- Email: [email protected]
Ammonia Extraction by Ventilation of Loose-housing Systems for Laying Hens
J. agric. Engng Res. (2000) 75, 17}25 Article No. jaer.1999.0481, available online at http://www.idealibrary.com on
RESEARCH PAPERS
Ammonia Extraction by Ventilation of Loose-housing Systems for Laying Hens G. Gustafsson; E. von Wachenfelt Department of Agricultural Biosystems and Technology (JBT), Swedish University of Agricultural Sciences, P.O. Box 86, S-230 53 Alnarp, Sweden; e-mail: [email protected] (Received 23 April 1998; accepted in revised form 11 August 1999)
Laying hens kept in loose-housing systems instead of in cages generally mean that more manure is stored in the buildings. This causes an increased release and concentration of ammonia derived from manure and straw bedding material. Removing as much as possible of the exhaust ventilation air adjacent to surfaces with exposed manure reduces the concentration of ammonia. In such a situation, it is important to achieve uniform extraction along the entire length of the building. Both theoretical analyses and model experiments have shown that there are good opportunities to create uniform ventilation along exhaust air ducts if the ratio between the area of the vents and the cross-section of the air channel is of the same size range. Investigations conducted in a loosehousing system for laying hens have shown that ammonia concentrations may be reduced by extracting the air in the proximity of the litter without the risk of increased emissions elsewhere in the buildings. ( 2000 Silsoe Research Institute
Notation P s P tot P u q v k v k,.!9 v .!9 v .*/ v s v s x z
pressure drop in exhaust vents, Pa total pressure, Pa static pressure before the vents, Pa air#ow rate m3/s air velocity along the duct, m/s maximum air velocity in duct outlet, m/s maximum air velocity through a vent, m/s minimum air velocity through a vent, m/s air velocity through a vent, m/s average air velocity in the vents, m/s distance along a duct, m relationship betwen the lowest and the highest air velocity in the extraction vents along a ventilation duct j friction factor of the air channel f the friction coe$cient for the exhaust vents s g ventilation e!ectiveness o air density, kg/m3
A the cross-section of the exhaust air duct, m2 k A the total surface area of the exhaust vents, s m2 A /A area ratio s k a total coe$cient of friction for a duct C ammonia concentration in exhaust air outcorr let, corrected according to the level of ventilation rate, ppm C concentration in exhaust air outlet, ppm ex C concentration at a certain location, ppm x D hydraulic diameter of a duct, m h ¸ length of duct, m l exhaust distance from a vent, m l minimum exhaust distance from a vent, m .*/ l maximum exhaust distance from a vent, m .!9 P static pressure, Pa P dynamic pressure, Pa dyn P pressure drop due to friction along a duct, Pa k
A number of investigations (Aarnink et al., 1993; Andersson, 1995; Carr et al., 1990; Freney et al., 1983; Gustafsson, 1988) have shown that the release of ammonia in livestock houses is a!ected by several important factors,
1. Introduction Ammonia is produced by decomposition of nitrogenous compounds in the manure in poultry houses. 0021-8634/00/010017#09 $35.00/0
17
( 2000 Silsoe Research Institute
18
G . G US T AF S S O N; E. V O N W AC H EN FEL T
namely: the storage time of manure inside the buildings; ventilation rate; ventilation techniques and air movement around manure surfaces; the composition of the foodstu!s; surface areas where manure is exposed; air and manure temperatures; moisture content of the manure; pH of the manure; carbon/nitrogen ratio (C/N) of the manure; and number and size of the animals. An international survey by Kangro (1993) of air pollutants in buildings for laying hens showed a wide range of concentrations (from 1 to 84 p.p.m) depending on the type of manure handling used. This survey indicated that the type of manure handling is the decisive factor in#uencing the release and concentration of ammonia. The lowest values for ammonia release have been found in systems using conveyors for manure removal and, in particular, in systems where manure is dried on the conveyors. Systems with litter and deep pit manure storage gave the highest values in this survey. In both Swedish (Gustafsson & Mas rtensson, 1990; von Wachenfelt, 1993) and other studies (Mannebeck & Oldenburg, 1990; Hillig, 1992; Hauser & FoK lsch, 1993; Groot Koerkamp et al., 1995; 1996) loose housing for laying hens has been found to cause enhanced concentrations of ammonia in comparison with those in cage systems with regular disposal of manure. The reason for the increased concentrations of ammonia in loosehousing systems is almost certainly to be found in the larger amount of manure that is accumulated inside the buildings when the hens are kept in loose housing systems (Gustafsson & Ma> rtensson, 1990; Mannebeck & Oldenburg, 1990; Hauser & FoK lsch, 1993). The increased concentrations of ammonia may cause not only a working environment problem (Drost & van den Drift, 1992, 1993; Whyte et al., 1993; Schlenker et al., 1987), especially regarding respiratory illness, but also may affect the livestock environment. High ammonia concentrations have been found to a!ect production e$ciency, feed conversion and performance of poultry (Reece & Lott, 1980; Canveny & Quarles, 1978; Charles & Payne, 1966). There is also a demand to restrict ammonia emissions to the surroundings from the exhaust ventilation air. Investigations at JBT (Andersson, 1995; Gustafsson, 1988) have proved that the release of ammonia will increase with increasing air #ow rate. The reasons are that any increase in the pressure di!erence between ammonia in the manure and in the air enhances the evaporation rate of ammonia from the manure and that any increase in the air velocity around exposed manure surfaces increases the mass transfer coe$cient. Since it is clearly urgent to develop a technique that can limit the occurrence of this gas in buildings for laying hens, it has been important to investigate whether extraction of ventilation air close to manure surfaces is able to
limit the concentrations of ammonia in loose-housing systems for laying hens. The amount of ammonia extracted in this way is determined by the ability of ventilation air to capture the gas at the emitting surfaces. To obtain the best possible e!ectiveness in extracting manure gases, it is necessary to achieve a long exhaust range but also uniformity when extracting exhaust air from manure surfaces in long livestock buildings. Uniformity of #ow from extraction ducts is determined by the distribution of pressure in the ducts. Further, the loss of static pressure in the ventilation system must not be so large that it will a!ect the dimensioning of the entire fan system. The main objective of this study was, thus, to obtain data on the dimensioning of extraction ducts and on the e!ectiveness in extracting ammonia with di!erent ventilation layouts. It has also been urgent to investigate whether extraction of air close to manure surfaces has any in#uence on the emissions to the surroundings because the technique proposed has a curative character (it does not prevent the release of ammonia).
