A Survey of Ventilation Rates in Livestock Buildings in Northern Europe

Transcription

1 J. agric. Engng Res. (1998) 70, A Survey of Ventilation Rates in Livestock Buildings in Northern Europe J. Seedorf ; J. Hartung ; M. Schröder ; K. H. Linkert ; S. Pedersen ; H. Takai ; J. O. Johnsen ; J. H. M. Metz ; P. W. G. Groot Koerkamp ; G. H. Uenk ; V. R. Phillips ; M. R. Holden ; R. W. Sneath ; J. L. Short ; R. P. White ; C. M. Wathes Tierärztliche Hochschule Hannover, Institut fu r Tierhygiene und Tierschutz, Bünteweg 17 p, Hannover, Germany; Danish Institute of Animal Science, Research Centre Bygholm, Department of Agricultural Engineering, PO Box 536, DK-8700 Horsens, Denmark; Instituut voor Milieu- en Agritechniek, Postbus 43, 6700 AA Wageningen, The Netherlands; Silsoe Research Institute, Wrest Park, Silsoe, Bedford MK45 4HS, UK (Received 27 August 1996; accepted in revised form 22 December 1997) Ventilation rates in 329 livestock buildings in Northern Europe (England, The Netherlands, Denmark and Germany) in winter and summer were estimated from a carbon dioxide (mass balance). On the basis of 500 kg liveweight, the mean ventilation rate across all countries was 341 m /h for cattle, 241 m /h for pigs and 451 m /h for poultry during winter. The corresponding summer ventilation rates were 404, 428 and 965 m /h (500 kg) liveweight, respectively. Recommended maximum ventilation rates in summer were not reached in some pig and poultry houses: the installed capacity may have been insufficient to avoid heat stress. Conversely, winter ventilation rates were not always sufficient to maintain an acceptable quality of air in some types of building, e.g. broiler houses Silsoe Research Institute 1. Introduction There has long been concern over the quality of air in livestock buildings and the provision of adequate ventilation. 1 The major purpose of a ventilation system is to provide an aerial environment in which animal health is maintained and productivity is satisfactory. The need for ventilation is governed by two requirements. The maximum ventilation rate is necessary to prevent hyperthermia, while the minimum ventilation rate is set to provide an acceptable thermal and aerial environment for animal performance. 2 The performance of a ventilation system can be evaluated by its ability to control air temperature, relative humidity and air speed at animal height and to maintain tolerable concentrations of gases, dust and airborne microorganisms. 1 The ventilation rate governs the emissions of aerial pollutants from the building and the design of the ventilation system is a major determinant of the environmental impact of a livestock building. Current emission rates of ammonia, dust, airborne microorganisms and endotoxins from the livestock buildings in this survey are reported elsewhere. 3 5 Recommended values for the minimum (winter) and maximum (summer) ventilation rates are given in Table 1, taken from Hilliger 6 but recalculated to 500 kg liveweight, although there can be some differences between countries due to local climate. The recommended ventilation rates are usually defined on an animal basis and have been extrapolated to 500 kg liveweight, i.e. a liveweight unit. In practice, ventilation rates may not meet the recommended minima and maxima because of poor design, substandard installation or inadequate maintenance. Given the importance of the ventilation system in the control of the environment in a livestock building, it is important to establish the extent to which current buildings meet the design specifications for ventilation rate. This paper describes the results of a survey of ventilation rates in 329 livestock houses in England, The Netherlands, Denmark and Germany during winter and summer. This work was part of a larger project, an overview of which is given by Wathes et al Materials and methods The methods for the measurement of ventilation rates, temperature and wind speed have been comprehensively described by Phillips et al., 8 and a brief description only is given in this paper. The carbon dioxide (CO ) mass balance method 9 was used to estimate the ventilation rate. A difference between outdoor and indoor concentrations of at least 250 p.p.m. CO was necessary for accurate calculation of the ventilation rate. The CO concentrations were /98/050039#09 $25.00/0/ag Silsoe Research Institute

