Ventilation investigations using a section of a livestock building and air flow visualization by bubbles

J. agric. Engng Res. (1972) 17, 323-331

Ventilation Investigations Using a Section of a Livestock Building and Air Flow Visualization by Bubbles G. A.

CARPENTER*;

L. J.

MOULSLEY*;

J.

M. RANDALL*

The design and use of an experimental full-sized section of an intensive livestock building for research on the control of environment is described. Features include an air flow visualization technique using illuminated liquid-film bubbles with photographic recording, a choice of ventilation systems, control of temperature and throughput of the ventilating air, variable pen lay-outs, and the use of simulated pigs.

1. Introduction The quantity of air required for the ventilation of a livestock building with a given type of animal, stocking density and ambient conditions, is well established 1 , 2 but the criteria have yet to be specified for designing ventilation systems that reliably produce an optimal environment with optimal utilization of fan power. Patterns of air movement resulting from the ventilation system have been studied using smoke as a visible tracer in full-sized livestock buildings," 4. s, 6, 7 in a model containing air," and in a model using particles suspended in a liquid medium," photographic records of the tracer being presented in several instances." 7. 8. 9 It is undesirable to use a full-sized house committed to animal production because it introduces too many variables. Even a specially built full-sized experimental livestock building can be unwieldy and expensive. The use of a model is attractive, but due to the difficulties of similitude, results may require verification on a full scale. A full scale section avoids scaling down, is manageable, and can be representative of many existing livestock buildings because the majority of them are long and narrow and have a repeated pattern of air inlets and outlets along their length. Air movements are then predominantly in planes perpendicular to the long axis of the building. The movement of the air contained in a section of a building taken between two such planes is therefore typical of that in the building as a whole. If also, the length of the section corresponds to a unit in the building-such as the distance between successive fans, or, in the case of piggeries, one pen width-then air movement not in these prescribed planes and resulting from asymmetry within this unit of length can also be investigated on a unit basis. It is possible to choose dimensions for the section that are representative of buildings for pigs, calves and poultry. A building section was constructed to a design dependent on three considerations. Its basic shape had to be derived from the complete hypothetical building of which it was a part, it had to be possible to control and modify several factors such as the ventilation system, fan speed, inlet air temperature, internal obstructions and internal sources of heat, and measuring and recording techniques had to be accommodated, particularly one for air flow visualization. 2. Size and shape of the building section Although livestock buildings of various shapes exist such as large square and wide span buildings'? for poultry and circular buildings for pigs," and although future trends could be towards buildings of wider span, a review" found that widths of nine brands of commercially manufactured two-row piggeries fell within 7,6-9,8 m and that a width of 7,3-8,2 m was suitable for four rows of calves. For poultry, battery houses varied from 4,9-23,2 m in width, although, if the cages were stacked vertically as opposed to terraced, the width was restricted to 4,9-12,2 m. A large proportion of buildings for layers in the U.K. are between 7·6 and 9·2 m wide." In Denmark a standardized width of livestock building of 9·6 m is recommended." • Farm Buildings Department, National Institute of Agricultural Engineering, Wrest Park, Silsoe, Beds,

323

324

VENTILATION INVESTIGATIONS OF A LIVESTOCK BUILDING

Because in the present work the initial emphasis was on pig housing, a span of 7·6 m and a length of 3 m were chosen. These dimensions permit the inclusion of two pens, one feed and two dunging passages as would occur in a two-row piggery (Fig. 1). They are also compatible with the usual spacing of side-wall mounted fans when there is a fan for every single pen. This is not quite so for ridge-mounted fans, the spacing of which may be greater than one per pen width. The height of the building section was chosen as 2·7 m to ridge and 2·1 m to eaves on the assumption that a lower false roof could be constructed inside if required .

