Study on the performance of central solar heating plants with seasonal storage using underground soil in North China and Norway

摘要

This thesis involves the work on a combined system consisting of a solarcollector，a geothermal heat pump and borehole ground storage.To fully utilize solar energy this study is based on a heating system deigned to store the solar thermal energy in an underground storage，using U-tube heat exchangers.Renewable energy sources are habitually out of phase with the heating demand,which makes them challenging to fully exploit.eat from the underground thermal energy storage will be discharged when the solar energy is not sufficient enough,as for the winter months.A simulationmodel,developed in TRNSYS,is used to simulate the performance of the proposed combined system. The heat load is a single residential building,and the simulation is performed for two different locations.Their difference in design and performance isthen analyzed and discussed.The locationsused for the system simulations are Trondheim in Norway and Siping in China.
　　The complexity of a combines system is high due to several options when deciding on the system design.Solar collectors will lift the groundsource temperature and in this way reducing the operation time of the heat pump.This will reduce the electricity use in combines systems.The purposes of this study have been to design a combined system for a single house at two different locations，Trondheim (63°N,10°E)and Siping (43°N,124°E).Studies on the performanceof these two systems have then been performed.The focus has been on the thermal energy ground storage，consisting of several boreholes and its temperature behavior.The simulation software TRNSYS was used to analyze the interaction between the differentcomponents，the heat losses and gains,the electricity savings and the load requirement.The concept house hasbeen designed in TRNBuild and Meteonorm provides the metrological data used for the different locations.A base case was used as stepping stone for the system optimization;the basecase is bases on previous related work.
　　The system is divided into four different modes simulated separatelyin TRNSYS. The four simulation modeswere solar thermal ground storage,solar direct heating, With the intention to achieve a sufficiently high enough storage end temperature for direct heating of the building when needed，the system design parameters where chosen.The results of the simulation confirmed that the size and design of the ground storage is ofgreat importance. The resulting design for the system located in Trondheim consists of 11boreholes spaced 1.5m apart.However for Siping the optimal design consists of 4 boreholes with a pacing of 2.5m.Both systems has ground storage volume of 623.24m3 at 30m depth，a solar collector of 200m2 and a water tank with a volume of 10 m2.With these parameters the storage end temperature was above 40oC for both and compliable for heating.The heating season was found to be from September to March for Trondheim and from October to May for Siping.
　　Simulations of the solar direct heating mode show that this mode can cover 19.2％of the heating load for the system located in Trondheim and as much as 47.5%for the system in Siping. The direct heat exchange with the ground covers 27.9% of the heating load in Trondheim，only 11.97%of the heating load is covered by this mode for Siping.The geothermal heat pump covers the largest part of the heating load in Trondheim with 52.9%,while it covers 40.53%of the heating demand in Siping.The initial depthof 30m resulted in freezing boreholes for both location and consequentlythe depth was changed to 150m for Trondheim and 200m for Siping.The COPwas found to be 2.78 and 2.54 for Trondheim and Siping respectfully.

目录

封面

上海交通大学硕士学位论文答辩决议书

致谢

英文摘要

Sammendrag

目录

Nomenclature

1. Introduction

2. Theory

2.1. Background

2.2. Energy consumptions in buildings

2.3. Seasonal Thermal Energy Storage

2.4. Underground thermal energy storages

2.5. Borehole Thermal Energy Storage

2.6. Geological formation

2.7. Balance of thermal loads

3. Overview of the proposes heating system

3.1. Working principles of the operation modes

3.2. Geothermal heat pump

3.3. Solar collector

3.4. Stratified water tank

4. Description of the TRNSYS Software

4.1. TRNSYS

4.2. Introduction to the concept house and location

4.3. Building layout and properties

4.4. Weather Conditions

5. Base Case Parameter

6. Simulation and results

6.1. Temperature and radiation

6.2. Simulation of the concept house

6.3. Simulation of Operation mode 1: The solar thermal ground storage mode

6.4. Simulation results of designing the solar ground storage model

6.5. Storage mode–simulation of the operation condition

6.6. Simulation and results of operation mode 1

6.7. Simulation of the different heating modes

6.8. Simulation of operation mode 2

6.9. Simulation of operation mode 3

6.10. Simulation of operation mode 4

6.11. Results

7. Conclusion

8. Further improvement

参考文献

Appendix A. Concept House

Appendix B. Component Description

Appendix C. Tables and Results for storage mode Trondheim, Norway

Appendix D. Tables and Results for storage mode Siping, China

Appendix E. Tables and Results the storage mode

Appendix F. Tables and Results the heating modes

G.1. Mode 2: Solar direct heating mode

Appendix G. Calculations

G.2. Calculations of Building heat load

G.3. Ratios and efficiencies

G.4. Calculations of the efficiencies in the solar collector, Trondheim

G.5. Calculations of the COP, Trondheim

G.6. Calculations of heat per tube length

G.7. Calculations of the new storage parameters for heating mode 4.