basics:passive_house_-_assuring_a_sustainable_energy_supply:determining_application-specific_per_factors
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basics:passive_house_-_assuring_a_sustainable_energy_supply:determining_application-specific_per_factors [2014/07/21 12:52] – cweber | basics:passive_house_-_assuring_a_sustainable_energy_supply:determining_application-specific_per_factors [2014/09/18 18:19] (current) – external edit 127.0.0.1 | ||
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+ | ====== Determining application-specific PER factors ====== | ||
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+ | The findings show that the supply structure that needs to be built and its efficiency depend greatly on energy-consuming applications' | ||
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+ | PE< | ||
+ | |||
+ | whereby E< | ||
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+ | PER = (E< | ||
+ | The results show that while PER factors determined with this equation are relatively stable compared to, say, changes in the primary power mix or the technology mix, they also depend //greatly on the individual energy application// | ||
+ | |||
+ | ===== Domestic electricity consumption (DEel) ===== | ||
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+ | In this paper, domestic electricity includes all electricity used in a dwelling except for power used for hot water, heating, and air conditioning; | ||
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+ | * all domestic appliances (refrigerators, | ||
+ | |||
+ | * lighting, \\ | ||
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+ | * electronics (televisions, | ||
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+ | * device controls, including for pumps, \\ | ||
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+ | * and ventilation systems. \\ | ||
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+ | Figure 6 shows how the PER factor for domestic power supply depends on the primary power mix used: with 90 percent wind, for example, it comes out to 1.75 kWh< | ||
+ | \\ | ||
+ | |{{: | ||
+ | |//**Figure 6: \\ Primary renewable energy (primary electricity) required \\ for total domestic power demand from PV, wind, and hydropower (high efficiency).**// | ||
+ | \\ | ||
+ | Figure 7 depicts the equivalent area for renewable generators that would be needed to cover total domestic electricity demand. A (very flat) optimum of only about 35 m² can be reached with a solar share of 35 to 75 percent. The actual area for PV (with a share of 55 percent) would come out to 19 m². Such a small area could almost always be located very close to the building in question, often directly on the roof. \\ | ||
+ | \\ | ||
+ | |{{: | ||
+ | |//**Figure 7: \\ Size of the equivalent PV array (primary electricity) needed to cover total domestic power \\ demand with PV, wind, and hydropower (with buffer storage in the grid and \\ seasonal P2G methane storage) with high efficiency.**// | ||
+ | \\ | ||
+ | |||
+ | ===== Domestic Hot Water Power Consumption (DHW-hp) ===== | ||
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+ | This study assumes a tap water schedule for a four-person household and a hot water heat pump with a seasonal performance factor SPF of 2.5, resulting in annual power consumption for hot water of 1, | ||
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+ | Figure 8 shows the PER factors from the simulation relative to the share of PV in the production mix for hot water supply. A quite flat optimum can be seen with a PV share of 55 percent. Because of the locally available storage, this subsystem requires very little power from seasonal storage (only 10 Nm³ of methane). With a small safety margin, the PER< | ||
+ | \\ | ||
+ | |{{: | ||
+ | |**//Figure 8: Renewable primary energy (primary electricity) needed to cover power demand \\ for hot water with solar, wind, and hydropower (grid buffer storage / seasonal P2G methane \\ storage); hot water heat pump with seasonal performance factor SPF of 2.5.//**|\\ | ||
+ | \\ | ||
+ | |||
+ | ===== Power demand for heating (heat-hp) ===== | ||
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+ | For our Passive House example, we have assumed a heat pump with a SPF of 2.53, resulting in annual power consumption for heating of 1, | ||
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+ | Electricity for heating could be considered the " | ||
+ | |||
+ | Expanding wind power is a particularly ideal solution for power supply for heating (see Figure 9), although a PV share of 10 to 50 percent is still acceptable. The rounded PER factors then come out to \\ | ||
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+ | PER< | ||
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+ | Heating thus requires much higher numbers when it comes to producing, converting, and storing energy. If PV provides 90 percent of renewable primary energy, the PER factor for heating increases to more than 2.6 kWh< | ||
+ | |||
+ | The amount of renewable power generation that needs to be installed to cover the Passive House heat pump amounts to about 22 m² of equivalent PV area, although this is mostly covered by a corresponding amount of wind power. Using P2G methane produced and stored in the summer to fill the winter gap requires at least 72 Nm³ of storage volume under normal conditions. The required storage is already available today (even if all buildings use heat pumps for heating), and the technology for electrolysis and methane synthesis could easily be installed on the grounds of combined-cycle plants used for reconversion. The main reason this would all be so simple is the very low heating demand required in the Passive House Standard. \\ | ||
+ | |||
