Part 4: Turning a Calculation into an App for Everyday Users

Why the Right Model Isn’t Enough

Many technical projects fail not because the model is wrong, but because real users can’t interact with it. For a PENB approximation app, this is especially important since the target audience isn’t just analysts.

A usable public app must meet three requirements at once:

• the user must understand what to enter,
• the system must receive consistent input,
• the output must be readable even without deep technical knowledge.

Five Steps Instead of One Overwhelming Screen

The current interface uses a logical breakdown into several steps: location, apartment, data, calculation, and result. This is important for practical reasons.

When people see everything at once, it’s easy to lose context. Guiding them step by step increases the chance of correct input.

This isn’t just a UX rule. It’s also a way to improve the quality of data that ultimately reaches the model.

The Form as Part of Domain Logic

A public app shouldn’t just be a thin layer over the backend. In this project, the form actively helps structure the input:

• guides users to the truly essential information,
• distinguishes between quick and detailed calculation modes,
• handles months without heating and hot water right at input,
• sets the stage for interpreting the result.

From this perspective, UX is not separate from data science. It’s one of the layers that determines whether the model receives meaningful input.

The result must be understandable, not just accurate

The user usually doesn’t need to know all the internal calibration parameters. They need to understand:

• what energy class the calculation yields,
• how reliable the estimate is,
• what the interpretation limits are,
• what the next logical step is.

That’s why the output combines the energy class, key metrics, a written comment, and an exportable report. The result serves as a communication artifact, not just a technical intermediate output.

Bilingualism as a product feature

An interesting part of the project is that the application isn’t just prepared for local testing. It has both Czech and English language versions. This increases usability for project presentations, sharing with clients, and further development.

Technically, this means more work. But from a product perspective, it significantly boosts the application’s overall value.

What’s next

In the final part, I’ll cover deployment, report export, current project limitations, and what I would expand or refine in the next iteration.