Sustainable Building Façade and

Advanced Fenestration Systems

Tin-Tai ChowBuilding Energy & Environmental Technology Research Unit

Division of Building Science and TechnologyCity University of Hong Kong

(http://www6.cityu.edu.hk/bst/BEET/project_page/index.htm)

Workshop on Potential Technological Developments for Zero Carbon Buildings

16-17 Oct 2013

Low-Carbon Building (LCB)Technology• Passive solar design• Daylight utilization• Efficient ventilation and airflow strategy• High performance system equipment• Energy management and optimization• Thermal and electric load shifting• Waste water and heat recovery• Minimum transportation• Material recycling and min. embedded energy

Stratum ventilationTimber building

Light pipe

Heat exchanger

Water film windows Green roof

Zero-Carbon Building (ZCB) Technology

• Low-carbon building (LCB) technologyPLUS Renewable energy sources

e.g. active solar design, wind energy utilization, biofuel utilization, etc.

Bio-diesel Gen-set

PV/T heat pump / heat pipe

Wind turbine

Roof-mount PV panels Solar-wind power street light

Solar wall and water heaters (ZCB)• Solar chimney

• Wall embedded water piping

• Vacuum-tube water heaters

• Building facade integration for maximum power output

• Energy generation in association with reduced building thermal transmission (reduced air-conditioning load) and heat reflection (reduced UHI effect)

Double skin facade

Vacuum-tube water heaters at balcony

Chow et al. Energy and Buildings, 43(12), 2011, 3467-3474.

Chow et al. Applied Energy, 83(1), 2006, 42-54.

Chow et al. Applied Thermal Engineering, 23(16), 2003, 2035-2049.

Opaque Facade: BiPV/T (ZCB)

Payback period (years)

Stand‐alone 

Building‐integrated 

Economical  12.1 13.8Energy  2.8 3.8GHG  3.2 4.0

Flat-box aluminum thermal absorberInvention patent CN 1716642

Stand-alone PV/TChow TT et al. Solar Energy, 80(3), 2006, 298-306.

Building-integrated PV/TChow TT et al. Applied Energy, 86(5), 2009, 689-696.

Life Cycle Analysis

Chow TT, Ji J, Int J Photoenergy, 2012 Special issue.

Glazed BuildingsExtensively-glazed buildings are widely in use

• Positive side: transparency; natural brightness; modernity; indoor-outdoor interaction

• Negative side: weak thermal element; energy wastage; global warming

Multi-pane window glazing (LCB)• Air-sealed glazing

• Gas-filled glazing

• Vacuum glazing

• Low-e glazing [IGU]

Chow TT, Li CY, Lin Z. Solar Energy Materials & Solar Cells, 94(2), 2010, 212-220.

Ultra-violet: 300-400 nmVisible light: 400-700 nmNear infra red: 700-2500 nm

New roles of advanced window systems

Two basic principles of ZCB window design for warm climate zone to reduce room heat gain:

1. To filter out infrared spectrum, but not visible light; and

2. To utilize solar radiation as renewable energy source.

absorptive glazing

Thin film PV glazing

See-through Photovoltaic Glazing

Chow TT, Qiu ZZ, Li CY, Solar Energy Materials and Solar Cells, 93, 2009, 230-238.

01000

20003000

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8000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

month

NV

D-P

V/C

cool

ing

load

, kW

h

S E N W

Monthly cooling load distribution for HK in 4 major directions

PV Ventilated Glazing – with power generation

PV glass

solar transmission

incident solar

radiation

indoor

thermal radiation & convection

air flow

clear glassnatural convection

thermal radiation exchange

outdoor

thermal radiation & convection

To DC load

With semi-transparent a-Si solar cells on glazing:

Advantages: energy saving through electricity generation together with reduction in air-conditioning and artificial lighting

Disadvantage: high investment costs

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month

cool

ing

load

, kW

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S-AB S-PV NVD-PV/C

Chow TT, Qiu ZZ, Li CY, Solar Energy Materials & Solar Cells, 93, 2009, 230-238.

Predicted monthly cooling loads for 3 different glazing systems in typical open-plan office

Water-flow Windowwith enclosed loop

Lower header

Upper header

Supply to hot water system

Water-to-water heat exchanger (at window frame)

Insulated distribution tube

Feed water

Thermosyphon-induced liquid flow up the glazing to the heat exchanger at the top for hot water preheating purpose.

Solar transmission through glazing is reduced and so space cooling load is lowered.

Quality of daylight is enhanced since water affects very little visible light spectrum.

Advantages:• thermal load reduction;• daylight utilization; and • useful heat gain for hot

water supply

Chow TT, Li CY, Lin Z. Building and Environment, 46(4), 2011, 955-960.