2 40 J. SEEDORF E¹ A. Table 1 Recommendation for ventilation rate, m 3 /(500 kg) liveweight Body Minimum Maximum Animal weight, kg winter summer Dairy cow Beef cattle Calf Sow Weaner Fattening pig Layer hen Broiler chicken 2) Source: Ref. 6, but recalculated to 500 kg liveweight. measured with an infra-red analyser (usually Series 7000, ADC, UK), which was controlled by a computer. Measurements were made each hour at seven sampling points within the animal house and a reference sampling point outside the animal house. Three sampling points were located at animal level, three points at the height of the human breathing zone and one point was close to an air outlet, an exhaust fan for example. The concentration at this latter point was taken as the indoor reference for estimation of the ventilation rate. The sampling system for measuring gases comprised a multipoint gas handling unit, two pumps and FEP-Teflon tubes. The gas handling unit comprised eight three-way valves, which selected sequentially each sampling point. Air was drawn by the sample pump from each sampling point in turn and pumped to the gas analysers. A by-pass pump sucked air from the other seven sampling points. Data were transmitted continuously by radiotelemetry and automatically logged by a computer. The measurements were made in cattle, pig and poultry livestock buildings in England (E), The Netherlands (NL), Denmark (DK) and Germany (D). A total of 329 animal houses were investigated in summer as well as in winter, four replicates of each building type were usually studied. Summer was defined arbitrarily from May to October and winter from November to April. A typical measurement period covered a survey over 24 h, starting at 0600 h. The survey started in August 1993 and was completed in December Mean ventilation rates were calculated over 24 h across the four replicates for each animal house type in each country. Ventilation rates (m /h) are expressed per animal, per heat production unit (hpu equivalent to 1 kw) and per 500 kg liveweight. This latter unit provides a standard for comparison among species with different body weights and herd size and therefore is mainly used for data presentation and interpretation. 3. Results Mean values of the estimated ventilation rates are shown in Tables 2 and 3. The minimum and maximum ventilation rates are the results for a single building of any one type. The mean and minimum ventilation rates in winter were always higher than the recommended values given in Table 1. In summer, the mean ventilation rates were lower than, and the maximum rates were similar to, the recommended values for dairy cows, beef cattle and calves. However, for sows on slats, weaners on slats, caged layers and broiler chickens, the maximum calculated ventilation rates were often much lower than the recommended summer rates. The coefficient of variation of the data was typically about 35% in both winter and summer: the largest coefficients of variation were recorded in pig houses. The mean ventilation rates across the four countries in both winter and summer were usually higher in buildings with litter than slats, with the exception of beef cattle in summer (Figs 1 3). On the basis of 500 kg liveweight the overall calculated ventilation rate across all countries was 341 m /h for cattle, 241 m /h for pigs and 451 m /h for poultry during winter. The corresponding summer ventilation rates were 404, 428 and 965 m /h (500 kg) liveweight, respectively. Analysis of the relative frequency distribution of the mean ventilation rate over all buildings and animal types showed that 40% of livestock buildings had mean ventilation rates between 200 and 400 m /h (500 kg) liveweight during winter. As expected, higher ventilation rates occurred in summer; 41% of buildings had a mean ventilation rate of greater than 600 m /h (500 kg) liveweight during summer but only 7% of all buildings during winter. Ventilation rates above 800 m /h (500 kg) liveweight were never observed in winter. 4. Discussion Ventilation rates in mechanically ventilated animal houses can be measured directly with calibrated fanwheel anemometers or indirectly with the aid of natural 10 or artificial 11 tracer gases (e.g. CO or SF, respectively). The carbon dioxide mass balance is the only suitable technique for surveys because it is straightforward and low cost. Installing fan-wheel anemometers is a timeconsuming procedure and is more suitable for long-term measurements in individual buildings than the shortterm measurements in a large survey. The accuracy of the CO technique is affected adversely by artificial CO sources, e.g. manure, and depends on the estimate of metabolic CO production, which varies according to body weight, health status, pregnancy, etc. Overall, the

