A contribution to the audit of an air-conditinioning system: modelling, simulation and benchmarking

This paper intends to show how benchmarks can help in the audit of a HVAC system and
how these benchmarks can be generated. The work presented is part of the European
‘AUDITAC’ project. How can an auditor declare that a given HVAC is ‘consuming too
much’? He can’t make any judgment, if not having some reference, i.e. some ‘benchmarks’
available. Focus is given here to cooling regime, but even then, heating cannot be forgotten
(for example, the remaining heating demand can be satisfied thanks some recovery on the
condensers of the chillers). The dramatic question is: what should be the consumption(s)
for such a building, in such a climate, with such occupancy, such internal loads and such
actual indoor environment? Better than to look for a (very hypothetical) global weather
index, similar to heating degree-days, it seems more rational to run a simulation model
on a few thousands of hours, corresponding to one (or to several) cooling season(s).
Current performances of simulation tools make this approach very expedient. The climate
can then be considered as it is, without any simplification.
The main simplification is still welcome on the system (buildingþHVAC) side, in order to
get calculation robustness, easy understanding and easy parameter identification. In this
perspective, the building has to be subdivided in a very limited number of zones and only
a few components of the HVAC system have to be included in the simulation model, with
as simple as possible control strategies.