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Energy efficiency optimization of combined ventilation systems in livestock buildings
Energy and Buildings 42 (2010) 1165–1171
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Energy efficiency optimization of combined ventilation systems in livestock buildings Olivera Ecim-Djuric, Goran Topisirovic * Institute of Agricultural Engineering, Faculty of Agriculture, Nemanjina 6, Belgrade - Zemun 11080, Serbia
A R T I C L E I N F O
A B S T R A C T
Article history: Received 27 October 2008 Received in revised form 25 October 2009 Accepted 30 October 2009
Good ventilation system in livestock buildings is necessary for removing excess moisture and heat and for improving building environment in general. Natural ventilation does not require energy consumption and on the other hand, animals would not be affected by electrical power failures. Because natural ventilation depends largely on temperature difference between inside and outside air and wind velocity and direction it is very important in early stages of building design to provide orientation and accurate opening areas. Numerical simulation of natural ventilation and computation of fluid dynamics in livestock buildings can be usefully integrated in whole ventilation system optimization and related energy consumption decrease. Even in mechanical system ventilation, from flow field obtained in numerical simulation it is possible to optimize these systems. CFD analysis is generally restricted to the study of buildings’ environment flows and space study, and the designer must supply boundary conditions in the form of external and internal buildings’ envelope/wall surface conditions. Finally, the needs for further research and engineering development are outlined. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Energy efficiency Natural ventilation Numerical simulations Airflow velocities
1. Introduction Energy efficient control of microclimate conditions in livestock buildings is of very importance for sustainable livestock production. The energy efficiency optimization of these buildings takes into consideration a number of measures for decreasing energy demands, possibilities for decreasing energy consumption for those minimized needs, possibilities for applying new ecological, clean technologies and renewable energy sources, as well as detailed analysis of relevant economical parameters. Energy optimization can be realized in early stages of designs, taking into consideration all relevant parameters for decreasing energy consumption. One of the main microclimate problems in livestock buildings is dust concentration. Research in the field of dust concentration production, designing of dust distribution models and dust concentration reduction in the last years are significantly intensified. Proofs of harmful effects of polluted emissions from livestock buildings on humans and animals health have been collected and supplemented over the last 10–15 years [1]. One of the first researchers in this field, Donham [2], noticed the growing interest of a large number of authors in this field, especially from the beginning of the 1980s until today. Their fields of interest are very different: dust production, types and characteristics, measurement
* Corresponding author. Tel.: +381 69 24 17 125; fax: +381 11 31 63 317. E-mail address: [email protected] (G. Topisirovic). 0378-7788/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2009.10.035
of concentration and dimensions, concentration threshold limits and standards, influence of dust on humans and animals health, environmental pollution, designing of dust concentration distribution models and dust concentration reduction. Dust concentration may be reduced by: air filtration [3,4], dust source treatment [5,6] and ventilation [7–9]. Zhang [10] investigated the efficiency of different methods of inside air filtration, for the purpose of reducing dust concentration. Characteristics of particular devices were comparatively presented. Any method of wet or dry filtration was too expensive and complicated for practical use in livestock buildings. Cyclone type devices, whose function is based on centrifugal force separation of the particles, had significant inside pressure drop and, consequently, very high energy consumption for overcoming the critical phase. Electrostatic sedimentation could be accepted, if the rational relationship between energy consumption for airflow enforcing and dust separation efficiency could be achieved. In the present conditions, this system is too expensive for application and maintenance. According to Wathes [1] ventilation is, in general, still one of the most efficient methods for reducing inside air pollutant concentration, but its real influence on dust concentration has recently been more seriously investigated. The research program of this work comprehends the analysis of applying ventilation for dust concentration reduction and control in swine buildings air. This method is based on using existing ventilation systems in stalls, and that is a very important advantage for application in practice.
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Nevertheless, along with this advantage, much unsolved problems also appear, such as working regime of ventilation system and choice of proper type of system itself, which precisely determine the ventilation system energy consumption and ventilation effects on inside air quality. The most important questions for particular cases in practice are: ventilation rate, inlet and outlet opening positioning and airflow directions through the building. Ventilation system, which causes fast and turbulent airflows, sometimes itself produces dusty ambient. Besides the other influences, important is intensive drying of internal surfaces, as well as re-suspended secondary dust [3]. Respirable dust concentration is increasing with increment of airflow velocity and turbulence intensity in the building, as well as increment of light intensity and animal disturbance [11]. Especially in pig houses, animal activity measurements have disclosed a close interrelationship with particle dynamics. A series of investigations determined in keeping specific and seasonal differences in preparatory and in finishing fattening houses. The investigations showed that, in addition to animal activity, indoor temperature, relative humidity and air volume flow had a strong influence on particle release [12]. Both mechanical and natural ventilation can be applied in most livestock buildings. Increased ventilation rate is often recommended as a method to reduce dust concentration. In mechanical ventilation systems ventilation rate is related to energy consumption, working regime and type of ventilation system. Natural ventilation is more suitable for large animals in final fattening stage. Younger animals require higher space temperatures in winter season and more precious environment control that can be supplied by natural ventilation. Houses can be acclimated through either forced or natural ventilation. Natural ventilation means energy saving and noise reduction, but is also dependent on the reliable functioning of the ventilation principle through the design of the construction cover, as well as the incoming and the outgoing air openings. Sufficient data on the emission and the immission characteristics of naturally ventilated livestock buildings are lacking. For designing animal houses with natural ventilation, as well as for making an ecorelevant assessment of these systems, knowledge about the through-flow in such buildings is necessary. More ideas are given in this contribution [13]. Natural ventilation is one of the techniques for lowering energy consumption compared to energy consumption with forced ventilation, which also improves energy efficiency of the building. Depending on temperature conditions in and around the building, by natural ventilation some cooling effect in the building can be achieved as well. In pig keeping, the ventilation systems are being improved or supplemented with components for saving energy. Fine adjustments play a big role in process measuring and control technology. The vast majority of pig production will continue to be indoors so that further coupling of the various parameters such as feeding and interior climate control is indispensable for optimal management [14]. Environmental conditions and energy use were evaluated in a new segregated early weaning (SEW) swine nursery for 9 months. Energy use and air quality were generally acceptable and followed expected trends. Mean electricity use ranged from 27 to 32 kWh/ day. Mean fuel gas use ranged from 30 to 40 m3 natural gas/day. Ranges for total, respirable, and inhalable dust concentrations were 0.50–3.13, 0.03–0.40, and 0.18–2.98 mg/m3, respectively. Carbon dioxide concentrations ranged from 1144 to 2614 ppm. Ammonia concentration was negligible (<1 ppm) throughout the study [15]. Today in practice many methods are applied for solving the problems of natural ventilation, and the choice depends on project requests. Some of those methods are used for preliminary model
