"Green School" (Green School) refers to on the basis of realizing the function of the basic education, guided by the sustainable development strategy, adjust measures to local conditions to adopt all kinds of energy conservation and environmental protection in construction technology, and in the work into the management and the teaching measures are beneficial to the environment, make full use of favorable conditions face-to-face, comprehensively improve the quality of the environment between teachers and students of the School. "Green school" will be a variety of active and passive green ecological technology measures and management means for reasonable, optimal integration, in the emphasis on energy efficiency, environmental benefits, but also into the humanities management benefits.

In order to serve the needs of the construction of "energy efficiency township" in ningbo city, chun hu town, fenghua city, chooses chun hu junior high school as a pilot project of renovation. Chun hu town, fenghua city is located in the east of fenghua, jiufeng mountain, xiangshan port bank chun lake town street east village, is the first batch of rural demonstration junior high school in zhejiang province. The school, formerly known as va lake district school junior high school, moved to its current site in 1991. The school is surrounded by mountains and water on three sides, covering an area of 33996m2, 20.1m2 per person, 17230m2 per person, 10.2 m2 per person. The basic situation of the current school buildings of chun hu junior high school is shown in table 1. This renovation is mainly aimed at the old teaching building, comprehensive laboratory building and teachers' dormitory built in the university with old age and old facilities.

Table 1 basic information of lake junior high school

Single name	Building area (m2)	Number of floors	Structural form	Construction age
Teaching building	2200	4layer	Brick structure	1989
Laboratory building	2200	4layer	Brick structure	1995
Teachers' dormitory	1156	4layer	Brick structure	1996
Teaching building	2400	4layer	Frame structure	2002
Dining hall	2200	2layer	Frame structure	2003
Student housing (male)	2339	5layer	Brick structure	2005
Student housing (female)	2339	5layer	Brick structure	2005
Office building	1996	4layer	Frame structure	2008

1. Investigation and analysis of the current situation of the school

The transformation of "green school" is a systematic project involving building envelope, water supply and drainage system, campus public facilities, renewable energy utilization and other aspects. The three buildings that need to be renovated are old in construction, so energy-saving design was not considered in the early stage, and the thermal insulation performance of the outer wall and roof was poor. Before the renovation of the teachers' dormitory, there were no independent sanitary facilities, only public cold water bath facilities. In addition, there are many problems such as substandard green rate, no water saving measures and poor campus environment in the school before the renovation. Through the transformation, the goal of building energy saving by 50%, water saving by 30%, waste recycling and "green building evaluation standard" by one star will be realized. The existing problems before transformation are shown in table 2.

Table 2 summary of investigation and analysis of renovation project of lake junior high school

Number	Question classification	Specific problems
1	Retaining structure	No insulation measures for exterior wall and roof
2		No energy saving outside window
3	Energy conservation and renewable energy utilization	Non-energy efficient lighting
4		No renewable energy can be used
5	greening	Green rate is not up to standard, and the form is single
6	Water supply and drainage	No permeable ground is provided
7		No rainwater collection system
8		The water supply and drainage pipes are old and old
9		The faucet is leaking badly
10	Campus environment	Not properly set up garbage collection facilities
11		The interior wiring was disorganized
12		Leisure and fitness facilities are not perfect
13		The interior walls are peeling and moldy

2. Reform plan of "green school

2.1 renovation of envelope structure

Ningbo is located in the hot summer and cold winter areas. The average temperature for many years is 16.5 ℃, the highest temperature in history is 38 ℃, and the lowest temperature is -6 ℃. Envelope structure transformation should take into account winter heat preservation and summer heat insulation.

2.1.1 modification of external wall thermal insulation

There are three types of exterior wall finishes for the three buildings to be transformed: external Mosaic/facing brick (mainly south facing wall, east west facing wall), perlite (north facing wall) and lime (corridor exterior wall). The original exterior wall is made of solid clay brick 240mm+ sand cement 10mm+ cement lime 8mm+ face brick (or Mosaic), without insulation layer.

