School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
sunhe@tju.edu.cn
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2013-07-15
2013-10-09
2014-03-05
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2014-03-05
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Abstract
With the wide use of light steel structure in industrial buildings, some problems such as air leakage, water dripping and condensation and so forth occur during the construction and operation phases. Through the onsite testing of a winery building in Huailai County, Hebei Province in China, the influence of infiltration on energy consumption in industrial buildings was studied. The pressurization test method and moisture condensation method were used to test the infiltration rates. The results show that the winery building is twice as leaky as normal Chinese buildings and five times as leaky as Canadian buildings. The energy use simulation demonstrates that the reduction of the infiltration rate of the exterior rooms to 1/3 and the interior rooms to 1/2 could help decrease a total energy consumption of approximately 20% and reduce a total energy cost of approximately $ 225000. Therefore, it has a great potential to reduce the energy consumption in this type of buildings. Enforcement of the appropriate design, construction and installation would play a significant role in improving the overall performance of the building.
Hejiang SUN, Qingxia YANG.
Influence of infiltration on energy consumption of a winery building.
Front. Energy, 2014, 8(1): 110-118 DOI:10.1007/s11708-013-0293-3
Light steel structure, famous for its external image, reasonable spatial structure, light weight, high intensity, and standardized production, is widely applied in industrial buildings [1]. However, during the construction and operation stage, some problems could occur in case of improper installation. For example, moisture may leak into the building in summer and condensation may occur on the interior surface of building envelopes in winter. Figure 1 shows the condensed water and ice in the building due to infiltration. An increase in moisture-related building failures has occurred where mold grows because of elevated moisture content for extended periods of time, which has created significant concerns about indoor air quality [2] that may threaten the health of the people and quality of products in the building. Solving these problems could help create a better environment.
A lot of studies on infiltration in such buildings were conducted. Pan [3] found that the air-tightness of 287 post-2006 newly built dwellings in the UK was 5.79 m3/(h·m2) on average at 50 Pa. The United States Department of Energy concluded that up to 40% of the energy consumed to heat or cool a building was due to air leakage into and out of buildings [4]. In China, the infiltration study is not as sufficient as that in developed countries. Chen et al. [5] studied the air tightness of residential buildings in North China and its effect on district heating. Their simulation result showed that the total energy use of district heating was reduced by 12.6% when the air change rate (ACH) was reduced from 0.98 h−1 to 0.5 h−1. Previous studies on air infiltration mainly focused on residential and public buildings [6,7]. However, infiltration studies of industrial buildings are seldom found in the literature.
Infiltration may bring about the high energy cost problem in industrial buildings. Energy efficiency has been recognized as an essential part of sustainable building assessment [8]. For industrial buildings that have strict control over the indoor environment, the energy consumption caused by air leakage could be high depending on the infiltration rate. Therefore it is necessary to incorporate air infiltration into design. On the one hand, in the ventilation system design, air infiltration is generally neglected and included in the air change rate due to mechanical ventilation system. Such a practice causes an increase in energy consumptions and an improvement in indoor air quality; as a consequence, a wrong assessment of the contribution of air infiltration can give rise to the oversize of the ventilation system design [9]. On the other hand, no provisions for the building’s air tightness have been included in Chinese standard such as Code for Acceptance of Energy Efficient Building Construction (GB50411— 2007), Code for Design of Clean Room (GB50073— 2001), and Code for Construction and Acceptance of Clean Room (GB50591—2010) [10,11]. This indicates that the air tightness of light steel structures have not been taken into consideration because of the special material used. However, the material, the structure selection and many design details should not be ignored.
The main objective of this paper is to determine the infiltration rate in the winery building and explore the effect of infiltration on energy consumption, and call attention to the infiltration problems of the industrial buildings both in the design and construction stage.
2 Materials and methods
2.1 Project information
The winery building in question is located in Huailai County, Hebei Province of China. Huailai has a monsoon-influenced, continental semi-arid climate, with cold, dry and windy winters due to Siberian anticyclone, and hot, humid summers driven by the East Asian monsoon. The monthly mean temperatures range from −7.4°C in January to 24.4°C in July and the annual mean is 9.6°C. There is little rainfall throughout the year, except in summer.
There are totally three buildings in the industrial building clusters: Building 1, Building 2, and Building 3. Buildings 2 and 3 are one-story buildings. Both of the two buildings have concrete roofs which could ensure a tight connection between the wall and the roof and thus have no air leakage problems. Building 1, the main production building with a total floor area approximately 1460 m2, adopts the portal of light-weight steel as its construction materials and is about 11 m high with a roof height of 15.8 m. Figure 2 shows the floor plan of Building 1.
