1 Project Overview
The project is located in Nanning City of Guangxi Zhuang Autonomous Region, which is an elementary school with 36 classes and 6 stories. Its height is 21.7m and the covered area is 24814.8 ㎡. The total calculated load of the project is 2055 kW (includes the second season of reserved electricity), and the second-level load is 100 kW (only in the first season). The project set the first 10 kW power supply introduced by municipal administration as its working power supply. Since the two 800 kVA dry-type transformers that bear all load of the first and second season cannot connect the second 10kV power supply or set it as back-up power, and also cannot connect other low-voltage power supply that meets the demand of the second-level load of power supply from neighboring units, so it decides to use self-provided diesel generator as its back-up power supply. After comparison and selection of these schemes, the author eventually agreed with the Party A that an outdoor container-type diesel generator with 200kW as its main power and 235kW as its back-up power will be installed on the ground near the school substation (It is shown in Figure 1). The project has received acceptance and been put into service in 2015.
Fig. 1 Outdoor container-type diesel generator
2 Comparative Analysis
The following is comparison between a home-made open-shelf diesel generator set with the main power of 200 kW and back-up power of 235 kW and another home-made outdoor container-type diesel generator set with the same power in the aspects of floor space, price, operation and maintenance from which some conclusions are drawn.
2.1 The Comparison of Floor Space
a. Scheme One: the scale of the open-shelf diesel generator set is 3600mm(L)*1250mm(W)*2100mm(H), the required area of blowing is about 2.5 ㎡and the ventilation area is about 2㎡. According to related requirements in the Civil Code, the collocation of it is shown is Figure 2.
Fig. 2 Layout of open-frame diesel generator room
The floor space of the generator room is 45.43㎡. When the generator room is set in the basement, the impacts of downcast shafts, ventilation shafts, the floor space of the exit flues on the ground, the area of the supporting evacuation passageway as well ae shear wall and shear column should also be considered. It also needs to consider that the index of the actual coverage area of the diesel generator room to the total area of the building is about 1.5~2, which is usually 70~90㎡. It will take the intermediate quantity of 80㎡ in here.
b. Scheme Two: the scale of the outdoor container-type diesel generator set is 6058mm(L)*2438mm(W)*2900mm(H), and its floor space is 14.77㎡, which is shown in Figure 3 and Figure 4.
Fig. 3 Cross-section of outdoor container-type
diesel generator set
Fig. 4 Top view in outdoor container-type
diesel generator set
According to the above comparison, the floor space of the first scheme is 5.4 times that of the second scheme, so the latter one can save more space. If the standard floor space of each parking space is 12.7㎡, then the first scheme needs about six parking spaces and the second scheme only needs one, so the latter one is better.
2.2 Comparison of Prices
a. Scheme One: the main power is 200 kW, the back-up power is 235 kW, and the price of the home-made open-shelf diesel generator set is about 120~150 thousand RMB. It will take the minimum amount of 12 thousand RMB in here; the civil construction cost of the basement is estimated to 2000/㎡, and the civil construction cost of manufacture of the 80㎡ basement is about 160 thousand RMB; the generator set almost covers 6 parking spaces with 150 thousand RMB of each one, and the intangible cost is about 900 thousand RMB. The above 3 items are about 1.18 million in total.
b. Scheme Two: the total price of the container-type diesel generator set of the same power is 135 thousand RMB (the actual purchase price of the project has been implemented in 2015) ; the civil construction cost of outdoor container-type diesel generator is about 10 thousand RMB, and almost covers one parking space with 150 thousand RMB of each. The intangible cost is about 150 thousand and the total price of the above three items is 295 thousand RMB.
From the above comparison, it can be seen that the manufacturing price of the first scheme is four times that of the second scheme with an extra money of 885 thousand RMB, so the economic value of the second scheme is quiet considerable.
2.3 Transportation, operation and maintenance
a.Scheme One: the generator set is in the basement, so the transportation is relatively difficult. The initial installation would be more difficult with longer time and louder noise, but the operation conditions is relatively better. The damp problem and other issues still exist. When the oil storage room is set in the generator room, the total storage should be less than 1 m³, otherwise it would be hard to add fuel to the generator set. The fire alarm devices , and fire extinguishing facilities that are matched with the capacity of diesel generators and the scale of the buildings should be set up. It should also set an automatic sprinkler system in the generator room.
b.Scheme Two: the generator set is on the ground with convenient transportation and hoisting, relatively shorter construction period, little effect of noise as well as convenient fuel-adding facilities. However, the operating conditions on the ground is not that good, since it has to be weathered by insulation, rainy, thundering and lightening, salt-fog and other terrible conditions. At the same time, it has a large probability of suffering man-made damage, so the practical life time of it will be shorter than scheme one, and it needs more maintenance. The fire-fighting joint control needs special design and treatment, and the project with heavy load capacity should not use this scheme.