Fig. 3 Comparative analysis of primary indicators (a) M1, M2, M3, (b)
H1, H2, H3
In order to further evaluate the level of low carbonization of each
household, this study analyzed the secondary indicators of each
household, as shown in Fig 4a, a total of eight secondary indicators in
M2 have a weighted evaluation score greater than M1 and M3, which all
contribute to the assessment of low carbonization. Checking the research
situation of M2, we found that the windows used in the building are
aluminum windows, which have very good heat insulation effect and play a
good role in reducing heat loss, and the exterior wall construction is
made of Sanchi wall, which is better than both M1 and M3, so the
building has higher heat insulation effect and plays an important role
in LCI. In the case of energy use, M2 uses more biomass, mainly tree
branches, and biomass has an important role in low carbon, and these two
indicators also show the importance of ”energy use” and ”envelope”,
which have a significant impact on improving LCI [22]. M3 is a
”high-carbon” case with the lowest evaluation score, and the analysis of
its score can help to improve the level of low carbonization in the
future. Generally, because M3 did not carry out envelope renovation and
energy renovation, the energy used is mainly bulk coal and cellular
coal, which is used a lot and causes relatively serious pollution. For
M3, the indicators with good weighted scores are ”per capita annual
household income” and ”window-to-wall ratio”, which shows that M3 has a
good per capita annual income level and has the economic ability to use
clean energy. The ”window-to-wall ratio” also lays a certain foundation
for future envelope renovation and does not require too many changes in
windows and doors.
Through the study of the renovated H1-H3, it was found that before the
renovation as M1-M3, the walls of the buildings did not have good
insulation materials, and they could only rely on burning large amounts
of coal for heating and as a source of energy consumption such as
domestic hot water and cooking in winter. However, in recent years,
through the transformation of the envelope structure and the change of
energy utilization, the insulation layer has been added to the exterior
walls of residential buildings, and the insulation material is mainly of
the polystyrene board type, which has a good thermal insulation effect
and guarantees an effective improvement of the indoor thermal
environment [23]. The energy used is also cleaner and low-carbon,
and the reduction in the amount of coal combustion has improved the
indoor air quality and changed the original ”dirty, messy, and poor”
situation. In terms of ”energy use”, biomass energy resources are
abundant in the study village, and the renovated buildings have
increased the use of new biomass stoves and solid-formed biomass
pellets, and in recent years have increased the use of solar
photovoltaic power generation, which can supplement household
electricity and reduce the use of coal compared with no energy
renovation. In terms of ”envelope”, the addition of wall insulation
systems has improved indoor temperatures, and windows have been replaced
with aluminum and plastic windows from the original wooden windows or
old-fashioned steel windows. The ”layout design” aspect, as an indicator
with limited changes during renovation, was also selected with different
regional conditions in mind, and although it did not change much in the
case study, it will play its importance in a broader range of uses in
the future [24]; the research site selected for this paper was
Zhejiang Province, so ”site rationality”, ”building orientation
arrangement”, and ”geographic location distribution” have not changed,
and ”living area per capita ” had some changes before and after the
renovation, but this paper only focuses on residential buildings, and
the renovation did not have an impact.