Heating monumental churches : indoor climate and preservation of cultural heritage

The structure of old monumental churches differs a lot from contemporary buildings. The structural materials were wood, bricks and stone. In order to construct high buildings with huge spans, thick massive walls and many massive columns were needed. Originally these buildings had no heating and for centuries the indoor climate of these buildings was mainly determined by the outdoor climate. Because of the massive walls, the large indoor air volume, the relatively small windows and most often relatively limited natural ventilation, the indoor climate was much more stable than the outdoor climate. There was hardly a difference between the day and night temperature. In summer the indoor air climate was cool compared to outdoors, in winter indoor conditions were warmer. As a consequence of the large heat and moisture capacity the indoor air and surface temperatures and the indoor air and surface humidity led to a reasonably even climate under our external climate conditions. The monumental interior of this kind of building stood up to the climate elements for centuries. Apparently the indoor climate in this kind of building was not very unfavorable to the monumental interior. In a large number of these buildings heating systems were installed, varying from warm air heating to floor heating, (infrared) radiant heating, radiator panel and convector heating, local and pew heating. From literature there is evidence that severe winters, like the winter of 1962 to 1963 in Western Europe, caused serious damage to church organs and other valuable church interior parts (Knol 1971). Further research showed that these were no isolated cases. Long periods of very low relative humidity, characteristic of the combination of heating and severe frost, appear to be correlated to damage to church organs and other parts of church interiors. Literature documents damage to pulpits, altars, wainscoting, and paintings like wall, ceiling and panel paintings. In the nineteen sixties and seventies the progressive understanding of these phenomena gave the insight to limit the unrestricted use of heating systems in churches. Due to rapid changes in society the demands of the churchgoers changed in the last decades. As a consequence of the high thermal comfort in modern day buildings, this was also required in churches. Another major change was attending the services without winter coats due to the use of cars by churchgoers. A heating system in the church had to compensate for the evident lack of thermal comfort. In the last 30 years church going decreased dramatically in a major part of Western Europe. Church buildings therefore had to be used for alternative purposes in order to provide for extra financial income. In the Netherlands, monumental churches are nowadays used for concerts and other musical events, exhibitions, dinners, examinations and several other events. People are dressed appropriately for these events, e.g. evening dress, but not in accordance with the indoor climate in a church.Thus, nowadays, the original use of the church is changing. Where a lot of churches are in need of a major restoration or renovation, adapting the heating system becomes an important point of study. In this study a distinction was made between the most important heating systems in the Netherlands and abroad. Making use of a literature study, laboratory research and several case studies in Dutch churches, common patterns and relations between typical church heating systems and their effects on the deterioration of monumental churches were identified. Drying out of the monumental wooden furniture, like organs, altars and other organic materials and the related shrinkage and damage to the materials under cold winter conditions; Surface condensation due to low surface temperatures on walls and stained and protective glazing, in combination with high air humidity due to excessive moisture sources like open-air infrared gas heating; Indirectly related problems are contamination due to pollution sources like soot from candles in relation to relatively large airflows, e.g. generated by floor heating; Related building physical aspects of church heating are annual energy consumption and thermal comfort problems due to relatively large airflows and low surface temperatures of walls and glazing. Performance requirements for church heating systems with respect to preservation, energy requirements, thermal comfort and aesthetics were formulated. When performance requirements are known, prognoses have to be made for the most suitable design of a heating system in a particular monumental church. Simulation models and tools and their application for monumental churches were proposed. Furthermore the church characteristic input for these models was determined. A final check is the measurement in situ to evaluate and to prove that the heating system meets the performance criteria. Methods of measurement and some new ways to interpret them are proposed. For the choice and design of a heating system advantages and drawbacks of different systems are summarized. Finally a checklist to structure the choice and design of a heating system is included.