I don't know of any lettuce variety that is happy with hot weather. I'm growing my lettuce indoors under florescent lights.

Kindly reply to my question on summer varieties, as we are facing problems with a hydroponics system which is already installed to produce lettuce. The outside temperature will reach here upto 55 degree celcious so inside will be more than that. However, the contractor didnt provide any provisions except foggers and ventillations to solve this problem. So we are looking for varieties which grow in such conditions, otherwise this system will be useless.

There is no lettuce that will do what you want. Better to focus on heat loving plants like eggplant and peppers. Good Luck. You also need evaporative coolers in that kind of heat. If your contractor doesn't want to put them in, then just shut the thing down.

thanks very much, we shall consider your suggestions

Jose, Is your setup a greenhouse? If so, one consideration ... does it have some kind of sunscreen to filter the sun's rays. How long is your summer. The use of a portable aircon system might be worth considering. The sun screen is something like a fabric what is installed overhead inside the greenhouse that you can draw out when the sun is too hot and and withdrawn when the atmosphere is cooler.

About the portable aircon, you probably would be using it only for the duration of summer. My impression is that Kuwait has cold nights and hot days in summer and cooler days in winter. In which case, the aircon can be turned off at night. This is just a thought. It's practicability depends on the conditions there which only you can assess. Check the website below.

http://www.labsafety.com/store/item/40770-1/

thanks, in kuwait the temperature will reach upto 50 degrees even in the night also. the greenhouse is already finished and trails are going on. unfortunately (for the contractor) the temperature hasnt gone up above 35 yet but sure it will go up soon.
there is already a screen inside the greenhouse to resist sunrays and ventillation, during hot the ventillation opens and air will come inside. but in kuwait, the temperature and sandstorms are synonyms. so all the dust will come inside when the vent opens. if donot open the temp get up, eventhough there is foggers.
still the aircon will be ok. how about evaporative coolers?

I am having a similar problem, in my case Texas is not that hot. Has anybody had any experience with a good tasting lettuce grown in direct sun during the summer?

I only have a small NTF setup with 3 lettuces since I am still learning. I have covered the plants with clear plastic, but I have a small opening. The plants are next to my covered patio facing SW and there is a big wall to the SE. So I do get sun starting at noon.

now we have >40 degree celcious heat. all the lettuces are getting either dried up or malgrowing. the temp will be up to 55 near future. possibly the greenhouse will be a big mistake.

Can someone explain to me why grow your own lettuce? Does it taste better than store bought ones?

There are several reasons one might wish to grow their own lettuce.
First, comercial produce is usually not bread for taste/nutrision. It is usually chosen for how well it holds up to production/transport and shelf life. If you grow your own, you can choose varietys that wouldn't do well comercially but taste great and are better for you. Those particular varietys are usually going to be quite $$ if/when they ever get to market.
Second, You can't get much fresher than harvest-rinse-plate all in the matter of minutes and you can't get that from store bought.
Third, if you grow it yourself, you know what gets used on it (chemicals/firtilizers). I took up hydroponics around the time of the spinach/ecoli problems last fall.
Finally, (this example is bassed on my own experience) if you buy a head of lettuce at the store, you usually only buy one variety since buying more would mean too much that couldn't be used before it went bad. If you are growing a variety at home, you only need cut as many leaves as you want off any one variety, hence you can have a salad of all different varietys without a bag of lettuce spoiling in the bottom of the fridge. I know, you could buy the bagged lettuce that sometimes has a variety but they get $$ and usually only last a short time before they spoil anyway.