BROILER HOUSE MICROCLIMATE IN LIGHT OF EXPERIMENTAL STUDIES

Jan Radoń, Wacław Bieda, Grzegorz Nawalany

ABSTRACT

This study presents and discusses the results of 2-year measurements of air temperature, air humidity, litter temperature and litter moisture in a broiler house and of ground temperature below the floor and outside the building. Except temporary overheating, air temperature was found to conform to animal breeding standards. Air humidity was too low at the start of rearing and had to be additionally increased. It was subject to considerable fluctuations in the summer cycles. Litter studies showed that broiler chickens were exposed to adequate temperature for 20 days during the winter production cycle and for just 7 days during the summer cycle. Changes in litter moisture showed an upward trend in time. Litter moisture was greater next to walls than in the centre of the production facility. The time course of litter moisture was approximated by a quadratic function. Results of ground temperature measurements revealed considerable heat accumulation in the ground and its cooling during technolo

Key words: broiler house, microclimate, litter, ground..

INTRODUCTION

The formation of livestock building microclimate is a continuous process, created dynamically throughout the year depending on external climatic influences and internal thermal and humidity processes. Microclimate shows different patterns in winter, in summer and in transition periods. Whatever the season of the year, however, livestock building microclimate should conform to animal hygiene standards [15].

Special microclimatic requirements of a broiler house characterized by a relatively high air temperature at the start of rearing and its gradual decrease during a 42- to 45-day production cycle, biothermal processes in litter, and technological breaks between production cycles in facilities operated on an all-in all-out basis mean that it is extremely hard to meet optimum environmental conditions on an annual scale in contemporary facilities.

To identify the dynamic formation of microclimate in actual production conditions, 2-year continuous measurements of the basic parameters of internal air and litter and ground temperature were made in a typical broiler house for 16 000-18 000 birds. The results and analysis of the measurements revealed the extent to which microclimatic conditions are fulfilled in the living area of birds. Also determined were some environmental interrelations (external climate, heat flows through the ground, ventilation) in the formation of microclimate in a broiler house with the floor management system.

MATERIALS AND METHODS

One of ten buildings of a large commercial poultry farm in Ujazd (Małopolska province) was used in the experiment. The facility is considered typical due to its geometry and production technology. It is a one-storey, windowless building (with windows in ancillary rooms only) having a flat roof. The building's longitudinal axis is facing east/west. It has a production area of 1001 m² and ancillary rooms with a total area of 62.5 m². Figure 1 shows a view of the building from the main entrance, Figure 2 its interior in the final stages of the production cycle, and Figure 3 a view and section of the building showing the layout of measurement points.

Floor in the entire building is made of concrete. Throughout rearing of broilers, floor in the entire production area is bedded with litter, which is removed during technological breaks. Broilers are fed and watered from automatic feeders and drinkers. The facility is heated by radiators located along the longitudinal walls. Hot air is blown by two water heaters. The mechanical, negative-pressure ventilation consists of ventilation openings in the south wall and exhaust fans in the north wall. The facility contains 20 fans, each having a maximum capacity of 8000 m³/h. Considering the broiler house's cubic capacity, this allows air to be changed 60 times per hour. Tables 1 and 2 provide the most important geometric and technological data of the broiler house.

During the experiment, several microclimatic parameters of the production facility were measured. Litter and ground below the floor were also tested. Measurements were taken in 2002-2003 during 4 full production cycles (Table 3).

The following parameters were measured:

• temperature of internal and external air,

• relative humidity of internal air,

• litter temperature at 10 measurement points,

• ground temperature below the floor and outside the building at 11 measurement points,

• litter moisture.

Temperature of air and litter was measured with resistance sensors type TOP 106 [10]. Litter temperature sensors were adequately secured and placed at half thickness of the litter. Measurements were taken automatically at 15-minute intervals and recorded on an Agilent 34970A logger [1]. Relative humidity of air was measured automatically at 15-minute intervals by means of relative humidity transducer PWW 100 [11]. Due to a limited number of the Agilent logger channels, the pattern of ground temperature was also measured by TOP 106 sensors, while the results were controlled and recorded by a DT50 logger [3] at hourly intervals. The measurement stand is shown in Figure 4.

