First, take a look at the energy breakdown in VistaPro. You can find this information at the bottom of the BRUKL certificate too. Identify what energy end uses have changed. Once you've figured that out, start asking why these changes occurred.
For instance, if the heating energy has increased, compare the results of the two simulations for the Actual Building. Look for a room where the sensible heating load has increased. You can usually find this information in the synopsis section, which provides the date and time of the maximum value. Focus on that day and explore the variables that influence the space heating load. This includes room air temperature, heating setpoints, solar gains, internal gains, conduction gains, and ventilation gains, among others.
Here's an example to illustrate this process:
Imagine a user who runs a fast-food restaurant for Part L2. Dining area served by ASHP system and Food prep served by FCU.
and they decide to improve the lighting in the food prep area.
Surprisingly, both the BER and TER improve.
By investigating the results in VistaPro, we discover that the reduction in lighting in the food prep area makes the heating system for that space more important as there is a significant decrease in radiant gains from the lighting
This, in turn, makes the food prep area's heating system more dominant overall, reducing the percentage of the overall heating demand served by the Heat Pump system which is assigned to the dining room. Since the Notional Building's PV system panel size depends mostly on the heat pump system's contribution to the overall heating demand, which also reduces, the amount of PV on the Notional Building increases.
You can find more details on the Heat Pump influence on the NB PV in this FAQ here
By dissecting the changes and their impacts step by step, we can pinpoint the reasons behind unexpected results, paving the way for compliant and sustainable buildings. If you ever find yourself in a similar situation, remember to rely on tools like VistaPro and detailed analysis to help you on your journey to regulatory compliance and better building performance. Happy modelling and achieving compliance!