+ | The picture is very different if the building is instead built as a Low Energy House with a heating demand of 56 kWh/ | ||
+ | \\ | ||
+ | |{{: | ||
+ | |**//Figure 9: \\ Renewable primary energy (primary electricity) needed for heating power demand \\ in a Passive House building, wind power and PV (grid buffer storage / seasonal P2G methane); \\ heat pump with an SPF of 2.53 (German test reference year 12).//**|\\ | ||
+ | \\ | ||
+ | |||
+ | ===== Cooling with electric compressors ===== | ||
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+ | In terms of time, potential cooling demand and direct primary power production seem to be well correlated at first glance – in the summer. \\ | ||
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+ | The remaining renewable electricity produced in seasons that do not require cooling can be completely used directly for other applications (for example heat pumps that urgently require power), thereby reducing the amount of power that needs to be drawn from storage. The factor for cooling as an isolated application is: \\ | ||
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+ | PER< | ||
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+ | At the same time, the marginal value relative to total power consumption is only about 0.5 kWh< | ||
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+ | A resulting insight significantly changes priorities related to building design as we have previously known them. In the future, it will be much more environmentally sound and cost-effective to use renewable energy to cover energy demand for any cooling that may be needed than for heating. In addition, since the same heat pump system can generally be used for both cooling and heating in Central Europe (and even the same distribution system in a Passive House building), the technical complexity required for cooling can also be drastically reduced. This situation has four consequences: | ||
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+ | 1. With climate change resulting in increasingly hot summers everywhere, including Central Europe, we will be able to provide people in Passive House buildings with a comfortable indoor temperature without environmental guilt or high costs, even in the summer. \\ | ||
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+ | 2. Of course, cooling demand should not be unnecessarily increased – all technical recommendations (such as those in AkkP 22, 31, and 41) for limiting summertime heat input should still be followed. But, now it is better to undertake optimisation measures to minimise cooling demand based using the PHPP's " | ||
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+ | 3. Especially expensive solutions for passive summertime optimisation (more complicated duct systems, larger duct cross-sections, | ||
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+ | 4. When solutions for conserving heating or cooling energy are competing, reductions in cooling have tended to be more important in central Europe. This priority will be turned on its head, since cooling energy can be provided with overall less ecological concern and lower costs (with an annual heat pump SPF of 2.5, a PER< | ||
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+ | These findings are revolutionary, | ||
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+ | |||
+ | ===== P2G Methane ===== | ||
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+ | P2G methane can be created with a conversion efficiency of 57 percent out of primary electricity with \\ | ||
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+ | PER< | ||
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+ | Here, we are purposely limiting the definition of P2G methane to methane synthesised as primary power from wind and/or PV systems (for energy budget reasons, the biogas share is considered separately – see next section). This renewable primary energy factor is almost as high as that of electricity for heating – a paradox only at first glance, since if P2G gas is used for, say, heating, it first needs to be completely synthesised from primary power, resulting in losses. If, however, energy is taken from the renewable power grid – even for heating – it is still mostly primary electricity; | ||
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+ | Methane' | ||
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+ | ===== Biogas, firewood, and biomass budgeting ===== | ||
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+ | In this scenario, biogas is also cleaned to its methane component and sent to the same gas network as the P2G gas discussed in the previous section. An average PER factor could therefore also be calculated for this type of energy when mixed in with gas from solar and wind, but doing so would cover up an important consideration: | ||
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+ | PER< | ||
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+ | At first glance, biogas therefore seems like it should be given priority for applications that rely on storable energy (traffic, heating, etc.). The problem, however, is that biogas is only available to a very limited extent [[basics: | ||
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+ | * first, **available space** in general, which amounts to about 2,300 m² of agricultural land and about 1,300 m² of forest per person (for all applications together in Germany; these figures are about the same as the global average, but there are significant regional differences throughout the world); \\ | ||
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+ | * **sustainable use**: for example, trees can only be felled in an amount that allows the forest to grow back, while growing energy crops for biomass that require large amounts of fertiliser and energy in agricultural areas is, of course, not an option for reasons related to sustainable preservation of cultivable land. Even with these limitations, | ||
