Disaggregating the causes of falling consumption of domestic space heating
energy in Germany
Dr Ray Galvin1 rg445@cam.ac.uk; Dr Minna Sunikka-Blank mms45@cam.ac.uk
Department of Architecture, University of Cambridge, 1-5 Scroope Terrace,
Cambridge CB2 1PX, UK
Abstract
Consumption of domestic heating energy (space and water heating combined) in
Germany has been falling in recent years. The most reliable figures indicate it fell by
23% in 2000-2011, from 669 to 515 TWh (temperature adjusted), while the
population fell by 2% and the number of occupied dwellings increased by 3.4%.
German policy has strongly promoted deep thermal retrofits through regulation,
information campaigns and subsidised loans. An important question is what portion of
the reductions are due to progressive energy efficiency upgrade policy and what are
due to other, non-technical factors such as demographic and behaviour change. We
use national statistics and existing empirical studies to disaggregate the contribution
of energy-efficiency improvements and non-technical factors to the reduction in
consumption. Our analysis suggests that around 13% of the reductions are likely to be
due to thermal retrofits of existing dwellings (insulation and new windows); 8% due
to boiler or heating system replacements; 1% due to replacement of old dwellings
with new, energy-efficient buildings; while over 50% of the savings cannot be
explained by these technical improvements. Most of these reductions appear to have
occurred in non-upgraded, non-new dwellings. Although we do not know what caused
these reductions, the finding is robust to very wide inaccuracies in figures for savings
through technical improvements in buildings’ energy-efficiency. More research is
needed to explore the extent to which this implies increasing fuel poverty, increasing
skills and motivation among non-poor households to heat more economically, or the
effects of demographic and lifestyle changes.
Key words
Home heating behaviour; domestic energy saving; German energy policy; thermal
retrofits; heating fuel consumption
Highlights
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1
German home heating energy consumption fell by 154 TWh in 2000-2011
Approximately 13% of this was due to thermal retrofits of existing homes
8% was due to boiler/heating system upgrades
Less than 1% was due to replacement of old with new stock
Over 50% came from homes with no energy-efficiency upgrades
This could imply rising fuel poverty or more skilful heating behaviour
Corresponding author
1
Disaggregating the causes of falling consumption of domestic space heating
energy in Germany
1. Introduction
There has been a steady fall in heating energy consumption (including both space and
water heating) in the German domestic sector since this peaked in the year 2000,
reducing from 669 TWh to 515 TWh, or 23%, from 2000 to 2011 in temperatureadjusted figures (Destatis, 2010; 2013). This reduction, of 154 TWh, indicates that
German householders spent €12 billion less on heating fuel in 2011 than they would
have if their consumption had stayed steady at the 2000 level, and caused around 30
million tonnes less CO2 emissions, even though the number of occupied dwellings
increased by 3.4% in 2000-2011. The 2.8 million new dwellings constructed during
this period were built to high energy-efficiency standards, while about half that
number of older, less energy-efficient buildings became unoccupied. Meanwhile
approximately 4 million existing homes benefited from thermal retrofits, including
insulation and/or window replacement, and the heating systems in 5.5 million
dwellings were upgraded to newer, more energy-efficient models. These
improvements resulted partly from the legal requirement in the Energy-Saving
Regulations (Energyeinsparverodnung - EnEV), introduced in 2002, to undertake
thermal improvements whenever a portion of a building envelope is being repaired or
replaced (EnEV, 2009); partly from new regulations concerning boilers; partly from a
series of well-funded, persistent government campaigns to encourage and persuade
homeowners to thermally upgrade their buildings; and partly from the effect of
subsidies from the German Development Bank (Kreditanstalt für Wiederaufbau –
KfW) (DENA, 2009; 2012; UBA, 2010).
There has been no attempt to quantify the proportions of domestic heating fuel
savings being made from non-technical as compared to technical measures. By ‘nontechnical’ we include such things as demographic changes, which might result in
empty rooms in large homes; lifestyle changes, such as people spending less time in
the home; and behavioural changes, such as households’ attempts to keep heating
consumption low by heating or ventilating more efficiently. Rehdanz (2007) noted
that it would be useful to disaggregate these proportions, and Gram-Hanssen (2010;
2011) argues from empirical evidence that both behavioural and technical measures
are significant in attempts to lower household energy consumption. The Federal
Environment Office (UBA, 2006) surveyed households in 1995-2005 and concluded
that changes in user behaviour were making a significantly greater contribution to
energy savings than technical, energy-efficiency improvements. Koch et al (2008)
investigated the types of user behaviour that would enhance the German
government’s domestic heating energy saving goals, while others have surveyed
German households to find out what skill and knowledge shortages need to be
addressed to enable willing households to reduce heating energy (Brohmann et al,
2000; Hacke, 2007). However, as yet there has not been an attempt to disentangle the
various causes of consumption reduction to see what proportion, if any, can be
attributed to non-technical measures.