3 SURVEY OF VENTILATION IN LIVESTOCK BUILDINGS IN NORTHERN EUROPE 41 typical accuracy 8, 12 is $15% and no more than +20%. To avoid such errors, artificial tracer gases are often used because the tracer gas source within the house is clearly defined and additional sources can be excluded. However, a further complication arises in naturally ventilated livestock buildings where detailed knowledge of the function of openings is required when tracer gas techniques are used. As a consequence, measurements of ventilation rates are more inaccurate in naturally ventilated houses when either tracer technique is used. Table 2 Ventilation rates in livestock buildings in winter for each country, expressed as m 3 /h (500 kg) liveweight Coeff. ofvariation Minimum in Maximum in Housing Country n Mean Standard deviation % one building one building Dairy cow, litter England )3 6) Netherlands )7 23) Denmark )7 26) Germany )7 40) Dairy cow, cubicles England )9 7) Netherlands )8 49) Denmark )7 31) Germany )5 32) Beef, litter England )5 8) Germany )9 58) Beef, slats Netherlands )0 10) Denmark )9 48) Germany )1 14) Calves, litter England )5 20) Denmark )6 37) Germany )3 1) Calves, slats Netherlands )2 27) Germany )2 26) Sows, litter England )2 40) Germany )6 56) Sows, slats England )2 47) Netherlands )6 40) Denmark )3 40) Germany )6 23) Weaners, slats England )9 125) Netherlands )0 65) Denmark )4 30) Germany )4 41) Fatteners, litter England )2 65) Denmark )4 19) Fatteners, slats England )1 48) Netherlands )4 33) Denmark )3 20) Germany )4 26) Layers, aviary England )2 79) Netherlands )6 16) Denmark )3 57) Layers, caged England )0 9) Netherlands )9 24) Denmark )0 0) Germany )5 26) Broilers, litter England )2 32) Netherlands )8 42) Denmark )8 46) Germany )2 17)

4 42 J. SEEDORF E¹ A. Further discussion of techniques for measuring ventilation rate in livestock buildings is given elsewhere. 13, 14 The two main objects of a ventilation system in a livestock building are to maintain environmental temperature and air quality within acceptable limits. 1 Extensive research and development over the past yr has led to a variety of systems of mechanical and natural ventilation that can satisfy the first purpose. This was confirmed in this survey 15 which showed that, for those species for which temperature control is desirable, air temperature was controlled satisfactorily over a wide range of ambient temperatures up to 17 C. Above this ambient temperature, the building temperature became dependent upon the weather unless a cooling system was in place. There are several explanations for this failure. First, the capacity of the ventilation system could be too low: the maximum ventilation rate is usually specified to keep the building s air temperature about 3 K above the ambient Table 3 Ventilation rates in livestock buildings in summer for each country, expressed as m 3 /h (500 kg) liveweight Coeff. ofvariation Minimum in Maximum in Housing Country n Mean Standard deviation % one building one building Dairy cow, litter Netherlands )2 10) Denmark )8 29) Dairy cow, cubicles Netherlands )9 23) Denmark )3 41) Beef, litter Germany )7 2) Beef, slats Netherlands )1 16) Denmark )8 15) Calves, litter England )1 9) Denmark )6 33) Germany )3 28) Calves, slats Netherlands )2 30) Germany )1 27) Sows, litter England )1 32) Germany )0 31) Sows, slats England )0 35) Netherlands )8 35) Denmark )4 53) Germany )3 42) Weaners, slats England )8 43) Netherlands )3 50) Denmark )8 63) Germany )8 56) Fatteners, liter England )5 65) Denmark )1 27) Fatteners, slats England )3 26) Netherlands )0 60) Denmark )3 30) Germany )6 50) Layers, aviary England )1 13) Netherlands )5 33) Denmark )5 67) Layers, caged England )8 26) Netherlands )2 36) Denmark )0 0) Germany )8 13) Broilers, litter England )9 31) Netherlands )4 38) Denmark )8 39) Germany )2 19)