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+ | * **land use competition!** Biomass is currently mostly used for food (agriculture) and raw materials (forestry). These priorities will only become more important in the future as an increasing global population requires more food. Biomass used as fuel therefore mostly consists of waste from other processes (food waste, leftover straw, scrap wood, wood shavings, etc.). Even these bits and pieces are increasingly – and sensibly – being used primarily as material for other processes (cellulose insulation, for example). If we subtract food and raw material use, energy from biomass gives us about 5,300 kWh per person or 11 percent of current primary energy demand. That is a rather small amount, and must still be subjected to another form of \\ | ||
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+ | * **use competition** related to energy: some applications clearly call for transportable fuel, particularly air traffic and individual vehicles driving long distances. Such applications could, of course, also use P2G gas – but they would become considerably more expensive. A simple appraisal of the situation shows that especially air traffic, which is in particular need of energy storage with high energy density, will use the majority of the bioenergy potential. \\ | ||
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+ | Clearly, there are significant limits on the use of bioenergy as a resource. It makes absolutely no sense to use it for hot water and domestic power in houses and other buildings, especially since direct electricity results in better PER factors; if there is still biomass available beyond traffic needs, it should therefore be sent to combined-cycle plants (perhaps with waste heat recovery). Overall, only a very small budget of 20 kWh/ | ||
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+ | ===== Heat from cogeneration ===== | ||
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+ | Analyses of combined systems always have to deal with a certain amount of uncertainty regarding how, exactly, the benefits are distributed to the various components. For the system in question here, we suggest a consistent electricity credit method, for the following reasons: \\ | ||
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+ | * Electricity is the backbone of renewable energy distribution and will be the type of energy most used in the sustainable energy supply of the future. The primary electricity shares of heat pump systems that get their final energy from the power grid result in excellent total primary energy expenditure values. \\ | ||
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+ | * The problem here is the low amount of primary power available in the winter, requiring seasonal P2G storage that results in conversion losses. Reducing these losses can decrease the expenditure for a completely renewable energy system. \\ | ||
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+ | * One option for reducing losses is using the heat from reconversion – exactly what is done with heat from cogeneration systems – for a heating application (preferably heating itself, since its PER is higher if P2G gas or electricity is used). \\ | ||
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+ | * If the cogeneration systems only produce electricity when none is available from renewable primary power sources or mid-term storage (electricity control mode), they can substitute power that would otherwise need to be reconverted from P2G gas (without cogeneration). In this case, it makes sense to use P2G gas demand for heat from cogeneration as the difference between the system' | ||
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+ | It is important to note that this method is appropriate here largely because the substituted energy source – P2G gas – is the same. This method would not work if the primary energy sources are different, especially when there is a mix of renewable and nonrenewable sources (see [[basics: | ||
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+ | Another important consideration is, that the heat distribution can be quite expensive and also leads to additional heat losses [[basics: | ||
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+ | In a renewable energy systems, cogeneration plants must have high conversion rates and conversion efficiency. The share of distributed heat from cogeneration (or a heat pump) must be higher than 75 percent (and a maximum of just 25 percent of the heat can come from peak boilers). Only combined-cycle systems and fuel cells are really interesting; | ||
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+ | With a combined-cycle conversion efficiency rate of 54 percent in cogeneration, | ||
+ | \\ | ||
+ | |**Cogen share of heat production**|0%|60%|65%|70%|80%|85%|90%|95%| | ||
+ | |**Combined-cycle district heat from P2G**|2.52|1.88|1.75|1.61|1.29|1.12|0.93|0.73|\\ | ||
+ | |\\ //**Table 1: PER factors for district heat from cogeneration** \\ For comparison' | ||
+ | \\ | ||
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+ | ===== Read more ===== | ||
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+ | ==== Previous sections ==== | ||
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+ | [[basics: | ||
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+ | [[basics: | ||
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+ | [[basics: | ||
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+ | ==== Following section ==== | ||
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+ | [[basics: | ||
+ | \\ |