Renewable Energies Perspective to the Energy Performance of Buildings

Transcription

1 Renewable Energies Perspective to the Energy Performance of Buildings J.J. Bloem, European Commission, DG JRC Institute for Energy Abstract Introduction of renewable energy technologies in the built environment gives opportunities to improve the energy performance of buildings. In particular the use of solar energy applications offers a variety of possibilities. The Energy Efficiency and Energy Service Directive [1] and the Energy Performance of Buildings Directive [2] require all Member States to implement national regulations within the near future. Other European Directives are stimulating further improvements in energy performance and energy efficiency in the building sector. Integration of renewable energy sources for heating and electricity in the built environment is also stimulated through national regulations in a few Member States. This paper presents renewable energy technologies and related CEN energy standards dealing with the built environment taking into account the overall energy demand of the building and placed in the overall energy context. Keywords: Renewable Energies, Energy Performance, standards Approach The philosophy underlying this study starts from the integral energy performance concept. The building can be considered as one entity that consumes energy to provide the required comfort to work and live in it. Most of the present national and regional regulations deal with components of the building, such as the maximum of thermal heat loss through the building envelope. All options for energy demand and supply must be considered together if society is to attain significant levels of energy efficiency and renewable energy deployment. The Trias Energetica should be considered as a philosophy for energy use (Novem 1996, [3]) and was further developed as a strategy applied for sustained energy (TU Delft). Its main aspects are: 1. Minimisation of Energy Demand (energy saving and energy efficiency) 2. Maximum use of Renewable Energies ( 3. Highest efficiency of other forms of energy These aspects are placed in order of priority. Integration of these elements is sometimes possible but should be studied in the context of economic feasibility. The philosophy of the Trias Energetica is applicable to the full range of energy sizes, e.g. from domestic to large office buildings. The philosophy is nicely illustrated in figure 1. Figure 1. Source: Sintef 1996 (NO)

2 The application however might be different for Member States considering national conditions and the mix of energy resources. The range of energy sizes can be: a residential building (solar energy), a building block, urban area (district heating), city, region (investment in energy saving lamps), country (power plant). In relation to this philosophy, priority areas may be recognized as defined by the European Parliament (Greens Party); Stimulating a Democratic Debate on FP7 for Energy and Nuclear Nov 5, Energy Efficiency and Saving 2. RE Fuel Production 3. RE Electricity 4. RE Heat and Cool 5. Smart Energy Networks 6. Knowledge for Energy Policy Making 7. Hydrogen and Fuel Cells 8. Carbon Capture and Storage 9. Clean Coal Technologies Conclusion from the Trias Energetica philosophy should be that renewable energy technologies become interesting after measures have been taken under item 1, such as insulating the building envelop (walls and windows; Construction Product Directive (1989), [17]) and applying energy efficient technologies for lighting. It might be clear that for building renovation from economic point of view it makes more sense to reduce building energy consumption for lighting and hot water production than to invest in photovoltaic technologies. There is still a lot to gain in the area on energy saving and efficiency, which is nicely illustrated in figure 2. [4] Figure 2. Source: McKinsey-Vattenfall report. The McKinsey-Vattenfall 2030 climate map report presents CO 2 abatement potentials in relation to investment. When it concerns buildings, insulation is by far the highest (1.7 Gt CO 2e ) contribution to reducing energy consumption and therewith CO 2 emissions; Water heating, air conditioning (0.5 Gt CO 2e ) Lighting (0.2 Gt CO 2e ) White good applications (0.2 Gt CO 2e ) and stand-by losses (0.2 Gt CO 2e ). Solar energy as a form of renewable energy applied for water heating would be supported by this report. The Directive on the Energy Performance for Buildings [2] is an important Directive for reducing energy consumption in buildings. A given building has typical energy consumption expressed in kwh/m 2 /year. Any change in the energy consuming components of the building for the improvement

