Manitoba Agriculture, Food and Rural Initiatives
Heat Stress Index CalculatorThe heat stress index calculator is designed to let you visualize how weather and barn ventilation specifications can alter the daily pattern of heat stress in a poultry flock. You can see the how not just the peak but the duration of heat stress is important. The calculator gives a picture of how heat stress patterns change as the ventilation specifications in your barn are changed. The calculator can be used for a variety of situations but is most appropriate for market age chickens or turkeys or mature laying hens. The calculator lets you make several choices:1) Type of Day a. Typical Warm Day - with a day time high temperature of 28 to 29 C. In Manitoba, about two weeks of weather each year fall into this range. b. Typical Hot Day - with a day time high of temperature of 30 C or higher. In Manitoba, about one week of weather falls into this range each year. c. Extremely Hot Day - with 12 hours of temperature over 30 C throughout the day. In Manitoba, an extremely hot day will occur once every one or two years. d. Record Humidex - with a peak humidex of 53 C based on the scale reported by Enviroment Canada on daily weather reports. The data is from July 25, 2007 when the record humidex for Canada was set in Carman, Manitoba. 2) Temperature Gain The temperature gain tells you how much hotter the temperature is inside the barn compared to outside the barn. As an example, if the outside temperature is 30 C and the barn temperature is 32 C, the temperature gain is 2 C. The calculator lets you choose between three different levels of temperature gain when all of the fans are running in the barn: a. 1 C - is the target for many barn designs. In practical terms, it is very difficult to obtain a temperature gain less than 1 C. b. 1.75 C - is a temperature gain slightly above target. c. 2.5 C - is a high temperature gain which often indicates an issue with the maintenance or design of the ventilation system. Unless it has a mist cooling system, the temperature inside the barn will always be hotter than outside the barn during the hot part of a summer day. 3) Airspeed at Maximum Fan Capacity You can choose between four different airspeeds at bird level when all of the fans are running in the barn: 60, 120, 180, or 240 feet per minute. Many cross-ventilated barns will have an average airspeed of 60 feet per minute. Adding extra fans or other design features can readily increase airspeed to 120 or possibly 180 feet per minute. An airspeed of 240 feet minute is very high for a cross-ventilated barn but on the low side for a tunnel ventilated barn. An airspeed of 60 per minute provides almost no wind chill for market age broilers or laying hens while 240 feet minute airspeed provides several degrees of wind chill. 4) Temperature When Fans Start Running at Maximum Capacity The temperature controller in the barn can be set to turn on all of the fans at a either 22 C or 26 C. It is fairly common for the all the fans the be running as barn temperature rises above 26 C in the morning and then start turning off as the barn temperature falls below 26 C in the late afternoon or evening. You can observe the impact of using a 22 C or 26 C set point for the highest stage of fan capacity. The heat stress index calculations are based on research conducted on market weight broilers by Dr. Hongwei Xin at Iowa State University. |
| Calculate how weather and barn conditions change the daily pattern of heat stress |
