Our Lord in the Attic: A Case Study

Visitor impact on the indoor climate

Sinterklaas 2007 (photo: museum Our Lord in the Attic)enlarge

Sinterklaas festival in the church in 2007.

Sinterklaas, the patron Saint of the church, visits the museum annually. This lively event attracts a crowd of children and their parents.

donwload Climate data canal room (XLS, 1.2 MB)

donwload Climate data sael (XLS, 1.2MB)

donwload Climate data in church (XLS, 2.0MB)

c Outdoor climate data (XLS, 1.1 MB)

Infrared thermographs of visitors in a museum (photo: B. Ankersmit)As the church in the museum is still in active use, there are times when the church may be filled to its maximum capacity, as set by the fire brigade. In addition, the museum participates in several events that bring much higher number of visitors through the building in one day than normal. It is interesting to analyze the effect that visitors have on the indoor climate during these events, which attract large numbers of visitors for both shorter and slightly longer durations. The following table represents the rate at which a human gives off moisture in different states of activity (after ASHRAE 2001).

Degree of Activity Moisture Generation (g hr-1)
Seated in the theater 30
Seated in the theater, night 35
Seated, very light work 45
Moderately active office work 55
Standing, light work 55
Walking, standing 70
Sedentary work 80
Light bench work 140
Moderate dancing 160
Walking 4.8 km/h; Light machine work 185

T, RH and AH plots in the church (God lamp low), sael, canal room and reception on Open Monument Day, September 9, 2005:

Monument Day T plot

T plot

Monument Day RH plot

RH plot

Monument Day AH plot

AH plot

The effect of high visitation events: Open Monument Day

Dutch 'Open Monumenten Dag' logoOpen Monumentendag (Open Monument Day) is designed to bring people into contact with the historic environment, and to encourage interest in and understanding of historical monuments and the need for their preservation. During the Open Monumentendag - every second weekend of September - thousands of historical buildings and sites (about 4,000) are open to the public free of charge. Besides opening their doors, many locations also organize on-site activities like exhibitions, music and guided tours. Each year around 80 to 85 percent of Dutch municipalities participate in the Open Monumentendag, organized by local committees. In recent years around 900,000 visitors have participated annually, making the Open Monumentendag one of the Netherlands' premier cultural events.

An extraordinarily high number of visitors (1,064) was recorded at museum ‘Our Lord in the Attic’ on Open Monument Day on September 9, 2005. Visitors entered the museum over a four-hour period, between 13:00 and 17:00.

The impact of visitors on the indoor climate was easily recognizable in temperature (T), relative humidity (RH) and absolute humidity/humidity ratio (AH) plots. Except in the reception area (the antechamber), temperature increases were observed starting at 13:00 in all parts of the building, with the largest increase (approximately 2.5°C) in the church and the least (0.5°C) in sael. The reception’s temperature drop during this period is probably due to the front door being opened continuously and the cooler outside air entering the room. Temperatures in the building returned to normal before midnight.

Both relative humidity and the humidity ratio increased significantly over the four-hour period in all rooms, including the reception. Surprisingly, the largest increase of relative humidity (from 60 to 77%) was observed in the space behind the altar. The smallest increase was observed in the sael. Relative humidity values throughout the building returned to normal by midnight.

Museum night T/RH

T and RH plot in the church on Museum Night, November5/6, 2005

Museum night AH plot

AH plot in the church, sael, and outside on Museum Night, November5/6, 2005.

The effect of high visitation events: Museum Night

Museum night posterMuseum Night is an initiative with which many museums in Amsterdam try to attract a different and younger audience - one November night per year they open to visitors from 19.00 to 2.00. In 2005, 2,300 visitors entered museum ‘Our Lord in the Attic’ over a seven-hour period from 19:00 on November 5 to 2:00 on November 6.

In 2006, the event was more controlled and 1500-1600 people visited the museum, with a maximum of 90 people in the church at any given time.

The temperature was approximately 20.2 °C when the event started and increased 3 °C to 23.2 °C by midnight, remaining at that temperature until the end of the event the next day. A large temperature decrease began after 3:00, and returned to the original value by 6:00.

The relative humidity was approximately 50% at the beginning of the event, then quickly increased and produced three peaks: 54% at 23:00, 58% at 1:00, and 56% at 2:00, the end of the event. Then, it reduced to 53% by 4:00, but rose to 54% where it remained until 09:00, the regular opening hour. The increase in the early morning hours may have been due to the fact that it was rainy outside, expressed by the relative humidity increase outside from 55 to 95% during the same period.

