Tag Archives: ventilation

Air Circulation & Humidity Control

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Even though many people would consider air circulation and humidity control as totally separate functions, they are closely intertwined.

You may have the proper sized openings to create the proper amount of air changes.

You could still have hot or cold spots in your greenhouse if you do not have proper circulation.

The same can be said about removing humidity.

For a ventilation system to have optimum efficiency and benefit, there must be balance. Having proper air circulation allows you to achieve that balance.

Horizontal air flow (HAF) fans typically come with a cage around the blades, a hanger bracket and a cord with plug. This allows them to be attached or suspended from the frame at the proper location. The motors are rarely more than 1/3 hp.

HAF fans always are installed in pairs and blow in opposite directions. A short greenhouse will have one in the front right corner and in the back left corner. A longer greenhouse will still have one in the front right and back left but also two half way down the length. The one on the right will blow in the same direction as the front right. The one on the left will be blowing in the same direction as the back left.

HAF fans should never be mounted in such a way that allows them to be blowing directly at plants. This would create an uneven drying. Some people will aim the fans slightly in the direction of the cover to ensure maximum air flow along the cover to maintain dry covers.

These fans run continuously to ensure that the temperature and humidity are spread evenly throughout. It also ensures that your thermostat or humidistat are reacting to air or moisture that is representative of what is going on in the greenhouse.

Ventilation is a difficult area of greenhouse production to get perfect. The more attention you pay to the details and modify what you are doing, the greater your production. The tricky part is that with all the variables, no two years will be the same. Carefully consider all your options and the situation you’re dealing with and you will have success!

Air Circulation & Humidity Control

Posted on by

Even though many people would consider air circulation and humidity control as totally separate functions, they are closely intertwined.

You may have the proper sized openings to create the proper amount of air changes.

You could still have hot or cold spots in your greenhouse if you do not have proper circulation.

The same can be said about removing humidity.

For a ventilation system to have optimum efficiency and benefit, there must be balance. Having proper air circulation allows you to achieve that balance.

Horizontal air flow (HAF) fans typically come with a cage around the blades, a hanger bracket and a cord with plug. This allows them to be attached or suspended from the frame at the proper location. The motors are rarely more than 1/3 hp.

HAF fans always are installed in pairs and blow in opposite directions. A short greenhouse will have one in the front right corner and in the back left corner. A longer greenhouse will still have one in the front right and back left but also two half way down the length. The one on the right will blow in the same direction as the front right. The one on the left will be blowing in the same direction as the back left.

HAF fans should never be mounted in such a way that allows them to be blowing directly at plants. This would create an uneven drying. Some people will aim the fans slightly in the direction of the cover to ensure maximum air flow along the cover to maintain dry covers.

These fans run continuously to ensure that the temperature and humidity are spread evenly throughout. It also ensures that your thermostat or humidistat are reacting to air or moisture that is representative of what is going on in the greenhouse.

Ventilation is a difficult area of greenhouse production to get perfect. The more attention you pay to the details and modify what you are doing, the greater your production. The tricky part is that with all the variables, no two years will be the same. Carefully consider all your options and the situation you’re dealing with and you will have success!

Air Circulation & Humidity Control

Posted on by

Even though many people would consider air circulation and humidity control as totally separate functions, they are closely intertwined.

You may have the proper sized openings to create the proper amount of air changes.

You could still have hot or cold spots in your greenhouse if you do not have proper circulation.

The same can be said about removing humidity.

For a ventilation system to have optimum efficiency and benefit, there must be balance. Having proper air circulation allows you to achieve that balance.

Horizontal air flow (HAF) fans typically come with a cage around the blades, a hanger bracket and a cord with plug. This allows them to be attached or suspended from the frame at the proper location. The motors are rarely more than 1/3 hp.

HAF fans always are installed in pairs and blow in opposite directions. A short greenhouse will have one in the front right corner and in the back left corner. A longer greenhouse will still have one in the front right and back left but also two half way down the length. The one on the right will blow in the same direction as the front right. The one on the left will be blowing in the same direction as the back left.

HAF fans should never be mounted in such a way that allows them to be blowing directly at plants. This would create an uneven drying. Some people will aim the fans slightly in the direction of the cover to ensure maximum air flow along the cover to maintain dry covers.

These fans run continuously to ensure that the temperature and humidity are spread evenly throughout. It also ensures that your thermostat or humidistat are reacting to air or moisture that is representative of what is going on in the greenhouse.

Ventilation is a difficult area of greenhouse production to get perfect. The more attention you pay to the details and modify what you are doing, the greater your production. The tricky part is that with all the variables, no two years will be the same. Carefully consider all your options and the situation you’re dealing with and you will have success!

What is and isn’t “proper ventilation”?

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Proper ventilation, in a nutshell, equals adequate air changes and movement while maintaining adequate light levels and humidity in a given area. Proper ventilation is about proper balance.

The challenging part of achieving this balance is that there is such a wide range of requirements for different plants. It is important to identify what is ideal for each variety that you are growing. It will not be feasible to have a perfect climate for each variety of plant, but you really should avoid grouping together plants with a wide difference in requirements. That would simply ensure that you are not doing very little properly.

Putting shade cloth over a greenhouse may lower the temperature to an acceptable level for your plants but that does not equal good ventilation. You may be depriving the plants of their critical light requirement plus you are not doing anything to enhance air movement.

Turning on an exhaust fan may create the required amount of air changes or movement, but with a temperature far below the plant optimum, your plants still will not achieve their potential. Fans also draw air in a straight line from intake to exhaust. This does not address “stagnant corners”.

Many times, light equals heat. They go up together and go down together. It is important to understand how and why they are controlled differently and where the overlap on that control is.

Generally speaking, proper air changes equals one air change per minute. Some plants require more and some can get by with less. For this, you will need to know what the air volume is for your building. It is a little trickier to calculate this on a gothic or quonset shaped structure. Using the length x width x 80% of peak height will give you a close enough number in either cubic feet or cubic metres.

With the next 4 posts we hope to create a more thorough understanding of how to achieve a good environment for your plants. This information will be helpful as to research options so that you can balance costs with benefits and return. Especially in the area of ventilation, many times expenses associated with proper ventilation will be offset by exponentially higher returns.

Roll Up Side Wall Considerations

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Ventilation can either be done passively through openings or mechanically with fans. Roll up sides are an economical way of getting lots of air movement since no electricity is required. Roll up sides become even more effective when used on longer buildings. Roll up sidewalls are often used in combination with a small exhaust fan for early and late season ventilation when opening the sides is not practical.

If a structure is very exposed, it is best not to open more then 3’ in height due to potential of wind damage. If a structure is extremely sheltered, it is best to go even up to 6’ to create maximum opening. Roll up sidewalls are most effective when used in combination with peak end wall vents to create a “chimney effect” to draw warm air out of the building, especially when it is very calm. These vents are effective for air movement when outside temperature does not allow opening of the sides.

When a structure has a low profile, you will need to be careful during rainy periods due to moisture getting into the structure area. High profile structures (with straighter walls) usually work better with roll up sidewalls. When preventing a floor draft is an issue, the roll up mechanism can be raised and then the structure is lined with a skirt for the bottom 2’-3’. When using this method of ventilation, it should always be done on both sides. An effective use of this method includes opening the “downwind side totally and the opposite side on marginally.

Download our Roll up Side Wall Installation information sheet for more information

27'wide with Roll Ups roll up sides

Properly Venting a Building

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Properly venting a building is a critical consideration when planning your building.

Getting rid of the initial ground moisture, quickly, when you have erected your new shelter is something many people do not think of. Quality air changes for plants or animals is something that automatically comes to mind. Getting rid of moisture is equally as important for storing your valuables.

Vent4Since warm air holds moisture and warm air rises, it is important to have venting capacity as high as is possible.

Venting through the roof, with individual turbines or a continuous roof vent, is the most effective but also the most costly.

This is only really necessary when you are in a very protected spot and there is a real need to keep the temperature down in a long building.

vent3Most medium length buildings that have the ends facing into the prevailing winds, can be adequately vented with gable end peak vents.

  • Make sure that these openings are as big as possible and as high as possible.
  • It is also important to make sure your “windows” can withstand the winds in your area.

Our centre pivoting gable vent has filled this requirement very effectively.

  • With part of the window going in and part of it going out, the wind can never get hold of it.
  • With the top and bottom rope through a double pully on the ridge, it is easy to maintain precise control over the opening area

As with all the other considerations, please do not hesitate to contact us with your specific set of circumstances and challenges