ارتقاء حرارتی از خانه های موجود در آلمان: کد ساختمان، یارانه، و بهره وری اقتصادی
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|21372||2010||11 صفحه PDF||سفارش دهید||محاسبه نشده|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Energy and Buildings, Volume 42, Issue 6, June 2010, Pages 834–844
One of the cheapest ways to reduce CO2 emissions is thermal renovation of existing homes. Germany is a world leader in this project, with a strict building code, generous state subsidies, and an advanced renovation infrastructure. The effects of its policies are here explored in the light of progressive tightening of the building code, and the strict criteria for subsidies. Data on costs and outcomes of residential building renovations are presented from published reports on renovation projects, and cross-checked with projects investigated directly. Comparisons are made in terms of euros invested for every kilowatt hour of heating energy saved over the lifetime of the renovations, for standards ranging from 150 kWh (the lowest standard) to 15 kWh (the highest) of primary energy use per square metre of floor area per year. It is found that the lowest standard is an order of magnitude more cost-effective than the highest, in terms of both energy saved per euro invested, and return on investment over the lifetime of the renovations, regardless of fuel prices. It is argued that this throws into question Germany's policy of progressively regulating for higher renovation standards, and offering subsidies only for projects that go beyond the minimum standard.
Human activities in existing buildings are the cause of around 40% of the world's total primary1 energy consumption (IEA, 2006). In the UK this figure is around 30% , of which about half comes from space heating . In Germany, where average winter temperatures are some 3 °C lower than in Britain, space heating accounts for over 75% of household energy use , and in the EU as a whole around 70% . Total energy used for home space heating in the EU is increasing, mainly due to the increasing number of households and larger size of dwellings . Since much of this energy comes from fossil fuels, energy consumption by households is a very significant issue in attempts to reduce GHG emissions. It has been variously estimated that space heating in buildings accounts for some 25% of EU countries’ GHG emissions, about half of which – around 12% – comes from households . Since there is a direct relationship between GHG emissions from space heating, and energy used in space heating, this sector is contributing to the current steady increase in GHG emissions worldwide. There is great potential for energy savings in household space heating ,  and . Renovating a 1950s German apartment block to the pre-2004 ‘minimum’ standard (see below) can cost less than 3 eurocents/kilowatt hour (kWh) of primary energy saved over the lifetime of the renovations . This compares to the much higher costs of generating energy from renewables such as wind power (8 cents) and photovoltaics (28 cents), and the spot-price of electricity (7 cents), or current heating oil costs (6 cents)  and . Refitting homes can, if planned sensibly, be one of the world's cheapest ways to save energy and reduce GHG emissions. Of course, this does not take into account subsequent changes in energy use patterns due to the rebound effect ,  and . For example, in their study of recent home heating upgrades in Britain, Milne and Boardman  found that upgrading can form a justification to consume more fuel, even though this costs more, because now the householder is getting better value for money. Hence the uncertainties due to human behaviour changes after thermal refits and other energy efficiency measures offer a caution of the necessarily tentative nature of the findings of studies such as this. The remainder of this introductory section outlines the relevant issues in the German building code, and how they relate to thermal renovation (TR) of existing homes (EHs) as compared to new builds. It also outlines the system of state subsidies for TR. Section 2 examines case studies of TR projects, developing a mathematical model for comparing the fuel saving economics of various TR standards. Section 3 draws out the implications of this for policy development and incentives. Section 4 looks at counter-arguments, while conclusions are developed in Section 5. 1.1. The German building code At the time of writing (August 2009) the rules for building renovations in Germany were given in the Energieeinsparverordnung für Gebäude 2007 ( , ‘Energy Saving Regulations for Buildings’). This is a successor to EnEV 2004, and is supplanted again in September 2009 by EnEV 2009 (see ). The government has announced its intention of supplanting this once more in 2012 . A crucial point that must be understood at the outset is that EnEV 2004, 2007 and 2009 are designed primarily for new builds, not renovations. They set down the standards of thermal retention which must be achieved in new building design and construction. These standards are driven by the government's commitment to reduce energy consumption in buildings, but are carefully negotiated with the construction industry to take account of its current and future capabilities, so that optimally energy-efficient new buildings can be constructed for reasonable costs—i.e. they must, the legislation declares, be ‘wirtschaftlich’ (‘economic’). The new regulations (EnEV 2009) raise the standards for whole-building heat retention ‘by 30%’. This means that the maximum permitted heat energy consumption per unit floor area is reduced to 70% of that permitted by EnEV 2007 . In 2012 it will be reduced again, to 70% of the EnEV 2009 value, i.e. 49% of the EnEV 2007  value. EnEV 2007 did not upgrade the previous standard, but used the standard set down in EnEV 2004, with minor changes. However EnEV 2004 was a 30% upgrade on the previous standards. Simultaneously, EnEV 2009 raises the standards for the average heat retention coefficient of a building's outer shell by 15%. This means that the maximum permissible ‘U-values’ (see below) are reduced to 85% of the EnEV 2007  values. Again, EnEV 2004 was a 15% upgrade on the pre-2004 U-value standards, and these will be raised by a further 15% in 2012. The core of EnEV 2007  is its (Table 1), an English translation of which is presented in Appendix A. This sets out the maximum permissible primary energy use for space heating and the heating of drinkable water in a new home, using two measures, corresponding to the two parameters outlined above, each of which must be adhered to. One is ‘QP’, the maximum permissible primary energy