C. BENNETT
Manitoba Agriculture, Food & Rural Initiatives
University Crescent, Winnipeg,
Manitoba, Canada
Minimising temperature gain, or the difference between the temperature inside and outside of a poultry house, is the first objective of any poultry ventilation system in hot weather.
Carbon dioxide measurements are a rapid method of evaluating the temperature gain and airflow in poultry houses. They are easier to conduct and appear to be less variable than direct measurements of temperature gain. In a study of 46 commercial poultry houses in Manitoba, a strong linear relationship (r2 = 97%) was observed between house carbon dioxide level and temperature gain. House carbon dioxide levels under 700 ppm were associated with a temperature gain of 1.5°C or less. Service people and farm managers can use hand held carbon dioxide monitors to provide quick estimates of airflow and heat build-up in poultry houses.
Introduction
During hot weather, minimising poultry house temperature gain is the major goal of any ventilation system. In a well-run system, the air temperature inside the house will be only 1°C warmer than outside the house (temperature gain of 1°C). In a poorly designed or operated system, temperature gain could be as high as 3°C. While the difference between a good and poor system may appear to be small, the impact on the number of hours of heat stress experienced by the birds can be significant. For example, under typical summer conditions on the Canadian Prairies where the day time maximum temperature averages 26°C in July, a 1°C reduction in temperature gain can reduce the hours of heat stress experienced by the birds by 50%.
While managing temperature gain is a primary objective, it is surprisingly difficult to accurately determine if temperature gain is being kept at 1°C during hot weather. One of the problems with accurately estimating temperature gain is the need to simultaneously measure temperature both inside and outside the house to within a few fractions of a degree. Temperature outside the house is particularly difficult to measure because it fluctuates throughout the day, changes with shifting wind direction, and can be noticeably different on the sunny and shady sides of the house. As an example, the air temperature on the sunny side of the house can be 2°C warmer than on the shady side of the house. All of these variables can cause fluctuations in outside temperature that are greater than the size of temperature gain that you are trying to measure. Variation in air temperature within the house can further complicate the attempt to accurately measuring temperature gain.
For service people and farm managers who do not have the time to conduct the many temperature measurements needed to gauge temperature gain, house carbon dioxide measurements may offer a good alternative. Carbon dioxide is a by-product of respiration and related to heat production by the birds; plus it builds up in the house when airflow is inadequate to remove the heat produced by the flock. As part of a study of commercial poultry houses, carbon dioxide monitoring was evaluated as method of estimating temperature gain and airflow.
Methods
Air temperature, carbon dioxide level, and airflow were measured in 46 poultry houses (nine broiler, 26 layer, eight breeder, one pullet and two turkey houses). All measurements were taken when the stoves were turned off and the birds provided the only source of heat in the houses. For cool weather conditions, (temperature gain over 15°C), all measurements were done in layer houses with manure belts or gutters where the manure could be removed regularly to prevent ammonia build-up.
Outside air temperature was measured with a digital probe thermometer at the outside face of the inlet or eaves where the air first entered the house. The thermometer was positioned to keep it out of direct sunlight.
During each farm visit, outside temperature was measured on two or more occasions at each of three or more locations. The same thermometer was used to measure temperature inside the house. In broiler houses, temperature was measured at six or more locations at bird height moving in a diagonal path across the house. In layer houses, the measurements were done at a minimum of two heights at six locations in a diagonal across the house. It was not unusual to conduct measurements at a dozen locations in layer houses.
Airflow through the houses was estimated based on the airspeed of the fan exhaust and the area of the fan opening. Fan airspeed was estimated based on nine measurements with a Kestrel vane anemometer. The method of determining fan airflow has been explained previously (Bennett, 2004).
Carbon dioxide was measured using an ACR Falcon 206 hand-held carbon dioxide meter (ACR Systems Inc., Surrey, B.C. Canada). Inside broiler houses, carbon dioxide was measured at the same locations as air temperature. Inside layer houses, measurements were taken at two or more heights at six or more locations. Temperature was measured at all locations where carbon dioxide was measured but in large layer houses, temperature was measured in more locations than carbon dioxide. The carbon dioxide outside the house was measured at one to four locations.
