At present, the commonly used building thermal insulation and energy-saving technologies are external thermal insulation, internal thermal insulation, self-thermal insulation and sandwich thermal insulation and so on. 
Each energy-saving technology has its advantages and disadvantages. 
(1) external thermal insulation technology. 
The external thermal insulation technology is to add a thermal insulation system on the outside of the external wall of the building to improve the thermal resistance of the external wall and reduce energy consumption. 
Because the external thermal insulation system is located in the outermost part of the building, it resists the (negative) impact of external climate change on the building, that is, the external thermal insulation system plays a certain role in protecting the internal building structure (foundation wall). 
Therefore, the external thermal insulation system itself must have good physical and mechanical properties, which can effectively avoid common building defects such as cracking and water seepage. 
In terms of thermal performance, when the room is heated or cooled for a long time (continuous), the base wall itself is relatively heavy, can absorb and store more energy, acts as a heat storage pool, and can balance the (large) fluctuation of indoor temperature. 
But in the gap heating (cooling), in order to increase (reduce) the wall temperature, it needs to consume more energy. 
(2) Internal thermal insulation technology. 
The internal thermal insulation technology is to add thermal insulation materials on the inside of the outer wall of the building to improve the thermal resistance of the external wall. 
However, it can not play a thermal insulation role in some specific parts of the external wall, such as the floor, the intersection of horizontal and longitudinal walls and other structural parts (called thermal bridge). 
Different from the external thermal insulation system, the internal thermal insulation system does not have to resist the influence of the external climate, and the technical performance requirements are not as high as the external thermal insulation system. 
At the same time, because the insulation area is relatively small, the construction cost of the internal insulation system is lower than that of the external insulation system. 
In terms of thermal performance, when heating or cooling for a long time (continuous) in a room, when using thermal insulation materials of the same thickness, due to the existence of thermal bridges, internal thermal insulation of the same thickness consumes more energy than external thermal insulation. 
But in the gap heating or cooling, it does not have to raise or lower the temperature of the external wall at the same time, it can quickly increase or decrease the indoor air temperature. 
(3) self-heat preservation technology. 
Self-insulation is that the external wall itself has good thermal insulation performance, which can meet the requirements of local energy-saving standards, auxiliary or additional thermal insulation measures should be taken if necessary. 
The self-insulation system requires as few thermal bridges on the exterior wall as possible, and as many walls with good thermal insulation performance as possible, so it is not applicable to any structural system. 
It is only suitable for steel structures, concrete frame structures, low-rise load-bearing structures and short-leg shear wall structures. 
The difficulty of the self-system is that the structural thermal bridge should be handled properly. 
In terms of thermal performance, self-insulation is different from external or internal insulation, it is usually a single material, not a composite structure. 
The self-insulation system realizes the integration of structure and heat preservation. 
(4) Sandwich heat preservation technology. 
The sandwich insulation is composed of two outer walls and a composite thermal insulation material in the middle. 
It helps to protect (organic) thermal insulation materials, prolong their service life, and is conducive to the diversity of exterior wall finishes. 
The difficulty of sandwich insulation is how to fix or tie the outer page wall. 
Sandwich insulation is usually used in low-rise masonry structures abroad, but it is not commonly used in frame-filled walls. 
To sum up, various building energy-saving technologies have both advantages and disadvantages, which should be given necessary attention in use. 
The summary is as follows: 
External insulation technology: more suitable for continuous heating or cooling buildings. 
Internal thermal insulation technology: more suitable for gap heating or cooling buildings. 
Self-insulation technology: must cooperate with the appropriate structure, should properly deal with the part of the hot bridge. 
Sandwich insulation technology: must cooperate with the appropriate structure, should properly deal with the part of the hot bridge.