Polytunnel ventilation

[Mark_Riga]

This year the temp in the polytunnel got to 50+ quite often even with the doors open. The nectarines in there didn't seem to mind, nor the sweet potatoes but the tomatoes, though I got a reasonable weight of toms, the quality was pretty poor.

The easiest thing to add I think ould be one of these:
https://www.northernpolytunnels.co.u...roof-vent.html

which entails cutting a hole in the roof and pushing it in. Has anyone got one and if so how effective is it? or does anyone have any other ideas that might be easy?

[lolie]

This year the temp in the polytunnel got to 50+ quite often even with the doors open. The nectarines in there didn't seem to mind, nor the sweet potatoes but the tomatoes, though I got a reasonable weight of toms, the quality was pretty poor.

The easiest thing to add I think ould be one of these:
https://www.northernpolytunnels.co.u...roof-vent.html

which entails cutting a hole in the roof and pushing it in. Has anyone got one and if so how effective is it? or does anyone have any other ideas that might be easy?

How big is your tunnel? Would it be practical to shade parts of it?

[Mark_Riga]

its 14'x25'. It is in full sun but definitely needs more ventilation - tried a fan in the doorway but that didn't seem to do much.

[lolie]

its 14'x25'. It is in full sun but definitely needs more ventilation - tried a fan in the doorway but that didn't seem to do much.

It will probably be easier to stop the heat building in the first place, with fleece or shadecloth, than to disperse it. You've got a large volume of air and even if you find a way to circulate it the fresh air will heat up quickly in full sun. You definitely need ventilation as well, though.

I've noticed a trend here away from transparent tunnels and towards either translucent covers or covers which have some degree of shade striping built in. I know that the latter works. My pop-over greenhouses have it and it keeps the temperature moderate even on 35C+ days while still providing plenty of light even in winter.

[MarkPelican]

I suppose it depends upon the design, but my polytunnel has a "tuck-in panel" over the door at each end which causes a through draft as the tunnel warms up. It still gets hot on "bad" days, but there's a noticeable flow of air. Could you create something similar without having to cut into the main fabric?