May 12, 2006 - FUTURE ENERGY SOLUTIONS. Prof A.S. ..... Faraday building refurbishment options are being assessed in terms of predicted future 'design.
FUTURE ENERGY SOLUTIONS Prof A.S. Bahaj and Dr P.A.B. James Sustainable Energy Research Group, School of Civil Engineering & Environment University of Southampton, Southampton SO19 1BJ, UK 1. Introduction Energy is fundament to life and development. In many countries, energy issues are driven by regulation due to pressures on the resources and impacts on climate change. This paper is developed as a late response to Hampshire County Council request on their Climate Change Commission of Inquiry - Impacts and Opportunities of a Changing Climate on key Infrastructure Priorities for Hampshire – Energy. As time does not allow for full and detail response to this commission, a brief paper is presented based on some of the work of the Sustainable Energy Research Groups at the University of Southampton. The paper briefly considers the following: 1. Microgeneration technologies. 2. The role of district CHP systems 3. Energy efficiency and the role of the user. 4. The impact of changing climate on the current built environment. Examples of successful areas are discussed in the following sections. 2. Microgeneration Microgeneration is seen by many advocates as a key part of the UK’s future energy mix. Moving away from GW scale fossil fuel thermal power stations to the building level, whether it be in the commercial of domestic sector has many attractions. Microgeneration is simply the generation of energy—heat or electricity—by individual buildings or small groups of buildings. The technology that provides this energy distinguishes itself from that traditionally used in that it gives occupiers the responsibility to produce energy to partly sustain their homes or buildings. Microgeneration technologies include photovoltaic installations, micro-combined heat and power systems, microwind, solar thermal systems, fuel cells and micro-hydro systems. There is a huge potential to utilise this type of technology in the urban built environment not only to satisfy demand and provide decentralised generation but also to help tackle fuel poverty and achieve reduction in emissions. In this paper microgeneration technologies are discussed in terms of application, carbon footprint and match between generation and demand [1]. There are opportunities and barriers for microgeneration across both technical and non-technical aspects as highlighted in Table 1.
Technical
Non-technical
Table 1. Opportunities and Barriers for Microgeneration Opportunities Barriers A new ‘type’ of electricity grid A new ‘type’ of electricity grid Electricity metering arrangements Early adopter risk Sustainability / CO2 savings Up front capital costs Planning Permission UK Tax Policy Green Credentials Planning Permission Part L trade off (UK interpretation of EU energy performance directive [2]) Raise end-user energy awareness – connect users to energy generation and consumption to achieve behaviour change Spreading the investment burden
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In terms of microgeneration the key criteria is (a) to understand the available resources (essentially the sun, wind and ground) and (b) the demand profile to ensure that there is a good match between the two. A typical 3 bedroom house in the UK consumes approximately 4000 kWh of electricity and 20,000 kWh of thermal energy for space heating, hot water and cooking. In terms of CO2 emissions UK mains electricity has an impact of ~ 0.45 kg CO2/kWhe compared to 0.19 kg CO2/kWht for gas. Table 2 compares a range of micro-generation technologies in terms of cost and environmental benefit per £ of capital investment (CAPEX). The analysis assumes a discount rate of 0% and the only operational costs (OPEX) considered are those associated with fuel where appropriate. This somewhat simplistic view will therefore, favour high CAPEX systems. In terms of maintenance cost, all the described systems have a potentially significant maintenance burden coupled with a high degree of early adopter risk. This is especially true for emerging technologies such as micro-CHP systems of which the first generation public release are starting to appear on the market. The technologies considered in this paper are broken down into three groups (i) thermal (solar thermal, ground source heat pumps), (ii) electrical (photovoltaics and micro-wind turbines) and (iii) combined thermal and electrical (CHP from either Stirling engine or fuel cell based devices). A typical capital cost per kW on a domestic house is shown (Table 2), which combined useful energy gives an indication of the economic and environmental return of the technologies. Whilst ground source heat pumps typically deliver four units of thermal energy for every unit of electricity consumed, this yield is compromised environmentally by the high CO2 differential between electricity and heat. Photovoltaics (PV) are at present an expensive technology with a relatively low energy density. For example, a 1kWp system would require ~ 9m2 of roof and produce an electrical output of ~ 800 kWh per annum