Page 39 - Uninterruptible Power Supplies

Standby Power Generating Sets
Standby Power Generating Sets 37

The types of area considered in the Memorandum are:
A. An undeveloped area where development is unlikely
B. A partially developed area with scattered houses
C. A built-up residential area
D. An urban area of mixed industrial and residential development
E. A large city or an urban area, of mixed heavy industrial and dense
residential development
Having calculated the uncorrected chimney height, the effect of nearby
buildings has to be considered, and the Memorandum describes the
method to be used to establish the corrected chimney height. The correc-
tion procedure applies to all buildings within a distance of five times the
uncorrected height, and to the building housing the generating set itself.
Clause 25 of the Memorandum introduces three additional require-
ments which are:

a. A chimney should terminate at least 3 m above the level of any adja-
cent area to which there is general access.
b. A chimney should never be less than the calculated uncorrected
chimney height.
c. A chimney should never be less than the height of any part of an
attached building within a distance of five times the uncorrected
chimney height.
The heights determined by these procedures should be rounded to the
nearest meter, and should be regarded as a guide rather than a mathe-
matically precise statement. The conclusions may need to be modified in
the light of particular local circumstances such as topographical features.

Example of Chimney Height Calculation
The manufacturer of a 180-kW generating set running on BS2869
Class A2 fuel advises that it uses 47 kg of fuel per hour when running
at full load.
The maximum permissible sulphur content (0.2%) of 47 kg of fuel is
0.094 kg which when burnt will result in the emission of 0.188 kg/hour
of sulphur dioxide.
Referring to Chart II of the Memorandum, the following uncorrected
chimney heights are obtained:

For Type A district 1.9 m
For Type C district 2.6 m
For Type E district 3.3 m

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