Litter moisture was tested every second week by taking samples from different zones (central area – longitudinal axis of the facility; wall area; and between these areas). The samples were weighed and dried to a solid form, which allowed determining their mass humidity in a straightforward way. The samples were taken from an area of a 10×10 cm square at all heights of the litter, which allowed calculating changes in litter moisture for the entire area of the production facility.

RESULTS AND DISCUSSION

The basic microclimatic parameters of the birds' living area are air temperature, air humidity, litter temperature and litter moisture. The values and temporal course of these parameters determine thermal and humidity comfort of the animals. Optimum air temperature in a building should range from 30 to 33°C at the start of rearing and be gradually decreased to 20-16°C by the end of rearing [9]. These requirements conform to the latest Regulation of the Minister of Agriculture concerning the minimal management conditions for different livestock species [14]. Air humidity is felt by the animals strictly in terms of its temperature [4, 6, 8]. During the entire production cycle, relative air humidity should be maintained at 60-70%, the optimum value being 65%. To preserve thermal equilibrium of the chickens in relation to the environment, and thus to the litter, which is the only partition the chickens are in direct contact with, litter temperature should be close to the air temperature required in rooms with spatial heating [5]. There is no information in the literature concerning the maximum permissible moisture of litter. Supposedly the desired humidity should be as low as possible, because high moisture content deteriorates the mechanical and thermal properties and negatively affects the perception of local thermal conditions.

The results of measurements demonstrate the actual pattern of broiler house microclimate and shed light on thermal and moisture processes taking place in litter and in the ground below. Figures 5 and 6 present the patterns of measured external and internal air temperature and litter temperature, characteristic of the winter and summer periods (1st winter cycle and summer cycle, see Table 3). The figures show the course of litter temperature at points 1 and 9 (see Figure 3), which are closest to the axis (centre of the production area) of the building (point 1) and closest to the external wall (point 9). The results of measurements at points 1, 3, 5, 7 and 9 were not much different from the results taken at points 2, 4, 6, 8 and 10, being evidence that at a certain distance from the gable wall, in the middle zone of the building, temperature distribution in the litter is two-dimensional (i.e., it depends only o n the distance from the building's axis).

When analysing the course of internal air temperature measured in the winter and summer production cycle (Fig. 5, 6) it was found that temperature in the production area of the broiler house had conformed to the broiler production requirements. It is easier to maintain the required air temperature in the poultry house when temperature of the external air is lower than temperature of the internal air. Whenever the internal temperature dropped below a set limit, heating was turned on to supply the rooms with adequate heat and ensure required temperature. Hence fluctuations in the internal air temperature were relatively small in the winter period and in the initial period of the summer cycle. A certain problem appeared when internal temperature increased as a result of birds emitting sensible heat, because it is only possible to reduce temperature through increased ventilation or cooling. Cooling is not commonly used for economic reasons. A barrier to r educing temperature by way of ventilation is the temperature of external air and the capacity of fans, because it is impossible to reduce the internal temperature below the external air temperature. Where the difference is small, the required exchange of air is very large, often exceeding the capacity of the ventilation system. Very intense ventilation is faced with the problem of excessive air motion (draughts) inside the building, which is unfavourable for young birds. This is why temperature fluctuations in the summer period were relatively high. Large emission of heat by the birds in the second half of the summer cycle and the high air temperature and greater insolation in the summer made the rooms overheated, as clearly shown by the pattern of curves in Figure 6. It was calculated that overheating occurred for about 22% of the time of the summer production cycle.

The course of temperature in the litter showed a characteristic pattern regardless of the stage of the production cycle. Litter temperature became equal to internal air temperature after about 18 days from the beginning of the cycle, after which it kept increasing to about 30-34°C (see Figures 5 and 6). In the final stage of the cycle it slightly decreased or remained constant. Bieda and Koźbiał [2] and Nawalany et al. [13] demonstrated that after about 2.5 weeks of rearing litter temperature came to increase, and at the end of the cycle it exceeded 30°C despite the fact that ambient temperature (internal air and floor temperature) was much lower during that time. The higher temperature of litter compared to air and floor temperature can be physically attributed to the presence of a heat source in the litter. Supposedly this source were fermentation processes in the litter and the heating of litter by the sitting birds.