This paper considers the possible contribution to domestic heating reductions of
technical measures, i.e.: thermal retrofits of existing homes (insulation and window
upgrades); boiler or heating system replacement; newly built dwellings; and dwellings
becoming unoccupied. We use the term ‘abandoned dwellings’ for the latter, as
2
statistics show that there is no direct correspondence between the numbers of
dwellings being demolished annually, and the number of inhabited dwellings
becoming unoccupied (Destatis 2004; 2010; 2012). We address the period 2000-2011,
as temperature-adjusted consumption peaked in 2000, while 2011 is the most recent
year for which reliable data is available.
The German Federal Statistics Office (Destatis), the Housing Ministry (BMVBS), the
Ministry for the Economy (BMWi), the German Energy Agency (DENA) and the
Federal Environment Office (UBA) publish national statistics of heating fuel
consumption, the number of new builds, and the number of occupied and unoccupied
dwellings. In Germany there are now also a number of credible, existing empirical
studies, either peer-reviewed or from major research institutes, that offer empirical
findings on other factors that need to be known for a study such as this. These are: the
measured heating energy consumption of newly built dwellings; the quantity of living
area that has benefited from thermal upgrades; the measured energy consumption
savings that have resulted from these upgrades; and the number of boiler/heating
system replacements and their increased efficiency.
By examining the results of these studies, together with national statistics, we will test
the hypothesis that not all the reductions in domestic heating energy consumption in
2000-2011 can be explained by these technical factors. The hypothesis will fail to be
confirmed if either (a) the technical factors are seen to have produced sufficient fuel
savings to account for the fall in consumption, or (b) uncertainties in the data are so
large as to make a clear conclusion impossible. If the hypothesis holds true we will
then suggest what other avenues of research would be necessary to identify the nontechnical factors that have been contributing to this steady fall in consumption.
Our methodology is set out schematically in Figure 1. The quantities denoted by
variables A, B, C, etc., which are displayed on this schematic, are given in Table 1.
Other quantities we will be referring to in our analysis are given in Table 2.
<INSERT Figure 1>
<INSERT Table 1>
<INSERT Table 2>
Starting at the top right of the schematic in Figure 1: in Section 2 we estimate the
number of dwellings newly constructed in 2000-2011 and their total heating
consumption in 2011, to give the quantity G. In Section 3 we estimate the total
number of dwellings that were ‘abandoned’ in 2000-2011 and their total consumption
in 2000, to give the quantity B. Here the word ‘abandoned’ is a mathematical variable
equal to the difference between the number of new dwellings built in 2000-2011 and
the rise in the number of occupied dwellings in 2000-2011. This is not the same as the
number demolished in 2000-2011. The demolition rate bears no direct relation to the
rate at which dwellings fall out of use (Destatis, 2004; 2010). It also fails to take
account of shifting numbers of unoccupied dwellings that are, for example, between
tenants or in under-utilised apartment blocks, for which there are no plans for
demolition. A certain number of the new builds can be seen as replacing, one-for-one,
the abandoned dwellings, and from this we can work out the number of new builds
3
that were additional to replacements, and the increases in national consumption they
caused, i.e. N=G-B.
In Section 4 we consider the contribution of thermal retrofits (insulation and new
windows; not counting heating system upgrades). To do this we first estimate the
number of dwellings retrofitted in 2000-2011 and their pre-retrofit consumption, to
give the quantity C. We then estimate their post-retrofit consumption to give the
quantity H. The fall in consumption in this sector is given by K= C-H. In Section 5 we
estimate the number of dwellings which had boiler or heating system replacements in
2000-2011 and the consequent average percentage energy efficiency increase. The
dwellings this affects include both retrofitted and non-retrofitted, so we display the
fall in consumption due to boiler/heating system replacement as a separate wedge on
the diagram. This consumption in 2000 that was eliminated by 2011 through these
replacements is represented by the quantity D.
In Section 6 we bring all these figures together to estimate the reductions in
consumption in 2000-2011, if any, that were not due to technical factors, namely:
L = E – I = (A – B – C - D) – (F – G – H)
Equation (1)
We draw conclusions from the results of this analysis and make recommendations for
policy and further research in Section 7.
It should be noted that we are looking at an 11-year time span in this analysis. Our
figures refer to the period 1 July 2000 to 30 June 2011, or the 11-year period closest
to these dates which each dataset used in the analysis relates to.
