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Solar blind system: solar energy utilization and climate mitigation in glassed buildings
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. (Thermal Energy Storage Group)ORCID iD: 55260338500
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.ORCID iD: 0000-0001-9556-552X
2013 (English)Conference paper (Refereed)
Abstract [en]

In the past few decades, energy scientists have focused on "renewable energy”,and solar energy in particular. Severaltechnologies are commercialized for utilizing solar energy in the buildings by absorbing solar radiation and converting it to heat and electricity. These technologies can be categorized into the passive and active systems. A special case is a commercialgreenhouse, whichcan be considered a passive solar building. A greenhouse is a structure which is covered by a transparent device such as glass in order to use solar energy while controlling the temperature, humidity and other parameters according to the requirements for cultivation andprotection of the particular plants. The cooling demandin the commercial greenhouses is commonly supplied by e.g. ventilation and thermal screen. In the ventilation method a portion of the absorbed solar energy will be lost through ventilation windows and by applying the solar shielding, solar radiation will be blocked. In this study, by considering the solar blind concept as an active system, PVT panels are integrated to absorb thesurplus solar heat(instead of blocking)which is thenstored in a thermal energy storage for supplying a portion of the greenhouse heating demand at a later time. The overall objective of this study is to assess the potential of cutting external energy demand as well as maximizing solar energy utilizationin a commercial greenhouse for Northern climate condition.Thus, a feasibility assessment has been carried out, examiningvarious system configurations with theTRNSYS tool. The results show that the heating demand for a commercial closed greenhouse with solar blind is reduced by 80%, down to 62 kwh/m2as compared to a conventional configuration. Also the annual total useful heat gain and electricity generation by solar blind in this concept is around 20 kwh/m2and 80kwh/m2, respectively. The generated electricity can be used for supplying the greenhouse power demand for e.g. artificial lighting and other devices. Moreover, the cooling demand in a closed greenhouse is reduced by 60% by considering the solar blind system.

Place, publisher, year, edition, pages
2013. Vol. 57, 2023-2032 p.
, Energy Procedia, ISSN 1876-6102
National Category
Energy Engineering
URN: urn:nbn:se:kth:diva-127940DOI: 10.1016/j.egypro.2014.10.067ISI: 000348253202016ScopusID: 2-s2.0-84922309405OAI: diva2:646685
2013 ISES Solar World Congress, SWC 2013; Cancun; Mexico; 3 November 2013 - 7 November 2013

QC 20130910

Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2015-03-25Bibliographically approved
In thesis
1. Energy Management in Large scale Solar Buildings: The Closed Greenhouse Concept
Open this publication in new window or tab >>Energy Management in Large scale Solar Buildings: The Closed Greenhouse Concept
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sustainability has been at the centre of global attention for decades. One of the most challenging areas toward sustainability is the agricultural sector. Here, the commercial greenhouse is one of the most effective cultivation methods with a yield per cultivated area up to 10 times higher than for open land farming. However, this improvement comes with a higher energy demand. Therefore, the significance of energy conservation and management in the commercial greenhouse has been emphasized to enable cost efficient crop production. This Doctoral Thesis presents an assessment of energy pathways for improved greenhouse performance by reducing the direct energy inputs and by conserving energy throughout the system.

A reference theoretical model for analyzing the energy performance of a greenhouse has been developed using TRNSYS. This model is verified using real data from a conventional greenhouse in Stockholm (Ulriksdal). With this, a number of energy saving opportunities (e.g. double glazing) were assessed one by one with regards to the impact on the annual heating, cooling and electricity demand. Later, a multidimensional energy saving method, the “Closed Greenhouse”, was introduced. The closed greenhouse is an innovative concept with a combination of many energy saving opportunities. In the ideal closed greenhouse configuration, there are no ventilation windows, and the excess heat, in both sensible and latent forms, needs to be stored using a seasonal thermal energy storage. A short term (daily) storage can be used to eliminate the daily mismatch in the heating and cooling demand as well as handling the hourly fluctuations in the demand.

The key conclusion form this work is that the innovative concept “closed greenhouse” can be cost-effective, independent of fossil fuel and technically feasible regardless of climate condition. For the Nordic climate case of Sweden, more than 800 GWh can be saved annually, by converting all conventional greenhouses into this concept. Climate change mitigation will follow, as a key impact towards sustainability.

In more detail, the results show that the annual heating demand in an ideal closed greenhouse can be reduced to 60 kWhm-2 as compared to 300 kWhm-2 in the conventional greenhouse. However, by considering semi-closed or partly closed greenhouse concepts, practical implementation appears advantageous. The required external energy input for heating purpose can still be reduced by 25% to 75% depending on the fraction of closed area. The payback period time for the investment in a closed greenhouse varies between 5 and 8 years depending on the thermal energy storage design conditions. Thus, the closed greenhouse concept has the potential to be cost effective.

