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praftery edited this page Sep 30, 2019 · 8 revisions

CBE

CBE Fan Tool User Guide

This User Guide is a work in progress.

Calculation method

Calculation method

This tool allows designers to quickly select and layout ceiling fans to meet given airspeed requirements (or other constraints) in a given room. It does this using models that predict the airspeed distribution in a given combination of room and fan related characteristics, and knowledge about constraints related to these inputs. The tool generates solutions using the following steps.

Step 1: Assess cell size and aspect ratio constraints:

For the room length and width defined by the user, the tool calculates a set of fan layouts such that:

  • the size of an individual fan cell is within a reasonable range (between 4.572m and 15.24m) given the underlying laboratory test dataset, and practically recommended room sizes for fans between 4 and 14 ft in diameter
  • the resulting fan cells are reasonably square (default length/width ratio < 1.25, can be modified in the Advanced Constraints input).
  • the number of fans in either direction is within the acceptable range defined by the user (default 1-10, can be modified by the user in the Fan Constraints input).

Step 2: Assess blade height constraints

Given the set of candidate fans selected by the user, the tool calculates whether or not the fan will 'fit' in the ceiling height defined, and at what height it will be mounted. There are several components to this.

  • the fan must be mounted at or above 7ft if it meets UL 507 criteria, and the fan must be mounted at or above 10ft if it does not.
  • the fan should be mounted at a distance from the ceiling that avoids 'starving '. The default value for this mount distance is 0.2 times the fan diameter (can be modified in the Advanced Constraints input).
  • the fan must be mounted within the acceptable range of blade heights defined by the user (default 7ft to 10ft, can be modified in the Advanced Constraints).

The tool only retains fans as candidates if they will fit

Limitations

The underlying models are based on full-scale laboratory tests. Though these tests covered a wide range of fans and room sizes, for all test cases, the fans were centered in a square room so as to provide the most coverage. Cases with non-square rooms an/or off-centered fans will yield less accurate results.

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