RWE AG TOWER ESSEN, GERMANY INGENHOVEN, OVERDIEK, KAHLEN & PARTNER

ARCH 366 Lily Kim

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RWE AG TOWER Essen, Germany | Ingenhoven, Overdiek, Kahlen & Partner by Lily Kim The RWE Tower or also known as the “Power Tower” is headquarters to

Germany’s largest producers of electricity. It is located in Essen, the business

capital of the Ruhr region in the western part of Germany. It is situated across

from the Aalto Theater and Stadtgarten Park, and very close to the Essen Central

Station. This unique tower is not only a landmark to the city of Essen but is the

one of the first instigator of incorporating sophisticated environmental principles in

the design of high-rises. Designed by Ingenhoven, Overdiek, Kahlen & Partner

and completed in December of 1996, the 162m reinforced concrete structure,

consisting of 29-storeys takes on a circular form, chosen for its maximum surface

to volume ratio. The 32m diameter floors use significant amounts of natural

ventilation through the transparent double-skinned façade, using inventive

techniques to make this ecological high-rise. ii

Fig.1 The RWE Tower seen from the Alvar Aalto opera house.i The RWE Tower The RWE Tower, as stated above, consists of 29 stories, which include a

mechanical floor and three basement levels.

Around the building is a 1,800sq.m landscaping zone, which includes a

garden and small lake. The major public spaces, such as the staff restaurant,

dining room, recreation rooms, etc. are located in first basement level, overlooking

the garden and lake, taking advantage of the city landscape and the elegant view.

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Office rooms are located on the 2-18 and 20-24 levels. They are laid along

the perimeter of the floor plan, around the main circulation core located in the

center. Elevators are placed independently at the side of the main building,

keeping the floor area open and free of any obtrusions.

The 19th floor is a double story height and contains the mechanical system

used during conditions of extreme temperatures and winds. The 25-28 floors

occupy the senior management offices and large conference rooms and finally, the

29th floor consists of a board room and an aerial garden. The aerial garden is

protected from damaging and strong winds by the glass façade of the tower.v

Fig.2 A vertical section of the tower.iii Double-Skin Façade The façade of the RWE Tower consists of a double-skin glazing. This “thermal-

flue” curtain wall insulates the space in all seasons. It consists of basically two

sheets of glass separated by an air space. This air space provides insulation

against fluxuating temperatures, shield from winds, and the absorption of sound.

At the top and bottom of the airspace expanding its width is a device the architects

call the “fish-mouth”. This device, which will be explained further in detail below,

draws external air into the airspace. Shading devices are installed in between the

two sheets of glazing and are electrically operable. (See Fig. 4)

On a typical floor plan in the RWE Tower, all the offices are placed around

the outer perimeter of the floor, giving each space ample amounts of natural light

and a beautiful panoramic view of the city. The placement of these spaces not

only allows every office to be illuminated with natural light but is directly related to

the natural ventilation system the double-skin façade provides. The outer façade

Fig.3 Typical floor plan with meeting rooms.iv

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Fig.4 Façade detailvi Scale 1:10

1 ”fish-mouth” device 2 stainless-steel point fixings 3 50/120 aluminum façade post 4 airspace: external air corridor

diagonally ventilated.

5 inner face with thermally insulated double glazing

6 outer façade: 10mm toughened flint glass

7 fixing head for traveling cradle 8 horizontal ventilation slit with natural anodized aluminum air deflectors 9 4mm natural anodized perforated sheet aluminum lining (unperforated in adjoining bay.) 10 4mm natural anodized aluminum sheet (perforated in adjoining bay), pivoting upwards 11 walkway for cleaning and inspection 12 panel abutment; construction joint 13 aluminum section at edge of floor 14 floor convector 15 stove-enamelled, sheet metal multi- function ceiling unit, partially perforated 16 anti-glare fabric blind 17 reinforced concrete floor slab 18 aluminum-louvre sunscreen blind

stretches a full storey and is made of extra clear toughened glass, fixed to glass

mullions with eight bolts. Separated by 50cm, the inner façade, which reaches

from floor to ceiling, is finished with a Low-E coating.viii Fresh air enters the

double-skin through slits located at the bottom of the façade. As absorbed air

moves through the airspace, fresh air is ventilated to the interior. The warm air

absorbed rises and is released through another set of slits, located at the top of the

airspace. The inner façade not only prevents the warm air from entering the

space, but it also helps block solar heat, keeping the office cool in the summer. In

the winter, the space captures solar heat from the sun and is released to the room

by the opening of the inner glass wall. This sliding glass wall opens to

approximately 15cm, allowing fresh air to filter in, which can be controlled by the

individual.

