5.4 The ICTA-ICP Rooftop Greenhouse Lab

(RTG-Lab): closing metabolic flows

(energy, water, CO2) through integrated

Rooftop Greenhouses

Esther Sanyé-Mengual1,2,* , Pere Llorach-Masana1,2 , David Sanjuan-

Delmás1,2, Jordi Oliver-Solà1,3, Alejandro Josa4,5, Juan Ignacio Montero6,1,

Joan Rieradevall1,7

1Sostenipra (ICTA-IRTA-Inèdit) research group, Universitat Autònoma de Barcelona (UAB), Campus de la UAB,

08193, Bellaterra (Spain)

2Institute of Environmental Science and Technology (ICTA), UAB, Bellaterra (Spain)

3Inèdit. Inèdit Innovació, S.L. UAB Research Park, Carretera de Cabrils, km 2 (IRTA), 08348, Barcelona, Spain

4Department of Geotechnical Engineering and Geosciences, School of Civil Engineering, Universitat Politècnica

de Catalunya-Barcelona Tech (UPC), 08034, Barcelona, Spain

5Institute of Sustainability, UPC, 08034, Barcelona, Spain

6Institute of Research and Technology in Agrifood Sector (IRTA), Environmental Horticulture, 08348 Cabrils,

Barcelona, Spain

7Chemical Engineering Department, UAB, Bellaterra (Spain)

*Corresponding author: Esther.Sanye@uab.cat

Abstract

The ICTA-ICP Rooftop Greenhouse Lab (RTG-Lab) is a research-oriented RTG situated in the UAB

Campus (Bellaterra, Barcelona). In contrast to current RTGs, the RTG-Lab integrates energy, water

and CO2 flows into the building’s metabolism. This integrated RTG (i-RTG) is an eco-innovative

concept that will enhance the sustainability of both systems involved while producing high-value

crops and maintaining indoor comfort in buildings with lower energy inputs. The RTG-Lab, within

the Fertilecity project, aims to demonstrate the feasibility of producing vegetables in i-RTGs in the

Mediterranean context and to quantify the environmental and economic performance of the

metabolic integration between the greenhouse and the building. To do that, experimental crops

(lettuce and tomato) in soil-less culture systems (perlite) will start on Fall 2014. Preliminary data of

the metabolic integration is described in this contribution. First, the residual heat from the

building will be introduced in the greenhouse to maintain crop temperatures. Moreover, the

692

airflow from the building will help the ventilation of the greenhouse in hot episodes. Second, the

rainwater collected in the rooftop of the building will be used for the irrigation of the crop, leading

into a 100% water self-sufficient crop. Third, the airflow from the building has a higher CO2

concentration than the greenhouse air. This CO2 will be used by the crop when supplied to the

greenhouse, as in current CO2-injection techniques in industrial horticulture.

Keywords: rooftop farming, building-integrated agriculture, urban agriculture, local production,

industrial ecology

Introduction

In response to the growing interest on urban food consumption and on the environmental

impacts of food systems, urban agriculture (UA) initiatives have spread over cities of developed

countries (Block et al. 2011; Mok et al. 2013; Tornaghi 2014). UA experiences vary from private

backyard garden to the development of community gardens in vacant lands (Cohen et al. 2012;

Gardiner et al. 2013; McClintock et al. 2013). Furthermore, recent UA initiatives tend to incorporate

agriculture in and on buildings. These building-based forms are included in the following

concepts: Vertical Farming (Despommier 2009), Building-Integrated Agriculture (Caplow 2009),

Zero-Acreage farming (Specht et al. 2014) and Skyfarming (Germer et al. 2011).

Among building-based forms, urban rooftop farming (URF) is growing in popularity as a way to

revaluate the rooftops, commonly unused spaces in densely built areas. Rooftop Greenhouse

(RTGs) are a common form of URF that refers to intensive production greenhouses installed on

rooftops, thereby enhancing urban food productivity (Cerón-Palma et al. 2012). Several RTG

projects have been carried out around the world, mainly concentrated in North America.

