Moisture: Its effects on the thermal performance of a low-slope roof system

Conference · Fri Jan 01 04:00:00 EST 1993

OSTI ID:6857939

Desjarlais, A O; Christian, J E; Kyle, D M ^[1]; Rode, C ^[2]

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1. Oak Ridge National Lab., TN (United States)
2. Danish Building Research Inst., Horsholm (Denmark). Energy and Indoor Climate Div.

To investigate the effects of moisture movement on thermal efficiency, and experiment was performed on a low-slope roof system containing permeable insulation. Five replicate test panels of the roof system containing a variety of vapor retarders were evaluated in a climate simulator. The test panels were outfitted with temperature sensors, heat flux transducers (HFTs), and two types of moisture probes. These instruments were installed on both sides of the insulation material; additional temperature sensors were located at the interfaces between the various layers of the roof system. The panels were subjected to an external diurnal cycle representative of a cloudy southern continental summer climate. During this initial dry'' run, only hygroscopic water was present in the panels. Water was then added to four of the panels and the experiment was repeated with diurnal cycles representing cloudy and sunny conditions being imposed. Significant differences in the outputs of the HFTs located on opposite sides of the insulation layer were noted in the dry'' run on panels containing impermeable vapor retarders. In this run, peak heat flows measured by the bottom HFTs were larger than those at the top of the insulation, in spite of the temperature variations being imposed on the top surface. It is theorized that the difference is due to latent heat effects and that these effects were due to the presence of hygroscopic moisture. After the addition of water, all of the bottom HFTs were surrounded with condensate and temporarily responded to the latent effects, whereas the top HFTs all responded like they did in the dry'' runs. A combined heat and mass transfer model that takes into account latent heat effects was used to estimate the latent and sensible heat flows for the test panels. The total heat flow predicted by the model approximated the output of the bottom HFT while the top HFT output approximated the calculated sensible heat flow.

• Research Organization: Oak Ridge National Lab., TN (United States)
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6857939
• Report Number(s): CONF-930675-1; ON: DE93010276
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
320107* -- Energy Conservation
Consumption
& Utilization-- Building Systems-- (1987-)
BUILDINGS
CONDENSATES
ENERGY CONSERVATION
ENERGY TRANSFER
ENTHALPY
HEAT FLOW
HEAT TRANSFER
MASS TRANSFER
MATHEMATICAL MODELS
MOISTURE
PHYSICAL PROPERTIES
ROOFS
TEMPERATURE MEASUREMENT
TESTING
THERMAL ANALYSIS
THERMAL INSULATION
THERMODYNAMIC PROPERTIES
TRANSDUCERS
TRANSITION HEAT
VAPORIZATION HEAT