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RESEARCH PAPERS

Theoretical Comparison of Solar Water/Space-Heating Combi Systems and Stratification Design Options

[+] Author and Article Information
E. Andersen

Department of Civil Engineering, Technical University of Denmark, Building 118, DK-2800 Kgs. Lyngby, Denmarkean@byg.dtu.dk

S. Furbo

Department of Civil Engineering, Technical University of Denmark, Building 118, DK-2800 Kgs. Lyngby, Denmark

J. Sol. Energy Eng 129(4), 438-448 (May 22, 2007) (11 pages) doi:10.1115/1.2770752 History: Received July 19, 2006; Revised May 22, 2007

A theoretical analysis of differently designed solar combi systems is performed with weather data from the Danish Design Reference Year (55 deg N). Three solar combi system designs found on the market are investigated. The investigation focuses on the influence of stratification on the thermal performance under different operation conditions with different domestic hot water and space heating demands. The solar combi systems are initially equipped with heat exchanger spirals and direct inlets to the tank. A step-by-step investigation is performed demonstrating the influence on the thermal performance of using inlet stratification pipes at the different inlets. Also, how the design of the space heating system, the control system of the solar collectors, and the system size influence the thermal performance of solar combi systems are investigated. The work is carried out within the Solar Heating and Cooling Programme of the International Energy Agency (IEA SHC), Task 32.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematics of the three system models: model 1 (top), model 2 (middle), and model 3 (bottom), and the successively numbered variations of the system models

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Figure 2

Power for the space heating systems and flow and return temperatures in the space heating systems, used in the calculations

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Figure 3

Left: annual net utilized solar energy as a function of the relative return inlet height from the space heating loop for model 1.1 and model 1.3; right: performance ratio relative to the optimal thermal performance of the system in question

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Figure 4

Left: annual net utilized solar energy as a function of the space heating demand and the domestic hot water consumption for model 1 and the step-by-step improvement of the models; right: performance ratio relative to the thermal performance of the least-advanced models, model 1.1

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Figure 5

Comparison of models 1–3—Left: annual net utilized solar energy as a function of the space heating demand and the domestic hot water consumption and the step-by-step improvement of the models; Right: performance ratio relative to the thermal performance of the similar system model 1

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Figure 6

The flow and return temperatures for the space heating systems as a function of the heating power demand

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Figure 7

Left: annual net utilized solar energy as a function of the relative return inlet height from the space heating loop; right: performance ratio, relative to the optimal thermal performance, of the system in question

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Figure 8

Performance ratio as a function of the relative return inlet height from the space heating loop. The performance is relative to the optimal thermal performance of the system with the standard space heating system.

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Figure 9

Different positions of the temperature sensor in the tank

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Figure 10

Left: annual net utilized solar energy as a function of the position of the temperature sensor in the tank and the minimum temperature differential of the pump in the solar collector loop; right: performance ratio relative to the thermal performance of the system with the highest thermal performance

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Figure 11

Left: annual net utilized solar energy as a function of the relative return inlet height from the space heating loop for different sizes of model 1.1 and model 1.2; right: performance ratio relative to the optimal thermal performance of the system in question (Top: 10m2 collector, bottom: 30m2 collector)

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Figure 12

Left: annual net utilized solar energy as a function of the space heating demand and the domestic hot water consumption for different sizes of model 1, and the step-by-step improvement of the model; right: performance ratio relative to the thermal performance of the least advanced model 1.1 (Top: 10m2 collector, bottom: 30m2 collector)

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Figure 13

Right: monthly net utilized solar energy for the three different size models 1.1, 1.2, 1.3, and 1.4 with solar collector areas of 10m2, 20m2, and 30m2; left: extra net utilized solar energy by using stratifiers

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Figure 14

Left: annual net utilized solar energy as a function of the solar collector area and heat storage volume; right: extra annual net utilized solar energy from stratifiers as a function of the solar collector area and heat storage volume. The annual thermal performances are shown for system model 1 and a step-by-step improvement of the system model

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Figure 15

Left: performance ratio as a function of the solar collector area; right: performance ratio as a function of the solar fraction. The reference system is the corresponding system model 1.1 with heat exchanger spiral in the solar collector loop and optimum fixed return inlet position from the space heating loop.

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