5 SURVEY OF VENTILATION IN LIVESTOCK BUILDINGS IN NORTHERN EUROPE 43 Fig. 1. Mean ventilation rates ($SD) of different livestock buildings in winter and summer expressed per 500 kg live weight in (a) winter and (b) summer air temperature. The system s capacity was not measured explicitly in this survey, but the maximum ventilation rates measured in certain housing types, i.e. sows and weaners on slats, caged layers and broiler chickens, were less than those recommended, 6 which implies that the installed capacity may have been too low. Second, there has been a tendency to raise stocking densities, e.g. of broiler chickens, with a required concomitant increase in ventilation capacity. While greater capacity may be installed in new livestock buildings, the original ventilation system in older buildings may be not capable of meeting the demand for rapid ventilation if the stocking density has been increased. Provision of fresh air is a fundamental tenet of livestock housing. Generally, the quality of air in most types of livestock buildings examined in this survey was

6 44 J. SEEDORF E¹ A. Fig. 2. Mean ventilation rates ($SD) of different livestock buildings in winter and summer expressed per animal in (a) winter and (b) summer satisfactory, as witnessed by the mean concentrations of airborne dusts and ammonia, which were usually within acceptable limits. 3,4 However, there were some noticeable exceptions, broiler chickens for example. This problem is the converse of that described above since it is often the result of the requirement to maintain a warm environmental temperature in winter by restricting the rate of ventilation. While the financial benefits of accurate temperature control in pig and poultry houses are well known, 2 the penalties of poor air quality have not been quantified financially with a few exceptions, e.g. the interaction between aerial pollutants and atrophic rhinitis in fattening pigs, because of the complexity of the causal mechanisms. 16 There is thus less incentive for the stockman to control air quality by adjustment of the ventilation rate, or other means.

7 SURVEY OF VENTILATION IN LIVESTOCK BUILDINGS IN NORTHERN EUROPE 45 Fig. 3. Mean ventilation rates ($SD) of different livestock buildings in winter and summer expressed per heat production unit, equivalent to 1 kw, in (a) winter and (b) summer The mean and minimum ventilation rates measured in winter in this survey were higher than the recommended values 6 given in Table 1. Given that air quality was judged to be unacceptable or unsatisfactory in certain types of buildings, then this implies that these measured ventilation rates could be too low, even though they were above the recommended values. The minimum ventilation rate to maintain a given concentration of pollutant can be easily calculated from knowledge of the concentration and rate of production of the pollutant. 1 For example, if the acceptable concentration of atmospheric ammonia is 20 p.p.m. (:14)2 mg/m at 20 C) for pigs and the rate of production is 1765 mg/h (500 kg) liveweight, 3 then the minimum ventilation rate should be at least 124 m /h (500 kg) liveweight if the concentration of ammonia is to be kept below this critical value.

8 46 J. SEEDORF E¹ A. A minimum theoretical ventilation rate can also be calculated to keep indoor dust concentrations below the recommended limits. An assumed limit of 3 mg/m for inhalable dust and a production rate of 567 mg dust/h (500 kg) liveweight for pigs, 1 requires a minimum ventilation rate of 189 m /h (500 kg) liveweight. Clearly, adoption of the rate to satisfy the dust criterion would also keep the ammonia concentration below the acceptable limit. These calculated ventilation rates are higher than Hilliger s recommendation, 6 which may be too low to maintain air quality in some buildings. Comparison of these minimum ventilation rates to keep ammonia and dust concentrations within acceptable levels with the measured rates given in Table 2, shows that the mean and minimum rates were too low in some pig buildings in some countries, e.g. fatteners on slats in the Netherlands. Similar calculations could be done for other types of livestock. While the above analysis allows gross deficiencies in ventilation rates to be identified, individual buildings must usually be assessed on a case-by-case basis for a variety of reasons. First, production rates may exceed the chosen value because they vary throughout the day (and season) due to animal activity, stocking density, state of the litter or manure, including its frequency of removal, etc. Second, there may be localized sources of gases and dust that will lead to zones of high gas and dust concentration. 