Predicted and in situ performance of a solar air collector incorporating a translucent granular aerogel cover

This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2012 ElsevierThere is an opportunity to improve the efficiency of flat plate solar air collectors by replacing their conventional glass covers with lightweight polycarbonate panels filled with high performance aerogel insulation. The in situ performance of a 5.4m2 solar air collector containing granular aerogel is simulated and tested. The collector is incorporated into the external insulation of a mechanically ventilated end terrace house, recently refurbished in London, UK. During the 7 day test period, peak outlet temperatures up to 45 °C are observed. Resultant supply and internal air temperatures peak at 25–30 and 21–22 °C respectively. Peak efficiencies of 22–36% are calculated based on the proposed design across a range of cover types. Measured outlet temperatures are validated to within 5% of their predicted values. Estimated outputs range from 118 to 166 kWh/m2/year for collectors with different thickness granular aerogel covers, compared to 110 kWh/m2/year for a single glazed collector, 140 k h/m2/year for a double glazed collector and 202 kWh/m2/year for a collector incorporating high performance monolithic aerogel. Payback periods of 9–16 years are calculated across all cover types. An efficiency up to 60% and a payback period as low as 4.5 years is possible with an optimised collector incorporating a 10 mm thick granular aerogel cover.This work is supported by the EPSRC, Brunel University, Buro Happold Ltd. and the Technology Strategy Board

Influence of the type of phase change materials microcapsules on the properties of lime-gypsum thermal mortars

In a society with a high growth rate and increased standards of comfort arises the need to minimize the currently high energy consumption by taking advantage of renewable energy sources. The mortars with incorporation of phase change materials (PCM) have the ability to regulate the temperature inside buildings, contributing to the thermal comfort and reduction of the use of heating and cooling equipment, using only the energy supplied by the sun. However, the incorporation of phase change materials in mortars modifies its characteristics. The main purpose of this study was the production and characterization of mortars with incorporation of two different phase change materials. Specific properties of two phase change materials, such as particle size, shape and enthalpy, were determined, as well as the properties of the fresh and hardened state of the mortars. The proportion of PCM was 0%, 10%, 20% and 30% of the total mass of the solid particles. In order to minimize some problems associated with shrinkage and consequent cracking of the mortars, the incorporation of polyamide fibers and superplasticizer was tested. It was possible to observe that the incorporation of phase change materials in mortars caused differences in properties such as compressive strength, flexural strength and shrinkage. Even though the incorporation of PCM microcapsules resulted in an increase in the shrinkage, it was possible observe a significant improvement in mechanical properties.The authors wish to express their thanks to the Portuguese Foundation for Science and Technology, for funding the project PTDC/ECM/102154/2008, Contribution of Thermal Active Mortars for Building Energy Efficiency

Comparison Of Three Transient Models For Slab Heating/Cooling Systems

Radiant floor heating and cooling systems can be beneficial in various applications such as heating or cooling buildings and in infrastructure applications such as de-icing of bridges and roads as well as snow melting. Such systems usually include a significant amount of thermal mass, thus providing energy flexibility in buildings. Models of embedded-tube radiant systems are therefore useful to predict their behavior (rate of heat transfer and outlet heat-transfer fluid temperature), which can be used for the development of predictive control strategies and optimal control algorithms. As a result, a comparison of different models is conducted in this paper. The TRNSYS simulation software provides three different ways of modeling radiant floor systems (Type 56, Type 653, and Type 993), which are compared in this paper with one another in order to assess their accuracy and limitations. Each approach is compared with measurements from an experimental set-up in a controlled environmental chamber. This paper aims at: (i) evaluating the appropriate model resolution for embedded-tube radiant floor systems, (ii) validating experimentally the three aforementioned TRNSYS types (which have been validated qualitatively only), and (iii) providing a mathematical explanation of Type 993 (whose description is still unavailable to TRNSYS users). A sensitivity analysis is also performed to estimate the impact of the different types’ parameters

A Study of the Effect of Zone Design Parameters on Frequency Domain Transfer Functions for Radiant and Convective Systems