As shown in Fig. 2, Building 1 is divided into four sections A, B, C and D. D101–D105 are fermentation rooms which should maintain a temperature of 18°C in summer and 15.6°C in winter. Rooms such as A110, A112, B102–B107, C111, C112 and C113 have a design temperature of 15.6°C both in summer and winter. The barrel rooms should maintain a relative humidity of 70%–80%. Auxiliary rooms such as C117 could maintain a higher temperature of 25°C in summer and 20°C in winter.
Building 1 was in operation in the winter of 2011. During the heating seasons, it was found that condensation occurred on the roof beams and condensed water dropped from the roof to the floor. On extremely cold weather conditions, condensation formed on the exterior roof metal panel and ice formed on the inner surface of the roof metal panel (Fig. 1(b)).
In summer, the factory staff reported condensed water dripping from the roof in many rooms of the building. Based on staff’s description, many field inspections were conducted in order to solve the problems. Figure 3 is a thermal imaging picture that shows that the temperature is high at the place where the roof and the wall joint. According to the design, the roof should have two layers of insulation. However, through field inspection, it was found that there was only one layer at some places, and there were even no insulation at all at other places (Fig. 4). The insulation of the ridge was not well fixed and large gaps existed. At places where there was no insulation, ventilation channels were formed (Fig. 5). Meanwhile, moisture was found on insulation materials. In addition, the vapor barrier was not paved so it could not effectively prevent the infiltration of air and moisture. Smoke visualization experiments also showed that the vapor barrier had failed to perform its function.
The insulation and vapor barrier failure caused air leakage into/out of the rooms and high energy consumption of this winery building that has strict temperature and humidity control over some production areas.
2.2 Infiltration test
It was found in the onsite inspection that infiltration was the major reason for condensation. The determination of the infiltration rate was, therefore, the key issue before taking measures to solve the problem. Amin et al. [12] used the tracer gas method to test the steady-state infiltration of industrial buildings. However, in testing large space buildings, it is always difficult for the tracer gas to be well mixed with the indoor air through infiltration. Another problem is that the outdoor condition changed with time, which affects the infiltration rate greatly through the driving force. Both of the two measurements were attempted in the present study, but the process was time-consuming. As the winery building is an industrial building, the volume is so large that the only use of the commonly used pressurization test method could not satisfy the required pressure difference to test the air tightness of the building. Therefore, the pressurization test method and the moisture condensation method were finally used together to test the infiltration of the building.
2.2.1 Pressurization test method
In pressurization test, a large fan or blower is mounted in a door or window and induces a large and roughly uniform pressure difference across the building shell. The air flow required to maintain this pressure difference is then measured. It can be described as
where Q is the airflow rate (m3/s); C, the flow coefficient (m3/(s·Pan)); ΔP, the indoor-outdoor pressure difference (Pa); and n, the flow exponent, dimensionless. Once the values of C and n have been determined from the test data, Eq. (1) can be used to predict the airflow rate through the building envelope at any given pressure difference.
Taking the log-logarithm for Eq. (1), Eq. (2) can be obtained,
Equation (1) is transformed to a liner regression between lgQ and lgΔP, as shown in Eq. (2), and it yields lgC as its intercept and n as its gradient, which makes it easier to calculate the values of C and n.
According to the Standard for Energy Efficiency Test of Public Buildings (JGJ/T177—2009) [13] and Determination of Air Permeability of Buildings (EN 13829) [14], the fan pressurization test method and the DG-700 double blower-door apparatus produced by the US TEC (the Energy Conservatory) company was chosen to test the permeability of the whole building. B102 and B104 of Building 1 were selected as the samples, and each room was tested under at least three conditions. Before testing, all the windows, doors, ventilators, the drainage ditch and all the openings of the tested rooms were sealed. Then the room was pressurized/depressurized, and the flow rate of the fan is equal to the infiltration rate.
The tests for B102 were conducted at different room pressures of 35 Pa, 30 Pa, 25 Pa, 20 Pa and 15 Pa respectively. As the volume of B104 is far greater than 4000 m3, and the capacity of the double blower is limited, the test in this room was conducted just at −10 Pa and −5 Pa.
2.2.2 Moisture condensation method
As the rooms adopt air coolers as the air cooling equipment, the moisture condensation method could be used in the infiltration test. Since there is no indoor moisture source in the rooms of the winery building, and this progress is at steady-state, the moisture condensation method could be used to test the infiltration of the rooms.
The principle of moisture condensation method is that the humidity of air that enters into a room through infiltration equals the sum of the indoor humidity and the condensing water flow rate. It can be expressed as
where Q stands for the mass flow rate of the infiltration (kg/s); dw, the moisture content of outdoor air (g/kg); dn, the moisture content of the indoor air (g/kg); and qln, the flow rate of the condensed water (g/s).
