... 4±2%, stable performance, life span 50 years;(2)Special design structure, 360°heat transfer, excellent thermal conductivity;(3)Optical low ... effect” shaped in the cavity, reduce heat loss;(4)Integrated frame design, nice outlook, stable structure, easy to install;(5)Integrated polyurethane ... and side insulation, less heat loss;(6)12 riser tubes design, better than the normal 7/ 8 tubes, absorber plate ...