A drainback system (DBS) installed and tested in 2014 in Montreal was validated and modeled. It consists of 4.3 m2 of flat thermal collectors and a 300-liter storage tank installed inside a room. The validation and simulation were developed using Trnsys software and the Python programming language. The isotropic model for the calculation of incident solar radiation was adopted, since in most cases the results of the comparison developed with Python and those measured in the laboratory reach 90 %. After validation, the system is simulated for a solar water heater (SWH) and for a combined system (heating and hot water). In the case of (SWH), the temperature of the water in the tank has increased from 16 °C to 26 °C. A difference of 10 °C while the ambient temperature oscillates between -17 ° C and -12 ° C for a typical day in the coldest month of the year (January). At the top of the tank, the temperature exceeds 50 °C and the losses caused by the piping exposed to the outside are insignificant in the order of 1.2 %. These results guarantee protection against freezing. The solar part for this day is 42 % and the efficiency of the system is 55 %. For the majority of days in the winter season, the solar rate exceeds 70 %. For others, the need for hot water is quite satisfactory even if the output is low. In some cases an additional external energy is necessary. During summer, despite the intensity of the sun, the temperature of the collectors does not exceed 100 °C, which fixes the problem of overheating. In the case of heating, a large installation is required to meet the thermal needs of 31700 kWh. Indeed, after energy analysis, for 44 m2 of collection area, the share of the sun is 47 %, which is not negligible. But, the yield is only 27, 9 %. In this case, the rest of the needs can be met by other forms of energy sources. It should also be noted that 1m2 of solar collectors makes it possible to avoid 297 kg of greenhouse gases (GHG) each year, a significant amount especially for large installations.
In Quebec, because of the low cost of electricity, the most famous solar thermal systems such as vacuum systems using toxic antifreeze are not as profitable and the payback period exceeds 25 years. A comparative study developed with drainbak systems shows that the latter are more advantageous both environmentally and economically than vacuum systems.
These results support the results of the 2014 experimental study based on CSA F379, ISO 9459-2 and ASHREA 95 which showed that the use of drainback systems is feasible. The installation is less expensive and more environmentally friendly than the evacuated tube installation using a non-degradable heat transfer fluid.
| Date | 31 Mar 2021 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Louis Lamarche (Supervisor) |
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Sam, F. (Author),
Lamarche (Supervisor),
31 Mar 2021Student thesis: Master's thesis › Master in Engineering: Environmental Engineering