Operations/Facility Layout

The facility layout model is used to place departments in rooms in order to minimize the total distance traveled as a function of the distances between the rooms and the flow between departments. In some cases it is necessary to fix certain departments to be located in specific rooms. Distances between rooms may or may not be symmetric. (Usually they are but this is not required.)

Data

The framework for layout is given by the number of departments or the number of rooms that we assume to be the same, since each department must be assigned to one and only one room.

The data that follows essentially consists of two tables of numbers - one for the flows and one for the distances.

Method. There are essentially two methods available. One is pairwise comparison. With this method we try exchanging departments until no exchange will reduce the total amount of movement. Unfortunately, this method is not guaranteed to always find the best layout. The method that is guaranteed to do so is explicit enumeration. Unfortunately, this can take a large amount of computation time for large problems.

Interdepartmental flows. The number of trips from one department to another is indicated in a table termed the flow matrix.

Distance matrix. The distance between rooms is entered in this table. Typically the distance matrix will be symmetric. The choice is made at the beginning of the module. That is, the distance from Room i to Room j is the same distance as for Room j to Room i.

A sample set of data appears in the preceding screen. Notice in this example that the distances are not symmetric.

Solution

The solution simply is to assign the departments to the appropriate rooms. The total movement is also noted.

Room assignments. On the right of each department row will appear the room in which the department should be placed. In our example department 1 should be placed in room 1, department 2 in room 5, department 3 in room 4, department 4 in room 2, and department 5 in room 3.

Total movement. The sum of the products of the number of trips multiplied by the distance is listed at the top. This is what we are trying to minimize.

It is possible to display the individual multiplications of room to room distances by process to process flows. This is shown (partially) in the screen that follows.

Fixing departments in specific rooms

If the room name appears in the column labeled "Fixed Room", that department will be fixed in that room. Suppose that in our previous example we are required to have department 5 placed in room 2. Then to accomplish this we place "room 2" in the row for department 5 in the "Fixed Room" column using the drop-down box.

The solution follows. The room assignments are, of course, different and the total movement is, of course, greater than before.