Solar-supported heating networks in multi-storey residential buildings

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7.1.2.3 The annual degree of system utilisation (SNutz) Systems for providing domestic hot water and heating display losses from the heat generation stage all the way to the actual consumer (residents' demand for domestic hot water and also the heat emission from the systems). These losses must be taken into consideration when evaluating the system designs. The efficiency of the overall solar-supported heat supply system can be described by using the annual degree of system utilisation. The annual degree of system utilisation is generally defined as output divided by input. The output is defined as the amount of energy supplied at the point of use (taps for domestic hot water as well as heat emission systems). The input is defined as all the heat quantities (from solar energy systems and conventional heat generators) that are supplied to the heat storage unit. The value therefore has the following definition: Equation 10: HW BW Annual degree of system unitlisation, S Nutz = Q konv We +QSolar QHW QBW 49 Q +Q Annual heating demand of the residential units in kWh Annual domestic water demand of the residential units in kWh Qkonv We Annual heat input of the conventional heat generator in kWh Qsolar 7.1.3 Annual heat input of the solar energy system in kWh Low-flow systems for solar energy facilities in multi-storey buildings — speed control and loading strategies 7.1.3.1 Low-flow vs. high-flow systems Large thermal solar energy systems should always be operated in accordance with the low-flow principle. This covers specific collector mass flow rates of approx. 5 – 20 kg/m²h. Compared to high flow systems (21 – 70 kg/m²h), which should only be used for small systems (solar energy systems in single-family homes), this results in a far higher temperature increase per collector cycle. Whereas the storage temperature is slightly increased during each collector cycle of a high-flow system (assuming that the intensity of solar radiation remains unchanged), low-flow systems can achieve their useful temperature (65 °C, for example) in a single collector cycle. To ensure that this high temperature level is made directly available to the consumer (without any intermixing if possible) the heat storage unit must be charged with heat at the appropriate temperature. [%]
Figure 48: Solar thermal system in a multi-storey residential building should be operated through the low-flow principle (picture source: AEE INTEC). If the appropriate hydraulic system and correctly sized system components are used, low-flow solar energy system operation in multi-storey buildings can result in the following benefits: • Because of their relatively low volume flows, low-flow systems require substantially smaller pipe dimensions for the supply lines (feed and return) and therefore result in lower capital costs. • Compared to high-flow systems, low-flow systems require and also enable long thermal lengths in the collector interconnection (long series connections). For this reason, serial fields measuring up to about 80 m² (in special cases up to 100 m²) of collector area can be flowed through, depending on the absorber geometries and the related drop in pressure. The amount of pipework required is therefore substantially reduced, as only a single feed point to each of the main lines (feed and return) is necessary for the entire field. In comparison, the limit for series flow collector area in high-flow systems is between 20 and 25 m², depending on the absorber geometries and the related drop in pressure. This advantage of low-flow systems substantially reduces not only the amount of hardware (pipes, insulation) needed, but also the amount of assembly work and therefore also the capital costs. • Compared to high-flow systems, the reduction in the amount of pipework required and the substantially smaller diameter of the remaining pipes significantly reduces the heat losses and therefore substantially increases the annual degree of system utilisation. • Because of the reduced volumetric flow rate, a substantially lower hydraulic pumping power is required and therefore also a lower electric pump power. • Because the useful temperature is quickly reached, the need for supplementary heating is reduced in correctly dimensioned and operated low-flow systems. Table 3 depicts the range of specific mass flow rates of the various operating modes of the solar installations and the differences in the total mass flow rate in the feed and return piping of an assumed collector area of 200 m². This example shows that large manifold cross-sections and electric pump power ratings are required when the high-flow operating mode is used in large-scale solar energy systems. The costs of installing and operating the system would therefore soon exceed acceptable limits. 50
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 and 12: Figure 4: Efficient solar-supported
Page 13 and 14: 3.2 Enhancement of the solar covera
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: 7.1.2.2 The specific solar energy y
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
Page 61 and 62: Figure 58: Solar thermal systems in
Page 63 and 64: It should be borne in mind that if
Page 65 and 66: • Mean temperature of the primary
Page 67 and 68: 7.2 The preceding information appli
Page 69 and 70: Figure 65 shows the block diagram o
Page 71 and 72: highest quality but also feature co
Page 73 and 74: term operation and maintenance. Fig
Page 75 and 76: Heat meter and water meter Figure 7
Page 77 and 78: temperature at which the heat stora
Page 79 and 80: system can be attained once again d
Page 81 and 82: that of a four-pipe network. In pra
Page 83 and 84: single tank system is to be recomme
Page 85 and 86: Figure 87 shows a two-tank system f
Page 87 and 88: energy aspects which are taken into
Page 89 and 90: Dimensioning for almost 100% covera
Page 91 and 92: Reading value for utilisation: appr
Page 93 and 94: Heating energy requirements: approx
Page 95 and 96: A correction nomogram was prepared
Page 97 and 98: with 20 flats the bath is filled on
Page 99 and 100: 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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