This paper presents a parametric study on the effect of a number of room design parameters for radiant and convective heating sources as well as solar gains. This study is performed using frequency domain modeling approach by means of which important room transfer functions are obtained and studied. Frequency domain modeling is a useful tool for analyzing building thermal dynamics as well as different design options. The phenomena affecting energy consumption inside a building such as solar gains, exterior temperature and heating/cooling sources are usually cyclic phenomena and can be modeled by means of frequency domain techniques assuming periodic conditions in the calculations. Using frequency domain techniques, the transient heat conduction inside the walls can be accurately modeled with no discretization for the thermal mass. However, there is difficulty modeling time-varying variables in the frequency domain. This is especially important in the case of convective and radiative heat transfer coefficients which are inherently non-linear elements. The coefficients are usually linearized in order to have a linear system of equation that can be presented by means of a linear thermal network[1]. In frequency domain modeling approach usually a constant value for the convective and radiative heat transfer coefficients is assumed. However, this assumption can produce significant errors when there are large differences between surfaces temperatures for example in the case of floor heating or direct gain rooms with large windows[2]. In this case, a sensitivity analysis on the magnitude of the important room transfer functions considering different values for convective and radiative heat transfer coefficients needs to be done. A room is considered with different types of heating (convective and radiative heating sources) and different levels of thermal mass on the floor. The effect of thermal mass and floor covering on the room thermal response considering different types of heating is investigated. Magnitude of the transfer functions between room air temperature and the convective heating source is a determining element in the room air temperature fluctuations considering thermal comfort aspects. Also, in the case of radiant heating, the transfer function between room air temperature and radiant heat source can be used to determine the room air temperature swings due to the floor radiant heating source. The sensitivity of the magnitude of the transfer functions versus different values of convective and radiative heat transfer coefficients is studied and compared. This study will guide future model predictive control (MPC) research by means of frequency domain techniques to make choices such as optimal thermal mass thickness for floor heating versus convective systems. It will contribute to linking design with MPC. [1] Athienitis, A.K. and O\u27Brien, W., Eds. (2015). Modelling, design and optimization of net-zero energy buildings, Solar heating and cooling, Berlin: Ernst, Wilhelm & Sohn 2015. [2] Saberi Derakhtenjani, Ali, Candanedo, Jos A., Chen, Yuxiang, Dehkordi, Vahid R., Athienitis, Andreas K. (2015), Modeling approaches for the characterization of building thermal dynamics and model-based control: a case study. ASHRAE STBE (Science and Technology for the Built Environment) Journal (21): 824-836

Effects of Fixed and Motorized Window Louvers on the Daylighting and Thermal Performance of Open-Plan Office Buildings

This study investigates the daylighting and thermal performance of open-plan office buildings with two scenarios of daylight louvers – fixed and motorized ones. Both types are for facade window applications. They redirect transmitted daylight to eliminate glare on occupants and increase daylight levels deeper in the interior space, but have significantly different daylight transmitting characteristics. In addition to daylighting, these louvers also affect solar heat gain. The tilt angle of slats in motorized louvers can be adjusted to control solar heat gain and daylight. In this study, an existing energy-efficient office building with fixed louvers is used. A combined thermal and daylighting model for a typical section of the building is developed using a simplified approach, and validated with measured data. The option of motorized louvers is then added to this model. The daylighting and thermal performance for different designs and seasons are assessed using the model. Results show that motorized louvers can effectively enhance useful solar heat gain and/or daylighting. The effect of building depth is also investigated

