To calculate the number of fans in a greenhouse, it is important to have three basic factors available. With these factors, we can calculate the number of greenhouse fans step by step.
Basic Factors
- Greenhouse dimensions: Start by calculating the total volume of the greenhouse and record its dimensions.
- Circulation rate: The circulation rate is the number of times per hour the air is circulated in a greenhouse. Typically, a circulation rate of 2 or 3 is chosen, but in some cases, it can be as high as 12 or more. The ideal circulation rate depends on the site conditions and the crop type.
- Fan specification: Determine how many m³ (cfm) of air a fan moves per hour and its maximum recommended throw. Our greenhouse fans are available in three capacities: 5,000, 7,000, and 8,500 m³/h (3,000, 4,000, and 4,750 cfm). This information is provided on the fan, in the brochure, or on the data sheet.
Current Situation
In this example, we assume a greenhouse volume of 160,000 m³ (5,650,000 cu ft). Multiplying this by a circulation rate of 3 gives a total air movement requirement of 480,000 m³ (16,950,000 cu ft) per hour.
Step 1: Calculate the Number of Fans
The total air movement requirement can be divided by the air volume moved by a single fan per hour. Depending on the fan chosen, the number of fans needed is as follows:
- 4,850 m³/h (2,850 cfm): 99 fans
- 6,500 m³/h (3,850 cfm): 74 fans
- 8,700 m³/h (5,100 cfm): 55 fans
Step 2: Determine Fan Spacing
To prevent airflow interference between fans, ensure the spacing does not exceed the recommended throw. Through practical tests, such as smoke tests, we verified the maximum usable throw. For example, if suspension points are available every 4 meters (13 ft), a fan with a recommended throw of 35 meters (115 ft) should be spaced at 32 meters (105 ft).
Step 3: Adjust for Greenhouse Dimensions
The fans should be evenly distributed along the greenhouse length. In practice, the greenhouse length often is not divisible by the fan spacing calculated in Step 2. In such cases, fans should be installed closer together to ensure optimal coverage and to avoid exceeding the maximum recommended throw.
Specialist Advice
Although you can calculate the number of fans yourself, we recommend an on-site assessment by a specialist for optimal results. Contact one of our specialists for advice.
Additional Resources
This article is part of our 5-page white paper on greenhouse ventilation and circulation. Download it here to receive a comprehensive guide on fan installation in greenhouses.
