A Climate Based Study on Ecological Energy-Saving Technologies

A Climate Based Study on Ecological
Energy-Saving Technologies Used in Buildings of China

By Abdullah, Daniali

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1. Introduction

Energy consumption is increasing at an alarming rate within the past
several decades due to global population growth and as a consequence, has a massive diverse
effect on ecosystem. Space heating and cooling consumes
approximately 60% (Hou et al, 2017) of the total energy required in buildings
and it is expected to increase due to the rapid urbanization all over the world. According
to World Bank data the population of China was about 1.311 billion while this
amount has been increased to 1.38 billion in 10 years. Hence adopting efficient
energy conservation techniques in buildings’ design is crucial. Although
commonly energy-saving technologies (ESTs) such as external insulation for roof
and external wall, shading technology and natural ventilation and etc. are
being implemented widely, but it has been poorly understood and somehow
neglected that same EST demonstrates different effects in different climatic
regions. For that reason in this paper it has been tried to analyze and
demonstrate the effect of regional specification on estimation of energy
conservation methods.

There are
several ESTs used around the world but this review tries to describe some
practical ESTs used in different cities of China regarding the different
climate types of these cities. For the purpose of illustration, Shenyang,
Beijing, Chengdu, Hangzhou and Guangzhou as the case study cities, since they
have different ecological conditions and a representative individual building
is selected as the case model. The purpose of this study is to review the most
practical materials and technologies in concept of energy-saving with the
consideration of the different climate conditions.

2. Methods

China has five different climate type, severe
cold regions (Shenyang), cold region (Beijing), hot summer and cold winter
(Chengdu- Hangzhou), hot summer and warm winter (Guangzhou) and temperate
regions which is not included in our studies due to low energy saving potential.

According to statistics (website: http://www.eldoradocountyweather.com),
the maximum room temperatures in Hangzhou, Shenyang, Beijing, Chengdu and
Guangzhou are 31 °C, 32.3 °C, 33.7 °C, 32.5 °C and 34.6 °C respectively, while
the minimum temperatures are 1°C, -16.9 °C, -7.3 °C, 4.7 °C and 9.8 °C
respectively. As it shows, the maximum temperature is achieved in Guangzhou
while the minimum temperature has been achieved in Shenyang. Based on Huo et
al. 2017 studies, the discomfort degree hours for the four cities are listed in
Table 4.
Considering the room comfort temperature which is among 18 °C and 26 ° C, any
room temperature upper 26 or lower 18 would require using a heater or cooler.

In this study, a one story experimental
building has been designed and the total area correspond to about 50 m2.

The thermal characteristics of the materials
used in this study are given in Table 1.

Material

k (W/m K)               

q (kg/m3)

      cp (J/kg K)

Reinforced concrete

1.74

2500

520

Cement plaster

0.93

1800

1050

Brick

0.81

1800

1050

Window

5.9

2500

840

Air

1.2                     

1013

                                                       

And the methods used are as follows:

2.1. Highly insulated building envelope

External insulation is the most efficient
measure in reducing the heat transfer across the roof and exterior walls (Huo
et al, 2017). Therefore, this study adopted external thermal insulation system.

2.1.1. Roof and wall

The whole exterior walls
were enclosed by the low thermal conductivity
plastic board with 8cm depth cavity, where was filled with rock wool material
superior to the current energy-saving standards of
Hangzhou. For the purpose of experiment, the roof insulation
system adopted lightweight metal sandwich plate as the structural layer, above
which was paved in turn by coating waterproof layer and XPS insulating plate,
forming the inversion roofing system.

2.1.2. Window

In this building, all the windows were
double-glazed Low-E glass combining with heat insulting off-bridge aluminum to
prevent heat gain in summer and heat loss in winter. As coated with a layer of
metal oxides, low-E glass can reflect much of the shortwave radiation in
summer, reducing the air-conditioning loads. On the other hand, this film layer
also can decrease the ability of absorbing long wave radiation in winter,
benefiting to obtain the solar thermal energy in winter.

2.2. Solar energy absorption wall

Considering implementing solar energy system
into the building design, the solar photovoltaic and thermal collectors were
placed on the outer surface of the wall and on the roof. The rooms are designed
with the thermal storage wall as the main component for acquiring heat: 300mm heavy
concrete was covered with dark color where the inlet and outlet were placed
separately close to the ceiling and floor, and an extra glass box was set with
the distance of 600 mm to the concrete wall, all of which formed a comprehensive
system of dynamic heat collection, storage and transferring. The solar energy
absorbed by the massive concrete wall with higher heat capacity and thermal
conductivity was transferred into the inter room in the following two main
ways: firstly, the heat absorbed by the outside surface of the massive wall was
conducted through the wall to the surface of the other side, and released into
the room by means of the convection and radiation. The excess heat stored in
the wall during the daytime would be send out in the night time by the same way.
Secondly, the air heated in the glass box rise up through the upper inlet into
the room and the cold air inside the room drop down through the lower outlet
into the glass box and is heated again, which acts as a thermal chimney shown
in Fig.6

2.2 Directly benefit from solar energy