Solar-supported heating networks in multi-storey residential buildings

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3.1 Low average collector temperatures as an energy-related success factor The average collector temperature ((Tinlet+Toutlet)/2) is the decisive value for the present high-quality collectors to attain high solar yields throughout the year. The lower the average collector temperature, the higher the efficiency rate of the collector and thus the solar yield. Without a doubt, it is wrong to believe that the demand for the lowest possible average collector temperature can only be adequately achieved by the solar thermal system alone. It is rather the case that apart from the dimensioning of the collector area, other aspects and parameters determine the temperature level at the collector: • Type and manner of integration of the conventional heat generator • Principle and dimensioning of domestic water heating • Principle and dimensioning of space heating supply • Dimensioning of the storage unit volume available for the solar thermal plant • Mixing rate of energy storage unit (water amounts, geometries of storage units, etc.) The influence of the interaction of the overall heating supply system on the average collector temperature, and thus on the efficiency of the collector, can be seen by way of example in Figure 6. Heating supply concepts adapted to the requirements of solar energy plants achieve much lower average collector temperatures and thus higher collector efficiencies in all operating points. η 0 1,00 0,90 0,80 0,70 0,60 0,50 0,40 0,30 0,20 0,10 A Collector Efficiency at Typical Operating Points B 0,00 0,00 0,02 0,04 0,06 0,08 (Tkm-Tu)/G [Km²/W] 0,10 0,12 0,14 0,16 11 Conditions Given: Collector Data: c 0=0,8 c 1=0.33 [W/m²K] c 2=0.012 [W/m²K²] Surrounding Temperature = 20 [°C] Average Collector Temperature A = 45 [K] Average Collector Temperature B = 60 [K] Radiation on the Collector Surface = 800 [W/m²] Figure 6: The influence of the temperature on the achievable collector efficiency. An Adapted holistic heating systems with lower mean temperature (operating point A) achieve essentially higher collector efficiency than for the example a solar thermal system with high return temperatures in the heat distribution system (operating point B). Only the integration of heat generators adapted to the needs of solar thermal systems or their heat emission components permits low average collector temperatures and thus the highest possible solar yields.
3.2 Enhancement of the solar coverage and reduction in auxiliary heating requirements as a result of very low heat losses in the system It is not only the solar yield which is of decisive significance in holistic considerations but also the overall annual system utilisation rate. Highly efficient solar thermal systems lose their relevance in the case of a thermally inefficient (lossy) residual system, which is reflected in very low solar coverage rates. Figure 7 shows the example of the system losses of a solar-supported heating supply system from the heat generators (energy input – without any losses during energy conversion) to the consumers (useful energies for domestic hot water and space heating). On the basis of numerous measurements, it becomes clear that considerable heat losses occur in the system sections of heat storage and heat distribution, which in the case of exceptionally inefficient heating supply systems can also lead to system efficiencies below 50%. Energy Flow [%] 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Losses Collector Circuit 4% Solar Input into the System Solar Yield in the Store 36% 32% 64% 64% Additional Heat into System Additional Heat into Store Losses Heat Store 6% 2% 27% Removal from Heat Store DHW 63% Removal from Heat Store H 12 Losses Heat Exchanger 19% 21% Useful Energy DHW 48% Useful Energy H Energy Input Into the Store Out of the Store H and DHW in the Homes Losses H-, DHW-Distribution Net 21% Useful Energy DHW 48% Useful Energy H Useful Energy H and DHW Figure 7: Exemplary description of the system losses of a solar-supported heating supply system (from the heat distributor to the end user with an annual degree of system utilisation of 69%). On the one hand, this problem has to be tackled by appropriate system hydraulics and, on the other hand, by an improved design of the thermal insulation standard. • Selection of simple system hydraulics with conceptionally reduced system temperatures avoiding pipework • Positioning of the energy storage unit at the shortest possible distances from the site of heat generation (solar collectors, conventional source of heat/energy) and to the consumers (domestic hot water and space heating) • Avoidance of outside pipework • Selection of one-storage-tank system without storage unit batteries • Improved standards with regard to storage unit insulation • Insulation of all indoor pipework in accordance with the requirements of ÖNORM M7580 • Improved insulation standards for outdoor pipework • Use of insulation for valves and fittings 31% System Losses 69% Annual System Utilisation Rate
Page 1 and 2: Solar-supported heating networks in
Page 3 and 4: Reprinting and translation, storage
Page 5 and 6: 6.2 Collector assembly with frame s
Page 7 and 8: 10 Investment costs, grants and eco
Page 9 and 10: 2.2 Innovations and the economic fa
Page 11: Figure 4: Efficient solar-supported
Page 15 and 16: 3.4 Systems with the greatest possi
Page 17 and 18: 4 • Reduction of heating requirem
Page 19 and 20: Radiation [kWh/m² and Day] 9,00 8,
Page 21 and 22: 35.000 30.000 25.000 Heat Demand 20
Page 23 and 24: Hot Water Demand [Litre per Person
Page 25 and 26: 5.1.1.2 Measurement of consumption
Page 27 and 28: Total Period for the Different Tapp
Page 29 and 30: The heating requirements indicate t
Page 31 and 32: Figure 20: Crain assembly of large-
Page 33 and 34: Figure 25: South orientated roof co
Page 35 and 36: Figure 29: Large-area collectors mo
Page 37 and 38: Another important issue when instal
Page 39 and 40: Figure 35: Results from research pr
Page 41 and 42: If a non-back-ventilated collector
Page 43 and 44: As a result, the absorbers need col
Page 45 and 46: The insulation of the storage unit
Page 47 and 48: This is made clear in the DVGW work
Page 49 and 50: 7.1.2.2 The specific solar energy y
Page 51 and 52: Figure 48: Solar thermal system in
Page 53 and 54: Kollektorfeld T1 T4 T5 T6 Figure 49
Page 55 and 56: Large-scale solar energy systems in
Page 57 and 58: Collector Field Figure 53: Cross-se
Page 59 and 60: Although the collector’s expansio
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It should be borne in mind that if
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• Mean temperature of the primary
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7.2 The preceding information appli
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Figure 65 shows the block diagram o
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highest quality but also feature co
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term operation and maintenance. Fig
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Heat meter and water meter Figure 7
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temperature at which the heat stora
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system can be attained once again d
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that of a four-pipe network. In pra
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single tank system is to be recomme
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Figure 87 shows a two-tank system f
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energy aspects which are taken into
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Dimensioning for almost 100% covera
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Reading value for utilisation: appr
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Heating energy requirements: approx
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A correction nomogram was prepared
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with 20 flats the bath is filled on
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QBW � maximum output for preparat
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Network Outward Flow Outward Flow C
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∆ TBW temperature difference in d
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In addition to the aspects mentione
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If, however, despite all these effo
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Figure 105: Pipe work for solar the
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10 Investment costs, grants and eco
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12,0 5,0 4,0 2,0 2,0 13,0 8,0 5,0 1
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System temperatures [°C] 100 90 80
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corresponding definition of fault s
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Christian Fink, Werner Weiß: Endbe
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Computersimulation von thermischen
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Solar-supported heating networks in multi-storey residential buildings

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