use per kilowatt hour per square metre of floor area per year (kWh/m2 a). The other, ‘HT’, is the maximum permissible heat transmission loss through the outer surface of the building (i.e. the average U-value), measured in watts per square metre of building envelope per degree Kelvin (W/m2 K). These figures have to be worked out on the basis of keeping an all-round indoor temperature greater than 19 °C. 2 Further, there is not one absolute figure for each of these two measures. Rather, there is a range given in the table, according to factors calculated from the shape and size of the building. This is because (a) larger buildings retain heat more easily than smaller buildings, as they have a smaller ratio of surface area to volume; and (b) cube-shaped buildings retain heat better than oblong or irregular-shaped buildings, as they, too, have a smaller surface area to volume ratio. The range of values in the table makes allowance for the difficulties of retaining heat in smaller or odd-shaped buildings—yet is nevertheless designed so as to incentivise the construction of the thermo-geometrically more efficient, larger, cubic-shaped buildings. All this is modified by one further factor: local climate. To work out whether a building will comply with the heat retention rules one has to know the average local temperature. This must be worked out from a further table, in which Germany is divided into 39 postcode districts, each centred on a particular weather station . (As from October 2009 this has been refined, to 8234 weather zones). Hence, for new builds, EnEV 2007  is an accomplishment of creditable technical sophistication, while the step to EnEV 2009 moves thermal retention requirements for new builds forward. Questions arise, however, in that the rules for renovating existing buildings are based directly on Table 1, which is designed for new builds. A mitigating factor – found in EnEV 2004, 2007 and 2009 – is ‘the 40% provision’: thermal retention standards of renovations of existing buildings are allowed to be 40% more lax than those of new builds. Numerically, this means that QP for renovations can be up to 1.4 times QP for new builds of corresponding shape and size. For buildings renovated from 2004 to September 2009, this means that QP for renovations of most buildings has to be in the range 110–160 kWh/m2 a, depending on size and shape of building. As from September 2009 this range becomes 75–110 kWh/m2 a. If the government's intentions for the 2012 adjustments are realised, the range will become 50–75 kWh/m2 a. Appendix B shows calculations of QP for a small and a large residential building, in each case both for new build and renovation standards, based on EnEV 2007. 1.2. New builds and thermal renovation There are three peculiarities which arise through tying the rules for TR to those for new builds. Firstly, there are no guarantees that thermal renovation technology will advance in parallel to new-build thermal technology. Many thermal features of old buildings are extremely expensive to change, such as orientation to the sun, size of windows, geometric shape, and thermal bridges. Secondly, the mathematics of energy saving is different for new builds compared to renovations. Before a new building is erected on a vacant lot, the vacant lot is using no heating energy and causing zero GHG emissions. Hence the thermal success of a new build may be measured in direct proportion to how small its annual heating energy is, and how low its consequent GHG emissions are. But energy use in existing buildings has a different profile. The buildings are already consuming energy and causing GHG emissions. Hence the crucial figure is the reduction in energy consumption through renovation, not its absolute value. Reducing the energy consumption of a building from, say, 300–40 kWh/m2 a is only 13% better than reducing it to 80 kWh/m2 a, even though the absolute values after renovation are in the ratio 1:2. Therefore in this physically, mathematically obdurate way, thermal renovation differs radically from new builds. With renovations, the mathematics suggests that tightening the standards and increasing cost does not bring a proportionate gain in energy saving. Thirdly, new builds cause a large ‘pulse’ of GHG emissions, due to the extraction and processing of heavy building materials, their manufacture and transportation to the building site, and the energy consumed in erecting the building . These ‘embedded’ GHG emissions have been estimated to be equivalent to about 50 tonnes of CO2 for a typical three bedroom house . Thermal renovation produces a much smaller pulse, as there are few heavy materials and much less work involved. This means that, even if a new building uses hardly any energy over its lifetime, it still takes 25–50 years before it starts to pay its way in comparison to an old building modestly renovated so as to reduce its emissions by 1 or 2 tonnes of CO2 per year. So building a new building always causes a jump in GHG emissions whereas TR always causes a reduction, a case could be made for forming much stricter thermal retention regulations for new builds than for TR. 1.3. Subsidies The main state subsidies for thermal renovation are awarded only to projects carried out to higher standards (lower QP and HT values) than the minimum requirements of the EnEV. The federal government's subsidy institution is the Kreditanstalt für Wiederaufbau (KfW; http://www.kfw-foerderbank.de), 3 which offers grants, and loans at subsidised interest, to renovators of residential properties. 4 However, the KfW does not recognise the ‘40% provision’, so its loans are only given to renovation projects which achieve the new-build levels ( Table 1). Further, an even lower interest rate and higher grant are offered to projects which achieve levels 30% stricter than the regulations. The best interest rate, then, can only be had for projects attaining 50–75 kWh/m2 a. If this policy is continued as from September 2009, this level will tighten to 35–50 kWh/m2 a. Other state subsidies are available from some local authorities. Munich City Council, for example, offers grants for residential projects which achieve the standard of 40 kWh/m2 a for QP and which also surpass the EnEV's highest HT standard 5 , proudly calling this ‘Der Münchner Standard’. Freiburg, too, offers grants, based on the achievement of specific thermal resistance levels for walls, windows, attics, etc., that go beyond minimum standards . Hence, there is pressure to tighten standards for thermal renovation, both in the progressive development of the building code, and in the state subsidies available for renovation projects.
