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Insulation material is lightweight with low thermal conductivity
Thermal insulation material
Some find slope at the same time to form slope. The thickness of the insulation layer depends on the local climate and the requirements for room temperature.
- Chinese name
- Insulating layer
- Foreign name
- insulation layer [4]
Insulation layer is divided into internal wall insulation and
External wall insulation
. With the development of the global economy, the energy situation is grim, building energy conservation has become the trend of today's world development, but also the need of today's world development. At home and abroad, the most widely used building external wall envelope energy-saving measures are
Exterior insulation system
. Appropriate thickness of external insulation layer can improve the thermal insulation performance of building envelope and reduce building energy consumption. The research on the thickness of insulation layer of external wall insulation system has become an important issue.
[1]
External wall insulation refers to the structural layer composed of thermal insulation materials, which plays the role of thermal insulation in the external thermal insulation system. According to the energy-saving standards promulgated by the state, from October 1, 2001, the new planning of the real estate must be mandatory to do the external wall insulation layer.
The main function of the insulation layer is to play the role of heat preservation and insulation of the house.
The existing residential buildings in cold areas of our country are mostly brick-concrete structures, and the thermal performance of the building envelope is poor and the wall is not insulated, resulting in high energy consumption of heating and air conditioning throughout the year. Improving the thermal performance of building envelope is the key to energy saving, and the energy saving of exterior wall plays a very important role in building energy saving
Life cycle method
By comparing several groups of load indexes with different thickness of insulation layer, the influence of insulation layer thickness on building load is analyzed, and the optimal economic insulation layer thickness is determined. The calculation method of "economic thickness" of insulation layer not only considers the basic principle of heat transfer, but also considers
Thermal insulation material
The influence of investment cost, energy price, loan interest rate, thermal conductivity and other economic factors on the thickness of insulation layer. According to the
Life cycle analysis
Based on the mathematical model of the total heating cost per unit area of the enclosure structure (only considering the roof), a simple formula for calculating the economic thickness of the insulation layer is obtained. Finally, it is verified by several sets of data and generalized as the best insulation layer thickness of other common insulation materials to further verify the correctness and rationality of the conclusions.
At present, China has put forward higher requirements for the thermal insulation performance of housing buildings, and many urban residential buildings are still simple flat-roofed houses. External thermal insulation is a kind of building thermal insulation energy-saving technology which is widely promoted at present. External insulation compared with internal insulation, the technology is reasonable, has its obvious advantages, the use of the same specification, the same size and performance of the insulation material, the effect of external insulation is better than that of internal insulation. External insulation technology is not only suitable for new structural engineering, but also suitable for old building transformation, suitable for a wide range, high technical content; The outer insulation package is on the outside of the main structure, which can protect the main structure and extend the life of the building; Effectively reduce the building structure
Thermal bridge
To increase the effective space of the building; At the same time, the condensation is eliminated and the comfort of living is improved. Under the guidance of a series of energy-saving policies, regulations, standards and mandatory provisions, China's residential construction energy saving work continues to deepen, energy-saving standards continue to improve, the introduction and development of many new energy-saving technologies and materials, vigorously promote the use of residential buildings. However, the current level of building energy conservation in China is still far lower than that of developed countries, and the energy consumption per unit area of buildings in China is still 3 to 5 times that of developed countries with similar climate. The building heating energy consumption in the northern cold region has accounted for more than 20% of the local social energy consumption, and most of them are used
Thermal power generation
and
Coal-fired boiler
At the same time, it brings serious pollution to the environment. So building energy saving or our country this century building an important subject. At the same time, the wall and the roof are important enclosure objects of the building, and the thickness of the insulation layer is an important parameter that determines the level of building insulation, so it is of great significance to design the optimal insulation layer thickness in order to enhance the insulation performance and save heat loss and energy waste.
Building energy consumption occupies a large proportion in the total social energy consumption, in western developed countries, building energy consumption accounted for 30% to 45% of the total social energy consumption, but in our country in the case of the social economic level and living standards are not high, building energy consumption has accounted for 20% to 25% of the total social energy consumption, is gradually rising to 30% [1], In addition, high building energy consumption leads to the use of fossil fuels, which brings more and more serious air pollution. In order to reduce building energy consumption, the state is currently implementing building energy-saving design standards to improve the thermal insulation performance of building enclosures.
