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A Novel BIPV-PCM Heat and Power Cogeneration System for Buildings

Final Report Summary - BIPV-PCM-COGEN (A Novel BIPV-PCM Heat and Power Cogeneration System for Buildings)

This Marie Curie research project is to develop a novel BIPV-PCM-slurry energy (heat and power) system involving several technical initiatives: (1) unique BIPV structure allowing the PCM slurry to flow across, and (2) dedicated PCM-slurry-to-refrigerant (water, air) heat exchangers appropriate for building ventilation and heating. These initiatives will have the potential to overcome the difficulties associated with existing BIPV and BIPV/thermal (water-based) systems, i.e. low efficiency, high cost and ineffective heat removal. The specific objectives of the research are:
(1) To design a conceptual PCM-slurry adapted BIPV module and associated energy (heat and power) system.
(2) To develop a computer model to optimize the configuration of the BIPV-PCM-slurry energy system and predict its operational performance.
(3) To construct and test a prototype BIPV-PCM-slurry energy system and validate the computer model using the experimental data.
(4) To carrying out economic and environmental analyses of the BIPV-PCM-slurry energy system.

Over the two-year project duration, all the above tasks have been successfully completed, briefed below:

Task 1: Conceptual design of the PCM-slurry adapting BIPV façade module and associated heat and power system (related to objective 1):
The conceptual BIPV-PCM slurry heat and power system was designed (see Fig 1 of the attached report). The critical components, i.e. the BIPV module, PCM slurry and slurry-to-refrigerant heat exchanger, were devised to enable effective heat transfer and lowest possible flow resistance when the slurry travels across the absorbing pipes. Other system components were also addressed. These include (1) connectors among the façade modules, (2) module fixing-up mechanism, (3) slurry circulating lines; (4) coupling measure with existing grid and water heating system; and (5) heat storage. Finally, the installation and connection of the system components were preliminarily planned, see Fig.1 of the attached report.
To brief, the BIPV module is proposed to be a multi-layer structure incorporating (1) glazing cover; (2) PV layer; (3) Serpentine tube with fins allowing PCM slurry to pass through; (4) insulation layer; and (5) frame set. Each module is sized of 1600mm in length x 800mm in width and has predicted heat output of 0.66 kW, electrical output of 135W, slurry flow rate of 40 kg/h and flow resistance of 125 pa per module.

The slurry is preliminarily selected as the mixture of micro-encapsulated PCM particles and water, which has variable concentration reflecting the PCM particles weighting ratio in the slurry and the optimised concentration will be determined through the follow-on simulation and experimental testing.

Heat exchanger is preliminarily selected as the compact plate type, which is initially sized of 206 mm in length, 76 mm in width and 55 mm in thickness, containing 20 pieces of flat plates with estimated heat transfer capacity of 1kW at the pre-defined operational condition.

Task 2. Development of a computer model to optimize system configuration and predict its operational performance (related to objective 2)
Task 2 addressed the computer model development and operation that are aimed to analyse the power generation, fluid flow and heat transfer problems occurring in the BIPV-PCM-Slurry system, detailed below:

BIPV-PCM-slurry-module performance: The impacts of the slurry flow state, concentration ratio, Reynold number and slurry serpentine size onto the energy performance of the PV/T module were particularly investigated. At a certain flow rate, increasing the PCM concentration ratio may not always lead to an increased heat transfer and enhanced PV/T energy performance. Although the PCM slurry can improve the PV/T module's energy performance compared to the pure water at both laminar and turbulent flow, the turbulent flow was a more desired flow state than laminar flow because it can achieve larger heat transportation than laminar flow. Under the turbulent flow condition, increasing the slurry concentration ratio led to the reduced PV cells’ temperature and increased thermal, electrical and overall efficiency of the PV/T module. However, the pressure drop of the slurry across the serpentine piping significantly grew with the increase in the slurry concentration ratio and as a result, the net efficiency of the PV/T module reached the peak level at the concentration ratio of 5% at a specified Reynolds number of 3,350 and beyond this figure, the net efficiency of the PV/T module fell with the increase in the slurry ratio. Remaining all other parameters fixed, increasing the diameter of the serpentine piping led to the increased slurry mass flow rate, decreased PV cells’ temperature and consequently, increased thermal, electrical, overall and net efficiencies of the PV/T module.

Heat exchanger performance: The compact plate heat exchanger is considered as an appropriate unit conveying heat transfer between the slurry and refrigerant. Heat transfer and fluid flow within an exchanger were simulated using the developed analytic model under the pre-defined operational conditions, i.e. slurry inlet temperature of 31℃, slurry mass flow rate of 0.02kg/s refrigerant inlet temperature of 15℃, and refrigerant mass flow rate of 0.012kg/s. Analysis of the simulation results indicated that (a) for the specific operational conditions, a 203mm×75 mm ×55 mm (height × width × thickness) of heat exchanger is appropriate, which contains 20 adjacent channels with the total heat transfer area of 0.3m2; (b) heat transfer rate varies from 200W to 3000W, depending upon the flow state; and (c) flow resistances on slurry and refrigerant sides are 0 – 206 Pa and 0 – 180 Pa respectively, dependent upon the flow rate, flow state and PCM mass fraction of the slurry.

