Environmental control system
With the intensification and industrialization of the swine industry, the issue of environmental control in pig houses has gradually gained recognition and attention. Among these, the ventilation conditions and temperature-humidity factors in pig houses are the most critical thermal environment factors for pigs' healthy living, and they also have the greatest impact on pigs' production performance. To this end, animal husbandry engineering technicians at home and abroad have carried out extensive work on the research and application of pig house ventilation, cooling and heating technologies, and have achieved certain results. A brief overview of these efforts is as follows:
1. Ventilation technology
Reasonable determination of pig house ventilation volume is the premise for a sound ventilation system design. Chinese scholars have conducted research on the design and calculation methods of ventilation volume: they introduced the theory of periodic unsteady heat transfer into the calculation of heat transfer effects through the enclosure structure of livestock houses, and proposed formulas for calculating the maximum summer ventilation volume and minimum winter ventilation volume. This provides a practical and feasible theoretical basis for the rational determination of pig house ventilation volume. Overall, pig house ventilation methods are broadly divided into two main types: natural ventilation and mechanical ventilation. With the research and development of ventilation equipment and related application technologies, high-efficiency, energy-saving mechanical ventilation systems dedicated to livestock houses (with adjustable air speed and volume) have emerged internationally. Currently, the negative-pressure ventilation system is widely applied; it features a relatively simple structure, low investment, and low management costs. However, this system is only suitable for houses with a span of less than 20 meters, and since it cannot adjust and control parameters such as the temperature and humidity of the incoming air, it is not ideal for use in areas with extremely harsh climates. By contrast, the positive-pressure ventilation system can heat, cool, and filter the incoming air, effectively maintaining the appropriate temperature, humidity, and clean air environment in the pig house. Thus, it is particularly suitable for use in extremely cold or hot regions—but it also has drawbacks such as complex structure, high cost, and high management expenses. In recent years, many researchers have also made significant progress in the research of vertical ventilation technology (the earlier-used type is the horizontal ventilation system). They have proposed scientific air inlet layout methods, calculation methods for the required area of air inlets and outlets, and matching fan arrangement methods. Compared with horizontal ventilation systems, vertical ventilation systems have advantages such as uniform air distribution, excellent ventilation, cooling, and sewage discharge performance; they can clearly separate clean aisles from dirty aisles, avoid cross-blowing and cross-breathing between adjacent pens, and easily eliminate dead zones where harmful gases accumulate. If this ventilation method is used in conjunction with a wet curtain (also called a water curtain), it can also achieve summer cooling very effectively. This application has been widely adopted in some hot-climate regions of China, with relatively ideal results.
2. Cooling technology
In terms of cooling technologies, animal husbandry engineering researchers at home and abroad have conducted in-depth studies and developed relatively mature, complete, and practical cooling solutions. Among these, evaporative cooling technology (which uses water vapor evaporation to absorb heat) has been widely applied; additionally, ventilation cooling and contact cooling via wet porous materials (wet pads) are also being further researched and improved. The evaporative cooling efficiency of the wet pad ventilation cooling system is typically 75%–78%, with a ventilation resistance loss of 10–40Pa. Research on this system began in the United States in the 1950s, and it was gradually refined and promoted. China only introduced this system in the 1980s; in 1988, Beijing Agricultural Engineering University successfully developed a wet pad ventilation cooling system suitable for China’s livestock production conditions. This system has significant cooling effects and reliable operation, but its efficiency decreases due to the deposition of air dust and water salts in the wet pad. Moreover, paper-based wet pads are prone to damage during storage, shrinkage and deformation after use, have a short service life, and are relatively expensive. They are also difficult to use in open or naturally ventilated spaces—these issues require further research on material durability. The fine mist evaporative cooling system mainly uses hydraulic or pneumatic methods to atomize water, then sprays fine mist directly into the pig house to be cooled, allowing evaporation to cool the air. Its cooling efficiency is lower than that of wet pad cooling: Timmons and Baughman measured a cooling efficiency of 10%–37% at a water pressure of 275–1380Pa. The biggest drawback of this system is its low cooling efficiency, but it has low investment and wide applicability, and is relatively widely used in protected agriculture in developed countries. The centralized atomization cooling system works by cooling outdoor air in a misting chamber (equipped with spraying devices) before it enters the pig house. Air evaporation is relatively uniform in the misting chamber, and there are no strict requirements for mist droplet diameter; unevaporated droplets can be recycled. The system has relatively small cooling capacity, but it has high requirements for the misting chamber. In China, Ma Chengwei et al. conducted research on the boiling-jet centralized atomization cooling system and achieved certain results. The centralized fine mist cooling system is another new type of pig house cooling system, mostly used in enclosed houses such as nursery pens. It consists of nozzle devices, airflow guide curtains, fans, and a water supply system: nozzles are concentrated to spray mist, and fans organize the airflow direction of the mist to achieve cooling. Its cooling effect is approximately 80%, reducing the temperature by 3°C–5°C. This system combines the advantages of fine mist evaporative cooling and centralized atomization cooling: it has significant cooling effects and low investment. However, small mist droplets tend to coalesce into water droplets, leading to incomplete evaporation and excessive humidity in the house—this is a problem that needs to be solved in the system’s further development. In response to this issue, the directional air supply method targets the head area of sows (while leaving piglets in a warmer environment) to cool only the sow’s head. Tests have shown that cooling the sow’s head with water droplets can increase the sow’s daily feed intake, which is beneficial to both sows and piglets.
3. Heating technology
Pig house heating technology is mainly applied in piglet nursery houses and cold regions. Traditional heating methods primarily rely on stoves or heating systems to achieve the desired temperature, but these often result in uneven air temperature inside the pig house and energy waste. In recent years, significant progress has been made in pig farm heating equipment R&D. For example, to address the issue that traditional infrared lamps are fragile and prone to water damage, researchers have developed thermal insulation boards with adjustable heating temperature and step-less infrared heating. Some manufacturers use infrared heaters paired with glass fiber insulation boxes, which have greatly improved thermal efficiency and durability—though drawbacks such as low energy utilization, irrational design, poor performance, and inconvenience of use still exist. Currently, newly developed thermal circulation insulation boxes and bottom-plate PTC heating insulation boxes are equipped with sensitive temperature control systems and control systems that prevent overly intense radiation. They also feature low daily power consumption and ease of use, which can significantly improve piglet survival rates. Ventilation system heat recovery technology is a system device that recovers waste heat through ventilation circulation. During pig house ventilation, the hot air inside the house transfers heat to the cold outdoor air via the heat recovery device, thereby raising the indoor temperature. Currently, plate heat exchangers are commonly used as heat recovery devices: they have a simple and compact structure, and can achieve relatively high heat recovery efficiency even with small temperature differences, enabling effective preheating and pre-cooling of air during ventilation. In recent years, Germany, Switzerland, and other countries have developed new heating and ventilation systems with large temperature differences. These systems fully meet the requirements of pigs for fresh, cool air (for respiration) while keeping their bodies in a warm and comfortable environment. When used in energy-saving insulated pig houses in cold regions, they offer good performance, low construction costs, and energy efficiency. Additionally, plastic warming nest insulation technology can provide effective heat preservation for open pig houses, though it is more suitable for small-scale household farms rather than large industrial pig farms.
Slatted floors have been widely adopted in pig farms, especially in modern elevated intensive pig farming systems—where full or partial slatted floor layouts are used for all stages of pig rearing, from gestation sows and farrowing sows to weaned piglets and finishing pigs. The use of slatted floors not only facilitates manure collection and achieves dry-wet separation, but also improves the sanitation and epidemic prevention conditions in the pig house.
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