dimensioning, but the others are very complex and can present the dynamic of annual building behavior. In livestock farming the climate within an animal house is a dominant factor for animal welfare. Dust, airflow velocity, temperature, humidity, CO2 and NH3 gas concentrations, germs and odor have to be observed. An important aim is to develop ventilation systems that not only produce good climate conditions but also minimize emissions. Mueller and Krause [16] carry out climate-specific investigations to develop suitable ventilation systems for animal houses, supported by flow simulations. The type of ventilation system (mechanically or naturally ventilated housing), the location and the design of the air inlets, and the velocity of the incoming air influence the indoor air quality and the emission flow rate. Knowledge about the connections between the ventilation system, the climate in the livestock building and emissions is a prerequisite for developing suitable ventilation systems. Such knowledge is acquired by means of: numerical models, physical models and experiments in real livestock buildings. The design of the structure of animal houses including ventilation system and discharge conditions of the exhaust air requires not only heat and mass balance calculation but also the investigation of the airflow behavior inside and outside the building. Different simulation methods make it possible to develop housing systems with a comfortable biological climate inside and low impact in the surrounding [16]. Zhang et al. [17] have developed a simulation model of a ventilation system for a modern swine confinement. The confinement is divided into two zones: the room where the pigs reside and the pit that stores the waste. Two fans located in the side wall of the room and one fan located in the end wall of the pit are used to control the indoor air quality (IAQ) within the confinement. IAQ in this study addresses thermal and pollutant factors. For each zone, the conservation of mass and energy equations are written. The conservation of mass equations can be applied for dust, ammonia, and water vapor concentration. The conservation of energy describes the air temperature of the zones. The equations contain heat generation terms for thermal energy due to lights, heaters, and pigs, and mass source terms due to dust, water vapor, and ammonia. Relations for the generation terms are presented. An icon-based software is used to solve the system of equations that represent the IAQ models. Results of temperature, humidity, and concentrations of ammonia and dust are obtained from the simulation model under different conditions. By successfully examining the example cases, further investigations are warranted on larger scale models having more complexity, components, control algorithms, and applications. All the methods are based on the way of building presentation that can be presented as single-zonal or poly-zonal model. By CFD – Computer Fluid Dynamics, as a very powerful tool, is possible for very precise determination of data about stream field in certain space, but particular capability is that observation of local fluid – air streams is also possible. CFD enables prediction of air temperature, air stream direction and velocity during the projecting, which makes possible local interventions by changes during the projecting, as concerns solution modifications until desired state of relevant parameters on the building is achieved. If a comprehensive analysis of certain building is needed, particularly important are the programs that are interrelating thermal simulations and CFD simulations. In those simulations detailed verification of input data is necessary, as it must enable fast solution convergence. One of the main advantages of this method is the prediction of the flow field around and inside the building and possibility of object changes. Examination of wind tunnels is one of the experimental methods, which unfortunately do not give confirmation of inside natural ventilation project effects, because it considers only the
O. Ecim-Djuric, G. Topisirovic / Energy and Buildings 42 (2010) 1165–1171
wind stream over the building surrounding, but this method determines relevant pressure field that gives reliable base for ventilation calculation. 2. Mathematical model of flow field Cross or single sided natural ventilation through a building consists of two components: the ventilation caused by thermal effects, and that caused by wind effects. Assuming that fluid is viscous and uncompressible, flow field around and inside the building is time dependent and fully developed turbulent flow, wall surfaces are non-isothermal and governing motion equations are given as follows: – momentum equations
@ @ @ @ ðruÞ ¯ þ ðru¯ uÞ ¯ þ ðrv¯ uÞ ¯ þ ðrw ¯ uÞ ¯ @t @x @x @x ¯ @P @ @u¯ @u¯ þ ru0 u0j ¼ m þ @x @x j @x j @x @ ¯ @ @ @ ðrvÞ þ ðru¯ v¯ Þ þ ðrv¯ v¯ Þ þ ðrw ¯ v¯ Þ @t @x @x @x @P¯ @ @v¯ @u¯ rv0 u0j ¼ þ m þ @x j @y @y @x j @ @ @ @ ðrw ¯ Þ þ ðru¯ w ¯ Þ þ ðrv¯ w ¯ Þ þ ðrw ¯w ¯Þ @t @x @x @x @P¯ @ @w¯ @u¯ rw0 u0j rbg T¯1 T¯ m þ ¼ þ @z @x j @x j @z
(3)
(9)
where is run inside air density (kg/m3), rsp is outside air density (kg/m3), hNN is neutral level high. According to the ideal gas low, correlation between inside and outside air density can be given through their temperature levels:
T un T s p T un
(10)
where Tun and Tsp are inside and outside temperatures. Airflow Q for a large opening A and discharge coefficient Cd: (11)
run
(4)
Result of last two equations is airflow rate depending on neutral level and inside/outside temperature difference: 2 T Ts p run g ðh hNN Þ un Q ¼ CdA run T un (5)
(6)
1=2 ghDT T av
Main goal of wind-driven ventilation is obtaining pressure distribution inside the building. For constant temperature, air pressure decrease linearly with high. Since temperature difference between inside and outside air is present, and pressure gradients are different, outside pressure becomes equal with inside pressure at neutral level. At this level there is now airflow out or in building. Pressure difference Dp (Pa), for given high h (m) can be obtained from:
1=2 2DP Q ¼ CdA
where A is the opening area, and U is the wind velocity. Airflow rate produced by buoyancy forces can be written as:
Q s ¼ 0:2A
(8)
DP ¼ run gðh hNN Þ
Due to the problems associated with experiments, most natural ventilation designs use empirical data and equations. Airflow rate produced by wind forces can be described as: Q w ¼ 0:05AU
1=2
Q tot ¼ ðQw2 þ Qs2 Þ
(2)
– energy equation @ @ @ @ rc p T¯ þ rc p u¯ T¯ þ rc p v¯ T¯ þ rc p w¯ T¯ @t @x @y @z @ @T¯ k rc p T 0 u0j þ q000 ¼ @x j @x j
where h is the opening hight, DT is the temperature difference of outside and inside air, Tav is the mean value of outside and inside temperature. Overall airflow rate in ventilation caused by wind and buoyancy forces can be obtained in the following form:
D p ¼ ðrs p run Þgðh hNN Þ (1)
– continuity equation
@ @ ¯ @ ðru¯ Þ þ ðrvÞ þ ðrw ¯Þ ¼ 0 @x @y @z
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(7)
(12)
Advance of this simplified method is explicit calculation of some terms in equation. Minimal opening area for every zone in building can be obtained from Eq. (12). Since the wind can be toward either side of the building, the intake or vent opening on each side should be at least as large as the ridge vent opening on top. Size of the vent openings can be determined using the equation: A¼
4:7Q U
(13)
It is convenient to optimize opening area for summer and winter seasons if automatic control of openings is present. Recommendations for winter and summer opening areas are given in Table 1.
Table 1 Recommended vent opening sizes for natural ventilation of housing for various livestock. Type housing
cm of opening per 10 cm of building width Summer side wall openingsb
Swine Reef Dairy Sheep a
Winter ridge and eave vent openingsa
Gable roof, both walls
Monoslope, back wall
Monoslope, front wall
0.0385 0.1539 0.0770 0.0192
1.0776 0.6927 0.4618 0.4618
0.5388 0.3848 0.3079 0.3079
1.6164 1.1545 0.9236 0.9236
Sized to provide cold weather ventilation at 5 m/s wind velocity. Minimum ridge opening should be 10 cm wide to prevent freezing. Gable-roof building openings sized to provide hot weather ventilation at about 0.5 m/s wind velocity. Monoslope-roof openings modified to take advantage of the ‘funneling’ effect that increases the velocity of incoming air in summer. b
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O. Ecim-Djuric, G. Topisirovic / Energy and Buildings 42 (2010) 1165–1171 Table 2 Performances of axial fans. Roof 3
Airflow volume (m /s) Total pressure (Pa) Blade angle (8) R.P.M. (min1) Nominal motor power (kW)
Fig. 1. Cross-section and plane of the finishing room.
