It is a common practice in building services design for designers to draw on their experience for rapid assessment of the approximate value of system design parameters and costs. This accumulated experience manifests itself as a set of guidelines or rules - known colloquially as "Rules of Thumb". In Hong Kong, however a publicly available set of such rules applicable to building services design does not seem to exist. On the other hand, local designers often tend to propose high value of rules of thumb to allow for so-called safety margin. This makes over-sizing a common practice in building services systems in Hong Kong. This paper reports on an evaluation of the rules of thumb in cooling load computation for office buildings in Hong Kong. Existing rules of thumb employed by a number of leading local consultants were reviewed, and new compromised ones for designing office buildings proposed, taking into consideration of energy efficiency, safe/flexible system design and operation, and peak loading conditions. Manual calculation, computer simulation and field measurement approaches have been employed during the evaluation.
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