External wall insulation has an obvious impact on energy saving effect, but it is difficult to attach external wall insulation board, especially for school buildings with large north-south window wall area. External wall insulation board will cause thermal bridge problem, which will not only increase the cost, but also have a negative impact on energy saving. As the surface of the brick is relatively smooth, the coating of inorganic thermal insulation mortar outside the brick does not meet the requirements of the relevant standards in the aspect of adhesion. Therefore, it is necessary to knock out the original brick layer, and then paint the inorganic thermal insulation mortar, the outer decorative layer of paint thermal insulation coating, double thermal insulation effect.

Through calculation and analysis, the thickness of exterior wall insulation mortar layer is determined to be 30mm, and the thickness of reflective coating layer is 5mm. At the same time, in order to improve the reflectivity of the paint, a light-colored heat-insulating reflective paint is used.

2.1.2 roof insulation renovation

The original roof of the three buildings that need to be transformed adopts SBS heat insulation and water-proof layer. Due to the long age and aging of roof materials, its thermal insulation and waterproof effect is poor. The heat transfer coefficient of the roof is calculated to be 3.85w /(m·K), exceeding the limit of the current local energy-saving design standard.

The transformation adopts inverted roof. Compared with the traditional construction method, this method can make the waterproof layer have no heat expansion and cold contraction phenomenon, and extend the service life of the waterproof layer, and the insulation layer provides a physical protection to the waterproof layer, preventing it from being damaged by external forces. The insulation layer is made of extruded polystyrene foam board (XPS), mainly considering that the XPS board has good thermal insulation performance, high strength, good weather resistance and good moisture resistance. After calculation, 30mm thick XPS board should be added to the roof. Due to the aging and cracking of SBS waterproof rolling material on the original roof, the outer layer of cement mortar has been seriously damaged, so it is necessary to scrape off the original cement mortar layer and SBS waterproof layer, clean the roof, dry it, and then construct the waterproof layer, thermal insulation materials, and paint the thermal insulation coating.

2.1.3 external window reconstruction

The exterior window is the weak link of the envelope insulation. When the thermal resistance of the wall is increased with the thermal insulation material, the heat loss of the Windows accounts for a larger proportion of the total energy consumption of the building, which is one of the main reasons affecting the thermal environment of the building and causing high energy consumption.

Before the renovation, the teaching building, the laboratory building and the teachers' dormitory building all adopted the steel frame Windows widely used in the 1980s. The glass is 3mm thick single-layer ordinary glass, and the heat transfer coefficient of the whole window is up to 6.4w /(m2·K). Some of the outside Windows were badly broken. Plastic steel window has the advantage of sound insulation performance, low price, will be replaced with plastic steel hollow glass window (5+9A+5), the heat transfer coefficient of the frame is 2.7W/(m2.k), the heat transfer coefficient of the whole window is 3.0w /(m2.k), shading coefficient is 0.85. The main body of the three reconstruction buildings adopts the form of outer corridor in the south direction, and there are no outer Windows in the west direction.

2.2 transformation of green lighting

The quality of lighting directly affects students' eyesight and learning efficiency. Chun hu junior high school teaching building, laboratory building, teachers dormitory building used before the renovation of lamps are divided into three kinds: (1) classroom, laboratory and dormitory are set in the low light efficiency, short life of 40W ordinary T12 fluorescent lamps; The corridor is equipped with a 40W ceiling light; The staircase is equipped with 15W incandescent bulb. It does not meet the target value requirements of energy saving power density of classroom lighting in building lighting design standard (GB 50034-2004). In addition, the use of lamps and lanterns for a long time, the illuminance significantly reduced, adverse effects on students' eyesight.

According to the class and arrangement of lamps in the classroom of the old teaching building, the illumination of the classroom is analyzed, and the results show that there are mainly the following problems in the classroom lighting: (1) the illumination of the classroom is insufficient, as shown in figure 1. The simulation results are below 150Lx, far below the requirements of GB 300Lx; The blackboard illuminance is lower, far below the requirement of GB 500Lx. Using inductive ballast and halogen powder lamp tube, the energy consumption of the inductive ballast is up to 8w; The light source is inefficient, only 59 lm/w. (3) the lamp aging is more serious, low reflection efficiency. According to the above conclusions, the following reconstruction plan is made.

