In Bayesian networks, it is possible to perform analyses and make estimations for any node by propagating the evidences through the network. For instance, for a flat type dwelling assumed to be facing to North, on the second floor, between 20–29 years old, heated by coal stove and between 120–179 m2, and also assumed to have 1 living room and 3 bedrooms but not to have external wall insulation or double glazing, Fig. 8 demonstrates the state of the Bayesian network when these evidences are propagated through the network.
Figure 8 shows that the space heating cost of this dwelling is estimated to be 400 TL or over with the highest probability of 52.5% and between 300–399 TL with a probability of 40%.
Some analysis results and discussions provided by the estimated Bayesian network are given below.
As far as floor level is considered, the dwellings on the ground floors and the first floors seem to pay the highest space heating cost compared to the ones on the other floors. 30% of the dwellings on the ground floor and 34.3% of the dwellings on the first floor pay 400 TL or more per month. On the other hand, third and fourth floors seem to be paying less than the others. They pay 100–199 TL on the average with a proportion of 29.3% for the third floors and 27.5% for the fourth floors. This result is consistent with results given by Ziemele et al. (2015) who report that the apartments located on the top and bottom floors of a building have more heat loss than the other floors. When floor level factor is considered along with building age, it is seen that the ground floors in new building pay 200–300 TL (38.3%) whereas in buildings that are aged 30 or over, the ground floors pay 400 TL or over (44.9%) just as the fifth or higher floors (27.6%). However using central heating or boiler in old buildings decreases the space heating costs of the ground floors to 300–399 TL interval (29.3%). Least space heating costs are paid by residents living on the third floors in new buildings as 100–199 TL (53.6%). If residents living on the third floors are living in old buildings and using coal stoves for heating, their space heating costs increase to 300–399 TL band with a probability of 36.2%
The size of the dwelling, as expected, increases the heating cost as it gets larger. The dwellings between 0–59 m2 pay 100–199 TL with the highest probability of 26.4% and the ones between 60–119 m2 pay 200–299 TL with the highest probability of 26.8%. However, when the size becomes greater than or equals to 120 m2 the most popular cost immediately becomes 400 TL or more with a probability of 28%. This result is supported by the findings of Rehdanz (2007) stating that heating costs decrease with the size of the property in Germany. While residents living in a comparatively large dwellings, such as 120–179 m2, that are located on the third floors pay 100–199 TL space heating costs (32.9%), the space heating costs increase to 400 TL or over if they are living on the the first floors.
In general, more than half of the dwellings having 3 bedrooms seem to pay the highest amount of cost 400 TL or more with a probability of 51.7%. The ones having 4 or more bedrooms also pay 400 TL or more with a probability of 38%. The dwellings having 1 bedroom and 2 bedrooms pay 300–399 TL with the highest probabilities of 26.2% and 33.4% respectively.
The average monthly space heating costs of the dwellings having external wall insulation appears to be 100–199 TL with the highest probability of 35.2%, while the ones which do not have external wall insulation pay 400 TL or more on the average with the highest probability of 31%. Thus, it can be concluded that the lack of external wall insulation almost doubles the space heating costs. Indeed, in the sensitivity analysis, external wall insulation appeared to be the most important factor affecting the monthly space heating costs. This result is supported by many other studies such as Alvarez et al. (2016) who showed that insulation reduces energy costs in low income housings in Mexico, Cheung et al. (2015) who suggest that as well as the presence of the external insulation, the thickness of the insulation is also significant to reduce the energy consumption of the high rise-apartments in Hong Kong.
Building age is another important factor affecting the space heating costs. In fact, older buildings seem to pay higher space heating costs compared to the newer ones. This result is consistent with the findings in United Nations (2018) stating that although new buildings are more expensive to build, they are more energy-efficient compared to the old ones. Kazanasmaz et al. (2014) also support this result by reporting that older buildings are less energy-efficient due to the lack of insulation in Izmir, Turkey. In addition, Rehdanz (2007) also suggests that old buildings are more expensive to heat in Germany. The average amount cost is 200–299 TL for the buildings 0–9 years old with the highest rate of 30.5%. However, for the buildings which are older than 30 years, the average rate of cost is 400 TL or over with the highest rate of 39.8%.
When the heating system used in the dwelling is considered, coal stoves appear to be the costliest one. Dwellings heated by coal stove spend 400 TL or more with the highest probability of 41.7%. Air conditioner and electric stoves also seem to be costly, since, 28% of the dwellings heated by these systems also pay 400 TL or more on the average. Central heating or boiler systems, however, are comparatively cheaper systems which lead to a cost 100–199 TL with the highest probability of 27.7%. These results are similar to the findings of Meier and Rehdanz (2010) in Great Britain. They state that space heating costs are highest if electricity is used while costs for gas are lowest. Rehdanz (2007) also found out that there is a strong effect of the kind of heating system on space heating costs in Germany.
Existence of the double glazing at the dwelling slightly changes the space heating costs. When it is available, the proportion of the costs is distributed almost equally among the second, third and fourth categories 100–199 TL, 200–299 TL, and 300–399 TL. However, when it is not available the most popular average monthly space heating costs increases to the category of 400 TL or more with a slight change in the highest probability which becomes 38.5%. Cheung et al. (2005) also supports this result by stating that the thermal insulation performances of external walls are more effective than those for windows, in their study in Hong Kong.
The study suggests that there is not a significant difference between the space heating costs of the detached houses and the flat type dwellings. In Great Britain, however, Meier and Rehdanz (2010) found out that tenants, who mainly live in flats, pay less heating costs than owners, who mostly live in detached houses. This difference can be explained by the energy efficiency of the flats compared to the houses. On the other hand, Rehdanz (2007) suggests that, in Germany, owners, who mostly live in houses, are likely to pay less space heating costs than tenants, who mostly live in flats. This is because the owners are more careful about the energy efficiency and insulation conditions of their houses.
It seems that facing direction of the dwelling does not appear to have a considerable amount of direct effect on the space heating costs of the dwellings. A study by Hassouneh et al. (2010) in Amman, Jordan, however, suggest that facing directions of the buildings are important when combined with the suitable kind of window glasses at the appropriate direction to reduce the costs of heating and cooling of the apartment type buildings.