In hot summer weather house design becomes critical in ensuring optimal airflow for the cooling and comfort of the birds. Yet when designing a modern broiler house the priority is all too often driven by the need for quick returns and not long-term bird performance. New longer and wider tunnel houses challenge the ventilation system’s ability to produce uniform conditions the full length of the house. Equally important is the challenge of providing sufficient air exchange and air speed needed to keep the birds comfortable – and their combined impact on energy costs? The broiler farmer stimulates feed consumption from the moment the chicks arrive on the farm, with the first seven days the most important. An extra gram then can be equivalent to five grams or more at 35 days. The other most challenging period, especially in summer, is after 25 days when birds are fully feathered and hot conditions will challenge feed consumption. Capital investment is often driven by the need for fast paybacks with investment decisions often made without optimizing design and airflow requirements. These are some essential design considerations: Well-insulated, smooth ceilings and walls; Good quality inlets for minimum and transition ventilation; Adequate static pressure control by thorough sealing; and Tunnel fan choice based on efficiency – not cost! The biggest challenge for houses longer than 120 meters is maintaining an acceptable temperature pick-up from the front to the back of the house, or commonly referred to as the T. The level of bird comfort ultimately drives daily feed consumption and even temperature distribution will help ensure uniform feed intake and uniform processing weights. The amount that the air in a house heats up depends primarily on threefactors: Metabolic heat added by the broilers; How quickly the air in the house is exchanged; and Thermal properties of the house. Heat flows through surfaces from hot to cold, entering the house through the ceiling, sidewalls or curtains. The higher the R-value of the surface, the lower the emissivity. By far the greatest amount of heat produced is that produced by the birds. The broiler is the greatest contributor to heat load. But the value of good insulation cannot be underestimated, and is vital for bird comfort and minimizing operational cost during both brooding and growing. During brooding it plays a vital role in reducing heating costs and during growing it helps reduce the heat load on the house. The transition ventilation system plays a critical role in temperature management during brooding through day 21. It ensures efficient air exchange and temperature management without creating excessive air movement at chick level. Until broilers have full feather development, they are very sensitive to air speed, which impacts feed consumption. Choice and installation of a high-quality inlet is often overlooked by growers in hotter regions of the world. Price rather than the long-term impact on early performance is too often the driver of what is essentially equipment that should be only about 3% of total capital cost on a new project. The quicker the air exchange rate, the cooler a house will be. Unfortunately a good air exchange capability alone will not guarantee bird comfort. Air speed is needed to remove sensible heat produced by the birds. Most tunnel houses are equipped with an evaporative cooling system, designed to keep the incoming air temperature below 29°C. Dropping temperature with an evaporation system increases humidity in the house, thus reducing the birds capacity to release heat through panting. By far the most important contributor to bird comfort is air speed. Future key design decisions will revolve around achieving the genetic potential at lowest operating costs. In the future electricity costs will be the greatest contributor to overall operational costs. One’s choice of tunnel fan will by far be the most important decision. Choice should be based not on unit cost but the following: Energy efficiency – cfm/Watt or m³/hr/Watt. A minimum of 21cfm/W at 25Pa. Airflow ratio – an indication of how well the fan will hold up under high static pressures. Airflow ratio should always be greater than 0.75. Only purchase fans that have been independently tested. Insulation, inlet choice and installation, ability to maintain adequate pressure and choice of tunnel fan are by far the key design decisions in any new project having a major impact on payback and future profitability.