Exergy based MPC formulation question

The paper is attached. Paper: link - http://ieeexplore.ieee.org/document/7... I was trying to understand Exergy MPC formulation but I failed to understand sme trems in it (9th equation): regadring term T with 'r' and 'k' subscripts. Is anyone can explain little bit it would be great.

P.S. I was trying to formulate this MPC for Energy plus formulation C:\fakepath\Screenshot.jpg

The term you are looking at is the room temperature (as denoted by the 'r'). The subscript 'k' is the time step.

Edit: looking at this a bit more thoroughly I think the subscript 'k' is actually the target temperature for the space, although that isn't stated within the image you have linked it would make more sense.