Ventilation is the key to a good glasshouse. To achieve a satisfactory air flow it is best to have both roof and side ventilation ensuring an even and strong air flow of air through the structure, minimising still air disease such as botrytis. There are two main types and both are normally top hung. All electric motors for roof and/or side vents can be operated via a dedicated Harrier GD controller, which can combine heating and/or vent operation. Full details of these can be found in the ‘Hot Water Heating’ section of ‘Heating Systems’.
These are normally operated manually and there are two options:
A. Individual vents are pushed out and set in position by a notched metal stay, known as a ‘monkey tail’ due to the typical twist at the end of the push rod.
B. For larger runs of vents it is more usual to operate these together. A bank of top hung vents, open a little, is better than one or two fully open individual vents. The operation is via a series of metal linkage, comprising attachment cleats, push rods, levers and a torque tube suspended by elegant cast tube carriers with nylon bushes. The linkage operating the vents being opened and closed via a wonderful solid cast lever handle.
These can be opened in a number of ways:
A. Manually – in a similar way to the side vents, with lever and links.
i, The preferred solution would be to utilize a commercial grade motor and gearbox and operate the vents via a series of toothed push rods. This has the advantage that they will run a very long bank of vents. The downside is that you need one motor and gearbox for every section of glasshouse.
ii, Individual vent motors – one per vent required.
iii, Wax filled – Bayliss vent openers. These push open the vents as the wax expands and they pull shut the vent in a similar way. They are a fine way of opening vents in smaller glasshouses.