研究目的
To analyze the thermal performance and economic viability of low flow systems in solar domestic hot water systems, particularly in Mediterranean climates, using up-to-date technology and comparing with high flow systems.
研究成果
Low flow systems (20 l/hm2) offer lower initial investment costs and reduced electricity consumption compared to high flow systems (80 l/hm2), with only a moderate penalty in thermal performance. The payback period for high flow systems is long (14-18 years), making low flow systems economically favorable, especially when considering embodied energy and maintenance costs. Design practices should be revised to promote low flow systems in non-extreme climates, with careful selection to avoid overheating.
研究不足
Tests were limited to flow rates between 20 and 80 l/(hm2) due to vaporization issues at lower flows and high pressure drops at higher flows. The study focused on Mediterranean climate, so results may not apply to other climates. Uncertainty in measurements, though analyzed, could affect precision. The use of specific collector and component models may limit generalizability.
1：Experimental Design and Method Selection:
The study involved testing a serpentine solar collector at different mass flow rates following the EN 12975-2:2006 standard to characterize thermal efficiency. Uncertainty analysis based on GUM (1995) was applied. System simulations were conducted using TRNSYS 16 software to model SDHW systems and evaluate costs.
2：Sample Selection and Data Sources:
A typical serpentine collector was tested. Meteorological data from AAE (2007) and SDHW demand data from Viti (1996) and Buckles and Klein (1980) were used for simulations in Málaga, Spain.
3：List of Experimental Equipment and Materials:
Test facilities included an adjustable structure for collectors, flow regulation valves, pyranometers (Class II), PT100 temperature probes, and various sensors meeting EN 12975-2:2006 accuracy requirements. Specific equipment: serpentine collector (details in Table 3), pumps (Grundfos models), heat exchangers (Alfa Laval models), tanks (LAPESA models), and piping materials.
4：Experimental Procedures and Operational Workflow:
Tests were conducted in steady-state regime with preconditioning at high flow to vent air. Data recorded every 5s and averaged every 30s. Flow rates tested from 20 to 80 l/(hm2), with inlet temperature variations. System simulations involved designing two SDHW systems (cases A and B) with different flow rates and components.
5：0s. Flow rates tested from 20 to 80 l/(hm2), with inlet temperature variations. System simulations involved designing two SDHW systems (cases A and B) with different flow rates and components. Data Analysis Methods:
5. Data Analysis Methods: Efficiency curves were adjusted using least squares fit. Uncertainty propagation was performed according to EN 12975-2:2006 annex. Simulations used TRNSYS models (e.g., TYPE 534 for tank) to calculate solar fraction, energy gain, and costs.
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pyranometer
Class II
Measuring solar irradiance
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PT100 temperature probe
Measuring fluid temperatures
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serpentine collector
Solar thermal energy collection
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pump
Magna 3 25-60
Grundfos
Circulating fluid in solar loop
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pump
Magna 1 40-180
Grundfos
Circulating fluid in solar loop
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pump
Alpha Solar 15-75 130
Grundfos
Circulating fluid in solar loop
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pump
Alpha Solar 25-145 180
Grundfos
Circulating fluid in solar loop
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heat exchanger
T2-BFG
Alfa Laval
Heat transfer between primary and secondary loops
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heat exchanger
T5-MFG
Alfa Laval
Heat transfer between primary and secondary loops
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heat exchanger
M3-FG
Alfa Laval
Heat transfer between primary and secondary loops
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tank
MVV4000 RB
LAPESA
Storage of hot water
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tank
MW2000 RB
LAPESA
Storage of hot water
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