(a) before and (b) after the renovation

FIG. 1 simulation results of classroom illumination before and after renovation in va lake junior high school

(1) all the fluorescent lamps and ceiling lamps were replaced with double-tube school special grille lights and blackboard special lamps with high light efficiency, long life and good color rendering. The light flux of the lamps was 104lm/w. The simulation results of illumination in the classroom before and after the reconstruction were shown in figure 1.

(2) in order to prevent glare and enable students to read the blackboard clearly, the teacher should also be able to see the students' facial expressions. The 24° shading Angle is an ideal Angle, as shown in figure 2.

(a) sectional view of the luminaire (b) side view of the luminaire

Figure 2 anti-glare lamp shading Angle design

(3) because the blackboard is vertical, if only rely on the ceiling lighting, the vertical illumination of the blackboard is not enough, so it is necessary to set up special lamps. The vertical illumination on the blackboard of the classroom is not less than 1.5 times of the horizontal illumination, in addition to the requirements of the blackboard lighting: (1) students should not be reflected by the blackboard glare, and can easily see the writing on the blackboard; Teachers do not feel glare when lecturing and writing on the blackboard; The vertical illumination on the blackboard should be arranged uniformly. The more uniform the illumination on the blackboard, the more you can see. Lighting the bottom of the blackboard, which tends to darken, is one way to make the illumination as even as possible. By calculation, 55° is the best Angle of uniformity. Make sure the students can't see the light source directly when the shading Angle is above 45°.

(4) the teaching building, the laboratory building and the corridor of the teachers' dormitory should be replaced with LED lights, and the time controller should be used.

2.3 solar water heating system

The solar energy resources in ningbo are in the transition zone from the rich area to the poor area. According to the meteorological data, the average annual sunshine hours in ningbo in recent ten years are about 1900 hours, and the average annual solar radiation is about 4585MJ/m2. In order to effectively utilize solar energy resources, solar water heating system should be installed in teachers' apartment buildings to improve teachers' living standards and build energy-saving apartment buildings with low energy consumption and low operating cost.

The solar collector based on all-glass vacuum tube has the characteristics of low cost, high solar absorption ratio and low infrared emission ratio. The vacuum interlayer of the vacuum collecting tube has a good thermal insulation performance, and the cylindrical heat-absorbing layer has a natural tracking property to the sun. As long as there is solar radiation, the vacuum collecting tube can work, and the hot water can be normally supplied throughout the year. Therefore, the direct insert full glass vacuum tube collector is selected.

In this project, the installation direction of the solar collector's lighting surface is the same as the orientation of the building, which is about 15° from the south to the west. In order to receive the maximum amount of solar radiation, the installation Angle between the designed solar collector and the horizontal roof is 30°, and the minimum spacing between the front and rear collectors is 0.45L (L is the north-south length of the collector, which can effectively avoid the self-shielding between collectors). According to the code for design, installation and acceptance of solar hot water systems for residential buildings (db33/1034-2007), the recommended total area of the system collector for each 100L of hot water is 1.8m2. According to the system type, the average household collector area is about 1.5~1.8m2.

Over the years, the lowest temperature in ningbo is about -6 ℃, and the vacuum tube can resist freezing at -10 ℃, no freezing problem. In order to ensure the 24-hour hot water supply in the dormitory, electric heating is adopted as an auxiliary heating measure, which is used when solar energy is not enough to provide 55℃ hot water due to cloudy weather such as rain.

2.4 water-saving transformation

2.4.1 replace water supply and drainage pipes and taps

The water supply and drainage pipes of the 3 buildings that need to be rebuilt are made of ordinary cast iron drainage pipes, which are easy to rust, self-important and inconvenient for transportation and construction, and have been basically eliminated. Some water supply and drainage pipes have rusted, some leakage is serious, resulting in wall cracking and other problems. Unified use UPVC (150 mm) Ø pipes. When using the same diameter of pipe to transport the same liquid, UPVC pipe than galvanized pipe, cast iron pipe resistance is 30% less; When the head loss is the same, the water carrying capacity of UPVC pipe is more than 20% larger than that of cast iron pipe. In addition, there are serious water leakage in the campus faucets, some of which cannot be closed, some of which have obvious water accumulation in the pools and serious water resource waste. All of them are replaced with ceramic spool faucets or induction faucets to save more than 5% of water.

