INTERIORS 5 161 CATHEDRAL COMMUNICATIONS THE BUILDING CONSERVATION DIRECTORY 2025 On the left is a more commonly found humidifier which introduces humid air into the internal wind system of the instrument. On the right the humidifier introduces steam into an enclosure. vapour may condense on colder elements of the structure, such as lead pipes, forming water runnels which pool in the chest or soundboard, causing the corrosion and related damage discussed above. In some instances, local air conditioning is used within the organ space to counter the effects of an insubstantial building envelope or the effects of the heating. While this can be an effective system for controlling the microclimate (although it is inefficient in terms of energy usage), great care has to be taken with the supply of the conditioned air. It is best to avoid air that has been heated or cooled for the general organ space from being delivered directly into the open pipes, thus affecting the internal conditions of the instrument. At least one section of pipes in an organ (the swell) is contained within a box. In larger instruments the choir and solo divisions may also be enclosed in this way. The boxes usually have at least one louvered front which can be opened and closed by a foot pedal operated by the organist. This provides a musical ‘crescendo’ or ‘diminuendo’. When the organ is switched off, it is usual for these mechanisms to automatically open the louvres. In mechanical organs they can inadvertently be left closed, resulting in an insulated microclimate within the swell box. If the temperature in the building changes, when the box opens the reed pipes in particular can be subject to a thermal shock which can make them suddenly ‘fly’ off their notes, causing serious tuning issues. TARGET ENVIRONMENTAL CONDITIONS As we have seen, for optimal and stable performance, an organ needs to be housed in a building with a stable temperature and relative humidity, and to be tuned to the operating temperature of the building. If different sections of the organ are located in different parts of the building these will need to have similar environmental characteristics, or at least environmental stability, within which the different sections of the organ can be tuned. Both short-term and long-term instabilities in temperature and RH (in both the air surrounding the organ Mould inside an organ is caused by high levels of humidity. The effects of sourcing wind from the interior rather than the exterior (with no mechanical tempering in the system) can be substantial. and the wind within it) can cause temporary and permanent acoustic distortion, and physical deterioration. It is therefore important to understand the environmental characteristics of both the building environment and the space from which the wind is sourced. Factors that are then likely to be deleterious to the performance and conservation of the organ can be understood and controlled. A range of target environmental conditions are commonly quoted for optimal performance of organs in historic buildings, generally in the region of between 15°C–20°C and 50%–70% RH4. If a specific target is to be used the authors would recommend 18°C and 55% RH. In practical terms, achieving such conditions will depend very much on the specific building, its condition and patterns of heating and use within it, as well as ambient external seasonal conditions. Of similar importance to the actual value is environmental stability, as sudden and large changes in both temperature and RH can cause significant physical stress on sensitive parts of the organ, leading to deterioration. These target figures are only guides and it is important that other relevant factors, including the conservation of other sensitive artefacts, the comfort of those using the building and energy costs, are considered when setting control levels for a particular building. DISCUSSION Church organs do not deteriorate or lose their tuning without cause. In almost all cases, the changes which result in deterioration of materials or a loss of tuning are due to exposure to adverse environmental conditions. In some cases, these conditions are inevitable due simply to the way in which the building is constructed or used. However, in many cases, deleterious conditions are caused because of the way the building is managed, and a lack of understanding or awareness of the impact that the resultant microclimate might have on the organ. It is important, therefore, that those who are charged with the care of churches and cathedrals with organs understand the effects that the building environment organ and the cost, both in conservation and financial terms, resulting from the poor conditions. On a day-to-day basis, this may simply involve the way in which the building is maintained, the heating used, the church ventilated or even the way in which the organ is humidified. When a building is being refurbished or when a new heating system is being designed, changes in the environmental conditions can be considerable and the
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