In the winter period, litter temperature at the measurement point located in the middle of the production area (point 1) was higher than at the point next to the external wall (point 9) (Fig. 3 and 5). To illustrate the pattern of litter temperature in light of hygienic standards, the range of temperatures in the analysed measurement field (cf. Fig. 3) was plotted against the course of optimum temperature of internal air in the winter and summer production cycle (Fig. 7). At the start of rearing, in each cycle litter temperature was too low, while at the end of rearing it was too high. Only for a certain period of the cycle were the birds able to find advantageous thermal conditions in the living area. In the winter cycle this period was about 16 days (38% of the time), and in the summer cycle only 7 days (17% of the time).

Another important parameter of internal microclimate next to temperature is air humidity. Figure 8 shows the course of relative air humidity measured inside the broiler house in the first cycle (winter) and in the spring cycle (cycle 3, Tab. 3). Because the relative air humidity sensors suffered a failure we were unable to record the course of air humidity in the entire summer cycle. The course of relative humidity shown in Figure 8 is unsatisfactory when seen from the viewpoint of hygienic requirements. During the first 10 days of rearing in cycle 1 (winter) air humidity in the broiler house fluctuated around 52%, at times even reaching about 42%, being considerably lower than the lower limit of this parameter (60%) considered permissible for broiler houses. In the remaining period, in the winter, fluctuations in humidity were relatively small, but the value of this parameter was either too high (above 70%) or too low (below 60%). In the summer per iod, average humidity would have been considered optimal were it not for the large fluctuations. Such a course of internal air humidity can be attributed to the ventilation control system, in which maintenance of air temperature overrode air humidity. Fans were only turned on when temperature grew excessively, which under intense ventilation caused a rapid fall in air humidity.

It is argued that in the initial period (first 10 days) of rearing the chickens humidity could be increased by decreasing ventilation. However, this is impeded by out-of-control infiltration of air and the requirement of minimum ventilation due to undesirable concentrations of carbon dioxide and ammonia. The desired air humidity at the start of rearing can be obtained by sprinkling the litter with water, as suggested by Herbut [4]. Air moistening also seems appropriate during periods of intense ventilation. However, it is not always possible to maintain the set humidity and temperature parameters, even when ventilation can be controlled very accurately. When the difference between internal and external temperature is small, air humidity inside the building can be reduced to a value of external humidity, but not more. Hence such large fluctuations in humidity observed in the summer.

In addition to temperature, also changes in litter moisture were investigated. Moisture measurements were made in cycle 2, 3 and 4 (see Table 3). The results obtained point to great spatial variation of this parameter. Mass moisture determined in samples taken at the same time, but from different areas, showed considerable differences. However, a tendency for the moisture content of litter to increase constantly was seen, with increments in moisture being higher in the second half of rearing. In the middle zone, i.e. in the longitudinal axis of the broiler house moisture was slightly lower than near the external walls. This probably results from the slightly higher litter temperature in the middle of the production facility, and from its better drying due to greater air circulation in this zone.

The main source of moisture in litter is water contained in bird excrements. Excrements are first absorbed in litter, after which part of the moisture evaporates into internal air. Litter thus acts as a buffer of moisture. Changes in litter moisture largely determine the emission of moisture in the building. The results of these measurements allowed determining these changes in an averaged way for each production cycle. The results of tests on changes in the moisture content of litter were averaged for the cycles and for the whole area of the production floor. Water content obtained was referred to the mass of dry straw spread at the beginning of production cycle. Then, a graph of changes was drawn for three production cycles (Fig. 9). The course of these changes was averaged and approximated with the second-degree curve (the least squares method) [12] after time, obtaining the function:

The curve that approximates changes in litter moisture is shown in Figure 9. Because there are similar thermal and moisture conditions and stocking density in each production cycle, it is assumed that changes in moisture can be estimated with the curve obtained.

