I have a building that has 6 20ton rooftops, 4 10ton rooftops and 3 71/2ton rooftops. All are 2 stage heat and 2 stage cooling. Do you guys know of anything I could use to have a central control system for these units? they are also gas heat and electric cooling. Not trying to spend $30,000.00 for some complicated e.m.s., but something like some remote stats i used to use. Building manager can control operation of systems. Right now they have standard mercury bulb stats and broken up lock boxes.