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By Maeva Sabre (CSTB)

UF_NF_Den_Haag_28052018 (54).JPG

Pilot Id

The building is a tall existing industrial building, the greenhouse was built directly on the roof in 2015, and production started in 2016. The building is in an industrial area close to the centre of Den Haag.

The building was formerly a Philips manufacture. It was abandoned, and Urban Farmer offered the city authorities of The Hague to study a project for its refurbishment and the implementation of a greenhouse on the roof and a fish production unit on the top floor.

Refurbishment work consisted of the reinforcement of the structure of the 5th floor, extension works above the flat roof of the 6th floor, and the construction of the greenhouse structure on the roof.

The “UF 002 De Schilde” greenhouse was installed at the top of an empty office block of the 1950’s that once belonged to the Dutch telecommunications powerhouse Philips. It is located above an abandoned reception desk and six floors of vacant office space. The greenhouse is located on the highest level on the roof, but Urban Farmer activity is also on the 6th floor with a welcome desk, a shop, a terrace, and fish production units.

The building is a brick-and-glass seven-floor building. It was built as a television and telephone factory for Philips in the 1950’s by the modernist architect Dirk Roosenburg. It has about 12,400 m² of total floor space, largely abandoned but too solid and expensive to knock down.

Key numbers: rooftop 1,200 m², greenhouse 700 m², aquaponics 300 m²

Architect: Space & matter; founder: Andreas Graber

Main activities: plant and fish production, events, visits, shops, etc., with 45 tons of vegetables (leafy greens, tomatoes, eggplant, basil) and 19 tons of fish (Tilapia).

Business – value creation

Energy costs are variable depending on the season of the year. These costs are 3,000 €/month in the summer months, while they rise to 15,000 €/month in the cold months.

NB: information was lacking about this section during and after the visit. For example, the business model was not provided, it usually remains confidential.


Access to the greenhouse is safe by the lift and stairs. The roof perimeter is enclosed by a 2-meter high wood frame. Inside the greenhouse, the lowest part of the facade is made of rigid sandwich panels. On the 6th floor, the existing terrace was not modified (the safety barrier seems to be convenient for use).

The existing rooftop was kept. It was originally made of hard concrete covered with bituminous waterproofing material. One part of the greenhouse structure was built directly on the roof.

An extension of the existing roof was built above the existing terrace on the 6th floor. The additional structure was built in concrete. The new concrete slab is 30 cm thick on average. Six new pillars along the existing 6th floor terrace have been added.

Access to the greenhouse is possible both by the main lift up to the 6th floor and by a staircase to the roof, and access to both is possible by a new steel staircase. The total load of the greenhouse is distributed to the existing bearing walls and beams. Single-glazed tempered glass had been used for the facade. The penetration of the concrete slab of the greenhouse roof are scarce, with only one area where the water and heating ducts can be passed.

The greenhouse is divided in two zones.

  • The first one is directly implemented on the existing waterproofing membrane. Farming equipment is light-frame steel, rolling on a free rail on the floor. The RTG structure is made of steel and fixed along the structural concrete wall.

  • The second one is built on an additional concrete slab. Farming equipment is hanging from the steel frame of the roof. Trolley rails are anchored on the concrete slab. The rail system is supplemented with heating pipes.

There is a 30-cm gap between the two zones of the greenhouse. A sign of failure is visible along the side of the concrete floor, probably due to differences in thermal dilation.

The facades are built with sandwich panels, and single-glazed tempered glass. The roof is made of single-glazed tempered glass.

The heating pipes are hooked to the vertical steel frame along the greenhouse perimeter.

There is no water outlet located in the greenhouse. All rainwater outlets are located outside, and water from surfaces (the roof and facades) is harvested. The pipe that brings water to the RTG is in the irrigation room, in which the PRIVA control system is installed. This software program manages the water quality parameters: pH 6 to 6.5 and conductivity. The entrance area contains a calcium tank, a sulphuric acid tank, etc.

Another room dedicated to fish food storage is temperature and humidity conditioned.

A concrete layer was laid on the existing floor. A siphon system was installed to manage water collection. There is no flooring on the concrete, no tiling, no resin. The slope of the concrete slab was studied; it seemed that after the first filling of the tank, the structure did bear this huge load but stabilised to a new slope after loading. We did not see any trace of stagnant water. Also, the water collection system runs correctly.

Tanks are made of plastic. There are 20 tanks of 4.5 m³ and 10 tanks of 3 m³ for a total of 120 m³. Their feet are made of stainless steel, each foot is 30 mm long x 30 mm wide. They are directly installed on the concrete floor. The pipes run on the floor. Pumps are located close to the water treatment tank.

NB: data were lacking about this section during and after the visit, e.g. about climate impacts (wind, snow, rain) because of the height of the building: how the greenhouse structure resists and what are the specific properties required from the materials (glass, steel…) or whether all parameters are controlled by PRIVA. It should be very useful for the project to be able to explain or compare the initial design hypotheses (wind speed, solar radiation, temperature) with the real data collected by the instruments (sensor, anemometer, thermometer, etc.).