for a south facing roof. Such a system at a typical 3kW residential scale would inevitably incur electrical export issues which at present are not fairly rewarded by metering schemes. Microgeneration does not have access to the ½ hourly ‘chunked’ tariffs of larger generators, which would undoubtedly aid PV whose generation is in phase with an increasingly important peaking cooling demand. The economic payback time is seen to be ~ 59 years, which far exceeds the component lifetime (30 years for DC side and 10 years life for the inverters). PV has the poorest annual operational CO2 saving per £ invested. The micro-wind yield is highly dependant on site with many urban locations having a very poor wind resource. It should be noted that these calculation does not consider the embodied energy of the technologies. Micro-CHP in the form of a Stirling engine potentially offers the best CO2 savings and economic return on investment. This scenario is based on a ‘heating system upgrade’ where an avoided cost of £2000 has been assumed for a traditional wet heating system. A Stirling engine device has a high thermal to electrical output (typically ~ 6:1) and so is only appropriate for dwellings with a high heat demand (old, thermally leaky or large modern buildings). Recent field trial results reported by the Carbon Trust of Stirling engine CHP have however, been a little disappointing [3] with carbon savings less than expected. Fuel cell CHP are predicted to have a near 1:1 thermal to electrical ratio which will make them far more appropriate for new build, energy efficient housing which has far lower thermal demands. However, fuel cell micro-CHP is still at the R&D phase and is probably 5 years+ from entering the market.
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Table 2. A comparison of microgen technologies in terms of their capital cost and carbon savings. Technology
Thermal Domestic hot water systems Ground Source Heat Pump
Description
Flat panel, evacuated glass tubes Horizontal coil network or vertical bore hole
Electrical Photovoltaics Micro-Wind Thermal and Electrical Stirling Engine
Fuel cell
Typical capacity per house
Capital Cost per kWp £
Energy yield kWh / kWp
Fuel cost per kWp (£/annum)
Simple economic payback CAPEX / OPEX (years)
Annual CO2 saving kg / £CAPEX
5 kWt
£600
800
Small electrical pump
24 years
0.28
10 kWt
*£600-1000 (horizontal)
3200
80
Heating from gas £103 Electricity for pump £83 30 years
0.52 – 0.31
800 438
**-40 (-76) **-44 (-64)
59 years 23 years
0.08 0.13
Additional gas cost £130 Electricity generated £220 11 years
0.51
£800-1250
3 kWe 1kWe
£4,500 £1,500
1kWe 6 kWht
**£1,000
1 kWe 1kWt
Not available
* Energy Efficiency Best Practice in Housing, Domestic Ground Source Heat Pumps: Design and installation of closed loop systems, Energy Saving Trust based on an assumed load factor of 5%. 90% efficiency for a conventional condensing boiler, COP of 4 for Ground Source Heat Pump ** Assumed 50% export from house for 3 kW PV system, no export for 1kW wind system *** Assumed premium over a normal condensing boiler system Costing Assumptions: Electricity 10p/kWh, Gas 2.8p/kWh, Renewables Obligation Certificate (ROC) 4.5 p/kWh
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3. District CHP In terms of take-up district scale CHP is far advanced compared to micro-CHP. Providing a building or scheme with sufficient heat load is in place. The economics in this case can be attractive even with the volatility in bulk gas prices. CHP is now increasingly being applied as tri-generation where electricity, heating and cooling is provided from the same source. The increasing need for summer cooling of commercial office space can be achieved through the use of absorption chillers enabling CHP to be run with load matching throughout the year. An example of such an application is the University of Southampton which operates a 2.8 MW CHP plant which serves half the main campus (32 buildings) providing heat, electricity and absorption cooling [4]. The £3.5M scheme was phased over 3 years, commencing in 2003. The replacement of existing boiler plant has reduced the carbon footprint of the heating system by over 23% (2000 tonnes CO2 per annum) with an annual saving of £240K per annum based upon a net present value over 20 years and current gas prices [4]. The University was awarded the HEEPI Green Gown Award 2007 for the CHP scheme. Such systems should be investigated as a future high efficient solution when regeneration or new large building schemes are being considered. This is especially important as biomass operated CHP would not only have environmental benefits but also in economic terms qualifying for ROCs (renewable obligation certificates). 4. Energy Efficiency and the Role of the User Connecting users to the impact of their behaviour is a key requirement to promote energy efficiency. Renewables such as PV can aid in behaviour change when homeowners can readily see and understand the energy flows in their home. User behaviour is the dominant factor in determining energy use. This has been highlighted through a study of low energy eco-homes in New Lane, Havant as shown in Fig.1. [1,5].
