Recommendations for energy saving

Building structure

Recommendations were made regarding the modernisation of the building structure based on the values for the heat transfer coefficient and the calculated specific heat loss coefficient. Structures that have a heat transfer coefficient close to the reference value should not be refurbished, due to the long payback time of such an investment. When the heat transfer coefficient for external walls is between 0.6 and 0.85 W/m2K, the suggestion is to add 8 cm of heat insulation to the outer surface of the walls; and when it is higher than 0.85 W/m2K, the suggestion is to add 10 cm of heat insulation. When the reference heat transfer coefficient value for the roof is low, more heat insulation is needed. When the heat transfer coefficient is higher than 0.6 W/m2K, the suggestion is to add 15 cm of heat insulation. Windows and doors with a heat transfer coefficient of ≤ 1.9 W/m2K should not be replaced, but where U > 1.9 they should be replaced with a new structure with a heat transfer coefficient of 1.5 W/m2K or even lower.

These values were approved by all the participating energy experts. In one of the countries there are several permitted values for heat transfer coefficients due to the country’s different climate zones. In this case, recommendations regarding the building structure were modified in order to meet these requirements. As a result of modernisation, average heat transfer coefficients for walls would decrease from 1.28 to 0.49 W/m2K; for roofs from 0.97 to 0.25 W/m2K; for windows from 2.57 to 1.6 W/m2K; and for doors from 3.0 to 1.57 W/m2K

(
Figure 44).

Average heat transfer coefficients before and after modernisation



Specific heat loss coefficients were recalculated for heat-insulated structures and replacement windows. After modernisation, the calculated specific heat loss coefficient was lower than the reference value in all the schools except one, which was a temporary building for which modernisation was no longer considered.

Figure 45

Building envelope index after modernisation

shows the distribution of the building envelope index after the modernisation of the building structure. A comparison of Figures 41 and 45 shows that the building envelope index is significantly lower following modernisation. Before modernisation, the average specific heat loss coefficient was 0.49 W/m3K, and the average for the building envelope index was 1.64 times higher than the reference value. After modernisation, the average specific heat loss coefficient would decrease to 0.19 W/m3K, and the average for the building envelope index would be 0.66 times lower than the reference value.



Better thermal characteristics of the building envelope ensure lower heating energy consumption and at the same time affect feelings of comfort. Adding heating insulation to external walls can improve perceptions of temperature among children, as the indoor surface temperature of the external walls will be higher. Replacing windows can also increase perceptions of thermal comfort, as the filtration of cold air through the new windows will be lower. However, the new windows must be regularly opened in order to ensure fresh air in the classrooms.

HVAC systems

Recommendations were also made for the modernisation of HVAC systems based on the data obtained via the energy questionnaire and the calculation of primary energy consumption. The recommendations were sent to the local energy experts, who gave their feedback on the final version, taking into consideration national standards and guidelines. The main recommendations for HVAC systems were that:

  • oil boilers should be changed to condensing oil boilers;
  • constant-temperature gas boilers should be changed to condensing gas boilers;
  • coal-fired boilers should be changed to biomass boilers, if there is sufficient space to store the heating fuel and if a biomass supply is available near the school;
  • a thermostatic valve should be fitted to every radiator;
  • variable speed pumps should be used;
  • balancing valves should be built into the return pipes of heating risers;
  • HVAC appliances in district heating centres should be heat insulated; and
  • indoor temperatures should be lowered at night and during the weekends following the modernisation of the building structure.

Analysis of the impacts of modernisation

Primary energy consumption was recalculated for the modernised building structure and HVAC systems. Before modernisation, the average total primary energy was 220.9 kWh/m2a, and after modernisation the average would fall to 108.0 kWh/m2a.

The total primary energy consumption shown in

Figure 46

Total primary energy consumption before and after modernisation (country averages)

is the average of the total primary energy consumption in the schools per country. Before modernisation, schools in Slovakia had the lowest primary energy consumption (127 kWh/m2a), thus they show the smallest reduction in energy consumption (21 kWh/m2a, or 16 percent). In schools in Belarus, the average primary energy reduction is 44 kWh/m2a (31 percent). A reduction of 40 to 45 percent can be achieved in schools in Bosnia and Herzegovina, Italy, Hungary, Albania and Kazakhstan. In Ukrainian and Serbian schools, the reduction in primary energy consumption would be over 50 percent, while the biggest reduction in primary energy consumption (80 percent) can be realised in Tajikistan.

