I have begun to look into the subject of for environmental modelling software capable of calculating, in detail, passive solar designs. In the course of this investigation I have heard that software, calculating using the CIBSE admittance procedure, is flawed, as it cannot model thermal mass properly.
As I understand it the failure of the CIBSE admittance procedure has something to do with “each day being that same as the day before” i.e. the model has no way of feeding historical data into the its calculation in order to predict the buildings true behaviour. An example would be when using night purging techniques in the summer so as to exploit the coolth of the thermal mass to prevent over heating. For this to be simulated correctly the calculation model has to remember what the remaining thermal capacity of the material was in the last calculation, when the thermal capacity is reached and the subsequent impact upon room temperature.
This failure to “remember” the past calculations means that, as far as the calcs go, the scheme will be shown, in terms of comfort standards, to fail i.e. over heat. A further consequence of this is that by default the thermal model suggests that additional cooling loads need to be introduced. This may be achieved through increasing the thermal mass (which this will result in the designs failure in reality as there will be an excess of thermal mass which will in turn lead to additional heating demand) or by introducing mechanical plant (as this kit is not actually required it costs the client more money and potentially has a negative impact upon the carbon footprint.)
Given the above, it would seem that the subject of building simulation is fraught with complexity insofar as there are a number of simulation techniques are available; some of which are more successful than others. Which technique is the most reliable for a passive solar building? Who produces software that uses this technique? Who has the best algorithms? And ultimately which software offers the best value performance?
The whole field of simulation seems to be dreadfully confusing for the uninitiated. Any help would be appreciated.