1 Comparative Life-Cycle Carbon Footprint Study of a proposed

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					16th    Annual   I nt ernati onal   Sustain able    Dev el opm ent     Research       Conference    2010



    Comparative Life-Cycle Carbon Footprint Study of a proposed District Cooling System and
            Conventional HVAC Systems for Hong Kong New Urban Developments
                                                                                  1
                       Dr. Felix Yat-hang WONG, PhD MBEnv(SustDev) BArch
                                   Y.T. TANG, MSc MIOA MHKIOA2
1
    Senior Environmental Consultant, AECOM, 11/F, Grand Central Plaza, Tower 2, 138 Sha Tin Plaza,
    138 Shatin Rural Committee Road, Shatin, Hong Kong.
2
    Executive Director, AECOM, 11/F, Grand Central Plaza, Tower 2, 138 Sha Tin Plaza, 138 Shatin
    Rural Committee Road, Shatin, Hong Kong.


In 2009, AECOM Environment completed a Life Cycle Assessment (LCA) Study for a proposed District
Cooling System design. The purpose of the proposed District Cooling System design was to serve
the air-conditioned space required. The study quantitatively measured the whole life-cycle carbon
footprint (tonne CO2 equivalent) of the District Cooling System and Conventional HVAC Systems in
the whole system life-cycle perspective, including (1) initial stage taking account of raw material
extraction, building material manufacturing, transportation and construction stage; (2) system
operation; (3) recurring repair and maintenance, and (4) final disposal stage.

This paper will report the following LCA findings of the study, including:

1. The comparison of the life-cycle carbon footprint of the proposed District Cooling System design
   and Conventional HVAC systems for the amount of air-conditioned space required
2. The comparison of the embodied carbon footprint of the proposed District Cooling System design
   and Conventional HVAC systems
3. The comparison of the operational carbon footprint of the proposed District Cooling System design
   and Conventional HVAC systems
4. The “hotspot” life-cycle stages of District Cooling System and Conventional HVAC system in terms
   of carbon footprint
5. The “hotspot” system component of District Cooling System and Conventional HVAC systems in
   terms of carbon footprint
6. The embodied carbon “payback” duration of the proposed District Cooling System design

This paper will discuss the advantages and disadvantages of the proposed District Cooling System
design in terms of the life-cycle carbon footprint. The premise is expected to reduce 20-35% of the
cooling electricity consumption of the new district and sets precedent for low-carbon building service
system designs in Hong Kong.




                                                    1                        30 May – 1 Jun 2010 Hong Kong
16th   Annual   I nt ernati onal   Sustain able   Dev el opm ent   Research      Conference       2010



1       STUDY SCOPE

The study extends previous Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) experiences
carried out in AECOM Environment. It covered the following life-cycle stages:




Initial Stage - Embodied carbon footprint (4-years) - measuring the embodied Global Warming
Potential (GWP) associated with (1) the raw-material extraction, (2a) building-material manufacturing,
(2b) transportation and (3) construction stages of the District Cooling System design
Operational Stage - Operational carbon footprint (50-years) – measuring the operational Global
Warming Potential (GWP) associated with the (4a) 50-year operational cooling electricity consumption
of the District Cooling System design
Repair and Maintenance Stage - Repair carbon footprint (50-years) – measuring the Global
Warming Potential (GWP) from the (4b) repair and maintenance of the District Cooling design
Disposal Stage - End of life carbon footprint (1-year) – measuring the disposal Global Warming
Potential (GWP)

The study was carried out using carbon dioxide equivalent (CO2-e). It accounts for six greenhouse
gases including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons
(HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride (SF6), included in the Kyoto Protocol to the
United Nations Framework Convention on Climate Change.

Once the base case – the conventional HVAC system was set up, it would then be possible to
determine the carbon payback period for the proposed District Cooling System design.


2       THE SERVED AIR-CONDITIONED AREA OF BASE CASE AND DESIGN CASE

The amount of the served air-conditioned area is equal for the provision under the conventional HVAC
systems and the proposed plants for District Cooling System.

The system boundaries of the base case and the design case are explained below:

Base Case - Conventional HVAC Systems to serve the air conditioned area required




    Building services elements of the conventional HVAC systems for Hong Kong office buildings to
    serve the amount of air-conditioned floor area required (approximately 17 office-buildings).
    Structural elements and finishing materials required to enclose the conventional HVAC
    systems to serve the amount of air-conditioned floor area required.