2.4.2 set up the rainwater collection system

Chun lake junior high school existing roof and road surface rainwater are discharged in the municipal sewer network through drainage ditch. The average annual rainfall in ningbo is about 1400mm, and the maximum monthly rainfall is 190mm (except the special rainstorm season). The roof and pavement area of chun lake junior high school can collect rainwater is about 3572m2, among which the roof rainwater area can collect is 2640m2. According to the existing road drainage ditch and the drainage ditch around each building, the rainwater collection route is set. According to the statistical calculation, the total length of rainwater collection pipe is about 360m, and the total length of rainwater collection ditch is about 875m. The reservoir is located in the open space on the north side of the school near the wall for easy construction and management. The reservoir covers an area of 60m2. The collected rainwater is treated and used for school greening irrigation and road surface washing.

2.4.3 permeable ground

There are four kinds of ground in the campus before the reconstruction: the road surface is hard cement surface; The floor in front of the two teaching buildings is cement brick floor with a short period of pavement. Green ground; Bare ground in front of the new complex and on the playground. The permeable ground is conducive to the recharge of surface water, reduces the pressure of sewer network, and plays an important role in improving environmental quality, reducing dryness and heat, and reserving water resources. The concrete pavement at the sidewalk on both sides of the road is transformed into permeable ground, and the permeable square brick is laid, which can be combined with the construction of pavement rainwater collection and drainage ditch. Grass permeable bricks should be installed in the empty space of the new complex building to the south. The newly added permeable ground area is about 1210m2.

2.5 campus environment renovation

2.5.1 ground greening and vertical greening

According to the statistics, chun hu junior high school has an existing green area of 4736m2, and the whole school covers an area of 33996m2. The green rate is only 14%, and the green form is undiversified. Therefore, it is reasonable to add green area on campus, and the green area is about 910m2.

FIG. 3 vertical greening structure diagram of outer corridor

The corridor is an important part of the main body of the three buildings, and the decoration of the corridor is directly related to the appearance of the building. Greening the outer edge of the corridor can not only achieve a certain shading effect, but also improve the appearance of the building and beautify the campus environment. The facade of the corridor outside the main body of the three buildings is made of Mosaic or brick, without any decorative components, which makes the corridor appear monotonous. A variety of drought-tolerant ornamental plants suitable for va lake are planted along the side of the original corridor, as shown in figure 3, to achieve a refreshing effect.

Considering that the staff is not often in the laboratory building, which is not convenient for daily maintenance, we choose to plant winter jasmine in this building. This kind of plant likes the light, likes cold, likes wet, withstands drought, is not strict to the soil. There are often people in the teaching building and teachers' dormitory, which is conducive to daily maintenance. Choose other plants with good ornamental properties, such as gardenia and Chinese rose, etc.

2.5.2 garbage classification and recovery

Modern recycling technology makes part of the household waste can be recycled. In order to save resources, garbage sorting and recycling must be vigorously advocated. According to the interview, only 8 garbage cans are set up in the whole campus, among which 3 are classified and recycled, 4 are simple plastic ones and 1 is stainless steel. Most students have no awareness of garbage classification. The existing garbage cans are not only limited in number, but also scattered. There are no garbage cans on the north side of the experimental building. In the campus, separate recycling bins are set up to replace simple plastic and stainless steel bins, and separate recycling bins are added. In addition, a notice board is set up next to the main sorting and recycling bins to tell students how to sort the rubbish into organic and inorganic categories.

2.6 behavioral energy saving

Behavioral energy saving is through the active behavior of users, to tap the potential energy saving space and potential in life, to achieve the effect of active energy saving. Campus is an important part of society, an important cradle and base for teaching and educating students and providing scientific and technological support for the country. The construction of "green schools" can reduce the cost of running schools, protect and optimize the ecological environment, and form a sustainable development of campus. This needs teachers and students to participate together, starting from the bit by bit, really realize the behavior of energy saving.

3. Reconstruction costs and benefits

3.1 reconstruction cost

The transformation cost of the green ecological technology system in chun hu junior high school is shown in table 3. The cost of building envelope reconstruction accounts for about 48% of the total investment, among which the external window reconstruction accounts for about 18% of the total investment.

