Accounting CO 2 emissions for electricity and district heat used in buildings – a scientific method to define energy carrier factors Jarek Kurnitski 11.5.2010 CLIMA 2010 Senior Lead, Built Environment Sitra, the Finnish Innovation Fund Adjunct Professor, Aalto University
Jarek Kurnitski's presentation at 10th anniversary REHVA seminar Clima2010 in Antalya, Turkey on 9-12 May 2010 Accounting CO2 emissions for electricity and district heat
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Accounting CO2 emissions for electricity and district heat used in buildings – a scientific method to define energy carrier factors
Jarek Kurnitski
11.5.2010
CLIMA 2010
Senior Lead, Built EnvironmentSitra, the Finnish Innovation FundAdjunct Professor, Aalto University
Assessment of emissions caused by energy used in buildings• Buildings use energy measured or calculated in kWh-s• The use of 1 kWh energy can cause very different emissions or
primary energy use, depending on production sources• This is usually taken into account with energy carrier factors in energy
performance regulation
Two main purposes of this assessment:• Estimate actual CO2-emissions or primary energy use caused by
energy production – can be calculated from energy statistics• Regulative purpose, derivation of energy carrier factors used in energy
performance requirements of building codes• Regulation has to take into account demand and capacity changes in
the market and direct construction according to energy policy
• EN 15603: calculation of energy ratings in terms of primary energy, CO2 emissions or parameters defined by national energy policy
• Based on net delivered energy (by all energy carriers), weighted energy rating (primary energy or CO2 emission) is calculated (used in majority of member states)
11.5.2010Jarek Kurnitski
Other services cause often
confusion as they are not included in the rating in all
Emissions [kgCO2] =energy flow [MWh] x specific emission factor [kgCO2/MWh]Primary energy = energy flow [MWh] x primary energy factor [-]Weighted energy rating = energy flow [MWh] x energy carrier factor [-]
• Example house with 18 MWh natural gas and 7 MWh electricity use:18 MWh * 200 kgCO2/MWh = 3600 kgCO2 = 3,6 tCO2 (natural gas)7 MWh * 300 kgCO2/MWh = 2100 kgCO2 = 2,1 tCO2 (electricity)in total 5,7 tCO2 per year
• Alternatively this calculation can be done with relative energy carrier factors defined in relation to some reference (gas), i.e. 1.0 for gas and 1.5 for electricity, to use kWh-units
• Primary energy use refers to the use of natural resources1
• Primary energy factor for fossil fuels is 1.0 if extraction, refinery, transport etc. are not taken into account
• 1/0.4=2.5 for electricity generated from fossil fuel with efficiency of 40% • Usually, only non-renewable primary energy is considered (i.e. the factor is
close to zero for hydropower, wind, solar)• Nuclear energy is difficult to treat within primary energy concept:
- Primary energy factor depends on the selection, which energy (thermal or electrical) is used as the primary energy form
- Thermal efficiency of 33% leads to primary energy factor of 3.0 (IEA, Eurostat) and if electricity is used as the first energy form, primary energy factor will be 1.0 (UNSD)
11.5.2010Jarek Kurnitski
1Definition (for a building): Non-renewable primary energy is the non-renewable energy used to produced the energy delivered to the building. It is calculated from delivered energy amounts of energy carriers, using conversion factors (EN 15603:2008).
Why primary energy factors are almost constant in the long run?• Major changes in Finnish energy production until 2030:
- Significantly increased share of nuclear energy- CHP is used as much as today, almost constant district heat production- Increased use of renewables (wind, bio, solar), as much as technically
feasible, but still less dominating than nuclear or CHP
• With IEA and Eurostat definition, primary energy equivalent of nuclear and conventional condensing power very similar, so, the compensating of condensing power will even slightly increase primary energy factor (40% vs. 33% efficiency)
• ⇒ cutting emissions with nuclear energy has no effect on primary energy factor…
Energy performance regulation:• Controlling and directing the demand change• How much and which energy is used in buildings• Straightforward for new buildings, more complicated for existing
• Regulation is often not directly linked to policies for energy production, however the both are important:- Regulation generates demand change in the existing market with
consequences for developments in the production side- Obviously to be fitted together so that emissions can be reduced most
efficiently
• Buildings account for 41% of primary energy use in EU (Eurostat) being the largest single potential for energy savings
Finnish case study to determine emission based energy carrier factors including demand-capacity coupling effects
• CO2-emissions from electricity generation and district heat production:- Hourly data of specific emissions from 2000-2007- Demand change analyses for electricity use- Demand change analyses for district heating use- Coupling with new capacity – scenarios- Derivation of energy carrier weighting factors based on energy system
scenario calculations to show how much one energy carrier is causing more emissions than another
• Average specific CO2-emissions 2000-2007:- 273 kg(CO2)/MWh) for electricity- 217 kg(CO2)/MWh) for district heat
• Or average relative energy carrier factors (previous ones divided by reference specific emission of oil 267 kg(CO2)/MWh)):- 1.0 for electricity- 0.8 for district heat- (reference: 1.0 for oil)
• These average factors would probably lead to increased use of electricity in buildings (electrical heating etc.) as 1.0 is very low compared to common primary energy factor of 2.5 for electricity
Specific CO2 emissions of total electricity generation as a function of outdoor temperature 2006–2008
• Generation of separate conventional thermal power in Finland can be high in summer period due to shortage of hydro power and lack of CHP which is generated against heat load of district heating + service breaks of nuclear power plants
Demand change analyses (emissions response to a step change in the demand)
• In the electricity production especially carbon-neutral capacity is limited• District heat CHP is produced against heat load without similar lack of
capacity (demand change has no effect on the specific emission)• Construction of new buildings or renovation of existing ones means
changes in the demand responded by electricity market• To account emissions of the step change we need to know a link between
a new or non-appearing energy use in a building and energy production source (i.e. which type of plant will generate or is cutting down this energy production)
11.5.2010Jarek Kurnitski
+ or – step change in electricity or district heat
• Results show that during 90% of the time of the year the demand change will be allocated to the separate conventional thermal power, 2% to CHP and the rest for carbon-neutral production (not shown in the Table).
