Reducing greenhouse energy consumption using novelty rooftop: a simulation

Recently, more than 80% of total energy of commercial greenhouse in the northern hemisphere is used just for heating. Mostly, the energy loss happens up to 40% caused by the poor U-value of the façades. Therefore, by lowering the U-value would decrease the energy consumption significantly. This simulation is conducted using EnergyPlus software to calculate the heat loss, heating demand and daylighting of a greenhouse with different envelope materials especially novelty rooftop. The orientation of buildings and its effect to electricity generated by semi-transparent PV double glazing are also discussed. In addition, the effect of the novel rooftop to daylighting inside the greenhouse is also investigated. The simulation shows that use materials with low U-value and novel rooftop could decrease the source energy consumption by 65% which is remarkable compared to commercial greenhouse. Besides, the best orientation for the PV module of the greenhouse in Nottingham, UK is facing west-south-east. While the indoor daylighting factor declined up to 65%. Therefore, using PVs with high efficiency would diminish the electricity losses and could be used for lighting energy alternative and others

Recent passive technologies of greenhouse systems: a review

There are 130 countries produces greenhouse vegetables commercially with more than 1.1 million acres in 2016. Most of the greenhouses deal with high operating costs due to the great energy needs. The high heat loss because of the greenhouse envelope material is responsible for the high energy demand in greenhouses. Nevertheless, each area having a specific need which affects to the energy level and conventional greenhouse technologies tend to have poor U-values. It causes energy for heating is very dominant up to 85% of the total greenhouse energy demand in cold climates countries. While, for the hot climate countries the energy for cooling is more prevalent. Therefore, this paper presents the latest technological developments used in greenhouses in various countries used to control the microclimate in the greenhouse focusing on passive techniques. It is found that PCM recently used to provide heating and cooling for Mediterranean climate. Moreover, closed greenhouse concept based system for Northern climatic improves the reduction energy demands by 80% with a potential payback of 6 years. Additionally, for most countries double glazing envelopes to be the most frequently powerful to increase the greenhouse performance

Thermal conductivity, structure and mechanical properties of konjac glucomannan/starch based aerogel strengthened by wheat straw

This study presents the preparation and property characterization of a konjac glucomannan (KGM)/starch based aerogel as a thermal insulation material. Wheat straw powders (a kind of agricultural waste) and starch are used to enhance aerogel physical properties such as mechanical strength and pore size distribution. Aerogel samples were made using environmentally friendly sol–gel and freeze drying methods. Results show that starch addition could strengthen the mechanical strength of aerogel significantly, and wheat straw addition could decrease aerogel pore size due to its special micron-cavity structure, with appropriate gelatin addition as the stabilizer. The aerogel formula was optimized to achieve lowest thermal conductivity and good thermal stability. Within the experimental range, aerogel with the optimized formula had a thermal conductivity 0.04641 Wm−1 K−1, a compression modulus 67.5 kPa and an elasticity 0.27. The results demonstrate the high potential of KGM/starch based aerogels enhanced with wheat straw for application in thermal insulation

Review of Heat and Mass Transfer Enhancement Techniques and Current Advancement for Adsorption Heating/Cooling Systems

Adsorption heating/cooling became an alternative to vapour compression system due to low ozone depletion potential (ODP) and global warming potential (GWP). However, more investigation is required due their low efficiency when compared to conventional heating/cooling systems. This review emphasizes on the mathematical modelling simplification and heat transfer enhancement method that applied by many researchers to improve the performance of adsorption heating and cooling technologies. Various techniques investigated by many researchers on solving low thermal conductivity and the different methods for enhancing heat and mass transfer in the adsorbed bed/pipe also discussed. Common techniques used to enhance heat and mass transfer in the adsorbed bed/pipe include the fin type adsorb-ent tube/ heat exchanger, amalgamated adsorbent bed with a metal foam, consolidated adsorbent, adsorbent coating and adsorbent with multi cooling tubes. Other than that, recent advancements in adsorption cooling/heating systems also discussed in this review

The advances of polysaccharide-based aerogels: Preparation and potential application

Polysaccharide-based aerogels have high application value as one kind of unique functional materials. Not only has it high porosity and low-density, but also the non-toxicity and biodegradability. In recent decades, a variety of natural raw materials and their combinations along with various preparation technologies have been investigated to develop polysaccharide-based aerogels with different functions for diverse applications. This review aims to clarify a general approach in the development of polysaccharide-based aerogels regarding pore structure design, polysaccharide selection and drying methods. The relevant researches and reports of polysaccharide-based aerogels have been also classified according to the applications in environmental engineering, buildings, medical practice, packaging and electrochemistry. Furthermore, some statistical graphs have been produced to summarize those publications during the past ten years, with an aim to indicate the distribution and research trend. Finally, the approaches to improve the quality of the aerogels are discussed and some perspectives are put forward to provide a reference for the future development of polysaccharide-based aerogels

Effect of drying temperature on structural and thermomechanical properties of konjac glucomannan-zein blend films

