Application of PV window for office building in hot summer and cold

winter zone of China

Wenwen Guo 1, a Zhongzhu Qiu 2, b, Peng Li 3, c, Jia He 4,d, Yi Zhang 5,e,

Qiming Li 6,f

1 Shanghai University of Electric Power, Shanghai, China

2 Shanghai University of Electric Power, Shanghai, China

3 Tongji University, Shanghai, China

4 Shanghai University of Electric Power, Shanghai, China

5 Shanghai University of Electric Power, Shanghai, China

6 Shanghai University of Electric Power, Shanghai, China

a guowenwen1204@163.com

Keywords: PV window, energy performance, simulation

Abstract. In this paper, three kinds of PV glazing system applied to office building of Shanghai

which located in hot summer and cold winter zone of China were studied. Building simulation

software Energy Plus was used to simulate thermal load, lighting electricity consumption, and PV

electricity generation. According to the simulation results of annual electricity consumption, taking

SC as the comparison basis, the saving rate of single PV glazing system (SPV) was 3.6%, double

PV glazing system (DPV) was 4.8%, and natural-ventilated PV glazing system (NVPV) was 6.7%.

Introduction

With the life level improved, people have higher demand on the comfort of their living and working

environment. There is no problem to realize the demand, but it needs more energy consumption [1]

.

In modern architecture, windows play an important role to reduce energy demands in respect of

heating and cooling loads and lighting requirement. Therefore, people paid more and more attention

to the interrelation between window design and thermal performance [2, 3]

. Zhi-ying Li [3]

using the

dynamic energy consumption simulating software ESP-r to simulate and analyze the relation

between shape coefficient, window to wall ratio of the glass curtain wall and cooling load. Research

showed that when the shape coefficient increases, the cooling load increases, so does the window to

wall ratio.

When window is integrated with photovoltaic, it acquires an additional function of electricity

production. The application of semi-transparent photovoltaic window had been received people's

attention. Tady[4]

evaluated the heat gain of semi-transparent photovoltaic modules for

building-integrated applications. It was found that the area of solar cell in the PV module has

significant effect on the total heat gain, the solar cell energy efficiency and the PV module's

thickness have only a little influence on the total heat gain. Tin-tai Chow[5]

evaluated the annual

Advanced Materials Research Vols. 347-353 (2012) pp 81-88Online available since 2011/Oct/07 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.347-353.81

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variations in thermal loads and electricity generation for two PV glazing systems as compared to the

common absorptive glazing in Hong Kong. The results indicate that by using the natural-ventilated

PV glazing the air-conditioning power consumption could reduce 28%.

The objective of this paper is to explore the energy performance of the SPV, DPV, and NVPV

used in Shanghai, which is at the hot summer and cold winter zone of China.

Experiment

Experimental setup and weather data. The glazing system of test room was an innovative natural

ventilated PV glazing system, the outer and inner glass panes were, respectively, PV glass and clear

glass, leaving a 35mm air gap between the glass panes. The test room indoor air temperature was

maintained at 22±0.5˚C round the clock. Two CMP6 pyrometers were used to measure the global

solar radiation conditions. The temperature conditions of the glass panes were monitored by

thermocouples attached to the outer and inner surfaces of each glass pane. The experimental data

were: ambient temperature, wind speed, wind direction, solar radiation intensity, indoor daylight

illumination, indoor temperature, glass surface temperature, PV power output. The automatically

data acquisition systems worked 24 hours every day.

Description of PV windows. In this paper, four kinds of window were studied, SC, SPV, DPV

and NVPV. DPV comprises a PV glass pane at the front and a clear glass pane at the back, between

them is airtight air. NVPV also comprises a PV glass pane at the front and a clear glass pane at the

back, but the difference is leaving an air cavity with the top and bottom openings facing the outside

or inside. In the summer the air from outside to outside, in the winter the air from inside to inside.

Three kinds of PV glazing systems are shown in Fig.1. Table 1 shows the optical properties of PV

glass.

