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Vivarium - air

The third factor of importance is ventilation, without ventilation several things will go wrong completely

All windows will fog up due to the humidity and the fact that the room temperature and humidity is usually lower as in the vivarium

Most plants will rot away, especially orchids and humidity sensitive bromelaids and tillandsias. Those plants are used to a lot of water, but also a lot of wind too in the higher parts of the trees in the forest.

The temperature will go out of control and more than 30 degrees celius is reached easily with several 100rds of Watts of lighting and heating.

Natural ventilation and convection

Not all vivaria require forced ventilation, but most larger ones do. When the front window exceeds 50 cm forced ventilation will keep the window from fogging up, which will almost inevitably happen otherwise. The standard tropical rainforest vivarium design uses somekind of opening under the front window ( several millimeters 3 - 4 cm above the water level ) through which fresh ( dry ) air can enter. A larger opening ( several centimeters ) is placed at the top, behind the lights at the back of the vivarium. Both openings should be covered with metal mesh capable of withholding fruit flies or at least the frogs. This system will cause a standard convection of air along the front glass. usually the plants and design of the vivarium will force the air to flow along the window and not too much into the vivarium causing draft. Generally the level of ventilation and heating by the lights should be capable of drying the leaves of the plants in a few hours, otherwise almost all plants will rot and die. The figure below illustrates the standard convection, which can be forced by an electrical horizontal ventilator on top of the ventilation slit in the top back part of the vivarium.

Forced ventilation

Forced ventilation is the third item which should be regulated to keep the balance in temperature and humidity in the vivarium. A change in ventilation will always affect both parameters.

High ventilation will result in high amounts of dry and cold air to enter the vivarium, via evaporation of water ( which reduces the temperature even more ) and heating of the lamps this stream of air will be treated to reach the adequate conditions. Too low temperatures can be solved with reduced ventilation, too high temperatures usually with increased ventilation.

Low ventilation will result almost immediately in fogged windows and eventually in high to very high temperatures. If the ventilation quits the temperature usually inceases with 5 - 8 degrees celcius in the vivarium.

Ventilation is usually reffered to in refresh rates. Based on the capacity of the ventilator the refresh rate in my vivarium will be 2 times a minute. But this value can be used as a rule of thumb for the start. The actual ventilation is not measured, but this will be reduced by the resistance of the front slit, the grids and the distance between low front and back top of the vivarium.

The ventilator requires the 3th timer to controll the vivarium conditions as it should be. As explained above the temperature will rise immediately when the ventilation quits, even when the lights are out the temperature first increases with several degrees Celcius and then lowers very slowly due to the insulation and heated mass inside. Therefore i leave my ventilation on during the night for several hours after the lights have been switched of. This will reduce the temperature in the vivarium towards the desired 20 degrees Celsius and not the 28 degrees Celsius i recorded when i bought a max/min thermometer. When the lights switch on, i switch on the ventilator one hour later. This will heat up the vivarium quicker and causes the desired temperature to be reached earlier. During misting the ventilation is switched off, since it blows out a lot of water and the mist is not very good for the electrical ventilator.

For my large vivarium I use an air circulation and heating system to control temperature, cool the lamps, heat the vivarium and keep the air moving to dry the plants quickly to prevent rot. With the 3 computer fans I use there I create the same ventilation rate, but the water evaporation and energy requirements are far less than without circulation. This system is very much advisable for large vivaria of more than 1 meter height. A thermostat with sensor insode the vivarium and a 300 W air heater in the bottom section controls the temperature to perfection.

Ventilation slit under sliding front window

It is not very simple to make a stable and sturdy ventilation slit under a sliding window which weighs quite a lot ( around 1 kg is easily reached ). The system i used is safe and simple. One H profile of aluminium of 6 mm width which and a aluminium U-profile of 4 mm. The U profile is fitted inside the H profile and a number of 3 mm holes are drilled in the H and U profile together. On the visible side ( the front ) one can drill a few ( 3 - 6 holes ) , but a lot of holes should be drilled at the other side ( inside of the vivarium ( at 1 cm intervals ). The sliding glass will fit in the top of the H profile and will slide through this. The U and H profile are kitted on top of the vertical bottom glass. For the sliding window 4 mm glass is used, for the bottom glass ( holding the water ) and the weighth , 6 mm glass is used. The illustration to the side demonstrates the principle ( bottom glass not drawn ).

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