Energy management

It is interesting to know that external climate conditions (average monthly high and low temperatures) in Den Haag are monitored to know the potential energy needs.
The greenhouse type is a standard Venlo greenhouse. Adjusted to a high altitude (>30m), the glass shell is double-glazed and the greenhouse structure itself has been reinforced. However, the divides between the different greenhouses (visitors’ greenhouse, fruit greenhouse, and salad greenhouse) are made of single-glazed glass.     
No energy advice was searched for while initially working on the concept, and apart from economic reasons, the need to reduce energy requirements was not a goal. Consequently, there is no use of existing energy flows and no connection between the greenhouse and the structure below. Since the building is still not fully occupied, gaining efficient synergy effects is not possible.
The RTG uses a gas boiler and heating is distributed by water pipes. It does not have a cooling system besides natural ventilation and shading. However, it has a movable shading screen, which can help to reduce heat losses although it is porous and air permeable.
The greenhouse is ventilated using traditional Venlo-type ventilators (roof ventilators, no side ventilators). Given the fact that the RTG is located on top of the 5th floor of the building, the wind regime is stronger than at the ground level, so vents should be enough to guarantee good growing conditions even in the hottest days. Nevertheless, UF mentioned that the vents were not opened completely to avoid pests.
Another cause of energy consumption is the artificial growing lights. These are sodium vapour lamps of 400 W each for the leafy-green greenhouse and 600 W each for the fruit greenhouse.
There is no CO² enrichment system in the RTG. The CO² from the fish room (which has a CO² concentration of 1,400 ppm) cannot be used because it is too humid, particularly in winter.

Potential improvements

  • Using F-Clean film instead of double-glazed windows to reduce the weight load of the greenhouse could lead to a different and cheaper support structure.

  • Installing thermal screens on the side walls, front walls and over the crops is a well-known technique that is not used among the UF De Schilde facilities. Once construction works are over, installing such screens is more difficult and expensive. Thermal screens would help to reduce energy consumption and associated CO² emissions.

  • Diffuse glass provides better light use efficiency than clear glass (8% increase in productivity have been reported in The Netherlands). Clear glass is more attractive visually, so perhaps a combination of clear glass on the front and side walls with diffuse glass on the roof would have been advisable. Also, antireflective treatment and low-emissivity treatment on the glass sides are generally recommended. Once the greenhouse has been built, replacing the cladding materials is unjustified, but this is something to be considered for future designs. The best covering material can reach more productivity with equal or lower energy inputs, so it helps to reduce CO² emissions per unit of produce.

  • Artificial CO² enrichment is strongly recommended. It is not an expensive technique; it can be retrofitted to existing greenhouses and it boosts productivity.

  • Integration to the building is not complete in terms of energy and CO² exchanges. Only water from the fish tanks, which is rich in nutrients, is interchanged from the building to the RTG. To reduce CO² emissions by the RTG, perhaps the RTG can benefit from waste heat from the building. Once the RTG is constructed it is not easy to use potential sources of waste heat produced in the building, but this point should be taken into account for future RTG designs.

NB: data were lacking about this section during and after the visit, e.g. the average heating consumption (kWh/year), the average electric consumption (kWh/year). Is the double-glazed glass anti-reflective glass? Does it have a low emissivity treatment in one of the internal glass sides? The GROOF experts observed that the RTG used more energy than conventional ground greenhouses, probably due to the different wind regime. Wind speed increases as height increases, and in turn energy losses by convection are higher. Besides, the RTG had no light screens, which are mandatory in the Netherlands to avoid light pollution.


The RTG is divided into three major areas:

  • the leafy green greenhouse (300 m²) is devoted to microgreens and leafy vegetables

  • the fruit greenhouse (750 m²) where tomatoes, peppers, cucumbers, and eggplants are produced

  • a shared service area, a visitors’ hall, etc. In total, the glass-covered area is 1,200 m²

A nursery tank shelters the young fish for several weeks until they are sufficiently mature. Then, they are transferred to the bigger tanks to stay there until harvested. The operation mode to kill the fish is based on an electrical discharge in the specific tank. Fish are processed in a room directly at The New Farm and delivered to a processing company that cuts the fillets and sends them back to The New Farmer to be packed.

The fish tanks were initially filled with local tap water. The water from fish production is used to fertilise the plants in the greenhouse. A treatment tank based on bio-chips lowers nitrate levels and oxygenates the water. UV treatment neutralises micro-organisms. A CO2 tower captures CO2 emissions. The purified water is sent to the greenhouse once every two weeks. Additives (calcium, sulphuric acid, etc.) can be added to the water. In case of insufficient water capacity, tap water is added to the fish tank. No tap water is used directly to irrigate the plants.

The plants are cultivated manually; vegetables are picked, placed in plastic boxes and directly carried to the shop on the 6th floor. Organic waste is regularly collected and directly carried to the ground floor. Vegetables are grown on trapezoidal rock wool growing media. The tomato branches are very long and strong, 5 to 10 meters each on average.

NB: One of the biggest RTGs in Europe went bankrupt in July 2018. Although the project was set up by experienced urban growers, why did it shut down so quickly? What are the main reasons for this unexpected bankruptcy?

A dedicated report has been written by GROOF partners on the reasons.

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