3 of the building comfort should not increase but lower this typical energy consumption and improve the energy performance of the building. Building simulation and energy calculation tools can help the building designer to assess the energy demand for renovated or new buildings. The integration of renewable energy technologies in the building requires not only the assessment of the individual system performance but in respect to the overall building performance instead. In this context it is noted that much interest is lately given to double skin facades. For example, during the winter period, warm air from a double skin PV system might be applied for pre-heating of ventilated air into the building. A proper analysis of building overall energy performance is therefore required and should integrate the calculation rules for thermal insulation, shading and other energy flows. Introduction The building stock and energy consumption. Energy consumption in buildings is rising over the last decades (481 Mtoe or 41% of the final energy consumption in 2005 according to Eurostat data, [5]) due to rising income, resulting in higher standards of living. In particular the demand for electric appliances for increased comfort levels, communication and information technology has increased the demand for electricity in this sector. Hunderd years ago energy was consumed for space heating only, while nowadays, on average in Europe, 2/3 is required for space heating and 1/3 (electricity) for other use in buildings. Although space heating and cooling are the most energy demanding the integrated energy consumption in buildings does not decrease as illustrated in figure 3 (exception to this might be Denmark). Figure 3. Source: ENOVA J.P. Burud (Tokyo 2005). In figure 3 are given data for buildings in Norway. The average over all buildings <1930 is 257 kwh/m 2 ; the average >1987 is 277 kwh/m 2. Similar data are reported by other national organisations. Efforts to reduce energy consumption by improving insulation are compensated by a higher electricity demand leading in some case to black-out due to electricity intensive air-conditioning. Continuous survey [20] of end-use electricity consumption in residential and tertiary sectors shows that the total electricity consumption for the residential sector for the EU-25 has grown by 10.8% in the period , from 690 TWh in year 1999 to 765 TWh in year 2004 and by 1.8% in the period The gas consumption of the residential sector has continued to grow in the period 1999 to 2004 in the EU-25 from 4721 PJ to 5399 PJ with an increase of 14%, while the yearly growth rate in the period has been 2.2%.

4 Renewable energy technologies in the built environment. As renewable energy technologies in the built environment are in general considered: solar energy, biomass and geothermal energy. The use of heat-pumps to convert heat from underground (shallow geothermal energy) and ambient (heat from air or surface water) to optimise energy use for heating is a growing application. The advantage of introducing solar energy, electrical and thermal systems in the built environment is often presented as an option to reduce primary energy resources and therewith the harmful emissions for our climate. However the impact of these systems on the overall energy performance of a building is a difficult measurable phenomena. Electrical output of a PV system can be measured but the impact of building integrated PV systems on the thermal behaviour of a building is more complicated and depends on a lot of parameters. Moreover, in the case of less efficient technologies in the building, for example incandescent bulbs, the impact of PV (and the investment as well) might be fully worthless. Solar energy can be consumed where or close to where it is produced. Geothermal (and the use of heat pumps) and the primary resource to end-use consumption. Biomass (indicate forest areas and cost for transport) and carbon neutral. The energy context Important is to place energy consumption in the context of the whole process of energy flow. The transformation, distribution and end-use of energy should be considered in order to get clear insight in the energy saving potential and the impact of renewable energy technologies and energy efficiency measures on the reduction of primary energy resources and CO 2 abatement. Figure 4. From Primary energy resource to useful energy delivered (including distribution). Source JRC; based on Eurostat data (2005). Fossil fuels account for 79.1 % and nuclear energy for electricity for about 14.2 %. Renewable energy sources account for 6.7% (2005 Eurostat data, [5]) of the total primary energy consumption in EU-27. Biomass takes the biggest portion with 4.4%. Solar energy accounts for about 0.7%. Environmental heat, using heat-pump conversion is not considered and therefore not traceable.

