1.Increased ventilation（qualitative & quantitative）
2.Environmental envelope material (qualitative & quantitative)
3.Indoor and Outdoor source of air pollution(qualitative)
5-4. IAQ QUALITATIVE DIAGNOSTICS
Figure 1 LEED Scored card of Pearl River Tower in Indoor Environmental Quality (U.S. Green Building Council，2013)
1.Increased ventilation
In Pearl River Tower, eight wind turbines are located (Hansen, 2007) at openings of dimension 6 x 6.8 m2 on two mechanical floors between the three main sections of the tower. Confining the turbines to the mechanical floors reduces the noise and vibration and also simplifies maintenance (Stewart, 2006). The Pearl River tower implements vertical axis Darreius wind turbines, Fig. (2), as they are capable of harnessing winds from prevailing wind directions with minor efficiency loss. The turbines are located on both the north and south sides of the tower in order to take advantage of prevailing southern winds (Fortmeyer, 2007, Wong, 2007). The wind causes a large buildup of positive pressure on the windward side of the building. Vortex shedding around the sides and over the top of the building creates a large negative pressure on the leeward side of the building. In allowing air to pass through the building openings, the differential pressure from front to back is reduced and the forces on the building are, in turn, reduced (Stewart, 2006, Fortmeyer, 2007), Fig. (3). This approach from the structural point of view allows for a reduction in the quantity of steel and concrete to maintain building's stability (Frechette and Gilchrist, 2008). The shape of the building's façade accelerates (Stewart, 2006, Fortmeyer, 2007)
the wind through the turbines. SOM engineers initially estimated that the wind speed would increase to 1.5 times the actual ambient wind, but the funnel shape of the structure at the mechanical floors resulted in increase of the wind speed by a factor as high as 2.5 (Koerner, 2006, Hansen, 2007).
When the wind blows, the air strikes the building and flows against the façade to find its way and avoid the obstacle. The brutal stop of the running air flow makes turbulences and creates a high pressure zone on the windward side. Then, the acceleration of the air when eventually it gets round the edge, creates a low pressure zone on the leeward side. This pressure differential generates constraints.
In Pearl river tower a part of the air can pass through the tunnels, so the forces applied on the structure are reduced. Then, thanks to the portal’s geometry, the air is led to the tunnel entrance, accelerates within it and rushes out on the other side of the tower.
Figures 4 illustrate the air circulation and the pressure differential on both sides of the tower, when the wind direction is lined up with the tunels. II-3 Wind tests A scale model of the Pearl river tower was assembled and tested in a lab. The model’s behavior was analysed under various wind conditions. The velocity of the air was measured on different points, approching the model then inside the tunnels, and compared with a wind speed reference. The model was then rotated to simulate winds coming from all possible directions. Measurements were led for upper and lower tunnels.
Figure 4 air circulation and the pressure differential on both sides of the tower. (Stewart, 2006, Fortmeyer, 2007)
Figure 5 Potential Power Generate by wind
(American Society of Civil Engineers,2008)
Figure 6 Wind Direction and Distribution (American Society of Civil Engineers,2008)
1.1 Shape Optimization for ventilation
PRT has been carefully shaped to minimize design load effects from wind forces. This measure also drastically reduced construction materials and costs. SOM wind tunnel tested its shape, using the results to adjust the design in order to achieve optimal performance.
Four openings in the tower’s south side accelerate the air and drive electrical power-producing vertical axis wind turbines (VWAT). The building’s geometry significantly enhances airflow through the wind turbines—up to 2.5 times the ambient wind speed. Generated power is converted into electrical power for the building.
1.2 Indoor Radiant cooling
“Chilled radiant” ceiling through perimeter chilled beams is used instead of normal ventilation and air conditioning. Cold water pumped (at approximate 14.5deg C) through copper pipes in the slab which cool curved metal plates used for the ceiling system and metal fins for the perimeter, consequently cooling the surrounding air. Chilled air cools the office space below and above.(Figure 8)
Figure 7 Wind Turbine (American Society of Civil Engineers,2008)
Figure8 Illustration of indoor radiant cooling. (Rasha Mazen*1, Magdy Radwan,2010)
1.3 Displacement ventilation
provides only fresh air that is cooled by the chilled-water system and delivered via araised access floor.(Figure 9)
Figure 9 Displacement ventilation (Rasha Mazen*1, Magdy Radwan,2010)
2. Environmental envelope material
High Performance Envelope: East & West Elevations
Pearl River Tower’s design incorporates a dynamic high performance building envelope that provides superior thermal performance, controls solar loads, and optimizes the transmittance of daylight into interior spaces. The east and west elevations use a unitized frit glass outfitted with external shades. The external glass is double silver low-E high performance glass, which provides the best balance between low heat gain and high transparency. This kind of material not only sustainable but also has no air pollution and zero chemical noxious gases emission.