Fig. J. Derivation of building section from two typical 2-pen-row piggeries: extract fans in side-waifs , side dunging passages (top ), extract fans in ridge, centre dunging passage (bottom)

2.1. Construction The main frame consists of 100X 100 mm section soft-wood on nine rows of brick walls 0·6 m high running in a direction parallel to the ridge. The roof, side walls and one end-wall are formed of removable panels consisting of softwood framing with 3·2 mm tempered hardboard inside and out with 38 mm infill of polyurethane insulation giving a calculated U value of 0·585 W m/m 2 °C (0·103 Btu ft/ft 2 h OF). The floor consists of removable reinforced concrete slabs 916 x 610 mm resting across pairs of the brick walls. Six lengths of 76 x 76 x 6·4 mm steel angle support the slabs across the width of the structure. The cracks between the slabs are filled with a non-setting mastic. One complete end is constructed of 6·4 mm thick clear perspex sheet with vertical glazing bars at 1·1 m centres and there is a 102 mm wide panel of similar material down the centre of each side. The roof and sides of the section are enclosed by a well-insulated shell, connected via ducts to a packaged chiller of capacity 8·8 kW (30,000 Btu/h) heat extraction. Cold air is blown by a centrifugal fan in the chiller through a duct-mounted 5 kW electrical heater into the shell where a duct distributes the air around the outside of the roof and sides of the section. For experiments where air with temperatures below ambient is required , the chiller operates continuously and the air temperature is automatically controlled by a motorized variable transformer supplying the heater. Humidity is also controlled by an on/off humidi stat operating a humidifier. 3. Experimental variables 3.1. Cross-sectional shape and dimensions The internal roof height can be reduced and varied by building a false floor or a false ceilingthe latter being either pitched or horizontal. A reduction in floor area is also possible using floor-to-ceiling partitions.

G. A. CARPENTER; L. J. MOULSLEY; J. M. RANDALL

325

3.2. The ventilation system Although classification of ventilation systems in fan-powered ventilated livestock buildings is an arbitrary procedure, an attempt to rationalize the various types encountered in practice must be made. Prosser" has suggested eight main types: extraction through roof from side walls, extraction through side walls from roof, cross ventilation, longitudinal ventilation, pressurized input, vertical air movement upwards and vertical air movement downwards. Although this list represents a good summary of existing practice'! this classification is based on positions of inlets and outlets, apparent air direction, and pressure distribution. For the present work, a better classification is based on the relative positions of air inlets and outlets as disposed in the principal parts of the building viz. ridge, ceiling, walls and floor. If consideration of longitudinal air movement is excluded, then gable entry or exit are not considered. It follows that there are six relative principal positions: ridge and walls, ridge and floor, ceilings and walls, ceiling and floor, walls and floor and wall to wall. In addition, the inlet and outlet can be reversed in each case except the last and, for each of these cases, the fan can either be upstream of an inlet (pressurized system) or downstream of an outlet (exhausted system). Of these 22 combinations, about ten are encountered in practice, some mentioned by Prosser and other important ones being highlevel inflatable ducts'? and pressurized plenum ceilings." "Push-pull" ventilation in which both the input and the output are fan-powered will not be considered: this arrangement is very uncommon in livestock buildings because their simple lay-out results in a low resistance to air flow compared with the complex air ducts of some industrial and office buildings. The design of the building section permits the incorporation of the essential features of the systems considered. 3.3. Design of components of the ventilation system Detailed design of air inlets and outlets must be considered including ducts, slots and plenums. Where the inlet or outlet constitutes a marked resistance to air flow, it must be possible to adjust this resistance (e.g. by adjusting the free area). If air velocity has to be measured at an inlet or outlet, a special design may be necessary. An important factor is the direction of discharge from any type of inlet whether a duct, or a slot in the walls or roof.

3.4. Livestock heat load The size of the section is such that, when simulating part of a piggery, each of the two pens will hold a maximum of the equivalent of fifteen 90 kg pigs which allows 0·5 m 2 of sleeping area per pig. Simulated pigs'" reproducing the heat production, shape, size, surface temperature and thermal capacity of real pigs (Fig. 2) are presently used for convenience and repeatability. As the sensible heat loss rate from a 90 kg pig in winter is 125 W at 20o e, the total maximum heat release rate in the section is 3·75 kW. 3.5. Internal obstructions For pigs, pen divisions and troughs constitute the dominant obstructions and in the experimental section these are constructed of interlocking plastic bricks. Although such bricks have little thermal mass, they are internal structures, the temperature of which will tend to be that of the internal ambient. Where the beam of light used for illuminating movement of particles strikes an internal wall, special transparent sections interlock with the surrounding opaque bricks. The simulated pigs also constitute a significant obstruction at floor level. 3.6. Air throughput rate A fan controlled by a variable transformer gives a 10 : 1 ratio of maximum to minimum rate. For a given system resistance however, the controller requires calibration in terms of total air flow. Although the section was constructed with a view to minimizing leakage, it must be taken into account.