5 With the policy targets of 2020 in mind, a contribution of 20% renewable energy to the energy enduse, it is worthwhile to colorize building delivered electricity, heat and fuel. Energy then becomes traceable for its origin and green-washing of fossil produced energy will be avoided. Fossil (black), nuclear (yellow) and renewable (green) produced electricity and heat becomes for the end-user a different product and can be calculated in correct way in statistical analysis. Figure 5. The energy delivery side of buildings. From building energy demand to energy enduse. This picture might be very different for fuel type and Member States energy mix. EPB directive At present Members States should have implemented the EPBD. When it concerns renewable energies the EPBD give: explicit attention to the positive contribution of renewable energies in the context of energy performance regulations A global view on the energy flows, whereby a correct integration of energy saving, renewable energies and efficient energy production technologies The present energy standards related to the EPB Directive dealing with renewable energy technologies are given below. These standards provide methods for calculating the energy contribution from installations. pren Provides methods for system efficiencies and/or losses and auxiliary energy. pren Part Heat pump systems pren Part Thermal Solar systems (including DHW) pren Part The performance of other renewable heat and electricity. pren Part Biomass combustion systems pren Heating systems in buildings - Method for calculation of system energy requirements and system efficiencies Part 3. Domestic hot water systems: Several Member States have put in place more drastic regulations in particular when it concerns new buildings, like Portugal and Spain where solar thermal energy for domestic hot water installations has given a high priority and are obligatory.

6 Solar Energy in the Built Environment Solar energy technologies may be distinguished in: Passive technology, e.g. building design, urban planning. Active technologies e.g. solar thermal and photovoltaics. Passive solar energy technology by definition do not need auxiliary energy to perform and is related to careful design taking into consideration the location, climate and level of solar radiation. Already centuries ago buildings were constructed in such a way that thermal mass and solar radiation were matching the need for a comfortable environment to live and work in. It is during the last half century that an energy careful design has received less attention due to the availability of appliances that provide and control a comfortable indoor environment. However, note that with electricity consumption for air conditioning units and hot water systems is increasing rapidly despite rising energy costs. Although a very important aspect of energy saving using solar radiation as primary energy resource, the passive solar technology is in general not considered as a renewable energy technology. Solar chimneys that recently gets more attention in Spain, might change that point of view. Concerning solar thermal systems the market is doing very well. Solar thermal systems in the built environment are used for: Domestic Hot Water systems (DHW), being the major application. Space Heating, mainly in Northern Europe Space Cooling by solar assisted cooling, in the Mediterranean area The applied solar thermal technology can be distinguished in: Flat glazed thermo-siphon systems of about 2-3 m 2 can be found mostly in Southern Europe. Flat glazed forced circulation systems of about 2-6 m 2 is installed in Mid- and Northern Europe. Evacuated Tube Collectors which have about 15% higher efficiency in south Europe and about 30% in northern Europe than the flat plate collector. Unglazed collectors. Evacuated Tube Collectors (ETC) take about 10% of the total collector sales in 2005 and are expected to become more popular. By far, most of the systems are used for Domestic Hot Water (90%). Other applications are space heating (in almost all cases these are combination systems) and pool water heating (mostly by unglazed collectors). See also the IEA report 1 [6]. Figure 6. Solar Thermal energy flow. Source K4RES-H project [16]. In general small systems (<10 m 2 ) are found in the residential and tertiary sector. Bigger systems (>10 m 2 ) are found in the tertiary and industrial sector. Renewable Energies from solar thermal (Qs) is produced if: (Qdhw-Ql) > (Qpc) 1