PRT’s performance is heavily impacted by the north and south elevations. In section, these facades break down into a double-wall, 300mm unitized system with a 240mm ventilated cavity that separates two layers of glazing. A low-E coated, insulating glass unit forms the exterior layer, and a single monolithic glazed panel forms the interior layer.The movement of room air through the ventilated cavity is critical to removing solar gain, especially on the tower’s south elevation. The internally ventilated double-wall helps keep the temperature on the inside surface of the exterior wall close to the room ambient air temperature.
The façade (quantitative)
The facade of the Pearl River Tower will feature an internally ventilated double-wall system made up of doubly glazed, insulated units integrated into 3.0 by 3.9 m unitized panel.(Figure 11) Two hinged 1.5 by 2.8 m singly glazed leaves will be fied to the back face of the mullion to create an approximately 200 mm deep cavity with a small air gap at the base. Within the cavity is a motorized silver venetian blind system in which the perforated blinds measure 50 mm wide. The position of these blinds—fully open, open at a 45 degree angle, or fully closed—will be controlled by a photocell that tracks the movement of the sun and is connected to the building management system. The exterior glazing will take the form of insulated, tempered glass with a low-emissivity coating; the inner layer will be an operable clear glass panel that can be opened for maintenance. The units will be suspended from the top at each level and laterally supported at the bottom. This integrated facade assembly provides exceptional thermal performance as well as good visibility through the glass, and it should allow for the enhanced use of natural lighting. In turn, this should make it possible to reduce the amount of artificial lighting required in the space while preserving the excellent viewsvia the perforationseven when the blinds are fully closed. Of greater importance, the doublewall arrangement will be a vital component in maintaining the balance between maximizing transparency and achieving a high standard of comfort for the building’s occupants. As sunlight strikes the exterior doubly glazed skin, some of the resulting solar heat gain will enter the cavity between the outer and inner glazed layers. Fortunately, the cavity will act as a natural chimney. The cooler air from the occupied office areas will enter the cavity via a gap at floor level and act as a pressure relief valve to allow more fresh air to enter the occupied areas. The trapped air in the cavity will then be extracted through the ceiling void to, depending on the outside temperature, either preheat or precool the interior air. By maintaining a low temperature on the interior layer of glass— the layer closest to the occupantsthe mean radiant temperature in the office space will be decreased. This will then reduce the operative temperature of the space from, say, 27ºC at the perimeter to 23ºC farther inside the office. This lower operative temperature will create an environment of improved thermal comfort at the perimeter zones and should directly improve the flexibility and usability of the areas closest to the exterior glazing. A similar system is used on both the southern and northern facades, in part for controlling glare but also because the northern facade is exposed to solar gains from the west in the late afternoon.
Figure 11 High Performance Envelope material
3. Indoor and Outdoor source of air pollution
Respirable Suspended Particles (PM10) are suspended airborne particles with a nominal aerodynamic diameter of 10 µm or less. The health impacts from inhalation of particles depend on size, shape and chemical reactivity. Outdoor sources are numerous, but vehicular exhaust and construction activity contribute significantly. Particulates from outside sources are carried into air-conditioned buildings through outside air intakes and through uncontrolled infiltration. Indoor sources include air ducts, equipment and user activities.
There are large proportion of greenery located outside of Pearl River Tower which could benefit to absorb the outdoor air pollution gases, and the main transportation of the building is the t secondary main road which will control the number of vehicles to exhaust gases compared with the main trunk traffic road.(Figure 12-14) .Meanwhile, the indoor car park of this skyscraper adopted the crossing ventilation which is much useful for the air quality of the car parking.(Figure 15)
Figure 12 Outside greenery distribution of Pearl River Tower (by group)
Figure 13 Outside greenery distribution of Pearl River Tower (by group)
Figure 14 Outdoor transportation of Pearl River Tower (by group)
Figure 15 The entrance of the car parking( by group)