Ventilation of the Cornell Open-Front Poultry House
by F.L. Fairbanks and H.E. Botsford, taken from USDA Bulletin #197, 1914 & 1930
The importance of poultry-house ventilation is generally conceded, but just what is meant by ventilation and how it may be accomplished is not so well known. It is becoming increasingly evident that adequate ventilation cannot be accomplished merely by throwing doors and windows wide open to let the wind blow into the house; the air conditions within the pen must be so controlled that weather has only a secondary effect.
Many Cornell open-front poultry houses are now in use throughout the State. Since these houses are affected by weather conditions at certain times of the year, it has seemed desirable to determine an efficient means of ventilation. To this end, research in poultry-house ventilation had been carried on at the Cornell University Agricultural Experiment Station, with the result that a satisfactory method of ventilation can be recommended.
Factors Influencing Ventilation
Air drainage, windbreaks, temperature, relative humidity, and air movement, all influence the ventilation of poultry house.
Almost any location for a poultry house, except in a hollow, is satisfactory. Since there is little or no air drainage in a hollow, it is difficult to ventilate a house in such a location.
A house that is exposed to strong winds is also difficult to ventilate. The wind, striking the house from almost any angle, upsets the natural flow of air in and thru the house, and invariably causes objectionable drafts unless a correctly designed ventilation system is installed. The house should be protected by a windbreak of trees (figure 2). Such a windbreak should, however, serve only to break the force of the wind, for to make the windbreak so tight that there would be no air movement on hot days is as great a mistake as to expose the house to the full force of the wind.
During the winter period there are cold snaps, or short periods of low temperature. The data available indicates that these extreme low-temperature periods are the cause of much of the difficulties in poultry-house ventilation.
During fair weather, the temperature in the Cornell open-front poultry house changes with the time of day; it is low at night and high in the daytime (figure 3). As a cold snap approaches, the temperature may start to drop and may stay down even in the daytime during the one or two days of the cold period (figure 3).
At present, the only known means of tempering these extreme conditions is by mechanical heating systems. How important this type of heating for poultry houses is, remains to be proved.
The amount of moisture in, the air has some effect on housing conditions but not so much with the poultry house as might be expected. Wet litter has been attributed to high humidity conditions, but air movement, or even high production, probably has more to do with it than has the relative humidity of the air. The humidity varies with the time of day, increasing at night and decreasing in the daytime (figure 4) except as it is affected by storm, when it will stay high during the day (figure 5). In poultry houses that have free air movement thru them, the relative humidity follows very closely the outdoor conditions.
In most parts of the country there is usually some air movement, or wind, both day and night. Generally this air movement is in a certain direction for given weather conditions; that is, for a definite locality, the fair-weather breeze is from one direction and the storm winds are from another direction. The United States Weather Bureau records indicate that at Albany the average wind velocity is 17.7 miles an hour and the direction of the prevailing wind is northwest; for New York, the velocity is 13.3 miles an hour and the direction of the prevailing wind is northeast; and so on for different sections of the State.
Under normal conditions this air movement outside does not seem to affect the birds in the house until it reaches a velocity of 5 miles an hour or more. When the temperature is low and the relative humidity is high, even this velocity may cause discomfort. It, therefore, seems desirable to protect the birds against high-humidity conditions during the winter months and eliminate or temper the undesirable low-temperature conditions in the pen during the cold snaps.
Air Flow Through the Pen
In addition to air drainage, windbreaks, temperature, relative humidity, and wind, there is the most important factor of air flow, or movement of air thru the pen.
This air movement is caused by the heat given off by the birds, and is affected by the wind. The heat given off by the birds causes the air to rise about their bodies, and thus an air movement is set up.