2 New builds in 2000-2011
Destatis (2012) figures reveal that 2,689,965 new dwellings were completed
in the 11 years from January 2000 to December 2010 (See Table 3). These had an
average ‘useful’ area (Nutzfläche)of 114 m2 (Destatis, 2010), giving a total new
‘useful’ area of 306,656,010 m2. ‘Useful’ area includes floor area inside the front door
plus a portion of service stairwells, landings, basements and lofts, and is on average
25% larger than ‘living area’ (Wohnfläche), which only includes the floor area within
the front door and excludes basements, lofts and internal access stairwells. Following
German practice for thermal standards, all calculations of heating fuel consumption
given in this paper are based on ‘useful’ area.
<Insert Table 3>
We now estimate how much these dwellings were consuming in 2011. Prior to
October 2002 the average2 maximum permissible heating fuel consumption for new
builds was 145 kWh/m2a; from October 2002 to September 2009 it was 100
kWh/m2a; and thereafter 70 kWh/m2a (Galvin, 2012). Federal subsidies led to many
homes being designed for higher thermal standards (DENA, 2012a), which would
have lowered the average consumption in each of these periods.
2
The Energy Saving Regulations (EnEV) prescribe a range of maximum consumption figures for
buildings depending on their geometry, size and connection to other buildings.
4
The most comprehensive peer-reviewed study of the energy performance of new
homes built within this period is Greller et al. (2010), though this does not extend
through to 2011. These authors analysed the metered consumption of 110,000 gas and
oil heated homes built from 1977 to 2006, including 25,650 in the period 2000-2006.
They found an average heating fuel consumption of 95 kWh/m2a for those built in the
years 2000-2006 inclusive (Greller et al. 2010) and a falling trend from 100 kWh/m2a
to 90 kWh/m2a over this period. This implies negligible rebound effect (Haas and
Miermayr, 2000; Sorrell and Dimitropoulos, 2008) since minimum standards were
tightened to an average of 100 kWh/m2a in 2002. Due to the further tightening of
standards in 2009 to 70 kWh/m2a we would expect average consumption to have
fallen to this standard or better by 2011. Hence we accept Greller et al.’s (2010) figure
of 95 kWh/m2a for 2000-2006 and suggest an average of 65 kWh/m2a for homes built
in 2007-2010. Weighting these according to the number of homes built in each of
these years gives a total heating consumption in 2011 from all these homes of 26.7
TWh (see Table 3).
The three main sources of heating fuel not covered in the analysis of Greller et al.
(2010) - district heating, wood and electricity - make up 7%, 7.5% and 3% of heating
consumption respectively (Schloman et al, 2004). District heating and wood are
associated with primary energy consumption 10% lower than average, and electricity
with up to three times its end-energy consumption. Hence the differences here tend to
cancel each other out, so we stay with the figure of 26.7 TWh. This is variable G.
3. Dwellings abandoned in 2000-2011
The number of ‘dwellings abandoned in 2000-2011’, as defined above, is equal to the
difference between the number of new dwellings built in 2000-2011 and the increase
in the number of occupied dwellings in this period. In 2000 there were 35,001,000
occupied dwellings and in 2011 there were 36,198,000, an increase of 1,197,000
(BMVBS, 2012). Since 2,689,965 new dwellings were built in this period, the number
of existing buildings that became abandoned (to the nearest 1,000) was 2,689,965 1.197,000 = 1,493,000.
There are no existing studies on the heating consumption of dwellings that become
unoccupied, but there are good reasons to assume their consumption was higher than
the national average. Dwellings become unoccupied for two main reasons in
Germany: internal migration; and poor quality of buildings. Migration is the major
factor in Germany as there have been large internal population shifts in Germany over
the last 20 years, mostly from East to West and North to South (Szymanska et al.,
2009). The housing stock in former East Germany was mostly of pre-World War II
thermal quality prior to reunification, and the Communist era Plattenbau
(prefabricated slab) apartment blocks were of low thermal quality (Flockton, 1998). In
the western states emigration occurs mostly from old industrial areas, such as the
Ruhr Valley. In regions of falling population such as these, relatively few homes have
been built in recent decades. Greller et al. (2010) show that the average consumption
of pre-Second World War dwellings is around 165 kWh/m2a and that of dwellings
built in 1946-64 around 160 kWh/m2a. Schröder et al (2011), using similar
methodology and datasets, estimate total national average consumption at149
kWh/m2a. This would put the consumption of pre-Second-World War dwellings about
5
10% higher than the national average, and as most abandoned dwellings are of older
stock, it would seem reasonable to assume their average consumption was around
10% above the national average.
As we noted above, the national domestic heating energy consumption in 2000 was
669 TWh and there were 35,505,000 occupied dwellings, so that average consumption
was 18,842 kWh/a per dwelling. If the buildings that were later abandoned were
consuming 10% above the average, their consumption would have been 20,727
kWh/a per dwelling. As there were 1,493,000 of these dwellings, their total heating
consumption in 2000 would have been 28.1 TWh. Hence variable B=28.1 TWh.