2. Theory For an extraction duct with a constant cross-section and with evenly distributed exhaust vents, the di!erent pressures in the duct are shown schematically in Fig. 1. The total pressure P is constant at any distance x along tot the duct which gives the pressure relation P (x)"P(x)#P (x)#P (x)"constant (1) tot dyn k where P is the static pressure, P the dynamic pressure dyn and P the pressure drop due to friction along the duct. k The dynamic pressure P is given by dyn o P (x)" v2 (x) (2) dyn 2 k where o is the air density and v the air velocity along the k duct. The pressure drop due to friction P is given by k j ox (3) P (x)" : v2 (x) dx k D 2 k h 0 where j is the friction coe$cient and D the hydraulic h diameter of the duct. The pressure drop P in the vents is given by s ov2(x) P (x)"f s "P !P(x) (4) s s 2 u where f is the friction coe$cient, v the air velocity in the s s vents and P the static pressure before the vents. The u static pressure at the location x in a duct with the length
19
AM M O N IA EX TR A CT IO N BY VE N TIL AT IO N FO R LA YIN G HE N S
expressed as
A B
Fig. 1. Pressure distribution in an extraction duct with a constant cross section; v and v , air volocities along the duct and in k s the vents, respectively; P and P , static and dynamic pressures in dyn the duct; P and P , pressure drops due to friction along the duct k s and in the vents, respectively; P , the static pressure before the u vents
¸ is given by P(x)"P(¸)#P (¸)!P (x)#P (¸)!P (x) (5) dyn dyn k k Equations (4) and (5) give the relation between the air velocities in the vents at the distances 0 and ¸ as
S
S
P (0) P (¸)!P (¸)!P (¸) v (0) s " s dyn k (6) z" s " P (¸) P (¸) v (¸) s s s where z is the ratio between the lowest and the highest air velocity in the extraction vents along a duct. The pressure drop due to friction P depends on k the variation in air velocity along the duct. It is not possible, therefore, to solve Eqn (6) analytically. However, the highest pressure drop is obtained when the air velocity in the vents is constant along the duct. This means that the air velocity inside the duct increases linearly according to x v (x)" v (¸) k ¸ k
(7)
Integrating Eqn (3) gives the pressure drop due to friction in the duct as j¸ ov2 (¸) k P (¸)" (8) k 2 3D h The average air velocity v in the vents can be approxis mated as
A B
z#1 v (0)#v (¸) q s "v (¸) v" s " (9) s s 2 2 A s where A is the sum of the areas of the vents and q the s total air#ow through the duct. The air velocities in the vents v , and in the duct v , at the distance ¸ can then be s k
q 2 v (¸)" (10) s A 1#z s q (11) v (¸)" k A k where A is the cross section of the duct. k The pressure drop P may be expressed as s v2(¸) f o q 2 2 2 P (¸)"f o s " s (12) s s 2 1#z 2 A s By using Eqns (6) and (12), the ratio between the lowest and highest air velocity in the vents, z, is given as
A BA B
1!1/4f (A /A )2(1#j¸/3D ) s s k h z" (13) 1#1/4f (A /A )2 (1#j¸/3D ) s s k h As expressed in Eqn (13), the variation of the air velocity in the extraction vents depends on the resistance f in the vents, the frictional resistance j¸/D in the duct s h and on the relationship between the sum of the areas of the vents and the area of the cross-section of the duct, A /A . s k The sum of static pressure drops in the vents and along the duct P , is expressed as tot fov2(¸) fo q 2 2 2 DP "P (¸)" s " s tot s 2 1#z 2 A s A 2 1 A 2 j¸ 2 fo s 1# (14) 1# " s v2(¸) k A 4f A 3D 2 k s k s h The required areas of the extraction vents A and the s cross-section of the duct A are determined by the unik formity of #ow in the vents desired along the duct and by the loss of pressure that can be accepted. According to Eqns (13) and (14), the area ratio A /A has a strong s k in#uence on both uniformity of #ow and loss of pressure. Fan systems for animal buildings in Sweden are normally dimensioned for a maximum total loss of pressure of 60 Pa. By this loss in pressure, a maximum of 15}20 Pa should originate from the extraction ducts.
A BC
A BA B A B A BD
3. Materials and methods The following ventilation properties were determined in a test duct during extraction of air namely: absolute change in air velocity along the duct; variation in exhaust distance along the duct; air velocity at di!erent distances from the vents; uniformity of #ow in the exhaust vents; and the variation in static pressure along the duct. These properties were measured at di!erent area ratios A /A and air velocities according to Table 1. The test s k
20
G . G US T AF S S O N; E. V O N W AC H EN FEL T
Table 1 Combinations (o) of area ratios As /Ak , and air velocities, vk,max investigated at the trials Max. air velocity (v ), k,max m/s 6)1}8)7 2)1}2)2 1)1}1)2 0)7
Test combinations (o) Area ratio (A /A ) s k 3)15
2)10
1)63
1)05
o
o o o o
o
o o o o
0)82 0)47 o
o o o o
duct was constructed in a testing room. It had a crosssection A of 0)3 m]0)3 m. The area ratio A /A was k s k varied by adjusting the areas of the vents A . The design s of the duct is presented in Fig. 2. For each adjustment, the air #ow was measured twice in a grid located in a circular ventilation duct attached to the fan. The air #ow was measured with a newly calibrated hot wire anemometer. Air velocities in the exhaust vents were measured in "ve di!erent parts of the duct with the same hot wire anemometer. The di!erence in static pressure to that of the ambient pressure was measured at "ve di!erent points in the duct (Fig. 2) with pressure heads attached by a plastic tube to an electric micromanometer. The change in static pressure was studied at di!erent area ratios A /A during s k exhaust events. For natural reasons (Bernouilli's law), the total out#ow of air a!ects the level of static pressure in the duct. The total loss of static pressure P in the duct was analysed according to the formula: aov2 P" k,.!9 2
(15)
where a is a coe$cient describing the total frictional losses in the entire duct and v is the maximum air k,.!9
velocity in the outlet of the duct. The coe$cient a depends on the design of the duct and the vents. The area ratio A /A was therefore considered to in#uence the s k value of the coe$cient of friction a. The length of extraction of air from the vents was determined using smoke ampoules and a measuring tape. The length of extraction was de"ned as the distance from the opening to the point where there was no air movement. Some of the test combinations in Table 1 were excluded from the analyses because of too low pressure or air velocity. Studies were also made in a climatic chamber (Fig. 3) at Alnarp SoK derga> rd farm where an aviary system (Marielund) was built for more than 700 laying hens. The climatic chamber provided the opportunity to control and simulate the outside climate, inside climate, ventilation rate, as well as the design and location of air outlets and inlets. The design of the climatic chamber is shown in Fig. 3. The exhaust air could be extracted at three di!erent places in the building, namely: at roof level at one end of the building; through an air duct with extraction vents located in the proximity of manure conveyors; and through an air duct with extraction vents located in the proximity of bedding litter on the #oor. Location of the air intakes also in#uences the occurrence of ammonia concentrations at di!erent places in the building. Consequently, four intake devices were studied, namely: a concentrated air intake with horizontal alignment of air at roof level; a slotted air intake with horizontal alignment of air at roof level; a perforated metal duct at roof level; and a perforated metal duct at #oor level. Ammonia concentrations were measured with reagent tubes (Kitagawa) in three di!erent locations: at human respiration height in the work passages; at hen respiration height in the work passages above the litter; and inside the tiers.