326

VENTILATION INVESTIGATIONS OF A LIVESTOCK BUILDING

Fig. 2. Associated apparatus: simulated 45 kg pig (top left), bubble generators in operation (top right), projector (bottom left), rotating shutter (bottom right)

3.7. Incoming air temperature When there is no source of livestock heat in the section, the air temperatures inside and outside the section are the same. When a source of heat is introduced, the inside air temperature is always above that of the incoming air. This temperature difference affects the manner in which the air circulates internally. The relationship between livestock body temperature, inside air temperature and incoming air temperature must be defined and therefore the latter must be controlled. All air entering or leaving the building section passes from or into the air conditioned surrounding enclosure and thus seasonal air temperatures can be reproduced without affecting the manner in which air enters or leaves when any particular design of ventilation system is used. 3.8. Wind Initial experiments have not taken into account the effects of wind but the local effect of wind on a specific opening could be simulated by a large fan.

4. Measuring and recording techniques Visualization using a beam of light and airborne particles is one technique used to detect air flow and define the micro-climate, and consideration of this technique has a great bearing on the design detail of the building section. The essential requirements of the visualization technique, fully described elsewhere" are a means of seeing into the building section, a parallel beam of light in the planes in which air flow is being investigated, a darkened viewing area on the outside of the building section, a rotating shutter to interpose between the camera and the transparent wall and a particle generator (Fig. 3).

327

G. A. CARPENTER; L. 1. MOULSLEY; 1. M. RANDALL

1
me-I --------~

rrr=====n' ~::x:::.=================::::::r~I'F' ===~rShell

E

Building section 000

Bubble generators

Conditioned air

\00

Light beam

Shell Return~ air

Transparent end wall Viewing area Rotating ShU!!er~

Blacked-out enclosure

~

Camera

Fig. 3. Plan view of building section showing locations of associated apparatus

It is convenient to position the lighting units at both sides and desirable to illuminate the fixed plane that is most representative of the air movement in the section as a whole; because any ridge or wall-mounted fan can be assumed to be half-way between the two gable-end walls and because these end walls might cause "edge effects", the most representative plane is likely to be on the centre line across the section from one side-wall to the other. A totally enclosed viewing area is required on the outside of the transparent end of a depth to permit a camera to be placed sufficiently far back so that at least half the width of the section can be brought into view with a wide-angle lens. The inner wall and roof surfaces both of the section and of the viewing area are painted matt black to avoid scattered and reflected light and so maintain contrast. In addition, both spaces are light-tight so that the parallel light beam is the only source of illumination. The visualization system required the development of three pieces of equipment: a particle generator," a lamp projector," and a rotating shutter." As regards the choice of particle using air as the medium, work on livestock buildings has involved the use of smoke" 4, 5. 6. 7. 8 but for work on rooms, metaldehyde crystals have found favour. 24 • 25 The latter however, may be toxic and is best suited to air-tight systems with moderate ventilation rates, for example, the rate for an office is only 1/20 of that for a piggery in summer." High ventilation rates demand a high particle generation rate. For the present work bubbles were chosen because they have advantages over smoke in that on a full scale, smoke diffuses into a fog when turbulence is present. Compared with metaldehyde, bubbles can be generated rapidly and predictably, are non-toxic, uniform in size, and can be made neutrally buoyant. Fig. 2 shows a 3-unit bubble generator in operation: several of these are installed inside the section and connected by p.v.c. tubing to air pumps, liquid pumps, air-interruption valves, a liquid reservoir and a helium cylinder situated outside the section (Fig. 4). The generators are at