17 Third, the efficiency of ventilation in each zone depends on the airflow pattern, which in turn is influenced by the geometrical configuration of inlets and outlets, 18 the air jet velocity and its spatial reach and the location of fixed equipment and the animals. 19 A more satisfactory solution is to develop a ventilation control system which uses ammonia, dust or other aerial pollutants as the control variable. The ventilation rates in this paper are expressed in three units. The least useful is the ventilation rate per animal, since this takes no account of an animal s weight or any other index of physiological activity. A ventilation rate per heat production unit clearly accounts for metabolic heat production and is therefore appropriate when temperature control is the main objective. This unit is, in turn, related to an animal s weight since basal metabolic rate is proportional to liveweight raised to the three-quarter power and to activity or any other physiological process that affects heat production, such as temperature. However, it is difficult to specify minimum and maximum rates a priori because many assumptions will also have to be made about physiological state. A ventilation rate per unit of liveweight (500 kg) is widely accepted, though it too has limitations, e.g. the lack of equivalence for animals differing in body weight. Where an environmental variable such as air temperature, humidity or pollutant concentration is controlled by a ventilation system equipped with an appropriate sensor, then an exact knowledge of ventilation rate is unnecessary and the choice of unit becomes irrelevant provided that minimum and maximum ventilation rates have been specified with reasonable accuracy when the ventilation system was originally designed. The cubic capacity per animal or other unit only becomes a limiting factor in the successful operation of a ventilation system when it is either much too small or too large, since its acceptable range is quite wide. 5. Conclusions Mean ventilation rates in livestock buildings in Northern Europe were in broad agreement with recommended values. There was indirect evidence that the installed maximum capacity of ventilation rate was too low in certain types of housing, e.g. sows and weaners on slats, caged layers and broiler chickens. Ventilation rates in winter were not always sufficient to maintain an acceptable quality of air: reported maximum concentrations of airborne dust and ammonia in some buildings, e.g. broiler chickens, gave grounds for concern over the operation of the ventilation and other aspects of intensive animal husbandry which affect pollutant dynamics. Acknowledgements The work was funded mainly by the Commission of the European Union as Project No PL Supplementary funding was also received in the UK from the Ministry of Agriculture, Fisheries and Food via Commission CC 0204; in Germany from the Hannover School of Veterinary Medicine and the Institut fu r Biosystemtechnik of the Bundesforschungsanstalt für Landwirtschaft; in the Netherlands from the Ministry of Agriculture, Nature Management and Fisheries and in Denmark from the Ministry of Agriculture and Fisheries. We thank the many technicians in all the partner countries, without whose help the project could not have been completed, and also Professor Th. Blaha, Head of the Unit of Epidemiology of the Hannover School of Veterinary Medicine, at Bakum, Germany, for his organisational and logistic support. We thank Chris Michael and his staff at Meaco Sales and Marketing for their enthusiasm and dedication in developing with us the novel wire-less data logging system. Finally, we thank the many farmers in England, Netherlands, Germany and Denmark who not only allowed access to their buildings for the measurements to be made, but also helped in many other ways.

