Published on: 01/04/2009
Publication: Zawya
Country: Gulf Construction Magazine

According to the U.S Department of Energy, building consumes approximately 37% of the total reservoir of energy and 68% of the electricity produced in the United States annually. As well, In UAE, where industry is respectively less developed, Residential & Commercial buildings consumes an average of 81% of the power exported from the power plants.

Insulating walls involves an additional investment, however that is by outweighed by the reduction of the Air conditioning system and associated electrical and civil works as it will be seen from the attached analysis. That is beside the future reduction of operating annual energy cost.

Apparently, cost of constructing external walls needs to be revised and reconsidered; meaning that the consumption of energy should necessarily be reduced. In an attempt to reduce the consumption of energy by extended walls, Dubai municipality has issued an administration decree No: 77 for the year 2001 that demands a U value =0.1Btu/Hr/Ft².°F for all external walls.

Furthermore, and in order to comply with the principles of LEED 2.2 (Leadership in Energy and Environmental Design) “chapter 3: Energy and Atmosphere”, and for projects following the prescriptive compliance method, all building wall components must meet the minimum insulation and max U-factor listed for the project climate zone.

In correspondence to that, the municipality of Dubai have chosen a suitable value of insulation in order to achieve a compromise between cost and energy saving. Laws set minimum requirements and further improvement is possible and sometime recommended. That is why several new development where considering to use a more stringent lower U value of  0.06 Btu/Hr/Ft².°F. This paper address this issue by evaluating the total capital cost and life cycle cost as compared to the wall with a U value of 0.1 Btu/Hr/Ft².°F.

Prior to the decree, the standard construction was utilizing non insulated masonry wall with U factor of 0.437 Btu/Hr/Ft².°F which is still being utilized in many places in the Middle East.

In this article, we are analyzed the different type of walls based on unit area (m2), where U values should of (U=0.1 Btu/Hr/Ft².°F), (0.06 Btu/Hr/Ft².°F) for Insulated wall, and (U=0.437 Btu/Hr/Ft².°F) for Un-insulated walls were analyzed.

Table 1 & 2 analyze the impact on air-conditioning load design capacity and anticipated annual cooling energy respectively.

Table 3 analyzes the total cost impact of wall insulation considering the wall insulation cost and the resulting reduction in the air conditioning system and associated electrical system cost.

Table 4 analyzes the annual operating cost savings in two area of the UAE, i.e. Abu Dhabi and Dubai & Northern emirates. Other countries need to adjust these cost in respective to their individual utilities rate.

In Addition to the financial analysis, the environmental impact is crucial as well. As the higher the insulation value is, the lower the electric consumption by the air conditioning system. For every kwh of electric power saved, an approximate amount of 0.7 Kg of CO2 emission is avoided at the electric power plant.

As another environmental effect of using insulated wall; the noise pollution from the AC’s and chillers room, in addition to the background noise penetration via external outside will be minimized.

Conclusion

Insulating of walls (U=0.1 Btu/Hr/Ft2.OF) reduce both construction cost and operating cost and hence the application of insulation is no brainer. Yet, one asks why regulation imposing insulation was necessary? The additional cost of 20 Dh/m2 of a wall is offset by reduced A/C system cost and its associated electrical system cost which lead to a net savings of 112.6 Dh/m2 of the wall area. The operating cost is significantly lower by 76%. Further, increased insulation (U=0.06 Btu/Hr/Ft2.OF) requires more careful analysis and has diminishing returns. The additional investment compared to an insulated wall (U=0.1 Btu/Hr/Ft2.OF) is 15.3 Dh/m2 of wall, while the operating cost saving would result in a payback period of 12.75 years in Abu Dhabi and 5.9 years in Dubai & NE.

Abdullah Abu Gallioun                            George Berbari
DC PRO Engineering                                  DC PRO Engineering
Mechanical Engineer, LEED AP                    CEO