Fig. 2. Design of the test duct; x, pressure sensor; o, measuring point for air velocity and extent of air suction; all measurements in mm
AM M O N IA EX TR A CT IO N BY VE N TIL AT IO N FO R LA YIN G HE N S
21
Fig. 3. The climatic chamber equipped with an aviary system; the arrows indicate air movements from air inlets and to air outlets; (1) air inlet; (2) air outlet; (3) air channel
The capacity of di!erent ventilation layouts (combinations of air outlets and inlets) to reduce ammonia concentrations at di!erent locations in the building was evaluated as an ventilation e!ectiveness g de"ned as C g" ex (16) C x where C was the ammonia concentration in the exhaust ex air outlet and C the concentration in a certain location x in the building. Whether the extraction of air in the proximity of manure conveyors or the litter on the #oor resulted in statistically signi"cant di!erences in ventilation e!ectiveness in comparison with extraction at roof level was analysed with the t-test. An e!ectiveness g of 1)0 means that the concentration of ammonia is completely mixed and spread out over the entire building volume. An e!ectiveness higher than 1)0 means that gas movement is restricted to a non-uniform distribution. The amount of ammonia released and extracted in the outlet is a!ected not only by the air#ow rate but also by the function (air movement) of the outlet. At those air#ow rates which occur in houses for laying hens, the release of ammonia increases at increasing air#ow rates. The concentrations measured in outlet have therefore been corrected (weighted) in relation to the actual air#ow rate, such that + (qC)
C " corr
+q
outlets and inlets. The air temperature in the house was kept at 20}213C during the experiments.
4. Results 4.1. ;niformity of -ow in the exhaust vents The uniformity of #ow in the exhaust vents was determined at di!erent area ratios, A /A . Analyses were made s k in all experimental series of the in#uence on area ratio on the relative variation of air velocity v /v in the ex.*/ .!9 haust vents (Fig. 4). The variation in air velocity in the vents was less than 40% (v /v "0)6) when the area .*/ .!9
(17)
where C is the corrected concentration. The level of corr the corrected concentration also gives the level of the emission of ammonia for di!erent combinations of air
Fig. 4. Air velocity ratio, v /v , in the exhaust vents as a funcmin max tion of the area ratio, A /A : , measurements which have been s k analysed; , regression line
22
G . G US T AF S S O N; E. V O N W AC H EN FEL T
Fig. 5. Relationship between minimum and maximum lengths of exhaust range, l /l , as a function of the area ratio, A /A : min max s k , measurements which have been analysed; , regression line 2 where y"0)86#0)4x#0)051 x ; coezcient of determination R 2"0)785
ratio was less then 1. This is considered as satisfactory for extraction ducts. The measurements con"rmed the importance of the area ratio A /A for the uniformity of air s k velocity as presented in Eqn (13). Studies were also made of the e!ect of area ratio A /A s k on the relative variation in the length of the exhaust distance l /l (Fig. 5). The uniformity of the exhaust .*/ .!9 distance was in#uenced in nearly the same way by the area ratio as the air velocity in the exhaust vents (compare with Fig. 4). Thus, it is desirable to keep the value of the area ratio at least below 1 to ensure acceptable ventilation. The length of the exhaust range l was a!ected by the air velocity and v and thus also by the size of the air k,max
Fig. 6. Length of exhaust range (average) as a function of the maximum air velocity, v , in the air duct: , measurements k,max which have been analysed; , regression line where y"58)3# 0)62x; coezcient of determination R 2"0)83
Fig. 7. Values of the total coezcient of friction during air extraction as a function of area ratios A /A s k
#ow. The importance of the air velocity was analysed and is shown in Fig. 6. It can be seen that the exhaust range was linearly dependent on air velocity. However, it should be observed that the exhaust ventilation had a limited range, maximum 0)3 m in these studies.
4.2. Fall in static pressure The value of the total coe$cient of friction a is largely una!ected by the area ratio during air extraction (Fig. 7)
Fig. 8. Total pressure drop in exhaust air ducts at diwerent maximum air velocities, v according to Eqn (15) where k, max a"0)80
23
AM M O N IA EX TR A CT IO N BY VE N TIL AT IO N FO R LA YIN G HE N S
and has assumed values within the interval between 0)69 and 0)92. On average, the value of the coe$cient a was 0)80. The in#uence of the highest air velocity in the duct on the total loss of pressure in the air duct during exhaustion according to Eqn (15) with a value for a of 0)8 is illustrated in Fig. 8.
4.3. Studies in a building for laying hens An increase in the air #ow gave some reduction in the ammonia concentration in the building. However, the ventilation #ow did not give an ideal dilution. The reason is that increased ventilation #ow causes an increase in the rate for release of ammonia from the manure as illustrated in Fig. 9. Extraction of air in the proximity of the litter on the #oor resulted in a statistically signi"cant di!erence in the ventilation e!ectiveness compared to that for extraction at roof level (reference) both at human respiration height in the work passages as well as inside the tiers with all types of air inlets (Table 2) which were examined. The ventilation e!ectiveness above the litter on the #oor was signi"cantly di!erent from that for extraction at roof level when slotted air inlets and recirculating inlets at roof level were used. Extraction of air in the proximity of the manure conveyors did not result in any signi"cant di!erence in e!ectiveness compared to extraction at roof level in any location. The in#uence of air outlets and air inlets on the level of release of ammonia is presented as a corrected ammo-
Fig. 9. The inyuence of ventilation rate on ammonia release when a perforated airduct at roof level was used as air inlet and when air was exhausted at roof level
nia concentration in the outlets in Table 3. Extraction of air adjacent to the litter on the #oor resulted in the lowest concentrations and release rates for all types of air inlets. The best function was received when slotted
Table 2 Determined averages of ventilation e4ectivenesse g at di4erent locations in the building for di4erent combinations of air outlets and air inlets
Air outlet
No. of tests
Breath level
Floor
¹iers
Roof Floor
12 5
0)69 (0)13) 1)16 (0)20) ?
0)65 (0)18) 1)08 (0)20) ?
0)71 (0)08) 1)22 (0)14) ?
Slotted air inlet in the roof
Roof Conveyor Floor
15 3 8
1)08 (0)24) 0)98 (0)23) A 1)34 (0)12) B
0)87 (0)21) 0)82 (0)32) A 1)16 (0)16) B
1)04 (0)22) 1)06 (0)18) A 1)30 (0)15) B
Perforated air-duct at roof level
Roof Conveyor Floor
17* 8s 4
0)93 (0)33) 1)03 (0)27) A 1)22 (0)07) B
0)90 (0)37) 0)95 (0)23) A 1)05 (0)04) A
0)96 (0)34) 0)90 (0)18) A 1)18 (0)09) E
Perforated air-duct at #oor level
Roof Conveyor Floor
6 4 3
0)84 (0)17) 0)96 (0)13) A 1)19 (0)17) E
1)02 (0)31) 1)09 (0)23) A 1)54 (0)40) A
0)88 (0)16) 0)92 (0)10) A 1)22 (0)20) E
Recirculation air inlet in the roof
Standard deviations in brackets; p, probability; *22 Tests at breath level and 23 at #oor level; - 10 Tests at breath level and #oor level; A Non-signi"cance against extraction at roof level; E Signi"cant di!erence against extraction at roof level, 0)05'p'0)01; B Signi"cant di!erence against extraction at roof level, 0)01'p'0)001; ? Signi"cant di!erence against extraction at roof level, 0)001'p.
