Baltic churches

DRAFT

HEATING AND INDOOR

CLIMATE IN NINE BALTIC

CHURCHES

Tor Broström

Joakim Hansson

Department of Building Conservation

Gotland University

Summary

Historic churches are an important part of the European cultural heritage. The buildings and their interiors; art objects, furniture, etc, are in themselves documents of our cultural heritage that must be preserved for coming generations. The indoor climate is a critical factor in conserving the building and the interiors, it must be controlled with respect to the conservation of materials while allowing for the use and appreciation of the building. The present report presents measurements of the indoor climate in nine historic churches in Estonia, Latvia and Sweden. The objective of this is to analyse and evaluate the indoor climate in each church with respect to conservation and to draw general conclusions that can be used to determine proper heating and climate control strategies for the future.

The report describes the indoor climate in each church with an analysis and recommendations. The results show that the intermittently heated church with background heating provides the most stable indoor climate. The indoor climate in the unheated churches is generally problematic with too high variations and levels of relative humidity.

DRAFT

2

Contents

Introduction 3

Lau Church 6

Öja Church 8

Väskinde Church 10

Kaarma St Paul’s and St Peter’s Church 12

Pöide St Mary’s Church 14

Valjala St Martins Church 16

Kandava Lutheran Church 18

Tukums St Trinity Lutheran Church 20

Dzirciema Lutheran Church 22

Conclusion 24

DRAFT

3

Introduction

Background Historical churches are an important part of the European cultural heritage. The building and its interiors; art objects, furniture, etc, are in themselves documents of our cultural heritage that must be preserved for coming generations. The indoor climate is a critical factor in conserving the building and interiors. An improper indoor microclimate will result in material damages to the building or it’s interiors. The indoor microclimate must be controlled with respect to the conservation of materials while at the same time allowing for the use and appreciation of the building and providing conditions for thermal comfort.

The medieval stone churches on the Baltic Sea Region have a common background in terms of architecture and construction. In modern times the buildings have been used very differently in the respective countries. In the old Soviet Union many churches were abandoned or used for other purposes. Presently we have a situation where some Swedish parishes no longer can afford to heat their churches. In the countries on the other side of the Baltic Sea, churches have been reopened and new heating systems will be reinstalled. An exchange of information would be beneficial to all parties. The churches that have been out of use clearly show the effects of no heating and poor maintenance whereas the Swedish experiences of heating churches certainly are applicable in other countries in the region.

The County Administration of Gotland organized seminars in Estonia 2002 and in Latvia 2003 about the problems of historic churches. The seminars showed that there are common problems and that there is a need for cooperation in seeking the solutions. At the seminars it was suggested that measurements should be made in order to compare and analyse the indoor climate in a number of historic churches in Estonia, Latvia and Sweden.

The Swedish churches are from Gotland, it is the churches in Lau, Öja and Väskinde. These churches have been in continuous use and they are generally in good condition. The measurements reflect the use of different heating strategies. The partners on Gotland have been Samfälligheten Gotlands kyrkor, the County Administration, the County Museum and Gotland University.

The Estonian Churches are all from the island of Saaremaa, an obvious choice from a Gotland perspective. The churches of Kaarma, Pöide och Valjala have been studied. These churches have no heating and there are severe moisture problems. The Estonian partners have been the National Heritage Board (Muinsuskaitseamet) represented by Anneli Randla och Kaire Tooming.

The Latvian Churches are from the Tukums region. The Regional museum in Tukums selected the churches from Kandava, Tukums och Dzirciema to reflect regional characteristics and different heating strategies. The partners in Latvia have been the Tukums Museum (Tukuma muzejs) through Agrita Ozola and the State Inspection for Heritage Protection (Latvijas Republikas Valsts kulturas piemineklu aizsardzibas inspecija) represented by Janis Asaris.

This project was initiated by the County Administration of Gotland, through Joakim Hansson. The technical part of the report was written by Tor Broström with the support of Gotland University. The project has been financed by SIDA, the Swedish National Heritage Board and the Swedish Department of Energy.

DRAFT

4

Objective The objective of this project is to:

- Measure and document the indoor climate in nine similar historic churches

- Analyse and evaluate the indoor climate with respect to conservation

- Draw general conclusions from the unheated churches that can be used in Swedish parishes that consider not heating their churches

- Draw general conclusions from different kind of heating strategies and systems that can be used for churches planning to install new heating systems.

- Identify the need and possible topics for continued studies

Theory The indoor climate in a church should provide reasonable comfort without causing damage to the building or its interiors. The main climate parameters that define comfort are air temperature, surface temperatures of walls, floors etc and air movements. The climate parameters in combination with clothing, level of activity, traditions and personal variations determine if we find the indoor climate comfortable or not. In northern Europe the temperatures during church services typically vary between 10 and 20 °C.