While this is not essential to our analysis, we note, also, that 1,493,000 of the new
builds in 2000-2011 can be seen as replacing abandoned dwellings. This is 56% of all
the new builds, hence their 2011 consumption was 56% of 26.7 TWh = 15.0 TWh.
Therefore the heating consumption of new builds that were additional to the number
of dwellings abandoned was the difference between the total new build consumption
of 26.7 TWh and this figure, i.e. 26.7-15.0 = 11.7 TWh.
An interesting result here is that the fall in consumption from dwellings being
abandoned, at 28.1 TWh, is close to the consumption from new builds, at 26.7 TWh,
giving a net reduction of only 1.4 TWh. The net effect of these two sectors on fuel
savings is to almost cancel each other out, as there were almost twice as many new
dwellings as abandoned dwellings.
4. Dwellings retrofitted in 2000-2011
4.1 General considerations
The most difficult part of our analysis is to assess the fuel consumption reductions due
to retrofits. Not only are the precise numbers of retrofitted dwellings in dispute, but
there is a variety of degrees of retrofit, up to a full project including wall, roof and
basement-ceiling insulation; window and door replacement; addition of ventilation
system (with or without heat recovery); boiler and radiator replacement (which is
considered in the next section); and installation of solar collectors. Further, as there is
no inspection of thermal (or other) building standards in Germany, the authorities do
not automatically have records of what retrofitting has taken place, and we have
observed a certain amount of ‘sub-standard’ retrofitting being carried out illegally.
We will consider national summary figures from peer-reviewed papers and from
research institutes commissioned by the Federal government. Since it is difficult to
get precision in this section, we will estimate the range within which the true value is
highly likely to fall, and carry these results forward to our final totals. Further, we will
frequently be referring to ‘equivalent dwellings’ rather than ‘number of dwellings’
here, as some studies estimate the savings due to partial retrofits in terms of their
equivalent number of dwellings or floor area fully retrofitted.
6
4.2 Annual rate of thermal retrofits
The German Energy Agency (DENA) estimates the annual rate of thermal retrofits at
0.8% of the residential building stock per year over the last decade (Stolte, 2011), i.e.
8.8% of the residential building stock over 2000-2011. Since the average number of
dwellings (occupied and unoccupied) in 2000-2011 was 39.2 million, this is
equivalent to 3.45 million dwellings.
Diefenbach et al (2010) found a retrofit rate of 0.83% per year in a survey of 7,500
building owners, equivalent to 9.1% over 2000-2011, or 3.57 million dwellings if
extrapolated nation-wide, though this is a limited sample size.
Friedrich et al (2007) estimate the equivalent living area of existing homes retrofitted
with insulation, new windows in each of the years 2000-2006 as amounting to an
accumulated total of 5.9% of the residential stock over these 7 years, which would
amount to 9.3% if it continued for the remainder of the 11 years, or 3.64 million
dwellings.
Weiss et al (2012) estimate an annual retrofit rate for walls at 0.8% and roofs at 1.2%.
Weighting walls and roofs according to their average thermal impact3 in the ratio 3:1
would give an annual retrofit rate of 0.84%, assuming windows were upgraded
correspondingly. This would amount to 9.24% of the residential stock over 11 years,
or 3.62 million dwellings.
While the figures from each of these studies do not precisely agree, they are
sufficiently close to be used in our analysis. We note their average, of 3.57 million
dwellings, with upper and lower bounds 3.64 and 3.37 million dwellings respectively.
We will carry forward both upper and lower bound figures in our analysis so as to
find whether the degree of imprecision defeats the hypothesis we are testing.
4.3 Pre-retrofit consumption in 2000
We now estimate the heating fuel savings achieved through these retrofits. To begin
with, there is no precise data as to their actual pre-retrofit heating fuel consumption.
The German Energy Agency targets dwellings with a calculated (i.e. based on the
thermal quality of the building) consumption of 225 kWh/m2a or more for retrofitting
(Stolte, 2011), but notes that actual consumption in Germany is, on average, 30%
below the calculated value (DENA, 2012a: 43). This accords with Sunikka-Blank and
Galvin (2012) who find the same figure, and who show that this gap between actual
and calculated consumption increases as the calculated consumption increases, i.e. as
buildings’ thermal quality diminishes.
This would give an actual pre-retrofit consumption of around 160 kWh/m2a. Data
from CO2Online’s (www.co2online.de) database of over one million dwellings
indicates an average pre-retrofit actual (measured) consumption of 160 kWh/m2a for
detached and semi-detached houses, and 150 kWh/m2a for multi-dwelling buildings.
The term ‘thermal impact’ means the relative contribution of each feature to the thermal quality of the
building, based on the area each contributes to the building envelope, and typical U-values of each.