328

VENTILATION INVESTIGATIONS OF A LIVESTOCK BUILDING

appropriate positions relative to the light beam and the air inlets and outlets of the particular system of ventilation being used, and together produce 4 mm diam bubbles at 1000/sec. These bubbles are filled with a 3 : I mixture of air and helium and a large proportion are neutrally buoyant. To ensure a long life for the bubbles, the air supplied to the building section from the outer shell is maintained at a humidity of above 60%. Gas reservoir

Air

Non-return vaive Liquid pump Helium cylinder

Liquid reservoir

Fig. 4. Components for generating bubbles

The total number of bubble generators required (n p ) can be estimated based on the population required for air-flow pattern discernability assuming complete mixing of the air or alternatively based on the distance travelled during bubble life at the lowest air speeds (nd)' Let Q = rate of bubble generation from one generator = number of bubbles required/unit volume for air movement pattern discernability q = ventilation rate of the enclosure (air volume/unit time) V = volume of the enclosure V m = minimum air velocity to be detected T = mean bubble life L 1 = width of building section L 2 = mean height of building section.

e

Then it has been shown"

and

In the apparatus described, n p is ===6 and nd===3, so that a total of six generators are required. In practice, the bubble generators must also be placed judiciously in relation to air inlets and outlets and the area being studied. Four projectors (Fig. 2) are stacked vertically on each side of the section to produce a narrow parallel beam of light of uniform intensity. The intensity needs to be sufficient to permit photographic recording of the tracks of high velocity bubbles. The beam also needs to be very narrow so that the observed movement of bubbles approximates to that in a plane. The rotating shutter (Fig. 2) carries the camera immediately behind it and has a wide range of speeds. Its purpose is to interrupt the images of the bubble tracks so that they appear as a series of dashes on the photograph. This is achieved by rotating a disc with one or more apertures, the latter being shaped so that each dash has a "head" indicating the direction of air movement. The velocity of the particles is calculated as follows :20

G. A. CARPENTER; L. J. MOULSLEY; J. M. RANDALL

329

If v = velocity of particle d = apparent length of bubble track N = number of dashes in length d a = number of apertures on the rotating shutter r = speed of revolution of rotating shutter Then

dra

v=N

It has been shown" that

.

Wh ere R = ratro x

0

f observed velocity . true velocity

= width of light beam

For the projector described, x = 100 mm and if R~0'9, then only particle tracks longer than 220 mm can be used for calculating velocities in this way. Fig. 5 is an example of a photograph obtained in a current series of experiments using the apparatus described but with no simulated animals present.

Fig. 5. Air movement pattern indicated by bubble tracks and viewed through transparent end wall

The lay-out represents a Danish type piggery with 2 rows of pens, 2 side feed passages and two centre dunging passages separated by a solid wall. The pen fronts are open bar-type with only feed troughs presenting obstruction to airflow. Air enters below the eaves and is exhausted at the ridge. At floor level, the direction of air movement is from dunging passage to lying area and not vice versa as might be expected from the relative positions of the inlet and fan. The 300 mm high trough deflects the air through 45° resulting in negligible air movement to the lee. The wide range of speeds is demonstrated by the differences in spacings of the dashes at the periphery of the rotating pattern and those to the lee of the trough. At the higher air speeds, the directional head is clearest, but the track is fainter. At the highest speeds, each dash is subdivided into dots due to the 100 Hz flicker of the lamp caused by the alternating mains supply. No significance should be attached to the relative numbers of tracks per unit area. The photographic details are as follows:-film: Kodak Royal X, pan, 1250ASA; negative size: 127 x 229 mm cut film; exposure time: 30 sec; aperture: /8; lens: Symmar,f 150 mm; speed of rotating shutter: 3 rev/sec (6 apertures/sec).

330

VENTILATION INVESTIGATIONS OF A LIVESTOCK BUILDING

5.

