Page 63 - JCAU-5-2

Journal of Chinese
Architecture and Urbanism Cooling energy-saving mechanism

A B

Figure 6. (A and B) Comparison of hourly load reduction based on outdoor dry bulb temperature. Source: Graph by the authors

that: (i) Due to the same climatic conditions, although the figure that the load reduction amount for 1 h within the
thermal performance of envelope vary greatly, the hourly range of 26°C – 27°C may be equal to 10 or even dozens
load reduction has similarity with the variation of outdoor of times of the hourly load reduction amount outside the
dry bulb temperature. (ii) When the outdoor dry bulb range. Therefore, the key to the annual absolute energy
temperature is lower than 26°C, there is no cooling demand, saving effect is behavioral energy savings. (v) In the lower-
and Guangzhou has the cooling demand for 3,341 h in the grade envelope, the maximum hourly load reduction in the
whole year, which has nothing to do with the envelope range of 26°C – 27°C is 110.18 kW, and only 79.07 kW in
performance. The outdoor dry bulb temperature is between the top-grade envelope. This is because the improvement
26°C and 27°C for 831 h, and the absolute energy saving at of the thermal performance of the envelope structure
these moments account for a large proportion of the total reduces the hourly cooling load demand of the building
absolute energy saving in the whole year. For the lower- at 26°C. According to the above, the hourly load reduction
grade envelope, the total absolute energy saving at all times of outdoor temperature between 26°C and 27°C is the
when the outdoor temperature is between 26°C and 27°C is hourly cooling load at the set-point of 26℃, which makes
9763.01 kwh, accounting for 58.30% of the annual energy a great contribution to annual absolute energy savings.
saving. For the top-grade envelope, the total absolute Therefore, the annual absolute energy saving scale with
energy saving at these times is 7257.67 kWh, accounting setpoint rise of 1°C shows a variation rule that decreases
for 79.35% of the annual energy savings. Therefore, in with the improvement of envelope performance. (6) For
the time of annual cooling demand, the micro absolute the time when the dry bulb temperature is >27°C, there is
energy saving of outdoor temperature between 26°C and a minimum value of hourly load reduction, and the hourly
27°C always constitutes the main contribution of the total load reduction values of all these moments are very close to
absolute energy savings after increasing the temperature by this minimum value. The minimum hourly load reduction
1°C. (iii) Although from the perspective of macro energy under lower-grade envelope is 2.77 kw, and it is only 0.74
consumption, the higher the performance of the envelope, kw under top-grade envelope. This is due to the decrease in
the lower the absolute annual energy saving of the K-value caused by the improvement in the performance of
building. However, from the microscopic analysis results, the envelope. According to the basic heat transfer formula
buildings with better envelope performance have a larger of Q = KFΔT, the energy savings from heat transfer by
percentage of behavioral energy savings in absolute annual temperature difference decreases. However, due to the
energy savings, so their contribution is greater. Therefore, large number of moments of heat transfer by temperature
behavioral energy saving measures cannot be ignored for difference, the energy-saving effect brought by these still
new buildings. (iv) For the moments when the outdoor needs to be paid attention to.
temperature is between 26°C and 27°C, energy savings Figure 7 shows the comparison of hourly load reduction
is resulted because the indoor temperature set-point is of low-grade and top-grade envelope with hourly cooling
artificially raised from 26°C to 27°C, and indoor cooling is load change before set-point rise. It can be seen from the
no longer needed, which saves all the cooling loads when diagram that: (i) Although the cooling load demand ranges
the setpoint is 26°C. The hourly load reduction caused by of the two grades of envelope are different, the distribution
set-point adjustment is much larger than the energy savings rules of hourly load reduction have great similarity. (ii) With
obtained by heat transfer due to temperature differences the increase of cooling load before set-point rise, the hourly
at other cooling moments. It can also be seen from the load reduction presents two distribution rules. One is the

Volume 5 Issue 2 (2023) 9 https://doi.org/10.36922/jcau.0877