3. Experimental setup and measurements Fattening pigs’ house was separated in two lengthwise parts. One part was stocked with growing fattening pigs and the other one with finishers. Experimental room was separated from the
2 68 16 200–940 0.37
Floor 4 218 16 300–1410 1.1
surrounding and prepared for obtaining controlled experimental conditions. It consisted of 18 boxes (2 9) (Fig. 1). Stock density was 10 finishers per box or 0.75 m2/pig. The room was ventilated by under-pressure forced ventilation system. Inside air was extracted at the same time through the fans in the roof and under the slatted floor. Fresh air entered through windows. Three axial ventilators (full capacity 4 m3/s) in three vertical extracting canals (diameter 60 cm) were positioned in the roof. Through the fully slatted floor, inside air was extracted by one axial fan (3.39 m3/s), positioned in the outside vertical extracting canal (diameter 80 cm). That canal was connected to the horizontal longitudinal canal under the central feeding passage, which was also connected, along its walls, to a few openings, to the slurry canals and slatted floor of the boxes. Performances of both roof and under floor fans are presented in Table 2. The whole building was equipped with liquid manure cleaning system and the floors of boxes were fully slated. Fatteners were fed ad libitum, with the dry flour feed, from the self feeders mounted on the side fences of the boxes, and watered from the nipple drinkers, mounted on the back wall of the box. During the control treatment, all the fans were switched off and all of the fresh air inlet openings were closed, so the fields of dust concentrations and airflow velocities over the measuring crosssection were almost stationary. First experimental treatment was conducted during the function of floor ventilation system in rooms. Second experimental treatment was conducted during the function of roof ventilation system in rooms. Third experimental treatment was conducted during the function of floor and roof ventilation systems together (both ventilations). Both inhalable (total) and respirable (<5 mm) dust concentrations were measured, along with the airflow velocities in the control points. Dust concentrations and airflow velocities were measured 30 min after establishing every experimental setup. It was supposed that 30 min was enough for the measured values to change and reach stabile levels [3] as well as for pigs to reduce their activities after the change and to become peaceful again. Measuring cross-section was positioned in the middle of the room, according to the recommendations of the previously published research results of a number of various authors. In similar investigations they agree that measurements from this position are the most valuable and reliable for comparison [18,19]. Nevertheless, during the preliminary measurements for the experiment preparations, this suggestion was approved on the spot. Airflow velocities and dust concentrations were preliminary measured along the room length axis. Measured values were identical or insignificantly differed from the values measured in the middle cross-section. Maximal variations were under 10%. Airflow velocity measurements were conducted when the room was empty. The intention was to avoid any influence of animal’s movements and heat emission from the animal bodies to the air movement. Measured airflow velocity values were exclusively
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Fig. 2. Measuring points disposal in the finishing room.
influenced by particular fan operations in certain experimental setups. Every measurement was repeated three times, and later average values were processed from these three results. Measurements were employed continually through three finishing periods, during the season spring–summer–autumn. During every period eight measurements at equal 7–9 day intervals were managed. Values were not measured during and immediately after feed distribution, in order to avoid increased dust concentrations from the feed and disturbed pigs. Dust concentrations and airflow velocities were measured at 20 measuring points. The points were disposed over the central measuring cross-section, in five vertical and four horizontal rows (Fig. 2). Horizontal rows were distanced from each other in 40 cm, so the lowest row of 5 points was positioned in the pigs breathing zone (40 cm), and the highest in the workers breathing zone (160 cm). Dust concentrations were measured by konimeter method, based on counting of dust particles in air sample (‘‘Konimeter 10’’, Karl Zeiss, Jena). Airflow velocities in ventilation canals were measured by turbine anemometer (measuring range 0–20 m/s, accuracy 0.1 m/s). Airflow velocities at measuring points inside the room were measured by hot wire anemometer (measuring range 0– 2 m/s, accuracy 0.03 m/s). Air temperatures and humidity were measured by digital hygro-thermometer with NiCr – Ni thermo par. 4. Experimental and simulation results Optimization of livestock ventilation was divided in two parts. First part of experiment was detecting dust concentration and airflow velocities inside the experimental room with mechanical ventilation system, as described above. Second part of experiment was numerical simulation of natural ventilation effect in experimental room assuming that mechanical ventilation system was switched off. Fresh air inlets were optimized for obtaining maximum airflow rate in summer period. Exhaust opening can be placed in side wall and in roof, for this simulation was set on side wall and in the fan ducts in the roof, with respect to building design. It was assumed that there was not any intervention on building design in order to maximize ventilation effect. Optimal air velocities in animal breathing zone in the range of 0.02–0.05 m/s were boundary value for optimizing natural ventilation. From meteorological data for building location, minimal and maximal wind velocities were determined during
Fig. 3. Air velocities vectors inside the building for wind velocity 0.5 m/s and direction normal to opening area.
the period when experimental measurements were performed. Wind velocity was changed from 0.5 to 2 m/s taking in account prevailing wind velocity in period when experimental measurements were performed. Wind direction was set up in interval from 0 to 908 relative to opening normal. The aim of wind direction is to provide minimal and maximal air velocities in opening plane. Ventilation in summer period is provided by large openings (usually one-third to one half of wall surface). Ventilation caused by thermal effect is about 10% of total ventilation, because there is no great difference between inside and outside air temperatures. Temperature difference between inside and outside air was from 0 to 8 8C, with 2 8C increment. Outside temperature was set in range from 14 to 22 8C. Most interesting for analysis is natural ventilation rate with minimal wind velocity. This minimal velocity is one of the major components in opening optimization. For higher velocities, opening area can be easily reduced taking into consideration optimal air velocities inside the building. In Fig. 3 air velocity vectors are shown inside the building for wind velocity 0.5 m/s and wind direction normal to opening area, for two positions in building, close to wall (a) and near the fan duct (b). The purpose of numerical simulation is to determine temperature and velocity field in defined space. It can be seen from Fig. 4 that fresh air from inlet moves through whole test room moving from top to bottom. This air movement determination is important in combining natural and mechanical ventilation for increasing ventilation rate. Fig. 4 shows inside air velocities for wind velocity 0.5 m/s and direction of 458 relative to opening area for two positions in building, close to wall (a) and near the fan duct (b). Reduced inside
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Fig. 6. Airflow dependence from wind incident angle.
Fig. 4. Air velocities vectors inside the building for wind velocity 0.5 m/s and direction of 458.
air velocities and velocity field result from incident angle change. Flow field also can show stagnation zones in closed space, where there will not be adequate air movement. In order to decrease dust concentration in these zones, partially mechanized ventilation should be observed. Minimal inside air velocities are shown in Fig. 5, where wind velocity is 0.5 m/s and wind direction is set at an angle of 908 relative to opening inlet norm also for two positions in building, close to wall (a) and near the fan duct (b). Low inside air velocities indicate that natural ventilation in this case is not useful in dust concentration reduction. Minimal fresh airflow rate that enters in test room does not result in intensive air movement, especially in zone of animal breathing. Airflow rate in this case practically does not exist, because velocity vector is parallel to opening. All the movements inside the test room are as a result of wall temperature differences and differences produced by animals or human occupants. Taking into account that ventilation rate due to thermal effect depends on temperature difference between outside and inside air, in summer period, with large openings these temperatures all almost the same, which affect the flow field as shown in Fig. 5. This is a boundary case for natural ventilation or a case when mechanical ventilation is needed. Wind direction causes airflow rate to decrease for any wind velocity. In case of higher wind velocities this will lead to a decrease in inlet velocity to optimal values, excluding when incident angle is 908 and actually fresh air does not enter into building. For wind velocity 0.5 m/s airflow dependence from incident angle is given in Fig. 6. 5. Energy consumption analysis
Fig. 5. Air velocities vectors inside the building for wind velocity 0.5 m/s and direction of 908.