3
7
However, the self-selection bias of CO2Online’s data might make these actual
consumption figures lower than national averages for pre-retrofit dwellings.
A further consideration is that many residential buildings in Germany that are
thermally retrofitted do not necessarily have especially high pre-retrofit consumption,
since thermal retrofitting is compulsory when the substance of the building is being
upgraded, rather than when the thermal quality is low (EnEV, 2009). Further, large
apartment blocks, which are among the most frequently retrofitted buildings, do not
generally have above-average pre-retrofit consumption as the volume to surface area
of these buildings makes them inherently more thermally efficient than the average
building.
Hence it is likely that the pre-retrofit actual consumption of dwellings that were
retrofitted in 2000-2011 was not far above the average (149 kWh/m2a), so we will
estimate it at 15% above this, at around 170 kWh/m2a. As above, however, we will
check at the end of our calculation whether the uncertainties in this figure defeat our
working hypothesis.
Since the average useable area in 2000 was 110m2 (living area 84m2), this gives a
heating fuel consumption of 65.6 TWh for dwellings that were retrofitted in 20002011. Hence our variable C=65.6 TWh, though it could be 10% higher or lower than
this (59.0 to 72.2 kWh/m2a).
4.4 Consumption reduction per retrofitted dwelling
We now estimate the reduction in heating fuel consumption achieved through these
thermal retrofits. Schröder et al (2011) investigated the heating energy consumption
of residential buildings of two or more dwellings throughout Germany for 2004-2008.
Buildings retrofitted or constructed since 1995 showed an average consumption of
110 kWh/m2a, while those constructed prior to 1995 and not subsequently retrofitted
consumed an average of 145 kWh/m2a – a difference of 35 kWh/m2a, or 24%.
A further nation-wide empirical study (Schröder et al, 2010) gives cumulative
frequency distribution curves for the heating energy consumption throughout
Germany of retrofitted and non-retrofitted apartment blocks of floor area larger than
700 m2. The mean is 140 kWh/m2a for those completely non-retrofitted and 90
kWh/m2a for those comprehensively thermally retrofitted, a fuel saving of 50
kWh/m2a, or 36%.
Regarding smaller buildings, Walberg et al (2011) investigated the nationwide retrofit
performance of 5 classes of 1-2 dwelling buildings and found an average measured
consumption reduction of 26%.
A comprehensive figure is offered by Tschimpke et al (2011), of an average of 38%
reductions achieved through retrofits of all building types, though this refers to
calculated, rather than actual, pre-and post-retrofit consumption figures. Clausnitzer et
al. (2009; 2010) estimate the calculated saving in retrofits with Federal subsidies from
the German Development Bank (KfW) at an average of 33%. If actual pre-retrofit
consumption is, on average, 30% lower than calculated consumption (see above), the
actual savings for both these studies would be significantly lower.
8
The German Energy Agency also estimates actual savings at 25% (DENA 2012b).
Figures from CO2Online indicate actual savings of around 33%, though this could be
higher than the national average due to self-selection bias in the data. However, we
cannot ignore Schröder et al.’s (2010) figure of 36% for large apartment blocks.
Hence we would suggest a mean of around 30% savings for equivalent
comprehensive retrofits carried out in 2000-2011, though this could be as large as
35% or as little as 25%.
We now bring these percentages together with the pre-retrofit consumption range
estimated above. The maximum reduction would arise if the maximum pre-retrofit
consumption were reduced by the highest of these percentages, i.e. 72.2 TWh reduced
by 35%, a reduction of Hmax=25.3 TWh. The minimum reduction would arise if the
minimum pre-retrofit consumption were reduced by the lowest of these percentages,
i.e. 59.0 TWh reduced by 25%, a reduction of Hmin= 14.8 TWh. The mid-point
between these is Hmid=20.1 TWh.
5. Replacement of boilers and heating systems
To calculate the reductions in heating energy consumptions due to replacement of
boilers/heating systems we count the number of new boilers and heating units sold to
the domestic sector, and take an average figure for the increase in efficiency of each
unit.
Table 4 shows the number of new boilers or heating units sold in Germany in the
years 2000-2009 according to their type (e.g. gas condensing boiler; heat pump), with
a composite estimate for 2010. Totals for residential and non-residential new builds
are also shown. Subtracting the number of new builds (residential plus nonresidential) completed each year from the total number of heating units sold each year
gives an estimate of the number of non-new dwellings that had new heating units
installed in the 11 years 2000-2010 inclusive, i.e. 5,162,000. This is 14.0% of the total
of 36,198,000 occupied dwellings in 2011.