                                                  2                        30 May – 1 Jun 2010 Hong Kong
16th     Annual   I nt ernati onal   Sustain able    Dev el opm ent   Research     Conference       2010




Design Case – Proposed District Cooling System Design to serve the same air-conditioned area




    Building services elements – central chillers’ plants containing chillers, seawater pumps and
    chilled water pump, cooling towers, condensing water pumps, air handling units, transformer,
    emergency generators, fire service systems, plumbing and drainage system and building
    management system of the proposed District Cooling System design to serve the amount of
    air-conditioned floor area required.
    Structural elements and finishing materials to enclose the plants and Seawater Pump House
    Distribution pipe work
    Heat exchangers


3        LIFE-CYCLE STUDY PERIOD

This study considered the carbon emission of the following study period of the proposed District
Cooling System design:

                                         Life-Cycle Study Period


           Initial Stage               Operational Design Life               Disposal Period




    1.   Raw-material extraction,       5.   Building operation
    2.   Building-material              6.   Repair and maintenance     7.   Disposal Stage
         manufacturing in factory,           stage
    3.   Transportation from
         factory gate to
         construction site,
    4.   Construction




             4 Years                           50 Years                          1 Year




                                                     3                       30 May – 1 Jun 2010 Hong Kong
16th                                             Annual    I nt ernati onal          Sustain able           Dev el opm ent      Research   Conference       2010



4                                                 LIFE CYCLE CARBON FOOTPRINT ASSESSMENT METHODOLOGY AND DATA
                                                  SOURCE

    4.1                                            Life Cycle Assessment (LCA) Overview

“Life Cycle Assessment (LCA) is an objective method to evaluate the environmental burdens
associated with a product, process or activity by identifying and quantifying energy and material uses
and releases to the environment, and to evaluate and implement opportunities to influence
environmental improvements. The method assesses the entire life cycle of the product, process or
activities, encompassing extracting and processing material; manufacturing, transporting and
distribution; use, reuse and maintenance; recycling and final disposal.” (Ref: The Society of
Environmental Toxicology and Chemistry 1993)

    4.2                                            Life Cycle Carbon Footprint Data Sources

District Cooling System design and conventional HVAC systems were made up of plenty of building
materials and building service components.         Transport distance, mode of transportation,
manufacturing process and energy mix during manufacturing of different building materials and
components were based on project procurement from the previous local projects. Electricity fuel-mix
of China Light Power (CLP) at 2008 was used to assess the operational-energy carbon footprint of the
District Cooling System design. The quantum data of materials used in the District Cooling System
was gathered from contractors and project engineers.

    4.3                                            Data Source of Operational Electricity Cooling Consumption

Project engineer modelled the cooling electricity consumption of the District Cooling System. Fig. 1
compares the cooling load of the District Cooling System and conventional HVAC systems to serve the
air-conditioned space required.     The Design of the proposed District Cooling System had 33.3%
lower cooling consumption than the conventional HVAC systems to serve the amount of
air-conditioned space required.

Fig. 1 Annual cooling electricity consumption of proposed district cooling system and conventional HVAC system
to serve the air-conditioning area required

                                                 150
    served air-conditioned area required (kWh)
    Annual cooling consumption per CFA of the




                                                 100




                                                  50




                                                  0
                                                       Proposed District Cooling System   Conventional HVAC System to serve
                                                                                           the air-conditioning area required




    4.1                                            Repair and Maintenance Data Source

The repair and maintenance pattern of the District Cooling System was based on contractors’
information or the repair frequency of the building systems and building components as shown in fig. 2
and fig. 3.




                                                                                                            4                        30 May – 1 Jun 2010 Hong Kong
16th    Annual        I nt ernati onal            Sustain able       Dev el opm ent     Research   Conference       2010



Fig. 2 Planned maintenance interval (year) of building systems


         Distribution pipeworks
             Centrifugal chillers

                    Transformer
                  Cooling tower
                Drainage sewer

        Condensing water pump
            Chilled water pump
                    Fire services

                Heat Exchangers
             Electrical generator
                Seawater pump

                       Plumbing
  Building Management Systems

                                    0        12       24      36         48        60

                                        Planned Maintenance interval of building
                                             systems / components (year)



Fig. 3 Planned maintenance interval (year) of building components


   Workshop door and ironmongeries
                         Workshop wall
                        Workshop floor
                      Workshop ceiling
                              Toilet wall
                             Toilet floor
                            Toilet ceiling
    Staircase door and ironmongeries
                         Staircase floor
                       Staircase ceiling
  Plant room door and ironmongeries
                        Plant room wall
                     Plant room ceiling
                      Plant room floor
     Passage door and ironmongeries
                            Passage wall
                           Passage floor
                         Passage ceiling
       Office door and ironmongeries
                              Office wall
                             Office floor
                           Office ceiling
                              Lobby wall
            Lobby reconstitute granite
                           Lobby ceiling
                                Roof slab
          Façade structural steel door
                   Façade glazed door
                          Façade louver
                       Façade windows
                        Façade painting
                           Façade tiling