24
G . G US T AF S S O N; E. V O N W AC H EN FEL T
Table 3 Release and concentrations of ammonia (corrected in relation to air6ow rate) in the exhaust air for di4erent combinations of air outlets and air inlets Air inlet
Air outlet
Corrected exhaust concentration, p.p.m
Relative value, %
litter. Consequently, this location of exhaust air outlets does not appear to be a risk for increased emissions to the surroundings in buildings with aviary systems for loosehousing of laying hens.
Acknowledgements
Recirculation air inlet in the roof
Roof Floor
3)27 (0)91) 2)10 (0)79)
100 64
Slotted air inlet in the roof
Roof Conveyor Floor
3)91 (3)97) 3)70 (0)68) 2)23 (1)36)
100 95 57
Financial support for this research has been provided by the National Board of Agriculture in Sweden, the Swedish Farmers Foundation for Agricultural Research and the Swedish Council for Forestry and Agricultural Research.
Perforated air-duct at roof level
Roof Conveyor Floor
4)69 (4)4) 7)88 (3)17) 3)92 (0)82)
100 168 84
References
Roof Conveyor Floor
4)13 (3)54) 4)88 (1)65) 3)50 (2)67)
100 118 85
Perforated air-duct at #oor level
Standard deviations in brackets.
air inlets at roof level were used. Extraction of air adjacent to the manure conveyors resulted in an increased release and concentration in those cases when perforated air ducts were used as air inlets both at roof and #oor level.
5. Conclusions Both the theoretical analysis and the model experiments have demonstrated that there are good possibilities to achieve relatively uniform extraction of air from ducts if the ratio between the vents and the cross-section of the duct, A /A , is not too large. Measurements have s k shown that this ratio should not be larger than 1 if acceptable uniformity is to be achieved. The size of the loss in pressure in the exhaust ducts depends both on the frictional resistance of the duct and on the air velocities in the duct. The value of the total coe$cient of friction has been determined to be 0)8 independent of the area ratio. With this value of the total coe$cient of friction, the maximum air velocity in the duct v should not exceed k,.!9 5)5 m/s so that the total pressure drop is restricted to less than 15 Pa according to Swedish recommendations. The studies have also shown that the best ventilation e!ectiveness and lowest ammonia concentration is obtained when exhaust air is extracted in the proximity of the litter on the #oor. Results from the studies also indicate that the litter is the major source for release of ammonia if manure is removed daily from manure conveyors as was the case in these studies. No increases in ammonia release was observed when air was extracted adjacent to the
Aarnink A J A; Wagemans M J M; Keen A (1993). Factors a!ecting ammonia emission from housing for weaned piglets. Proceedings of First International Symposium on Nitrogen Flow in Pig Production and Environmental Consequences 1993, EAAP Publication No 69, 286}294 Andersson M (1995). Ammonia volatilization from cow and pig manure. Swedish University of Agricultural Sciences, Department of Agricultural Biosystems and Technology, Lund, Sweden, Report 98, 66 pp Canveny D D; Quarles C L (1978). The e!ect of atmospheric ammonia stress on broiler performance and carcass quality. Poultry Science, 57, 1124}1125 Carr L E; Wheaton F W; Douglas L W (1990). Empirical models to determine ammonia concentrations from broiler chicken litter. Transactions of the ASAE, 33(1), 260}265 Charles D R; Payne C G (1966). The in#uence of graded levels of atmospheric ammonia on chickens. British Poultry Science, 7, 177}198 Drost H; van den Drift D W (1992). Working conditions in an aviary system for laying hens. Proceedings of the World Poultry Congress, Vol. 2, pp. 734}738. Amsterdam, The Netherlands Drost H; van den Drift D W (1993). Health e!ects in relation to exposure to aerial components in aviary systems for layers. Proceedings of the XXV CIOSTA CIGR Congress, pp 198}204. Wageningen, The Netherlands Freney J R; Simpson J R; Denmead O T (1983). Volatilization of ammonia. In: Gaseous Loss of Nitrogen from Plant}Soil Systems (Freney J R; Simpson J R eds), pp 1}33. Martinus Nijho!, The Hague Groot Koerkamp P W G (1996). Concentrations and emissions of ammonia in livestock houses in Northern European countries. Proceedings: Seminarium nr 268, NJF-Teknik}96, 30 October}2 November, Aarhus. Nordiska Jordbruksforskares FoK rening Groot Koerkamp P W G; Keen A; Van Niekerk Th G C M; Smith S (1995). The e!ect of manure and litter handling and indoor climatic conditions on ammonia emissions from a battery cage and an aviary housing system for laying hens. Netherlands Journal of Agricultural Science, 43, 351}373 Gustafsson G (1988). Luft-och vaK rmebalanser i djurstallar [Air and heat balances of animal houses]. Swedish University of Agricultural Sciences, Department of Farm Buildings, Lund, Sweden, Report 59, 385 pp
AM M O N IA EX TR A CT IO N BY VE N TIL AT IO N FO R LA YIN G HE N S
Gustafsson G; Mas rtensson L (1990). Gaser och damm i fjaK derfaK stallar [Gases and dust in poultry houses]. Swedish University of Agricultural Sciences, Department of Farm Buildings, Lund, Sweden, Report 68, 88 pp Hauser R H; FoK lsch D W (1993). The quality of poultry house air in alternative systems for farming laying hens. Proceedings: Livestock Environment IV, pp 671}677. ASAE, St. Joseph Hillig J (1992). Ammoniakemissionen aus Aufzucht- und LegehennenstaK llen bei unterschiedlichen Haltungsverfahren [Ammonia emissions from houses for chickens and laying hens in di!erent housing systems]. In: Geruchs- und Schadgasemissionen aus der Tierhaltung, Vol. 174, pp. 74}79. Darmstadt, KTBL, Arbeitspapier Kangro A (1993). LuftfoK roreningar i vaK rphoK nsstallar [Air contamination in buildings for laying hens]. Swedish University of Agricultural Sciences, Department of Farm Buildings, Lund, Sweden, Report 88, 124 pp
25
Mannebeck H; Oldenburg J (1990). Comparison of di!erent systems on ammonia emissions. In: Odour and Emissions from Livestock Farming (Nielsen, Voorburg; Hermite eds), pp 42}49. Elsevier Applied Science, London Reece F N; Lott D B (1980). The e!ect of ammonia and carbon dioxide during brooding on the performance of broiler chickens. Poultry Science, 59, 1654 Schlenker E H; Parry R R; Hellickson M A (1987). Respiratory characteristics of poultry labourers. Proceedings: CIGRSeminar on Latest Developments in Livestock Housing, pp 127}136. Urbana-Champaign, IL, ASAE, St. Joseph, MI Whyte R T; Williamsson P A M; Lacey J (1993). Air pollutant burdens and respiratory impairment of poltry house stockmen. Proceedings: Livestock Environment IV, pp 709}716. ASAE, St. Joseph, MI von Wachenfelt E (1993). Air contamination in poultry production systems. Proceedings: Fourth European Symposium on Poultry, Edinburgh, September 18}24
RESEARCH PAPERS