(a) SPV (b) DPV (c)NVPV summer mode (d)NVPV winter mode

Fig.1 Schematic structure of three PV windows

82 Renewable and Sustainable Energy

Table 1 Optical properties of PV glass

Components Data

Solar cell type

Effective transmittance(thermal)

Effective transmittance(visible)

Solar heat gain coefficient

Shading coefficient

Output power

PV efficiency

Max power voltage

Max power current

Open circuit voltage

Short circuit current

Amorphous silicon

0.102

0.106

0.24

0.27

38.0W

4%

58.6V

0.648A

91.8V

0.972A

Mathematical models and validation

Thermal model. Energy plus calculates thermal loads of buildings by the heat balance method, it

takes into account all heat balances on outdoor and indoor surfaces and transient heat conduction

through building fabric, which is more accurate than the weighting factor method used in DOE-2[6]

.

Three days measured data of PV glass and clear glass surface temperature in the summer were

compared with the simulated data, shown in Fig.2. On a whole, the simulation results of the glass

temperature are in good agreement with the measured data.

Fig.2 Comparison between the measured and simulated temperature of the glass

PV output power model. “Equivalent One-Diode” module was used in the simulation. The

module employs a “four-parameter” equivalent circuit to model PV modules [7,8]

.

The power output of the PV panel is:

(1)

Fig.3 showed the experimental data and the simulated data of PV power output. In general, the

simulation results of the glass temperature are in good agreement with the measured data.

Advanced Materials Research Vols. 347-353 83

Fig.3 Comparison of the measured and simulated power output

Daylighting model. The Energy Plus programme carries out the calculation of internal

luminance through the external luminance and the daylight factor (DF)[9]

. The DF is determined

through the relation between the luminance of the point of reference Ep and the external horizontal

luminance Ehext.

(2)

Fig.4 showed the experimental data and the simulated data of indoor daylight illumination.

Again good matching can be observed.

Fig.4 Comparison between the measured and simulated indoor daylight illumination

Energy performance simulation of an office building

Description of the office building simulated in the study. In modern cities, most high office

buildings have identical floor plans, so in this paper, only the standard floor is studied. The indoor

temperatures of the upper and the lower floors were assumed to be maintained at the same as the

standard floor. This model is a 40.8m×40.8m open-plan office and the floor-to-floor height is 3.6m,

which is one typical case taken from the reference [10]. The floor has four office zones, which were

oriented to the north, south, west, and east, respectively. The central zone is a core zone. A

perspective view of the office model is shown in Fig.5.

84 Renewable and Sustainable Energy

Fig.5 Perspective view of the simulation model

Building location. In order to research the energy performance of PV windows which used in

hot summer and cold winter zone of China, Shanghai was taken as a representative city, its

longitude is 121.4E, latitude is 31.2N, annual mean solar radiation is 172.6, heating period is

11.7--4.21 and cooling period is 5.17--10.10, and the data from reference[11] and [12].

Simulation results and discussion

Thermal loads. The monthly thermal loads were obtained through simulation. Fig.6 and Fig.7

show the monthly heating load and cooling load. Form Fig.6 it can be seen that the four curves have

very similar patterns, with the SPV curve at the top, which means it need the most heating load,

followed by the SC, and the NVPV curve at the lower end, it need the least heating load. In the

heating period, the indoor temperature is higher than outdoor, the more solar radiation heat gain the

better, because solar radiation can cut down the heating load. The lower U-value the better, the

lower U-value, which means that the window has a good thermal insulation, the lower heating load.

The solar heat gain coefficient of SPV is the least one of the four, and its U-value is 6.0, the largest

one, so SPV need the most heating load. Though SC allowed the most solar heat gain, but its

U-value is similar to SPV, the thermal insulation of SC is not good, so SC is the second one. The

solar heat gain coefficients of DPV and NVPV are larger than SPV and less than SC, and their

U-values are less than both SPV and SC. NVPV allowed inside ventilation, the warm air through

the gap and warms the window, reducing the heat loss from the window, so its effect is better than

DPV. Compared with SC, the heating load saving rate of DPV was 3.7%, NVPV was 10.4%, and

the increasing rate of SPV was 30.7%.