Energy consumption analysis was derived from the results of the experimental measurements during the summer period, which includes maximum ventilation rate in all of the investigated regimes required inside the buildings. In these conditions, targeting the top energy consumption, only the highest regimes of the installed fans were considered, including 24-h operation. Roof fans electro motors nominal and effective power was 0.37 and 0.32 kW, respectively. At floor fans electro motors, both power values were 1.1 and 0.80 kW, respectively. Under the mentioned conditions, total daily energy consumption of fan electro motors during the second (under floor ventilation), third (roof ventilation) and fourth (both systems) regime were: 26.64, 26.4 and 53.04 kWh/day, respectively. According to the results it was concluded that considerable savings in energy consumption can be achieved by operation of floor ventilation, instead of both ventilation systems, in conditions that do not require maximum ventilation rate, such as during the night in summer period. Regarding optimal air velocity (0.02– 0.05 m/s) and very strong correlation between dust concentration
O. Ecim-Djuric, G. Topisirovic / Energy and Buildings 42 (2010) 1165–1171
and airflow velocity during the floor ventilation, there are particular situations in which floor ventilation can fulfill the optimal dust concentration and microclimate requirements. From numerical simulation of natural ventilation for the same period in experimental measurement, airflow rates, and relevant velocities are obtained including all outside parameters that affect natural ventilation rate. Numerical simulations showed that in summer period by natural ventilation it is possible to reduce over 60% use of mechanical system ventilation. In summer period for 92 days, energy consumption for roof and floor ventilation was 4879.68 kWh. By including natural ventilation, energy consumption in same period could be 2927.81 kWh lower. Optimizing mechanical ventilation by including only floor ventilation, energy consumption in the same period was 2635.8 kWh, and including natural ventilation would be 1581.48 kWh lower. With automatic control of opening size and connection between natural and mechanical ventilation these values can be much higher, and energy consumption can be 80% lower, for the same period. 6. Conclusion Optimizing any ventilation system in livestock building is aimed to reduce dust concentration in animal breathing zone (close to building floor) and human breathing zone (close to building roof). Optimal air velocities in animal breathing zone are from 0.02 to 0.05 m/s. From experimental results with mechanical ventilation airflow velocities under 0.02 m/s and over 0.08 m/s caused increment in dust concentration. Numerical simulation is a powerful tool for temperature and flow field determination. It strongly depends on boundary condition and outside meteorological data. Numerical simulation can be used for livestock building with natural ventilation optimization. Prediction of natural ventilation in correlation with mechanical ventilation system can significantly decrease energy consumption. Airflow velocities inside the room depend on wind velocity and incident angle in plane of opening. Higher values of wind velocities will not lead to healthy conditions inside the building. Replacing mechanical ventilation with natural ventilation in energy consumption in summer can be reduced by almost 60%. For more energy savings, it is necessary to obtain automatic controls of inlet and exhaust openings from one side, and automatic correlation between natural and mechanical ventilation system from the other side.
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References [1] C.M. Wathes, in: C.M. Wathes, D.R. Charles (Eds.), Air and Surface Hygiene. Livestock Housing, CAB International, 1994, pp. 123–148. [2] K. Donham, D. Cumra, Setting maximum dust exposure levels for people and animals in livestock facilities, in: International Symposium on Dust Control in Animal Production Facilities. Proceedings, CIGR, EurAgEng, NJF, DJS, Denmark, (1999), pp. 93–110. [3] G.A. Carpenter, Dust in livestock buildings — prevention and reduction, in: J.M. Bruce, M. Sommer (Eds.), Agriculture. Environmental Aspects of Respiratory Disease in Intensive Pig and Poultry Houses, Including the Implications for Human Health. Proceedings, 1987, pp. 101–110. [4] G.A. Carpenter, The Design of an Internal Ceiling-Mounted Air Filter Unit and its Application in an Early-Weaner Unit. Division Note DN/1128, National Institute Agricultural Engineering, Silsoe, 1982. [5] S. Pedersen, Staubreduzierung in Schweinesta¨llen, Deutsche Tiera¨rztliche Wochenschrift 105 (6) (1998) 247–250. [6] Y. Zhang, M.E. Barber, F.J. Patience, R.J.J. Feddes, Identification of oils to be sprinkled in livestock buildings to reduce dust, ASHRAE Transactions 101 (Pt. 2) (1995) 1179–1192. [7] D.S. Bundy, Electrical charge plays role in dust-collections system, Feedstuffs 63 (12) (1991) 30. [8] N.O. Breum, H. Takai, H.B. Rom, Upward vs downward ventilation air flow in a swine house, Transactions of the ASAE 33 (5) (1990) 1693–1699. [9] C.E. Klooster Van’t, P.F.M.M. Roelofs, L.A. den Hartog, Effects of filtration, vacuum cleaning and washing in pig houses on aerosol levels and pig performance, Livestock Production Science 33 (1993) 171–182. [10] Y. Zhang, Engineering control of dust in animal facilities, in: International Symposium on Dust Control in Animal Production Facilities Proceedings, CIGR, EurAgEng, NJF, DJS, Denmark, (1999), pp. 22–29. [11] G.L. Wicklen Van, Respirable aerosol sampling in poultry and swine housing, in: C.M. Wathes, J.M. Randall (Eds.), Aerosol Sampling in Animal Houses. Proceedings of a Workshop, University of Bristol, Department of Animal Husbandry, 26–28 July, Commission of the European Communities Directorate – General Telecommunications, Information Studies and Innovation, Luxembourg, 1989 , pp. 117– 122. [12] C. Nannen, W. Bu¨scher, Effect of animal activity on particle composition in various pig fattening housing systems, Landtechnik 63 (3) (2008) 170–171. [13] B. Mo¨ller, H.J. Mu¨ller, M. Gla¨ser, U. Wanka, T. Heidenreich, Quantitative assessment of air flow inside naturally ventilated animal houses, Landtechnik 62 (4) (2007) 234–235. [14] G. Franke, Trends in animal house climate control technology, Landtechnik 63 (6) (2008) 332–334. [15] M.C. Pumaa, R.G. Maghiranga, J.P. Murphya, P.R. O’Quinnb, J.L. Nelssenb, Energy use and dust levels in a segregated early-weaning swine nursery, Indoor and Built Environment 7 (1998) 224–231. [16] H.J. Mueller, K.H. Krause, Flow simulation for design of ventilation systems in animal houses, Building Simulation 2007 Proceedings (2007) 932–936. [17] L. Zhang, T.F. Smith, P.T. O’Shaughnessy, Development of a simulation model for a ventilation system for swine confinement, in: R.R. Stowell, R. Bucklin, R.W. Bottcher (Eds.), Livestock Environment VI: Proceedings of the 6th International Symposium, Louisville, Kentucky, USA, 21–23 May, (2001), pp. 293–300. [18] M. Lyngbye, C.R. Boon, Particle movements in mechanical ventilated piggeries – numerical simulations and experimental verification, in: International Symposium on Dust Control in Animal Production Facilities Proceedings, CIGR, EurAgEng, NJF, DJS, Denmark, (1999), pp. 204–212. [19] X. Wang, Y. Zhang, G.L. Riskowski, Dust spatial distribution in a typical swine building, in: International Symposium on Dust Control in Animal Production Facilities Proceedings, CIGR, EurAgEng, NJF, DJS, Denmark, (1999), pp. 48–55.