The average efficiency improvement of new heating units in this period is estimated
at 18% by CO2online (Heimann, 2012), and this accords with figures from UBA
(2011: 97). Hence the overall increase in heating efficiency of the existing German
building stock due to these replacements can be estimated as 14.0% of 18%, i.e.
2.52%. The consequent reduction in heating energy consumption would have
consequently been slightly more than this, due to the peculiarities of the mathematics
of increases in efficiency. Starting from an average boiler/heating system efficiency of
82.27% in 2000 (calculated from UBA, 2011: 97), an efficiency increase of 2.52%
represents a rise to 84.79% by the beginning of 2011. Hence, to get the same level of
energy services in 2011 as in 2000, the German residential building stock needed to
consume only 82.27/84.79 = 0.9703, or 97.03% of the energy it consumed previously,
a reduction of 2.97%.
However, the rebound effect, or price elasticity of demand for heating fuel, must be
considered here, as studies consistently show that when energy services become
cheaper, consumers take more of them, and vice-versa. (Haas, 2000; Sorrell and
9
Dimitropoulos, 2008). Estimates of price elasticity of demand for domestic heating in
Germany vary from around -0.2 to around -0.5 (e.g. Madlener and Hauertmann, 2011;
Rehdanz, 2007), so we take a middle value of -0.35. This means that for every 1% fall
(or rise) in the price of heating energy services, the amount of energy service taken
increases (or decreases) by 0.35%. This would imply that 65% of this saving of 2.97%
is realised, i.e. 1.93%. In short, the effect of boiler/heating system replacements
throughout Germany in 2000-2010 inclusive resulted in an estimated heating fuel
consumption reduction of 1.93% for the whole country’s residential building stock,
compared with 2000 levels, by 2011.
Total heating energy consumption in 2000 was 669 TWh, and 1.93% of this is 12.9
TWh. Hence we estimate that the replacement of boilers/heating systems in existing
buildings in 2000-2010 inclusive resulted in a saving in 2011 of 12.9 TWh. This is
variable D.
6. Reductions due to non-technical or unexplained factors
We now have sufficient information to estimate the savings in 2000-2011 that are not
explained by thermal retrofits or new builds. These are represented by the variable L,
where (recalling Equation 1):
L = E – I = (A – B – C - D) – (F – G – H)
= (A – B – D – F + G) – (C – H)
The values for A, B, D, F and G are known to a high degree of certainty. For C and H
we have estimated upper and lower bounds and a middle, or most likely value. The
highest value of C together with the lowest value of H will give the lowest estimate
for L:
Lmin = (669 – 28.1 – 12.9 – 515 + 26.7) – (72.2 – 14.8)
= 82.3 TWh.
The lowest value of C together with the highest value of H will give the highest
estimate for L:
Lmax = (669 – 28.1 – 12.9 – 515 + 26.7) – (59.0 – 25.3)
= 106.0 TWh.
This suggests that heating fuel reductions in 2000-2011 that are not attributable to
retrofits, heater/boiler upgrades or new builds are most likely to be in the range 82.3106.0 TWh. This would represent 53.4 - 68.8% of the total reductions, or a middle
value of 61.1%. The percentage fall in consumption within this sector would be:
Q = 100 x (E – I) / E
= 100 x [(A – B – C – D) – (F – G – H)] / (A – B – C – D)
10
The lowest estimate would result from the highest value of C and the lowest of H, i.e.
14.8%. The highest estimate would result from the lowest value of C and the highest
of H, i.e. 18.6%. Table 5 gives all the quantities of heating fuel calculated.
<Insert Table 5>
The price of heating fuel rose by 58.9% during this period (BMWi, 2011; 2011a). The
reductions that are not due to technical factors, i.e. 14.8-18.6% of their 2000 value,
would therefore represent a long-run fuel price elasticity of demand of -0.25 to -0.32
in respect of heating consumption reductions that were not due to technical measures.
This range accords with the lower band of fuel price elasticities reported above.
7. Discussion and conclusions
There is a wide range of uncertainty in two of our variables: the pre- and post-retrofit
consumption of homes that benefitted from thermal retrofits in the 11 year period.
This leads to a wide range of uncertainty in the quantity of energy saved through
thermal retrofits carried out in the 11 year period, i.e. 14.8-25.3 TWh. However, this
range is not so great as to swamp the likely range of values of residual consumption
reductions that do not seem to have come from technical changes4. As we have seen,
allowing for the highest estimate of savings through retrofits still leaves a gap of 82.3
TWh or 53.4% of the total reductions that does not seem to be explained by any of the
technical measures considered. This gap could be as large as 106.0 TWh, or 68.8% of
the total reductions, if the reductions though retrofits were at the smaller end of the
range.
