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4. Energy Features
4.1 Energy Performance of Building Envelope 4.2 Chiller Plant Design 4.3 Air-conditioning System 4.4 Electrical Power Supply 4.5 Lighting System 4.6 Building Management System 4.7 Lifts and Escalators 5. Other Interesting
Features
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| 4. Energy Features | ||
 
Building Envelope |
 4.1
Energy Performance of Building Envelope
The curtain wall of the building was carefully designed to achieve good energy performance and aesthetical appearance. The visual panels are double glazed with silver or gold reflective glasses and spandrel panels have an additional 50 mm mineral wool insulating backing. The shading coefficient (SC) of the glazing portion is as low as 0.13 to 0.2. Thus, the solar radiation imposed on the air-conditioning is reduced. The building perimeter is lined with a row of thick R.C. columns and the space between the columns and the curtain wall is also insulated with mineral wool which further reduces the heat conduction through the building envelope. The thick R.C. columns also adds more thermal mass to the building structure and help to affect heat transfer and peak cooling load by its thermal inertia. |
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Chiller layout |
4.2 Chiller Plant Design The total cooling tonnage of the building is 5,536 TR (refrigeration tons) and the whole system was divided into three separate zones, each with its own chiller plant of approximately 1,800 TR cooling capacity. The plants are located on three multiple storey mechanical floors, namely, 5-6/F, 44-45/F, 70-72/F. With this arrangement, the system was simplified to just like three medium rise buildings with one stacked on another. One problem of such an arrangement is how to resolve the heat rejection of the chillers installed indoor on different levels, without affecting the aesthetics of the building facades. Another problem is how the building operator can efficiently operate the three scattered chiller plants. Various heat rejection proposals such as seawater cooled, air-cooled using radiators and air cooled condensers were compared. After careful analysis and evaluation, the first two schemes were dropped owing to technical constraints, time limitations and economic considerations. The direct air-cooled package chillers proposal was finally adopted, which is a flexible and cost effective scheme for the project. Aesthetical considerations required all chillers to be installed indoor. For proper heat rejection, particular arrangements were made to separate each mechanical floor into two levels. The chillers are placed on the lower level while the upper level is used as a common discharge plenum for the hot condenser air. Thus, no discharge ductings for the condenser fans connecting to outdoors are required. Condenser fans are changed from normal propeller type to vane axial type to overcome the extra pressure loss introduced by intake and discharge louvres as well as silencers. At no wind condition the air will intake from the lower level and discharge freely on all three directions on the upper level. When wind is blowing, positive wind pressure will be exerted at windward side, while negative wind pressure or suction will be exerted n leeward side. When the differential wind pressure gradually increases, up to a certain value, the hot air discharge by the chiller will be directed by the wind and blown out through the leeward side of the building. In order to efficiently remote monitor, control and operate the three independent chiller plants, an intelligent direct digital control (DDC) building automation system was employed and the central control room is located at 6th floor Engineer's Office and 1B/F Management Office.
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Typical floor VAV system |
4.3 Air-conditioning System
For better air quality and zone independent temperature control, all-air single duct with perimeter zone reheat VAV (variable air volume) system incorporating high efficiency air filters was used. During the partload operation the supply air quantity will be automatically regulated to suit each individual zone's cooling or heating requirements. Hence, fan power and the corresponding energy supply are reduced. Meanwhile, since the air handling units and water pipes are way from the office area and air is ducted to the occupied space, quieter operation of the system can be achieved. Routine maintenance can be carried out in the AHU room with minimum disturbance to the tenants. Various VAV systems and fan coil system for the typical office floor were compacted in the preliminary design stage. The results show that:
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Simplified electric scheme |
 4.4
Electrical Power Supply
Based on the areas and usages of the building, the total electricity loading of the building was estimated to be 24,000 kVA. The high rise geometric nature of the building design makes the siting of substations for general power supply and generators for essential supply an important issue. As the vertical span of the building is 292 metres above ground, significant energy loss in the power distribution system will result, should traditional centralised substation arrangement be used. The major load centres inside the building are air-conditioning plants which are located on M1/F, M2/F and M3/F. To locate the power distribution substations close to the load centres, the power company's substations were situated in 5/F, 44/F and 70/F. However, these upper floor substations created a problem in providing transportation and maintenance access to the transformers. The solution is to employ 500 kVA single phase transformers which can be wired in star connection to form 1,500 kVA three phase transformers. Since the physical size of a 500 kVA single phase transformer is very much smaller than that of an 1,500 kVA three phase one, the single phase transformer can be delivered from ground floor to the upper floors by a service lift. The aim of the lighting system is to achieve maximum output and quality of illumination with least energy consumption. The building was provided with an efficient, high quality lighting system to minimise both the energy consumption by the fixtures and the air-conditioning system which tends to remove the heat gain given off by those fixtures. In order to cope with the need in developing a modern office environment, the lighting system is also suitable for an automatic or computerised office. The standard fitting for the office area is a 600 x 1,200 mm light box with parabolic louvre reflector and 36 Watt fluorescent lamps producing an average illumination level of 500 lux at a wattage density of about 15 W/m2. 4.6 Building Management System The
building
management system (BMS) is the METASYS series supplied by Johnson Controls.
There are 2 central control stations located in B1/F Management Office
and 6/F Engineer Office. The system is able perform the following
functions:
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Lifts and escalators
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4.7 Lifts and EscalatorsThe design and space requirements for the lifts serving the office tower have a major impact on the usable space on the floors and the core design. By carrying out a lift traffic analysis, a design criteria was set for the anticipated population in the building. This assumption set for population criteria is one of the most important steps that has to be made in the whole lift study. Any variation in this assumption after the fixing the core design will ruin the previous lift study or in the worse case, additional lifts might be required which again may affect the completed core design. After a field survey, a population density of 11.15 m2 usable floor area per person was suggested and the total population of about 8,700 was calculated.Based on the above population and the design criteria of 35 to 40 seconds average interval between lifts leaving the main lobby and 5 minutes handling capacity of 12% of total population, seven lift zones with four lifts per zone were required. However, because of the inherent constraint of the triangular core, it was not possible to accommodate all the 28 passenger lifts and two service/fireman lifts all the way up from the main lobby on second floor to their destination with reasonable usable floor area efficiency. To improve this, reducing the number of lifts shafts originated from the main lobby was worth considering. Sky lobby concept would be the solution.
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| 5. Other Interesting Features | ||
Central-neon |
neon 5.1 Neon Light Tubes(a) Neon tubings - using 1,000 neon transformers totalling 6,000 m to create a glittering image of the facade. [see demonstration here](b) By installing neon tubes on the tower top, the building can signal the time through the changing colours of the 4 sets of neon tubes. Each hour is represented by a different colour. Every fifteen minutes, one of the four horizontal neon tubings changes into the representative colour of the next hour, from the top tubing to the bottom. The time signals are sent to Central Plaza by Hong Kong Observatory. [see demonstration here]
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