William Wrennall wrote chapter 8.2 Facilities Layout and Design in Maynard's IE Handbook, 5th Edition.
Space planning identifiers (SPIs). An SPI represents a function, department, or feature that requires space, impacts placement, or has flow or non-flow relationships with other SPIs.
SPIs may be:
• product-focused (e.g., a lamp assembly cell);
• functional departments (e.g., a powder paint unit);
• storage areas (e.g., tool crib); or
• building features (e.g., loading dock).
Within the SPI definitions, the items, areas, and functions that are included and excluded should be noted. This is done to ensure that the fundamental elements are communicated.
Affinities and relationships. An affinity is the degree of closeness between two SPIs. The affinity is based on material flow and non-flow considerations or a combination of the two. Affinity values and their generally accepted definitions include:
• A is absolute/adjoining
• E is "especial"/close (touching, if possible)
• I is important/nearby
• O is ordinary/conveniently near
• U is unimportant
• X indicates that proximity is not desirable
• XX indicates that separation is important
These are demonstrated best on an affinity chart (which is similar to a mileage chart), with the SPIs listed along the side and the affinities posted in the look-up intersections.
This is a good time to develop and agree on tiebreakers, which are rules to apply when procedures do not provide a definite design choice. In many cases, the tiebreakers may create a placement protocol that incorporates elements from operations and manufacturing strategy.
The affinity chart is converted into a graphical form called a configuration diagram that organizes the SPIs into an arrangement based on affinities . The arrangement is accomplished by using several SPI placement iterations. The A and E affinities are placed first, with subsequent iterations adding the I, O, X, and XX affinities.
Lines indicate the affinity between SPI pairs. Line designations include:
• A = 4 red lines
• E = 3 orange lines
• I = 2 green lines
• O = 1 blue line
• X and XX = black, spring-like lines
Space requirements for each SPI. The space required for an SPI should reflect growth, either positive or negative, for each SPI over the planning horizon. The planning horizon should be between five and 10 years. This interval is best because any less may not allow for necessary growth and any more is probably a guess.
The SPI with the incorporation of space is the space-planning unit (SPU).
Layout primitive. Space-planning units are substituted for their corresponding SPIs in the configuration diagram. The result of the substitution is a layout primitive . The layout primitive is important because it is an unconstrained macro (block) layout. The next step will implement any constraints, including the building or its footprint.
Macro layouts. Apply constraints to the layout primitive. The layout primitive is constrained into a footprint, which sometimes causes several solutions to present themselves. These multiple solutions are the primary macro layout options.
A number of considerations have to be taken into account during this step, including the SPI space and shape. The variability of changes to the shape or geometry of space indicates the dynamic nature of usable blocks of space and should be considered block dynamics. Block dynamics describe how the block assumes a characteristic geometry based on the population and orientation of the population. In addition, columns and column spacing have an impact on block dynamics.
Populating the layout. Populate the selected layout option is placement of individual facilities or equipment in the block of space specified for a space planning identifier. The term "populate" is more appropriate than "detail." Although detail is being incorporated, the population of the block validates the space planning unit with its associated block space and geometry.