The wellbeing of materials in general is primarily governed by relative humidity (RH), secondly by temperature. We aim to provide a stable indoor climate with respect to the relative humidity. This means that both short and long-term variations should be limited and that extreme values should be avoided.

The heating of historic churches generally means that we have to find a compromise between requirements for thermal comfort and for conservation. Heating with respect to comfort only will cause an unsuitable climate for the materials. An appropriate heating strategy and technical solution should be determined for each individual building according to the following principles:

- Maintain a stable RH with respect to the climate history of the building.

- Avoid extreme values of RH.. RH should be in the interval 30-80%.

- If freezing is a problem, the temperature should be kept above 5°C.

- Avoid condensation on sensible surfaces.

- Minimize air movement and particle content.

The indoor climate is a result of the function of the building itself and different measures to control the climate. The building provides a climate shell separating the outdoor climate from the indoor climate. The function of the building is determined by air tightness, moisture transport, insulation and its ability to buffer heat and moisture.

The indoor climate can be controlled by heating, ventilation and, in exceptional cases, dehumidification. The major influence on the indoor climate is in most cases from heating.

DRAFT

5

Churches are heated continuously or intermittently, which has very different effects on the indoor climate. Heating affects not only temperature, but also relative humidity. Heating for comfort in the winter will give dangerously low RH. Conservation heating, i.e. low level heating, can be used to avoid too high relative humidity.

Method Within the limited scope of this project, it is not possible to make a comparative study of all relevant climate variables. The present work will focus on the variations of relative humidity in relation to conservation.

The measurements were made using Tinytag dataloggers1.

The sensors have the following specifications:

Temperature Relative Humidity

Resolution 0,01°C, <0,3%

Inaccuracy 0,45°C RH 3%

Time constant 25 min

Values for temperature and relative humidity were collected each hour. The datalogger was placed in a central and representative location in the church.

The results are displayed with common time graphs, giving a qualitative view of both short and long term variations. The variations are quantified by using minimum and maximum values. The standard deviation is the mean deviation from the average value for the whole period. A small standard deviation indicates a stable indoor climate. Particular events of certain interest are analyzed more closely.

1 www.intab.se

DRAFT

6

Lau Church

Background Lau church is located on the southeast part of Gotland. The church is constructed in limestone and was built in the 13th century. Since the 1950’s, this church has not been heated, with the exception of small electric fans. In spite of this, the church has been in continuous use, even in the wintertime.

Problems related to the indoor climate have been heavy condensation on the floors in the springtime and salt efflorescence on the walls.

Measurements The measurements were made in year 2002 from January to December. The datalogger was placed centrally in the church about 2 m above the floor. The results are shown in the graph 1 below. Average values and standard deviation are shown in table 1.

2002-01-01 2002-03-01 2002-05-01 2002-07-01 2002-09-01 2002-11-01 2003-01-01

0

10

20

30

40

50

60

70

80

90

100Lau

RH (%)Temperature (C)

Date

Graph 1 Relative Humidity and Temperature in Lau Church

DRAFT

7

Average Std Dev Max Min

Relative Humidity

69,9% 9,4% 100% 41%

Temperature 11,7°C 5,9°C 21°C -1°C

Table 1 Average values and standard deviations for Lau Church

Analysis The temperature varies seasonally with the outdoor temperature, typically there is a delay of about 1 month due to the thermal inertia of the building. The temperature span is from –1 °C to 21 °C. The relative humidity has no distinct seasonal variation. There are fairly rapid variations around an average value of about 70%. From January to April, the relative humidity drops from over 90% to around 40%. Intensive airing of the church over several weeks in May causes big and rapid oscillations in relative humidity. Over the year, the standard deviation of relative humidity is nearly 10 percentage points. This shows that an unheated church does not necessarily provide a stable relative humidity.

In the spring, the temperature and the relative humidity may have been affected by construction activities. Around Christmas time there has been some heating from electric fans and visitors.

There are two main problems with the indoor climate in this church. The first is the lack of comfort, this can only be solved by heating the church. The second problem is the variations in relative humidity. This causes a risk for damage on the wooden objects in the church and it may also accelerate the deterioration due to salt crystallization. The relative humidity can be stabilized by the use of conservation heating and controlled ventilation. (In 2004 a heating system for local intermittent heating was installed in the church.)

DRAFT

8

Öja Church

Background Öja church is located on the southern tip of Gotland. It is built in sandstone. The church is intermittently heated with a relatively high background temperature. There have been no problems reported in relation to the indoor climate other than that thermal comfort is limited.

