If a warm calf barn is desired (>10°C), it can be ventilated either naturally or with mechanical fans but regardless of which type of system is chosen supplemental heat must be added. Whether calves are housed in elevated crates, individual pens or group pens, they are often stressed and cannot tolerate any further environmental stresses. Therefore, barn temperature must be in the acceptable range and kept free from temperature swings. The air speed must be low such that no drafts are occurring and yet fresh air is being distributed to all areas of the room.
The building should:
- Have a ceiling height of 9 feet to provide the desired air volume per calf. The high ceiling also allows more headroom for the installation of the ventilation and heating equipment and reduces the potential for drafts at calf level.
- Have a good quantity of insulation to keep the heat in during the winter and the heat out in the summer. An R30 ceiling and R20 wall insulation is recommended. In addition, the perimeter foundation wall should have R7 insulation. If the entire attic is used as the fresh air plenum, then R5 insulation should be added to the underside of the metal roofing. This will prevent hot attic air during the summer months.
- Have few or no windows. Windows are a source of heat loss during the winter and heat gain during the summer causing unnecessary temperature fluctuation within the room. If, for aesthetic reasons, windows are desired, they should be double-glazed, located on the south side of the barn and not used for ventilation purposes.
- Be well constructed and reasonably air tight such that typical cross-flow ventilation systems can function properly.
- Have an interior surface lining which is bright and easy to clean. Provide a smooth ceiling, which will not obstruct air movement.
The ventilation system must provide fresh air without drafts and temperature fluctuations to every pen in the nursery. This will require a well-controlled air inlet, an internal air circulation system, a supplementary heating system, and properly sized and staged exhaust fans.
Most often a cross-flow, slot type of air inlet is used. Sufficient air inlets should be installed to allow fresh air into all pens and provide at least 2 square feet per 1000cfm of exhaust fan capacity. Often times this can be achieved with a row of discontinuous, self-adjusting air inlets along the ceiling. Depending on the width of the room, these can be located either along one side wall or half way across the ceiling. Once initially set-up, these inlets will only require seasonal adjustment to obtain the correct amount of opening. Incoming air speed at the inlets should be in the range of 400-800 feet per minute. This will promote good mixing and air distribution from the inlet. A static pressure gauge (or manometer) should be installed in the room to assist the operator in controlling the air inlet opening. This gauge senses the vacuum created by the exhaust fans and gives a water pressure reading, which corresponds to an air velocity measurement. The inlets should be adjusted so that the room operates between 1 and 2 mm (0.04-0.08 inches) on the gauge.
A continuous side wall air inlet with hand winch control is also satisfactory, but will require more adjusting to keep the proper air inlet opening. A smooth ceiling liner is essential for good airflow across the building. Painted plywood provides a very practical and durable, smooth ceiling surface. If corrugated, galvanized steel is used as the liner, the steel sheets must be installed so that the corrugations are placed parallel to the airflow.
Fresh air can be obtained either from the soffit and eave area directly or from the attic space. To prevent the use of overly hot attic air during the summer months, it is necessary to either insulate the underside of the roof steel to R5 such that the entire attic is the fresh air plenum or construct an insulated fresh air duct within the attic space to provide 2 ft2 of capacity for every 1000cfm of fresh outside air required.
Internal Air Circulation System
An internal air circulation system is recommended to guarantee a uniform airflow pattern as well as eliminate dead spots and temperature stratification. It also provides an excellent way to distribute the supplemental heat. This circulation system should be located directly under the fresh air inlet such that it assists the flow of cooler, incoming fresh air and helps to mix and warm it prior to reaching the pen area. Ideally, incoming air should enter a preheated room or alley where it can be warmed to take the chill off of the air before it enters the stocked area. This feature (shown in Figure 1) allows a fair amount of flexibility in how this air is then allowed into the calf nursery. Sometimes this air will be further heated within the room itself depending on the temperature kept in the preheat area.
The circulation fan is designed to operate continuously and circulate approximately 1cfm of room air per square foot of floor area. The air circulation duct or plastic air tube is sized to keep the air speed less than 1000 ft per minute (1ft2/1000cfm) through the duct. An oversized duct is not a bad thing – the lower the duct air speed, the more uniform the air speed through the holes along the duct.
The number and size of holes is carefully chosen to obtain high speed action at the holes, but still have the air’s energy dissipated by the time it reaches the side walls of the building. This is required to prevent drafts and achieve slow moving air through the pens. Table 2 gives a general guide for choosing the hole size based on distance of travel to the side wall. The number of holes is based on obtaining a jet velocity of approximately 1000ft/min at each hole.
