Building Mass
The floor area of the design is divided into three groups:
Group 1 – Radiative Coupled Mass
This group is comprised of rooms that have south facing windows, these spaces are the initial collectors of solar energy. When the sunlight enters the room and strikes a surface the energy is converted to heat (radiant) energy that is dispersed throughout the space. This radiant energy heats materials and the air within the room. If the materials are of high mass then they can absorb much of the energy, storing the heat for release at a later time. The air which is heated sets up convective flows which can move the heat to adjacent rooms. The elements within this group that are effective in storing heat energy are walls, ceilings and floors that are directly illuminated by sunlight. In calculating the floor area illuminated directly by the sun a figure roughly 1.5 times the window area should be used. However, placing the same amount of mass in walls rather than the floor will result in very little difference in performance. Mass should be distributed as evenly as possible throughout the room with at least 6 sq. ft. of mass surface for each 1 sq. ft. of glazing and should be of a light color to promote diffusion of light as much as possible. On a per pound basis mass in thin layers is more effective than thick layers.
Group 2 – Convective Coupled Mass
Are rooms that are connected to Group 1 spaces with openings that allow the flow of air from the Group 1 rooms. The convective flow of heated air can in-turn heat the materials within Group 2 rooms which stores the heat for later release. The surfaces within these spaces that are effective in receiving convective heat transfer are walls and ceiling elements. For practical purposes walls are the major opportunity to introduce massive elements into your design. BGW also automatically calculates storage for furnishings and light weight materials within Group 2 spaces based on floor area.
Group 3 – Non Interactive
Are rooms that are isolated from Group 1 rooms and do not contribute to the heating or cooling of the building.