Research on Energy Saving of the Existing Public Building in China
Mei Wang1、Yi Wang2
1.School of Management, Xi’an University of Architecture &Technology, China；2.China United NorthwestInstitute for
Engineering Design & Reash
(iceagemay@126.com)
Abstract-In this paper, in order to evaluate the
economic performance of energy-saving retrofitting in
existing buildings, we have researched the Chinese
public building energy consumption structure. An
existing public building was taken as an example in
order to best evaluate the economic performance
based on comparison between the annual electricity
consumption before and after retrofitting, and also to
analyze energy conservation of retrofitting. The results
show that selecting the appropriate energy-saving
technology canlead to a more satisfactory economic
benefit in energy-saving commitments over the coming
years.
are 18.1kgce/㎡.
Keywords-Existing
public
building;
energy
consumption analysis; energy saving retrofitting;
economic evaluation
A . Building Envelop Energy Consumption
I. INTRODUCTION
China is a high energy consumption country. The
construction industry consumes roughly a third of the
energy in the process of construction and use. Up to 2010,
Chinese public building amassed some 45 billion square
meters, and the area of the public building is 10.7% of the
urban-rural house area1. But the public building energy
consumption is 20.7% in construction energy
consumption. Chinese energy supply security will suffer
stress when the public consumption remains obstinately
high, which makes energy-saving retrofitting an
imperative in China’s future.
II. THE STATUS OF CHINESE PUBLIC
BUILDING
There is 20 billion square metersof new floor space
created in China every year, but 80%~90% of it doesn’t
reach the International Energy Conservation standard, and
the unit floor area heating consumption is three times
thatof developed countries 2 . The public construction
segment makes up 16% of the entireChinese construction
area,and although large public structures arejust 11% of
all Chinese structures, their energy consumption is 19%
of total.According to the survey, Chinese public
construction’s power consumption is up to1.41 billion tce.
The electric power consumption of average unit area is
48.6kWh/(㎡·a),and the energy consumption of unit area
III. ANALYZE THE CONSISTS OF PUBLIC
BUILDING ENERGY CONSUMPTION
Heating and refrigeration consume 50%~60% energy
of the public building energy consumption all year round,
and lighting costs 20%~50%.20%~50% of energies are
consumed by the building envelop in refrigeration energy
consumption3. Therefore, public building energy saving is
focus on building envelop, heating and lighting
equipment.
Building envelop thermal performance determines
heating and refrigeration energy indication 4 . Handing
practices to building envelop are usually constructed:
1)Wall. Solid clay brick masonry wall is 240mm
thick,20mmthick wipe inside and outside the mixed
mortar, heat transfer coefficient K value of approximately
1.873W/(m · K)and the value of the national energy
efficiency standards for the 0.52W/(m·K)is three times
that. 2) Roof. Does not reach the roof thermal energy
standard, which will influence the performance of roof
insulation. 3) Doors and windows. Most are wooden
doors and steel windows, which have a large gap rate,
thus it is difficult to ensure the quality of the indoor
environment5
B.
Heating System Energy
The heating energy of our country is about
1.3million tons of coal throughout a year. The average
energy expended is 2-3 times of developed countries with
a similar climate. Heat loss of heating system is about 15%
to 30%. Heating system design and construction lack
necessary adjustment and measurement instruments,
which result in high energyexpending heating systems .
C . Air Conditioning System Energy
Different types of air conditioning energy systems
within public buildings range between the13 ~ 45kw • h /
(m • a)6.Unreasonable building design and ventilation,
unreasonable system and selection of equipment and
operating methods, and unreasonable operating systems
have led to the high energy consumption with in air
conditioning systems of public buildings7.
D.
Building
Equipment
Energy
Consumption
of Electrical
Survey indicates that building energy consumption
of electrical equipment mainly reflects in the following
areas: 1) Equipment efficiency. Not using the right
equipment leads to low efficiency and high energy
consumption,
resulting
in
energy
waste.
2)
Air-conditioning equipment. Public buildings are always
equipped with central air conditioning, while air
conditioning cold caloric needs long-distance transport,
during which losses of energy consumption in the
transportation process are caused. 3) User habits. Actions
such as daytime lights, keeping computers and air
conditioning working when get off work all seem to be
insignificant, but the amount of potential actual energy
saving could be huge8.
IV. EXISTING PUBLIC ENERGY SAVING
BENEFIT ANALYSIS
A.
