Sharing Energy Supply and Low Carbon Energy Supply

Transcription

1 Sharing Energy Supply and Low Carbon Energy Supply Dr Andy Wright Institute of Energy and Sustainable Development De Montfort University, Leicester

2 Overview Where we re coming from Thermal demand for heating Comparison of heating supplies Solar energy Wind energy Shared supplies Conclusions

3 Carbon trends by school age Best electricity Best gas 12 kg of Carbon / m2 /year electricity contribution gas contribution total carbon pre Post 1995 Source: Identifying the benefits of sustainable development for schools, Leyden R, MSc thesis, Cranfield University, from BRE data

4 Carbon performances of recent schools against national benchmarks All new schools here much higher on electricity, lower on gas, only one better than national best practice (stock) overall kg co2/m2/y carbon gas carbon elec 10 0 Riverhead (2002) national best practice Notley Green (1999 / 2004)* national good practice Kingsmead (2004) Source: Identifying the benefits of sustainable development for schools, Leyden R, MSc thesis, Cranfield University, from BRE data

5 Thermal demand Heat balance Gas and biomass boiler characteristics District heating

6 Heat balance Pupils in a classroom will compensate for all fabric losses and a major part of ventilation heat losses. Equipment and solar gains further reduce the heating demand. During pre-heat the ventilation loss will be minimal. [source: page 11, Building Bulletin 87]

7 Heating demand 3 m 8 m 16 m Classroom 128 m 2, two external walls 33% glazed, negligible heat transfer floor/ceiling, 25 pupils Uninsulated: Wall U=1.5, window U= Part L2a regs; Wall U=0.35, window U=2.0 Low energy; Wall U=0.1, window U=0.8, heat recovery on vent.? > Excel spreadsheet

8 Heating pattern, 19 th & 20 th century schools Usually radiators or fan convector heaters During occupancy, significant heat requirement in cooler weather Large load to warm up, reduced load during occupancy due to gains Hot water load usually from main system Historically poorly controlled balance point 17.7 C measured for schools! 17.7 C is also Heathrow average August temperature

9 Heating pattern, low energy school During occupancy, zero or minimal heat requirement mostly ventilation Typical requirements are brief spikes to warm up before occupancy Underfloor heating will have smoother load profile slow response Plus hot water load can store so input heat any time

10 Gas demand, new schools [1] 16 Gas consumption over 3 days in February, modern junior school #1 Occupied Gas use (half hour meter) / Outside temperature C : : : : : : : : : : : :00 Date (February 2008), hour 07 00: : : : : : :00

11 Gas demand, new schools [2] Gas consumption over 3 days in April, modern junior school #2 Occupied period Gas use (half hour meter) Outside temperature C : : : : : : : : : : :00 Date (April 2008), hour 22 20: : : : : : : :00

12 Thermal simulation tells a similar story classroom, January 13-15, Heathrow TRY 12 External temperatures (RHS) People, equipment gains Heating system input Gain (kw) 4 2 Solar gain 4 Temperature ( C) Fabric loss Ventilation loss -6-4 Mon Tue Wed Thu Date:Mon 13/Jan to Wed 15/Jan Space conditioning sensible: Music2 (cns_heatinggatwick_jan.aps) Internal gain: Music2 (cns_heatinggatwick_jan.aps) Solar gain: Music2 (cns_heatinggatwick_jan.aps) Natural vent gain: Music2 (cns_heatinggatwick_jan.aps) External conduction gain: Music2 (cns_heatinggatwick_jan.aps) Dry-bulb temperature: (Hrow9697.fwt)

13 Boiler characteristics Gas Fast response Easy to turn on/off Compact boiler, no fuel storage Low cost Low-ish carbon, but no green credits High efficiency 90%+ Biomass (wood pellet, chip) Slower response Need to leave on for long periods Large boiler Baseload only? Fuel delivery & storage Higher cost Near-zero carbon, so green credits High efficiency 90%+ Use with storage?