Gotham greens (http://www.gothamgreens.com) is a company situated in a former warehouse in

Brooklyn (New York, USA) that produces six varieties of lettuce and basil in an RTG farm of 1,400

m2. The Vinegar Factory (http://www.elizabar.com) is a specialized shop placed in Manhattan

(New York, USA) that cultivates tomatoes, salad greens and herbs in a 830m2-RTG on the rooftop.

Lufa Farms is a local producer in Montreal (Canada) that owns a 2,900m2-RTG to produce greens,

tomato, cucumber, pepper and eggplants, which are distributed through a Community Supported

Agriculture (CSA) model (Resh 2012). Other small-scale RTGs are placed in services or research

buildings, such as in the Fairmont Royal Hotel in Toronto (Canada) (http://www.fairmont.com).

There are several projects in Vancouver and Toronto (Canada) and in New York (USA) which will

expand the contribution of RTGs to local production in this area. In Europe, Vida Verde is a Dutch

floriculture company based in Honselersdijk that built an RTG on top of its logistics centre for

temporary product storage (Pers.Comm. Vida Verde). Other RTG experiences are still incipient and

aimed at research or educational purposes.

Integrated RTGs (i-RTGs)

Current RTG projects are greenhouses isolated from the building where they are placed. However,

RTGs can integrate their flows in the metabolism of the building, thereby increasing the resources

efficiency of the systems. Integrated RTGs (i-RTGs) can exchange energy, water and gaseous flows

with the building (Figure 1).

693

Figure 1. Metabolism of isolated and integrated RTGs.

Preliminary research on RTGs has focused on four aspects. Cerón-Palma et al. (2012) and Specht

et al. (2013) noted the barriers and opportunities of these systems within the urban agriculture

context. Sanyé-Mengual et al. (2013) quantified the environmental savings associated to the

avoided distribution stage of local products from RTGs. Specifically, 1 kg of tomatoes produced in

an RTG in the city of Barcelona (Spain) could avoid 441 g of CO2 eq. and 12 MJ of energy consumed.

The environmental impact reduction relies on the fact that local tomatoes could substitute

tomatoes from Almeria (Spain; 900 km away), which is the main source of this vegetable. A GIS-

based guide to quantify the implementation potential of RTGs in logistics and industrial parks was

designed by Sanyé-Mengual et al. (2014).

With regard to i-RTGs, Cerón-Palma (2012) performed a preliminary assessment of exchanging the

energy flow. An office building was the case study for the energy modelling study. The results

quantified that introducing residual heat from the greenhouse into the building could substitute

87 kWh of the heating demand, on an ideal winter day. Furthermore, the reduction in the heating

demand from non-renewable sources could thus reduce the environmental burdens of the

building.

The Rooftop Greenhouse Lab

The Rooftop Greenhouse Lab (RTG-Lab) is a research-oriented RTG placed on the rooftop of the

ICTA-ICP building in the Universitat Autònoma de Barcelona (UAB) campus (Bellaterra, Spain). The

RTG-Lab consists of two i-RTGs of around 125 m2 (Figure 2). The RTG-Lab is the case study of the

“Fertilecity” project funded by the Spanish Ministry of Economy and Competitiveness. The RTG-

Lab aims to demonstrate the feasibility of producing food in RTGs in Mediterranean areas and to

analyse and quantify the opportunities of i-RTGs that exchange flows.

The greenhouse of the RTG-Lab is similar to a Mediterranean unheated greenhouse. The structure

is made of steel, polycarbonate, LDPE and concrete. The culture system of the RTG-Lab is a soil-

less crop where perlite is used as substrate. The irrigation is automatic and provides the fertilizers

requirements (NPK). The experimental crops (lettuce, tomato) will start on Fall 2014. The RTG-Lab

will integrate the energy, water and CO2 flows with the building. As a result, the RTG will utilise, as

a first step, residual heat from the building (e.g., lab air), the higher CO2 concentration in this

residual air (i.e., which will be used as natural fertiliser), and rainwater collected from the rooftop.

i-RTGs are expected to perform a symbiosis with the building by providing and receiving flows in a

bidirectional relation. Nevertheless, the RTG-Lab only integrates, for the moment, the flows in a

694

monodirectional way due to legal constraints. The current Spanish building law, the Building

Technical Code (BOE 2006) requires that all the incoming air to a building must be outdoor air. As

a result, the greenhouse cannot introduce its residual air to the building.