Table 3 summary of economic analysis of renovation of junior high school in va lake

Specific problem  quantity total investment/yuan	unit floor area cost/yuan	The number of	Total investment/yuan
Exterior wall painted with heat-insulating reflective paint	20 yuan/m2	2, 305m2	46100
Exterior wall shall be painted with inorganic insulation mortar	70 yuan/m2	2, 305m2	161350
Roof insulation	230 yuan/m2	1, 325m2	304750
Outside window reconstruction	280 yuan/m2	1, 111m2	311080
Special light for school + special light for blackboard + high-efficiency fluorescent lamp (for dormitory)	510/415/240 yuan/lamp	160/40/56 lamp	111640
Solar water heating system	1, 800 yuan/m2	57.5m2	103500
Replacement of water supply and drainage pipeline is	50 yuan/m	357m	17850
Replacement of water-saving faucets	150 yuan/m2	80	12000
Add 330 yuan/m vertical greening	330 yuan/m2	180m	59400
Additional permeable ground	60 yuan/m2	1, 210 m2	72600
Additional rainwater collection and utilization system	500, 000 yuan/set	1 set of	500000
Garbage sorting and recycling	700 yuan/a	6	4200
Additional leisure fitness equipment	1, 500 yuan per set	ten	15000
Behavior energy saving	50 yuan/m2	40 m2	2000
The total is	1, 721, 470yuan
The initial investment per unit building area is about	About 100 yuan/m2

 

3.2 reconstruction income

The energy consumption simulation of the envelope reconstruction technology and the overall reconstruction scheme was carried out for the main body of the three buildings. The results are shown in table 4. After the reconstruction, all the three buildings met the 50% energy saving requirement of the public buildings in the design standard for energy saving of public buildings in zhejiang province.

Table 4 analysis results of energy saving rate of the main part of the reconstruction of the three buildings

Building construction	Single energy saving rate				Overall energy saving rate
	Heat-insulating reflective paint	Inorganic insulating mortar	Plastic steel hollow glass Windows	Roof XPS insulation
The teaching building	3.04%	8.65%	15.05%	8.92%	52.40%
The lab building	3.23%	8.92%	15.15%	9.03%	52.76%
The teacher dormitory	3.35%	9.04%	14.92%	9.14%	52.85%

Indoor thermal comfort is an important index to evaluate the classroom environment, which directly affects students' listening mood and physical and mental health. The coldest month (February) and the hottest month (July and August) were winter and summer vacations, and the worst indoor thermal comfort was in January and September. The natural room temperature before and after the renovation of three buildings was simulated and analyzed. The average outdoor dry bulb temperature in ningbo was 5.2 ℃ in January, and 26.8 ℃ in September. The results show that the indoor thermal comfort has been significantly improved after the renovation (table 5).

Table 5 comparative analysis results of natural room temperature before and after modification

Building construction	Average indoor temperature /℃ in January		Average indoor temperature /℃ in September
	Before modification	After transforming	Before modification	After transforming
The teaching building	14.9	16.6	26.8	24.2
The lab building	13.8	14.7	26.5	24.7
The teacher dormitory	13.5	15.7	27.5	24.7

Adjust measures to local conditions is the soul of "green school" technology application, Chun lake middle school "green school" transformation according to the specific environment and school characteristics, a reasonable choice for the local system of green ecological technology, in school the whole life cycle of conserving energy, water, land and materials in ensuring that build health, suitable and efficient learning space, and is the energy conservation and environmental protection education for the students. The adoption of various ecological technologies has reduced the building energy consumption, improved the indoor environment quality, and the renovation cost has been controlled within a reasonable range, which has provided an important reference for the construction and renovation of "green schools" in China, with demonstration significance and promotion value.

References:
[1] green building evaluation standard (GB/T 50378-2006), 2006
[2] architectural lighting design standards (GB 50034-2004), 2004
[3] code for design, installation and acceptance of solar water heating systems for residential buildings (db33/1034-2007), 2007
[4] design standard for energy conservation in public buildings of zhejiang province (db33/1036-2007), 2007

Source: tian huifeng