                                             0                       7                  14

                                                    Planned maintenance interval of
                                                      building components (year)




                                                                     5                       30 May – 1 Jun 2010 Hong Kong
16th      Annual   I nt ernati onal              Sustain able            Dev el opm ent             Research        Conference   2010



5         FINDINGS

    5.1     Life-Cycle Carbon-Footprint Findings

5.1.1     Findings on embodied carbon footprint (Initial 4-year life cycle – including raw-material
          extraction, building material manufacturing, transportation and construction stages)

Figure 4 shows the comparison of elemental breakdown of the initial embodied carbon footprint
between the proposed District Cooling System and conventional HVAC systems to serve the
air-conditioned space required.

The structural elements of the proposed District Cooling System had 70 times higher GWP than that of
the conventional HVAC system. It is because the conventional HVAC systems are within the office
buildings. Therefore, the base case did not require foundations and reinforced concrete structures to
support and enclose the HVAC systems but the District Cooling System did require. However, the
finishing and the building services elements of the District Cooling System would have 79% less initial
embodied GWP than the conventional HVAC systems to serve the air-conditioned space. The
additional distribution pipe works and the substations of the District Cooling System increased the
initial embodied carbon footprint of the systems. The initial embodied GWP of District Cooling System
increased the Global Warming Potential (GWP) than that of Conventional HVAC systems by 55%.

Fig. 4 Elemental breakdown of the initial embodied carbon footprint of the proposed District
       Cooling System and the conventional HVAC systems to serve the air-conditioned space
       required

                                 140,000

                                 120,000
                                                                                                       Heat Exchangers (14
                                 100,000                                                               DCS substations)
                   Tonne CO2-e




                                  80,000                                                               Distribution Pipeworks


                                  60,000                                                               Building Services
                                                                                                       Elements
                                  40,000
                                                                                                       Finishings
                                  20,000
                                                                                                       Structural Elements
                                      0
                                           Proposed District Cooling       Conventional HVAC
                                                   System               Systems to serve the air-
                                                                       conditioned space required




5.1.2     Findings on operational carbon footprint (50-year Operational life-cycle stages)

Project Engineer modelled the annual cooling electricity consumption of the District Cooling System.

Fig. 5 shows the Global Warming Potential (GWP) of the District Cooling System and conventional
HVAC system. The proposed District Cooling System had 33% lower operational Global Warming
Potential than the conventional HVAC systems to serve the air-conditioned space required. The
increase embodied carbon footprint of the system can be quickly “payback” by the reduction of the
operational carbon footprint within 11 months.




                                                                         6                                30 May – 1 Jun 2010 Hong Kong
16th     Annual   I nt ernati onal   Sustain able   Dev el opm ent   Research     Conference       2010



Fig. 5     The total Annual Operational Global Warming Potential (GWP) of the proposed
           District Cooling System and Conventional HVAC systems to serve the
           air-conditioned space required




5.1.3    Findings on Repair carbon footprint (50-year recurring repair and maintenance
         life-cycle stages)

Based on the repair and maintenance patterns of the District Cooling System shown in fig. 2 and fig. 3,
AECOM Environment modelled the repair Global Warming Potential (GWP) of the district cooling
system.    Figure 7 shows the repair Global Warming Potential (GWP) of the District Cooling System
and the conventional HVAC system.

93% of the repair CO2-equivalent emissions came from building service elements and heat
exchangers of the District Cooling System. The District Cooling System decreases 82% of repair
CO2 emission from the conventional HVAC system to serve the amount of air-conditioned space
required. It is because Conventional HVAC system had more building service systems that had
repair and maintenance needs.


Fig. 6     The total Repair Global Warming Potential (GWP) of The District Cooling System and
           conventional HVAC systems to serve the air-conditioned space required




5.1.4    Findings on Disposal carbon footprint (disposal stage of 1 year)

AECOM Environment modelled the disposal Global Warming Potential (GWP) of the district cooling
system from transportation of demolition waste to landfill or public fill reception facilities. Figure 7
shows the disposal Global Warming Potential (GWP) of the District Cooling System and the
conventional HVAC system.




                                                    7                       30 May – 1 Jun 2010 Hong Kong
16th     Annual     I nt ernati onal   Sustain able   Dev el opm ent   Research   Conference       2010



Fig. 7             The total Disposal Global Warming Potential (GWP) of The District Cooling
                   System and Conventional HVAC systems to serve the air-conditioned space
                   required




The District Cooling System has 57% higher disposal GWP than the conventional HVAC systems to
serve the amount of air-conditioned space required. It is because District Cooling System comprised
of structural components that increased the disposal carbon footprint.