Two distinctly different conditions in the poultry house affect the ventilation: the daytime condition, when the birds are on the floor feeding, and the nighttime condition, when all the birds are on the perches. When the birds are on the floor, the heat from their bodies is fairly well distributed over the floor space, and the air that comes in thru the lower ceiling, along the ceiling, and out of the front-rafter ventilator (figure 6). When all the birds are on the perches, the air that enters the lower part of the center opening falls to the floor, and moves across the floor to the perches; then the heat from the birds’ bodies causes the air to rise and to move along the ceiling between the rafters and out thru the front-rafter ventilator (figure 7).
Along with the air movement just described there is another and important movement that aids materially in reducing the dusty conditions that are apt to prevail in a closed pen. This air movement is due to the wind entering the house, and will be in the direction indicated in figure 8 or the reverse, depending upon the direction of the wind, except when the wind strikes the front of the house straight on. The air enters at one side of the center opening (figure 8), makes a long sweep, or swing, to the back of the house, and goes out of the other side of the center opening. If the pens are not too long, the swing will be of moderate intensity; but if long houses are not partitioned, the velocity of this air movement will become so high as to be objectionable.
The Ventilation System
Any ventilation system must have both outtakes and intakes. The outtakes permit the foul air, dust and excess moisture to escape from the pen. The intakes admit fresh air for the needs of the birds, replacing the air exhausted thru the outtakes, and distribute and assist in the diffusion of the fresh incoming air.
The Cornell open-front house has a rear-rafter ventilator, a front-rafter ventilator, and a set-out curtain intake. This combination is termed a rafter ventilation system.
The Rear-Rafter Ventilator
The rear-rafter ventilator (figure 9) is not used in winter but is opened only for summer, or hot-weather, ventilation. In the summer, poultry house ventilation is dependent almost entirely on the wind, or outdoor-air movement. Therefore, there should be openings in two or more sides of the pen, to permit cross-ventilation. Hence the rear-rafter ventilator is open in the summer to permit the breezes to blow or move thru the house from back to front or from front to back, depending on the direction of the outdoor air currents.
The Front-Rafter Ventilator
The front-rafter ventilator (figures 10, 11, and 12) is used both winter and summer. In the summer, it serves the same purpose as does the rear-rafter ventilator described in the preceding paragraph. In the winter, however, the front-rafter ventilator is the exit thru which the foul air and the excess moisture escape.
The front-rafter ventilator door may be closed or opened by a cord (figure 10).
During mild weather the best circulation of air within the house is maintained when the front-rafter ventilator door is down, or open. If, however, the front-rafter ventilator door is left open during cold, raw, windy weather, when the wind is apt to shift suddenly or to blow steadily or gustily against the front of the house, the wind whips in thru the front-rafter ventilator and produces objectionable drafts in the pen which may reach as far back as the perches. The cold wind tends also to chill and stop the outward-moving foul moist air. This, of course, destroys the convection-current ventilation action.
In some of the older shed-roof houses, the front-rafter ventilator door was constructed similar to the rear-rafter ventilator door which, when closed, sealed the opening over the plate. This, of course, kept the wind out but prevented the escape of the foul, moisture-laden air from the pen. Therefore, the front-rafter ventilator door is now made one inch narrower than the opening (figure 10). When this door is closed, the wind cannot blow thru the front-rafter ventilator but the moisture-laden air may escape. If this one-inch opening is not provided and the front-rafter ventilator door is closed, frost and moisture will collect on the roof boards and objectionable housing conditions will result.
The Set-Out Curtain Intake
One of the chief characteristics of the open-front poultry house is the comparatively large front opening which permits the entrance of air and sunlight. The curtains which cover this opening keep the wind and storm out, and are made of a frame covered with a coarse-woven cheesecloth or muslin. Some air will, of course, pass thru such a coarse-woven material when it is clean, but it is obvious that if these curtains become covered with dust or coated with sleet no air could be expected to enter the pen thru the curtain material. Therefore a set-out curtain intake should be constructed to facilitate the entrance of pure fresh air.
