Paper title: Towards an Automated Technique for Optimising the Design of Thermosyphon Solar Water Heaters Mohammad Abdunnabi Dennis Loveday Department of Civil and Building Engineering, Loughborough University
Thermosyphon systems: Pump-free devices used to provide households with hot water for domestic purpose Can be found in different configurations - the system under consideration Flat plate collector (fin and tube) Insulated storage tank (horizontal vertical)
This paper is a part of PhD research : Design Tool for Thermosyphon Solar Water Heaters Thermal performance of the system Optimisation Method TRNSYS Programme Genetic Algorithms
This paper is a part of PhD research : Design Tool for Thermosyphon Solar Water Heaters TRNSYS component Type 45 Experimentally-determined information Type 210 Type 211 Collector characteristics component Pipe-Tank heat losses component Modelling Validation Its effect
Collector characteristics component Type 210 Modelling Flat plate solar collector CoDePro programme Kirchhoff and Billups Model (Model 1) Prabhakar et al. Model (Model 2) Modified Model 1 (Model 3)
Model Validation The Models are examined against experimental results from three different collector test reports according to EN-12975-2
0.85 efficiency 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 y(exp) = -4.3665x + 0.7662 y(co) = -4.379x + 0.7826 y(m1) = -4.965x + 0.817 y(m2) = -4.793x + 0.781 y(m3) = -4.365x + 0.781 Experiment CoDePro Model 1 Model 2 Model 3 0.4 0 0.01 0.02 0.03 0.04 0.05 0.06 (Tm-Ta)/Gt
Model Validation The Models are examined against experimental results from three different collector test reports according to EN-12975-2 The results of average RMS errors shown that Model three is the best with least RMS error of 1.06% compared to Model 1 with RMS error of 2.7% Model 2 with RMS error of 1.21% CoDePro with RMS error of 2.21% Therefore, Model 3 is chosen to represent collector characteristics component Type 210
Incorporating Type 210 in TRNSYS Outputs Parameters Inputs Type 210 Type Type 45 145
Original and Modified TRNSYS Models Original Model Type109 Type45 Flow mixer Output devices Flow diverter Type14 Modified Model Type 210 Type109 Flow diverter Type145 Flow mixer Output devices Type14
Modified TRNSYS Model Validation Two thermosyphon systems were used for the validation (sys1 & sys2) - Operation conditions 0.16 150 Litres/ day 60 ºC Simple load pattern Weather data of Tripoli - Libya Normalized Usage 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 0 4 8 12 16 20 24 Time(hr)
Modified TRNSYS Model Validation System 1 0.85 0.80 Yearly average error < 2% 0.75 Solar Fraction 0.70 0.65 0.60 0.55 2.9 % MM OM 0.50 0.45 1 2 3 4 5 6 7 8 9 10 11 12 Months Monthly solar fraction of system1
Modified TRNSYS Model Validation System 2 0.90 0.85 Yearly average error < 3.9% 0.80 Solar Fraction 0.75 0.70 0.65 0.60 0.55 5.6 % MM OM 0.50 0.45 1 2 3 4 5 6 7 8 9 10 11 12 Months Monthly solar fraction of system2
Optimum thermosyphon system design Optimum collector area of system 1 Strategy Optimum distance between risers Optimum aspect ratio
Effect of number of risers on the system yearly solar fraction 0.75 Solar Fraction 0.7 0.65 0.6 0.55 0.5 0.45 0.4 2 4 6 8 10 12 14 16 18 20 Number of Risers w=(wc-0.06)/nr =0.113 m
Effect of collector aspect ratio on system yearly solar fraction 0.71 0.705 0.7 Solar Fraction 0.695 0.69 0.685 0.68 0.675 0.67 0.35 0.75 1.15 1.55 1.95 2.35 2.75 3.15 3.55 3.95 Collector Aspect Ratio (Lc/Wc)
Effect of collector area on the system yearly solar fraction Solar Fraction 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 1 2 3 4 5 6 7 8 Collector Area m2
Conclusions Adding new component to TRNSYS to simulate the performance and to optimise the design parameters of thermosyphon system gives acceptable predictions Modified TRNSYS model enhances flexibility by offering the ability to vary collector design parameters This can be considered an important step towards development of an automated technique for designers to optimise thermosyphon system design
Thanks for your Listening any Questions?