Why not just move the plants downstairs for a week and see if it makes a difference before you throw in the towel?

freemangreens,

And what I do next summer with the plants in the green house? I'm really not ready to throw in the towel - but I do need to figure out how to grow a bunch of plants in water under all kinds of conditions.

Mike

On another thread, someone (Joe maybe?) suggested putting water in some bottle and freezing that. then you can drop those in your reservoir to cool it down and it won't dilute your solution.
When you say 'upstairs', do you mean in the attic? what are the ambient air temperatures around your plants and reservoir?
If you're having heat problems with hydro, you'd have the same problem with soil in the same environment.

The ambient temp yesterday afternoon was about 85 degrees. It's not an attic, just an extra bedroom.

Mike

You can also make a swamp cooler for your nutrient:

{{gwi:1012844}}

if the surrounding air is only 85°, your rez must be collecting heat from somewhere else to be 91°(31°C. find out and remove the source of extra heat and the temp should only be around 85, which is not too high (not great, but it'll work)It could be radiant heating striking your medium, warming that which thus, in turn, warms your solution. If so a reflective piece of aluminum foil would help. Plus it will bounce light back onto your plants.
Williards idea will work with two caveats:
1. you have to put a hole in your house to move the air in. not good if this is a temporary situation.
2. swamp coolers also produce an abundance of humidity. might not be something you want to crank into your house.
But they are very good systems at cooling the air.

Yeah, I use half gallon milk jugs filled 3/4 of the way and squeeze some air out of the bottles a bit before freezing to make up for expansion. You still might get some dilution if the cap unscrews at all with the temp changes, but you can always attach a rope to the handle to keep the cap above water. I've not found much comes out, though, even without a rope. The other good thing about the bottles is that if there is a power outage, the ice blocks can be used to keep your food cool in the fridge for longer. Had that happen and I don't have a generator to power the fridge.

I might have to check into that swamp cooler stuff. . .

Swamp coolers also reduce the temperature of the liquid to around the wet-bulb temperature. 90F dry bulb 75% RH air temp is about 80F wet bulb.

Route the air with flex duct so it leaves the space if you are worried about humidity.

I went a little overkill on my system. One of my biggest problems is that during the week Monday-Friday, may garden is 100 mles from where I am. So that means it needs to take care of itself for the week. To combat the temperature problem I just have an aquarium chiller plumbed inline between my resevior and my plants. The chiller turns on when the temp of the nutrient solution goes above 75 degrees F. I grabbed the chiller for 100 bucks like 7 years ago.
Bryan