Fig.5 Fresh air filters in through the lower “fish-mouth” and enters the interior space. Warm air rises and filtered out through the “fish-mouth located at the top of the airspace.vii

“Fish-mouth” Each office consists of a minimum of two bays of glazing with at least one operable

window. Fresh air that filters into the double-skin façade enters through an

innovative element called a “fish-mouth”. Used for the natural ventilation of the

office spaces, this convex shaped device consists of 15cm-wide slits and over

sheet metal deflectors above and below the slits. These devices are located at the

bottom and top of each bay. The tapered shape of the device maximizes the

admittance of natural light and improves the day lighting of the interior space by

20%.ix The outside air is absorbed by the “fish-mouth” and enters through the slits

at the bottom, as shown in Fig. 5. The over sheet metal deflector above the slits is

perforated for the air to flow through into the airspace. The speed of the air stream

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is adjusted as it goes through the device, making it slower or faster, depending on

the wind velocity outside. The air naturally moves up the airspace due to the “fish-

mouth” located above, which has perforations on the lower deflector instead of the

upper, and by convection hot air can be released through the device. The “fish-

mouth” with a perforated metal deflector on the upper side of the slits is located at

the bottom of the double-skin and occurs at every other bay specifically for the

intake of air. The layout is reversed at the top for the exhaust of air to ensure that

diagonal streaming of air occurs. (See Fig. 7). This laterally staggered layout and

the designation of intake and exhaust paths is important so as to avoid any stale

air from re-entering the airspace and is essential in avoiding the short-circuiting of

the air.xii

Fig.6 A view of the façade at night reveals the staggered layout of the perforated “fish-mouths”.x

The sheet metal deflector can be raised, which reveals a horizontal metal

foot-plate for maintenance. With a tool, the inner façade can fully open, giving

maintenance personnel access to the landing for the cleaning of the façade, when

necessary.xiii

Sunshading and Thermal Storage

Within the airspace, a set of 80mm-wide aluminum blinds are installed and are

electronically operable. The outer façade protects them from wind and rain and

the inner façade prevents them from transmitting heat into the room. The blinds

shield the space from the sun and glare, and assists in reflecting heat away. A set

of roller shades made of fire proof cloth are also installed along the inside of the

inner façade providing another means of shading.

Fig.7 Due to the staggered layout of the perforated deflectors, the air moves in a diagonal direction through the airspace.xi

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The efficient use of natural light through the clear façade minimizes the use of

electric light, which in turn, reduces the amount of heat gain in the space. As a

result, cooling loads are further reduced. The architects take advantage of the

thermal lag of the ceiling’s exposed concrete slab, using it for thermal storage.

The mass of the heat-storing structure absorbs extra heat emitted during the day

and radiates it back into the space at night through perforated holes in the ceiling

panel unit.

The ceiling panel unit consists of acoustical absorption, sprinkler heads,

loudspeakers and adjustable down-light fixtures as well as a radiant cooling

system. Cold water flows through pipes integrated into the unit providing a

mechanical cooling device system.

Hot water convectors are built in the floor by the window side for heating.

Fig.8 The entrance to the tower is sheltered by an array of photovoltaic louvers attached to a trellis.xiv

Photovoltaics Another environmental technology is used in the RWE Headquarters is

located at the entrance of the building. Above the entrance are a series of

photovoltaic louvers mounted on a trellis exhibiting the possibilities of this

technology. These power-generating cells provide shading for the entrance as

well as convert the sunlight directly into electricity. Although this is not very

effective during cloudy periods, it displays yet another technology concerning

sustainable systems.xv

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Environment control In the design of this ecological tower, the user is given a high level of control over

the environment. An electronic keypad next to the door jamb can be set by the

individual to regulate not only the temperature of the room, but also control over

the lighting, the electronically-operable blinds and ventilation louvers.

The building’s environment is also consistently regulated through computers

in the central administration room by sensors built into each room and on the

exterior of the building. This sensor sends the computer information about the

outside condition and of each individual space. Based on this information, it can

control the adjustment of sunshades and ventilators and activate the mechanical

ventilation system if required. For example, when wind speeds and rain become

too strong, an alarm will sound to warn individuals to shut their windows. When a

window is opened, the sensor responds to it and sends the information to the

computer, which gives instructions to turn off the convector of that specific room.

During days when the outer skin must be closed, the artificial air supply system

takes over which is installed on the 19th floor.

Sound control The outer façade and the “fish-mouths” are not only good insulators and ventilators

of natural air but are also effective in sound control. The outer façade keeps the

noise from the outside traffic from entering the interior spaces. The “fish-mouths”

do the same but in the vertical direction due to its unique shape. Partitioning glass

located at each office division obstruct sound in the horizontal direction.

