Lawrence and Tomas visited Germany in April as part of our Technology Strategy Board (TSB) work, designing for future climates. We visited The Victoria House (also known as the ‘Great Pavilion’) at the Botanical Garden in Berlin which has recently undergone 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 facade and glazing system, new heating and ventilation, and the innovative application and installation of phase change materials (PCM).
Two approximately 12m high ‘PCM 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.
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, providing cool air to the plants. During the night the air at the top of the green house cools down. This air is 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.
Whilst in Germany, Lawrence and Tomas also attended the 16th International Passive House Conference in Hannover.
Notes from the study trip can be read below: