Fans
Some greenhouses are fitted with a mechanical fan in the gable end opposite the door and work as the air flows through them. Opening the door or the vents should set them in motion, but their effect is minimal. Alternatively, if you have electricity installed, you could have a motorized fan. Extractor fans of the sort installed in bathrooms and kitchens are also suitable for greenhouses. Choose one with a thermostat so that it runs only when the greenhouse reaches a certain temperature, and make sure it has louvred 'storm guards', which drop into place when it is not working, to avoid draughts. Some greenhouse fan heaters can be set to run without the heating element. However, unless the thermostat set-up is particularly sophisticated (sensing heat as well as cold), they will run more or less continuously, which could prove to be quite costly.
Solar-powered extractor fans are available at a price comparable to electric ones, but their extracting abilities are not nearly as good. Fans are rated by the cubic volume of air they can shift in an hour. For a smallgreenhouse of 2 x 2.5m (6 x 8ft) you want a fan that shifts about 300cu m (10,000cu ft) an hour — solar ones provide less than one sixth of this.
Don't forget
If you open the door in summer, it is worth considering fixing a net over the space to keep birds out. A warm greenhouse is also a rather popular sleeping area for cats, who you may want to discourage.
When it comes to ventilation, sliding doors are best, because they can be opened just a crack during cooler weather and fully when it is warmer.
Door
The door is an invaluable source of extra ventilation on hot days, and can be used to increase air circulation on days that are too cool for the automatic vents to work. Sliding doors are the most versatile as they can be opened in tiny increments. They also don't need propping to prevent them slamming in a breeze. Nevertheless, be wary of opening them on windy days — strong draughts are not wanted inside a greenhouse, because they cause havoc among plants and can even adversely affect the structure itself.
Doors are usually the only form of ventilation in a polytunnel. Very basic, roll-up types can be secured partly open, as can pricier sliding ones; polythene hinged doors may slam, but at least they won't break.
Avoiding wind damage
On very windy days, check that your automatic openers are up to the job and don't allow your vents to bang to and fro. Tie them down temporarily if necessary. If the wind does get inside a greenhouse, it can behave like a set of bellows, creating quick changes of pressure, which may pop panes out of place. For this reason, if a glass pane ever gets broken you must replace it straight away, otherwise it will start a domino effect, and more will go.
You can visit this flower guide for more information about this article.
No comments:
Post a Comment