24-Hour variations of the humidity ratios in the church, sael, and outside during Museum Night were plotted. Three large peaks identified in the relative humidity plot were reduced to small saw tooth-like peaks in the plot of the humidity ratio.  This indicates that the rate of visitation was steady throughout the event. The increase of humidity ratio was approximately 3.5 g of water per kg of air during the specified period. This was smaller than the increase recorded during Open Monument Day when the museum had about 1,100 visitors over a 4-hour period. This could probably be due to the infiltration of outside air of lower humidity ratio into the church. The humidity ratio in sael was very similar to that of the church during the event.  This high level of humidity ratio is due to low infiltration of dry outside air into sael.

Wedding day (21 May 2005) AH plot

AH plot in the church, sael, canal room and outside on May 21, 2005.


The effect of short events: spring wedding

Wedding 5/5/1962On May 21st, 2005, the church was used for a wedding. At 13:00 the museum closed briefly for normal visitation to accommodate the wedding, which started at 14:30 and finished by 15:30. A total of 110 persons gathered in the Church, according to records kept by museum staff.

24-Hour variations of humidity ratios in the church, canal room, sael and outside air on May 21st, 2005 were plotted. Between midnight and 09:00, the museum’s opening hour, the humidity ratio was constant at 8 g/kg throughout the building. At 09:00, visitors began to enter the museum. Evidence of the visitors’ presence can be noted as the humidity ratios in various locations in the building increase. When the wedding attendees started to enter the church soon after 13:00, the church’s humidity ratio was at 8 g/kg, which was the same as outside. Initially the humidity ratio in the church exponentially increased; however, the increase soon reduced to linear, then plateaued at 10 g/kg by 15:30, indicating that the attendees started to leave. 

While the church air had a significant increase in humidity ratio, both the canal room and sael were only slightly affected, mainly by the attendee traffic near these spaces - the guests did not physically enter these rooms during the event. After all the wedding attendees left the building, museum visitors were allowed back into the building at 15:30. Museum visitors gradually exited the museum around 17:00 and the humidity ratios of all spaces dissipated towards that of outside. All spaces equilibrated at 8.2 g/kg in 5 hours by 22:00.

During the wedding, the temperature and relative humidity increased from 20.9 °C to 22.6 °C and 54% to 60%, respectively. Relative humidity returned to 54%, a normal value without visitors, within two hours after the event.

Mass Dec. 4, 2005, T and RH plot

T and RH plots in the church (God Lamp (low)) on December 4, 2005.


Mass Dec. 4, 2005, AH plot

AH plot in the church, sael, canal room and outside on December 4, 2005.

The effect of short events: special church mass in winter

Mass, date unknownAccording to museum records, a group of 151 artists attended a special mass on December 4th, 2005. The mass started at noon and lasted for one hour. 24-Hour variations of relative humidity and temperature recorded on December 4th, 2005.

The temperature was stable at 19°C until the museum opened at 9:00 and had a low increase at the rate of 0.3 °C/hour to 20 °C by noon. Then during the mass, the rate increased to 3.0 °C/hour during the first 30 minutes, and 2.0 °C/hour to 22.8 °C in the second 30 minutes.

Relative humidity showed a similar trend, with a 3.3% increase from morning visitors. Attendance at the mass produced an approximate 3.5% increase to a peak of 52% at 12:30.  However, the value dropped slightly during the next half hour due to heat produced by the attendees. Both the temperature and relative humidity peaks quickly dissipated after the mass ended. And by 17:00, both values returned to normal.

During the event, the humidity ratio increased approximately 4 g/kg. This increase quickly dissipated after mass had ended. Within three hours the humidity ratio returned to its pre-mass level. The values in the church, located at the highest point in the building, were approximately 0.7g/kg higher than that of the sael, the lowest situated room, during non-visiting hours. Museum visitors increased the humidity ratio in the church more than in other parts of the building. And by noon, the difference was nearly 1.8 g/kg. Although a peak relative humidity was recorded at 12:30, the peak value of humidity ratio in church was at 13:00, the same time as the peak temperature measurement. Morning visitors produced a humidity ratio rate of 1 g/kg/hr until 12:00. During the mass, the rate increased to approximately 1.5 g/kg/hr during the first 30 minutes, then dropped to 0.3 g/kg/hr during the second 30 minutes. This reduction may be due to the automatic operation of humidifiers/dehumidifiers, the infiltration of outside dry air, or a combination of the two.

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