Trying to get IES CIBSE Cooling Load to Match Calculation

[JosephG]

I'd check the following items:

1. Check that the materials in the calculations are the same as defined in IES, and that they have been properly applied to the model.

2. Ensure that you've selected the correct location and the correct summer design day conditions.

3. Run a dynamic thermal simulation and check the results at peak conditions, they shouldn't be far off from the cooling loads.

[JosephG]

I'm not sure I understand. You're doing a cooling loads calculation, right? If the room temperature is 28°C and the outside condition is 24.1°C, then the presence of rooflights should reduce, not increase the conduction cooling load.

You have a 4°C temperature difference. A rooflight has a higher conductivity than a solid wall (well, it's supposed to). In a cooling scenario, the conduction is greater with a rooflight, which means that the cooling load associated with conduction will be lower since the conduction results in heat leaving the room, i.e. conduction through the rooflight results in cooling.

So I don't quite understand how your conduction cooling load was reduced by 20kW by removing the rooflights.

[ijmccall]

Hello,

I have also noticed that VE tends to over estimate the Heating loads ... when it is compared to other BS programs (ESP-r). I notice a difference of 8% in my very simple example (with no internal gains). Has anyone else noticed this or have an explanation? (I have is I have also double checked my input data.)

Interesting Note when I added internal gains to the building, VE almost matches perfectly ESP-r. Again any ideas?

Questions related to the above discussion
1) Leo - Did you take into account the Thermal Bridges?
2) Leo - How did you VE to calculate the conduction load?
3) What is the best way to calculate the conduction load in VE?

regards,