The paper presented is based on work done within the IEA ANNEX 10 'system simulation' group.There, eight research instituts discussed and agreed on simulation models for heating and air conditioning components. The models are documented in so called 'component specifications'. These specifications contain a description how to simulate the steady state and also in a first estimation the dynarnic, hydraulic and aeraulic behaviour. The computer codes, developed on the base of these models (extension of the TRNSYS code or own programs), allow a comprehensive calculation of the energy consumption, and energy flow, within the building, system and plant. The simulation work should not stop, when all energies are calculated. A good presentation and an evaluation of the energies has to be done. Tls necds an evaluation method. Several methods, Eke thermodynan-dc evaluation, comparison with ideal processes or the efficiency theory are discussed. In the fllowing, additional work is done to improve the efficieney theory. All theories demand a clear defiltion of the boundaries of each. process within the building, the systems and the plants. If all energies at these boundaries are known the different processes, like hot-and cold-water or steam production, eneray distribution, air-treatment within the air conditiorng system, heating and cooling in the room and energy use of the building, can be evaluated. Of course a good graphical representation is necessary to have a better understanding of the results. The comprehensive simulation work gives much more information than only energy. These can be the frequency of oceurence of eyelin-of components, control behaviour, pressure distribution etc.. The evaluation of this values can be done using more general methods Eke cost or penalty functions or knowledge based evaluation methods. The described methods are used to evaluate the energy use of an office building with two kind of air conditioning systems.