• This means that an hourly weighted specific emissions by new or non-appearing electricity use is as high as 814 kg(CO2)/MWh that is average emission of total generation by factor 3.
Specific CO2 emissions by new or non-appearing electricity use (demand change) for current situationCurrent situation (year 2007) Total
electricity generation
Separate conventional
thermal power
CHP electricity generation
Industrial CHP
Weighted average specific
emission
Specific emission kg(CO2)/MWh 279 893 439 190 814
Share of the demand change 90 % 2 % 0 %
Current situation (year 2007) Total electricity generation
• We calculated a simple scenario, where new 1600 MW of nuclear energy will replace only separate conventional thermal power with no changes in energy demand structure (calculated with 2007 data)
• 1600 MW new nuclear power decreased an average specific emission by almost of factor 2, but the ratio of the demand change and average specific emission values even increased to 3.4.
Specific CO2-emissions of the demand change for the scenario where 1600 MW new nuclear energy replaces only separate conventional thermal power
1600 MW new nuclear power replaces only separate conventional thermal power
Total electricity generation
Separate conventional
thermal power
CHP electricity generation
Industrial CHP
Weighted average specific
emission
Specific emission kg(CO2)/MWh 137 893 439 190 466
Share of the demand change 24 % 57 % 0 %
1600 MW new nuclear power replaces only separate conventional thermal power
Demand change in district heating energy use • The total CO2 emissions of Finnish electricity generation and district heating
production if electricity use is kept constant, but district heating is reduced (e.g. additional insulation of existing multi-storey buildings) or increased
• ⇒ Due to CHP, the total emissions do not depend on the amount of district heat used
0
5
10
15
20
25
30
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.295 1.3 1.4 1.5
Ratio of the district heat demand change (1 = current situation, 0.5 = 50% reduction, 1.5 = 50% increase)
District heat replacing electricity use or vice versa • The total use of electricity and district heat is kept constant:
- The ratio of 1 corresponds to the current situation, the ratio 0.5 means that half of current district heating energy used is replaced by electricity use and 2 that the current district heating use is doubled and electricity use reduced correspondingly
• ⇒ Replacing district heat by electrical heating drastically increases total emissions
• Main principle: energy system model allowing both changes in the demand and production capacities, annual balance calculation
1. Select reference electricity and district heat production (e.g. 90 TWh el. and 33 TWh DH, repeat the calculation for other relevant values)
2. Define rules for production sources/capacities allowing to introduce new capacity to cover increased demand:
- production sources with fixed capacity, hydro and nuclear (fixed capacity can be selected as input parameter)
- production sources with flexible capacity, in this case condensing power and CHP- limits for district heat produced by CHP, 70…80% in this case- wind power and solar electricity fixed in this case, but can be treated with similar
rules if considered flexible
3. Introduce a step change of heat and electricity demand (+3 TWh in this case) and solve energy production balance by minimizing emissions or production cost
4. Results: emissions and cost caused by +3 TWh electricity or heat production ≡ specific emission factors of the studied scenario
• +3 TWh step change of heat or electricity demand• 80 and 90 TWh reference electricity production and 33 TWh district heat
production• Flexible capacity of separate condensing power and CHP• Nuclear energy capacity fixed, several capacity values calculated• Hydropower and wind power fixed • Limits for district heat produced by CHP, to be between 70 and 80%Specific emission (energy method) and cost data used:
• + 3 TWh electricity increased emissions by factor of 4,0 relative to + 3 TWH district heat (0.68 Mt vs. 2.7 Mt)
• This factor of 4 would change to 3, if separate district heat production is not used• Results confirm that relevant selection of energy carrier factor for electricity should
be close to the demand change values, not average values of specific emissions
• Energy carrier factors may be based on CO2-emissions, primary energy (usually non-renewable) or on energy policy considerations
• Primary energy factors are relevant for fuels, but for nuclear energy depend by factor 3 on the definition used
• Specific CO2-emissions factors are scientifically sound (independent on definitions), but average factors cannot be used for regulative purposes, because they may guide to increased electricity use, which will consequently increase emissions as shown in the Finnish case study
• Finnish average specific emission based factors (2000-2007):- electricity 1.0 - district heat 0.8- oil 1.0 (reference)
• Average factors for electricity and district heat are very close, but replacing district heat by electrical heating drastically increased total emissions in the Finnish case study and vice versa
Conclusions 1/2• Hourly demand change allocation increased electricity factor from 1.0 to 3.0
and analyses both with fixed and flexible capacity showed that the factor caused by demand change is 3 to 4 times higher than the average one
• Energy system scenario calculations confirmed that relevant selection of energy carrier factor for electricity should be close to the demand change values, not average values of specific emissions
• Using the rule of 3 x average specific emission, one can easily calculate electricity factors for future scenarios, i.e. if the Finnish average factor will be reduced to 0.6 in 2020, the electricity factor will be 1.8
• Higher energy carrier factor for electricity means in the energy performance design that electricity is more valuable energy than fuel energy or district heat. Such building regulation will generally promote for more effective electricity use in buildings and limit wasteful use of electricity.
• Energy carrier factors are not constant, as depending on production sources, and are subject of revision with relevant interval of about 5 years