PSI 8386-M (temperature range −10°C to 60°C, resolution 0.1°C, accuracy±0.3°C, relative humidity range 0 to 95%, accuracy±3% rh, resolution 0.1% rh) was used to test the temperature and relative humidity. The humidity could be gained through the psychrometric chart. Graduated measuring cylinder SCHOTT 1000 mL (range 0 to 1000 mL, resolution 10 mL, accuracy ±10 mL) was selected and ZSD-009 stop watch was used when collecting condensed water.
The outdoor air temperature was less than 30°C and relative humidity approximately 55% with little wind. The first measurement was conducted from 16:00 to 18:00 on August 16, 2012, and the air temperature and relative humidity of outdoor air and indoor air were recorded. The flow rate of the condensed water was measured by collecting the flow in a container within 2 min. Due to the fact that the leakage was rather large, two repeated tests were done at 15:00 and 16:30 on August 19, 2012. Table 1 lists the measured data of the three tests. During onsite test, the condensing pipe of B102 and B103 were not available to collect condensed water.
The pressurization test method could give the information about the leakage of the building in summer and winter design conditions, but not the leakage at the time when the test was performed. The moisture condensation method could measure the real-time air leakage compared to the pressurization test method, but it could not gain the infiltration rate of the design conditions. The combination of the pressurization test method and the moisture condensation method could provide the credible information needed.
2.3 Energy simulation
By using the two methods, the infiltration of the winery building was obtained, which showed that the infiltration was high. Energy simulation was conducted in order to see the effect of the retrofit effect and the energy consumption condition. EnergyPlus is a whole building energy simulation program that engineers, architects, and researchers use to model energy use in buildings [15,16]. EnergyPlus 6.0 was used to analyze the hourly energy consumption of Building 1 for a standard year.
The Typical Meteorological Year (TMY) of Huailai was used to simulate the energy consumption. The energy rate in Huailai is as follows: electricity $ 0.16/kWh, $ 0.67/m3. The thermal conductivity of the enclosure is shown in Table 2.
Through the onsite survey and inspections, the internal load of the year was found to be as follows: fermentation rooms (D101–105) are in use all year around. Except inspections and examinations, the rooms have no occupants and no general lights. Room C117 has two people. The welding equipment is normally not in operation. Room C113 is used once or twice per month. Thus, the internal load due to occupants, equipment, and lighting is small. C111 is used only 2–3 times per year. Again, no internal load is considered. C110 is the bottling room in which 7–8 staff work. Other rooms normally have no occupants, no equipment load, and no lighting load. The building is operated from 8:00 am to 12:00 noon and 1:30 pm to 5:30 pm, Monday to Friday. The results of the survey are presented in Table 3.
Six air-cooled hermetic screw water chillers (two are spared) are used to supply 6°C chilled water for the rooms. The air coolers are equipped in B102, B107 and other rooms to cool the rooms to their designed temperature. In winter, four boilers provide hot water at a temperature of 82°C for air heaters to heat the rooms. Humidifiers are installed in rooms which need humidity control such as B102, B103 and so on to maintain their humidity. Other parameters were set according to the designed files.
3 Results and discussion
3.1 Infiltration rate
3.1.1 Analysis of results of pressurization test
B102 and B104 were used as the test samples. The infiltration rates of the rooms were obtained after the pressurization test.
Figure 6 demonstrates the linear relationship between lgQ and lg∆P of Room B102. The relation curve of the difference between building leakage and envelope pressure of B102 is expressed in Eq. (4),
The indoor and outdoor difference is approximately 13 Pa in the design condition in winter, so the air change rate is 3.3 h−1.
Figure 7 depicts the relationship between lgQ and lg∆P of Room B104. The relation curve of the difference between building leakage and envelope pressure of B104 is shown in Eq. (5).
The indoor and outdoor pressure difference of interior room is approximately 10 Pa in winter design condition, so the air change rate is approximately 3.1 h−1.
The infiltration rates are approximately 3 h−1 for Room B102 and B104. However, the air change rate of buildings which have the same structure as the building studied is 1h−1 in Beijing. The winery building is at least twice leakier than normal Chinese buildings and five times leakier than Canadian buildings [17].
3.1.2 Analysis of results of moisture condensation test
By using the moisture condensation method, the infiltration rate and air change rates of the rooms tested are tabulated in Table 4.
The outdoor temperature is not so high and the wind velocity is small according to the recorded weather condition, but the air infiltration is rather large. B107 has the most exterior walls and exterior windows but its infiltration is not larger than others, which indicates that the exterior walls and windows are not the main factor for the infiltration problems. The air change rates of interior rooms are different from each other, which suggests that the insulation are not evenly distributed, and the technique needs to be improved during the construction of roof. The infiltration rates for the interior rooms is approximately 0.4 h−1, which is the maximum under summer design day when outdoor air temperature is 33°C and windy. Under the weather conditions when the tests are conducted, the normal infiltration should be between 0.1 h−1 and 0.2 h−1.