Impact of an Energy Efficiency Regulation in Northern Canada

Extreme cold climates and Canada’s sparsely populated Northern regions have limited human and infrastructural capacity making it difficult to build energy-efficient homes. Despite such differences, homes are built based on codes and standards developed for Canada’s South. In 2008, a by-law was passed in Yellowknife, Canada requiring a minimum EnerGuide Housing (EGH) rating of 80 for all new single-family and two-family residential buildings. The EnerGuide’s Energy Rating Service (ERS) program is an energy assessment program for residential housing formerly known as the EnerGuide Rating for Houses (EGH). Homes are rated between 0 to 100; lower numbers represent homes that are less efficient and 100 represents an airtight and well-insulated house that is net-zero energy. 1002 homes from the City of Yellowknife evaluated since 1950s were studied from the ERS database, Performance metrics studied include energy intensity, EGH rating, ACH rating, window types, the thermal resistance of the building envelope, primary heating and hot water heating equipment’s efficiencies, total electricity used, and total energy used. The analysis identified the current state of housing in Yellowknife, past and present housing trends, and determined the effect of the city of Yellowknife’s new building by-law had on housing performance. The preliminary finding shows a pathway to significantly improve the energy efficiency of the housing stock in Yellowknife. This regulation shows other municipalities in Canada that legislations pushing energy efficient buildings can be very effective

Mortars with incorporation of phase change materials (PCM): physical and mechanical properties and durability

O despertar da consciência ambiental pela sociedade, tem levantado problemas até então ignorados tais como os consumos energéticos. Numa sociedade com um elevado ritmo de crescimento e padrões de conforto cada vez maiores, surge a necessidade de minimizar os elevados consumos energéticos, tirando partido de fontes de energia renováveis. As argamassas com incorporação de materiais de mudança de fase (PCM) possuem a capacidade de regular a temperatura no interior dos edifícios, contribuindo desta forma para o aumento do nível de conforto térmico e diminuição do recurso a equipamentos de climatização, apenas com recurso à energia solar. Contudo, a incorporação de materiais de mudança de fase em argamassas modifica algumas das suas principais características. Portanto, o principal objetivo deste estudo consistiu na caracterização física e mecânica de argamassas aditivadas com PCM, assim como na avaliação da sua durabilidade. Para tal foram desenvolvidas 12 composições distintas, à base de diferentes ligantes e dopadas com 40% de PCM. Tendo sido possível observar que a incorporação de PCM provoca diferenças significativas em propriedades tais como a trabalhabilidade, resistência à compressão, resistência à flexão, aderência, absorção de água por capilaridade, absorção de água por imersão e resistência a ações de gelo-degelo. Contudo, foi possível concluir que a incorporação de PCM nas argamassas pode ser realizada com sucesso. Sendo que, as alterações verificadas nas argamassas podem ser contornadas através da incorporação de uma maior dosagem de ligante, superplastificante e até mesmo a inclusão de fibras. Apesar dos resultados desta investigação serem promissores é importante referir que outras investigações devem ser realizadas com o intuito de observar a influência do PCM em argamassas constituídas por outros materiais.The awakening of environmental awareness by society has raised issues previously ignored such as energy consumption. In a society with a high growth rate and increased standards of comfort arises the need to minimize the currently high energy consumption by taking advantage of renewable energy sources. The mortars with incorporation of phase change materials (PCM) have the ability to regulate the temperature inside buildings, contributing to the thermal comfort and reduction of the use of heating and cooling equipment, using only the energy supplied by the sun. However, the incorporation of phase change materials in mortars modifies its characteristics. The main purpose of this study was the physical and mechanical characterization, as well the evaluation of the durability. Twelve compositions were developed, based in different binders and doped with 40% of PCM. It was possible to observe that the incorporation of PCM in mortars caused significant differences in properties, such as workability, compression strength, flexural strength, adhesion, water absorption by capillarity, water absorption by immersion and degradation after freeze-thaw cycles. However, it was concluded that the incorporation of PCM in mortars can be performed successfully. Being that the changes in mortars can be solved by incorporating a higher content of binder, superplasticizer and the inclusion of fibers. Although the results of this investigation are promising it is important to note that further investigations should be performed aiming to observe the influence of PCM in mortars composed by other materials.Fundação para a Ciência e Tecnologia pelo financiamento deste trabalho de investigação desenvolvido no âmbito do projeto “ Contribuição de Argamassas Térmicas Ativas para a Eficiência Energética dos Edifícios” (PTDC/ECM/102154/2008) e à atribuição da bolsa individual de doutoramento com referência SFRH/BD/95611/2013