Originally Posted by mr_X
In my case, the air from outside was a better option than the extremely humid air inside. I had mold problems and before the fan pulling fresh air, I had puddles of water on all the window sills throughout the house, even a floor away. After the fan, which was only 30 watts anyway, the water disappeared. I also should mention, I was pulling air, not pushing it, so I was removing air from the basement and it was being replaced by air coming from the rest of the house.
Ok, my situation is different. The building is isolated from the main house and is independently heated. I did a bit of research into fans.
A basic sucker/blower fan is the least economical and the worst for heat preservation as it has no physical defence against the wind.
A basic sucker/blower with mechanical actuators to close the vent is the next best thing.
The problems with both types of fan, they are not geared towards anything you need, humidity control (that's partly why you get puddles) and heat loss, key items for a tropical environment. Maybe in a house you may not consider the heating as it is already on but I needed to heat the room and preserve that heat. I plan to use an ordinary fan with flaps, wired up to a thermostat (T-) to prevent overheating during late summer, not sure if I need it yet? It's rained all year!
Next up is a humidistat based fan, same thing applies, the type with a mechanical actuator is better. These in either configuration are overall a better choice as they only work when they need to, a level that you can set and adjust.
The only problem with these humidistat controlled fans is heat loss. It is better than regular fans as it isn't working full time. At least you have some control.
For all fan types the mechanical flap type is better for heat preservation, except those fans with re-circ. In all fan types heat loss is a real problem. You heat your tanks, they are capable of keeping an unheated room at or around 17C in deepest darkest winter, ok that room is damp, but warm. Add a fan, you get numbers around 10C room temp. Now with a heater you get whatever air temp you choose. 22c is what I heat the room to. It's cheaper than individual tank heating, it also offers more stability to the tank temps, from 22c each tank is lifted to its correct T by normal in tank heaters. It's very cheap this way. Now to preserve that heat?
I'm not saying you are wrong. The transport of moist air from the room to the outside is the goal, any fan will do. I think there are much more economical ways of doing it. The running cost of the heat recovery unit is similar to an ordinary fan, it just saves you money every second of the day, eventually it will pay for itself.
If the room air temp is considerably colder than the moisture content of the air (assuming it's tank water) you get cold strike, that's where the moisture sticks to cold surfaces normally externally fixed metal/glass and possibly plastic. This is apparent on windows during winter, closed up bedroom windows spring to mind, and copper pipes in the bathroom.
The heat recovery fan I use runs 9watts full time and 46w on boost mode.
Kair Heat Recovery Room Ventilator K-HRV150 | Kair Ventilation
The boost mode is dependent on R/h & T. It's on sometimes but mostly it runs at trickle speed. Also the night mode keeps it from switching on during darkness/lights off, handy for keeping the neighbours happy, whisper quiet perfection. The difference this thing makes is unquestionable.
(Based on my tests