Simulation of Energy Consumption Data
To achieve lower energy consumption is both the
target of energy-saving in public buildings and the
evaluation criteria. Accurately measuring or calculating
the amount of energy consumption is fundamental for the
proper economic evaluation of existing public buildings’
energy saving transformation 9 . Building energy
simulation software can simulate the total energy
consumption and the sub-entry energy consumption of
reconstruction，which can be used to compare the levels
of energy saving before and after, and soachieving the
comparison and analysis of energy level of the energy
saving transformation.
B . Energy Transformation of The Economic Model
When conducting the economic evaluation of public
buildings energy-efficiency, we must consider the
relationship between the energy-saving one-time
investment and the building energy costs. We must also
take into account both the economic and energy-saving
standards of the comprehensive benefits. In this paper, by
using the financial evaluation method to conduct the
economic evaluation of public buildings’ energy saving
transformation, we analyzed and calculated the costs of
energy-saving and energy saving benefits after the
transformation, and calculated the economic evaluation
index of the energy-saving project, all to study the
profitability of energy-saving projects and best judge the
economic feasibility of energy saving.
C.
Calculation Of The Cost Of Energy-saving
The main difference between energy-saving building
and non- energy-saving building is the material fee of the
direct expense of a project, therefore, the estimation of the
energy-saving construction cost is largely the analysis of
the cost of consumption of energy-saving materials.
Energy-saving costs include energy-saving materials’
costs and construction costs.
I0 = ∑ki=1(a i + bi )si
(1)
The equation (1) shows the energy saving cost, the
unit price of i kind construction materials used in the
energy-saving building, the unit cost of construction of i
kind materials used in the transformation, the quantity of i
kind energy saving materials used in the energy saving
building, while k is for the type of the energy-saving
building materials used in energy-saving building.
D.
Calculation Of Energy-saving Benefits
The reduced energy consumption fees of public
buildings energy-saving transformation can be called
energy-saving gains. The characteristics of public
buildings in China's energy consumption are as follows:
heating energy consumption is mainly in the north while
air-conditioning and lighting energy consumption is in the
south. Therefore, the income can be estimated with
energy consumption index:
I0′ = (𝑄𝑡 − 𝑄𝑡′ )p
(2)
(2) shows the energy saving benefits of the existing
public buildings and the power consumption difference of
the energy-saving construction transformation; p is for
energy prices.
E. Analysis Model Of
Energy-saving Project
Financial
Evaluation
Of
In this paper, giving full consideration to energy
prices and the discount rate, the actual energy efficiency
has an impact on the cost changes of existing public
buildings’ energy-saving.Energy efficiency also impacts
uponcumulative annual net cash flow and net cash flow in
calculating the energy-saving payback period, and in
clarifying the economic benefits enjoyed during the
operation period. Energy cost savings per year in net cash
NCTt :
NCTt = αp(Qt − Q′t )(F⁄P , μ, 𝑡)(P⁄F , i, 𝑡)
flow10used
(3)
Because Energy-efficient buildings reduce energy
consumption, the energy-efficient gains achieved by
Energy-efficient buildings besides cost of its available
energy saving in economic life used ANCTt :
ANCTt = ∑n−1
t=1 αp(Q t −
′ )(F⁄
Qt
P, μ, 𝑡)(P⁄F , i, 𝑡) − γI0 (4)
Energy-efficient buildings in the course of the time
of energy-saving benefits cover the cost of it’s energy
saving retrofitting could be represented by dynamic
investment recovery period Pt′ :
Pt′ = 𝑚 − 1 +
|ANCTm−1 |
（5）
NCTm
In equation(5),(F/P,μ,n)is payment of the final value
of the coefficient;(P/F,i,n)is discount factor is construction
phases of economic life; α is actual energy saving
efficiency; μ is the growth rate of energy prices; i is
discount rate; is the year when cumulative NPV began to
appear positive age.
dust with a good sound insulation effect. When making
energy-saving windows, the original single-layer hollow
glass windows are replaced by single-layer steel
sliding-sash window frames, which do not move.
C.
Building Energy Consumption After Energy-saving
After the transformation of existing public buildings
to maintain the structure summarized in table II:
V. EXAMPLE ANALYSIS
TABLE II
A.
Engineering Overview
Energy saving design
In this paper, the total construction area of
12,700square meters of a University Library is to be
usedas an example of before and after annual energy
consumption, energy-saving and cost analysis of energy
saving. The library is located in Xi’an, and is in
possession of anopen-shelf reading room, lecture hall,
meeting rooms, other electronic reading rooms and
various administrative spaces. The height of these
respective spaces is 2.9meters, witha total of five layers.
The building includes outer walls of reinforced concrete,
an exterior wall outside the mortar, and brush brown
acrylic paint. Retrofitting of the library before the
insulation is regarded as beingpoor and has had a
significant impact to the students self-study and
borrowing experience. Table I is envelope overview.
