Who is paying for floodlights, pitch maintenance, heating, initial preparation to get it ready, health and safety checks, hot water, cleaning the changing rooms? The tooth fairy?
Let's take an objective look at this and break it down for you.
First off pitch maintenance and underground heating will currently be a fixed cost to keep it in condition. This is a sunk cost and ACL will have to pay this if there are teams playing there or not. The additional maintenance costs required as a result of a team playing matches will be built into the charge levied. For this academy club, this cost will be very low as they will only be playing 8 matches and the stress to the pitch will very small.
Floodlights costs may or may not be relevant as it depends on when the team plays.
Other costs are entirely dependant upon the volume of people expected to attend. In this case I would say a couple of hundred at most. In which case, costs will be very low as only part of one stand would be opened. Stewarding will almost certainly be taken up by the academy themselves. This is an entirely different beast to opening up the entire stadium to a League one team which is subject to far more stringent stewarding, policing, H&S requirements as well as the variable costs resulting from thousands of fans versus a couple of hundred.
In any case, ACL will make a profit by allowing the academy to play. It is important to understand that income received will be greater than the increased costs incurred.
As for the tenancy, it is a misnomer to state that this academy are 'THE' tenants. They will be 'A' tenant, as they will certainly not have any exclusive rights to the arena. They will have approached ACL to ask to play there and ACL are entirely correct to allow them. CCFC aren't playing there currently and it is the correct business decision to make.