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Energy Saving Status From the initial date in the use of the building, the energy efficiency of the building

has been monitored. The results of making the double-skin façade to naturally

ventilate the building have made this building more energy efficient in comparison

to a typical building type.

RWE consumes approximately 22% less energy than a typical tower.

The energy consumption for air-conditioning is calculated at approximately

50% less in comparison with single-glazed façades of standard Germany

buildings.

Cooling and heating consumption is approximately 30-35% less than other

typical buildings. For approximately 70% of the year, controlled natural ventilation is used.

The installed mechanical system is operated two times an hour at most, while

conventional buildings require ventilation four to six times hourly. Due to the double glazing and unique device used for the ventilation system, the

initial construction cost for the building exceeded that of the typical building type.

However, as a result of the energy efficiency of the building, the extra cost of the

façade is balanced out by the minimal running costs for the ventilation system.

The overall ratio of the construction cost and running cost of the RWE building will

continue to increase as the natural ventilation system is continually used. xvii

Fig.9 The RWE Towerxvi

The RWE Headquarters demonstrates a radical step towards ecological building

designs and the use sophisticated approaches to achieve this. The double-skin

façade and the design of the “fish-mouth” successfully filter in fresh air to the

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space as well as keeping the temperature at a comfortable level during all seasons

of the year. The double glazing allows the space to be naturally lit, reducing the

need for the use of artificial light. Although on an environmental standpoint high-

rises generally consume too much energy, this is a good example in bringing about

a solution to the ever-growing construction of this building type. The clever use of

the double-skin façade provides natural ventilation to the building and allows it to

capture a delicate transparency, blending it into the surrounding environment with

the use of clear glass. While a mechanical cooling and ventilation system had to

be installed, it proves that an ecological high-rise is possible, one that is both

efficient and appealing.

ii http://www.nsg.co.jp/spm/sm81~90/sm86_e_index.html iiii http://www.nsg.co.jp/spm/sm81~90/sm86_e_index.html iii Ingenhoven, Christoph. Hauptverwaltung RWE. Bauwelt, v.85, no.26-32, 8 July 1994, p.1486-1487. iv Pepchinski, Mary. RWE AG Hochhaus – Essen, Germany. Architectural Record, v.185, no.5-8, June 1997, p. 144-151 v http://www.nsg.co.jp/spm/sm81~90/sm86_e_index.html vi Company Headquarters Tower in Essen. Detail, v.37, no.3, p.355-362 vii Ingenhoven, Christoph. Hauptverwaltung RWE. Bauwelt, v.85, no.26-32, 8 July 1994, p.1486-1487. viii http://www.nsg.co.jp/spm/sm81~90/sm86_e_index.html ix Evans, Barry. Through the glass cylinder. Architect’s Journal, v.205, no.18-25, 15 May 1997, p.42-45 x Pepchinski, Mary. RWE AG Hochhaus – Essen, Germany. Architectural Record, v.185, no.5-8, June 1997, p. 144-151 xi http://www.nsg.co.jp/spm/sm81~90/sm86_e_index.html xii Company Headquarters Tower in Essen. Detail, v.37, no.3, p.355-362 xiii http://www.nsg.co.jp/spm/sm81~90/sm86_e_index.html xiv Pepchinski, Mary. RWE AG Hochhaus – Essen, Germany. Architectural Record, v.185, no.5-8, June 1997, p. 144-151 xv Company Headquarters Tower in Essen. Detail, v.37, no.3, p.355-362 xvi Pepchinski, Mary. RWE AG Hochhaus – Essen, Germany. Architectural Record, v.185, no.5-8, June 1997, p. 144-151 xvii http://www.nsg.co.jp/spm/sm81~90/sm86_e_index.html

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Bibliography

Company Headquarters Tower in Essen. Detail, v.37, no.3, March 1997, p.355-361

Evans, Barry. Through the glass cylinder. Architect’s Journal, v.205, no.18-25, 15 May 1997, p.42-45

http://www.fes.uwaterloo.ca/architecture/faculty_projects/terri/research.html

http://www.iclei.org/EFACTS/PHOTOVOL.HTM

http://www.nsg.co.jp/spm/sm81~90/sm86_e_index.html (RWE Tower—Glass Tower in Essen)

Ingenhoven, Christoph. Hauptverwaltung RWE in Essen. Bauwelt, v.85, no.26-32, 8 July 1994, p.1486-1487

Pearson, James. Delicate Essen. Architectural Record, v.202, no.1205-1210, July 1997, p.40-45

Pepchinski, Mary. RWE AG Hochhaus – Essen, Germany. Architectural Record, v.185, no.5-8, June 1997, p. 144-151