Conclusions

(1) For the investigation of patterns of air movement in intensive livestock buildings, the use of a full-scale section of a building is a valid and useful technique. (2) Visualization of air movement using bubbles and a profiled shutter effectively displays a directional pattern of air movement in an enclosure in two dimensions. Very high ventilation rates can be accommodated. (3) The bubble-generating device can be used to show air movement in occupied livestock buildings and other commercial agricultural enclosures such as glasshouses, mushroom houses and ventilated stores. Acknowledgements

The authors acknowledge the contribution made by J. E. Owen (now lecturer at Reading University), and D. N. Boothroyd (N.LA.E.) towards developing the apparatus, B. A. Watt and P. Burr (N.LA.E.) for the photography, and J. C. Hawkins (N.LA.E.) for his encouragement and direction. REFERENCES 1 2 3

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5

6 7

8

9

10

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15 16

17

18

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20

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Sainsbury, J. Animal Health and Housing. Bailliere, Tindall and Cassell, 1967 Anon. Farm electrification handbook No. 10: Controlled environment. The Electricity Council, 1969 Lilleng, H. Ventilation tests in livestock sheds. Norwegian Agricultural College, Vollebekk, Rep. No. 35, 1961 Lilleng, H.; Esmay, M. E. Investigation of air flow patterns and temperature distribution in cage-laying houses. Norwegian Agricultural College, Vollebekk Debruyckere, M.; Neuckermans, G. Ventilation-some aerodynamic aspects. Farm Buildings Digest, 19683 (15) 11 Zeisig, H. D. Air circulation in livestock houses. Grund!. Landtech., 196919 (3) 79 Kadlec, V. Visualizing airflow in ventilated localities. Zemed. Tech., 197117 (2) 75 Griffin, R.; O'Callaghan, J. R.; Promersberger, W. J. The model house approach to studying mechanised ventilation systems in livestock housing. Intern. J. Farm Buildings Res., 1966 July 9 Kloeppel, R. Animal environment II: fans and ventilation. Report of the Agricultural Institute, Preetz, 1969 Anon. Housing, environment and health of table chicken. Report of the Farm Buildings Centre, Kenilworth, 196761 Anon. Round house piggery. Farm Buildings Digest, 19683 (17) 25 Dobson, C. The feasibility of standardized dimensions for farm buildings. Thesis for M.Sc., University of Reading, 1969 Spencer, P. G. Private communication Jensen, P. H.; Mortensen, E. Design and environmental control ofpoultry houses, Vo!. 1. Danish State Buildings Institute (SBI) Report No. 31, 19709 Prosser, H. W. Poultry house ventilation. Proc. World Poultry Assoc. Australia, 1969 Tilley, M. F. Physical and mechanical considerations in ventilation. Environmental Control in Poultry Production (Ed. T. C. Carter), 196769 Carpenter, G. A. The design of permeable ducts and their application to the ventilation of livestock buildings. J. agric. Engng Res., 1972 17219 King, A. W. M.; Charles, D. R.; Spencer, P. G.; Walker, G.; Benham, C. L. Air hygiene studies: the glass fibre ceiling. World's poultry Sci. J., 196824319 Owen, J. E.; Randall, J. M.; Carpenter, G. A. A simulated pig for Use in ventilation studies. N.LA.E. Dep. Note FBj168j3020, 1971 (unpublished) Carpenter, G. A.; Moulsley, L. J. A visualization techniquefor studying air movement in large enclosures over a wide range of ventilation rates. J. Instn. Heat. Vent. Engrs, 197239 279 Moulsley, L. J.; Boothroyd,D. N. A device for producing small bubbles for use in the visualization ofair movements. J. agric, Engng Res., 1971 16 364 Moulsley, L. J. A lamp unit for use in the visualization ofair movement in farm buildings. N.LA.E. Dep. Note FBj036j3020, 1970 (unpublished)

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Mousley, L. J. A rotating camera shutter for the photography of moving particles. NJ.A.E. Dep. Note FBj094j3020, 1971 (unpublished) Daws, L. F.; Penwarden, A. D.; Waters, G. T. A visualization technique for the study of air movement in rooms. J. Instn. Heat. Vent. Engrs, 1965 33 (1) 24 Sherratt, A. F. c.; Howarth, A. T.; Morton, A. S. Facilities for investigating room air movement. Proes 5th Intern. Congress for Heat. Vent. Air Condo Vol. 1, 1971 53 Anon. Instn. Heat. Vent. Engrs Guide, 1965 244