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Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Energy efficiency optimization of combined ventilation systems in livestock buildings Olivera Ecim-Djuric, Goran Topisirovic * Institute of Agricultural Engineering, Faculty of Agriculture, Nemanjina 6, Belgrade - Zemun 11080, Serbia
A R T I C L E I N F O
A B S T R A C T
Article history: Received 27 October 2008 Received in revised form 25 October 2009 Accepted 30 October 2009
Good ventilation system in livestock buildings is necessary for removing excess moisture and heat and for improving building environment in general. Natural ventilation does not require energy consumption and on the other hand, animals would not be affected by electrical power failures. Because natural ventilation depends largely on temperature difference between inside and outside air and wind velocity and direction it is very important in early stages of building design to provide orientation and accurate opening areas. Numerical simulation of natural ventilation and computation of fluid dynamics in livestock buildings can be usefully integrated in whole ventilation system optimization and related energy consumption decrease. Even in mechanical system ventilation, from flow field obtained in numerical simulation it is possible to optimize these systems. CFD analysis is generally restricted to the study of buildings’ environment flows and space study, and the designer must supply boundary conditions in the form of external and internal buildings’ envelope/wall surface conditions. Finally, the needs for further research and engineering development are outlined. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Energy efficiency Natural ventilation Numerical simulations Airflow velocities
1. Introduction Energy efficient control of microclimate conditions in livestock buildings is of very importance for sustainable livestock production. The energy efficiency optimization of these buildings takes into consideration a number of measures for decreasing energy demands, possibilities for decreasing energy consumption for those minimized needs, possibilities for applying new ecological, clean technologies and renewable energy sources, as well as detailed analysis of relevant economical parameters. Energy optimization can be realized in early stages of designs, taking into consideration all relevant parameters for decreasing energy consumption. One of the main microclimate problems in livestock buildings is dust concentration. Research in the field of dust concentration production, designing of dust distribution models and dust concentration reduction in the last years are significantly intensified. Proofs of harmful effects of polluted emissions from livestock buildings on humans and animals health have been collected and supplemented over the last 10–15 years [1]. One of the first researchers in this field, Donham [2], noticed the growing interest of a large number of authors in this field, especially from the beginning of the 1980s until today. Their fields of interest are very different: dust production, types and characteristics, measurement
* Corresponding author. Tel.: +381 69 24 17 125; fax: +381 11 31 63 317. E-mail address: [email protected] (G. Topisirovic). 0378-7788/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2009.10.035
of concentration and dimensions, concentration threshold limits and standards, influence of dust on humans and animals health, environmental pollution, designing of dust concentration distribution models and dust concentration reduction. Dust concentration may be reduced by: air filtration [3,4], dust source treatment [5,6] and ventilation [7–9]. Zhang [10] investigated the efficiency of different methods of inside air filtration, for the purpose of reducing dust concentration. Characteristics of particular devices were comparatively presented. Any method of wet or dry filtration was too expensive and complicated for practical use in livestock buildings. Cyclone type devices, whose function is based on centrifugal force separation of the particles, had significant inside pressure drop and, consequently, very high energy consumption for overcoming the critical phase. Electrostatic sedimentation could be accepted, if the rational relationship between energy consumption for airflow enforcing and dust separation efficiency could be achieved. In the present conditions, this system is too expensive for application and maintenance. According to Wathes [1] ventilation is, in general, still one of the most efficient methods for reducing inside air pollutant concentration, but its real influence on dust concentration has recently been more seriously investigated. The research program of this work comprehends the analysis of applying ventilation for dust concentration reduction and control in swine buildings air. This method is based on using existing ventilation systems in stalls, and that is a very important advantage for application in practice.
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Nevertheless, along with this advantage, much unsolved problems also appear, such as working regime of ventilation system and choice of proper type of system itself, which precisely determine the ventilation system energy consumption and ventilation effects on inside air quality. The most important questions for particular cases in practice are: ventilation rate, inlet and outlet opening positioning and airflow directions through the building. Ventilation system, which causes fast and turbulent airflows, sometimes itself produces dusty ambient. Besides the other influences, important is intensive drying of internal surfaces, as well as re-suspended secondary dust [3]. Respirable dust concentration is increasing with increment of airflow velocity and turbulence intensity in the building, as well as increment of light intensity and animal disturbance [11]. Especially in pig houses, animal activity measurements have disclosed a close interrelationship with particle dynamics. A series of investigations determined in keeping specific and seasonal differences in preparatory and in finishing fattening houses. The investigations showed that, in addition to animal activity, indoor temperature, relative humidity and air volume flow had a strong influence on particle release [12]. Both mechanical and natural ventilation can be applied in most livestock buildings. Increased ventilation rate is often recommended as a method to reduce dust concentration. In mechanical ventilation systems ventilation rate is related to energy consumption, working regime and type of ventilation system. Natural ventilation is more suitable for large animals in final fattening stage. Younger animals require higher space temperatures in winter season and more precious environment control that can be supplied by natural ventilation. Houses can be acclimated through either forced or natural ventilation. Natural ventilation means energy saving and noise reduction, but is also dependent on the reliable functioning of the ventilation principle through the design of the construction cover, as well as the incoming and the outgoing air openings. Sufficient data on the emission and the immission characteristics of naturally ventilated livestock buildings are lacking. For designing animal houses with natural ventilation, as well as for making an ecorelevant assessment of these systems, knowledge about the through-flow in such buildings is necessary. More ideas are given in this contribution [13]. Natural ventilation is one of the techniques for lowering energy consumption compared to energy consumption with forced ventilation, which also improves energy efficiency of the building. Depending on temperature conditions in and around the building, by natural ventilation some cooling effect in the building can be achieved as well. In pig keeping, the ventilation systems are being improved or supplemented with components for saving energy. Fine adjustments play a big role in process measuring and control technology. The vast majority of pig production will continue to be indoors so that further coupling of the various parameters such as feeding and interior climate control is indispensable for optimal management [14]. Environmental conditions and energy use were evaluated in a new segregated early weaning (SEW) swine nursery for 9 months. Energy use and air quality were generally acceptable and followed expected trends. Mean electricity use ranged from 27 to 32 kWh/ day. Mean fuel gas use ranged from 30 to 40 m3 natural gas/day. Ranges for total, respirable, and inhalable dust concentrations were 0.50–3.13, 0.03–0.40, and 0.18–2.98 mg/m3, respectively. Carbon dioxide concentrations ranged from 1144 to 2614 ppm. Ammonia concentration was negligible (<1 ppm) throughout the study [15]. Today in practice many methods are applied for solving the problems of natural ventilation, and the choice depends on project requests. Some of those methods are used for preliminary model