The wall is the main body of the outer protection, to reduce the energy consumption of the building, we must first consider the energy saving of the wall, so
External insulation composite wall
The design of insulation layer thickness has also attracted more and more attention [1~2]. Although improving the thermal insulation performance of the external wall can reduce the heating energy consumption cost of the building, it will also increase the construction cost of the external wall and increase the construction fund of the builder. Moreover, the service life of the thermal insulation layer is limited, so the thickness of the thermal insulation layer cannot be increased without limitation to reduce the energy consumption cost. The thickness of the insulation layer should be reasonably selected to minimize the sum of heating energy consumption cost and insulation cost caused by the external wall in the life cycle of the insulation layer.
[2]
The structure of the roof from the inside out is 0.1(cm) paint, 1.5(cm) cement mortar 20(cm) floor, 2(cm) cement mortar, perlite insulation layer, 2(cm) cement mortar, 1(cm) three felt and four oil
Waterproof material
. In northern areas, the surface temperature of such a roof under the sun can reach 75 degrees Celsius in summer and minus 40 degrees Celsius in winter. In order to maintain a better comfortable temperature in the room and not cause waste, the best insulation layer thickness is designed and the best insulation material is selected.
A. Suppose that the object of the study is an air-conditioned building with indoor air maintained at a set suitable value.
b. The heating heat load of the building in winter includes the heat consumption of the envelope structure and the heat consumption of cold air penetration, which believes that the heat consumption of cold air penetration does not directly affect the thermal resistance of the envelope structure, and only the influence of the roof heat consumption is considered when calculating the optimal thickness of the insulation layer.
c. Assume that the roof structure and insulation material are uniform, and the heat conduction coefficient is constant.
d. The indoor temperature and outdoor temperature remain unchanged, and the heat transfer process is in a stable state.
e. The temperature difference between the indoor air and the inner surface of the envelope is allowed to be 4 degrees Celsius, that is, in winter, the indoor air of the flat-roofed house is 4 degrees Celsius higher than the inner wall.
f. In northern areas, the surface temperature under the sun in summer is up to 75 degrees Celsius, and in winter it is minus 40 degrees Celsius.
Description of the main parameters used in the model
Q Heat loss through the roof per unit area, W/ m2
K Heat transfer coefficient of the enclosure, W/ (m2·℃)
ΔT indoor and outdoor temperature difference, ℃.
Qn annual heating heat consumption, J/m2
Ri Heat transfer resistance from inside to outside roof structural materials, m2·K/W
R Thermal resistance of insulation layer, m2·K/W
di Thickness of roof structural material from inside to outside, m
d Thickness of the insulation layer
i Thermal conductivity of each layer of the material, W·m/K
λ thermal conductivity of thermal insulation layer, W·m/K
W Total annual heating cost per unit area, ￥/ m2;
WT unit area insulation layer investment cost, ￥/ m2;
WN Annual heating cost per unit area
WY heating annual operating cost per unit area, ￥/ m2·a
PWF discount coefficient
i Bank profit
I spot rate
N Service life
P Cost per unit volume of insulation material
C Electricity price per unit time, ￥/h
H Heat output per unit area per unit time, J/h
The total efficiency of the η heating system
Vi Number of heating or cooling days, d
(1) For a uniform medium with a thickness of d, the temperature difference between the two sides is ΔT, then the heat Q per unit area from the side with a high temperature to the side with a low temperature is proportional to ΔT, that is, Q= Kδt, k is the heat conduction coefficient, where k=, R is the heat transfer resistance of the medium
(2) PWF- Discount Factor (Present Worth Factor) is the process of converting money received or paid at a certain date in the future to present value. The present value of one yuan's funds in different periods is called the discount coefficient, which is to convert the future value of the funds into the present value.
(3) The number of Heating Degree Days (HDD) is the cumulative number of degrees over a period of time (month, season or year) when the average daily temperature is below 65 °F(18.3 ° C). If the average daily temperature is above 65 °F, there are no heating degree-days for that day.
