The air conditioning of the housing environments
The ventilation of the barn, as well as the maintenance of optimal humidity values, are essential interventions to ensure a good state of health of the animals and, therefore, to guarantee ideal levels of well-being and productivity
Ahousing environment that guarantees adequate breeding conditions in terms of the microclimate is undoubtedly a fundamental basis for ensuring good milk production, with healthy animals and with an optimal level of welfare. The main parameters usually monitored are temperature and humidity; however, air speed and quality also play a key role. The recommended temperature values are between 20-25°C, while the relative humidity should be between 60 and 70%. The two data are often combined in the Temperature Humidity Index (THI), which is an indicator designed to detect a possible state of thermal stress in the barn. In the literature there are several formulas for the calculation of THI; one of the simplest is: THI =0.8*T + RH*(T-14,4) + 46,4. The cut-off value is 72, but there is often a drop in production and some behavioural changes already with values of around 66-68. It is therefore essential to respect some construction precautions, such as the use of insulating materials on walls and roofs, a correct orientation of the structure and adequate openings to the dome and to the sides of the barn, such as to encourage natural ventilation, which among the microclimate control systems is obviously at no cost. However, when the structure is not able to meet these conditions, it is necessary to resort to forced ventilation, using mechanical systems.
Mechanical ventilation. It must guarantee excellent air exchange performance in both hot and cold seasons, with low energy costs, through the adoption of resistant materials and silent operation so as not to cause chronic noise disturbance to the animals. In the barns of the Po Valley, in the spring-summer period, the fans work almost continuously: the containment of electricity consumption and the operation of structures with a low risk of damage and limited noise pollution therefore become fundamental needs. The energy consumption of each fan varies according to the size, type of use and mechanical characteristics, generally varying between 100 and 1,200 W. In addition, to ensure a good service life of the blades and the central pin which are subjected to intense stress, but also to avoid the creation of strong air currents that are harmful to animals, the rotation speed is generally quite low. Longitudinal axis fans (called "destratifiers") usually rotate at 300-500 rpm, while vertical-axis fans have higher speeds, between 700 and 1,000 rpm. In both cases, the goal is to achieve an airflow speed of up to 4-5 m/s, which is useful in the hottest summer periods to conveniently dissipate heat. This type of ventilation is also useful in winter, to ensure appropriate changes of the stale air that is created in the barn, to remove typical pollutants such as carbon dioxide, methane, ammonia and hydrogen sulfide. In such a case, the flow velocity should not be higher than 0.5-1 m/s.
The types of fans. It is very important that the air movement points are located in the areas where the animals stay the longest, i.e. in the resting and feeding areas, but also in the waiting room and in the milking room. In resting areas and in the milking room, the most suitable fans are large diameter destratifiers (up to 5-7 m) which, despite the limited rotation speed, move large volumes of air and are therefore suitable for handling very large surfaces conveniently. The efficiency of these fans is enhanced by the shape and inclination of the blades and the flaps that direct the air: a destratifier of 1.5-2 m in diameter is able to cover a circular area of about 120-180 m².
Alternatively, it is possible to install vertical blade fans, which have smaller dimensions but higher rotational speeds. In this case, ventilation efficiency is high even in critical conditions, such as crowded waiting rooms. However, the electricity consumption is slightly higher than that recorded by the destratifiers, for powers of about 1-1.5 kW, depending on the size of the blades and the manufacturer's specifications. A protective grid is often installed to prevent accidental contact with the rotating blades.
In both cases, the shape and inclination of the blades must be aimed at moving good volumes of air with low power requirements. In addition, in order not to weigh down the structure unnecessarily, the material of the blades must be light, such as aluminum, PVC or even thin sheet steel, reinforced with specific ribs.
The blade tilt function is often implemented, for a more homogeneous distribution of air in the barn, achieved by means of blade tilt adjustment brackets, for a very wide angle, even variable between 0 and 90°.
Brushless motors with permanent magnet rotors are typically used to drive the fans, which show excellent reliability, have low maintenance requirements and are silent in operation.
From the market. Elivent of Reggio Emilia offers destratifiers equipped with a fall arrest kit, for a higher level of safety for parked animals, in case of damage to the blades. Elettrouno, also based in Reggio Emilia, has patented a solution for tilting the blades up to 10° with an optimized profile, for an effective modulation of air flows in the environment. In addition to ventilation, CMP in Calvisano (BS) also offers complete cooling systems to maximize the heat loss of the animals. In the same context, TDM of São Paulo (BS) sells mechanical zone ventilation systems managed by controllers, possibly integrated by anemometers that can automatically block the fans in the event of excessive air speed.
Water sprinkling
In the feeding aisle and in the milking waiting room, vertical fans can be combined with misting systems that sprinkle the animal coat, to be practiced when climatic conditions are particularly critical. In such cases, sprinkling contributes to ventilation to maximize heat loss by the animals. In practice, predefined cycles of nebulized water supply are started through nozzles, lasting about 1 minute, interspersed with periods of 5-6 minutes of ventilation only.
The sprinkling must necessarily be intense but not excessively long, to avoid the percolation of water on the coat and the consequent pollution of the udders and water stagnation on the floor, factors that increase the probability of the onset of mastitis and foot lesions. To optimize the use of water, some companies, such as CMP, propose the installation of sensors in the feeding aisle that start sprinkling only if the animals are present.
Automatic start
Ventilation systems normally provide for the automatic start of the system when the control units detect that the predefined temperature and humidity threshold values are exceeded. For this purpose, specific sensors are placed in the barn, whose data are processed to obtain the THI (or only the air temperature), in order to intervene when the thermal stress threshold is reached. An interesting future evolution involves the development of algorithms capable of predicting the climatic trend based on the data collected in the previous days, in order to anticipate the occurrence of stress conditions in the herd. In this regard, as part of the European EIT Food DairySust project, with the support of Agricolus as a technological partner and the University of Bologna as a Research Unit, the "DairySust" digital platform has been developed, which has as its general objective to pursue animal welfare objectives, supporting the decision-making processes of farmers and professionals for the optimization of the sustainability and productivity of the herd, including climate comfort.