dimensioning, but the others are very complex and can present the dynamic of annual building behavior. In livestock farming the climate within an animal house is a dominant factor for animal welfare. Dust, airflow velocity, temperature, humidity, CO2 and NH3 gas concentrations, germs and odor have to be observed. An important aim is to develop ventilation systems that not only produce good climate conditions but also minimize emissions. Mueller and Krause [16] carry out climate-specific investigations to develop suitable ventilation systems for animal houses, supported by flow simulations. The type of ventilation system (mechanically or naturally ventilated housing), the location and the design of the air inlets, and the velocity of the incoming air influence the indoor air quality and the emission flow rate. Knowledge about the connections between the ventilation system, the climate in the livestock building and emissions is a prerequisite for developing suitable ventilation systems. Such knowledge is acquired by means of: numerical models, physical models and experiments in real livestock buildings. The design of the structure of animal houses including ventilation system and discharge conditions of the exhaust air requires not only heat and mass balance calculation but also the investigation of the airflow behavior inside and outside the building. Different simulation methods make it possible to develop housing systems with a comfortable biological climate inside and low impact in the surrounding [16]. Zhang et al. [17] have developed a simulation model of a ventilation system for a modern swine confinement. The confinement is divided into two zones: the room where the pigs reside and the pit that stores the waste. Two fans located in the side wall of the room and one fan located in the end wall of the pit are used to control the indoor air quality (IAQ) within the confinement. IAQ in this study addresses thermal and pollutant factors. For each zone, the conservation of mass and energy equations are written. The conservation of mass equations can be applied for dust, ammonia, and water vapor concentration. The conservation of energy describes the air temperature of the zones. The equations contain heat generation terms for thermal energy due to lights, heaters, and pigs, and mass source terms due to dust, water vapor, and ammonia. Relations for the generation terms are presented. An icon-based software is used to solve the system of equations that represent the IAQ models. Results of temperature, humidity, and concentrations of ammonia and dust are obtained from the simulation model under different conditions. By successfully examining the example cases, further investigations are warranted on larger scale models having more complexity, components, control algorithms, and applications. All the methods are based on the way of building presentation that can be presented as single-zonal or poly-zonal model. By CFD – Computer Fluid Dynamics, as a very powerful tool, is possible for very precise determination of data about stream field in certain space, but particular capability is that observation of local fluid – air streams is also possible. CFD enables prediction of air temperature, air stream direction and velocity during the projecting, which makes possible local interventions by changes during the projecting, as concerns solution modifications until desired state of relevant parameters on the building is achieved. If a comprehensive analysis of certain building is needed, particularly important are the programs that are interrelating thermal simulations and CFD simulations. In those simulations detailed verification of input data is necessary, as it must enable fast solution convergence. One of the main advantages of this method is the prediction of the flow field around and inside the building and possibility of object changes. Examination of wind tunnels is one of the experimental methods, which unfortunately do not give confirmation of inside natural ventilation project effects, because it considers only the
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wind stream over the building surrounding, but this method determines relevant pressure field that gives reliable base for ventilation calculation. 2. Mathematical model of flow field Cross or single sided natural ventilation through a building consists of two components: the ventilation caused by thermal effects, and that caused by wind effects. Assuming that fluid is viscous and uncompressible, flow field around and inside the building is time dependent and fully developed turbulent flow, wall surfaces are non-isothermal and governing motion equations are given as follows: – momentum equations
@ @ @ @ ðruÞ ¯ þ ðru¯ uÞ ¯ þ ðrv¯ uÞ ¯ þ ðrw ¯ uÞ ¯ @t @x @x @x ¯ @P @ @u¯ @u¯ þ ru0 u0j ¼ m þ @x @x j @x j @x @ ¯ @ @ @ ðrvÞ þ ðru¯ v¯ Þ þ ðrv¯ v¯ Þ þ ðrw ¯ v¯ Þ @t @x @x @x @P¯ @ @v¯ @u¯ rv0 u0j ¼ þ m þ @x j @y @y @x j @ @ @ @ ðrw ¯ Þ þ ðru¯ w ¯ Þ þ ðrv¯ w ¯ Þ þ ðrw ¯w ¯Þ @t @x @x @x @P¯ @ @w¯ @u¯ rw0 u0j rbg T¯1 T¯ m þ ¼ þ @z @x j @x j @z
(3)
(9)
where is run inside air density (kg/m3), rsp is outside air density (kg/m3), hNN is neutral level high. According to the ideal gas low, correlation between inside and outside air density can be given through their temperature levels:
T un T s p T un
(10)
where Tun and Tsp are inside and outside temperatures. Airflow Q for a large opening A and discharge coefficient Cd: (11)
run
(4)
Result of last two equations is airflow rate depending on neutral level and inside/outside temperature difference: 2 T Ts p run g ðh hNN Þ un Q ¼ CdA run T un (5)
(6)
1=2 ghDT T av
Main goal of wind-driven ventilation is obtaining pressure distribution inside the building. For constant temperature, air pressure decrease linearly with high. Since temperature difference between inside and outside air is present, and pressure gradients are different, outside pressure becomes equal with inside pressure at neutral level. At this level there is now airflow out or in building. Pressure difference Dp (Pa), for given high h (m) can be obtained from:
1=2 2DP Q ¼ CdA
where A is the opening area, and U is the wind velocity. Airflow rate produced by buoyancy forces can be written as:
Q s ¼ 0:2A
(8)
DP ¼ run gðh hNN Þ
Due to the problems associated with experiments, most natural ventilation designs use empirical data and equations. Airflow rate produced by wind forces can be described as: Q w ¼ 0:05AU
1=2
Q tot ¼ ðQw2 þ Qs2 Þ
(2)
– energy equation @ @ @ @ rc p T¯ þ rc p u¯ T¯ þ rc p v¯ T¯ þ rc p w¯ T¯ @t @x @y @z @ @T¯ k rc p T 0 u0j þ q000 ¼ @x j @x j
where h is the opening hight, DT is the temperature difference of outside and inside air, Tav is the mean value of outside and inside temperature. Overall airflow rate in ventilation caused by wind and buoyancy forces can be obtained in the following form:
D p ¼ ðrs p run Þgðh hNN Þ (1)
– continuity equation
@ @ ¯ @ ðru¯ Þ þ ðrvÞ þ ðrw ¯Þ ¼ 0 @x @y @z
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(7)
(12)
Advance of this simplified method is explicit calculation of some terms in equation. Minimal opening area for every zone in building can be obtained from Eq. (12). Since the wind can be toward either side of the building, the intake or vent opening on each side should be at least as large as the ridge vent opening on top. Size of the vent openings can be determined using the equation: A¼
4:7Q U
(13)
It is convenient to optimize opening area for summer and winter seasons if automatic control of openings is present. Recommendations for winter and summer opening areas are given in Table 1.
Table 1 Recommended vent opening sizes for natural ventilation of housing for various livestock. Type housing
cm of opening per 10 cm of building width Summer side wall openingsb
Swine Reef Dairy Sheep a
Winter ridge and eave vent openingsa
Gable roof, both walls
Monoslope, back wall
Monoslope, front wall
0.0385 0.1539 0.0770 0.0192
1.0776 0.6927 0.4618 0.4618
0.5388 0.3848 0.3079 0.3079
1.6164 1.1545 0.9236 0.9236
Sized to provide cold weather ventilation at 5 m/s wind velocity. Minimum ridge opening should be 10 cm wide to prevent freezing. Gable-roof building openings sized to provide hot weather ventilation at about 0.5 m/s wind velocity. Monoslope-roof openings modified to take advantage of the ‘funneling’ effect that increases the velocity of incoming air in summer. b
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Airflow volume (m /s) Total pressure (Pa) Blade angle (8) R.P.M. (min1) Nominal motor power (kW)
Fig. 1. Cross-section and plane of the finishing room.