Analysis of problem
The roof is an important enclosure of the building to ensure that it maintains room temperature and reduces heat loss. Especially in the cold area, in the case of ensuring that the indoor temperature in the cold area in winter meets the due standard, it is also necessary to take its heating cost as an important consideration. The thickness of insulation layer is an important parameter to determine the level of building insulation. Generally, with the increase of the thickness of the insulation layer, the adiabatic performance of the enclosure structure is improved, thus reducing the building load, and the cost of heating equipment and the operating cost of heating system are correspondingly reduced. However, at the same time, the construction cost of the envelope also increases accordingly, so there must be a specific thickness of the insulation layer, that is, the economic thickness d, so that the total cost of the building (the sum of construction costs and operating costs) is minimum. Therefore, the objective function of the total cost W is considered to be established, which includes the investment cost of insulation layer and the cost of heating heat consumption. For the cost of heating good heat, the mathematical model of energy-saving building design is established by adopting the life cycle method considering economy and energy saving. The relation of thermal insulation layer thickness d is established to obtain the relation of calculating economic thickness, so that the objective function W is minimum, corresponding to the optimal thickness d. Thus, the optimal insulation thickness is obtained, and the thermal conductivity is only replaced when the insulation material is changed, and the optimal insulation material is obtained by combining the data.
Comparative analysis of optimum thickness of insulation layer for different materials
Optimum thickness of insulation layer for different materials
Actually insulation effect:
Polyurethane foam
The best, extruded board followed, benzene board worst;
Cold and heat resistance: polyurethane foam is the best, extruded board is the second, benzene board is the worst;
Water absorption: the extruded board is the lowest, followed by polyurethane, and benzene board is the easiest to absorb water;
Service life: polyurethane foam is the longest, extruded board is second, benzene board is the worst;
Price: polyurethane foam is the highest, extruded board is the second, benzene board is the lowest;
Polyurethane foam (spraying) can be directly sprayed on the spot forming (liquid expansion), forming, convenient transportation; The other two plates need to be transported and pasted, which is more troublesome and there will be certain damage, and there are patchwork joints.
For the calculation of indoor and outdoor temperature difference, this paper adopts half of the maximum temperature difference between the indoor and the outside world when the appropriate temperature is reached as the average temperature difference over a period of time, but in fact, the temperature difference changes with the external climate, environment, time and other factors. Therefore, for the calculation of outdoor temperature difference, the relationship between dynamic load and insulation layer thickness should be considered.
This paper focuses on determining the optimal insulation layer thickness from the perspective of economics. However, in fact, the choice of insulation layer thickness is not only related to energy conservation issues, but also related to environmental protection issues, the increasing shortage of energy and domestic and even the world increasingly serious recently more important and necessary. If the selection of the insulation material considers its impact on the environment, as well as the amount of pollutants generated by the required consumption of heat source fuel, the selected thickness has the best economic and environmental benefits.
In the setting of centralized heating buildings, the heat transfer resistance of the envelope structure in addition to the technical and economic comparison is determined, and to meet the requirements of the relevant national energy conservation standards, the minimum thermal resistance of the building envelope such as the residential flat roof house should be added according to the structure calculated by the calculation formula, and the minimum heat transfer resistance is determined according to the following calculation:
Rmin -- Minimum heat transfer resistance of enclosure structure (m2·K/W)
ti - Indoor temperature calculation in winter, generally 20°C.
te -- Winter outdoor calculated temperature of the enclosure, unit: °C.
n -- temperature difference correction coefficient, external wall, flat roof 1.00.
ΔT - The allowable temperature difference between the indoor air and the inner surface of the enclosure.
Rk -- inner surface heat transfer resistance (m2·K/W)
[3]
Therefore, the evaluation condition is added in the built model: the minimum insulation layer thickness d should meet, which is also of great significance for determining the thickness of the insulation layer in practical engineering.
Due to the ever-changing actual situation, there are always small errors in the data and assumptions we get in the actual operation, so a good model must not lead to big changes in the results from these small changes. In order to carry out a more comprehensive test on the model we made, and taking into account the actual situation, we set some reasonable initial conditions under the conditions of selecting appropriate parameters, and use the computer to test the model to get the best insulation thickness of a series of insulation materials, including the pearl insulation layer. The calculated results are also close to the thickness of insulation layer used in actual engineering design.
The choice of insulation layer thickness is related to the economical problem of cost and operation cost of energy-saving building. The mathematical model for calculating the economic thickness of insulation layer by life cycle cost analysis takes into account the heating energy consumption of the building in its life cycle, which is scientific, simple and convenient. When there is a lack of heating system data, the use of design specifications is better targeted and adaptable, has a certain reference and application value for engineering design, and can be used for new or old building transformation and new
Thermal insulation material
The design calculation. However, in the call for people-oriented, comprehensive, coordinated and sustainable development today, from the economic and environmental aspects of the comprehensive consideration of insulation layer thickness, should be more reasonable, more significant.
[2]
