PCM Tower Botanical Garden Berlin Study Tour Notes

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Design for Future Climates Research Technology Strategy Board (TSB) Innovative PCM applications to limit overheating in buildings Study Tour, Germany April 2012 Notes

Gale & Snowden Architects & Engineers April 2012


Gale & Snowden Architects

Notes from PCM Applications, Study Tour, Germany

PCM Applications, Study Tour Germany, April 2012 Notes Prepared by:

Tomas Gaertner

Checked by:

David Gale

Project:

PassivOffice

Version:

1

Date:

April 2012

Job No:

B1113

Reference:

B1113 CCA Passive Office\Reports\PCM Applications Germany Study Tour Notes

Rev No

Comments

Date

Gale & Snowden Architects Ltd 18 Market Place Bideford Devon EX39 2DR T: 01237 474952 F: 01237 425449 www.ecodesign.co.uk Company No. 5632356 VAT Registration No. 655 9343 06

April 2012

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Gale & Snowden Architects

Notes from PCM Applications, Study Tour, Germany

1.0 Introduction The following details the findings and observations from the Gale & Snowden PCM Applications Study Tour to visit the ‘Great Pavilion’ in Berlin’s Botanical Gardens.

2.0 Details of the Victoria House/Great Pavillion 2.1 Introduction Building name: Victoria House, ‘Great Pavilion’ in Berlin’s Botanical Gardens Completed:

1906, refurbished in 2009

Floor area:

1750m², 60 m long, 29 m wide and 26.5 m high

Building type:

tropical green house

No of Floors:

2 including a basement

Figure 1: The Great Pavilion, Botanical Garden Berlin The Victoria House (also known as ‘the Great Pavilion’) at the Botanical Garden in Germany's capital Berlin is one of the largest greenhouses in the world. It was built in 1907, covers an area of about 1,750 m2 and has a capacity of 40,000m3. The average temperature inside is maintained at 30 °C and air humidity is kept high. Over a period of three years the building underwent a complete restoration (completed in 2009) in order to maintain the historical basic structure and to reduce energy requirements by 50%. Refurbishment work included a new façade and glazing system, new heating and ventilation and installation of ‘PCM towers’.

2.2 Key features The refurbishment of the building included an innovative application of phase change materials to control internal temperatures and to reduce energy demand for heating and cooling. Two approximately 12m high towers have been placed at either end of the green house. To blend in with the tropical plants they have been designed as hollow giant trees.

April 2012

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Gale & Snowden Architects

Notes from PCM Applications, Study Tour, Germany

Their purpose is to guarantee an optimal vertical temperature distribution in the greenhouse. The core of these towers is filled with aluminium panels containing a special PCM (in this case salt hydrates) operating at 25°C. A ‛phase-change material‛(PCM) is a substance with a high ‛heat of fusion‛ which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. PCMs, such as water, paraffin, salt hydrates, etc. are able to absorb, store and release large amounts of heat or cold at comparatively small temperature change by changing their physical state, as for example from solid to liquid, solid to solid or through evaporation of the storage material. The heat stored is called latent heat, therefore materials are also referred to as ‚LATENT HEAT STORAGE MATERIAL‛. The towers at the Great Pavilion store ‚heat‛ or ‚coolth‛ depending on the ambient air temperature. During the day the air at the roof of the greenhouse heats up due to solar gains. An extractor fan at the top of the tower pulls in the air and pushes it down the tower, past the PCM panels and down to the plants. On its way down heat is absorbed from the air and stored in the PCM, provided cool air to the plants. During the night the air at the top of the green house cools down. This air is again pulled in via the extractor fan, heated by the energy stored in the PCM material on the way down and supplied as warm air at plant level. According to the engineer involved with the development of the PCM panels, key to optimise the performance of the PCM is ventilation. The PCM needs to be exposed to adequate, constant air flow across its surface to effectively store and release energy. Where these materials are built into walls or ceilings (e.g. as an additive to plasters and plasterboard) the surrounding material (e.g. gypsum) and furniture/wall coverings provide a too high thermal insulation which reduces the effectiveness of the PCM. An ideal technical solution would be a combination with a fan driven ventilation system that controls the air flow across the PCM surface. Using containers with large surface to volume ratio, made of highly conductive material (e.g. aluminium) for the PCM further increases its potential to store and release heat.

Figure 2: Rubitherm PCM panel used at the Great Pavilion, Berlin (Photo: Rubitherm)

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Gale & Snowden Architects

Notes from PCM Applications, Study Tour, Germany

2.3 Technical Details (per tower) Manufacturer: Ventilation Volume: Pressure drop: Fan Power: Heat Storage capacity: PCM – mass:

Rubitherm GmbH 7,500 m³/h 50 Pa 1.1 kW 110 kWh / cycle (8 h/d) ca. 3000 kg

2.4 Monitoring Results

Figure 3:

Temperature monitoring ‘Victoria House’ (Source: Rubitherm GmbH) and schematic of cooling tower (the black line represents ambient air temperature at high level, red line represents air temperature at the top end of the towers, pink line indicates air temperature at the supply side at the bottom of the towers)

According to a monitoring study carried out by the manufacturer of the PCM panels the system effectively moderates ground level temperatures. As can be seen from figure 1, with the ventilation system to the towers switched off, the ambient air temperature at ground level follows the high level temperature but with a ~3 degree temperature difference. This difference is explained with the cooling effect from the ground, transpiration cooling from plants and the effect of heat rising. When the towers are ‘switched on’ internal temperatures at ground level are maintained at even temperature range of ~27 degree C throughout the day. The system appears to provide effective cooling via heat storage during the day and supplements the heating over night. The manufacturer confirmed that additional heating during night needs to be provided all year round. Rubitherm estimates that with this system operating on approximately 200 days per year (= 200 cycles) ca. 22,000 KWh of energy can be saved (equivalent to 5 tonnes of CO2).

2.5 Design for Future Climate (D4FC) Adaptations The ‘PCM towers’ at the Great Pavilion represent an innovative solution to moderate high daily temperature swings within buildings. This method could be applied to office buildings where high ‘non-useful’ internal heat gains during working hours could be stored providing a cooling effect.

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Gale & Snowden Architects

Notes from PCM Applications, Study Tour, Germany

Instead of simply removing the heat, the stored energy could be used during the heating season to maintain background heating when the building is not in use and thus contribute to reducing the energy demand of a system. If combined with a MVHR system that already forms part of most low energy office buildings, the effectiveness of the PCM could be optimised whilst at the same time providing a more cost effective solutions. Further investigations are required to establish how this methodology could be implemented into the design and services strategy of a modern office building and also how a retrofit solution might work.

2.6 Images

Figure 4: one of the PCM towers at the Graet Pavilion, Botanical Gardens Berlin

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Gale & Snowden Architects

Notes from PCM Applications, Study Tour, Germany

Figure 5: Supply opening at the bottom of the tower

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