Full-scale triple-glazed water-flow window at environmental chamber

3 components from outdoor to indoor :

one layer of clear glazing (12mm thick)

one layer of flowing water (30mm thick);

one layer of low-e double glazing (24 mm IGU);

Chow TT, Li CY. Building and Environment, 60, 2013, 44-55.

Experimental results• Water temperature increase can be > 10oC in the afternoon. • Water in window circuit kept absorbing heat from the adjacent glass

panes and the incident solar radiation during daytime. • The highest water temperature rise occurred at around 4-5pm.

Performance validation with ESP-r

Normal incident solar radiation on the window from experiment and ESP-rsimulation

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1 3 5 7 9 11 13 15 17 19 21 23Hour number

Solar

radia

tion l

avel

Solar radiation from experiment measurement (W/m2)Solar radiantion from simulation (W/m2)

Outer glazing temperature comparsion between experiment and ESP-rsimulation

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1 3 5 7 9 11 13 15 17 19 21 23Hour number

Outer surface temperature of outer glazing-experimentOuter surface temperature of outer glazing-simultion

Inner glazing temperature comparsion between experiment and ESP-rsimulation

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1 3 5 7 9 11 13 15 17 19 21 23Hour number

Inner surface temperature of outer glazing-experimentInner surface temperature of outer glazing-simulation

Double clear glazing with reflective coating at inner glass pane

Chow TT, Li CY, Clarke JA, BS2011, IBPSA Conference, Sydney

Water-flow window performance with application in DHW of Sports Center

• 6 rows of water-flow windows on inclined roof

• Each 29.6m x 1.4m (clear glass with reflective coating)

• DHW demand in line with room opening hours: 7am - 10pm

• Occupant, equipment and lighting operating schedules from Performance-based Building Energy Code Guidelines

• Indoor temperature: 20oC during winter and 24oC during summer

• Feed water temperature same as ambient air temperature; feed rate by gravity or mechanical device.

Year round performance

Water tempeature at the inlet and outlet of the window zone in typical winter week

12

15

18

21

24

27

1 13 25 37 49 61 73 85 97 109 121 133 145 157

Hour of typical winter week

Wat

er te

mpe

ratu

re

Ambient temeprature (oC) Water flowing rate at 0.05kg/s (oC)Water flowing rate at 0.1kg/s (oC) Water flowing rate at 0.15kg/s (oC)Water flowing rate at 0.2kg/s (oC) Water flowing rate at 0.4kg/s (oC)

Water tempeature at the inlet and outlet of the window zone in typical summerweek

25

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35

40

45

1 13 25 37 49 61 73 85 97 109 121 133 145 157

Hour of typical summer week

Wat

er te

mpe

ratu

re

Ambient temeprature (oC) Water flowing rate at 0.05kg/s (oC)Water flowing rate at 0.1kg/s (oC) Water flowing rate at 0.15kg/s (oC)Water flowing rate at 0.2kg/s (oC) Water flowing rate at 0.4kg/s (oC)

Typical summer week

Typical winter week

For a range of feed water flow rates, the year-round space cooling load can be reduced from 22% to 35%.

Within a typical year, more than 20% of the total incident solar energy can be utilized by the DHW system.

PV/T water-flow window• With PV glass pane as the outer pane

– sc-Si cells laminated between two 6mm clear glazing – 15% electricity generation efficiency at STC – 88% packing factor

• 30mm water flow cavity

• 12mm clear glass pane as the inner pane

Month

Indoor heat gain through PV/T

water-flow window

System thermal

efficiency

System electrical efficiency

System integrated efficiency

(% transmitted) (%) (%) (%) Jan 6.7 14.7 13.12 49.3 Feb 3.8 13.9 13.15 48.5

Mar 9.7 11.1 13.16 45.7

Apr 21.8 6.7 13.15 41.3

May 21.1 8.1 13.14 42.6

Jun 25.8 5.8 13.14 40.4 Jul 26.3 5.7 13.13 40.2

Aug 25.2 6.3 13.13 40.9

Sep 22.4 6.5 13.12 41.0 Oct 19.2 9.4 13.10 43.9

Nov 11.1 12.4 13.12 47.0

Dec 10.9 13.5 13.13 48.0 Overall 16.4 9.9 13.13 44.5

Monthly energy performance

Conclusion• Zero carbon building design calls for new roles of

opaque facade and window systems

• Innovative facades can utilize large amount of solar energy without occupying extra space

• A range of practical solutions and products are available that carry both passive / active roles

• Water-flow window for example is able to absorb solar heat and reduce indoor heat gain, and so to save AC and DHW electricity consumption without disturbing the indoor visual environment

• More R&D works are in need for new initiatives and full utilization

Thank you