Figure 2. Layout of the RTG-Lab, situation in the ICTA-ICP building, rooftop greenhouse dimensions and

image of the crop system.

Objectives

This contribution aims to further detail the opportunities of i-RTGs by describing the metabolic

exchanges of energy, water and CO2 flows between the greenhouse and the building, using the

ICTA-ICP RTG-Lab as case study. For each flow, a description of the exchange and the potential

benefits is provided.

The energy flow

i-RTGs aim to take advantage from the thermal difference between the building air and the

greenhouse air to improve the thermal conditions of the spaces. This practice aims to provide

thermal comfort in the building and a more efficient environment for crop production. The RTG-

Lab will use the residual air of the offices and laboratories as a source of thermal difference to

regulate the greenhouse temperature. The building air can be used for both heating and cooling

the i-RTG. When the temperature of the greenhouse air is higher or lower than optimal limits for

crop production, yield can be negatively affected. In the Mediterranean context, greenhouses

should not exceed 30ºC or be inferior to 15ºC to reach the expected crop yield.

695

During the day and in particular in summer, the RTG-Lab will introduce air from the offices and

laboratories with a lower temperature to support the cooling of the greenhouse, when it exceeds

30ºC. On the contrary, the RTG-Lab will introduce warmer air from the building into the

greenhouse when its temperature is lower than 15ºC (i.e., during the night and in winter) (Figure

3). According to Cerón-Palma (2012), future i-RTGs can offer further benefits to the building by

providing warm air for heating purposes (e.g., daytime in winter).

Preliminary data indicates that the temperature of the offices and laboratories of the ICTA-ICP

building can satisfy the thermal requirements of the crop production. The ICTA-ICP building is a

self-regulated building that monitors the temperature of the different spaces. As a result, the

temperature of the offices ranges between 18-25ºC degrees. On the other hand, the laboratories

that will provide the residual air to the RTG-Lab are steady-temperature spaces that maintain a

20ºC condition. Therefore, both spaces can act as a source of residual air for heating or cooling the

greenhouse space to support the thermal regulation of the space and optimize the crop

performance (Figure 3).

Figure 3. The energy exchange between the greenhouse and the building of the RTG-Lab.

The water flow

i-RTGs aim to use the water flows from the building as a water source for irrigating the crop.

However, irrigation water has to ensure a minimum quality to avoid health risks. In developing

countries, wastewater is commonly used a source of irrigation water due to water scarcity. This

practice can lead to negative health impacts, such as skin infections (Rutkowski et al. 2007;

Raschid-Sally et al. 2009). As a result, the RTG-Lab will only use the rainwater collected on the

building roof. The rainwater is stored in a water tank (135 m3) placed in the basement of the

building and where a physical treatment is applied. Then, rainwater is supplied to the greenhouse

to satisfy the crop water demand (Figure 4).

Preliminary data indicates that the rainwater collection on the ICTA-ICP rooftop could completely

satisfy the crop water demand. According to climatic data, around 1,5000 m3 could be collected in

one year. An experimental crop of tomato during one year will consist of two cycles: spring-

696

summer and autumn-winter. The combination of these cycles will result in a water demand of

0.797 m3·m-2 per year, according to calculations through the Fundación Cajamar software program

“PrHo v2.0 for irrigation systems of greenhouse horticulture” (González et al. 2008). The total

water demand of the greenhouse for a tomato crop would be of 381 m3. Thus, the crop can be

water self-sufficient as the rainwater could satisfy 450% of the demand.

