TT is our new model, we design it for the market where has a tropical climate. We added a mini tank in the big tank basis on non pressruized solar water heater. The heating system is non pressurized, so the cost is much more lower than pressurized solar water heater. But because of the mini tank, the hot water output is pressurized, same with the pressurized system. We  have tested it in our factory, the efficiency is good.