Konjac glucomannan (KGM)/zein blend films were successfully prepared by solution casting at different drying temperatures (40, 50, 60, 70 and 80 °C). The effects of drying temperature on the films' structural, thermomechanical, mechanical and water barrier properties were investigated. Microstructural observations indicated that zein particles were homogeneously dispersed in KGM continuous matrix, and the blend film dried at 60 °C showed the most compact and smooth surface. Dynamic mechanical thermal analysis curves showed that with increasing drying temperature from 40 to 60 °C, glass transition temperature (Tg) of films increased; however, with further increase in temperature, the Tg decreased, indicating the compatibility of film components was the highest when dried at 60 °C. The hydrophobicity of blend film dried at 60 °C was significantly stronger than that of other blend films, supported by the highest water contact angle, and the lowest swelling ratio and solubility. Moreover, the film dried at 60 °C showed the highest tensile strength, elongation at break, and the lowest water vapor permeability. Therefore 60 °C was preferred for KGM/zein blend film preparation. This study indicated that intermolecular interactions among film components were greatly influenced by the drying temperature, and should be carefully noticed for film preparation

Fabrication and characterization of a novel konjac glucomannan-based air filtration aerogels strengthened by wheat straw and okara

The konjac glucomannan (KGM)-based aerogel as an air filtration material was fabricated through sol-gel and freeze-drying methods. Results showed that gelatin and starch addition could increase the filtration efficiency and compressive strength of aerogel significantly, due to the appearance of more microporous structure and the formation of dense structure in aerogel. The addition of wheat straw could decrease the filtration resistance and increase the breathability of KGM-based aerogel, which was attributed to the multi-cavities of wheat straw. The aerogel with wheat straw had a filtration efficiency of 93.54% for particle matters ≥ 0.3 μm, a filtration resistance 29 Pa, and an air permeability 271.42 L/s·m2. Okara addition could increase the hydrophobicity of KGM-based aerogel by increasing the water contact angle and decreasing the equilibrium water content. The water contact angle of the aerogel containing okara reached 105.4°, and the equilibrium water content was decreased by 17.03%–81.10% compared with that without okara, with relative humidity 0%–80%. The results demonstrated that the KGM-based aerogel had good performance on filtration, mechanical and hydrophobic properties, indicating high potential application as an air filtration material

Emission and economic performance assessment of a solid oxide fuel cell micro-combined heat and power system in a domestic building

Combined heat and power (CHP) is a promising technological configuration for reducing energy consumption and increasing energy security in the domestic built environment. Fuel cells, on account of their: high electrical efficiency, low emissions and useful heat output have been identified as a key technological option for improving both building energy efficiency and reducing emissions in domestic CHP applications. The work presented in this paper builds upon results currently reported in the literature of fuel cells operating in domestic building applications, with an emission and economic performance assessment of a real, commercially available SOFC mCHP system operating in a real building; under a UK context. This paper aims to assess the emission and economic performance of a commercially available solid oxide fuel cell (SOFC) mCHP system, operating at The University of Nottingham's Creative Energy Homes. The performance assessment evaluates, over a one year period, the associated carbon (emission assessment) and operational costs (economic assessment) of the SOFC mCHP case compared to a ‘base case’ of grid electricity and a highly efficient gas boiler. Results from the annual assessment show that the SOFC mCHP system can generate annual emission reductions of up to 56% and cost reductions of 177% compared to the base case scenario. However support mechanisms such as; electrical export, feed in tariff and export tariff, are required in order to achieve this, the results are significantly less without. A net present value (NPV) analysis shows that the base case is still more profitable over a 15 year period, even though the SOFC mCHP system generates annual revenue; this is on account of the SOFC's high capital cost. In summary, grid interaction and incubator support is essential for significant annual emission and cost reductions compared to a grid electricity and gas boiler scenario. Currently capital cost is the greatest barrier to the economic viability of the system

Fuel cell technology for domestic built environment applications: state of-the-art review

Fuel cells produce heat when generating electricity, thus they are of particular interest for combined heat and power (CHP) and combined cooling heat and power (CCHP) applications, also known as tri-generation systems. CHP and tri-generation systems offer high energy conversion efficiency and hence the potential to reduce fuel costs and CO2 emissions. This article serves to provide a state-of-the-art review of fuel cell technology operating in the domestic built environment in CHP and tri-generation system applications. The review aims to carry out an assessment of the following topics: (1) the operational advantages fuel cells offer in CHP and tri-generation system configurations, specifically, compared to conventional combustion-based technologies such as Stirling engines, (2) how decarbonisation, running cost and energy security in the domestic built environment may be addressed through the use of fuel cell technology, and (3) what has been done to date and what needs to be done in the future. The article commences with a review of fuel cell technology, then moves on to examine fuel cell CHP systems operating in the domestic built environment, and finally explores fuel cell tri-generation systems in domestic built environment applications. The article concludes with an assessment of the present development of, and future challenges for, domestic fuel cells operating in CHP and tri-generation systems. As fuel cells are an emergent technology the article draws on a breadth of literature, data and experience, mostly from the United Kingdom, Germany, Japan, America and Australia. Fuel cells are a technology of the future here today, providing a change in the way heat and power are supplied to end users. Fuel cells operating in CHP and tri-generation systems in domestic built environment applications could finally provide the means by which energy generation can transfer from centralised to decentralised locales in a sustainable and effective manner

Numerical determination of energy losses at duct junctions

The pressure-loss coefficient for a duct junction of square cross-section was determined using computational fluid dynamics (CFD). The predicted junction pressure-loss coefficient for combining flows was generally in good agreement with experimental data from the literature. The junction pressure-loss coefficient was associated with the flow from the side branch to the duct carrying the total flow.