Our Lord in the Attic: A Case Study

Historic indoor climate


Infra Red thermograph of the facade (photo: TU/e)enlarge

Infra Red photo of the facade.

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Launch image viewer of climate installations

History of heating in the building

Stove in the canal room (photo: TU/e)The building is built in such a way that has limited insulation properties. The walls are relatively thin, there are large windows and the roof structure is fairly open. The outdoor climate has therefore an almost immediate affect on the indoor climate. In summer, the sun rapidly heats up the building on the front (south-east facing facade) and the roof, and the top floors become quite warm. In winter, without heating, the temperatures would have normally dropped to uncomfortable levels.

In the past, localized heating with peat, wood or coal fires and stoves would have been used to provide human comfort. In the church, heating for human comfort was done with small wooden stoves, containing an earthenware container for glowing peat, which the church goers would carry with them. Peat was stored on the first gallery, behind the altar.


First central heating in church (photo: TU/e)It is known that in 1938 some form of central heating was installed in the building. It remains unclear exactly in which rooms it was installed and what it may have looked like, but it is recorded that the generated heat was comfortable throughout the building. This system was later replaced, but the now inactive heating at the bottom of the fixed benches for dignitaries in the church may date back to this period.

From 1954-1960 the museum was restored and the entire building was fitted with central heating. The museum is nowadays heated by means of 2 gas stoves and a central heating system (current indoor climate).

Psychometric data of the outdoor climate in the Netherlands in the 20th Century:

Psychometric data of the outdoor climate in the Netherlands in the 20th Centuryenlarge
Psychometric data of the outdoor climate in the Netherlands in the 20th Centuryenlarge
Box plot legendenlarge

Legend for the box plots.

Box plot of outdoor T and RH (PDF, 118 KB)

Historic outdoor climate

The historic indoor climate was modeled using existing historic data of outdoor climatic conditions in the Netherlands. 20th Century data was downloaded from the KNMI web site (Royal Dutch Meteorological Institute). The daily average temperature and humidity data were derived from existing data from two locations; De Bilt (just outside the city of Utrecht more or less in the middle of the country) for the period 1901-1950 and Schiphol (Amsterdam airport) for the period 1951-2000. It is assumed that the climatic conditions in Amsterdam were similar to Utrecht and Schiphol, since they are only 45 and 15 km apart respectively. The relative humidity is almost always higher than 60% and temperatures vary from –10 to 25 °C.

This data was then put in the psychometric chart - data points in blue represent October-May and the red data June-September. As there is overlap between summer and winter-designated points and in order to enhance visually distinction between the 2 seasons, the first chart shows winter points atop those of summer and the second chart shows the summer points atop those of winter.

Another way to represent the data is the use of box plots, which show the average seasonal changes of temperature and relative humidity. From these it can be seen that the monthly average outdoor temperature values during the 20th century range from 2 °C in January to 16 °C in July. The data within the 80% limit of the box plot are more or less similar throughout the year, with a slightly larger spread in winter. The monthly average outdoor RH values range from 75% in May and June to 90% in December and January. An interesting aspect of the data within the 80% limit of the box plot is that the monthly RH variations in winter (i.e. October through February) are smaller (between 75% and 95%) than the variations observed in summer (between 60% and 90% in April through September).

In order to estimate the most extreme indoor climate conditions, the most extreme situations outdoors, i.e. coldest winter, hottest summer, most humid summer and driest winter that occurred in this century were identified. The coldest winter occurred in 1963, the hottest summer in 1947, 1965 was the most humid summer, and 1964 turned out to be the driest winter.

  Coldest winter
Hottest summer
Most humid
summer (1965)
Driest winter
  T °C
T °C
T °C
T °C
Max 1.3 1.3 24.6 26.1 97.0 94.0 93.0 95.0
Mean -5.0 -5.0 18.8 19.8 82.5 79.3 82.3 78.9
Min -10.2 -10.2 12.2 15.5 69.0 67.0 62.0 59.0
SD 3.60 3.60 3.50 2.59 5.50 5.91 8.26 11.77

Average (mean), maximum, minimum and standard deviation (SD) of the most extreme seasons.

From this table it can be seen that the average lowest outdoor mean temperature was –5 T °C and that it was not dryer than approximately 80% RH. The hottest months had an average temperature just below 20 T °C with an RH of around 80% for prolonged periods of time. These average values were used to establish the historic indoor climate in museum ‘Our Lord in the Attic’.


Historic indoor climate

Before the indoor temperature and relative humidity was estimated, several relevant parameters had to be defined:

1. How much air leaked into or out of the building?
The current air exchange rates of the building were measured by Technical University Eindhoven (TU/e) and it is assumed that these were similar in the past; the air exchange rate in winter would have been lower than in summer, when windows were opened for human comfort. For this reconstruction of the historic indoor climate, the air exchange rate is estimated in winter to have been around 1 to 1.5 air exchanges per hour, while during summer it would have increased to 2 to 3 times per hour.

2. What was the temperature of the air inside the building in winter and summer?
The building would have heated up during summer by the radiation of the sun. The outside air that entered the building would have also been heated to a certain extent. Measurements from the summer of 2005 show that indoor air temperatures never dropped below 17.5 °C. In winter, the building was (or some rooms were) heated to provide human comfort. The heating systems changed over the years from localized heating with fire places and stoves to central heating the 20th Century.

3. Were there any sources of moisture in the building that may have influenced the humidity ratio indoors?
Even though the building was both a church and house, it is assumed that the amount of moisture released by human activity from the period 1901–1990 can be ignored. After 1990 humidification and dehumidification were implemented using local (de)humidifiers to create better environmental conditions for the preservation of objects.

Three different indoor climate periods can therefore be distinguished:

© J. Paul Getty Trust / Netherlands Institute for Cultural Heritage / Museum Ons' Lieve Heer op Solder