2.2.2 General Guidance

Thermal blocks and the HVAC zones and space functions that they contain are user inputs; they are not automatically generated by COMNET accredited software. This section provides some general rules and guidance on how to effectively define the thermal blocks. Albert Einstein once said “everything should be made as simple as possible, but no simpler” and that is the challenge when creating thermal blocks1. The energy simulation model should include as few thermal blocks as possible, but as many as are needed. Breaking a building into thermal blocks is a step of the energy modeling process that requires considerable judgment.

Because of differences in the capabilities and limitations of various simulation tools and the extreme variety in size and complexity of buildings to which the rating method may be applied, a rigid set of rules for defining thermal blocks is not possible. Some exercise of user judgment will be required in most cases to determine the most appropriate way to subdivide and model a building.

Defining appropriate thermal blocks will save time for the user and will help to ensure accurate results. However, regardless of how the user chooses to subdivide the rated building, for most purposes, identical subdivisions will be used in modeling the baseline building. It is difficult to predict what impact a faulty decision would have on percent savings, but there is little doubt that the impact on proposed design energy use could be significant.

• 1. "On the Method of Theoretical Physics" The Herbert Spencer Lecture, delivered at Oxford (10 June 1933); also published in Philosophy of Science, Vol. 1, No. 2 (April 1934), pp. 163-169.