Effect on Building Space Heating and Cooling Loads and Electricity Production

Table 3 presents the electricity production obtained with TRNSYS for the three BIPV curtainwall constructions (scenarios 2, 3 and 4). As it can be observed, systems in Yellowknife and Iqaluit generate approximately the same amount of electricity, whereas the ones in Montreal produce between 4 and 7% less electricity. This can be explained by Yellowknife and Iqaluit greater annual south-facing vertical radiation and lower ambient temperature throughout the year. This table also indicates that scenario 4 is the worst in terms of electricity generation with a production reduced by more than 22% compared to scenarios 2 and 3. The building heating and cooling loads for each one of the 5 scenarios and 3 cities considered are shown in Fig. 6. From this graph, it can be seen that for every city, the lowest heating loads are obtained in scenarios where spandrel is used as the non­vision section, with a difference of only 2 to 3% between the double-glazed and triple-glazed cases (scenario 1 and 5). This variation is small considering that the triple-glazed curtainwall construction of scenario 5 has greater thermal resistance, but this assembly also has a lower solar heat gain coefficient and thus, provide less passive solar heating. The influence of changing from a double-glazed to a triple-glazed system on the space cooling energy requirements is only noticeable for Montreal, but is more important than for space heating with a difference between the two scenarios in the order of 6%. When comparing the substitution of spandrel panels with BIPV curtainwalls, it can be observed that it affects more significantly the space heating load than the cooling load, and the double-glazed systems than the triple-glazed systems. In fact, the heating load increases by 8.9-10.6% when going from scenario 1 to 2 and only by 4.6-5.3% and 5.6-6.3% when going from scenario 5 to 3 and 5 to 4, respectively.

Table 3. Annual DC electricity production for vertical curtainwall assemblies.

# DC electricity production (kWh/m2 floor area)*

Yellowknife

Iqaluit

Montreal

2

6.21

6.28

5.90

3

6.22

6.29

5.90

4

4.79

4.84

4.41

image494

Scenario

Fig. 6 Building heating and cooling loads for the 5 scenarios.

2. Conclusion

This study showed that double-glazed and triple-glazed BIPV curtainwalls with a PV laminate used as the outer pane have similar electrical performance. When a PV laminate is used as the middle pane in a naturally ventilated triple-glazed fenestration system, however, a reduction in electricity generation in the order of 22% can be expected due to the smaller amount or radiation reaching the cells and the heating up of the PV. A possible benefit of this last configuration was found to be the reduction of perimeter heating in the winter caused by greater inner glazing temperature. In locations with important cooling load, however, this temperature could potentially create discomfort in the summer. When using BIPV curtainwalls for the non-vision sections of a south­facing curtainwall facade of a small office building, the heating load was found to increase by 8.9­10.6% for the double-glazed systems and 4.6-5.3% for the triple-glazed ones.

References

[1] M. M. Karteris, K. P. Papageorgiou, A. M. Papadopoulos, (2006). Integrated Photovoltaics as an Element of Building’s Envelope, Int. Workshop on Energy Performance and Env. Quality of Buildings, Greece.

[2] J. Ayoub, L. Dignard-Bailey, W., Richardson, (2003). Promoting Grid-Tied Solar Electricity on Buildings in Canada, SESCI 2003 Conference, August 18-20, Kingston, Ontario.

[3] J. Ayoub, (2006). National Survey Report of PV Power Applications in Canada, International Energy Agency Co-Operative Programme on Photovoltaic Power System.

[4] P. W. Wong, Y. Shimoda, M. Nonaka, M. Inoue, M. Mizuno, (2008). Semi-Transparent PV: Thermal Performance, Power Generation, Daylight Modelling and Energy Saving Potential in a Residential Application, Renewable Energy, 33, 1024-1036.

[5] T. Fung, H. Yang, (2008). Study on Thermal Performance of Semi-Transparent Building-Integrated Photovoltaic Glazings, Energy and Buildings, 40, 341-350.

[6] D. Curcija, W. P. Goss, (1995). New Correlations for Convective Heat Transfer Coefficient on Indoor Fenestration Surfaces – Compilation of More Recent Work, ASHRAE/DOE/BTECC Conference, Thermal Performance of the Exterior Envelopes of Buildings VI.

[7] R. J. Cole, N. S. Sturrock, (1977). The Convective Heat Exchange at the External Surface of Buildings, Building and Environment, 12, 207-214.

[8] J. L. Wright, (1996). A Correlation to Quantify Convective Heat Transfer between Vertical Window Glazings, ASHRAE Transactions, 102, Pt. 1, 940-946.

[9] ASHRAE, (1998). Standard Method for Determining and Expressing the Heat Transfer and Total Optical Properties of Fenestration Products, Public Review Draft of Standard 142P, American Society of Hating, Refrigerating and Air Conditioning Engineers, Atlanta.

[10] Y. Poissant, L. Couture, L. Dignard-Bailey, D. Thevenard, P. Cusack, H. Oberholzer, (2003). Simple Test Methods for Evaluating the Energy Ratings of PV Modules Under Various Environmental Conditions, Proc. 2003 ISES Solar World Congress, Junte 14-19, Goteborg, Sweden.

[11] SEL (Solar Energy Laboratory), (2005). TRNSYS 16 – A Transient System Simulation Program, University of Wisconsin, Madison, Wisconsin.

[12] D. E. Holte, (1995). A Parametric Study of the Impact of High Performance Windows (and Curtain Walls) on Building Heating and Cooling Loads, Energy Use & HVAC System Design, Conf. Proc. Window Innovation’95 Toronto, Canada, June 5-6, 500-508.

[13] Enermodal, (2001). FRAMETMplus 5.0 developed for Natural Resources Canada.

[14] Natural Resources Canada, (2005). RETScreen Int. 4.0 – Clean Energy Project Analysis Software.

[15] Caneta Research Inc, (2001). Development of Generic Office Building Energy Measures, Report prepared for Public Works and Government Services Canada.

[16] National Research Council Canada, (1997). Canadian Model National Energy Code for Buildings 1997.

Nomenclature

Symbols

cv

Convective

Specific heat at constant pressure (kJ/kgK)

g

Glazing

c

Specific heat at constant volume (kJ/kgK)

gnd

Ground

F

View factor (dimensionless) 2

i

Inner

h

Heat transfer coefficient (kJ/hm2K)

in

Inlet

H

Window height (m)

Li

PV laminate glazing facing indoor

m

Mass flow (kg/h)

Lm

PV laminate middle layer (PV+EVA)

Ppy

PV cells power (kJ/hm2)

Lo

PV laminate glazing facing outdoor

R

Thermal Resistance (hm2K/kJ)

o

Outer

t

Thickness (m)

out

Outlet

T

Temperature (K)

rd

Radiative

S

Absorbed solar energy (kJ/hm2)

sky

Sky

W

Window width (m)

sur

Surroundings

Subscripts

Greek symbols

a

Air cavity

є

Emissivity (dimensionless)

amb

Ambient

P

Density (kg/m3)

cd

Conductive

a

Stefan-Boltzmann constant (kJ/hm2K)

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