my opinion is that you have size the wrong chiller for large volume capacity (6 ft) and demanding 22 deg C. If you looking at about 26 deg C, TR20 should still be manageable.
For your requirement, i think you may need TR30.
Why not you get another chiller to take away the heat to 22 deg C since by getting another bigger chiller you may need to come out with almost same amount of $. With that, you can have another chiller as back up too.
My thinking is if I need a big chiller and I demand lower temp,I will not get One chiller to do this job. 1st reason - u stretched the chiller operation duration i.e. more $ eventually. 2nd reason - the cost of one big chiller is almost comparable to a 2 medium size chiller. 3rd reason - double chiller can always act as back up in the system.
Forget what I suggest, if dun make sense to you.
cheers