What Calculation(s) is/are taking place?!


What calculation is taking place in the Sefaira web applicaiton?

Typical questions include;

  • Why is adding shading dramatically affecting peak cooling but not energy?
  • How to I get my energy value down with my envelope inputs?
  • I have the best envelope but energy is still high, now what?
  • Why is my AHU load so low and my zone load so high?

Starting at the beginning, there are two concurrent simulations being run in the web application;

  1. Peak Loads using Design Days, and,
  2. Annual Energy using Annual Weather Files

 Peak Loads using Design Days

 Here is where the peak loads information is in the web application. 

These results come from temperatures from the selected weather flle and conditions specified by ASHRAE. They give the peak size of plant under location-specific, fixed, extreme/design conditions but do not require the entire year to be simulated. 

Cooling conditions include all internal loads and Heating conditions do not. 



The blue dial download circled in the image above allows a deeper look at the underlying analysis using standard formatted .html reports from the Energy Plus run.

Here are the design temperatures in Celsius for London - -3oC in winter and 24.8oC dry bulb. Four summer months are calculated to find the peak cooling conditions and consequent sizing.



You can then look at specific zones and see a further breakdown of how large the peak loads are, when they occur and why;



In this example, the largest load during cooling peak conditions is 31,913W on the 21st August at 10am and is driven mainly by solar gain (Fenestration Solar) followed by internal loads such as equipment, lights and people.




Annual Energy using Typical Weather Files

Here is where the Annual information is in the web application;


These results come from an 8,760 hour simulation from the selected weather file given standard starting conditions and the interaction of all internal and external loads across the year.

 Here you can see that Lighting and Equipment consume nearly 75% of the energy across the year. This relates to some of the questions we discussed in the beginning - in this case, changing heating or cooling parameters or adding shading will have some effect on the energy but not that much. Those changes may change the peak conditions and load significantly but if we want to reduce energy consumption we need to follow a different strategy.

As above, with Peak Loads, you can download the .html file to look at further information. In this example, you can look at the conversion between site and source energy, if that is relevant to your project. We report the site energy in the web application and show the conversion factors which you can then post-process for your specific project.



There are two complementary but different simulations taking place in the Sefaira web application. Both are useful for different purposes and can have an important impact on the design of the building given understanding of the different simulation conditions. 

For any additional queries or project related questions please contact support@sefaira.com 

Was this article helpful?
0 out of 0 found this helpful