نتیجه گیری انگلیسی
There is, roughly, an inverse power–law relationship between the amount of money invested in thermal renovation and the amount of energy saved per euro. Costs of renovating to standards above 60 or 70 kWh/m2 a rise exponentially while the amount of energy saved rises only a very small amount. For a house that previously consumed 300 kWh/m2 a of heating energy, there is hardly any difference in energy saved between reducing this by 240 kWh/m2 a, to the 60 kWh/m2 a standard, and reducing it by 270 kWh/m2 a, to the 30 kWh/m2 a standard (a 12.5% difference in energy saved), but the costs per unit of energy saved can differ by over 100%. Most attempts to justify renovations to the higher standards do so on grounds of higher absolute return, and thereby make a common error: they fail to consider the heating fuel consumed by the buildings that were not renovated, but could have been, if all the money had not been spent on the one building that was renovated to a very high standard. There is huge potential for thermal renovation, to a minimum or modest standard, among Germany's millions of flat-façade apartment blocks. This could be achieved very cheaply in terms of euros invested per kilowatt hours of energy saved. It would more than pay for itself, provided the chosen standards of renovation were to keep this cost below the price of heating fuel, currently about 6 cents/kWh. This opportunity will be lost when the minimum standard for thermal renovation is pushed 30% above its  level. It will double the cost threshold, making it unaffordable to many private homeowners and landlords. It will also reduce the return on investment in terms of energy saved per euro invested. In light of these findings the following recommendations are made for policy makers and for further research. 5.1. Recommendations for policymakers Firstly, the legislation upgrading the building code for thermal renovation of existing buildings  needs to be modified so that renovation of these buildings will not have to conform to a standard 30% stricter than that permitted by EnEV 2007 . This can be achieved by changing the phrase ‘nicht mehr als 40 vom Hundert’, in : §9.B2, to ‘nicht mehr als 100 vom Hundert’. With this change, renovators would use the new 2009 values but could overrun the figures by 100%, which is equivalent to overrunning the 2007 figures in Table 1 by 40%. Legislators must then revisit this issue when finalizing plans for further tightening of the building regulations in 2012. Secondly, the KfW needs to broaden its loan criteria to include renovation projects that conform to the 40% provision in . This will ensure that state-subsidised loans are available for the projects that save the most energy per euro invested, and thereby result in a more effective use of state funding. It will also make low-income people more able to renovate their homes and reap the benefits of improved comfort and lower fuel bills. Thirdly, municipalities such as Munich and Freiburg need to lift the restrictions on their grants to thermal renovation projects, making them available to all who plan to renovate within the law. Again, this will result in a far more effective use of public funds, and make benefits more accessible to low-income homeowners. Fourthly, municipalities and states need to cease their practice of seeking to persuade homeowners to renovate above the minimum standard. Fifthly, municipalities need to cease the practice of renovating social housing to stricter standards than the minimum. This spends public money non-optimally, while denying or delaying thermal comforts to thousands of tenants. 5.2. Recommendations for further research Firstly, there needs to be research on the effect of ‘cost threshold’ (see Section 3.3) on the likelihood of renovation being undertaken. If and when the minimum standard for renovation is tightened by 30%, this threshold could increase by up to 100%, and a further 100% for a further 30% tightening. We need to find out the extent to which this will put renovation beyond the reach of increasing numbers of people. Secondly, there needs to be research on how much private money public subsidies could cause to be spent on renovations if these subsidies were made available for projects at the minimum standard. There is an assumption that, by offering incentives only for strict-standard projects, this causes the greatest amount of private money to be spent on energy saving. However there is no cited empirical evidence in support of this. It may be completely erroneous. Perhaps there would be a flood of renovations if subsidies were offered at the low end of the market. We do not yet know. Thirdly, there needs to be research on the resale value of properties which have been thermally renovated, particularly in terms of value recouped in proportion to moneys invested. Finally, there needs to be social science research on why the current subsidy, regulatory and promotional characteristics of thermal renovation of existing homes in Germany are the way they are. Why is it that subsidies are so inappropriately directed, in terms of achieving their stated goal of saving energy? Why is the KfW out of step with EnEV minimum standards? Why are such expensive but cost-ineffective projects so consistently praised, while inexpensive, extremely cost-effective projects are not only looked down upon, but are being legislated into non-existence? These are fascinating questions. If they could be answered, perhaps ways could be found of redirecting the German home renovation project onto a more fruitful and cost-effective path.