Hence we can conclude that our hypothesis stands, namely, that not all the reductions
in domestic heating energy consumption in 2000-2011 can be explained by technical
factors. It appears that a considerable portion – possibly well over 50% - are not
explained by the effects of thermal retrofits, replacement of boilers/heating systems,
or the replacement of abandoned dwellings with new builds.
However, this does not imply that all the unexplained reductions took place in homes
that had no retrofits or boiler replacements. Some of the reductions could have taken
place in homes which also produced reductions from technical upgrades, and some
could have taken place in new builds. The figures merely imply that a large
proportion of the reductions seem to have occurred as a result of non-technical
factors, without prejudice to which sort of homes these factors pertained in.
Nevertheless, since homes that had little or no technical improvement consumed the
largest amount of heating energy, these were most likely the homes in which the
largest reductions through non-technical means took place, even if every home made
the same proportional contribution to non-technical reductions. A 14% reduction in a
1950s home consuming 20,000 kWh per year is much greater than a 14% reduction in
a low-energy house consuming 4,000 kWh per year.
An anonymous reviewer has pointed out that: ‘ the methodology has some strong limitations,
however is acceptable given the lack of detailed information required for such an assessment. Even
with the limitations, the analysis gives a good idea about the directions and magnitudes of different
components of decline of heating in German buildings'
4
11
A further interesting point is that the reductions due to replacement of abandoned
dwellings with new builds appear to be very small, at 1.4 TWh, or 0.9% of the total
reductions. This is because nearly twice as many new homes were built in 2000-2011
as the number that were abandoned, even though the population fell in 2000-2011
from 82.2 to 81.8 million (BMVBS, 2012). This accords with the demographic trend
of smaller households. Average household size fell during this period from 2.16 to
2.02 persons per household (BMVBS, 2012). This trend should lead to caution in
predicting that significant nationwide reductions in domestic heating energy
consumption are likely to result from increasing the rate of construction of new builds
(though there may be other good reasons to increase this rate). Our analysis has
shown that significantly greater reductions have come from both thermal retrofits and
heating system upgrades.
It remains to be asked what factors might be causing the large reductions that are not
explained by technical factors. To begin with, demographic trends seem to play a role.
The reduction in household size implies that many existing homes are becoming
emptier: the number of bedrooms in Germany is increasing as the population is
falling. This suggests that many homes had more empty rooms in 2011 than they had
in 2000. It would seem to follow that many of these householders would now heat less
of their living area, and possibly also for less time per week, because with fewer
occupants a house is likely to be empty more often and for longer periods. In a sense,
many old homes are exporting some of their heating consumption to new builds, as
former household members take up residence in them.
A further factor is price elasticity of demand for heating fuel. With studies
consistently showing elasticities of between -0.2 and -0.5, this implies that
households, on average, reduce their consumption in response to fuel price rises. One
concern here is that this could be leading to fuel poverty. The German Energy
Agency’s analysis of the heating consumption of a sample of 35,000 German homes
shows that actual consumption is, on average, 30% lower than dwellings’ calculated
energy rating (DENA, 2012a). This accords with Sunikka-Blank and Galvin’s (2012)
analysis, which adds that the percentage gap increases considerably for the less
energy-efficient homes. This lends weight to the suggestion that households take less
energy services when the cost is high. Some of the datasets in Sunikka-Blank and
Galvin’s (2012) analysis show very low consumption for some homes with very high
energy ratings, indicating that many people could be failing to heat their homes
adequately.
However, these non-technically induced reductions might also indicate that some
households are becoming more skilled at getting the level of energy services they
want, without consuming a great amount of fuel. These households may be heating
fewer rooms, or for shorter periods, or to lower temperatures, or some combination of
these, than they used to, or ventilating less adequately, a possibility explored in
Galvin (2013). Some households may be motivated by economic thrift, environmental
concern, or other factors we about which we do not yet have clear knowledge. It
might be possible to learn from such people since, as some of the works cited above
appear to have found, user behaviour plays just as important a role in heating energy
consumption levels as technical measures play. More research is needed to identify
the reasons for this steady reduction in heating energy consumption, particularly
12
among less energy-efficient homes, and whether it indicates increasing fuel poverty,
smart heating skills, or some combination of these in Germany.
Finally, the results of this paper suggest that Germany is saving considerable sums of
money through non-technical causes of heating fuel consumption reduction. The 82.3106.0 TWh saved in this way equate to a saving of around 6.6-8.5 billion euros in
2011, and 16.5-21.2 million tonnes of avoided CO2 emissions. These considerable
savings would tend to support the suggestion that the specific causes of nontechnically induced heating fuel reductions should be systematically investigated.
