CIBSE Loads and Dynamic Simulation results don't mach

[ieser]

I am getting confused with different results obtained from dynamic simulation and CIBSE Loads report.

In randomly picked room I can see pick load from apachesim as 3.5 kW but in heating loads report file it shows only 0.83 kW
The total room load for all rooms ends up in report as 110 kW (over hundred apartments). In individual flats loads analysis it looks more correct/expected.

I have used DHW profile based on realistic consumption profile, hence the total plant load is based on peak consumption of HW at particular hour and is something in order of 330 kW.

Now the question is whether the unused hot water plant power is utilised for heating if profiles do not overlap? If that is the case I still cannot understand why room load shows less than in dynamic simulation result.

I hope my explanation is clear enough. I appreciate your comments.

Thanks

P

[ieser]

I think the problem was identified. Basically CIBSE Loads tool selected 'default' day/time for loads calculation. The one was during reduced temperature period and not in the coldest day/month of the year hence significantly reduced loads.

When manually set to day/time that load was expected to be high result was also high. Conclusion is that there is very little use of CIBSE Loads tool and one that do not have clue how it works or what it is for (like me) may waste lots of time unnecessarily.

[farahghanem]

That is generally the case with many features in IES. You need to know exactly what you want the software to do/tell you and how to do/see what you need.

I would advice you sign up for some of the training they offer, although it may be costly, but it does save you a lot of time.

[bootsam]

Cibse loads are static results and rely upon winter temp of say -4°C and summer of 30/21. Dynamic uses a weather file with ambient temps varying from day to day dependant upon which file you use. CIBSE is great for peak loads and finding out how big your boiler needs to be under worst case scenario's, whereas DSM is great for ascertaining annual energy patterns. But give the engineers DSM results and theyll all be scratching their bonces and asking for the CIBSE loads. They dont care about annual patterns as the controls guys deal with that. They just want to know what size boiler do I need and not one will risk undersizing their plant. Furthermore DSM is reliant on the weatherfile, which is historic and not a forecast. Each year differs and even the DSY is a bit of a 'guess'. CIBSE for sizing plant, DSM for assessing annual energy. Basically CIBSE has all the fudge factors, back of fag packet and margins built in and that makes the engineers happy.