Livestock and poultry housing experts offer advice on how to effectively use wet‑pad cooling systems during the summer.

Principle of Evaporative Cooling with Wet Curtains

Evaporative cooling using wet pads works on the principle of heat absorption during water evaporation, thereby reducing the temperature of air entering the poultry house and lowering the internal temperature. In hot weather, under normal conditions, passing hot air through a wet pad can reduce its temperature by 5.5–6.5°C; when combined with the wind‑cooling effect, the perceived temperature for the birds can drop by as much as 8°C. The cooling performance depends on the wet‑pad area, pad thickness, pad permeability, and the degree of air tightness of the system.

1. Wet curtain area

The wet pads are installed at the air inlets on the gable and side walls of the poultry house. During installation, insulated extension sheds should be mounted externally to increase the inlet area and prevent cold drafts from blowing onto the birds.

Wet curtain area = Total ventilation volume in the house / Air velocity through the curtain / 3600 s

Taking a chicken house with a stock of 10,000 birds as an example, if the average body weight per bird is 1.8 kg and the maximum ventilation rate per bird is 8 m³/h/kg, then the total ventilation rate in the house equals 10,000 birds × 1.8 kg/bird × 8 m³/h/kg = 144,000 m³/h.

Based on an air‑flow rate of 1.7 m/s across the wet pad, the required installation area for the wet pad in this chicken house is calculated as follows: total ventilation volume inside the house divided by the air‑flow rate and converted to square meters per hour: 144,000 m³/h ÷ 1.7 m/s ÷ 3,600 s = 23.5 m².

2. Wet Curtain Thickness

The typical thickness of wet‑curtain paper is 10–15 cm. With a 10‑cm‑thick curtain, the air velocity across the curtain is 1.5 m/s; with a 15‑cm‑thick curtain, it is 1.8 m/s.

3. Wet-Curtain Permeability

The permeability and surface area of the wet‑curtain paper’s ventilation holes determine the cooling effect.

4. Wet Curtain Airtightness

When installing the wet curtain, ensure a tight seal. When activating the wet curtain, close the small ventilation windows on both sides to achieve optimal cooling. Maintain a negative pressure of 20–25 Pa in the poultry house, and keep the air velocity across the curtain at 1.5–2.0 m/s; higher speeds do not necessarily yield better results.

How to Use a Wet Curtain

1. Wet curtain activation at different ages

During the brooding period (0–3 weeks of age), evaporative cooling with wet pads is not recommended. In the early rearing phase (4–10 weeks of age), the system should be activated at 34°C; in the late rearing phase (11–18 weeks of age), at 32°C; and from 19 weeks of age onward, maintain a temperature range of 28–32°C.

2. Opening wet curtains at different humidity levels

Under conditions of relative humidity below 60% and high temperatures with low humidity, use air cooling if the day’s maximum temperature is below 35°C; if it is 35°C or higher, wet‑pad cooling is required, with the activation threshold set at 32°C.

When the relative humidity is ≥70% and the weather is hot and humid, use air cooling if the day’s maximum temperature is below 32°C; if it is 32°C or higher, wet‑pad cooling is required, with the activation threshold set at 30°C.

When relative humidity is ≥80% and conditions are extremely hot and humid, use air cooling if the day’s maximum temperature is below 29°C; if it is 29°C or higher, employ wet‑pad cooling, with the activation threshold set at 28°C.

3. Duration of wet curtain operation

Use both a temperature‑controlled timer and a time‑controlled timer to regulate the operating duration of the wet pad system. For the initial activation, set it to run for 10 seconds and pause for 4 minutes and 50 seconds, allowing the flock to acclimate to the cooling effect. Thereafter, adjust the wet pad runtime based on outdoor temperature, humidity, and in‑house air velocity.

Typically, the wet pad becomes fully saturated within 0.3 to 1 minute after activation; a cycle of 5 or 10 minutes is recommended—either running for 1 minute and pausing for 4 minutes, or running for 1 minute and pausing for 9 minutes.

4. Precautions for Using Wet Curtains

1. Do not use the wet curtain until all fans have been turned on;

2. For evaporative cooling pads, a lower circulating water temperature is not necessarily better;

3. Visually, the wet curtain paper should appear wet when moist and dry when dry, ensuring effective cooling.

Maintenance of the Wet Curtain

1. Before using the wet curtain, first remove any debris from the curtain paper and rinse it 1–2 times with Ouke disinfectant. Next, inspect the water pump, power supply, inlet pipe, spray nozzles, and the filter on the water line to ensure they are clear and unobstructed. Fill the reservoir with clean water to keep the water delivery system flowing smoothly and the motor operating properly. Finally, cover the wet curtain with a mesh screen to prevent chicken feathers and willow catkins from clogging the ventilation holes in the curtain paper.

2. During operation of the wet curtain, monitor whether water distribution is uniform, check for leaks in the water‑delivery pipes, and ensure the water level in the reservoir remains normal. Also assess the curtain’s airtightness and look for any ingress of hot air. Inspect the system daily and regularly observe the negative pressure inside the poultry house. If, with the fan operating normally, the negative pressure rises abnormally, this indicates that the wet‑curtain paper’s ventilation holes are blocked and should be cleaned promptly.

3. After using the wet curtain, clean the mesh screen covering the wet curtain paper once daily; conduct a weekly test of the generator and water pump, and check cable temperature and any unexpected fan shutdowns; flush the inlet pipe filter every two weeks; and remove debris from the water storage tank once a month.

4. After the wet curtain is taken out of service, drain the water from the supply pipes and the reservoir, and seal the reservoir tightly to prevent dust and debris from entering. Store the pump motor properly to protect it from freezing damage. Cover the wet‑curtain paper with canvas or plastic sheeting to keep it clean and insulated. Keep heavy objects away from the wet curtain, and avoid exposing the wet‑curtain paper to corrosive substances such as disinfectants or quicklime. Before transferring the flock, thoroughly wash the wet‑curtain paper from top to bottom, perform a complete disinfection, allow it to dry completely, and then set it aside for use.