My large indoor highland chamber is cooled by a combination of frozen 2 litre pepsi containers and a drop in aquarium chiller. My chamber is constructed completely with 1/4 inch glass. On one side of the chamber is a modified swamp cooler that holds 3 - 2 litre frozen bottles and the aquarium chiller drop in coil. There is a fan at the top which also doubles as my circulation fan. This fan blows warm air from top of chamber around the frozen bottles and aquarium chiller coil. Cool air is vented/comes out at the bottom of the chamber. I also strategically locate 4 - 2 litre frozen bottles at various spots in the chamber. This routinely gives me a temp drop to 55 - 60F with inside air temp at 72 - 74F for about 8 hours. I have been running this setup for about 10 months now. It may sound labor intensive but is not. Lights and aquarium chiller are on an automatic timer. All I have to do is add the frozen 2 litre bottles nightly and remove same in the morning. It takes about 10 minutes in the morning and about 15 minutes at night.
I never thought I could grow highlanders but with this chamber I have had great success so far. Although my chamber is filled to capacity and there are so many more highlanders I would love to grow.