Contrary to the air flow (i.e., energy and CO2), the water flow can be bidirectional. The wastewater

from the crop can then be redirected to spaces of the building to satisfy the water demand for

different purposes. The “Fertilecity” project will also pay attention to the potential uses of this

water flow. The quantity and quality of the wastewater from the greenhouse will be analysed to

determine the optimal uses in the building. For instance, this output could be directly used for

irrigation of the garden spaces of the building (indoor and outdoor). However, other uses in the

building depend on the water quality, such as for toilettes.

Figure 4. The water exchange between the greenhouse and the building of the RTG-Lab.

The CO2 flow

i-RTGs aim to use the high CO2 concentrations of the residual air from the building to enhance the

crop production. CO2 enrichment or carbon dioxide fertilization has been analysed in the literature

as a way to increase the crop production. This is based on the consumption of carbon dioxide by

the plants in the photosynthesis process. The higher is the carbon concentration in the

greenhouse, the more efficient becomes the photosynthesis process. Particularly, CO2 fertilization

has been proved in Mediterranean greenhouses (Savé et al. 2007; Stanghellini et al. 2008;

Stanghellini et al. 2009; Castilla 2012).

The RTG-Lab will use the CO2 concentration in the residual air of the offices and laboratories as a

source of carbon enrichment. Therefore, this provides two benefits to the crop production: an

increase in the crop yield and a CO2 source free of economic costs and environmental burdens. In

contrast to the energy flow, the CO2 exchange is expected to have the same results along the year

697

(Figure 5). According to the current legislation, the CO2 flow is monodirectional (from the building

to the greenhouses). Nevertheless, future i-RTGs could provide the building with a fresh air with a

low CO2 concentration through a greenhouse-building exchange.

Preliminary data indicates that the greenhouse (with no crop production) has a CO2 concentration

of 300 ppm. This value will be lower once the experimental crop starts as plants will consume the

available CO2. As expected, the offices and laboratories have a higher CO2 concentration that can

reach 450 ppm, depending on the daytime and the use. Consequently, the introduction of the

residual air from the building into the greenhouse will allow to rise the carbon concentration of

the greenhouse up to 450 ppm, thereby increasing the carbon availability for the plants and the

resulting crop yield without using external CO2 sources.

Figure 5. The CO2 exchange between the greenhouse and the building of the RTG-Lab.

Global performance of the RTG-Lab

The RTG-Lab will result into a food production system that optimises the resources consumption

by exchanging the energy, water and CO2 flows with the building. The food production of the

greenhouse benefits from the use of the residual air (i.e., energy and CO2) and the rainwater from

the building. As a first experimental i-RTG, the flows exchange will be only monodirectional, from

the building to the greenhouse due legal constraints. Although the water flow can be bidirectional,

there is a need to first analyse the water quality of the greenhouse wastewater to determine the

potential uses in the building.The exchange of energy flows in the ICTA-ICP RTG-Lab can face

current limitations in conventional greenhouses in the Mediterranean areas, where extreme

temperatures can affect the plants thereby reducing the crop yield. The use of the residual air

698

from the building can thus increase the crop efficiency with no consuming external resources (e.g.,

non-renewable resources for heating purposes).

The use of the rainwater from the building in the RTG-Lab can make local production self-

sufficient, in contrast to conventional technologies where water is usually pumped from the

ground. Besides, this can contribute to face water scarcity in the Mediterranean context, where

the irregular rainfall pattern can lead to drought periods.

The exchange of the residual air can provide CO2 enrichment to the crop. In conventional

greenhouses technologies, CO2 is injected as a carbon fertilization to support the photosynthesis

process. In the RTG-Lab the air from the building, with a higher CO2 concentration becomes a

carbon source free of economic or environmental costs. Crop yield can be therefore increased by

using the residual CO2 enrichment.

