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Blickpunkt Asia Pacific, Newsletter 12/2009

Towards CO2 Neutral Urban Redevelopment – Presenting the Rotterdam Energy Approach and Planning (REAP)

Marc Joubert - Joubert Architecture (JA), Rotterdam*

By the year 2025 Rotterdam aims to have halved its CO2 emissions; an ambitious plan that will require a revolutionary approach to urban areas. One proactive response to this challenge is an exploratory study of the Hart van Zuid area. An interdisciplinary team has investigated how to tackle CO2-issues in a structured way. This has resulted in the Rotterdam Energy Approach and Planning (REAP) methodology. REAP supports initial demand for energy, propagates the use of waste streams and advocates use of renewable energy sources to satisfy the remaining demand. REAP can be applied at all levels: individual buildings, clusters of buildings and even whole neighbourhoods. Applying REAP to the Hart van Zuid, Rotterdam has shown that this area can become CO2 neutral. Best of all: REAP can be applied everywhere.


Ten years ago few people thought that the climate was changing and even fewer realised that mankind was influencing the change. Since then opinions have altered and now the world is generally convinced of the seriousness of the situation: the climate is changing at an unprecedented rate, mankind is one of the major causes as acknowledged by the IPCC [1] and fossil fuels are rapidly running out. Because of this, attention is concentrated on energy consumption and the consequences of this. However there are other forms of damage to both the environment and public health that cannot be ignored. It is possible to arm ourselves against, or if required to flee, the consequences of climate change. However the biggest problem is not climate change but the depletion of our energy reserves; a socio-economic problem rather than a technical one. In September 2008 so-called ‘peak oil’ was reached, the point at which more oil is consumed than can be produced. From now on the situation can only get worse. We are so dependent on the easy supply of fossil energy that we have imperceptibly become addicted. Just before the start of the current world-wide economic crisis the price of oil reached a previously inconceivably high level (nearly 140 dollars a barrel) and at the time experts expected the price to double. Energy affects everyone, but especially the poor and the people living the furthest away from amenities. The current economic crisis will come to an end and the price of oil will once again rise to a realistic level. It would be wise to use our time now in developing a different energy system, especially where it matters most, the urban centres of newly developed countries.


The energy crisis does not mean that we have to cut ourselves off from the outside world and only use energy that we can generate ourselves – even if that were possible – but it is wise to make better use of our own energy potential. For example the surface area of the Netherlands is sufficient to generate enough sustainable energy (solar, wind, water) to supply the economy of the whole world [2]. Technically it is possible to realise a completely sustainable energy system but for the time being costs are prohibitive. We require a smart way of dealing with what we have and intelligent methods of making use of our resources.

The old three step strategy

Since the end of the 1980’s sustainable approaches to urban areas have followed the three step strategy:

01 Reduce consumption
02 Use renewable energy
03 Supply the remaining demand cleanly and efficiently

Figure 1: The 3-step strategy

This strategy towards energy use is known as the Trias Energetica [3]. It forms the guideline for a logical, environmentally conscious approach but in the twenty years that it has been in use it has not led to the required sustainability. In particular, the degree of penetration of renewable energy sources, step two, is minimal. Sustainable buildings in the Netherlands mainly concentrate on step 3. Time for reformulation.

New stepped strategy

The New Stepped Strategy adds an important intermediate step in between the reduction in consumption and the development of sustainable sources, and incorporates a waste products strategy.

01 Avoid energy demand (using intelligent and bioclimatic design)
02 Reuse waste energy streams
03 Generate renewable energy and reuse waste for food or energy
04 Supply the remaining demand cleanly and efficiently

Figure 2: The new stepped strategy

The New Stepped Strategy has a new second step that makes optimal use of waste streams – waste heat, waste water and waste material – not only for each individual building but also on a city wide scale. Waste streams from one chain may be used in a different chain. For example, waste water can be purified and the silt fermented to form bio-gas which can be reused in the energy chain. Step 4 will continue to be necessary for the coming years, but eventually this will no longer be possible. The development of new areas or the re-development of existing areas should already take this into account because the fourth step will remain a painful necessity in many other regions.

Old energy system versus sustainable energy system

If we consider the organisation of our energy system it is clear that a lot of primary energy (98% from fossil or nuclear sources) enters our society but at the same time a lot of energy is lost (in the air, water or ground) and nothing useful is done with the many waste products. A more sustainable system based on the usage of waste heat for example (a so-called low-exergetic system [5]) would require significantly less primary energy and this primary energy would only be used by the most high-grade functions [6]. This system is very effective: we could become 6 times more sustainable (600% improvement in energy usage), while we are currently plodding away at methods to achieve an improvement in efficiency of as little as 10%.


