Hi email@example.com, The summer heat can be a challenge... there is no one "magic bullet" solution to keeping the TG cool (yet). Some suggestions - leaving out the "Move the TG Indoors" option as per your request:
Keep the TG nutrient tub full
Keeping the nutrient tub full at all times slows down the rate at which the nutrient solution increases (or decreases) its temperature.
Insulate the TG nutrient tub
Wrapping the TG nutrient tub with water resistant insulation will help keep heat out and cold in.
Keep the TG off the ground
Use a TG Dolly or similar device to provide an air gap between the TG and the ground.
Place frozen water bottles in the TG nutrient tub
Rotate frozen water bottles daily between the freezer and the TG. Tip: If you don't use a Support Cage or do use a Support Cage but do not lock it down to the TG tub, you can fill old 1-gallon TG Mineral Blend bottles 5/8 full with water and freeze them. If you cannot lift the TG base to insert large bottles into the tub then use the largest food grade plastic bottles you can find that will fit through the TG tub access port.
Shade the TG from direct sunlight
Use shade cloth or move the TG inside a screened-in patio / lanai or move the TG to an area that receives direct sunlight in the morning and dappled sunlight in the afternoon.
Stick to growing heat tolerant plants
Know which plants grow best during hot summer months in your area... and which ones do not.
Build a nutrient chilling system
If designed properly, a nutrient chilling system is an extremely effective solution to keeping your TG cool. Unfortunately, it is an expensive option that can easily cost several hundreds of dollars. There is currently no off-the-shelf system available for the TG so you would have to be famiular with the design requirements, purchase the parts, and DIY.
Take the hot summer months off from growing
Sometimes fighting mother nature is just not worth the effort. Use this time to break-down the TG and perform a complete system cleaning and prepare / plan for growing soon as the weather improves.
Here are a few reference articles you may find helpful:
Helpful Advice for Gardening in the Heat
6 Summer Season Tower Garden Tips
How to Grow a Stellar Garden, Even In the Shade
Planting Calendar by Location
(the following docs are important no matter where/when you grow with the TG)
Tower Garden Fundamentals
How to Mix TG Nutrients
TG Nutrient Solution Strength Selection