7 where (Qpc) is primary energy input (for electric power). Market and resources Industrial associations and IEA statistics provide enormous amount of information [7, 8, 9,10 and 14] and report the potential for growth. This paper will concentrate on solar and geothermal energies. For information on biomass reference is made to the biomass association [9]. Solar thermal data (Figures 7 and 8) are available from the European Solar Thermal Industry Federation 2 (ESTIF, [7]) and are usually expressed in square meters (m 2 ) sold or installed area. The International Energy Agency's Solar Heating & Cooling Programme, together with ESTIF and other major solar thermal trade associations have decided to publish future statistics in MW th (Megawatt thermal) and have agreed to use a factor of 0.7 kw th /m 2 to convert square meters of collector area into MW th Figure 7. Solar thermal capacity in Source ESTIF. In 2006, almost 2200 MW th of solar thermal capacity (3.1 million m 2 of collector area) was newly installed in Europe 26% more than in the previous year. The traditional lead markets Germany, Austria and Greece, are responsible for about ¾ of the operational capacity in Europe and have all performed well in Some very good developments in several of the high-potential markets like France and Spain can be noted. At the end of 2005, the total capacity in operation in the EU and Switzerland was 11,175 MWth ( m 2 of collector area). To calculate the produced heat energy from solar thermal collectors, one needs to know its location and the annual solar radiation and that site. Since the amount of solar radiation is not equally distributed over Europe the calculation is a complex task. In figure 10 is given an impression of how much thermal energy could be produced by a 1 m 2 solar collector area in Europe. Roughly twice more collector surface area is required in Scandinavian countries than for Mediterranean countries. The Spanish implementation of the EC Directive on the Energy Performance of Buildings, with the new technical building code (CTE) includes an obligation to cover 30-70%, depending on climate zone, of the Domestic Hot Water (DHW) demand with solar thermal energy. It is expected that the CTE will support the boom in the solar collector market in Europe. In addition the European certification scheme, the Solar Keymark for solar thermal collectors (EN 12975) and factory made systems (EN 12976) is more and more accepted, both by the industry and by public authorities. 2

8 Figure 8. Share of solar thermal market in Source ESTIF. A more recent picture (2006 data, figure 9) shows the solar thermal capacity and energy in relation to other Renewable Energy resources. For clarity reasons, biomass and hydropower are left out. Figure 9. Renewable Energy technologies Capacity and Produced Energy. Source IEA-SHC [6].

9 Figure 10. Solar map produced by EC JRC IES Renewable Energies Unit 3. Building Integrated PV The integration of PV in the building envelope requires not only the assessment of the electrical performance. PV awning applications will avoid overheating of the building while at the same time it reduces peak electricity demand. In the winter period the warm air in a double skin PV system might be applied for pre-heating of ventilated air into the building. Including a building integrated PV (BIPV) calculation module into the ESP-r simulation tool [15] will allow to make a proper analysis of building overall energy performance since it integrates the calculation rules for thermal insulation, shading and other energy flows. Simulation of such systems under different climate and boundary conditions would help a lot to understand the integration in the build environment. Some considerations about the introduction of PV technology in the build environment in relation to the calculation method have to be made. In terms of energy performance one is interested in the annual power production from the PV system. However the produced energy is depending on daily and seasonal climate conditions. During hot summer days the produced electricity from PV systems can support the reduction of peak power demand while at the same time shading parts of the building. During the winter period the warm air behind a PV façade can preheat the air for ventilation. Thus the overall impact on the building energy performance should be considered and not only the produced power. Several ways have been studied to present an integrated energy performance for buildings. Interesting reading can be found [11, 12 and 13]. 3

10 Figure 11. Source EPIA 2007 Global PV markets (policy driven scenario). According to EPIA 4 market expectations [18] the market for thin-film PV modules will grow significantly. In addition to the established c-si capacity, approximately 4 GW of thin-film capacity is expected to be available by the end of This would represent 20 % of the overall module production capacity. Although all technologies face high expansion rates, thin-film capacities are currently expanding at a faster rate than capacities for other technologies. Figure 12. Three groups of interest Member State Industries Building users In general there are three parts (figure 12) involved when evaluating energy savings in buildings. 1 - The EU Commission and Member State governments, where its strategy is to reduce energy consumption and to abate CO 2 emissions. Targets are 20% in 2020 while at the same time the integration of renewable energy resources is stimulated, 10% in the electricity production. Three important building energy related EC Directives are supporting that strategy: EPBD, EESD and the forthcoming RES. 4