Fig.1 New lane, Havant Eco-home housing scheme. The scheme consists of nine, essentially identical houses each with a 1.53 kWp PV system and a solar thermal hot water collector. The houses incorporate numerous other efficiency measures such as sunrooms, low-energy lighting, water saving and under floor heating. The electricity demand profiles on a monthly basis are shown in Fig. 2. It is striking to note that for identical ‘fit out’ houses aside from white good appliances there is such wide variation in energy demand.
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1000
Electricity Consumption, kWh per month
H2 H1
H6 H5 H4 H3 H2H2 H1 H7 H8 H9
800
H7 H8 H9
H6 H5 H4 H3 H2 H1 H7 H8 H9
600
400
200
M AR 05
FE B0 5
05 N JA
04 D EC
N O V0 4
4 T0 O C
SE P0 4
AU G 04
L0 4 JU
N 04 JU
M AY 04
AP R 04
0
Month of the Year, 2004-05
Fig. 2. Variation in monthly energy demand for nine identical eco-homes with PV system. The economics of microgeneration of electricity are dependant on the use of electricity ‘on-site’, export is often of no financial benefit to the homeowner. It is interesting to note therefore, that homeowners such as H2 in Fig. 2 are effectively penalised by current electricity metering schemes for their energy efficiency. During the summer months, H2 exports up to 70% of the monthly generation to the grid, whereas an ‘energy hungry home’ such as H5, is around 30%. This raises the question as to the fairness of current metering schemes and raises the possibility of ‘levelling the playing field’ through policy change to address these issues [6]. Initial studies on the Havant scheme have indicated that visible renewables such as PV can help with behaviour change. Targeting of information to high energy users has brought some level of success in moderating consumption [1]. In the workplace, behaviour change may be more difficult with users having less of a ‘cause and effect’ connection. Users are not impacted by fuel bills and the actions of only a few users in an office space may have a disproportionate effect on energy consumption. At its simplest this may be seen as leaving windows open overnight [7] or lights on. Office buildings are increasingly struggling to address summer overheating issues. This is a key area where behaviour change can make a difference. It is important that users understand the principles of a building and the strategies that make the building work. A facilities manager should ask himself/ herself the following questions: To what extent are building occupiers aware of sustainability and its impact on living or working spaces? What mechanisms are in place to educate and disseminate a building’s function / impact? Does our understanding of existing control systems allow optimal work / living environment with minimum resource use? How to ensure an occupier is aware of a building’s design intentions? Can UK learn from other countries?
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It is important to try and connect with users and to try and manage expectations. In naturally ventilated buildings it is clearly unrealistic (and not environmentally acceptable) to maintain office temperatures at 21 deg C in the summer months. Peak clipping of office temperatures through mixed mode operation (mechanical support of natural ventilation) should be the preferred option. 5. The impact of changing climate on the current built environment A naturally ventilated 1960’s office tower at Southampton University is currently undergoing a major £19million mid-life refurbishment (Fig.3). The building; like most of this era; has an identical façade on all elevations which takes no account of solar geometry.
