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

the error in using equation 2.15 was usually 50% (Etheridge 1996). The magnitude of the errorsassociated with equation 2.15 depends on the distribution of both inlet and outlet openings andthe flow characteristics of those openings. However, at present there are not many simplifiedmethods available for calculating the ventilation rate when wind and buoyancy are acting at thesame time.Air change is driven in part by thermal conditions, so it is important to include a ventilationcomponent in an energy balance on a space. Performing an energy balance on a simple room,the total airflow, ρc P Q T ΔT, added to the conduction of heat through the building envelope mustequal the interior heat loads under steady state conditions. The material properties, surface areas,and temperature difference between the interior and exterior environment are used to calculatethe conduction through the walls and windows, Q walls+windows =UAΔT. The internal loads, Q loads ,typically include heat due to occupants, equipment and lights. For steady state conditions, theenergy balance equation is:Qloads Tc TTUA T (2.17)2.3 Design CharacteristicsIOPIOBuilding details, from the macro-scale, such as how to site the building, taking in to account itssurroundings, to the micro-scale, as in the details of a window type and location, can impact theeffectiveness of natural ventilation in an office building. Some of the design characteristicsparticular to naturally ventilated buildings, including the details of those used in the prototypebuilding are presented in this section,.2.3.1 Building LayoutLarge-scale building design decisions, such as orientation and surrounding conditions, canimpact both the thermal and ventilation performance of a naturally ventilated building. From themacroscopic perspective, this influence begins with the choice of a site location itself, and thecharacteristics of the surrounding area. Other building forms can impact the flow of air on thesite, either enhancing or detracting from the airflow relative to the building under consideration.The orientation and geometry of the building is often determined by the lot of land on which thebuilding will be sited, and can impact whether or not cross ventilation or single sided ventilationis an appropriate means to ventilate the building.For natural ventilation to be effective, the depth and layout of the floor space must be consideredalong with the natural ventilation scheme used to ventilate the space. In cellular-type officeplans, single sided ventilation is prevalent due to the configuration of offices, not allowing forcross-ventilation. With this configuration, air enters and leaves the space on the same façade ofthe building. If the window opening is only at one height, then the NPL falls in the mid-point ofthe window; air enters in the lower half and exits out of the upper half of the window. Thisdesign would have a tendency to create a concentration of warmer air at the ceiling and cooler airat the floor. An alternate configuration could use windows at two heights; the lower windowthen becomes the air inlet opening, while the upper window removes the exhaust air, thus havingthe capacity to remove more heat and lower the space temperature better than the single window31