11 The Member States will have to implement regulations to support that strategy but will have to consider also their energy-mix which in the context of the EU energy-mix might lead to different strategies and national regulations and incentives. 2 - At the bottom end are the building user or owner (in case of rented offices, residential buildings, etc) who may have a more economic evaluation. The energy bill is often the major concern for residential and tertiary buildings owners and users. Energy prices and capital investment might lead to different solutions. A proper approach for existing buildings would be to follow the Trias Energetica; invest in energy saving measures before introducing new renewable energy installations. The driving factor here is an economic evaluation. 3 - In between the industry is positioned. They want to sell their products, being buildings, heat or cool installations, domestic appliances, air-conditioners, etc. Some of these products on the European market are of high energy efficiency and quality but would not necessarily much contribute to the goals of the European strategy if the Member State energy mix is not taken into account. Industries play an important role for introducing renewable energy and innovative technologies into the market. Products have to be reliable, efficient, a high quality and well priced. In the calculation method the primary energy demand should be the final result, starting from building energy consumption. With the above in mind, the solar hot water (but also heat-pump) installations should be considered. This will lead to different situations for different Member States. The restriction to evaluate only fossil-fuel hot water installations will give a distorted view on the matter. Electricity for hot water in general should be included too. Hot water in buildings (residential and tertiary) is produced in different ways and it should not be neglected the impact of white good appliances, such as dish-washers and washing machines that use electricity to heat water. The calculation method will lead to improved results when these appliances will have 20 or 30 degree input water temperature which might be produced by existing fossil fuel boilers. These means that the potential is higher but also might be an option for building owners and users. Industry is able to produce dishwashers and washing machines for this purpose. Returning to the primary energy demand, it is clear that electricity produced by fossil fueled power plants give a complete different result than in cases of electricity produced from wind or hydro-power plants. Also in cases of gas-boilers the energy and economic evaluation will be different. Therefore the energy saving potential should address three points of view and consider the potential of all cases where electricity is used for water heating in relation to the national (or sometimes regional) energymix and the related energy prices. Example: Scandinavian countries like Sweden and Norway will promote the use of electricity for domestic hot water and heat-pumps because of their huge electricity produced from renewable resources in the energy mix. It is clear in their implementation of EU Directives that a different regulation is the result than it would be for the UK, Spain or Italy. Heatpump applications A heat pump is by definition any device that accepts heat at one or more temperatures and rejects heat at a higher temperature. A heat-pump is a thermal conversion technology that consumes electricity. It is mostly used in geothermal and environmental thermal applications. The heat produced might be considered as renewable heat. Heat pumps are nowadays becoming popular choices for space heating as well as for cooling, especially in areas with less severe winters. Further information is provided by EGEC [8]. In general heat pumps are more effective for heating than for cooling if the temperature difference is held equal. Ground-source heat pumps typically have higher COP s than air-coupled heat pumps, because they draw heat from ground or groundwater, and this is at a relatively constant temperature all year-round below a depth of about 2.5 m. The trade-off for this improved performance is that a ground-coupled heat pump is usually more complicated due to the need for wells or buried coils, and thus is also usually much more expensive to install than an air-coupled heat pump.

12 The performance of such a system should be considered in a proper way. Being an energy system in a building it should contribute in a positive way to the overall energy performance of that building. However, important as well is its performance in the whole energy chain, cq. from primary energy resource to energy end-use. The term "renewable heat" covers all heat that is the result of a conversion process of renewable resources or that contain renewable resources (waste or hybrid power plants). It is important to describe the conversion processes or systems, including the conversion efficiency and the renewable energy input resource. Figure 13. Schematic energy conversion chain. Input side Auxiliary Conversion Output side Primary resource Energy Efficiency [%] Mtoe or MWth Since the information and data comes from different origin a lot of attention has to be given to accuracy of the data, conversion of parameter values and efficiencies of the heat conversion installations. In particular the amount of operation hours should be treated carefully for all applications and calculation methodologies. Coefficient of performance (COP) is the ratio of the output heat to the power input. The greater this value, the greater the efficiency of the unit and the quicker the initial costs can be recuperated. to describe the ratio of useful heat movement to work input. When comparing the performance of heat pumps, it is best to avoid the word "efficiency" which has a very specific thermodynamic definition. An important consideration is the application of heat pumps in buildings. The high COP can be achieved at certain temperature levels which make the heat-pump system good for floor-heating (spaceheating). Most commonly, heat pumps draw heat from the air or from the ground. Air-source heat pumps do not work well when temperatures fall below around 5 C. In all ground source heat pump systems (GSHP), there is a basic difference between the heat output to the heating system, and the geothermal heat input into the system (Qg in the figure 12 below). Figure 14. Geothermal energy flow; source K4RES-H project [16]. Renewable Energies from geothermal heat (Qg) is produced if: (Qu-Ql) > (Qpc + Qph) where (Qpc + Qph) is primary energy input (for electric power)

