Indicadors per descriure el sistema platja-duna i quantificar-ne el potencial de

From the results, and the topics discussed in sections 6.2 and 6.3, it is reasonable to assume that the building’s thermal inertia has a different effect in each of the calculation methods (EN 13790 and CIBSE TM41). To analyze this effect, both calculations were performed on different building types. Table 6.3 displays the values of annual heating energy consumption for different buildings; these buildings have the same dimensions, and weather conditions as the Case Study, but different parameters that influence the effects of building inertia. The values of the parameters for building inertia were taken from Table 12 in EN 13790, which shows default values for different building classes which may be used for the calculation. The trend shows that heavier buildings will produce more similar results when performing the calculation using different methods.

Table 6.3 Theoretical comparison - Effects of building inertia over annual heating energy consumption

Building class Cm* Hm* CIBSE TM41 EN13790 Difference

- MJ/K kW/K MW/h MW/h %

Very light 1.52E+05 23.23 1478 1186 22%

Light 2.10E+05 23.23 1540 1219 23%

Medium 3.13E+05 23.23 1620 1321 20%

Heavy 4.92E+05 25.00 1829 1534 18%

Very heavy 7.02E+05 26.26 1981 1702 15%

* = values obtained from Table 12 of EN 13790 It is important to note that the values in this table are default values which depend on the surface area of building elements. As this standard is general and has no considerations for large space buildings, most likely the default values in the table are for average height buildings, 3 m – 4 m. This indicates that in order to take these values for a calculation for a large building, a correction should be considered to account for the height.

The results are graphically compared in the graph in Figure 6.4.

CONCLUSIONS

The calculation of annual heating energy consumption by the methods proposed in EN 13790 and CIBSE TM41 was performed and later extended to take into account the losses of the heat emission system using the calculation of EN 15316-2-1. After analyzing the results it is possible to come to the following conclusions.

 The EN 13790 standard provides a calculation procedure to determine the annual heating energy consumption for residential and non-residential buildings, however, there are no special considerations that take into account the non-uniform temperature distribution due to uncommon building height ( > 4 m).

 The CIBSE standard also provides a calculation procedure to determine the annual heating energy consumption for residential and non-residential buildings using degree-days, this method is more simplified than the one in EN 13790 and also doesn’t include special considerations for large space buildings.

 It is possible to obtain more accurate values of heating energy consumption of large space buildings by using one of the calculation methods proposed in standard EN 15316-2-1, which takes into account the heating losses of the emission system and also considers a correction for heights above 4 m.

 The calculation method proposed in EN 15316-2-1 indicates that the heating consumption (monthly, seasonal or annual), should be obtained using EN 13790. However, CIBSE TM41 also provides a calculation method for the heating consumption; therefore, the results from CIBSE TM41 may also be used as inputs for EN 15316-2-1.

 The results of EN 15316-2-1 are linked to the calculation of heating energy consumption, so the error is carried from the calculation of the net heating consumption to the total heating consumption (including losses of the emission system, effects of non-uniform temperature distribution and efficiencies of different radiant heating systems).

 A simple flowchart was developed to display the procedure in which the calculation of heating energy consumption of large space buildings may be performed by using

the combination of either EN 13790 or CIBSE TM41 and EN 15316-2-1 (section 6.1).

 The calculation of net annual heating energy consumption was performed using two different standards. The results obtained by using EN 13790 and CIBSE TM41 presented a difference of 38% even though the inputs used for both calculations were the same.

 After an analysis of the equations both methods, it was assumed that the discrepancies occur due to the way each calculation method takes into account the heat accumulation of the building.

 The effects of intermittent heating affect each calculation method in different proportions.

 A theoretical comparison was performed by calculating the annual heating energy consumption of five buildings, each of a different building class. It was observed that the percentage difference between the calculations using EN 13790 and CIBSE TM41 decreases as the building thermal capacitance increases. From the results obtained, it is possible to assume that the results will be more similar for buildings in the class “very heavy.

 It would be beneficial to perform the calculations for different case studies where the heating energy consumption has been measured in order to determine the accuracy of each calculation method. It may also be helpful in determining whether one of the two calculation methods studied is more or less accurate depending on the building class.

In summary, it is possible to calculate the annual heating energy consumption of a large space building by following the simple calculation methods presented in EN 13790 or CIBSE TM41. These results may be complemented with the calculation of energy losses of the emission system and effects of non-uniform temperature distribution and efficiencies of radiant heating systems by following the methods described in EN 15316-2-1. Special attention must be paid when considering the effects of heat accumulation and intermittency.

REFERENCES

1. ISO/FDIS (2006). Energy performance of buildings — Calculation of energy use for space heating and cooling. ISO/FDIS 13790 : 2006.

2. The Chartered Institution of Building Services Engineers. Degree-days: Theory and Application. TM41 : 2006

3. Technical Committee CEN/TC 228. Heating systems in buildings - Method for calculation of system energy requirements and system efficiencies - Part 2-1: Space heating emission systems. EN 15316-2-1 : 2006.

4. Brož, K., Šourek, B. Alternativní zdroje energie. Skriptum ČVUT v Praze : 2003

5. Technical Committee CEN/TC 228. Heating systems in buildings – Method for calculation of the design heat load. EN 12831 : 2003.