Cold bridge,Thermal bridgeIt is the name of the same thing phenomenon in the north and south: it mainly refers to the heat transfer coefficient of some parts of the building envelope is significantly higher than that of other parts when the building envelope conducts heat with the outside world, which makes the heat transfer from these parts concentrated quickly, thus increasing the air conditioning, heating load and energy consumption of the building.
Chinese name
Cold bridge
Foreign name
cold bridge
Object
building
Role
Destructive effect
Results
Increased cooling consumption, waste of cooling energy, etc
Cold bridge has a destructive effect on buildings. It will increase the cold consumption of rooms and waste cooling energy;There will be condensate at the high temperature side, which will affectThermal insulation materialThermal insulation performance;It also affects the use of rooms at the high temperature side.To avoid these situations, the number and area of cold bridges should be minimizedThermal insulation materialPackage.[1]
Concept of cold bridge
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In the refrigeration industry, the concept of cold bridge is defined as follows: due to the different local structures in the thermal insulation structure of the cold storage, the thermal insulation performance of this part is reduced, and it becomes a channel for mass transfer of cooling capacity, which is called "cold bridge".Cold bridges are bridges that transfer heat.Another term is called "hot bridge". In fact, they are the same.It mainly refers to the heat transfer coefficient of some parts of the building envelope is significantly higher than that of other parts when the building envelope conducts heat with the outside world, which makes the heat transfer from these parts concentrated and fast, thus increasing the air conditioning, heating load and energy consumption of the building. Now it is generally referred to as heat bridge.This is a commonly accepted definition in the north and south, but due to custom, the northern region is still called Lengqiao.[1]
Hazards of cold bridges
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Because the cooling capacity felt by the surface of the structure near the cold bridge is concentrated to the cold bridge, the cooling capacity loss caused by the cold bridge greatly exceeds the value calculated simply according to its sectional area.The existence of the cold bridge in the building not only causes heat loss, but also the cold bridge part becomes the weak link of the insulation structure, causing condensation, frosting, icing, moisture failure of the insulation layer on the side where the temperature of the insulation structure is higher, and even freezing damage to the structure layer in serious cases.Specifically, there are the following hazards: 1. Cold bridge will increase the cold consumption of rooms (including warehouses) and waste heat energy, which is the most direct impact.2. At the position where cold bridge occurs, condensation water will be generated at the high temperature side (if the temperature at the low temperature side is too low, it may even freeze), which will reduce the thermal insulation performance of the insulation material.Sometimes it also affects the use of rooms at the high temperature side, for example, the high temperature side has strict requirements on temperature and humidity.3. The long-term effect of condensed water or frost will cause damage to the building structure and shorten the service life of the building.[1]
Treatment of cold bridge
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The above impacts and hazards are undesirable for all of us. We must take measures to avoid or reduce the above hazards.It is particularly important to take necessary measures, especially in the current social situation of pursuing energy conservation and efficiency.The intercooling bridge in the construction project mainly occurs in the balcony plate, air conditioning hole, canopy, the root of daughter wall, the side of door and window openings, the cantilever plate of outdoor air conditioner and other parts.At present, the heat insulation structure of the cold storage warehouse mostly adopts the construction method of internal heat insulation, so there must be many cold bridges in the structure.In order to prevent the heat transfer from affecting the stability of the warehouse temperature and preventing the damage of the building structure, attention must be paid to reducing the number and area of cold bridges as much as possible during the design, construction and use.If there is an inevitable cold bridge due to the building structure or other reasons, various measures must be taken to reduce the impact of the cold bridge, such as using thermal insulation materials for wrapping.The author is an ordinary employee in the refrigeration industry. Having done design and construction work, he would like to introduce some common bridge forms and treatment methods based on what he has learned. He hopes to be helpful to his peers. I hope everyone can criticize and correct the mistakes, and I will accept them with an open mind.1. Floor cold bridge.When selecting the storage site, the general cold storage often focuses on the problem of land and water transportation, so the cold storage is often built in coastal cities or river banks, ports, where the soil quality is generally poor and the groundwater level is high.If the foundation design of the cold storage is not well designed, the drainage below the floor and the heat insulation treatment are not good, it is easy to form a cold bridge on the floor, and in serious cases, the frost heaving and cracking of the foundation and floor will occur, which will cause much more serious damage to the cold storage than other freeze-thaw damage.In order to prevent the frost heaving of the foundation and floor, the site selection should be taken into consideration during the construction and structural design of the cold storage, and a reasonable design scheme should be made and proper structural treatment should be carried out.For example, in terms of the location selection of the warehouse, when considering the traffic problems, try to avoid places with poor soil quality and high groundwater level. If not, increase the heat insulation capacity of the foundation in the design, reduce the drainage below the floor, and the construction personnel shall strictly follow the specifications and design requirements.2. Hanging steel cold bridge Some single-layer slope roof cold storages often use the structure form of suspending the ceiling under the large-span roof truss to form a pavilion floor, which will lead to the problem of hanging steel cold bridge.If the cold storage building adopts the structural scheme of setting hanging bars from the roof truss to tie the floor beams and slabs, the hanging bars shall be galvanized round steel to prevent corrosion, and hardwood insulation blocks shall be set below the hanging bars.In addition, the anchor components of each floor and exterior wall of the multi-storey cold storage should also be galvanized round steel, wrapped with thermal insulation materials.3. Column cold bridge is often used in multi-storey cold storage or single-layer flat roof cold storageReinforced concrete beam slab structureOr the non beam structure forms the structure form of the attic floor, which has the advantages of good rigidity and integrity, tidy space in the attic, good construction and operation conditions of the thermal insulation layer, etc., but there is a problem of cold bridge in the column body.[1]
