Environmental Impacts of Multi-Storey Buildings Using Different ...

- 44 -5.2.3 Buildings’ Thermal Envelope DescriptionsTable 5.3 shows the different construction of the office area envelope walls, including wallthickness, R/values (heat loss) and the percentage of the section of each wall configurationtype within the total wall for each of the walls involved in the envelope of the main body ofoffices, for each of the Concrete, Steel, Timber and TimberPlus buildings. This informationis of importance because only the office areas use HVAC (mixed with natural ventilation), sothere is significant energy consumption required to keep a comfortable range of temperatureinside those areas, with heat losses through walls having a particularly large impact.As seen in Table 5.3, a significant difference between the Concrete building (with highthermal mass) and the three other buildings (with lower thermal mass) - Steel, Timber andTimberPlus - is that the Concrete building has a much thicker wall in the east and westfacades (Thermomass) than the east or west facades of the Steel, Timber or TimberPlusbuildings. Despite this much greater thickness, the R/Values are lower for the Concretebuilding than for the Steel, Timber and TimberPlus buildings. The wall description in all fourbuildings is segregated into cavity walls and structural walls.All light weight envelope walls in the Steel, Timber and TimberPlus buildings, including thesouth façade internal wall of the Concrete building, have 90 mm thick fibre-glass insulation.There was no variation in the thickness of insulation between any buildings, so the finalR/value differences between light weight walls is due to the influence of different linings,claddings and air cavity thicknesses. The TimberPlus building normally has higher R/valuesthan the Timber building, due to timber external claddings and interior linings.Table 5.3 is a summary of detailed wall specifications. Total R/Values were calculated by theDesignBuilder software used for simulations.When looking at light weight walls in any of the four buildings, the cavity is the section of thewall that contains insulation between the internal linings and the external air cavity under thecladding, and the structure is the section of the wall that contains the studs and nogs(blocking) all added together, acting as a thermal bridge. In the case of the Steel building, thepart of the wall structure acting as a thermal bridge is only the web of the cold-rolled steelchannel used as studs. On the other hand, in a timber frame wall, the area acting as a thermalbridge is the complete timber stud width. Nevertheless, thermal conductivity is much higherin steel (45.3 W/mK) than in timber (0.11 W/mK) so the incidence of the small portion ofsteel in a steel framed wall is as significant as a much larger portion of wood in a timberframed wall (ASHRAE American Society of Heating, 2005).Because of the high thermal conductivity of steel, the main structural system of the steelbuilding was left inside the offices and not within envelope walls so it doesn’t drasticallyincrease the heat losses. On the other hand, in the Concrete, Timber and TimberPlusbuildings, the structural systems are rather similar and the shear walls are part of the structuralsystem. This means that in the east and west facades, the structural walls are part of theenvelope walls, somewhat decreasing the total R/Value. In the Concrete building, there is alayer of extruded polystyrene in the core of the structural walls but in the Timber andTimberPlus buildings no extra insulation has been added to the shear walls. The influence ofstructural components on the thermal envelope is the main reason why all four buildingscannot have exactly the same R/Value, even when the same insulation is used.