The curtain guides are so constructed that the frame is held one inch from the front of the house (figure 11). Thus, when the curtain is pulled to the top, there is a vertical opening, one inch wide and the length of the curtain, between the curtain frame and the window sill (figure 11). This vertical opening directs the entering air upward, thus preventing any draft in the house regardless of the velocity of the air. All of the curtains for any pen should be arranged in this manner to obtain the most uniform distribution of the entering air.
MANAGEMENT OF THE CORNELL OPEN-FRONT POULTRY HOUSE
The method of operating a Cornell open-front poultry house by means of “rafter-ventilation,” as suggested in the following paragraphs, has been found to give excellent results. Birds have maintained normal production and have kept in good health.
About October 1 all windows should be cleaned and fastened tightly in their places, where they should remain until spring (figure 13). Do not tip the windows in at the top at any time.
The curtains may be kept down, leaving the center opening uncovered, (figures 12 & 13) except when (1) the outside temperature drops to 15°F or lower; (2) when a strong, or gusty, wind is blowing which would produce an objectionable draft in the pen; or (3) when rain or snow is blowing into the pen. Under any of these circumstances the curtain should be pulled to the very top, completely covering the center opening except for the one-inch vertical slot at the bottom of the curtain.
The curtains may also be kept closed throughout the night for all late fall, winter, and early spring weather. This practice safeguards the pen from any sudden change in the weather which often occurs during such periods.
The rear-rafter ventilator door should be closed about October 1 or as soon as the weather becomes cold. This door should be tightly closed all winter.
The front-rafter ventilator door may be left open for all weather except (1) windy weather which would tend to produce objectionable drafts in the pen; (2) cold winter weather, and (3) at night when the weather is apt to change suddenly from quiet to windy or mild to cold or threatening to storm.
If any of these conditions exist, the front-rafter ventilator door should be closed tight except for the one-inch opening along its front edge.
As previously stated the summer ventilation depends largely on the outdoor air movement, and for this reason the front- and rear-rafter ventilators and the front and rear windows should be open to permit the summer breezes to move thru the pen.
About April 1 or May 1, when the weather conditions become fairly well settled, the front windows should be removed and stored away, either in racks in the pen or in a protected place elsewhere.
The rear windows may be removed later in the summer when very warm weather make it desirable for additional movement of air within the house.
The curtain frame should be dropped so that the entire opening is uncovered (figure 14). This opening should not be covered by the curtains except in case of a severe rain or wind storm, and then only for the duration of the storm.
Rain in the house during the summer does no particular harm unless it blows in and drives the birds into a corner. The curtains are a protection against this possibility. Such moisture will not remain in the building long because of the drying effect of the air that is continually passing thru the pen.
The front-rafter ventilator door is open at all times during the summer (figure 14).
The rear-rafter ventilator door is opened when cold weather is over (April 1 to June 1) and is left open until fall.
VENTILATION OF THE INSULATED OPEN-FRONT POULTRY HOUSE
The value of insulation on the walls and ceiling of the unheated open-front shed-roof house has not been fully determined. It is known, however, that insulation does tend to assist in maintaining a slightly higher temperature in the pen during periods of low-temperature weather.
The ventilation system for such a house is the same in principle as for the uninsulated open-front house; that is, a front-rafter ventilator exhausts the moist warm foul air and the set-out curtain intake admits fresh air.
The ceiling insulation does not extend clear to the front of the house but is stopped 6 inches from the front at headers between the rafters (figure 15). Headers are also built in at the ceiling doors of the rear-rafter ventilator to prevent a rapid circulation of air between the roof and the insulation.
The front-rafter ventilator door is constructed exactly the same for all shed-roof poultry houses; that is, with the one-inch slot the full length of the house. The center-opening curtains are set out one inch, as previously described, to form the intake.
The rear-rafter ventilator is of the usual construction, and door is provided in the ceiling in front of the perches to permit the air to enter the pen in mild or summer weather. The inside and the outside rear-rafter ventilator doors are kept closed during the winter.