Following these results, energy management pathways have been examined based on the proposed thermo-economic assessment. From this, it is clear that the main differences between the suggested scenarios are the type of energy source, as well as the cooling and dehumidification strategies judged feasible, and that these are very much dependent on the climatic conditions

Finally, by proposing the “solar blind” concept as an active system, the surplus solar radiation can be absorbed by PVT panels and stored in thermal energy storage for supplying a portion of the greenhouse heating demand. In this concept, the annual external energy input for heating purpose in a commercial closed greenhouse with solar blind is reduced by 80%, down to 62 kWhm-2 (per unit of greenhouse area), as compared to a conventional configuration. Also the annual total useful heat gain and electricity generation, per unit of greenhouse area, by the solar blind in this concept is around 20 kWhm-2 and 80 kWhm-2, respectively. The generated electricity can be used for supplying the greenhouse power demand for artificial lighting and other devices. Typically, the electricity demand for a commercial greenhouse is about 170 kWhm-2. Here, the effect of “shading” on the crop yield is not considered, and would have to be carefully assessed in each case.

Abstract [sv]

Hållbarhet har legat i fokus under decennier. En av de mest utmanande områdena är jordbrukssektorn, där. kommersiella växthus är ett av de mest effektiva odlingsalternativen med en avkastning per odlad yta upp till 10 gånger högre än för jordbruk på friland. Dock kommer denna förbättring med ett högre energibehov. Därför är energieffektivisering i kommersiella växthus viktig för att möjliggöra kostnadseffektiv odling. Denna doktorsavhandling presenterar en utvärdering av olika energiscenarios för förbättring av växthusens prestanda genom att minska extern energitillförsel och spara energi genom i systemet som helhet.

För studien har en teoretisk modell för analys av energiprestanda i ett växthus utvecklats med hjälp av TRNSYS. Denna modell har verifierats med hjälp av verkliga data från ett konventionellt växthus i Stockholm (Ulriksdal). Med denna modell har ett antal energibesparingsåtgärder (som dubbelglas) bedömts med hänsyn till de totala värme-, kyl-och elbehoven. En flerdimensionell metod för energibesparing, det s.k. "slutna växthuset", introduceras. Det slutna växthuset är ett innovativt koncept som är en kombination av flera energibesparingsmöjligheter. I den ideala slutna växthuskonfigurationen finns det inga ventilationsfönster och värmeöverskott, både sensibel och latent, lagras i ett energilager för senare användning. Daglig lagring kan användas för att eliminera den dagliga obalansen i värme-och kylbehovet. Ett säsongslager introduceras för att möjliggöra användandet av sommarvärme för uppvärmning vintertid.

Den viktigaste slutsatsen från detta arbete är att ett sådant innovativt koncept, det "slutna växthuset" kan vara kostnadseffektiv, oberoende av fossila bränslen och tekniskt genomförbart oavsett klimatförhållanden. För det svenska klimatet kan mer än 800 GWh sparas årligen, genom att konvertera alla vanliga växthus till detta koncept. Det årliga värmebehovet i ett idealiskt slutet växthus kan reduceras till 60 kWhm-2 jämfört med 300 kWhm-2 i ett konventionellt växthus. Energibesparingen kommer även att minska miljöpåverkan.

Även ett delvis slutet växthus, där en del av ytan är slutet, eller där viss kontrollerad ventilation medges, minskar energibehovet samtidigt som praktiska fördelar har kunnat påvisas. Ett delvis slutet växthus kan minska energibehovet för uppvärmning med mellan 25% och 75% beroende på andelen sluten yta. En framräknad återbetalningstid för investeringen i ett slutet växthus varierar mellan 5 och 8 år beroende på design av energilagringssystemet. Sålunda har det slutna växthuskonceptet potential att vara kostnadseffektiv.

Mot bakgrund av dessa lovande resultat har sedan scenarios för energy management analyserats med hänsyn till termo-ekonomiska faktorer. Från detta är det tydligt att de viktigaste skillnaderna mellan de föreslagna scenarierna är den typ av energikälla, samt kyl- och avfuktningsstrategier som används, och dessa val är mycket beroende av klimatförhållandena.

Slutligen, föreslås ett nytt koncept, en s.k. "solpersienn", vilket är ett aktivt system där överskottet av solstrålningen absorberas av PVT-paneler och lagras i termiskenergilager för att tillföra en del av växthuseffekten värmebehov. I detta koncept minskar den årliga externa energitillförseln för uppvärmning i ett slutet växthus med 80%, ner till 62 kWhm-2. Den totala värme- och elproduktionen, med konceptet "solpersienn" blir cirka 20 kWhm-2 respektive 80 kWhm-2. Elproduktion kan användas för artificiell belysning och annan elektrisk utrustning i växthuset.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 149 p.
TRITA-KRV, ISSN 1100-7990 ; 13:07
Thermal Energy Storage, Energy Saving, Thermoeconomic Assessment, Energy Management Scenario, Micro Climate Control, Solar Building, Closed Greenhouse
National Category
Energy Engineering Energy Systems
Research subject
SRA - Energy
urn:nbn:se:kth:diva-127911 (URN)978-91-7501-851-5 (ISBN)
Public defence
2013-09-27, M235, Brinellvägen 68, KTH, Stockholm, 09:00 (English)

QC 20130910

Available from: 2013-09-10 Created: 2013-09-09 Last updated: 2014-01-31Bibliographically approved

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