Ammonia Extraction by Ventilation of Loose-housing Systems for Laying Hens G. Gustafsson; E. von Wachenfelt Department of Agricultural Biosystems and Technology (JBT), Swedish University of Agricultural Sciences, P.O. Box 86, S-230 53 Alnarp, Sweden; e-mail: [email protected] (Received 23 April 1998; accepted in revised form 11 August 1999)
Laying hens kept in loose-housing systems instead of in cages generally mean that more manure is stored in the buildings. This causes an increased release and concentration of ammonia derived from manure and straw bedding material. Removing as much as possible of the exhaust ventilation air adjacent to surfaces with exposed manure reduces the concentration of ammonia. In such a situation, it is important to achieve uniform extraction along the entire length of the building. Both theoretical analyses and model experiments have shown that there are good opportunities to create uniform ventilation along exhaust air ducts if the ratio between the area of the vents and the cross-section of the air channel is of the same size range. Investigations conducted in a loosehousing system for laying hens have shown that ammonia concentrations may be reduced by extracting the air in the proximity of the litter without the risk of increased emissions elsewhere in the buildings. ( 2000 Silsoe Research Institute
Notation P s P tot P u q v k v k,.!9 v .!9 v .*/ v s v s x z
pressure drop in exhaust vents, Pa total pressure, Pa static pressure before the vents, Pa air#ow rate m3/s air velocity along the duct, m/s maximum air velocity in duct outlet, m/s maximum air velocity through a vent, m/s minimum air velocity through a vent, m/s air velocity through a vent, m/s average air velocity in the vents, m/s distance along a duct, m relationship betwen the lowest and the highest air velocity in the extraction vents along a ventilation duct j friction factor of the air channel f the friction coe$cient for the exhaust vents s g ventilation e!ectiveness o air density, kg/m3
A the cross-section of the exhaust air duct, m2 k A the total surface area of the exhaust vents, s m2 A /A area ratio s k a total coe$cient of friction for a duct C ammonia concentration in exhaust air outcorr let, corrected according to the level of ventilation rate, ppm C concentration in exhaust air outlet, ppm ex C concentration at a certain location, ppm x D hydraulic diameter of a duct, m h ¸ length of duct, m l exhaust distance from a vent, m l minimum exhaust distance from a vent, m .*/ l maximum exhaust distance from a vent, m .!9 P static pressure, Pa P dynamic pressure, Pa dyn P pressure drop due to friction along a duct, Pa k
A number of investigations (Aarnink et al., 1993; Andersson, 1995; Carr et al., 1990; Freney et al., 1983; Gustafsson, 1988) have shown that the release of ammonia in livestock houses is a!ected by several important factors,
1. Introduction Ammonia is produced by decomposition of nitrogenous compounds in the manure in poultry houses. 0021-8634/00/010017#09 $35.00/0
17
( 2000 Silsoe Research Institute
18
G . G US T AF S S O N; E. V O N W AC H EN FEL T
namely: the storage time of manure inside the buildings; ventilation rate; ventilation techniques and air movement around manure surfaces; the composition of the foodstu!s; surface areas where manure is exposed; air and manure temperatures; moisture content of the manure; pH of the manure; carbon/nitrogen ratio (C/N) of the manure; and number and size of the animals. An international survey by Kangro (1993) of air pollutants in buildings for laying hens showed a wide range of concentrations (from 1 to 84 p.p.m) depending on the type of manure handling used. This survey indicated that the type of manure handling is the decisive factor in#uencing the release and concentration of ammonia. The lowest values for ammonia release have been found in systems using conveyors for manure removal and, in particular, in systems where manure is dried on the conveyors. Systems with litter and deep pit manure storage gave the highest values in this survey. In both Swedish (Gustafsson & Mas rtensson, 1990; von Wachenfelt, 1993) and other studies (Mannebeck & Oldenburg, 1990; Hillig, 1992; Hauser & FoK lsch, 1993; Groot Koerkamp et al., 1995; 1996) loose housing for laying hens has been found to cause enhanced concentrations of ammonia in comparison with those in cage systems with regular disposal of manure. The reason for the increased concentrations of ammonia in loosehousing systems is almost certainly to be found in the larger amount of manure that is accumulated inside the buildings when the hens are kept in loose housing systems (Gustafsson & Ma> rtensson, 1990; Mannebeck & Oldenburg, 1990; Hauser & FoK lsch, 1993). The increased concentrations of ammonia may cause not only a working environment problem (Drost & van den Drift, 1992, 1993; Whyte et al., 1993; Schlenker et al., 1987), especially regarding respiratory illness, but also may affect the livestock environment. High ammonia concentrations have been found to a!ect production e$ciency, feed conversion and performance of poultry (Reece & Lott, 1980; Canveny & Quarles, 1978; Charles & Payne, 1966). There is also a demand to restrict ammonia emissions to the surroundings from the exhaust ventilation air. Investigations at JBT (Andersson, 1995; Gustafsson, 1988) have proved that the release of ammonia will increase with increasing air #ow rate. The reasons are that any increase in the pressure di!erence between ammonia in the manure and in the air enhances the evaporation rate of ammonia from the manure and that any increase in the air velocity around exposed manure surfaces increases the mass transfer coe$cient. Since it is clearly urgent to develop a technique that can limit the occurrence of this gas in buildings for laying hens, it has been important to investigate whether extraction of ventilation air close to manure surfaces is able to
limit the concentrations of ammonia in loose-housing systems for laying hens. The amount of ammonia extracted in this way is determined by the ability of ventilation air to capture the gas at the emitting surfaces. To obtain the best possible e!ectiveness in extracting manure gases, it is necessary to achieve a long exhaust range but also uniformity when extracting exhaust air from manure surfaces in long livestock buildings. Uniformity of #ow from extraction ducts is determined by the distribution of pressure in the ducts. Further, the loss of static pressure in the ventilation system must not be so large that it will a!ect the dimensioning of the entire fan system. The main objective of this study was, thus, to obtain data on the dimensioning of extraction ducts and on the e!ectiveness in extracting ammonia with di!erent ventilation layouts. It has also been urgent to investigate whether extraction of air close to manure surfaces has any in#uence on the emissions to the surroundings because the technique proposed has a curative character (it does not prevent the release of ammonia).