The course of temperature in the ground under the building's floor and outside the building in two selected production cycles (3rd spring cycle and 4th summer cycle, cf. Table 3) and in-between them is shown in Figure 10. At the start of the breeding cycles, ground temperatures in cross-section I (on the building's axis, cf. Figure 3), measured at two different depths, are almost equal (the difference not exceeding 2.5 K). During rearing the temperature increases, with the fastest increases occurring at the junction of the floor and ground. Temperature increments decrease with depth. It was observed that the time of temperature increments was longer at greater depths and even encompassed the initial period of the break, when the production facility was not heated. The time difference between temperature maxima at points I-0 and I-3 (a depth difference of 1.5 m) is about 13 days. Such a large time shift is caused by the high ther mal inertia of the ground. During the technological break, temperatures in the ground decrease and at the start of the next cycle they become almost equal. A similar pattern is shown by ground temperatures at cross-section II. However, their values are clearly lower than the temperatures measured at the same depths at cross-section I. Outside the building, there is also a temperature increment in the ground and a slight decrease during the technological break.

The patterns of temperature in the ground indicate that heat accumulates there during the production cycle and cools down during technological breaks. Thermal coupling of the litter and floor with the ground causes litter temperature at the start of rearing to be much lower than the temperature of internal air. The ground takes heat from the litter, causing it to cool down. Bieda and Koźbiał [2] hold the view that heat accumulated in the ground could be better used in the subsequent production cycle if straw was more rapidly bedded during the technological break, thus decreasing the cooling of floor and the ground below, because dry straw has a relatively high insulating value. Lower temperatures of the ground in the vicinity of external walls and the course of temperatures in the ground outside the building result from the influence of external climate and are evidence that heat escapes the building via the ground into the external air. This phenomenon results in lower temperature of the l itter in the vicinity of external walls than in the middle area of the building. Heat flows in the ground thus significantly affect the microclimatic conditions in the living area of birds.

CONCLUSIONS

Based on the study results and their analysis it is concluded that:

1. It is easier to maintain the optimum internal air temperature in a broiler house during the periods when external air temperature is lower than the required internal temperature. The shortage of heat is supplemented by heating, while its excess is removed by increased exchange of air. The results of measurements showed the occurrence of satisfactory internal temperature during winter, spring and autumn periods and in the initial stage of the summer production cycles.

2. The high emission of sensible heat and the occurrence of other heat sources (solar radiation, fermentation processes in the litter) coupled with external air temperature that is higher or slightly lower than the required internal temperature, results in temporary overheating of the production facility. This phenomenon becomes intense in the second half of the summer production cycles. Measurements showed that overheating accounts for 20% of the time of the summer production cycles.

3. Litter temperature in the initial period of rearing was considerably lower than the required air temperature, and considerably higher in the final period. Taking into account that chickens may choose their area during the winter production cycle, it can be assumed that favourable thermal conditions in the living area occurred for approximately 16 days, which is just 38% of the production cycle length. Favourable thermal conditions in the living area of broilers during summer rearing occurred only in the second week, which constituted about 17% of the production cycle.

4. The high air temperature and the low emission of moisture at the start of rearing (first 10 days) make the relative air humidity too low. This state persists also during the periods of intense ventilation. In the remaining period, both in the winter and summer cycles, moisture shows considerable fluctuations, making it periodically either too low or too high. Moistening of air during the periods of insufficient humidity can increase its humidity to the required level. However, when the temperature and humidity of external air is high, it is impossible to decrease relative humidity inside the production facility without drying the air.

5. Tests of litter moisture showed the following relationships: a clear increment in moisture in time and greater moisture content in the area next to the wall than in the middle area of the production facility, as well as changes in moisture in time, which have a significant effect on humidity emission in the building.

6. The course of temperature in the ground demonstrated that heat accumulates there during the production cycle and cools down during technological breaks. This phenomenon has a significant effect on the pattern of litter temperature. The results of measurements confirmed that litter, floor and the ground are an integrated heat conductance centre that is highly important to the energy balance of the heated livestock building, with particular elements interacting with each other.

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