Greenhouse Fan CFM Calculator

Choose Greenhouse Style:

Peak Height:

Sidewall Height:

Width:

Length:

Air Exchange Rate (%):

Greenhouse Cubic Footage:

Ideal Fan CFM for Air Exchange Rate:

1. What is a Greenhouse Fan CFM Calculator?

Definition: This calculator determines the ideal fan CFM (Cubic Feet per Minute) required for air exchange in a greenhouse, based on its style, dimensions, and desired air exchange rate.

Purpose: It is used in greenhouse design to ensure proper ventilation, maintaining optimal temperature and humidity for plant growth.

2. How Does the Calculator Work?

The calculator uses the following steps:

Volume Calculations:

Quonset Hut: \( \text{Volume} = \pi \times \left(\frac{\text{Width}}{2}\right)^2 \times \text{Length} \)
Gabled A-frame: \( \text{Base Volume} = \text{Sidewall Height} \times \text{Width} \times \text{Length} \), \( \text{Roof Volume} = 0.5 \times \text{Width} \times (\text{Peak Height} - \text{Sidewall Height}) \times \text{Length} \), \( \text{Total Volume} = \text{Base Volume} + \text{Roof Volume} \)
Lean-to: Same as A-frame but divided by 2
Geodesic Dome: \( \text{Volume} = \frac{\pi \times \text{Peak Height}^2}{3} \times (3 \times \text{Radius} - \text{Peak Height}) \), where \( \text{Radius} = \frac{\text{Diameter}}{2} \)

CFM Calculation: \[ \text{CFM} = \text{Volume} \times \left(\frac{\text{Air Exchange Rate}}{100}\right) \]

Steps:

Select the greenhouse style (Quonset Hut, Gabled A-frame, Lean-to, or Geodesic Dome) from the dropdown
Enter the peak height, width (or diameter for Geodesic Dome), and length (if applicable), selecting the unit (ft, m, in, cm)
Enter the sidewall height for A-frame and Lean-to styles
Enter the air exchange rate as a percentage
Convert all dimensions to feet
Calculate the volume based on the selected style
Calculate the CFM using the air exchange rate

3. Importance of Greenhouse Fan CFM Calculation

Proper ventilation is crucial for maintaining a healthy greenhouse environment. Calculating the correct CFM ensures adequate air exchange, preventing issues like overheating, high humidity, and poor plant growth.

4. Using the Calculator

Examples:

Quonset Hut: For \( \text{Width} = 20 \, \text{ft} \), \( \text{Length} = 30 \, \text{ft} \), \( \text{Peak Height} = 10 \, \text{ft} \), Air Exchange Rate = 100%:
- Volume = \( \pi \times \left(\frac{20}{2}\right)^2 \times 30 = 9424.78 \, \text{cubic feet} \)
- CFM = \( 9424.78 \times 1 = 9424.78 \, \text{CFM} \)
Gabled A-frame: For \( \text{Width} = 20 \, \text{ft} \), \( \text{Length} = 30 \, \text{ft} \), \( \text{Peak Height} = 10 \, \text{ft} \), \( \text{Sidewall Height} = 6 \, \text{ft} \), Air Exchange Rate = 150%:
- Base Volume = \( 6 \times 20 \times 30 = 3600 \, \text{cubic feet} \)
- Roof Height = \( 10 - 6 = 4 \, \text{ft} \)
- Roof Volume = \( 0.5 \times 20 \times 4 \times 30 = 1200 \, \text{cubic feet} \)
- Total Volume = \( 3600 + 1200 = 4800 \, \text{cubic feet} \)
- CFM = \( 4800 \times 1.5 = 7200 \, \text{CFM} \)

5. Frequently Asked Questions (FAQ)

Q: What is CFM?
A: CFM (Cubic Feet per Minute) is the volume of air moved by a fan per minute. It indicates the fan’s capacity to ventilate the greenhouse.

Q: Why is the air exchange rate adjustable?
A: The air exchange rate allows you to adjust the ventilation speed. A higher percentage (e.g., 150%) means faster air turnover, which may be needed for hotter climates or specific plant requirements.

Q: Why does the Geodesic Dome not require a length input?
A: The Geodesic Dome is approximated as a spherical cap, where the diameter (width) and peak height are sufficient to calculate the volume.

6. Reference

https://greenhouseemporium.com/greenhouse-fan-cfm-calculator/

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