According to the weather statistical data of Huailai from 1971 to 2000, the average wind speed is greater than 1.8 m/s, which shows that Huailai has a little strong wind speed. Such a wind speed would lead to a high air infiltration rate and then a high energy consumption of the building. Therefore, the roof needs rebuilding. In this building, rooms B102, B104, A110, A122 etc. have strict control over temperature and relative humidity. In view of the local climate and production requirement, the designers should consider air tightness problem in the design process. But design handbooks have no provisions on this issue. So it is proposed that the standard should have air infiltration design recommendations if the building may have a high air leakage. At the same time, enforcement of supervision and inspection in the installation process is significantly important to reduce air infiltration.
3.2 Analysis of results of energy simulation
Before simulation, the infiltration rates should be determined. The interior rooms use the condensation tested data as infiltration rates. The total pressure difference is the sum of the stack pressure difference and wind pressure difference. The indoor and outdoor pressure differences of other seasons were determined. Then Eq. (5) was adopted to calculate the air change rate in other seasons. The condensation method results show that the infiltration of B102 is not leakier than the interior rooms. As there are no summer test data of B102, the result of the pressurization test method 3.3 h−1 was used. The real condition is a little different from the design conditions and the design conditions could not stand for the average conditions. Using corrected infiltration rates as simulation parameters could be more approximate to the real energy consumption. So correction factor was used to reflect the real infiltration condition. Then the same method as the one used for interior rooms and Eq. (4) were used to determine the infiltration rate in other seasons. As the constructions and materials are the same for exterior rooms, the same infiltration rate was used for every exterior room. The detailed infiltration parameters are given in Table 5. Table 6 shows the average infiltration rates in different seasons of scenario (1) after rebuilding the roof. Scenario (1) refers to reducing the infiltration of the exterior rooms to 1/2 and interior rooms to 1/3 of the existing conditions.
Energy simulation was conducted to optimize the performance of the building. The simulation results of current design and scenario (1) were compared in order to evaluate the effect of infiltration. Figures 8 and 9 display the monthly electricity and gas consumption of current condition and scenario (1). It can be seen that approximately 20% of the total energy consumption is reduced after reducing the infiltration of the winery building. As shown in Table 7, approximately $ 225000 of the total energy cost is reduced, accounting for 37.4% of the annual cost of the building before roof rebuilding. For buildings that have strict control over environment, the energy consumption by infiltration should not be neglected.
3.3 Suggestions for infiltration design and construction
The large energy consumption caused by infiltration calls attention to incorporate the infiltration into design and construction stage. According to the actual experience, the following suggestions were proposed. During the design stage, two aspects should be considered. First, because roof panels play an important role in preventing the condensation, the panels that can ensure the good seal of the joint should be used. For industrial buildings that have large span roofs, priority should be given to roof panels with a high peak and good seal performance in choosing roof panels if water drainage is taken into account. Second, the infiltration rate should be carefully considered as there are no provisions about it. Design or construction standard should have recommendations on the infiltration of the buildings. During the construction phase, the designs normally satisfy the requirement of standard, but the installation quality has led to bad performance of the thermal insulation. Onsite spraying foam may be a better method to seal the gaps. The vapor barrier should be correctly considered and it is necessary to ensure that the vapor barrier and the thermal insulation are linked tightly. The design and construction have a great influence on the infiltration of industrial buildings, while quality control and supervision are of great significance in reducing the energy consumption caused by infiltration.
4 Conclusions
Steel structures in industrial buildings are extensively used in modern design. However the air infiltration is not satisfactory due to the poor insulation and installation. In buildings which require strict control over temperature and humidity, infiltration affects not only the energy cost of the building, but also the indoor environment and the product quality. In this paper, an industrial building in Huailai County, Hebei Province was investigated to quantify the infiltration rates by onsite tests and its influence on energy consumption through EnergyPlus.
By using the pressurization test method, the air change rate of the rooms studied in design conditions is approximately 3 h−1. The building is twice as leaky as normal Chinese buildings and five times as leaky as Canadian buildings. The moisture condensation method was used to test the air leakage of some rooms. The results show that the infiltration rates of most interior rooms are three times as high as that of the same type of buildings. It is proposed that the design standard should have air infiltration recommendations for the buildings having a high air leakage. At the same time, enforcement of supervision and inspection on the insulation and installation process is significantly important to reduce air infiltration.
Energy simulation shows that if the infiltration rate of exterior rooms is decreased to 1/3 of the infiltration rate tested and that of interior rooms reduced to 1/2, approximately 20% of the total energy consumption could be reduced. It has a great potential in reducing the energy consumption in this type of buildings. Since the poor environment in the building studied is mainly caused by infiltration, enforcement of the design and construction process would play a significant role in improving the overall performance of the building.
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