additional ventilation from other loads selected

(applies only to Air Conditioning versions of the program)

Quite separately from both powered ventilation systems designed into the overall project and also natural infiltration which may or may not occur, are the possible source of additional powered ventilation resulting from extraction systems fitted to certain other items of equipment. For example air extraction fitted to kitchen cooker hoods and Electrostatic Precipitators (kitchen cooking oil mist removal systems).

The air extraction system fitted to such equipment can be substantial and the effect of their operation on the cooling or heating load of the overall space under consideration should not be underestimated. Care should therefore be taken to ensure that realistic 'Power Factors' are applied which reflect the actual amount of time such equipment is likely to be operational. Simply accepting the 'worst case' and program default setting of 100% Power Factors when selecting equipment with very high air extraction rates, when in practice these may only be operational for a very small proportion of the working day, could result in excessively high calculated heat energy gains or losses relative to other energy sources in the study.

Another equally important consideration must be in deciding how much of the air extracted by the equipment is supplied from air that is conditioned. A substantial proportion of the make-up air might be supplied locally from ambient or from an adjacent space and which therefore will not be contributing substantially to the cooling or heating load.

The Power Factor tool should therefore be used judiciously to de-rate the combined effects of both equipment usage times and actual sources of make up air. However this is an area of estimation that no computer program or experienced supposition can substitute for actual empirical measurement on a case by case basis. Professional expertise and good client advice will be invaluable. Power Factors as little as 10% may often not be unreasonable.

It should be noted that ventilation rates arising from selection of equipment from the 'Other Loads' database has no effect on ventilation and/or infiltration rates selected or entered in the program main procedure. Also, ventilation rates arising from selection of equipment from the 'Other Loads' can only be cancelled or edited in the 'Other Loads' procedure.

See also:-

air changes (per day [24 hours])
ventilation air at temperature other than ambient