TABLE I
Overview of existing public buildings envelope
Name
Materials
Roof
20mm thick surface layer
of fine
aggregate
concrete,
waterproof layer,110mm thick reinfor
ced concrete layer, 25mm thick plaster
Wall
Window
B.
Heat
transfer
coefficient
/
（W/(㎡·K)）
20mm thick cement
mortar,
180mm thick clay
brick,
20mm thick gray lime mortar
Steel single layer pull/push window
2.7
Name
Material
Roof
25Mm thick extruded
polyphone board
200mm
thick
aerated
concrete block
empty glass window
Wall
Window
coefficient
of
heat
transfer /（W/(㎡·K)）
0.97
0.75
2.7
The statistics, the library before and after the years
of energy-saving power consumption, see Table III:
TABLE III
The library’s electric power consumption before and
after retrofitting
Name
The library before energy
saving transformation
The library after energy
saving transformation
Years power consumption (kWh/㎡)
898760
436237
D. Energy Consumption Analysis Based on Economic
Evaluation of Energy Saving
Cost and Energy Saving Energy Saving Calculation
of earnings
The cost of energy-saving type (1) calculated with
reference to the 2009 "construction project in Shaanxi
Province lists" computing the price of materials. Cost
Analysis of Energy Saving in Table IV below:
2.53
TABLE IV
5.0
Determination Of Energy-saving Design
1. Roof
Roof heat transfer coefficient 2.7 W / (m • K);this
higher than the "public building energy efficiency design
standards";The roof being capped with 25mm thick
extruded polyethylene board.
2. Wall
Wall heat transfer coefficient is 2.53 W / (m • K);
higher than the "public building energy efficiency design
standards". Aerated concrete blocks are used to achieve
better thermal insulation properties.
3. Window
The project for the single-layer steel sliding sash
windows, the heat transfer coefficient is 5.0 W / (m • K);
the plastic-steel windows can reduce the external
radiation on the human body, both hot and cold, and also
Cost of energy saving retrofitting
Energy-saving
technology reform
25mm thick extruded
polyphone board
200mm thick aerated
concrete block
Empty glass window
Amount
Quantities
（㎡）
Comprehensi
ve unit price
（yuan）
Total
price（yuan）
108.26
57673.34
4260.26
88.86
378566.70
2036.58
-
204.45
-
416378.78
852618.82
532.73
The current price of electricity in Shaanxi Province
is 0.7486 RMB / kWh, energy saving retrofitting costI0 =
852618.82 RMB, the profit after energy saving
retrofitting could be work out by equation(2).This library
can save energy fee I0′ =346244.72yuan after retrofitting.
E.
Financial Analysis Of Energy Saving
The assumed energy price growth rate is 7%.
Assumed public building actual energy-saving efficiency
is 100%, with a discount rate of6%. Because the public
building energy-saving operational period must be short
relative to its cost, the cost of the energy-saving
rate-of-change is 100%, the construction ageis 1a, and
operation period is 49a; where 1a refers to one full year.
NCTt = 100% × 346244.72 ×
(F⁄P , 7%, 3)(P⁄F , 6%, 3) ANCTt = ∑49
t=1 100% ×
346244.72 × (F⁄P , 7%, 𝑡)(P⁄F , 6%, 𝑡) − 852618.82
WhenANCTt ≥0,force t to assume integral values, the
calculation shows that ANCT2 =-150296.37
yuan, ANCT3 =205819.78 yuan,t≥3a.
Compute dynamic investment recovery period Pt′ :
NCTt =
100% × 346244.72 × (F⁄P , 7%, 3)(P⁄F , 6%, 3)
= 356116.16
|−150296.37|
′
Pt = 3 − 1 +
= 2.4a
356116.16
Through analysis, the electric power consumption
fell 51.46% after retrofitting, this in line with
requirements that energy-saving buildings should save
energy at around the 50%mark after retrofitting. When
energy prices rose 7%,the dynamic investment recovery
period sits at 2.4a. Chinese ‘Public Building Energy
Efficiency Design Standards’ allow for the increasing of
energy-efficient buildings only provided that the payback
period does not exceed ten years, so retro-fitting is
feasible in the library.
VI. CONCLUSION
This paper analyzes the composition of public
building energy consumption and, on this basis, selected
energy-saving measures in public buildings, as well as the
use of financial analysis and economic evaluation of
existing public buildings for energy saving. The results
show that existing public buildings would be best served
by taking full advantage of the energy-saving thermal
performance of building envelope improvements as well
as the use of natural ventilation; both with the view to
improve energy efficiency and to reduce energy-saving
costs associated with the running and maintenance of
existing public buildings.
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