ASHRAE Journal - September 2009 - 28

significantly. However, the scheduled internal gains are maintained. This shows the importance of focusing on internal gain reduction, as well as façade improvements when targeting net zero energy design. For example, if the equipment and lighting gains can be reduced by 25%, along with using good solar shading (Case 7), the annual gains are reduced to 5.16 kWh/ft2 · yr (55.5 kWh/m 2 · yr). Aggressively conserving by 50% (Case 8) reduces the overall gains to 3.87 kWh/ft2 · yr (41.6 kWh/ m2 · yr). Methods to reduce these gains can include energyefficient lighting, lighting sensors (daylight and occupancy), ENERGY STAR equipment, and minimization of standby power loads. From the information garnered from the model for internal gains, overall annual building energy consumption was established for each scenario. To do this, infiltration, ventilation and domestic hot-water (DHW) demands were estimated, assumed equal for each of the eight building scenarios, and added to the sensible cooling (occupants, window and wall demands) and plug loads (lighting + equipment) described previously. An infiltration rate assumption of 0.25 ach was used, as well as a ventilation rate as per Standard 90.1-2007 (5.30 cfm [2.5 L/s] per person and 0.64 cfm [0.3 L/s · m2]) to determine infiltration and ventilation loads. For domestic hot-water calculations a supply of 1 gallon (3.7 L) per occupant per day, heated from 86°F [30°C] to a hot water supply temperature of 140°F (60°C) was used. Occupant density was assumed to be 276 ft2 (25 m2) per occupant. Finally, an equivalent total electrical building energy demand was calculated using a chiller COP of 5. This annual equivalent energy consumption is shown in Figure 2. The results in this figure highlight that the energy impact of infiltration is approximately the same as that of a high performance façade (cooling). Further, the load contribution from outside air requirements for the occupants is of the same magnitude as the sum of plug and façade driven cooling loads. Focusing on the façade as the exclusive driver of total building energy demand will not lead to a net zero energy building. When a high performance façade is selected that effectively reduces solar gain and infiltration loads, a significant load contribution from plug and lighting loads still must be addressed through optimization of daylight penetration, internal lighting controls and use of energy efficient appliances. This ultimately means that there is diminishing value from focusing on the façade, and that design teams must also concentrate on internal and latent loads. Renewable Energy Harvesting www.info.hotims.com/25208-12 The available solar radiation in Abu Dhabi makes the harvesting of solar energy an obvious first choice for renewable energy production. With the relatively low average wind speeds for the region, wind energy typically may be less feasible in terms of likely lower power production for roof-mounted, micro wind turbines compared to solar energy for the same roof area.2 In September 2009 28 ASHRAE Journal

ASHRAE Journal - September 2009

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