From building to neighbourhood

If the New Stepped Strategy is applied to an individual building it will undoubtedly generate a more sustainable building, but within the whole urban context this would be a missed opportunity. No use is made of the direct surroundings. The energy consumption per building can, and must, be reduced. After this it is useful to determine whether waste streams from the building can be usefully employed. This is already being done for example by recycling heat from ventilated air and waste shower water. In short: after step 2 there is still a significant demand for energy that according to step 3 must be solved using renewable energy sources. As has already been mentioned, this is technically possible but requires huge investment. A better idea is to consider a cluster of buildings and to determine whether energy can be exchanged, stored or cascaded (see schematic diagram). In other words, if at individual building level all the waste energy has been recycled, the remaining demand for heat or cooling can probably be solved by buildings with a different pattern of energy requirements, buildings with an excess of the required energy or which produce waste heat (or cold). Also for example generating electricity and heat from waste biomass, while at the same time cleaning waste water.

01 An example of exchange in the Netherlands: due to internal heat production, modern offices start cooling as soon as outdoor temperatures exceed 12º C. At these temperatures homes still require to be heated. This provides opportunities for heat exchange during spring and autumn. Another example is the combination of supermarkets (always cooling) with homes (frequent heating).

02 An example of energy storage at cluster level: heat and cold are only available in excess when there is little demand for them. For an optimal energy balance energy should be stored during seasons when the exchange as mentioned in example 1 is not required. This can be done in subterranean aquifers at about 80m depth.

03 An example of cascading: a greenhouse captures much passive solar energy which usually disappears as waste heat into the air. A heat exchanger could enable this waste stream (usually about 30º C) to be used to heat homes, provided these homes are well insulated and make use of a low temperature heating system. If all waste streams at cluster level are being used optimally it then becomes possible to see if primary energy can be generated sustainably. Although solar panels and solar collectors or a heat pump with ground collector systems can be installed in each individual building, it is much more economical to set these up at cluster level.

Figure 3: Schematic diagram of cascading from high temperature demand to lower temperature

Figure 4: The REAP methodology

From neighbourhood to city

If a project is connected to its surroundings, additional benefits can be found in the form of exchange of waste energies between different buildings with differing energy demands. Because of the larger scale it will become feasible to balance the heat and cooling demand, as well as make it possible to develop functions only possible on this scale. Examples of this are bio-gas fermentation installations that recycle biomass from waste water and use power-heat coupling to generate heat and electricity. Geothermic energy is also only feasible on a grand-scale.

Integrated neighbourhoods for living, working, health, sports facilities, entertainment have the largest potential benefit from such an approach. Leading not only to more energy efficient areas, but also to more lively and liveable urban surroundings. This is a tool for urban planning, where energy, next to investment, demand, infrastructure, becomes a deciding factor in urban planning. REAP has the potential to save energy while improving the quality of life of a cities inhabitants.

On an even larger or regional scale integrated systems on city scale can be useful, such as the possibility to use waste heat from industrial processes for housing and offices. But due to the lack of public funding in many developing countries and the prohibitive cost of large scale infrastructure investment, it is much more sensible to look for energy production opportunities on a local scale first.


How can REAP be applied to an existing, complex urban area, in this case the HvZ area in Rotterdam, Netherlands? Which decisions within the methodology must be made if the desired reductions in CO2 emissions are to be achieved, decisions at economic, political, public, urban development and architectural level? And what are the consequences for the buildings in a city and the open spaces in between? In addition the examples explicitly look for combinations of measures for CO2 reduction together with sustainable development by means of a combination of functions, social integration and integration of food production in the urban landscape (urban agriculture): CO2 reduction as spatial design.

How can this cluster, with its mix of ‘60s urban development and ‘80s architecture, once again become attractive in and for the city? It is currently mainly a shopping centre, attracting people from the south of the city, with an unusual mix of infrastructure (the busiest bus station in the Netherlands!) and a theatre but with no activities after opening hours and with no links to the surrounding areas. At the same time, the building devours energy; heating in the winter and cooling in the summer. How can this urban development problem be transformed into a future oriented, attractive development?