3. Experimental setup and measurements Fattening pigs’ house was separated in two lengthwise parts. One part was stocked with growing fattening pigs and the other one with finishers. Experimental room was separated from the
2 68 16 200–940 0.37
Floor 4 218 16 300–1410 1.1
surrounding and prepared for obtaining controlled experimental conditions. It consisted of 18 boxes (2 9) (Fig. 1). Stock density was 10 finishers per box or 0.75 m2/pig. The room was ventilated by under-pressure forced ventilation system. Inside air was extracted at the same time through the fans in the roof and under the slatted floor. Fresh air entered through windows. Three axial ventilators (full capacity 4 m3/s) in three vertical extracting canals (diameter 60 cm) were positioned in the roof. Through the fully slatted floor, inside air was extracted by one axial fan (3.39 m3/s), positioned in the outside vertical extracting canal (diameter 80 cm). That canal was connected to the horizontal longitudinal canal under the central feeding passage, which was also connected, along its walls, to a few openings, to the slurry canals and slatted floor of the boxes. Performances of both roof and under floor fans are presented in Table 2. The whole building was equipped with liquid manure cleaning system and the floors of boxes were fully slated. Fatteners were fed ad libitum, with the dry flour feed, from the self feeders mounted on the side fences of the boxes, and watered from the nipple drinkers, mounted on the back wall of the box. During the control treatment, all the fans were switched off and all of the fresh air inlet openings were closed, so the fields of dust concentrations and airflow velocities over the measuring crosssection were almost stationary. First experimental treatment was conducted during the function of floor ventilation system in rooms. Second experimental treatment was conducted during the function of roof ventilation system in rooms. Third experimental treatment was conducted during the function of floor and roof ventilation systems together (both ventilations). Both inhalable (total) and respirable (<5 mm) dust concentrations were measured, along with the airflow velocities in the control points. Dust concentrations and airflow velocities were measured 30 min after establishing every experimental setup. It was supposed that 30 min was enough for the measured values to change and reach stabile levels [3] as well as for pigs to reduce their activities after the change and to become peaceful again. Measuring cross-section was positioned in the middle of the room, according to the recommendations of the previously published research results of a number of various authors. In similar investigations they agree that measurements from this position are the most valuable and reliable for comparison [18,19]. Nevertheless, during the preliminary measurements for the experiment preparations, this suggestion was approved on the spot. Airflow velocities and dust concentrations were preliminary measured along the room length axis. Measured values were identical or insignificantly differed from the values measured in the middle cross-section. Maximal variations were under 10%. Airflow velocity measurements were conducted when the room was empty. The intention was to avoid any influence of animal’s movements and heat emission from the animal bodies to the air movement. Measured airflow velocity values were exclusively
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Fig. 2. Measuring points disposal in the finishing room.
influenced by particular fan operations in certain experimental setups. Every measurement was repeated three times, and later average values were processed from these three results. Measurements were employed continually through three finishing periods, during the season spring–summer–autumn. During every period eight measurements at equal 7–9 day intervals were managed. Values were not measured during and immediately after feed distribution, in order to avoid increased dust concentrations from the feed and disturbed pigs. Dust concentrations and airflow velocities were measured at 20 measuring points. The points were disposed over the central measuring cross-section, in five vertical and four horizontal rows (Fig. 2). Horizontal rows were distanced from each other in 40 cm, so the lowest row of 5 points was positioned in the pigs breathing zone (40 cm), and the highest in the workers breathing zone (160 cm). Dust concentrations were measured by konimeter method, based on counting of dust particles in air sample (‘‘Konimeter 10’’, Karl Zeiss, Jena). Airflow velocities in ventilation canals were measured by turbine anemometer (measuring range 0–20 m/s, accuracy 0.1 m/s). Airflow velocities at measuring points inside the room were measured by hot wire anemometer (measuring range 0– 2 m/s, accuracy 0.03 m/s). Air temperatures and humidity were measured by digital hygro-thermometer with NiCr – Ni thermo par. 4. Experimental and simulation results Optimization of livestock ventilation was divided in two parts. First part of experiment was detecting dust concentration and airflow velocities inside the experimental room with mechanical ventilation system, as described above. Second part of experiment was numerical simulation of natural ventilation effect in experimental room assuming that mechanical ventilation system was switched off. Fresh air inlets were optimized for obtaining maximum airflow rate in summer period. Exhaust opening can be placed in side wall and in roof, for this simulation was set on side wall and in the fan ducts in the roof, with respect to building design. It was assumed that there was not any intervention on building design in order to maximize ventilation effect. Optimal air velocities in animal breathing zone in the range of 0.02–0.05 m/s were boundary value for optimizing natural ventilation. From meteorological data for building location, minimal and maximal wind velocities were determined during
Fig. 3. Air velocities vectors inside the building for wind velocity 0.5 m/s and direction normal to opening area.
the period when experimental measurements were performed. Wind velocity was changed from 0.5 to 2 m/s taking in account prevailing wind velocity in period when experimental measurements were performed. Wind direction was set up in interval from 0 to 908 relative to opening normal. The aim of wind direction is to provide minimal and maximal air velocities in opening plane. Ventilation in summer period is provided by large openings (usually one-third to one half of wall surface). Ventilation caused by thermal effect is about 10% of total ventilation, because there is no great difference between inside and outside air temperatures. Temperature difference between inside and outside air was from 0 to 8 8C, with 2 8C increment. Outside temperature was set in range from 14 to 22 8C. Most interesting for analysis is natural ventilation rate with minimal wind velocity. This minimal velocity is one of the major components in opening optimization. For higher velocities, opening area can be easily reduced taking into consideration optimal air velocities inside the building. In Fig. 3 air velocity vectors are shown inside the building for wind velocity 0.5 m/s and wind direction normal to opening area, for two positions in building, close to wall (a) and near the fan duct (b). The purpose of numerical simulation is to determine temperature and velocity field in defined space. It can be seen from Fig. 4 that fresh air from inlet moves through whole test room moving from top to bottom. This air movement determination is important in combining natural and mechanical ventilation for increasing ventilation rate. Fig. 4 shows inside air velocities for wind velocity 0.5 m/s and direction of 458 relative to opening area for two positions in building, close to wall (a) and near the fan duct (b). Reduced inside
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Fig. 6. Airflow dependence from wind incident angle.
Fig. 4. Air velocities vectors inside the building for wind velocity 0.5 m/s and direction of 458.
air velocities and velocity field result from incident angle change. Flow field also can show stagnation zones in closed space, where there will not be adequate air movement. In order to decrease dust concentration in these zones, partially mechanized ventilation should be observed. Minimal inside air velocities are shown in Fig. 5, where wind velocity is 0.5 m/s and wind direction is set at an angle of 908 relative to opening inlet norm also for two positions in building, close to wall (a) and near the fan duct (b). Low inside air velocities indicate that natural ventilation in this case is not useful in dust concentration reduction. Minimal fresh airflow rate that enters in test room does not result in intensive air movement, especially in zone of animal breathing. Airflow rate in this case practically does not exist, because velocity vector is parallel to opening. All the movements inside the test room are as a result of wall temperature differences and differences produced by animals or human occupants. Taking into account that ventilation rate due to thermal effect depends on temperature difference between outside and inside air, in summer period, with large openings these temperatures all almost the same, which affect the flow field as shown in Fig. 5. This is a boundary case for natural ventilation or a case when mechanical ventilation is needed. Wind direction causes airflow rate to decrease for any wind velocity. In case of higher wind velocities this will lead to a decrease in inlet velocity to optimal values, excluding when incident angle is 908 and actually fresh air does not enter into building. For wind velocity 0.5 m/s airflow dependence from incident angle is given in Fig. 6. 5. Energy consumption analysis
Fig. 5. Air velocities vectors inside the building for wind velocity 0.5 m/s and direction of 908.
