Page 60 - JCAU-5-2

Journal of Chinese
Architecture and Urbanism Cooling energy-saving mechanism

region. Hence, Guangzhou is selected as the case study city 3. Macroscopic comparison of energy
with the following main climate parameters: The annual saving
average temperature is 22.5°C, the average temperature
in the hottest month is 32.9°C, the annual maximum 3.1. Annual energy saving
temperature is 36.1°C, and the annual total solar radiation Figure 3 shows the comparison diagram of the annual
is 1072.1 kWh/year. absolute and relative energy savings of the same office
The characteristic temperature method (CTM) based building when the temperature set-point increases by
on building energy consumption theory is a dynamic 1°C from 26°C under an envelope of four grades. The
simulation method used to calculate the heating (cooling) result presented in Figure 3 shows that: (i) When the
load and energy consumption of the building, which temperature set-point of air conditioning increases by
can reveal the relationship between the building load or 1°C, office buildings with different grades of envelope get
energy consumption and various factors affecting solar different degrees of absolute energy savings under the same
radiation, indoor heat gains from lighting, and equipment, climate. A better insulation performance of the envelope
etc. (Long, 2005a). The reliability of this method has been structure results in the less energy saving throughout the
verified by experiments and software comparisons in a year. The lower-grade envelope has the largest cooling
large body of literature (Long, 2005b; Qian et al., 2022; Qi consumption and energy saving, whereas the annual
et al., 2023). cooling consumption and energy savings of top-grade
envelopes are the minimum. (ii) The annual energy-saving
In this study, the CTM method was used to simulate rate of air-conditioning decreases with the improvement
and predict the hourly dynamic cooling load of buildings of the insulation performance of the envelope structure
under the condition of four grades of envelopes with air- because the annual cooling consumption and absolute
conditioning temperature setpoints of 26°C and 27°C, energy-saving decrease with the improvement of the
respectively, and then the hourly load of buildings was envelope performance, but the reduction range is different.
accumulated monthly and annually to obtain the cooling Before the set-point rise, the annual cooling consumption
consumption on different time scales. By calculating of the top-grade envelope is 70% of that of the lower-grade
the load difference before and after the set-point rises, envelope, but after the set-point rises, the annual absolute
the hourly cooling load reduction value or monthly energy saving is only 50% of that of the lower-grade
and annual cooling consumption reduction value was envelope, and the reduction in absolute energy saving is
obtained, that is, absolute energy savings. Based on the greater than the cooling consumption. This shows that
load or cooling consumption before set-point rise and after vigorously improving the thermal performance of the
divided by absolute energy saving, the hourly dynamic envelope, increasing the temperature set-point of the air-
load reduction rate and the monthly and annual cooling conditioner by 1°C does not achieve the same degree of
consumption reduction rate were obtained, namely, energy savings. Therefore, the energy conservation retrofit
the relative energy-saving rate. The simulation assumes of existing buildings should not pay too much attention
that the cooling load is zero when the outdoor dry bulb to increasing the thermal resistance and reducing the
temperature is lower than the temperature set-point. heat transfer coefficient of the old building envelope but
When the indoor characteristic temperature is lower should comprehensively consider the potential of guiding
than the setpoint, the cooling load is also zero. All the the behavioral energy conservation of existing buildings of
moments with an air-conditioning load were included in
the analysis. To more significantly reveal the influence
mechanism of the single factor of the envelope thermal
characteristics on the energy-saving effect of the set-
point rise and exclude the influence of secondary factors
and personnel behavior uncertainty, in the simulation,
the influences of internal heat sources such as personnel,
equipment, and lighting were ignored, the air exchange
rate was 0.5 h , the shading coefficient of external
-1
windows was 1, and the transmission coefficient of solar
radiation glass is 0.8 (Guo et al., 2019). To ensure the
integrity of the research results, the statistics included
all moments when the set conditions were satisfied and a Figure 3. Comparison of annual energy saving of four grades of envelope.
cooling load was needed. Source: Graph by the authors

Volume 5 Issue 2 (2023) 6 https://doi.org/10.36922/jcau.0877