For example, the internal air circulation system for a room 20′ x 25′, housing 12 calves, would need to have a capacity of 500cfm and a duct cross-section of at least 0.5ft2 (6? x 12?, but 12? x 12? would be even better). If the circulation system were located in the middle of the room, then air would be circulated approximately 9 feet in both directions. From Table 2, the recommended hole size would be 1 inch diameter and the number required to jet 500cfm at 1000ft/min would be (500cfm/1000ft/min) 0.0055ft2/hole equals 90 holes. With half the holes on each side of a 23 foot long duct, the hole spacing would be every 6 inches or 2 per foot.
Additional heat is required to both maintain the desired room temperature, and allow adequate air exchange to control the respired moisture and odours. The recommended room temperature for a calf nursery is 10-13°C (50-55°F). Warmer temperatures require larger heaters, which tend to over dry the air such that respiratory problems become more common. There are several types of heating systems available to heat the entire air volume in such a room; but many of them, including hot air furnaces and hot water boilers, are usually too large. Their use can result in hard to control systems with large, rapid temperature fluctuations which stresses the calves.
Small fan-forced electric heaters have been the most common heat source for these rooms. Often times, even the standard 4800 watt construction heater (milkhouse or utility heater) is oversized for the room. The unit heaters are available in 2, 3 and 5 kilowatt sizes and you should obtain the correct size for your room to minimize temperature fluctuations.
The heater needs to be located near the internal air circulation fan so that the heat is picked up and uniformly distributed throughout the room. However, in barns where a hallway or room is provided on the air inlet side of the barn, the heat may be added at this location before the air enters through the inlet.
The most important aspect of any heater is its controller. Unfortunately, these unit heaters do not come equipped with a thermostatic controller. Yes, they have a control dial, but it is simply a limit switch that prevents the unit from overheating. This allows the heater to cycle on and off like a thermostat, but is has little relationship to the desired room temperature. Essentially, all heaters operating on this basis are running wild and waste considerable energy. This is easily corrected by having a qualified electrician wire a room thermostat into the heater circuit so that it now can be set to maintain the desired room temperature.
The second point about heater control is the need to ensure that the ventilation system is not wasting heat. The simplest arrangement is to have the heating and ventilating thermostats side-by-side and manually ensure that the heater setting is lower than the additional ventilation setting so that heat is off before the volume of ventilation increases.
The ventilation and heating systems can be electrically interlocked to ensure that excess ventilation does not occur while the heat is on. In recent years, several commercial heat-cool controllers have become available to perform this function. With these controls, the heat must go off before additional ventilation can occur. Some even have built-in time delays between the heating and cooling modes.
Exhaust fans are required to control the rate of air exchange in the room. The ventilation required varies from a minimum, continuous winter rate of 10cfm per calf to 1 summer level of 150cfm or more per head. In fact, the minimum rate may need to be increased to about 4 air changes per hour to adequately control the barn odours.
Ideally, a small exhaust fan should handle this continuous low level of ventilation. The fan should be sized for that specific ventilation rate and allowed to run 24 hours per day without any thermostatic control. This procedure allows the heater to maintain the desired room temperature with that quantity of air exchange only.
One problem is that there are very few, if any, heavy-duty farm fans small enough to deliver 120cfm (10cfm x 12 calves). Generally, this problem is not too critical since 4 air changes per hour will usually push the minimum ventilation rate up into the 300cfm range. This rate can be achieved by a number of different fans. If a variable speed fan is used, it is important to not allow it to increase its air delivery rate at the expense of the heating system. A manual speed controller or interlocking heat-cool control will prevent this situation.
A separate fan or fans should be used to achieve at least 3 more levels of ventilation between this minimum rate and the summer maximum rate. This additional ventilation should be staged such that each rate increase does not more than double the current exchange rate. That is, 4 air changes per hour should not jump to any more than 8 air changes per hour and then 16 air changes, and finally 32 air changes per hour. Thermostats set at various temperature levels above the desired room temperature would activate these fans. Variable speed fans can provide excellent staging and limit the temperature fluctuations often found n these small rooms.
The thermostats are in control of the room environment. For this reason, it is important that they be located to sense the average room temperature at eye level in an accessible location. Thermostats need to be checked and cleaned regularly. A maximum-minimum thermometer will aid this checking and alert you to undesirable temperature fluctuations.
In summary, the key to successful ventilation is to maintain a consistent barn temperature and introduce and distribute fresh air without causing drafts. If you as a producer are able to achieve this, your calves will be healthier and should be very productive for your farm business.