Fig.6 Monthly heating load of four windows

Advanced Materials Research Vols. 347-353 85

The monthly cooling load distributions are given in Fig. 7. It indicated that the four curves have

very similar patterns, with the SC curve at the top, followed by the SPV, and the NVPV curve at the

lower end. In cooing period, the indoor temperature is lower than outdoor, the less solar heat gain

the better, which means less solar heat gain less cooling load. So the lower solar heat gain

coefficient is the advantage of PV windows. Compared with SPV and DPV, NVPV allowed outside

ventilation, it can reduce the cooling load by expelling some of the solar heat absorbed by the

window glass. Compared with SC, the cooling load saving rate of SPV was 23.4%, DPV was 25.4%,

NVPV was 29%.

Fig.7 Monthly cooling load of four windows

PV output power. Fig.8 indicated the PV output power of PV windows. We can see that the

output power of DPV is least, SPV and NVPV are little more than DPV, they have almost the same

output power. The monthly mean solar radiation is also shown in Fig.8. The variation trend of PV

output power are very similar to that of mean solar radiation, this demonstrate that solar radiation

has a decisive influence on the PV output power.

Fig.8 Monthly PV output power and mean solar radiation

Total electricity consumption. Fig.9 showed a bar chart indicating end-uses of annual

electricity consumption for the four windows case with lighting control. The details of each

component were shown in Table 2. The electricity consumption of HVAC system was calculated by

simply dividing the thermal load by taking a cooling COP of 3.0 and a heating load of 4.0. The

electricity production from the PV was denoted as negative values. It could be observed that the

electricity consumption for lighting was the most significant factor among the electricity end-uses.

The SC need least lighting electricity consumption because of its visible transmittance was the

largest. The total electricity consumption curve demonstrated that SC consumes the most electricity,

followed by SPV, and NVPV need the least.

86 Renewable and Sustainable Energy

Fig.9 Annual total electricity consumption

Table 2 Annual electricity consumption by window type

Lighting Heating Cooling PV output Total Saving rate

SC 73014 8003 45043 - 126060 -

SPV 89749 10459 34509 -13192 121526 3.6%

DPV 91679 7703 33585 -13012 119955 4.8%

NVPV 91679 7167 31997 -13170 117673 6.7%

Conclusions

In the research, the application of PV windows of office building in hot summer and cold winter

zone of China was investigated. The analyses on the thermal load and PV output power and annual

electricity consumption were carried out, and the optimum PV window was found.

For heating load, taking SC as the comparison basis, the saving rate of DPV was 3.7%, NVPV

was 10.4%, and the increasing rate of SPV was 30.7%.

For cooling load, taking SC as the comparison basis, the saving rate of SPV was 23.4%, DPV

was 25.4%, and NVPV was 29%.

For PV output power, DPV was the least one, SPV and NVPV are little more than DPV, they

have almost the same output power.

For annual electricity consumption, taking SC as the comparison basis, the saving rate of SPV

was 3.6%, DPV was 4.8%, and NVPV was 6.7%.

Acknowledgement

This paper is partly supported by Shanghai Science and Technology Commisson (09DZ1207200),

the fifth Key Subject of Shanghai Education Commission(G51304) and the third phase of

undergraduate education center constructin project of Shanghai Education Commisson

Advanced Materials Research Vols. 347-353 87

Nomenclature

γ empirical PV curve-fitting parameter k Boltzmann Constant,1.38×10-23

J/(K·mol)

TC cell temperature, K I the cell terminal current, A

IL light generated current, A Io diode reverse saturation current, A

V the output voltage q the electron charge 1.602×10-19

C

P panel power output, W m number of parallel connected cells, dimensionless

N number of panels in surface, dimensionless n number of series connected cells, dimensionless

DF daylight factor, % Rs module series resistance

Ep luminance of the point or reference, lux Ehext the external horizontal illuminance, lux

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