Product Information / Glass curtain wall skylights alleviate local overheating in buildings

Glass curtain wall skylights alleviate local overheating in buildings

10-29-2024

Return

Every summer, I often receive inquiries about "localized overheating" in buildings, especially in recent years. What are the typical scenarios of indoor "local space overheating", why does this problem occur, and how can it be solved? Please correct any inappropriate aspects!
 

1. Background
 

The phenomenon of "localized overheating" in glass curtain wall skylights has become a hot topic in recent years, and related inquiries are often received. The typical scenario is as follows:
 

Scenario 1: This summer, the Beijing area has been experiencing a continuous high temperature of 40 ℃. In order to alleviate the discomfort of passengers under sunlight, dozens of "sunshades" have been erected in the waiting hall of Beijing South Station, which has attracted the attention of CCTV.
 

Scenario 2: In a certain office building, when the sun is shining in the west in the afternoon, the temperature in the west facing office is too high. Although the air conditioning temperature is turned to the lowest, it is still difficult to work for a long time.
 

Scenario 3: XX Square, with a large area of glass skylight in the middle. When the sun shines directly, the temperature on the inner surface of the skylight is too high, causing thermal discomfort for the top floor merchants or customers.
 

Some people say that this year will be the coolest year in the next few decades. Regardless of right or wrong, the "localized overheating" of glass curtain walls and skylight buildings has become a focus of attention.
 

2. Why did this situation occur?
 

Why does the problem of "local space overheating" occur? This is related to the heat transfer of glass curtain wall skylights and the thermal comfort of the human body.
 

In summer, there is a continuous high temperature outdoors, and heat is transferred indoors through glass curtain walls and skylights, mainly through: (1) solar radiation transmission, which is related to the SHGC value of the solar heat gain coefficient; (2) Temperature difference transmission is related to the heat transfer coefficient K value; (3) Air convection heat transfer is related to air tightness. Among them, direct solar radiation transmission is the most important way for summer heat to enter indoors.
 

Due to the decoration style, many office buildings inevitably have some small office spaces facing south to west, which are exposed to direct sunlight in summer and result in excessively high room temperatures; Even in winter, there is a problem of high temperature in some rooms facing south in office buildings.
 

Residential buildings also have similar problems. The south facing second bedroom in a certain residence is only about 10 square meters. With winter heating and direct sunlight at noon, the room overheats. It is necessary to open windows for ventilation from time to time to reduce indoor temperature and improve thermal comfort.
 

When it comes to thermal comfort, the authoritative research materials at home and abroad are mainly ISO 7730 "Human ergonomics of thermal environment - Analysis, determination and interpretation of thermal comfort by calculating PMV and PPD indices and local thermal comfort criteria" [1].
 

In the standard, PMV and PPD are used to represent the overall thermal or cold discomfort of the human body, but thermal dissatisfaction can also be caused by specific parts of the body being cooled or heated unintentionally, which is called local discomfort. The standard provides a range of parameters for local thermal discomfort.


Picture

 

The most common reasons for local discomfort in the standard are the feeling of blowing, high vertical temperature difference between the head and ankles, floor being too hot or too cold, and asymmetric radiation temperature being too high.
 

In summer, the "local space overheating" of glass curtain wall skylight buildings is mainly related to high indoor temperatures and asymmetric radiation temperatures. There's no need to explain why the indoor temperature is too high.
 

There have been many experimental studies on the effects of asymmetric radiation on human thermal comfort, such as Nielsen, Gage, McNair and Biddison, Hall and Klemm, etc.
 

The results indicate that within the asymmetric radiation range that may be involved in ordinary hot environments, it will not have adverse effects on human comfort; When the wall temperature exceeds the air temperature by 30 ℃, significant discomfort caused by asymmetric radiation will occur.
 

3. How can this situation be alleviated?
 

The problem of "local space overheating" in glass curtain wall skylight buildings is mainly related to temperature difference transmission, airtightness, and direct sunlight exposure, and is mainly caused by solar radiation. Therefore, we consider minimizing the amount of solar radiation entering the indoor space as much as possible.
 

So what are the tricks to deal with it?
 

Tip 1: External shading (blinds, hard roller blinds, awnings)
 

There are also various forms of external shading for buildings, such as sunshade louvers, hard sunshade roller blinds, sunshade canopies, etc. Due to the fact that external shading blocks heat outside the room and carries it away through airflow, the shading effect is the best.
 

The disadvantage of external shading is that it requires specialized shading, which is costly; Considering the safety of external shading, it is generally necessary to have a reliable connection with the structure, so most of them need to be designed as a whole during construction.
 

Tip 2: Low-E Glass
 

Low-E glass has a certain sun shading effect, especially double silver and triple silver Low-E glass, which is particularly suitable for new buildings.
 

In mid July this year, the air temperature in Beijing reached as high as 40 ℃, and I saw many passengers leisurely playing with their phones in the sunshine at Chaoyang Station in Beijing. I experienced it in the past and found that the incoming sunlight only felt warm, without any burning sensation, thanks to the insulation function of Low-E glass.

Return

Find the best solution? Contact us immediately！