A new type of enclosed evacuated tube solar collector integrated with building envelopes is introduced. The distinguished feature of this new device is that gaps between the evacuated tubes are filled with sheet glass and the evacuated tubes, sheet glass and edges form an enclosed cover on the building envelope. The heat loss behind this kind of solar collector is studied theoretically and experimentally and compared with conventional open evacuated solar collector. The results of research indicate that: 1) The air chamber temperature of the enclosed solar collector is rising with the increasing outside temperature and it is much higher than the outside temperature, owing to the enclosed chamber and the solar heat gain in the chamber. For the open solar collector, the air temperature behind the evacuated tubes is nearly the same as the outside temperature. 2) In the night, the heat loss of integration with the closed air chamber door is less than the open one, but the difference is not large. In the daytime, the heat loss through the building envelopes behind the enclosed solar collectors is significantly reduced with the closed air chamber doors.