What is the reason for the cold in most parts of southern China?

Every winter, the Siberian cold current begins to move southward, where the cold current goes, the temperature gradually drops, and strong cold air flows to form strong winds, resulting in heavy snow and cold weather. Snowstorm weather in the south is rare this year, and the weather is always unpredictable.

-

Why is it so cold in southern China only in winter?

Peng Xu

The coldest winter is in the south of China.

Mark Twain said that the coldest winter in the world is the summer in San Francisco. He has never been to the south of China, nor has he spent the winter in the Yangtze River valley. If he is lucky enough to go, he will definitely change his mind-the coldest winter in the world is the indoor winter in the south of China. Summer in San Francisco is cold because it is unexpected and unpredictable. I went in summer clothes, only to find that San Francisco actually needed sweaters in July. Winter in the south of China is the same. Northerners think that going to the south is to bid farewell to the snowy north, but their hands and feet are sore with cold in winter in the south.

In southern China, heating has been a problem that has puzzled people for many years. Every winter comes, southerners always expect to live as warm as the north. Then let's analyze, what causes heating in the south to become a problem? Why is only China facing the heating problem in the south? Why don't North America, southern Europe, Japan, and even underdeveloped Mexico and other countries or regions with similar climate zones have the same problems?

When it comes to southern heating, many people in the industry tend to put the blame on experts in the former Soviet Union. In 1950s, Soviet experts helped China to formulate building heating standards. According to China's economic development conditions at that time, the areas north of Qinling Mountains and Huaihe River, where the annual average daily temperature is less than or equal to 5℃ and the daily average temperature is greater than or equal to 90 days, are defined as central heating areas, and central heating measures need to be taken, while central heating is not considered in southern areas. In 1950s, fireplaces in some old houses in Shanghai were even demolished. A simple red line has made hundreds of millions of people in southern China bid farewell to the warm winter, and it has also influenced the people of China for more than 60 years.

But is this really the case? Is the pain of heating in the south really caused by experts from the former Soviet Union? So why did a mistake last for more than 60 years and no one corrected it? How did the mistake continue? There is no central heating in Japan, South Korea, the southern United States and most parts of southern Europe, but why haven't we encountered the unique southern heating problem in China? In fact, central heating is a unique phenomenon with planned economy. Except the former Soviet Union, there is no central heating facility in most parts of the world, even in cold areas. But even without central heating facilities, I haven't seen these areas and countries cry cold in winter.

Let's take a look at the heat transfer calculation formula of buildings in winter:

q =σ(KA)*？ (tin map)

Q is the heating capacity, that is, the heating capacity needed to maintain a certain temperature indoors. K is the heat transfer coefficient of the building envelope, which represents the thermal insulation performance of the building. The greater the k, the worse the thermal insulation performance of the house. ? A is the surface area of heat transferred from the building to the outside. σ in front of KA represents sum, and represents multiple sums of external windows. ? Tin is the indoor temperature and Tout is the outdoor temperature.

This formula is easy to understand. When the outdoor temperature is constant, the higher the indoor temperature, the greater the heating capacity required; The worse the thermal insulation performance of the building, the larger the area of the building envelope, and the greater the required heating capacity.

Then let's compare the thermal insulation performance of buildings in China and other parts of the world.

The three charts in the annex respectively show the requirements for thermal insulation performance of external windows, external walls and roofs of buildings in the building standards of various countries of the Organization for International Economic Cooperation (OECD). These countries include developed countries and regions such as Europe, North America, Australia and Japan, as well as less developed countries such as Greece, Turkey, Mexico and Chile. Among them, the winter climate characteristics of some countries in southern Europe are very similar to those in southern China. IECC is the abbreviation of international energy-saving code and an international building standard. The abscissa of the chart is the number of heating hours in winter, and Shanghai, a typical city in the south, is in the middle; The ordinate is the heat transfer coefficient, and the greater the heat transfer coefficient, the worse the heat preservation performance. Some countries have multiple points in the chart because they are distributed in different climatic zones.

As one of the most developed areas in southern China, the heat transfer coefficient of windows is 1.3 times of the international average, the heat transfer coefficient of external walls is 2-4 times of the international average, and the heat transfer coefficient of roofs is 5- 10 times of the international average.

It is good that heating can be realized in the south, but the money in the pockets of ordinary people is limited and the budget is limited. Then let's calculate, assuming the same heating capacity is obtained under the same economic conditions, how will the indoor temperature in southern China compare with the international level?

According to the above heat transfer calculation formula, the indoor temperature is obtained:

tin = Q/σ(KA)+Tout

Indoor temperature is the temperature change obtained by dividing heat by heat transfer coefficient and area on the basis of outdoor temperature.

Assuming that the outdoor temperature is 8 degrees Celsius, the total KA value in Shanghai is about three times that of the international level. If the indoor temperature can be raised to 18 degrees in other countries to meet the comfort requirements, the indoor temperature in Shanghai can only be heated to 1 1.3 degrees, which is far below the comfort requirements.

On the one hand, the thermal insulation performance of buildings in southern China is poor; On the other hand, the heat transfer area is larger than other countries. Because indoor heating is generally not turned on in southern China, a single-family heating house will not only transfer heat to the outside through external walls, windows and roofs, but also transfer heat to neighbors through floors and partitions. These ceilings, floors and internal partitions are not insulated. According to comprehensive estimation, the total value of KA in Shanghai is more than 10 times that of similar areas in other countries.

If the total value of KA is more than 10 times, then if the same amount of heating can increase the indoor temperature by 10 degrees in other countries, it can only increase the indoor temperature by 1 degree in southern China such as Shanghai! So it is difficult for a single household to reach a higher heating temperature.

Therefore, in the south of China, families using air-conditioning heating can only heat in a limited space and time, and the electricity bill for air-conditioning heating is too high to afford.

So if you bid farewell to the ordinary class, regardless of the cost, can you bid farewell to the cold? Can local tyrants in the south welcome warmth? The answer is no, in the south, gas heating is not common because of gas price and environmental impact. It is widely used in heating and cooling air conditioning based on heat pump system. In winter, the heat rises from the cold end to the warm end, just like a well-drilling pump, hence the name. But the outdoor temperature is very low in winter, and the output and heating capacity of the heat pump system will decrease with the decrease of outdoor temperature. At the same time, the lower the outdoor temperature, the more heat is needed indoors. The two are drifting away and can't match. In addition, local tyrants' luxury houses usually have large areas, especially large windows. Glass needs more heat because of its poor heat insulation. Therefore, it is very common for local tyrants in southern China to wear long trousers or even cotton trousers at home, which is probably a very special phenomenon among the rich all over the world.

Why is it so cold in southern China only in winter? It's not the experts from the former Soviet Union, but our own buildings are not done well. The indoor cold is not only due to the lack of heating, but also the poor thermal insulation performance of buildings in the south of China, which is far from the world average. A well-insulated house can be heated with little heat. In the final analysis, this phenomenon is caused by the low requirements of building standards in China. Why is the building standard too low? Not because of economic reasons, the cost of thermal insulation materials is only tens of dollars in the construction area, but because the concept of standard formulation lacks foresight, and the current standard lacks regular professional evaluation and update by full-time personnel.

In short, heating in the cold winter in the south is not a problem, but building insulation is the real problem. Has little to do with Soviet experts.

Appendix 1: Comparison of Thermal Insulation Performance of Windows between Shanghai and Other Countries in the World

Appendix II: Comparison of External Wall Insulation Performance Requirements between Shanghai and Other Countries in the World

Appendix III: Comparison of Roof Insulation Performance Requirements between Shanghai and Other Countries in the World