design requires complex mathematical models of the dynamics of moisture transfer in buildings. Because material properties may age at different rates and thermal and moisture transfer affects the long-term performance of most construction materials, a thorough knowledge of the hygrothermal properties of the constituent materials and assemblies is needed.

Objectives

  • Develop laboratory facilities for measurement of the hygrothermal properties of building materials
  • Develop testing methods and standards
  • Support modeling activities by supplying needed material characterization of hygrothermal material properties and durability attributes of materials

Research
For several years, moisture transfer in building envelope systems, especially roofs, has been studied. This research has involved experiments in the Large Scale Climate Simulator, outdoor tests, and simulations using the MOIST, WUFI, and MATCH computer programs. In order to run these programs, input data are required on the hygrothermal properties of the specific materials used in construction of the test sections.

A world-class laboratory capability for measurement of the hygrothermal properties of building materials is being set up. Properties to be measured include moisture capacity in both the hygroscopic (low moisture content) and capillary (high moisture content) regimes, water vapor permeability, liquid diffusivity, liquid uptake, two-dimensional distributions of moisture using nuclear magnetic resonance or gamma-ray methods, thermal conductivity, specific heat, and air-flow permeability. The dependence of these properties are factors such as temperature and relative humidity or moisture content will be determined, and a database of material properties will be created and published.

News

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