Contribution to urban sustainability

i-RTGs can positively contribute to urban sustainability. From the environmental point of view, i-

RTGs can support the local production of food with a lower environmental impact. The integration

of flows in the metabolism of the building can increase the crop yield and reduce the energy

demand as well as the water consumption. Moreover, RTG products can be almost km.0-products,

avoiding the environmental burdens of the distribution stage. Furthermore, the implementation

of i-RTGs can optimise the metabolism of buildings, such as by using the wastewater from the

crop (e.g., irrigation of garden areas).

The society can also benefit from i-RTGs. The accessibility to healthy food products can increase

and RTG products can improve the traceability of food. The enhancement of local businesses can

support community development. The insulation of building can increase the thermal comfort of

buildings, leading to more liveable buildings. Finally, i-RTGs also show economic opportunities. A

decrease in food costs is expected due to lower production and transport costs. Furthermore, a

reduction in the use costs of buildings is associated to the energy consumption reduction.

Further research

The experimental crops of the ICTA-ICP RTG-Lab and the “Fertilecity” project will shed light on the

flows exchange between greenhouses and buildings through i-RTGs. In particular, the main

motivation of the research is to demonstrate the feasibility of this integration, characterize the

exchange of energy, water and CO2, and quantify the environmental burdens and economic costs

of i-RTGs as local production systems.

The “Fertilecity” project will use multidisciplinary tools to assess the performance of i-RTGs. The

flows exchange will be monitored through sensors (e.g., CO2 concentration). In particular, the

energy flow will be modelled by means of the energy modelling software TAS (EDSL). The crop

production will be analysed according to agronomic parameters, such as the total and

commercial yield. The environmental and economic performance of the system will be quantified

from a life cycle perspective by applying the environmental Life Cycle Analysis (ISO 2006) and the

Life Cycle Costing (ISO 2008) methods. Finally, GIS systems will be used to observe the

implementation of i-RTGs at the urban level.

699

Acknowledgements

The authors thank the Spanish Ministerio de Economía y Competitividad (MINECO) for the

financial support to the research project “Agrourban sustainability through rooftop greenhouses.

Ecoinnovation on residual flows of energy, water and CO2 for food production” (CTM2013-47067-C2-

1-R), and the Spanish Ministerio de Educación for awarding a research scholarship (AP2010-4044)

to Esther Sanyé Mengual.

References

Block, D. R., Chávez, N., Allen, E., & Ramirez, D. (2011) Food sovereignty, urban food access, and

food activism: contemplating the connections through examples from Chicago. Agriculture and

Human Values, 29(2), 203–215. doi:10.1007/s10460-011-9336-8

BOE (2006) Real decreto 314/2006, de 17 de marzo, por el que se aprueba el Código Técnico de la

Edificación. Boletín Oficial Del Estado, 74, 11816–11831.

Caplow, T (2009) Building Integrated Agriculture: Philosophy and practice. In: Urban Futures 2030:

Urban Development and Urban Lifestyles of the Future (pp. 48 – 51). Heinrich-Böll-Stiftung.

Castilla, N. (2012) Greenhouse Technology and Management. Oxfordshire: CABI.

Cerón-Palma, I. (2012) Strategies for sustainable urban systems: introducing eco-innovation in

buildings in Mexico and Spain. Thesis, Universitat Autònoma de Barcelona.

Cerón-Palma, I., Sanyé-Mengual, E., Oliver-Solà, J., Montero, J., & Rieradevall, J. (2012) Barriers

and Opportunities Regarding the Implementation of Rooftop Eco.Greenhouses (RTEG) in

Mediterranean Cities of Europe. Journal of Urban Technology 19(4): 87–103.

Cohen, N., Reynolds, K., & Sanghvi, R. (2012) Five Borough Farm: Seeding the Future of Urban

Agriculture in New York City. New York: Design Trust for Public Space.

Despommier, D. (2009) The rise of vertical farms. Scientific American 301(5): 80–87.

EDSL (2014) TAS building modelling and simulation tool. Milton Keynes: EDSL Ltd.