Fig. 8      The cumulative life cycle carbon footprint profile of the District Cooling System and
            the Conventional HVAC systems to serve the air-conditioned space required




                              Point which Increased
                              embodied carbon
                              footprint of District
                              Cooling system
                              pay-back by reduced
                              operation carbon
                              footprint




    Initial Stage                        Operational Design Life             Disposal Period


         4 Years                                50 Years                          1 Year




                                                      8                     30 May – 1 Jun 2010 Hong Kong
16th    Annual   I nt ernati onal   Sustain able   Dev el opm ent    Research     Conference       2010



5.1.5   Findings on Whole Life-Cycle carbon footprint (the whole life-cycle)

Figure 8 shows the life cycle and cumulative carbon footprint profile of the District Cooling System and
the conventional HVAC systems to serve the air-conditioned space required.

Figure 9 shows the life-cycle stage breakdown of carbon footprints of the District Cooling System and
the conventional HVAC systems. The District Cooling System reduces the operational and repair
GWP by 33% and 82% but increases the initial and disposal GWP by 57.5% and 57.3% respectively.
The percentage reduction of the life-cycle Carbon Footprint of the District Cooling System design from
conventional HVAC system is 36%.

Figure 8 shows the life-cycle profile of District Cooling System as well as the conventional HVAC
system. It shows the conventional HVAC system has 57.46% lower initial carbon footprint than
District Cooling System. However, the 50-year operational life of the District Cooling System design
can reduce the carbon footprint from the conventional HVAC system by 33%.

Figure 8 shows the cumulative life-cycle profile of District Cooling System as well as the conventional
HVAC system. It shows the conventional HVAC system has 36% higher cumulative whole life-cycle
carbon footprint than District Cooling System. The carbon payback period happens at 11 months
after the completion (the life-cycle year of 4 years and 11 months of the system’s life cycle).
Cumulatively, the District Cooling System reduces the carbon footprint from the conventional HVAC
system by 36%.

Fig. 9 The Life-Cycle carbon footprint per cooling areas breakdown of the District Cooling
Systems and conventional HVAC systems to serve the air-conditioned space required




                                                   9                        30 May – 1 Jun 2010 Hong Kong
16th   Annual    I nt ernati onal   Sustain able    Dev el opm ent    Research      Conference       2010



6       CONCLUSIONS

The following can be drawn from the study:

-       The design of the District Cooling System increases the initial embodied CO2-e of the
        Conventional HVAC systems by 57% (4-year initial stage).

-       The design of the District Cooling System reduces the operational CO2-e of the Conventional
        HVAC systems by 33% (50-year operational stage).

-       The design of the District Cooling System can reduce the repair CO2-e of the Conventional
        HVAC systems) by 82% (50-year repair and maintenance stage).

-       36% fewer carbon footprints can be expected for the entire life-cycle of District Cooling
        Systems.

District Cooling System reduces life-cycle carbon footprint, particularly the carbon footprint from the
repair and operational carbon footprints. However, District Cooling System had the higher carbon
footprint from initial and disposal stage that required more carbon mitigation measures that reduced
the footprint. Therefore, from the whole life-cycle perspective, we can draw the conclusion that the
District Cooling System can reduce the Global Warming Potential (GWP) and hence the climate change
potency of the public and private non-domestic buildings that applied District Cooling System in cooling.


References

Amato A., Wong Y.H., Felix (Dec 2006). Sustainability Assessment Of A Public Housing Block In Hong Kong
With A Combined Life Cycle Assessment (LCA) And Life Cycle Costing (LCC) Methodology And The Implication
                  nd
To Future Study; 2 Mega-Cities International Conference 2006, Guangzhou, China, 1-3 Dec 2006.
Amato A., Wong Y.H.F (April 2006), Combined Life Cycle Assessment (LCA) And Life Cycle Costing (LCC) Study
On The Sustainability Performance Of A Public Housing Block In Hong Kong, International Sustainable
Development Research Conference 2006, Hong Kong 6-8 April 2006.
Alex Amato, Felix Wong, Steven Humphrey, In Consultation With Martin Choi (Dec 2004), A Case Study Of
Sustainable Refurbishment In Hong Kong: An Energy-Efficiency Assessment Of The Parkside Apartments
Refurbishment Carried Out For Swire Properties, Presented At The International Workshop On Integrated
Life-Cycle Management Of Infrastructures, The Hong Kong University Of Science And Technology, Hong Kong
SAR,PRC, December 9-11, 2004.
Wong Felix, Dr. Alex Amato, (2003), Operational Model For A Combined Life Cycle Assessment/Life Cycle
Costing Study Of Building Materials/Components For Public Housing, Presented At The CIB Student Chapters
International Symposium 2003.




                                                   10                         30 May – 1 Jun 2010 Hong Kong

				
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