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Energy Management in Large scale Solar Buildings: The Closed Greenhouse Concept
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. (Thermal Energy Storage Group)ORCID iD: 0000-0001-9426-4792
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.
Series
TRITA-KRV, ISSN 1100-7990 ; 13:07
Keyword [en]
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
Identifiers
URN: urn:nbn:se:kth:diva-127911ISBN: 978-91-7501-851-5 (print)OAI: oai:DiVA.org:kth-127911DiVA: diva2:646622
Public defence
2013-09-27, M235, Brinellvägen 68, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20130910

Available from: 2013-09-10 Created: 2013-09-09 Last updated: 2016-12-15Bibliographically approved
List of papers
1. Energy management in horticultural applications through the closed greenhouse concept, state of the art
Open this publication in new window or tab >>Energy management in horticultural applications through the closed greenhouse concept, state of the art
2012 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 16, no 7, 5087-5100 p.Article, review/survey (Refereed) Published
Abstract [en]

The commercial greenhouse has the highest demand for energy as compared to all other agricultural industry sectors. Here, energy management is important from a broad sustainability perspective. This paper presents the state-of-the-art regarding one energy management concept; the closed greenhouse integrated with thermal energy storage (TES) technology. This concept is an innovation for sustainable energy management since it is designed to maximize the utilization of solar energy through seasonal storage. In a fully closed greenhouse, there is no ventilation which means that excess sensible and latent heat must be removed. Then, this heat can be stored using seasonal and/or daily TES technology, and used later in order to satisfy the heating demand of the greenhouse. This assessment shows that closed greenhouse can, in addition to satisfying its own heating demand, also supply the demand for neighboring buildings. Several energy potential studies show that summer excess heat of almost three times the annual heating demand of the greenhouse. However, many studies propose the use of some auxiliary system for peak load. Also, the assessment clearly point out that a combination of seasonal and short-term TES must be further explored to make use of the full potential. Although higher amount of solar energy can be harvested in a fully closed greenhouse, in reality a semi-closed greenhouse concept may be more applicable. There, a large part of the available excess heat will be stored, but the benefits of an integrated forced-ventilation system are introduced in order to use fresh air as a rapid response for primarily humidity control. The main conclusion from this review is that aspects like energy efficiency, environmental benefits and economics must be further examined since this is seldom presented in the literature. Also, a variety of energy management scenarios may be employed depending on the most prioritized aspect.

Keyword
sustainable energy management, closed greenhouse, thermal energy storage, system modelling, energy analysis
National Category
Energy Engineering Energy Systems
Identifiers
urn:nbn:se:kth:diva-48036 (URN)10.1016/j.rser.2012.04.022 (DOI)000307909800065 ()2-s2.0-84862740275 (Scopus ID)
Note

QS 20120328. Updated from submitted to published.

Available from: 2011-11-15 Created: 2011-11-15 Last updated: 2017-12-08Bibliographically approved
2. Energy management strategies for commercial greenhouses
Open this publication in new window or tab >>Energy management strategies for commercial greenhouses
2014 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 114, no SI, 880-888 p.Article in journal (Refereed) Published
Abstract [en]

Growth in population and the ever-increasing development of new production technology leading to rising energy use in the agricultural industry. Although the greenhouse is one of the most energy intensive sectors in the agricultural industry, it is important because of its ability to intensify production. This paper has assessed energy management strategies (including single and combined energy conservation opportunities), with special emphasis on Nordic climates, where fossil fuel-based heating is still significant, despite a recent conversion to biomass boilers. The results show that the "Double thermal screen" and "Double glazing" with 60% reduction in energy demand are the most effective single opportunity for energy conservation. However, the highest improvement (80%) is obtainable using the closed greenhouse concept, with a potential payback of 5-6 years under favorable conditions. It can be concluded that some of the single opportunities can be more practical in terms of their PBP in comparison to a complex concept, requiring a combination of measures, such as the closed greenhouse.

Keyword
Energy management, Energy performance, Commercial Greenhouse, Closed greenhouse
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-127935 (URN)10.1016/j.apenergy.2013.08.089 (DOI)000330814100088 ()2-s2.0-84888851478 (Scopus ID)
Note

QC 20140313. Updated from accepted to published.

Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2017-12-06Bibliographically approved
3. Energy analysis and thermoeconomic assessment of the closed greenhouse: The largest commercial solar building
Open this publication in new window or tab >>Energy analysis and thermoeconomic assessment of the closed greenhouse: The largest commercial solar building
2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 102, 1256-1266 p.Article in journal (Refereed) Published
Abstract [en]

The closed greenhouse concept has been studied in this paper. The closed greenhouse can be considered as the largest commercial solar building. In principle, it is designed to maximize the utilization of solar energy by use of seasonal storage. In an ideal fully closed greenhouse, there is no ventilation window. Therefore, the excess heat must be removed by other means. In order to utilize the excess heat at a later time, long- and/or short-term thermal storage technology (TES) should be integrated. A theoretical model has been derived to evaluate the performance of various design scenarios. The closed greenhouse is compared with a conventional greenhouse using a case study to guide the energy analysis and verify the model. A new parameter has been defined in this paper in order to compare the performance of the closed greenhouse concept in different configurations - the Surplus Energy Ratio showing the available excess thermal energy that can be stored in the TES system and the annual heating demand of the greenhouse. From the energy analysis it can be concluded that SER is about three in the ideal fully closed greenhouse. Also, there is a large difference in heating demand between the ideal closed and conventional greenhouse configurations Finally, a preliminary thermo-economic study has been assessed in order to investigate the cost feasibility of various closed greenhouse configurations, like ideal closed; semi closed and partly closed conditions. Here, it was found that the design load has the main impact on the payback period. In the case of the base load being chosen as the design load, the payback period for the ideal closed greenhouse might be reduced by 50%. On the other hand, glazing type, ventilation ratio, and the closed area portion have a minor impact on the payback period.