2. Theory For an extraction duct with a constant cross-section and with evenly distributed exhaust vents, the di!erent pressures in the duct are shown schematically in Fig. 1. The total pressure P is constant at any distance x along tot the duct which gives the pressure relation P (x)"P(x)#P (x)#P (x)"constant (1) tot dyn k where P is the static pressure, P the dynamic pressure dyn and P the pressure drop due to friction along the duct. k The dynamic pressure P is given by dyn o P (x)" v2 (x) (2) dyn 2 k where o is the air density and v the air velocity along the k duct. The pressure drop due to friction P is given by k j ox (3) P (x)" : v2 (x) dx k D 2 k h 0 where j is the friction coe$cient and D the hydraulic h diameter of the duct. The pressure drop P in the vents is given by s ov2(x) P (x)"f s "P !P(x) (4) s s 2 u where f is the friction coe$cient, v the air velocity in the s s vents and P the static pressure before the vents. The u static pressure at the location x in a duct with the length
19
AM M O N IA EX TR A CT IO N BY VE N TIL AT IO N FO R LA YIN G HE N S
expressed as
A B
Fig. 1. Pressure distribution in an extraction duct with a constant cross section; v and v , air volocities along the duct and in k s the vents, respectively; P and P , static and dynamic pressures in dyn the duct; P and P , pressure drops due to friction along the duct k s and in the vents, respectively; P , the static pressure before the u vents
¸ is given by P(x)"P(¸)#P (¸)!P (x)#P (¸)!P (x) (5) dyn dyn k k Equations (4) and (5) give the relation between the air velocities in the vents at the distances 0 and ¸ as
S
S
P (0) P (¸)!P (¸)!P (¸) v (0) s " s dyn k (6) z" s " P (¸) P (¸) v (¸) s s s where z is the ratio between the lowest and the highest air velocity in the extraction vents along a duct. The pressure drop due to friction P depends on k the variation in air velocity along the duct. It is not possible, therefore, to solve Eqn (6) analytically. However, the highest pressure drop is obtained when the air velocity in the vents is constant along the duct. This means that the air velocity inside the duct increases linearly according to x v (x)" v (¸) k ¸ k
(7)
Integrating Eqn (3) gives the pressure drop due to friction in the duct as j¸ ov2 (¸) k P (¸)" (8) k 2 3D h The average air velocity v in the vents can be approxis mated as
A B
z#1 v (0)#v (¸) q s "v (¸) v" s " (9) s s 2 2 A s where A is the sum of the areas of the vents and q the s total air#ow through the duct. The air velocities in the vents v , and in the duct v , at the distance ¸ can then be s k
q 2 v (¸)" (10) s A 1#z s q (11) v (¸)" k A k where A is the cross section of the duct. k The pressure drop P may be expressed as s v2(¸) f o q 2 2 2 P (¸)"f o s " s (12) s s 2 1#z 2 A s By using Eqns (6) and (12), the ratio between the lowest and highest air velocity in the vents, z, is given as
A BA B
1!1/4f (A /A )2(1#j¸/3D ) s s k h z" (13) 1#1/4f (A /A )2 (1#j¸/3D ) s s k h As expressed in Eqn (13), the variation of the air velocity in the extraction vents depends on the resistance f in the vents, the frictional resistance j¸/D in the duct s h and on the relationship between the sum of the areas of the vents and the area of the cross-section of the duct, A /A . s k The sum of static pressure drops in the vents and along the duct P , is expressed as tot fov2(¸) fo q 2 2 2 DP "P (¸)" s " s tot s 2 1#z 2 A s A 2 1 A 2 j¸ 2 fo s 1# (14) 1# " s v2(¸) k A 4f A 3D 2 k s k s h The required areas of the extraction vents A and the s cross-section of the duct A are determined by the unik formity of #ow in the vents desired along the duct and by the loss of pressure that can be accepted. According to Eqns (13) and (14), the area ratio A /A has a strong s k in#uence on both uniformity of #ow and loss of pressure. Fan systems for animal buildings in Sweden are normally dimensioned for a maximum total loss of pressure of 60 Pa. By this loss in pressure, a maximum of 15}20 Pa should originate from the extraction ducts.
A BC
A BA B A B A BD
3. Materials and methods The following ventilation properties were determined in a test duct during extraction of air namely: absolute change in air velocity along the duct; variation in exhaust distance along the duct; air velocity at di!erent distances from the vents; uniformity of #ow in the exhaust vents; and the variation in static pressure along the duct. These properties were measured at di!erent area ratios A /A and air velocities according to Table 1. The test s k
20
G . G US T AF S S O N; E. V O N W AC H EN FEL T
Table 1 Combinations (o) of area ratios As /Ak , and air velocities, vk,max investigated at the trials Max. air velocity (v ), k,max m/s 6)1}8)7 2)1}2)2 1)1}1)2 0)7
Test combinations (o) Area ratio (A /A ) s k 3)15
2)10
1)63
1)05
o
o o o o
o
o o o o
0)82 0)47 o
o o o o
duct was constructed in a testing room. It had a crosssection A of 0)3 m]0)3 m. The area ratio A /A was k s k varied by adjusting the areas of the vents A . The design s of the duct is presented in Fig. 2. For each adjustment, the air #ow was measured twice in a grid located in a circular ventilation duct attached to the fan. The air #ow was measured with a newly calibrated hot wire anemometer. Air velocities in the exhaust vents were measured in "ve di!erent parts of the duct with the same hot wire anemometer. The di!erence in static pressure to that of the ambient pressure was measured at "ve di!erent points in the duct (Fig. 2) with pressure heads attached by a plastic tube to an electric micromanometer. The change in static pressure was studied at di!erent area ratios A /A during s k exhaust events. For natural reasons (Bernouilli's law), the total out#ow of air a!ects the level of static pressure in the duct. The total loss of static pressure P in the duct was analysed according to the formula: aov2 P" k,.!9 2
(15)
where a is a coe$cient describing the total frictional losses in the entire duct and v is the maximum air k,.!9
velocity in the outlet of the duct. The coe$cient a depends on the design of the duct and the vents. The area ratio A /A was therefore considered to in#uence the s k value of the coe$cient of friction a. The length of extraction of air from the vents was determined using smoke ampoules and a measuring tape. The length of extraction was de"ned as the distance from the opening to the point where there was no air movement. Some of the test combinations in Table 1 were excluded from the analyses because of too low pressure or air velocity. Studies were also made in a climatic chamber (Fig. 3) at Alnarp SoK derga> rd farm where an aviary system (Marielund) was built for more than 700 laying hens. The climatic chamber provided the opportunity to control and simulate the outside climate, inside climate, ventilation rate, as well as the design and location of air outlets and inlets. The design of the climatic chamber is shown in Fig. 3. The exhaust air could be extracted at three di!erent places in the building, namely: at roof level at one end of the building; through an air duct with extraction vents located in the proximity of manure conveyors; and through an air duct with extraction vents located in the proximity of bedding litter on the #oor. Location of the air intakes also in#uences the occurrence of ammonia concentrations at di!erent places in the building. Consequently, four intake devices were studied, namely: a concentrated air intake with horizontal alignment of air at roof level; a slotted air intake with horizontal alignment of air at roof level; a perforated metal duct at roof level; and a perforated metal duct at #oor level. Ammonia concentrations were measured with reagent tubes (Kitagawa) in three di!erent locations: at human respiration height in the work passages; at hen respiration height in the work passages above the litter; and inside the tiers.
