Termisk komfort och fördelning av tilluft i svinstallar : teori och ventilationsförsök
The demands on climate control in animal houses increases as the methods for production improve. The relationship between maximum and minimum ventilation rate in Swedish houses for fattening pigs, around 1:15, causes problems with the distribution of fresh air. The same type of inlets for fresh air are usually used under both ventilation rate conditions. Independently of the ventilation rate the inlets should offer thermal comfort. A prototype to a new inlet (air distributor) has been developed by Sveaverken Agri AB as an attempt to solve the distribution problem within a wide range of thermal conditions. The prototype consists of a vertical air penetrable textile tube and a bottom which can be lowered creating a circular slotted inlet. This project was initiated by Sveaverken Agri AB in order to test the inlet on a farm with pig production. The aim of the study was to: - identify the demands of thermal environment in a house for finishing pigs by a literature review - compare two inlets for fresh air, the new prototype and a conventional slotted inlet A house containing two compartments for finishing pigs was used for the study, one of the compartments had slotted inlets and the other one the new prototype. Tests were made during summer conditions, 1996. Animal growth and health aspects were excluded from the study. The literature review shows that temperatures between 15 and 25 °C are suitable for finishing pigs. The air speed can vary between 0,2 and 0,8 m/s, lower air speeds during lower temperatures and faster when it is warmer. The idea behind the air distributor has been to provide the pigs with a slow, diffuse air movement during the winter and stronger air stream during the summer. A tube of textile is used for distribution of fresh air when the incoming air is cold. As the temperature rises in the house the air distributor opens and the airflow pattern changes to reach the animals directly. Measurements were made to study the abilities of the air distributor considering the expected air flow pattern. The compartment with slotted inlets was used as a reference. The construction of the air distributor was expected two induce greater convective cooling than the slotted inlets. During the test period several parameters were measured two compare the two different air inlets. In each compartment respectively temperatures and air humidity were registered by computer loggers, inside as well as outside the stable. The effect of convective cooling was considered by calculating the chill factor. For this reason air speed, skin- and air temperature were measured in tree pens in each compartment. Smoke was used to trace the air flow pattern. The pen and animal hygiene was controlled in 13 pens in each compartment. The static pressure between each compartment and the attic was measured to find possible differences in the regulation of the ventilation systems. Occasionally the concentration of carbondioxide was measured to calculate the ventilation rate. The results from the measurements show that the new air distributor has a greater capability to stratify the temperature than the slotted inlets. This was proved by calculating the differences between temperatures at pen level and the average temperature in each compartment. Both inlets showed greatest temperature differences when the incoming air was cold. The lowest temperature measured of incoming air was -5 °C, which gives a 20 °C difference (∆t) between temperature of the stable and the incoming air. Calculations of the chill factor proved no greater difference between the two air inlets. The slotted inlets showed slightly higher values. Non of the inlets reached the recommended level of 60-80 W/m2. The study of the air flow pattern showed that a lower ∆t reduced the ability of incoming air to reach the lying area of the pens, independently of the type of inlet. The air distributor was expected to direct incoming air towards the lying area. This ability was proved to be overestimated. The fast air stream passed above animal level. A comparison between air and skin temperatures implied that the cooling effect was higher with the air distributors than the slotted inlets. This was confirmed by the results from the study of hygiene. Animals and pens reached a better level of hygiene with the new inlet. Knowledge of the concentration of carbondioxide and relative humidity of air was used to estimate the ventilation rate in each compartment. The calculated ventilation rates were higher in the compartment with slotted inlets, despite equivalent exhaust fans. Non of the compartments reached the Swedish recommendations for maximum ventilation rate. Minor adjustments were made to improve the ability of the new inlet to direct incoming air towards the lying areas in the pens. This effects of these adjustments were not studied carefully but the air speed seemed to increase over the lying area. Considering the results, the new inlet functions at least as well as ordinary slotted inlets during summer conditions. The air distributor has several advantages, greater capability to stratify temperature, greater cooling effect under warm conditions and with that better pen and animal hygiene. The adjustments of the new inlet seem to improve the ability to convective cooling. The new inlet has not been tested during winter conditions but by adjusting the inlet height above floor level, there should be no difficulty to prevent cold air from falling down on the animals.
Fattening pigs; ventilation; air inlets; chill factor; thermal comfort; hygiene
Rapport - Sveriges lantbruksuniversitet, Institutionen för lantbruksteknik
Publisher: Institutionen för lantbruksteknik, Sveriges lantbruksuniversitet
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