14 Other options District heating supply Fast response Easy to turn on/off Compact heat exchanger, no boiler Simple, low cost Carbon, green credits depend on heat source Some distribution losses Like giant thermal store Need DH system available to plumb into! Complementary demand profile to some other demands Flexible for future heat supplies, like electricity grid CHP (natural gas etc.) Slow response Need to leave on for long periods (4000 hrs/year) Large installation Baseload only Reduces electricity costs Complex, high capital, maintenance costs Low carbon, green credits High efficiency 90%+

15 Summary heating Really low energy schools have very low net heating requirement, if designed right zero or almost during occupancy Most heat required for short periods Usually, no baseload heat requirement Choice of boiler should match load characteristics Gas well suited to typical demand profile Biomass less so, unless large site and/or swimming pool and/or thermal storage District heating similar to gas boiler Biomass, DH may need (gas?) system for peaks

16 Solar energy Characteristics of solar energy Solar thermal (heat > hot water) Photovoltaic (electricity)

17 Annual average solar radiation falling on 1m 2 surface, inclined at 30 to the horizontal 5 Monthly solar radiation on south facing 30 slope, Bracknell (CIBSE Vol J) 4 Monthly kwh/m Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

18 W/m Hourly surface radiation W/m2 Heathrow TRY Sunny Overcast Hour of year

19 Solar thermal Output available as % maximum School holidays Solar thermal for hot water Holidays? lose about 20% of output compared to no holidays Also lose some weekend heat unless sports use Time of production in 24 hr not v. important since stored Most cost-effective renewable available? Removes need to drain system in summer

20 Solar thermal: Navigation Road Primary, Altrincham, Cheshire

21 Electricity: primary school profile / 00:14 24/ 06:14 24/ 12:14 24/ 18:14 25/ 00:14 25/ 06:14 25/ 12:14 25/ 18:14 26/ 00:14 26/ 06:14 26/ 12:14 26/ 18:14 27/ 00:14

22 Photovoltaics

23 2500 PV output, August Output Watts / 00:00 28/ 12:00 29/ 00:00 29/ 12:00 30/ 00:00 30/ 12:00 31/ 00:00 31/ 12:00 01/ 00:00 Day/ time 2500 PV output, 29th August Output Watts / 06:00 29/ 07:12 29/ 08:24 29/ 09:36 29/ 10:48 29/ 12:00 29/ 13:12 29/ 14:24 29/ 15:36 29/ 16:48 29/ 18:00 Day/ time

24 Photovoltaic characteristics Much higher output (x4) summer than winter months Highly variable, by day and sometimes by minute Not economic to store, so use or export Only generates during daytime! High capital cost, low running cost (but inverters need replacing) Most schools pv generates small fraction of total electricity (< 5%) Not very site dependent, but need to avoid shading Educational value?

25 Wind Nature of wind resource Patterns of generation Effect of time averaging and exports

26 Europe wind energy map Energy Q speed3 SE England speeds: ms-1 sheltered ms-1 open plain Minimum viable wind speed around 4 ms-1 (RETscreen international) So region just viable for wind

27 Hourly wind speed m/s Heathrow TRY m/s Hour of year

28 Real exports higher than 30 minute averaging suggests Win d 1 se co n d Wind output Watts :25 10:25 11:25 12:25 13:25 14:25 Time w ind 60s w ind 30 min :21 10:21 11:21 12:21 13:21 14:21

29 Wind characteristics Higher output winter but much less seasonal variation than solar Highly variable, by day, hour, second Very site dependent not for urban sites Small micro-wind not viable due to turbulence, low output Large turbines best on open site but likely to be major planning issue Not economic to store, so use or export 24 hour, intermittent generation Medium capital cost, low running cost Off-site turbine more effective investment, if rules allow Educational value?

30 Grid as infinite battery Solar - National Grid Wind + System CHP Technically true, but tariff structures may not reflect this!

31 Conclusions Thermal demands in new schools very different from older schools Need to design out need for heat rather than design in low carbon heat supply District heating a good option if available Do we have the skills for this? On-site renewables are expensive Need to design out electricity demand rather than design in low carbon supply Should think of renewable electricity in national terms rather than within the site