Fig. 2. Design of the test duct; x, pressure sensor; o, measuring point for air velocity and extent of air suction; all measurements in mm
AM M O N IA EX TR A CT IO N BY VE N TIL AT IO N FO R LA YIN G HE N S
21
Fig. 3. The climatic chamber equipped with an aviary system; the arrows indicate air movements from air inlets and to air outlets; (1) air inlet; (2) air outlet; (3) air channel
The capacity of di!erent ventilation layouts (combinations of air outlets and inlets) to reduce ammonia concentrations at di!erent locations in the building was evaluated as an ventilation e!ectiveness g de"ned as C g" ex (16) C x where C was the ammonia concentration in the exhaust ex air outlet and C the concentration in a certain location x in the building. Whether the extraction of air in the proximity of manure conveyors or the litter on the #oor resulted in statistically signi"cant di!erences in ventilation e!ectiveness in comparison with extraction at roof level was analysed with the t-test. An e!ectiveness g of 1)0 means that the concentration of ammonia is completely mixed and spread out over the entire building volume. An e!ectiveness higher than 1)0 means that gas movement is restricted to a non-uniform distribution. The amount of ammonia released and extracted in the outlet is a!ected not only by the air#ow rate but also by the function (air movement) of the outlet. At those air#ow rates which occur in houses for laying hens, the release of ammonia increases at increasing air#ow rates. The concentrations measured in outlet have therefore been corrected (weighted) in relation to the actual air#ow rate, such that + (qC)
C " corr
+q
outlets and inlets. The air temperature in the house was kept at 20}213C during the experiments.
4. Results 4.1. ;niformity of -ow in the exhaust vents The uniformity of #ow in the exhaust vents was determined at di!erent area ratios, A /A . Analyses were made s k in all experimental series of the in#uence on area ratio on the relative variation of air velocity v /v in the ex.*/ .!9 haust vents (Fig. 4). The variation in air velocity in the vents was less than 40% (v /v "0)6) when the area .*/ .!9
(17)
where C is the corrected concentration. The level of corr the corrected concentration also gives the level of the emission of ammonia for di!erent combinations of air
Fig. 4. Air velocity ratio, v /v , in the exhaust vents as a funcmin max tion of the area ratio, A /A : , measurements which have been s k analysed; , regression line
22
G . G US T AF S S O N; E. V O N W AC H EN FEL T
Fig. 5. Relationship between minimum and maximum lengths of exhaust range, l /l , as a function of the area ratio, A /A : min max s k , measurements which have been analysed; , regression line 2 where y"0)86#0)4x#0)051 x ; coezcient of determination R 2"0)785
ratio was less then 1. This is considered as satisfactory for extraction ducts. The measurements con"rmed the importance of the area ratio A /A for the uniformity of air s k velocity as presented in Eqn (13). Studies were also made of the e!ect of area ratio A /A s k on the relative variation in the length of the exhaust distance l /l (Fig. 5). The uniformity of the exhaust .*/ .!9 distance was in#uenced in nearly the same way by the area ratio as the air velocity in the exhaust vents (compare with Fig. 4). Thus, it is desirable to keep the value of the area ratio at least below 1 to ensure acceptable ventilation. The length of the exhaust range l was a!ected by the air velocity and v and thus also by the size of the air k,max
Fig. 6. Length of exhaust range (average) as a function of the maximum air velocity, v , in the air duct: , measurements k,max which have been analysed; , regression line where y"58)3# 0)62x; coezcient of determination R 2"0)83
Fig. 7. Values of the total coezcient of friction during air extraction as a function of area ratios A /A s k
#ow. The importance of the air velocity was analysed and is shown in Fig. 6. It can be seen that the exhaust range was linearly dependent on air velocity. However, it should be observed that the exhaust ventilation had a limited range, maximum 0)3 m in these studies.
4.2. Fall in static pressure The value of the total coe$cient of friction a is largely una!ected by the area ratio during air extraction (Fig. 7)
Fig. 8. Total pressure drop in exhaust air ducts at diwerent maximum air velocities, v according to Eqn (15) where k, max a"0)80
23
AM M O N IA EX TR A CT IO N BY VE N TIL AT IO N FO R LA YIN G HE N S
and has assumed values within the interval between 0)69 and 0)92. On average, the value of the coe$cient a was 0)80. The in#uence of the highest air velocity in the duct on the total loss of pressure in the air duct during exhaustion according to Eqn (15) with a value for a of 0)8 is illustrated in Fig. 8.
4.3. Studies in a building for laying hens An increase in the air #ow gave some reduction in the ammonia concentration in the building. However, the ventilation #ow did not give an ideal dilution. The reason is that increased ventilation #ow causes an increase in the rate for release of ammonia from the manure as illustrated in Fig. 9. Extraction of air in the proximity of the litter on the #oor resulted in a statistically signi"cant di!erence in the ventilation e!ectiveness compared to that for extraction at roof level (reference) both at human respiration height in the work passages as well as inside the tiers with all types of air inlets (Table 2) which were examined. The ventilation e!ectiveness above the litter on the #oor was signi"cantly di!erent from that for extraction at roof level when slotted air inlets and recirculating inlets at roof level were used. Extraction of air in the proximity of the manure conveyors did not result in any signi"cant di!erence in e!ectiveness compared to extraction at roof level in any location. The in#uence of air outlets and air inlets on the level of release of ammonia is presented as a corrected ammo-
Fig. 9. The inyuence of ventilation rate on ammonia release when a perforated airduct at roof level was used as air inlet and when air was exhausted at roof level
nia concentration in the outlets in Table 3. Extraction of air adjacent to the litter on the #oor resulted in the lowest concentrations and release rates for all types of air inlets. The best function was received when slotted
Table 2 Determined averages of ventilation e4ectivenesse g at di4erent locations in the building for di4erent combinations of air outlets and air inlets
Air outlet
No. of tests
Breath level
Floor
¹iers
Roof Floor
12 5
0)69 (0)13) 1)16 (0)20) ?
0)65 (0)18) 1)08 (0)20) ?
0)71 (0)08) 1)22 (0)14) ?
Slotted air inlet in the roof
Roof Conveyor Floor
15 3 8
1)08 (0)24) 0)98 (0)23) A 1)34 (0)12) B
0)87 (0)21) 0)82 (0)32) A 1)16 (0)16) B
1)04 (0)22) 1)06 (0)18) A 1)30 (0)15) B
Perforated air-duct at roof level
Roof Conveyor Floor
17* 8s 4
0)93 (0)33) 1)03 (0)27) A 1)22 (0)07) B
0)90 (0)37) 0)95 (0)23) A 1)05 (0)04) A
0)96 (0)34) 0)90 (0)18) A 1)18 (0)09) E
Perforated air-duct at #oor level
Roof Conveyor Floor
6 4 3
0)84 (0)17) 0)96 (0)13) A 1)19 (0)17) E
1)02 (0)31) 1)09 (0)23) A 1)54 (0)40) A
0)88 (0)16) 0)92 (0)10) A 1)22 (0)20) E
Recirculation air inlet in the roof
Standard deviations in brackets; p, probability; *22 Tests at breath level and 23 at #oor level; - 10 Tests at breath level and #oor level; A Non-signi"cance against extraction at roof level; E Signi"cant di!erence against extraction at roof level, 0)05'p'0)01; B Signi"cant di!erence against extraction at roof level, 0)01'p'0)001; ? Signi"cant di!erence against extraction at roof level, 0)001'p.
