Heating monumental churches : indoor climate and preservation of cultural heritage
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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.