Energy consumption analysis was derived from the results of the experimental measurements during the summer period, which includes maximum ventilation rate in all of the investigated regimes required inside the buildings. In these conditions, targeting the top energy consumption, only the highest regimes of the installed fans were considered, including 24-h operation. Roof fans electro motors nominal and effective power was 0.37 and 0.32 kW, respectively. At floor fans electro motors, both power values were 1.1 and 0.80 kW, respectively. Under the mentioned conditions, total daily energy consumption of fan electro motors during the second (under floor ventilation), third (roof ventilation) and fourth (both systems) regime were: 26.64, 26.4 and 53.04 kWh/day, respectively. According to the results it was concluded that considerable savings in energy consumption can be achieved by operation of floor ventilation, instead of both ventilation systems, in conditions that do not require maximum ventilation rate, such as during the night in summer period. Regarding optimal air velocity (0.02– 0.05 m/s) and very strong correlation between dust concentration
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and airflow velocity during the floor ventilation, there are particular situations in which floor ventilation can fulfill the optimal dust concentration and microclimate requirements. From numerical simulation of natural ventilation for the same period in experimental measurement, airflow rates, and relevant velocities are obtained including all outside parameters that affect natural ventilation rate. Numerical simulations showed that in summer period by natural ventilation it is possible to reduce over 60% use of mechanical system ventilation. In summer period for 92 days, energy consumption for roof and floor ventilation was 4879.68 kWh. By including natural ventilation, energy consumption in same period could be 2927.81 kWh lower. Optimizing mechanical ventilation by including only floor ventilation, energy consumption in the same period was 2635.8 kWh, and including natural ventilation would be 1581.48 kWh lower. With automatic control of opening size and connection between natural and mechanical ventilation these values can be much higher, and energy consumption can be 80% lower, for the same period. 6. Conclusion Optimizing any ventilation system in livestock building is aimed to reduce dust concentration in animal breathing zone (close to building floor) and human breathing zone (close to building roof). Optimal air velocities in animal breathing zone are from 0.02 to 0.05 m/s. From experimental results with mechanical ventilation airflow velocities under 0.02 m/s and over 0.08 m/s caused increment in dust concentration. Numerical simulation is a powerful tool for temperature and flow field determination. It strongly depends on boundary condition and outside meteorological data. Numerical simulation can be used for livestock building with natural ventilation optimization. Prediction of natural ventilation in correlation with mechanical ventilation system can significantly decrease energy consumption. Airflow velocities inside the room depend on wind velocity and incident angle in plane of opening. Higher values of wind velocities will not lead to healthy conditions inside the building. Replacing mechanical ventilation with natural ventilation in energy consumption in summer can be reduced by almost 60%. For more energy savings, it is necessary to obtain automatic controls of inlet and exhaust openings from one side, and automatic correlation between natural and mechanical ventilation system from the other side.
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References [1] C.M. Wathes, in: C.M. Wathes, D.R. Charles (Eds.), Air and Surface Hygiene. Livestock Housing, CAB International, 1994, pp. 123–148. [2] K. Donham, D. Cumra, Setting maximum dust exposure levels for people and animals in livestock facilities, in: International Symposium on Dust Control in Animal Production Facilities. Proceedings, CIGR, EurAgEng, NJF, DJS, Denmark, (1999), pp. 93–110. [3] G.A. Carpenter, Dust in livestock buildings — prevention and reduction, in: J.M. Bruce, M. Sommer (Eds.), Agriculture. Environmental Aspects of Respiratory Disease in Intensive Pig and Poultry Houses, Including the Implications for Human Health. Proceedings, 1987, pp. 101–110. [4] G.A. Carpenter, The Design of an Internal Ceiling-Mounted Air Filter Unit and its Application in an Early-Weaner Unit. Division Note DN/1128, National Institute Agricultural Engineering, Silsoe, 1982. [5] S. Pedersen, Staubreduzierung in Schweinesta¨llen, Deutsche Tiera¨rztliche Wochenschrift 105 (6) (1998) 247–250. [6] Y. Zhang, M.E. Barber, F.J. Patience, R.J.J. Feddes, Identification of oils to be sprinkled in livestock buildings to reduce dust, ASHRAE Transactions 101 (Pt. 2) (1995) 1179–1192. [7] D.S. Bundy, Electrical charge plays role in dust-collections system, Feedstuffs 63 (12) (1991) 30. [8] N.O. Breum, H. Takai, H.B. Rom, Upward vs downward ventilation air flow in a swine house, Transactions of the ASAE 33 (5) (1990) 1693–1699. [9] C.E. Klooster Van’t, P.F.M.M. Roelofs, L.A. den Hartog, Effects of filtration, vacuum cleaning and washing in pig houses on aerosol levels and pig performance, Livestock Production Science 33 (1993) 171–182. [10] Y. Zhang, Engineering control of dust in animal facilities, in: International Symposium on Dust Control in Animal Production Facilities Proceedings, CIGR, EurAgEng, NJF, DJS, Denmark, (1999), pp. 22–29. [11] G.L. Wicklen Van, Respirable aerosol sampling in poultry and swine housing, in: C.M. Wathes, J.M. Randall (Eds.), Aerosol Sampling in Animal Houses. Proceedings of a Workshop, University of Bristol, Department of Animal Husbandry, 26–28 July, Commission of the European Communities Directorate – General Telecommunications, Information Studies and Innovation, Luxembourg, 1989 , pp. 117– 122. [12] C. Nannen, W. Bu¨scher, Effect of animal activity on particle composition in various pig fattening housing systems, Landtechnik 63 (3) (2008) 170–171. [13] B. Mo¨ller, H.J. Mu¨ller, M. Gla¨ser, U. Wanka, T. Heidenreich, Quantitative assessment of air flow inside naturally ventilated animal houses, Landtechnik 62 (4) (2007) 234–235. [14] G. Franke, Trends in animal house climate control technology, Landtechnik 63 (6) (2008) 332–334. [15] M.C. Pumaa, R.G. Maghiranga, J.P. Murphya, P.R. O’Quinnb, J.L. Nelssenb, Energy use and dust levels in a segregated early-weaning swine nursery, Indoor and Built Environment 7 (1998) 224–231. [16] H.J. Mueller, K.H. Krause, Flow simulation for design of ventilation systems in animal houses, Building Simulation 2007 Proceedings (2007) 932–936. [17] L. Zhang, T.F. Smith, P.T. O’Shaughnessy, Development of a simulation model for a ventilation system for swine confinement, in: R.R. Stowell, R. Bucklin, R.W. Bottcher (Eds.), Livestock Environment VI: Proceedings of the 6th International Symposium, Louisville, Kentucky, USA, 21–23 May, (2001), pp. 293–300. [18] M. Lyngbye, C.R. Boon, Particle movements in mechanical ventilated piggeries – numerical simulations and experimental verification, in: International Symposium on Dust Control in Animal Production Facilities Proceedings, CIGR, EurAgEng, NJF, DJS, Denmark, (1999), pp. 204–212. [19] X. Wang, Y. Zhang, G.L. Riskowski, Dust spatial distribution in a typical swine building, in: International Symposium on Dust Control in Animal Production Facilities Proceedings, CIGR, EurAgEng, NJF, DJS, Denmark, (1999), pp. 48–55.