## 2 Materials and Methods
H = H\({}_{\text{T}}\) + H\({}_{\text{V}}\),  
where H--specific heat loss, H\({}_{\text{T}}\)--specific heat loss through transition, H\({}_{\text{V}}\)--specific heat loss through ventilation  
The specific heat loss through the transition is calculated according to the following relationship:  
H\({}_{\text{T}}\) = \(\sum\)b\({}_{\text{xi}}\)\(\times\) u\({}_{\text{i}}\)\(\times\) A\({}_{\text{i}}\) + \(\Delta\)u \(\times\)\(\sum\)A\({}_{\text{i}}\)  
The specific heat loss through ventilation is calculated as follows:  
H\({}_{\text{V}}\) = \(\rho\)a \(\times\) c\({}_{\text{p}}\)\(\times\) n \(\times\) V  
where the coefficient n is based on the geometric properties of the building  
\[\text{n}=3600\ \times\ \frac{\sum(\text{i}_{\text{h}}\)\(\times\) I) \(\times\) B \(\times\) M \begin{table}
\begin{tabular}{l l l l} \hline \hline  & **House No. 1** & **House No. 2** & **House No. 3** \\ \hline Construction type & \multicolumn{3}{c}{area [m\({}^{2}\)]} \\ \hline Perimeter wall & 165.03 & 159.17 & 234.50 \\ \hline Ceiling to outside & 102.27 & 104.16 & 138.06 \\ \hline Floor & 90.28 & 89.6 & 129.85 \\ \hline Windows & 12.59 & 25.37 & 21.4 \\ \hline Doors & 4.7 & 1.83 & 6.7 \\ \hline Construction material for walls & bricks & bricks & precast concrete \\ \hline Wall insolation & NO & Mineral wool 5 cm & Mineral wool 16 cm \\ \hline Roof insolation & NO & Mineral wool 10 cm & Mineral wool 30 cm \\ \hline Windows and doors & Uw = 3 & Uw = 1.4 & Uw = 0.9 \\ \hline Energy class & F & C & A \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Dimensions of the model houses—reference buildings. Figure 2: Three-dimensional model of one reference building. Average temperatures for the city of Zilina were used, as shown in Table 3. Solar in-plane irradiation was calculated at a value of 1309.55 kWh/m\({}^{2}\)[4]. As mentioned in the first chapter, an important parameter is the number of sunny days during the year. In Figure 3, the number of sunny days is shown. Solar thermal gains are gains that depend on the solar radiation available at a given location, the orientation of the collection surfaces, permanent shading, solar transmittance, and absorption and thermal transmittance of the collection surfaces. \[\text{Q}_{\text{sol}}=\sum_{\text{k}}\left[\text{ }\text{I}_{\text{sol}} \times\text{t}\times\sum_{\text{n}}\text{A}_{\text{sol,n}}\right]\]  
After expressing the specific heat loss, it is possible to express the need for heat for heating without heat gains:  
\[\text{Q}_{\text{B}}=\text{H}\times\left(\text{\theta}_{\text{i}}-\text{ \theta}_{\text{e}}\right)\times\text{n}\times 24.10^{-3}\]  
where \(\left(\text{\theta}_{\text{i}}-\text{\theta}_{\text{e}}\right)\) is the difference between inside \(\left(\text{\theta}_{\text{i}}\right)\) and outside temperature \(\left(\text{\theta}_{\text{e}}\right)\). Coefficient n represents the number of days for a specific month. With this, the current energy needed for heating was calculated. The result of this calculation was the heat demand for every reference building. Since the electricity consumption for family houses is not evaluated in terms of valid technical standards in Slovakia, the average electricity consumption for individual houses was determined on the basis of [4], where average energy consumption is presented from current statistical data. Results are shown in Table 4.  
After heat demand calculation, energy classes for houses in selected city districts were assigned according to made survey [4]. In Table 5, the number of houses in each energy class is evaluated. Figure 3: Sunny days during the year in Slovakia. \begin{table}
\begin{tabular}{c c c c c c} \hline January & February & March & April & May & June \\ \hline \(-\)3.2 & \(-\)1.2 & 3.2 & 8.7 & 13.0 & 15.9 \\ \hline July & August & September & October & November & December \\ \hline
17.4 & 16.8 & 13.7 & 8.5 & 3.1 & \(-\)1.5 \\ \hline \end{tabular}
\end{table} 
Table 3: The average temperature in individual months for Zilina City [\({}^{\circ}\)C].