Investment costs

The cost of modernisation, including heat insulation for walls and roofs, replacement windows and the modernisation of heating systems, naturally varies from country to country. The thermal insulation of walls costs between EUR 35 and 46 per m2, and for roofs between EUR 36 and 50 per m2. Replacing doors and windows involves the biggest investment, costing between EUR 180 and 200 per m2.

The price of energy, including natural gas, oil, district heating and electricity, also varies among the analysed countries and has a big impact on the payback time of an investment. In most of the SEARCH II countries, the price of electricity, for example, is between EUR 0.08 and 0.11 per kWh, although in Tajikistan, where there are many hydroelectric power plants, electricity is far cheaper at EUR 0.027 per kWh. This is probably one of the reasons that schools in Tajikistan are heated with electricity.

The price of natural gas also varies significantly in the analysed countries: it is most expensive in Italy and Serbia (EUR 0.094 to 0.097 per kWh), where the price is nearly four times higher than in Tajikistan and Kazakh-stan (EUR 0.023 to 0.026 per kWh).

The number of heating degree days (HDD) can also differ even within a single country, if that country has several climatic zones. A higher number of HDD results in greater heating energy consumption, thus the same modernisation of a building does not result in the same energy savings in the different climatic zones. The number of HDD therefore also has a big influence on the payback time of a modernisation investment. The highest HDD (6,286) was found in Astana, Kazakhstan, and the lowest (751) in Palermo, Italy.

The payback time for the proposed modernisations is shortest in Belarus, Kazakhstan, Serbia and Ukraine, at typically less than 10 years.

Conclusion

Data on building structures, HVAC systems and energy consumption in 95 schools were gathered and analysed. The specific heat loss coefficient, primary heating energy, energy for the DHW supply, lighting, air handling and cooling, as well as annual gas, district heating and oil consumption were calculated based on the input data. From these calculations it can be concluded that:

  • only 15 percent of buildings had a lower heat loss coefficient than the reference value; and
  • nearly 50 percent of buildings had a heat loss coefficient over 1.5 times higher than the reference value.

In a first calculation, all buildings were assumed to be situated in the same location. The specific heat loss coefficient and primary energy needs were calculated. Two indexes were created, school by school, in order to compare the buildings from the point of view of thermal characteristics:

  • The building envelope index (qi) — the calculated value of the specific heat loss coefficient of a given school divided by the reference value of the specific heat loss coefficient. The calculated specific heat loss coefficient is generally 164 times higher than the reference value.
  • The energy index (ei) — the calculated value of total primary energy consumption of a given school divided by the reference value for total primary energy consumption. The average primary energy consumption was 220.9 kWh/m2a for the 95 analysed schools. The calculated primary energy consumption was generally 1.7 times higher than the reference value, thus it can be concluded that the modernisation of building structures and HVAC systems has a very large energy-saving potential.

In the second calculation, in which the energy consumption of the buildings was calculated using the actual location, the calculated and real energy consumption were compared and the values were found to be similar. The building simulation models can therefore be considered useful for further investigations. Recommendations were made for the modernisation of the building structures and HVAC systems and discussed with the local energy experts.

The specific heat loss coefficient, building envelope index, total primary energy consumption and energy index were estimated after modernisation, school by school. Following modernisation:

  • the average specific heat loss coefficient would decrease from 0.49 W/m3K to 0.19 W/m3K;
  • the average building envelope index would decrease from 1.64 to 0.66;
  • average total primary energy consumption would decrease from 220.9 kWh/m2a to 108.0 kWh/m2a, thus the average potential energy saving is more than half the primary energy consumption; and
  • the improved thermal characteristics of the building envelope would ensure lower heating energy consumption and at the same time improve perceptions of comfort among children.
 
Ministero Dell'ambiente Italian Trust Fund