Figure 5: The ‘Hart van Zuid’ area, Rotterdam, Netherlands (from Google earth)

Step 00 Make an inventory of the current energy consumption.
Step 01 Reduce energy demand through isolation. New functions are added: 20.000m2 shops, 6.000m2 supermarket. A theatre and busstation will be renewed.
Step 02 Reuse of waste streams > The addition of housing will create a better heat-cold balance. The use of the waste heat generated by the supermarket and the typical morning and evening energy consumption in homes means that the match is perfect: 1m2 supermarket can heat 7m2 of housing! If 665 apartments are added, the heat-cold ratio becomes 1:1, so we can exchange energy and develop a business case.
Step 03 Renewable energy generation > The remaining demand for heat can be solved by the addition of greenhouses on the first floor, these could be public areas (or greenhouses for growing tomatoes) or by the addition of PVT-panels. PV panels could also be installed on the roof to supply electricity for the shopping centre.

Figure 6: Adding 665 apartments to a shopping centre balances energy demand (JA-Joubert Architecture)

Figure 7: Roofs are used for PVT panels producing electricity and heating (JA-Joubert Architecture)


The stepped approach as a method can be applied in any climate zone, but of course the energy demands vary depending on geography or location.


For example in warm climates the usage of air-conditioning systems has had a devastating effect on energy demand. Air-conditioning systems need 10x the amount of energy for 1 deg. temperature difference compared to heating systems. So what kind of solutions would be possible?


Water retention and treatment are becoming more and more important elements in our urban environment. On the one hand waste water should be treated before it is released into our environment, but it is also a source of energy. Biomass from wastewater can be used for energy production in the form of heat or electricity.

Water retention is getting more attention as urban areas have increasing amounts of hard surface areas, leading to flooding of overtaxed drainage systems. All water which can be stored for a period of time improves this problem.

Energy exchange

A test case was developed in Albania, where rain- and waste water is cleaned in a filtering lake and used for evaporative cooling. The temperature can already be reduced considerably by 8 deg. (from 34 deg. outdoors to 26 deg.) reducing the energy demand for additional air-treatment by a substantial amount.

Figure 8: Water retention and treatment for evaporative cooling and irrigation Korca, Albania (JA-Joubert Architecture with Arup engineers, Amsterdam)

Figure 9: Watertreatment integrated into architecture (JA-Joubert Architecture)

Figure 10: Waterfilters for evaporative cooling and water treatment in Shopping Center, Korca, Albania (JA-Joubert Architecture)


In a warmer climate the possibilities for solar energy are enormous, using solar collectors for electricity and heat production can lead to huge savings. Cost will remain a factor, but more efficient collectors will reduce prices continually.

Using waste energy

Exchange between different functions is always a possibility, one has to look carefully at what kind of balance is feasible. First we need to reduce the energy demand of buildings by better isolation and intelligent use of the bioclimatic situation. Then we can have a look at how the waste streams can be used in other functions, such as collective use and exchange through collective biomass power production. Functions such as Offices and housing could combine use of centralised airtreatment systems, greatly increasing efficiency.

Energy storage

Production and demand will not necessarily occur at the same time. Storing this energy is essential to succesful exchange. Storing heat or cold in still underground aquifers (water layers) is an economically feasible method, especially if used collectively


The REAP-method of reduction of both energy consumption and CO2 emissions, is based on a realistic approach to economic, social, political and organisational structures.

The search for the perfect solution at the right place depends on different guiding factors – money, technology, organisation, information – which all change with time. In the future optimum solutions will be different from now.

CO2- neutral urban development is possible! After applying REAP, calculations have shown that CO2 neutral urban development within existing built up areas is possible.

In new urban areas the advantages are even greater and can tackle future challenges right now, thereby not only saving energy but improving the quality of people’s lives while doing it!


[1] IPCC (Intergovernmental Panel on Climate Change); Climate Change 2007: Fourth Assessment Report; IPCC, 2007.
[2] Jong, T.M. de (ed.), Moens, M.J., Akker, C. van den & Steenbergen, C.M. 2004, Sun Wind Water, Earth Life and Living – Legends for design, Delft: TU Delft.
[3] Trias Energetica
[4] McDonough, W. & Braungart, M. 2002, Cradle to Cradle - Remaking the Way We Make Things, NorthPoint Press.
[5] LowEx,
[6] Dobbelsteen, A. van den, Gommans, L., Roggema, R., Smart vernacular planning: sustainable regional design based on local potentials and optimal deployment of the energy chain, SB84 – Delft:TU Delft


1 City of Rotterdam, dS+V and Department of Building Technology, Faculty of Architecture, Delft University of Technology
2 Department of Building Technology, Faculty of Architecture, Delft University of Technology,
3 Joubert Architecture, Rotterdam,
4 City of Rotterdam, Gemeentewerken
5 DSA Rotterdam Architecture

(*) Marc Joubert M.Sc. Arch
JA-Joubert Architecture
Westzeedijk 399
3024 EK Rotterdam
+31 104131011