Integrated system: An analytical model for the integrated system was established and used to simulate the energy performance of the novel PCM-slurry compatible BIPV system. Taking the efficiency, system COP as the major measures, comparison among these systems was undertaken under different operational conditions. Analyses of these results indicated that (a) the overall Coefficient of Performance (COP) of the system was 8.22 under the weather data of London’s typical summer day, which was nearly fourfold of the conventional air-source heat pump water heating system (ASHP), and around twice of the integral-type solar assisted heat pump system (ISAHP); (b) the size of the system is flexible to adapt the scale and function of buildings. During this simulation, only a small system comprising one BIPV module was considered; while the large scale system is expected to achieve even better performance, by making the appropriate connection (e.g. in parallel or in series) between the modules.

Task 3 Construction and Laboratory Testing of the Prototype BIPV-PCM-slurry Energy System (related to objective 3)
The experimental prototype was constructed and tested under the laboratory condition with the aim of examining the operational performance of the prototype BIPV-PCM-slurry system. The pre-defined testing conditions are: solar radiation in the range 525 to 825 W/m2, ambient temperature of 29.5oC heat-pump evaporation and condensation temperatures of 15 and 70oC, refrigerant flow rate of 0.012kg/s water inlet temperature of 24.75oC and water flow rate of 0.0042 kg/s. Under the above condition, the system could provide 585-895W of heat in form of hot water of 60oC, 97-150 W of electricity. The average overall COP of the system is 8.14; while the solar efficiency of the BIPV-PVM-slurry module is 83.8%. The impacts of solar radiation, flow state (represented by Reynolds number, Re), MPCM particles mass fraction on operational performance of the module and associated energy system were experimentally investigated under the selected operational conditions. The testing results indicated, the module’s electrical and thermal efficiency decrease and system’s coefficient of performance (COPBIPV/T) increase when increasing solar radiation from 525 W/m2 to 825W/m2; The module’s electrical and thermal efficiency and system’s coefficient of performance (COPBIPV/T) increase when increasing Reynolds number (Re) from 1742 to 3389. The module’s electrical and thermal efficiency and system’s coefficient of performance (COPBIPV/T) increase when increasing the MPCM particles mass fraction from 0wt.% to 10wt.%. Comparisons between the modelling and the experimental results suggested that the model could achieve the acceptable accuracy in predicting the system’s operational performance, with the error scale in the range 0.37% to 8.8%.

Task 4 Economic and environmental analyses of the BIPV-PCM-slurry energy system (related to objective 4)
Feasibility: The new BIPV-PCM-slurry system is more suitable for southern European region than northern. The energy output of the system in the northern part is much less than that in southern part. Taking the Madrid and Stockholm as the examples that can represent the typical southern and northern European climatic conditions respectively, the annual electricity and heat yields of the system in Madrid are 367.4 kWh and 1986.3 kWh respectively; while the system yields in Stockholm are only 202.7 kWh and 1034.8 kWh. This indicates that the system is more energy productive in southern Europe than that in northern Europe, mainly owing to the higher solar radiation and ambient temperature of southern part relative to the northern part.

Economic and environmental benefits: For a Madrid building with the potential to install the BIPV, BIPV/water and BIPV-PCM-slurry systems, the relevant payback periods are 41.3 7.6 and 4.7 years respectively. For a Stockholm building with the potential to install the BIPV, BIPV/water and BIPV-PCM-slurry systems, the relevant payback periods are 41.3 7.6 and 4.7 years respectively. Both cases in combination indicated that the BIPV-PCM-slurry system demonstrated that greater economic benefits than the other two systems.

The life cycle costs (LCCs) per kWhe output in the three systems varied with the climatic conditions. In Madrid which has a typical southern European climatic condition, the LCCs per kWhe output for the BIPV, BIPV/water and BIPV-PCM-Slurry systems are 0.39 €, 0.15 €, and 0.34 € respectively. In Stockholm which has a typical northern European climatic condition, the LCCs per kWhe output for the three systems are 0.85 €, 0.23 €, and 0.05 € respectively. Compared to the other two systems, the BIPV-PCM-slurry system can obtain the greater benefits in terms of return-for-investment.

The CO2 Emission Reductions potentials of the three systems are also climatic dependent. For the southern European climatic condition represented by Madrid, the carbon emission reduction values of the three systems relative to the conventional heat and power systems are 1.6 tons, 14.2 tons, and 26.3 tons per annum respectively. For the northern climatic condition represented by Stockholm, the carbon emission reduction values of the three systems relative to the conventional heat and power systems are 0.8 tons, 7.5 tons, and 13.2 tons per annum respectively, which are much smaller than that in Madrid. Of the three comparable systems, the BIPV-PCM-slurry system presents the greatest potential in cutting the carbon emission to the environment.