9 SURVEY OF VENTILATION IN LIVESTOCK BUILDINGS IN NORTHERN EUROPE 47 References 1 Wathes C M; Jones C D R; Webster A J F Ventilation, air hygiene and animal health. Veterinary Record, 1983, 113(24), Charles D R Comparative climatic requirements. In: Livestock Housing (Wathes C M; Charles D R, eds), CAB International, Groot Koerkamp P W G; Metz J H M; Uenk G H; Phillips V R; Holden M R; Sneath R W; Short J L; White R P; Hartung J; Seedorf J; Schröder M; Linkert K H; Pedersen S; Takai H; Johnsen J O; Wathes C M Concentrations and emissions of ammonia in livestock buildings in Northern Europe. Journal of Agricultural Engineering Research, 1998, 70, Takai H; Pedersen S; Johnsen J O; Metz J H M; Groot Koerkamp P W G; Uenk G H; Phillips V R; Holden M R; Sneath R W; Short J L; White R P; Hartung J; Seedorf J; Schröder M; Linkert K H; Wathes C M Concentrations and emissions of airborne dust in livestock buildings in Northern Europe. Journal of Agricultural Engineering Research, 1998, 70, Seedorf J; Hartung J; Schröder M; Linkert K H; Phillips V R; Holden M R; Sneath R W; Short J L; White R P; Pedersen S; Takai H; Johnsen J O; Metz J H M; Groot Koerkamp P W G; Uenk G H; Wathes C M Concentrations and emissions of airborne endotoxins and microorganisms in livestock buildings in Northern Europe. Journal of Agricultural Engineering Research, 1998, 70, Hilliger H G Stallgebäude, Stalluft und Lu ftung (Livestock Building, Indoor Air and Ventilation). Stuttgart; Ferdinand Enke Verlag, Wathes C M; Phillips V R; Holden M R; Sneath R W; Short J L; White R P; Hartung J; Seedorf J; Schröder M; Linkert K H; Pedersen S; Takai H; Johnsen J O; Groot Koerkamp P W G; Uenk G H; Scholtens R ; Metz J H M Emissions of aerial pollutants from livestock buildings: overview of a multi-national project. Journal of Agricultural Engineering Research, 1998, 70, Phillips V R; Holden M R; Sneath R W; Short J L; White R P; Hartung J; Seedorf J; Schröder M; Linkert K H; Pedersen S; Takai H; Johnsen J O; Groot Koerkamp P W G; Uenk G H; Scholtens R; Metz J H M; Wathes C M The development of robust methods for measuring concentrations and emission rates of gaseous and particulate air pollutants in livestock buildings. Journal of Agricultural Engineering Research, 1998, 70, van Ouwerkerk E N J; Pedersen S Application of the carbon dioxide mass balance method to evaluate ventilation rates in livestock houses. Proceedings of the XIIth World Congress in Agricultural Engineering (AgEng), Milano, 1994, 1, CIGR Climatization of animal houses. Report of working group. Scottish Farm Building Investigation Unit, Craibstone, Aberdeen, Scotland, Gustafsson G Spargasteknik som method fo r att bestämma ventilations-effektivitet och spridning av luftfo roreningar i djurstallar (Tracer gas technique as a method to determine ventilation effectiveness and distribution of air contaminants in animal houses). Swedish University of Agricultural Sciences, Department of Farm Buildings, Report no. 84, Hinz T; Linke S A comprehensive experimental study of aerial pollutants in and emissions from livestock buildings. Part 2: results, Journal of Agricultural Engineering Research, 1998, 70, van t Klooster C E; Heitlager B P Determination of minimum ventilation rate in pig houses with natural ventilation based on carbon dioxide balance. Journal of Agricultural Engineering Research, 1994, 57(4), Demmers T G M Ventilation of livestock buildings and ammonia emissions. PhD Thesis, University of Nottingham, Seedorf J; Hartung J; Schröder M; Linkert K H; Pedersen S; Takai H; Johnsen J O; Metz J H M; Groot Koerkamp P W G; Uenk G H; Phillips V R; Holden M R; Sneath R W; Short J L; White R P; Wathes C M Temperature and moisture conditions in livestock buildings in Northern Europe. Journal of Agricultural Engineering Research, 1998, 70, Turner L W; Wathes C M; Audsley E Dynamic probabilistic modelling of respiratory disease in swine, including production and economic effects. Livestock Environment IV. Proceedings of a Conference, Coventry, UK, 6 9 July 1993, Barber E M; Dawson J R; Battams V A; Nicol R A C Spatial variability of airborne and settled dust in a piggery. Journal of Agricultural Engineering Research, 1991, 50(2), van t Klooster C E; Roelofs P F M M; Gijsen P A M Positioning air inlet and air outlet to reduce dust exposure in pig buildings. Livestock Environment IV. Proceedings of a Conference, Coventry, UK, 6 9 July 1993, Smith J H; Boon C R; Wathes C M Dust distribution and airflow in a swine house. Livestock Environment IV. Proceedings of a Conference, Coventry, UK, 6 9 July 1993,