Keyword
Closed greenhouse, Energy conservation, Heat transfer, Solar commercial building, Sustainable energy management system, Thermal energy storage system
National Category
Energy Engineering Energy Systems
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-48033 (URN)10.1016/j.apenergy.2012.06.051 (DOI)000314190800130 ()2-s2.0-84870728102 (Scopus ID)
Note

QC 20120328. Updated from submitted to published.

Available from: 2011-11-15 Created: 2011-11-15 Last updated: 2017-12-08Bibliographically approved
4. Thermal energy storage strategies for effective closed greenhouse design
Open this publication in new window or tab >>Thermal energy storage strategies for effective closed greenhouse design
2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 109, 337-343 p.Article in journal (Refereed) Published
Abstract [en]

The closed greenhouse is an innovative concept in sustainable energy management. In principle, it is designed to maximize the utilization of solar energy through the seasonal storage. In a fully closed greenhouse, there is not any ventilation window. Therefore, the excess sensible and latent heat must be removed, and can be stored using seasonal and/or daily thermal storage technology. This stored excess heat can then be utilized later in order to satisfy the thermal load of the greenhouse. Thermal energy storage (TES) system should be designed based on the heating and cooling load in each specific case. Underground thermal energy storage (UTES) is most commonly chosen as seasonal storage. In addition, a stratified chilled water (SCW) storage or a phase change material (PCM) storage could be utilized as short term storage system in order to cover the daily demands and peak loads. In this paper, a qualitative economical assessment of the concept is presented. Here, a borehole thermal energy storage (BTES) system is considered as the seasonal storage, with a PCM or a SCW daily storage system to manage the peak load. A BTES primarily stores low temperature heat such that a heat pump would be needed to supply the heat at a suitable temperature. A theoretical model has been developed using TRNSYS to carry out the energy analysis. From the economical feasibility assessment, the results show that the concept has the potential of becoming cost effective. The major investment for the closed greenhouse concept could be paid within 7-8 years with the savings in auxiliary fossil fuel considering the seasonal TES systems. However, the payback time may be reduced to 5 years if the base load is chosen as the design load instead of the peak load. In this case, a short-term TES needs to be added in order to cover the hourly peak loads.

Keyword
Heat transfer, Energy conservation, Closed greenhouse, Solar commercial building, Sustainable energy management system, Thermal energy storage system
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-125836 (URN)10.1016/j.apenergy.2012.12.065 (DOI)000321724000038 ()2-s2.0-84879288674 (Scopus ID)
Note

QC 20130815

Available from: 2013-08-15 Created: 2013-08-15 Last updated: 2017-12-06Bibliographically approved
5. Application of thermal energy storage in the closed greenhouse concept
Open this publication in new window or tab >>Application of thermal energy storage in the closed greenhouse concept
2012 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Lleida: , 2012
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-127937 (URN)
Conference
The 12th International Conference on Energy Storage
Note

QC 20130910

Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2016-12-15Bibliographically approved
6. Thermal energy storage systems in closed greenhouse with component and phase change material design
Open this publication in new window or tab >>Thermal energy storage systems in closed greenhouse with component and phase change material design
2013 (English)Conference paper, Published paper (Refereed)
Keyword
Thermal energy stora ge, PCM, Phase diagram, Cost analysis, Closed greenhouse
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-127938 (URN)
Conference
Sustainable Energy Storage in Buildings (SESB) Conferenc
Note

QC 20130910

Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2017-08-25Bibliographically approved
7. Solar blind system: solar energy utilization and climate mitigation in glassed buildings
Open this publication in new window or tab >>Solar blind system: solar energy utilization and climate mitigation in glassed buildings
2013 (English)Conference paper, Published 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.

Series
Energy Procedia, ISSN 1876-6102
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-127940 (URN)10.1016/j.egypro.2014.10.067 (DOI)000348253202016 ()2-s2.0-84922309405 (Scopus ID)
Conference
2013 ISES Solar World Congress, SWC 2013; Cancun; Mexico; 3 November 2013 - 7 November 2013
Note

QC 20130910

Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2016-12-15Bibliographically approved
8. Energy analysis of a solar curtain concept integrated with energy storage system
Open this publication in new window or tab >>Energy analysis of a solar curtain concept integrated with energy storage system
2013 (English)In: Proceedings of the 5th International Conference on Applied Energy ICAE 2013, Pretoria (South Africa), 2013, 2013, Paper ID: ICAE2013 - 417- p.Conference paper, Published paper (Refereed)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-127942 (URN)
Conference
The 5th International Conference on Applied Energy ICAE 2013, Jul 1-4, 2013, Pretoria, South Africa
Note

NQC 20140127

Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2016-12-15Bibliographically approved

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