Gardiner, M. M., Prajzner, S. P., Burkman, C. E., Albro, S., & Grewal, P. S. (2013) Vacant land

conversion to community gardens: influences on generalist arthropod predators and

biocontrol services in urban greenspaces. Urban Ecosystems 17(1): 101–122.

Germer, J., Sauerborn, J., Asch, F., Boer, J., Schreiber, J., Weber, G., & Müller, J. (2011) Skyfarming

an ecological innovation to enhance global food security. Journal Für Verbraucherschutz

Und Lebensmittelsicherheit 6(2): 237–251.

González, M., Céspedes López, A., & González Céspedes, A. (2008) PrHo V. 2,0: Programa de Riego

para cultivos Hortícolas en invernadero. Serie Las Palmerillas - Cuadernos técnicos 01.

ISO (2006) ISO 14040: Environmental management - Life cycle assessment - Principles and

framework (Vol. 2006). Geneva: International Organization for Standardization.

700

ISO (2008) ISO 15686-5: Buildings and constructed assets - Sevice-life planning - Part 5: Life-cycle

costing. Geneva: International Organization for Standardization.

McClintock, N., Cooper, J., & Khandeshi, S. (2013) Assessing the potential contribution of vacant

land to urban vegetable production and consumption in Oakland, California. Landscape and

Urban Planning 111: 46–58.

Mok, H.-F., Williamson, V. G., Grove, J. R., Burry, K., Barker, S. F., & Hamilton, A. J. (2013)

Strawberry fields forever? Urban agriculture in developed countries: a review. Agronomy for

Sustainable Development 24(1): 21–43.

Raschid-Sally, L., Jayakody, & P. (2009) Drivers and characteristics of wastewater agriculture in

developing countries: results from a global assessment. Colombo: International Water

Management Institute.

Resh, H. (2012) Hydroponic food production: A definitive guidebook for the advanced home

gardener and the commercial hydroponic grower. New York: CRC Press.

Rutkowski, T., Raschid-Sally, L., & Buechler, S. (2007) Wastewater irrigation in the developing

world—Two case studies from the Kathmandu Valley in Nepal. Agricultural Water

Management 88(1-3): 83–91.

Sanyé-Mengual, E., Cerón-Palma, I., Oliver-Solà, J., Montero, J., & Rieradevall, J. (2013)

Environmental analysis of the logistics of agricultural products from roof top greenhouses in

Mediterranean urban areas. Journal of the Science of Food and Agriculture 93(1): 100–109.

Sanyé-Mengual, E., Cerón-Palma, I., Oliver-Solà, J., Montero, J., & Rieradevall, J. (2014) Integrating

horticulture into cities: A guide for assessing the implementation potential of Rooftop

Greenhouses (RTGs) in industrial and logistics parks. Journal of Urban Technology (in press).

Savé, R., De Herralde, F., Codina, C., Sanchez, X., & Biel, C. (2007) Effects of atmospheric carbon

dioxide fertilization on biomass and secondary metabolites of some plant species with

pharmacological interest under greenhouse conditions. Afinidad 64(528): 237–241.

Specht, K., Siebert, R., Hartmann, I., Freisinger, U. B., Sawicka, M., Werner, A., Thomaier, S.,

Henckel, D., Walk, H., & Dierich, A. (2014) Urban agriculture of the future: an overview of

sustainability aspects of food production in and on buildings. Agriculture and Human Values

31(1): 33–51.

Stanghellini, C., Incrocci, L., Gázquez, J., & Dimauro, B. (2008) Carbon diozide concentration in

Mediterranean greenhouses: How much lost production? Acta Horticulturae (ISHS) 801:

1541–1550.

Stanghellini, C., Kempkes, F., & Incrocci, L. (2009) Carbon dioxide fertilization in Mediterranean

greenhouses: When and how is it economical? Acta Horticulturae (ISHS) 807: 135–142.

Tornaghi, C. (2014) Critical geography of urban agriculture. Progress in Human Geography (First

online)

701