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ANALYSIS OF AN UNDERGROUND ELECTRIC HEATING SYSTEM WITH SHORT TERM ENERGY STORAGE
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Bassem H. RAMADAN
|
Univ. |
Michigan State |
Spec. |
Mechanical Engineering |
Deg. |
Year |
Pages |
|
D.Sc. |
1991 |
155 |
The principal commercially active heat storage application where concrete is used as the storage media is in the use of subfloor electric heaters. The resistance heaters are energized when utility off-peak rates are in effect. The sand and concrete floor are then heated to some predetermined temperature. The floor then releases heat slowly and remains warm during the subsequent period of high demand.
Analysis of the slab-heating system for varying design parameters, such as the depth of placement of the heaters, the thickness and the placement of insulation beneath the heaters, soil properties, the thickness of the sand layer below the heaters, and heat input was considered.
The system was optimized, based on life-cycle costs, by varying the above system parameters, for a prototypical building in four representative U.S. cities.
A one-dimensional transient heat conduction computer program was used in the analysis of the below-grade region. For the above grade region, energy consumption of the building and peak load calculations was done using the ASEAM2.1 computer program. Load profiles were calculated using hourly weather data for January.
It was found that the response of the system was strongly affected by soil properties and the depth of placement of the heaters. Optimal insulation levels for the prototypical building in each of the representative cities were obtained. These optimal insulation levels were found to change when the soil thermal properties were varied. For no insulation, the heat lost to the ground below the mats was 30 percent of the heat input for sand with 20 percent moisture content, and about 48 percent for dry sand. The amount of heat lost to the ground was found to be also a function of mat depth when dry sand was used.
The study suggests that the heaters may need to be turned on during on peak rates to prevent the slab surface from becoming cool during the afternoon hours. Because of the difficulty of controlling the space temperature, an expensive controller that implements load prediction algorithms is needed.
