Air circulating fan- no energy cost Solved

[Ernie]

Sometimes at bedtime other interests are but a memory so I apply my mind to eccentric issues such as designing useless things that I can put to practical use.

In order to save electric costs and thus help the planet (dont lets go there again!) I have been drawing plans for an air circulating fan operated by the wind. In the next few weeks I intend to hit my lathe and make a spindle to run in low resistance precision bearings One end of the spindle will have an efficient propeller wind driven and inside the greenhouse will be the usual fan blade you see on commercial units. If I get this right even a slight wind will turn the prop and thus I have perpetual air circulation at no cost.


Well that the theory. may need to think about gearing it and wind direction comes into the equation but I think its worth the effort. Maybe I can save some coin to buy more plants!


Elaine thinks I am eccentric well she may just be right!


I hope this is not too far of topic if it is mods then feel free to pull it I wont complain.

[Roy]

Hi Ernie,
I posted this idea some time ago. At the time I was considering a bicycle wheel hub as a bearing and making the outer blades larger than the inner blades to compensate for the inevitable resistance of the bearing.
Never did get around to producing it.
I think another factor that has to be given serious thought is the balance and the structural strength of the mount, I would hate to have a side of the greenhouse damaged by a tearaway fan during a gale whilst I was away

Ps Now I come to think of it they used to manufacture a plastic ventilation device about 9" across that you could fit in a window and operated in a similar manner - maybe they still make them?

[ralphrmartin]

Sounds like an interesting idea.

Its pretty clear this could help keep temperatures reasonable in summer, and help prevent scorch.

However, I have always been rather in two minds about having a fan going in autumn / winter / spring:

The positive side: should help to keep moulds and other fungi at bay.

The negative side: keeps pushing the warmer air in the middle of the greenhouse to the windows, and will increase heat losses => higher heating bills (and not environmentally friendly).

What do others think?

[Vic]

My fans run 24/7/365 and I've never had any problems, I can only think they must be beneficial - it can't hurt to have air circulation all year round.

[Ernie]

Ralph. When I started building and designing high speed hydroplane models I studied aerodynamics and I think I can design vanes on the inside of the greehouse to create optimum flow around the entire structure.

Because My greenhouse is self built primarily of wood i can build a structure into one panel that wont tear out in high winds but I recognise your point.

[Guest]

I run fans 24/7/365 to circulate the air and keep the temperature roughly the same at all levels. I draw air from the roof levels and though a pipe system pump it out at the low staging level. I also use gas heaters and this system makes them highly efficient because the air circulates and passes over the thermostats. This stops the problem of warm air being trapped at the top of the greenhouse and the lower levels being very cold, incidentally where the thermostats for the gas heaters are making then highly inefficient.
I like Ernie's idea but worry that on the hot still days of summer when scorching is a problem there will be no circulation.
I may be off target but wouldn't a solar panel powering a fan be better as it would generate more power when the sun is strongest just when we need summer air circulation.

[Nick]

I think the major route for heat loss in a g/h is thru the ceiling - with no fan, hot air from the heater goes directly to the roof, giving a disproportionately high temperature up there where there are usually no plants, and a cold base area. Having a fan will give you a lower differential between internal and external temperatures hence reducing heat loss and therefore reduce heating bills, though you would need to offset the fan running cost against this.
I`m not exactly sure how the rate of heat loss relates to temperature difference, but it`ll be somewhere between a square and fourth power relationship i.e. if you double the diffence between outside and inside your heating bills will increase from between 4 and 16 fold. Basically, you want g/h to be at the lowest temp to keep plants alive, and for there to be no hot spots,
NIck

[Chris43]

Its a neat idea, Ernie, I wonder what level of wind / size of external - internal blades would be needed to create the same amount of air movement as an electric fan.

My fans (x2) run all year round, and the energy cost is, apparently, ?30 approximately per year, and they each move, according to specs 460cu m per hour. Its not a huge cost either in ? or energy use, and I'm sure I can do many other things to try to save energy in the greenhouse, like trying 1C less on the thermostat, or two layer sof bubble glaze on the roof....

But its the equivalence to electric fans that I'd be interesting in seeing - any views?

[Cactus Jack]

What about using two old car radiator fans poss. various sizes ??

[Ernie]

Whitestone gardens used to have two greenhouses that utilised big truck radiators and a big fan.

As I remember it hot water ran through pipes into the radiator and the big fans blew air through the radiator thus circulating the warm air. Neat idea. The two greenhouses in question have gone due to the high winds in yorkshire.( They were the ones behind the big sales house)

Stephen I intend to visit the local scrap yard to see what I can find, dont want the electrics just the fan blade. I have a prop for the outside its similar to the ones you see on wind turbines.

Still air up here in north East England is about as scarce as an honest politician therefore I doubt it will be inoperative very often!