Fig. 3. Sir Basil Spence designed, Faraday Tower, University of Southampton. South and West elevations are visible. This leaky, international style building has very poor thermal performance in terms of both winter heat loss and summer overheating. Refurbishment runs the risk of producing a high performance winter building which will simply overheat in the summer months. The impact of climate change is therefore, an important consideration. Heatwaves, such as experienced in the summer of 2006 are expected to become the norm and this will lead to many more buildings failing. Faraday building refurbishment options are being assessed in terms of predicted future ‘design summer years’ in effect modelling weather files for the 2020’s, 2050’s and 2080’s. At present such ‘morphed’ weather files are not generally available and have to be produced ‘in house’ by adapting existing CIBSE weather data [8]. Figure 4 shows the predicted performance of the open plan space within a refurbished tower based on the ‘medium high’ climate change scenario from UKCIP for a 3 day period in July.
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40
40
35
35
30
30
25
25
20 4880
4890
4900
4910
4920
4930
Temperature (deg C)
Temperature (deg C)
DSY CIBSE DSY 2020s DSY 2050s DSY 2080s
20 4940
Hour of the Year
Fig. 4. Predicted office and ambient temperature for a refurbished tower with solar control and night cooling strategy. Ambient temperature shown as solid lines, office space as dotted lines. Even with solar control and night purging strategies employed the peak office temperatures are predicted to be very close to ambient. The internal loads within present day offices due to high occupancy, computing requirements and artificial lighting will make non-air conditioned buildings difficult. Strategies such as home working (to reduce peak occupancy), changes in working hours and dress code combined with management of user behaviour and expectations are all needed 6. Conclusions The above sections are prepared in response to the call mentioned in section 1. The areas covered are aimed at provoking debate on the issues related to energy and the built environment - a sector responsible for ~ 40% of our emissions. The discussion given in the sections link generation technologies, buildings, behaviour and the impact of climate change. This approach is likely to warrant more discussion which we hope we can provide at the commission hearing. The paper however, does not cover large scale power generation either from fossil fuels or renewables. An in dept analyses of these will require more time (to understand and quantify available resources) and the input from current energy providers in the region. Nevertheless it is clear that the region may have potential resources for large wind and ocean energy generation (www.energy.soton.ac.uk). Such resources if developed collaboratively with neighbouring regions will undoubtedly provide a reliable and sustainable resource for energy production. These issues can also be part of the discussion at the commission hearing. REFERENCES: [1]. (a) Bahaj A.S. and James P.A.B. (2006), “Urban energy generation: The added value of photovoltaics in social housing”, Renewable and Sustainable Energy Reviews, In Press, Corrected Proof, Available online 12 May 2006. (b) Bahaj A.S., Myers L. and James P.A.B. (2007), “Urban energy generation: Influence of micro-wind turbine output on electricity consumption in buildings”, Energy and Buildings, Volume 39, Issue 2, February 2007, pp 154165. [2]. EU Energy Performance in Buildings Directive 2002/91/EC. [3]. The Carbon Trust’s Small-Scale CHP field trial update, report CTC513, November 2005. [4]. Turner 2007, Energy Manager, Estates and Facilities, University of Southampton, Green Gown Awards 2007 submission.
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[5]. Keirstead J. (2007), Behavioral responses to photovoltaic systems in the UK domestic sector, Energy Policy 35, pp 4128–4141. [6]. Watson J, Sauter R., Bahaj A.S. and James P.A.B. Myers L., Wing R., “Unlocking the Power House: Policy and system change for domestic micro-generation in the UK”, published in October 2006, ISBN 1-903721-02-4. [7]. James P.A.B., Jentsch M.F. and Bahaj A.S. (2006), Window opening and blind usage patterns in a naturally ventilated office building: to what extent does user behaviour compromise potential building performance?, Proceedings World Renewable Energy Congress (WREC-IX), Florence , 19-25 August 2006. [8]. Jentsch et al 2007, Generating TMY2 weather files for environmental building simulation of future climates, In preparation to be submitted to Building Services Engineering Research and Technology.
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