Shape factor method for computing heating loads from building slab-on-grade foundations

摘要

A shape factor method, designated the Z-shape factor, is presented which provides a simple, hand calculation technique of predicting daily, weekly, or seasonal heat loads due to the effects of slab-on-grade earth coupling. This semi-analytic method accommodates a wide range of time periods and local soil and weather conditions, and is limited to vertical insulation schemes. The unique feature of the Z-shape factor method is that it allows a user to input soil conductivity and several site-specific geometric parameters. This extends the usefulness of the general shape factor method available in the ASHRAE Handbook and other recent publications since more site-specific inputs can be utilized in the below-grade heat loss estimation. Predictions derived from the shape factor method are compared to other simplified prediction procedures and to field data. The field data collected from an earth-coupling experiment being conducted at a laboratory are used to check the predicted heat loss by the Z-shape factor method from both an insulated and uninsulated slab-on-grade. Results are within 10% of the altemative computations and of the field data, which suggests the procedure is 'suitable for most annual heat and peak heating load calculations for slab-on-grade structures.