24
G . G US T AF S S O N; E. V O N W AC H EN FEL T
Table 3 Release and concentrations of ammonia (corrected in relation to air6ow rate) in the exhaust air for di4erent combinations of air outlets and air inlets Air inlet
Air outlet
Corrected exhaust concentration, p.p.m
Relative value, %
litter. Consequently, this location of exhaust air outlets does not appear to be a risk for increased emissions to the surroundings in buildings with aviary systems for loosehousing of laying hens.
Acknowledgements
Recirculation air inlet in the roof
Roof Floor
3)27 (0)91) 2)10 (0)79)
100 64
Slotted air inlet in the roof
Roof Conveyor Floor
3)91 (3)97) 3)70 (0)68) 2)23 (1)36)
100 95 57
Financial support for this research has been provided by the National Board of Agriculture in Sweden, the Swedish Farmers Foundation for Agricultural Research and the Swedish Council for Forestry and Agricultural Research.
Perforated air-duct at roof level
Roof Conveyor Floor
4)69 (4)4) 7)88 (3)17) 3)92 (0)82)
100 168 84
References
Roof Conveyor Floor
4)13 (3)54) 4)88 (1)65) 3)50 (2)67)
100 118 85
Perforated air-duct at #oor level
Standard deviations in brackets.
air inlets at roof level were used. Extraction of air adjacent to the manure conveyors resulted in an increased release and concentration in those cases when perforated air ducts were used as air inlets both at roof and #oor level.
5. Conclusions Both the theoretical analysis and the model experiments have demonstrated that there are good possibilities to achieve relatively uniform extraction of air from ducts if the ratio between the vents and the cross-section of the duct, A /A , is not too large. Measurements have s k shown that this ratio should not be larger than 1 if acceptable uniformity is to be achieved. The size of the loss in pressure in the exhaust ducts depends both on the frictional resistance of the duct and on the air velocities in the duct. The value of the total coe$cient of friction has been determined to be 0)8 independent of the area ratio. With this value of the total coe$cient of friction, the maximum air velocity in the duct v should not exceed k,.!9 5)5 m/s so that the total pressure drop is restricted to less than 15 Pa according to Swedish recommendations. The studies have also shown that the best ventilation e!ectiveness and lowest ammonia concentration is obtained when exhaust air is extracted in the proximity of the litter on the #oor. Results from the studies also indicate that the litter is the major source for release of ammonia if manure is removed daily from manure conveyors as was the case in these studies. No increases in ammonia release was observed when air was extracted adjacent to the
Aarnink A J A; Wagemans M J M; Keen A (1993). Factors a!ecting ammonia emission from housing for weaned piglets. Proceedings of First International Symposium on Nitrogen Flow in Pig Production and Environmental Consequences 1993, EAAP Publication No 69, 286}294 Andersson M (1995). Ammonia volatilization from cow and pig manure. Swedish University of Agricultural Sciences, Department of Agricultural Biosystems and Technology, Lund, Sweden, Report 98, 66 pp Canveny D D; Quarles C L (1978). The e!ect of atmospheric ammonia stress on broiler performance and carcass quality. Poultry Science, 57, 1124}1125 Carr L E; Wheaton F W; Douglas L W (1990). Empirical models to determine ammonia concentrations from broiler chicken litter. Transactions of the ASAE, 33(1), 260}265 Charles D R; Payne C G (1966). The in#uence of graded levels of atmospheric ammonia on chickens. British Poultry Science, 7, 177}198 Drost H; van den Drift D W (1992). Working conditions in an aviary system for laying hens. Proceedings of the World Poultry Congress, Vol. 2, pp. 734}738. Amsterdam, The Netherlands Drost H; van den Drift D W (1993). Health e!ects in relation to exposure to aerial components in aviary systems for layers. Proceedings of the XXV CIOSTA CIGR Congress, pp 198}204. Wageningen, The Netherlands Freney J R; Simpson J R; Denmead O T (1983). Volatilization of ammonia. In: Gaseous Loss of Nitrogen from Plant}Soil Systems (Freney J R; Simpson J R eds), pp 1}33. Martinus Nijho!, The Hague Groot Koerkamp P W G (1996). Concentrations and emissions of ammonia in livestock houses in Northern European countries. Proceedings: Seminarium nr 268, NJF-Teknik}96, 30 October}2 November, Aarhus. Nordiska Jordbruksforskares FoK rening Groot Koerkamp P W G; Keen A; Van Niekerk Th G C M; Smith S (1995). The e!ect of manure and litter handling and indoor climatic conditions on ammonia emissions from a battery cage and an aviary housing system for laying hens. Netherlands Journal of Agricultural Science, 43, 351}373 Gustafsson G (1988). Luft-och vaK rmebalanser i djurstallar [Air and heat balances of animal houses]. Swedish University of Agricultural Sciences, Department of Farm Buildings, Lund, Sweden, Report 59, 385 pp
AM M O N IA EX TR A CT IO N BY VE N TIL AT IO N FO R LA YIN G HE N S
Gustafsson G; Mas rtensson L (1990). Gaser och damm i fjaK derfaK stallar [Gases and dust in poultry houses]. Swedish University of Agricultural Sciences, Department of Farm Buildings, Lund, Sweden, Report 68, 88 pp Hauser R H; FoK lsch D W (1993). The quality of poultry house air in alternative systems for farming laying hens. Proceedings: Livestock Environment IV, pp 671}677. ASAE, St. Joseph Hillig J (1992). Ammoniakemissionen aus Aufzucht- und LegehennenstaK llen bei unterschiedlichen Haltungsverfahren [Ammonia emissions from houses for chickens and laying hens in di!erent housing systems]. In: Geruchs- und Schadgasemissionen aus der Tierhaltung, Vol. 174, pp. 74}79. Darmstadt, KTBL, Arbeitspapier Kangro A (1993). LuftfoK roreningar i vaK rphoK nsstallar [Air contamination in buildings for laying hens]. Swedish University of Agricultural Sciences, Department of Farm Buildings, Lund, Sweden, Report 88, 124 pp
25
Mannebeck H; Oldenburg J (1990). Comparison of di!erent systems on ammonia emissions. In: Odour and Emissions from Livestock Farming (Nielsen, Voorburg; Hermite eds), pp 42}49. Elsevier Applied Science, London Reece F N; Lott D B (1980). The e!ect of ammonia and carbon dioxide during brooding on the performance of broiler chickens. Poultry Science, 59, 1654 Schlenker E H; Parry R R; Hellickson M A (1987). Respiratory characteristics of poultry labourers. Proceedings: CIGRSeminar on Latest Developments in Livestock Housing, pp 127}136. Urbana-Champaign, IL, ASAE, St. Joseph, MI Whyte R T; Williamsson P A M; Lacey J (1993). Air pollutant burdens and respiratory impairment of poltry house stockmen. Proceedings: Livestock Environment IV, pp 709}716. ASAE, St. Joseph, MI von Wachenfelt E (1993). Air contamination in poultry production systems. Proceedings: Fourth European Symposium on Poultry, Edinburgh, September 18}24