Results and discussion
Carbon dioxide levels were relatively uniform between different locations in the poultry houses. Contrary to popular belief, the carbon dioxide levels were not higher near the floor compared to several feet above it. The carbon dioxide produced by the chickens was warm and tended to rise and mix in with the general airflow in the house. The highest carbon dioxide levels were instead found in areas of the house which were not in the direct path of the fresh air as it entered the house. Measuring the average carbon dioxide level inside the house appeared to be fairly easy.
In Figure 1, data for carbon dioxide and temperature gain in the 46 poultry houses are displayed. No supplemental heat was provided in the houses at the time of these measurements.
A strong linear relationship between carbon dioxide level and temperature gain was observed:
Temperature Gain (°C) = -6.4542+0.0108 x CO2 (ppm), r2 = 97%.
The steady increase in carbon dioxide as temperature gain increased was expected due to the low airflows needed to trap bird heat in the cool months when a large temperature gain was needed.
The strong linear trend was partly a reflection of the very wide spread in temperature gain observed over the study. Looking at the cases where temperature gain was under 3.5°C, considerable variation was observed – in part due to the challenge of estimating the temperature gain. Still, within this subset of the data, lower temperature gain was associated with lower carbon dioxide levels.
For the 15 houses with a temperature gain of 1.5°C or less, the carbon dioxide levels averaged 682 ppm whereas in the houses with a temperature gain of 1.5°C to 3.5°C, the average carbon dioxide level was 865 ppm. The increase is in basic agreement with the above regression equation which predicts a temperature gain of 1.5°C at a carbon dioxide level of 737 ppm. A reasonable objective for hot weather ventilation would be to keep the carbon dioxide levels below 700 ppm.
In addition to predicting temperature gain, the carbon dioxide levels provided an estimate of airflow in the houses. In Figure 2, the relationship between carbon dioxide and airflow relative to live body mass is displayed. As airflow increased above the minimum winter ventilation rate, (approximately 0.15 litres/s/kg of live weight), carbon dioxide levels dropped dramatically. At flow rates over 1.5 litres/s/kg, however, further drops in carbon dioxide level were difficult to discern. Increasing fan capacity over 1.5 litres/s/kg did not appear to measurably reduce the build-up of carbon dioxide (and thus body heat) in the house. If fan capacities over 1.5 litres/s/kg are built into a house, the benefits will most likely come from increased airspeed instead of reduced temperature gain.
In poultry houses with misting cooling systems, carbon dioxide levels can be used to separate the effect of airflow and mist cooling on the temperature inside the house. For example, a poultry house with 950 ppm carbon dioxide would be expected to have a temperature gain of 3°C in the absence of mist cooling. If operating the misters drops the house temperature to 2°C below the outside temperature at the same time that 950 ppm of carbon dioxide is observed, the total amount of cooling is 5°C. The mist system should be given “credit” for eliminating the expected temperature gain as well as the drop below outside temperature that it produces.
In interpreting the data, it is interesting to note that the air immediately outside the houses had more than the 330 to 370 ppm of carbon dioxide normally expected in fresh air. Instead, in most cases, the air entering the houses contained 400 to 450 ppm of carbon dioxide. The elevated carbon dioxide reflected the large amounts of the gas exhausted by the house fans into the immediate surroundings.
Conclusions
A hand-held carbon dioxide monitor can be used to rapidly provide service people and farm managers an estimate of temperature gain and airflow in their poultry houses. A digital carbon dioxide monitor costs $850 Cdn. and requires little maintenance. Average carbon dioxide levels can be easily estimated in the time required to walk the length of the house. The relationship between temperature gain is strong and linear. House carbon dioxide levels below 700 ppm are indicative of a temperature gain of 1.5°C or less and are a sign of good airflow during hot weather. Carbon dioxide testing is a simple and practical method for evaluating summer ventilation in poultry houses.
References
Bennett, C. (2004). Poultry Service Industry Workshop, Banff, Alberta, Canada. Available at
http://www.poultryworkshop.com/Presentations/Carlyle%20Bennett/Summer%20Ventilation.pdf
From Proceedings of the “19th Australian Poultry Science Symposium”, New South Wales, Australia.