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16
Fig 1. Schematic showing the possible contribution of five different factors to the fall in
domestic heating consumption in Germany in 2000-2011: abandonment of dwellings; new
builds; thermal retrofits (insulation and windows); new boilers/heating systems; and nontechnical influences.
energy
consumption
(TWh)
B
Dwellings
abandoned in
2000-2011
C
retrofits
new builds
D
new boilers
A
G
non-technical factors
H
E
F
I
Non-technical causes
(35.505 million
2000 occupied dwellings)
17
(36.089 million
2011 occupied dwellings)
Table 1. Quantities of heating energy displayed in Fig. 1. Note that there will be
overlap between these categories in some cases.
Symbol
A
B
C
D
E
F
G
H
I
Quantities of heating fuel consumed Quantities of heating fuel consumed
in 2000 by:
in 2011 by:
All dwellings in 2000
Dwellings abandoned in 2000-2011
Dwellings retrofitted (Insulation &
Windows) in 2000-2011
Dwellings with boiler/heating system
replacement in 2000-2011
Dwellings not upgraded in 2000-2011
All dwellings in 2011
Dwellings constructed in 2000-2011
Dwellings retrofitted (insulation &
windows) in 2000-2011
Dwellings not upgraded in 2000-2011
Table 2. Other symbols, and composites, used in the analysis
Symbol Quantity of heating fuel
K
Savings through thermal retrofits of existing dwellings
L
Savings made through non-technical means
Total Reductions 2000-2009
M
Savings through new builds replacing abandoned dwellings
Additional consumption through excess of new builds over
N
abandonments
P
Net saving through new builds and abandonments
18
Equal to
C-H
E-I
A-F
G-B
Table 3. Numbers of new dwellings built in Germany in the years 2000-2010 inclusive, giving estimated heating energy consumption based on an average
‘useful’ floor area of 114 m 2 per dwelling, to give an estimate of heating energy consumption in 2011 of all dwellings built in this period. Source: Destatis
(2012).
year
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Total
No.
348340
290978
274117
296823
268679
240571
247793
182771
174691
177570
187632
2689965
Est. heating
consumption
(kWh/m2a)
95
95
95
95
95
95
95
65
65
65
65
Heating
consumption
(TWh)
3.773
3.151
2.969
3.215
2.910
2.605
2.684
1.354
1.294
1.316
1.390
19
26.661
Table 4. Sales of new boilers/heating systems in Germany 2000-2009, with estimated figure for 2010, alongside figures for new builds, to give numbers of
dwellings with new boilers/heating systems installed in 2000-2010 incusive. Sources: UBA (2011: 96); Destatis (2012) and Statistica:
http://de.statista.com/statistik/daten/studie/199380/umfrage/baugenehmigungen-von-wohnungen-seit-2000/ plus own calculations.
Totals
New units (1000s)
Lowtemp (Gas)
Lowtemp (Oil)
Condensing (Gas)
Condensing (Oil)
Heatpumps
Biomass (central)
TOTAL (1000s)
New Builds (Residential)
2000
385
218
230
4
9
9
855
348340
2001
314
216
248
8
13
9
808
2002
271
188
254
11
13
14
751
2003
245
180
276
14
14
19
748
2004
239
187
307
17
16
28
794
2005
212
164
288
21
19
31
735
290978
274117
296823
268679
240571
2006
152
118
344
39
49
54
756
247793
2007
112
65
271
37
46
19
550
182771
2008
105
47
308
58
62
36
616
174691
2009
109
44
330
72
55
27
637
177570
2010
650
187632
7900
0
2689965
New builds (nonresidential)
TOTAL new builds
7610
355950
5473
296451
5189
279306
4259
301082
4054
272733
3600
244171
4143
251936
3872
186643
3360
178051
3293
180863
3148
190780
48001
2737966
new boilers/heating
units in old dwellings
499050
511549
471694
446918
521267
490829
504064
363357
437949
456137
459220
5162034
20
Table 5 Estimates of quantities of heating energy for each variable in the analysis
Symbol Estimate (TWh)
Quantities of heating fuel
consumed in 2000 by:
Quantities of heating fuel consumed in
2011 by:
A
669.0
All dwellings
B
28.1
C
59.0 - 72.2
D
12.9
E
555.8 – 569.0
Dwellings abandoned in 2000-2011
Dwellings retrofitted in 2000-2011
(insulation & windows)
Dwellings with new boilers/heating
systems in 2000-2011
Remaining consumption in 2000
F
515.0
All dwellings
G
26.7
Dwellings constructed in 2000-2011
H
14.8 - 25.3
Dwellings retrofitted in 2000-2011
(insulation & windows)
I
463.0 – 473.5
Remaining consumption in 2011
M
15.0
N
11.7 (additional)
New builds additional to replacements
P
1.4
Net saving through new builds and abandonments
L
82.3 – 106.0
Reductions due to non-technical factors
Changes in quantities of heating fuel 2000-2011 due to
New builds replacing abandoned dwellings
21