Low temperature heating and high temperature cooling systems using Phase Change Materials for new buildings and energy renovation of existing buildings

Eleftherios Bourdakis*

*Corresponding author for this work

Research output: Book/ReportPh.D. thesisResearch

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Abstract

Residential and commercial buildings are accountable for approximately 40% of the energy use in the European Union (EU), and two-thirds of this energy is used for space heating. Nevertheless, the demand for cooling is expected to rise, due to global warming, increased comfort requirements (e.g. all cars have air-conditioning nowadays), increased internal loads, better insulated and airtight buildings keeping the internal loads inside, resulting in temperature increase. The EU has recently set updated targets for energy use reduction by the year 2030, while it recognises the importance of the construction sector in achieving these targets and especially the importance of addressing the issues related to the existing building stock, as this was underlined in the amended version of the Directive on Energy Performance of Buildings.
The aim of the present dissertation is to examine the potential of incorporating active ceiling panels containing Phase Change Material (PCM) in office buildings, using both numerical and experimental means. The main objectives of the projects were to examine experimentally the possibility of combining PVT panels to produce cold water through the process of nocturnal radiative cooling with PCM ceiling panels for space cooling and to create and validate a model of the aforementioned system in TRNSYS to conduct parametric studies and optimise it without being affected by the contingency of the outdoor weather conditions.
The most important findings of the research conducted for this dissertation are summarised below.
People who had higher metabolic rate than sedentary activity due to walking to work, were accessible to lower temperature than what suggested by the European Standard EN 15251 at the beginning of the occupancy period. That would enable higher utilisation of nighttime ventilation for cooling office buildings passively.
Fanger’s thermal comfort model is applicable also in cases with non-steady conditions, although it was developed using data from experiments conducted under steady-state conditions.
Active ceiling panels containing PCM are an efficient method for providing an acceptable thermal environment. Furthermore, nocturnal radiative cooling process can reduce the energy use of the refrigerant equipment substantially and combined with the electricity produced by the PVT during daytime, it can result in a surplus of electricity, if the weather conditions are in favour.
Nocturnal radiative cooling was beneficial in all locations simulated, although the performance varied significantly among the different locations. The higher the latitude, the higher the effectiveness of the nocturnal radiative cooling, due to the lower negative impact from convection. On the other hand, the lower the latitude, the better the thermal environment provided by the active ceiling panels containing PCM, due to the more vertical position of the sun.
A correct design of passive PCM panels can result in substantial energy savings, but a wrong design can result in increasing the energy use of the building to maintain the desired thermal environment. A thorough investigation about the appropriate materials and panel parameters (PCM surface area, panel thicknessn etc.) should precede the panel construction.
Although PCM tiles add additional thermal mass and contribute in reducing the energy use of the HVAC equipment, they cannot stand alone as a cooling system and should only be considered as a secondary system supplementing the main system, either all-air
or radiant system.
In case of active PCM panels, to ensure the full discharge of the PCM, the pipes should be embedded in the PCM layer to take advantage of the better contact between PCM and the cooling medium.
For passive PCM panels the ideal thickness was 20 mm, while for active PCM panels 30 mm. That would result in significantly higher thermal mass in the case of incorporating active PCM panels compared to passive panels.
Active ceiling panels containing PCM and PVT panels are two technologies that can greatly contribute in achieving the targets for reduction of the energy use in the construction sector and realise a decarbonised building stock, and at the same provide the desired thermal environment. PCM tiles require further investigation before they can be considered a potential option for providing an acceptable thermal environment.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages217
ISBN (Electronic)87-7877-514-0
Publication statusPublished - 2018

Bibliographical note

PhD Thesis R-416

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