13 The auxiliary energy (mainly Qph in the figure 14) is always higher than 5 % and is typically in the order of % of the final energy output. Thus it cannot be neglected. Electricity supply from fossil power plants with an efficiency of 40% requires a heat-pump with at least a COP of 2.5 (the heat-pump technology is advancing a lot and a COP of 3 to 4 can be reached). In Scandinavian countries with a major supply of electricity from hydro-power plants and more and more wind, the situation is much different and would favour the use of air-to-water heat-pump systems. In this context it is important to consider the energy mix of the Member State and sometimes also the regional availability of energy. Heat pumps extract the heat stored in the ground, air or water in order to warm homes and could provide sanitary hot water. In areas where natural gas is not available, heat pumps are a popular alternative, but using only a heat pump for all heating needs wouldn't be economical, or even possible. Most heat pumps use electricity as a power source, and most of them do not operate at highest efficiency in very cold weather. Supplementary energy for heat such as gas, oil, electric and wood is used when the temperature falls below about 5 C. When used for heating a building on a mild day, a typical heat pump has a COP of three to four, whereas a typical electric resistance heater has a COP of 1.0. The work does not make heat, but instead moves existing heat "upstream". When there is a wide temperature differential, e.g., when heating a house on a very cold winter day, it takes more work to move the same amount of heat indoors as on a mild day. Note that the system must periodically melt the ice on the outdoor heat exchanger. Conclusions on heat pump application. Under certain conditions (climate, energy costs, resource and national energy mix) the use of heat pumps contributes to a positive impact on reducing final energy end-use. Conclusion Challenges exist for renewable energy technologies in the built environment, in particular for domestic water heating (solar energy) and space heating (pellet burners). Geothermal energies might be interesting when the conditions are an advantage for energy and economical reasons. The use of heat-pumps should be considered in the context of the national energy-mix in order to support the reduction of CO 2 emissions. National regulations and incentive schemes should take away barriers for private investment while industries should provide products and appliances that offer to end-user and government all aspects to reduce primary energy and emissions.

14 References [1] DIRECTIVE 2006/32/EC Directive on Energy end-use Efficiency and Energy Services. [2] DIRECTIVE 2002/91/EC on the Energy Performance of Buildings. [3] The Trias Energica: Solar Energy Strategies for Developing Countries Erik Lysen, Eurosun in Freiburg sep [4] Vattenfall s Climate Map [5] EUROSTAT Pocketbook (2006): Energy, Transport and Environment Indicators; data 2005, EC, ISBN Luxembourg [6] [7] Solar Thermal Markets in Europe ESTIF European Solar Thermal Industry Federation [8] EGEC European Geothermal Energy Council [9] AEBIOM European Biomass Association [12] Bloem J.J., Baker P.H. Strachan P.A. (2004) Energy Performance of Buildings and the Integration of Photovoltaics. IEECB Conference, Frankfurt [11] S. Citherlet J. A. Clarke and J. Hand. ESRU, University of Strathclyde, Glasgow G1 1XJ, UK. Integration in building physics simulation Energy and Building Volume 33, Issue 5, May 2001, Pages [13] Evaluation of PV Technology Implementation in the Building Sector J.J. Bloem, A. Colli, Strachan P.A., Palenc Conference, Santorini, 2005 [14] IEA/Eurostat/OECD Energy Statistics Manual, data service at [15] ESRU; ESP-r System, [16] K4RES-H. Key Issues for Renewable Heat in Europe [17] DIRECTIVE 1989/106/CE. Construction Products Directive (or CPD). [18] EPIA European Photovoltaic Industry Association [19] DIRECTIVE 2001/77/EC Promotion of electricity produced from Renewable Energy Sources in the internal electricity market. [20] Status report 2006: Electricity Consumption and Efficiency Trends in the Enlarged European Union. Report 2006.pdf