Methodology for the Evaluation of Natural Ventilation in ... - Cham

of cooling required by 30 percent or more, and decrease internal room temperatures by 5°C(Daniels 2003) when compared to lower mass buildings. During summer months thermal masscan be exposed to the lower, nighttime temperatures, in effect pre-cooling the interior spaceduring un-occupied hours. This effect is often created by drawing in cooler night air, andthereby pre-cooling the thermal mass. The pre-cooled thermal mass is then able to temper theinterior temperature during occupied hours, counteracting the build up of heat due to interiorloads. The cooling period takes advantage of the natural diurnal swings of the exteriorenvironment, capturing the cooling energy provided by the lower outside temperatures. In thisway, the internal temperature of the building is moderated; not getting as cold as the environmentduring the nighttime, but also not reaching the high temperatures occurring during midday toearly afternoon. Thermal mass is known for causing ‗peak shifting‘, when the peak internaltemperature occurs well after the peak outside temperature. Sometimes the peak internaltemperature occurs at the end of the workday when there are fewer occupants. In the heatingseason, the thermal mass retains heat generated by the internal loads during the daytime hours,and releases the heat during nighttime hours so that the building does not get as cold or require asmuch additional heating during un-occupied hours.2.3.4 Integration of Design DetailsThe above described techniques are important to the enhancement of natural ventilationindividually; however they can increase the performance of a naturally ventilated building muchmore when two or more are integrated in the building design. It is not uncommon to havewindow type and location selected based on the layout of the building floor plan due to the typeof ventilation, single-sided or cross ventilation, that is planned. Through careful design, many ofthese building characteristics can be incorporated into the overall design of a naturally ventilatedbuilding to ensure proper airflow, occupant comfort, and overall building performance.2.3.5 Prototype Building CharacteristicsThe prototype building, described in detail in Chapter 3, included several of the above naturalventilation enhancing techniques. The building was located in a relatively open office park, withbuildings of similar height. Attention to details such as the selection of building material,increasing daylight within the office space, decreasing solar gain and glare, and office layoutresulted in a naturally ventilated commercial office building that functions well without the needfor mechanical cooling.The material selection for the façade differed from the north to the south side, in part due toarchitectural aesthetics, but also due to the orientation of the building. On the southern façade,light colored materials help reflect some of the solar isolation, whereas on the northern façade,bricks were used as the facing material. Other design details that were incorporated into theprototype building include solar shading to reduce direct solar glare, and light shelves to allowthe natural daylight to penetrate deeper into the office space. Through the use of the lightshelves, the electric energy consumed by the general lighting can be reduced because the fixturesare outfitted with photo-sensors and are dimmable down to 10 percent. The building usesthermal mass to help temper the interior temperature by leaving small, upper windows open atnight during the summer months to pre-cool ceiling soffits. The cross section of the ground floorof the prototype building with these design characteristics is shown in Figure 10.34