Keeping Small Rooms Cool / regulated with larger adjacent rooms

[musicroom]

Hello, we are building some small music rooms (80-90sqft), where 2 people will be at a time. In the past, we had trouble keeping the inside of these rooms cool, while the outside hallway (where the thermostat was) was cool. There are several factors which we have done to improve this in our new build:

1. Spray Foam insulation vs traditional
2. MUCH smaller window in the room (before was two large windows, now only one small one)
3. Larger Air Vents and intakes

But, we are deciding this time between a 16 Seer Single Stage System, and a 17 Seer 2-Stage system. What I am wondering is if we get a 2 stage system, will it keep blowing cooler air at a lower rate longer, helping to regulate the smaller music rooms better, so we don't have the same issue as before. Or have we addressed the main issues with the above improvements?

Any thoughts or suggestions are very welcome!

Thank you!

- on a side note- does anyone know how having a 2-stage system affects one's "demand" charges for their commercial energy rates?

[pecmsg]

You need an engineered Constant Volume System.