For the cold bridge of the column body, we suggest: (1) The lower section of the column at the bottom of the cold storage shall be wrapped with thermal insulation materials within 1.5m from the ground, and protective facilities shall be provided around the thermal insulation materials to prevent cargo collision.When the temperature difference between the upper and lower floors (including the attic floor) is more than 5 ℃, in addition to the floor should be insulated, the lower section of the upper column within 1.5m from the floor should also be insulated.(2) In the freezing room with lifting rails, the weight of food, hanging and loading tools is transferred from the lifting rails to the load-bearing structure. The lifting rails can be transferred to the beams and slabs or directly to the pillars in the freezing room through the rods. If a large-span thermal insulation ceiling is used, another pillar must be erected. It is recommended that the pillars be erected on the turnouts of the ground floor, so as to avoid the pillars directly leading to the ground to form a cold bridge.If the reserved size of pipe holes at the insulation wall and floor of the pipeline cold bridge cold storage is smaller than the required insulation thickness, the cold bridge will also be caused, and the nearby wall and floor will be dewed and dripped, causing damage to the insulation layer.(1) The pipes through the wall shall be concentrated as much as possible to facilitate cold bridge facilities.The reserved cavity should not be too large or too small, and the required thickness of insulation layer can be reserved. In order to facilitate operation, it can be increased appropriately.Board shall be sealed around the reserved wall opening, and the damp proof course shall be made. After the pipeline is installed, it shall be filled with crushed cork chips mixed with asphalt.At the bottom of the board in the rice hull layer, the measures of sinking and hollowing of rice hull should also be considered.(2) To prevent the suction line from contacting the supportCold bridge phenomenonWood blocks soaked in asphalt shall be placed between the pipe and the support.(3) Insulation measures shall be taken for the frost flushing drainage pipe in the freezing room. The interface between the drainage pipe and the steel plate water pan under the air cooler must be tight without leakage. The underground part of the drainage pipe or the part passing through the high-temperature warehouse must be wrapped with heat insulation and moisture-proof materials to the external wall.5. The floor of the cold storage door of the cold storage bridge is often iced at the foot of the door due to the cold bridge of the door passage.The door of the freezing material cold storage room should preferably be opened in the low-temperature hall, so that the frozen food can be warehoused through the low-temperature hall, which can reduce the cold consumption in the warehouse and ensure the stability of the warehouse temperature. However, the low-temperature hall needs to be insulated and equipped with refrigeration equipment, so the cost is relatively high, so at present, it is more used as a normal temperature hall.Air curtains shall be installed on the refrigerated doors directly opening to the normal temperature hall to reduce the exchange of cold and hot air inside and outside the warehouse.In order to avoid moisture and water dripping in the normal temperature hall, windows can be opened to receive sunlight and increase the temperature of the inner surface of the hall (slightly higher than the air dew point temperature). At the same time, anti cold bridge treatment should be carried out on the upper, lower, left and right sides of the cold storage door. The structure of the normal temperature hall outside the warehouse can be separated from the main warehouse structure or combined, but anti freezing treatment must be done when combining.In addition, in the same floor, when the temperature difference between two adjacent warehouses is above 5 ℃, in order to avoid the formation of cold bridges, the insulation layer of the insulated inner wall should be connected with the insulation layer of the insulated outer wall and the floor.The top of partition wall shall be insulated within 1.2m from the top plate bottom of the side with higher temperature to the wall.In general, there are two measures to reduce the impact of cold (hot) bridges: one is to connect the thermal insulation layer and vapor barrier and damp proof layer of all parts of the enclosure structure as a whole, so as to avoid direct contact between the thermal insulation layer and the external air;Second, the components and pipes that form the cold bridge shall be subject to local heat insulation, steam insulation and moisture proof treatment around and along the length direction, so as to prevent condensation water or frost at the high temperature side.The thickness, width and length of the insulation layer used to reduce the impact of cold (hot) bridge shall be determined according to the temperature difference on both sides, the materials of cold (hot) bridge components, and theThermal insulation materialIt is different.[1]
Cause of cold bridge
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1. Whether the construction materials are stolen during the construction of the house.2. Because of the need to reduce costs, many projects now do not do wall insulation, and the wall laying thickness is not enough.According to the standard, the wall body should be added with 12cm bricks for wall insulation.threeThermal insulation materialIt is also an important factor to prevent cold bridge.Many real estate companies use the cheapest thermal insulation materials, which are low in value, but have poor thermal insulation effect.4. At present, bricks are not required in construction projects. Most buildings are made of concrete, so condensation water is easy to appear in the buildings.5. Human factors.If the designer does not understand the performance of the insulation material, he has no idea of what kind of material should be used and how thick it should be, and does not notify the construction personnel when modifying the drawings, etc.[1]
