Finally, I cannot think of any possible way a two storey 50 square home could be cooled by a single evap unit. It just doesn't sound possible. Assuming you have 460 square meters, 2.7m ceilings there is around 1300 cubic meters of air to push around. The biggest Breezair I could find airflow specs for (TBA550) pushes 10830 cubic meters per hour, or a bit over 8 changes per hour. You're a long way short of the target right there. Even two wouldn't be much good. You'd end up with moisture, heat and frustration. Putting a single cooler in is either a cost cutting measure or wishful thinking. Sorry
Lots of very good and valid points made in Lurgen's post. There are also a lot of other considerations that could be made in terms of cooling e.g.
1) House eaves
2) Exterior blinds to shade windows
3) Plants to shade windows
4) Low E Glazing for windows