Measurements The measurements were made from November 1993 through October 1994. The datalogger was placed in the middle of the church about 2,5 m above the floor. The results are shown in the graph 2 below. Average values and standard deviation is shown in table 2.

1993-11-01 1994-01-01 1994-03-01 1994-05-01 1994-07-01 1994-09-01 1994-11-010

10

20

30

40

50

60

70

80

90

100Öja

Realtive Humidity (%)Temperature (C)

Date

Graph 2 Relative Humidity and Temperature in Öja Church

DRAFT

9


Relative Humidity

64,7 3,8 76,4 54,3

Temperature 13,6 4,3 22,7 8,1

Table 2 Average values and standard deviations for Öja Church

Analysis The temperature varies over the year between 8 and 23 °C with an average of 13,6 °C. The background temperature is set to 10°C, when the church is used, the temperature is increased to around 15°C. Note that the measurements were made in the middle of the church, the pew temperature was around 3 °C higher. The relative humidity varies between 54 and 76%. The standard deviation of relative humidity is only 3,8 percentage points.

From a conservation point of view this is a good and exceptionally stable indoor climate, the variations of relative humidity are less than 10% both in the short and long term. This of course is due to the limited temperature span, with a rather high base temperature and relatively low temperatures for services.

Due to the relatively high average temperature, the energy cost is considerable. A lower background temperature would decrease energy consumption. The relative humidity would still be stable, but at a slightly higher level.

DRAFT

10

Väskinde Church

Background Väskinde church is located in the middle of Gotland, near the west coast. The walls are made of limestone. The church is intermittently heated with no heating in between services. There have been some problems with mould, but no other problems in relation to the indoor climate.

Measurements The measurements were made from November 1993 through October 1994. The datalogger was placed centrally in the church about 2 m above the floor. The results are shown in the graph 3 below. Average values and standard deviation are shown in table 3.

1993-12-01 1994-02-01 1994-04-01 1994-06-01 1994-08-01 1994-10-010

10

20

30

40

50

60

70

80

90

100Väskinde

Relative Humidity (%)Temperature (C)

Date

Graph 3 Relative Humidity and Temperature in Väskinde Church

DRAFT

11


Relative Humidity

66,6 7,6 83,0 47,4

Temperature 11,5 4,6 19,6 1,3

Table 3 Average values and standard deviations for Väskinde Church

Analysis Over the year, the temperature varies from 1 °C to 19,6°C with an average of 11,5°C. In the heating season, the temperature was raised around 10 °C from the base level when the church was used for services. In the pews, the temperature would be around 3 °C higher. The relative humidity had an annual variation from 47%, in the winter, to 83% in the summer. The standard deviation of the relative humidity was 7,6%, twice as much as Öja church, but less than Lau church.

Moderate background heating, for conservation, both in the winter and late summer would decrease the variations in the relative humidity both over the year and during the heating cycles in the winter.

DRAFT

12

Kaarma St Paul’s and St Peter’s Church

Introduction Kaarma St Paul's and St Peter's church is situated in the centre of Saaremaa. It was built as a single nave church on the second half of a 13th century. Soon the vaults of a church collapsed probably because of poor foundation or possible soil problems. The church was rebuilt again but without vaults. The church was vaulted again in the beginning of a 15th century. The church is still in use as a parish church. The church is unheated.

Measurements The measurements were made from November 2002 to October 2003. The datalogger was placed centrally in the church. The results are shown in the graph 4 below. Average values and standard deviation are shown in Table 4.

2002-11-01 2003-01-01 2003-03-01 2003-05-01 2003-07-01 2003-09-01-20

-10

0

10

20

30

40

50

60

70

80

90

100Kaarma


Date

Graph 4 Relative Humidity and Temperature in Kaarma Church

DRAFT

13


Relative

Humidity.

84,7 10,1 100 54%

Temperature 5,9 8,5 22 °C -11 °C

Table 4 Average values and standard deviations for Kaarmas Church

Analysis The indoor temperature varies seasonally with the outdoor temperature, the temperature span is quite big, from –11 °C to 21 °C. The humidity level is extremely high, with an average of nearly 85%. The relative humidity has no distinct seasonal variation but there are fairly rapid variations up to 30 percentage points. The standard deviation is 10 percentage points. Again, this shows that the unheated climate does not necessarily provide a stable relative humidity.

The main problem in this church is the constantly high level of humidity. In the summer time, this is likely to cause biological growth such as mould, algae etc. Wooden objects are at high risk due the strong variations in RH.

Measures to control moisture transport and leakage should be taken as a first step. Conservation heating and appropriate ventilation should reduce both the level and the variations of relative humidity.

DRAFT

14

2002-11-01 2003-01-01 2003-03-01 2003-05-01 2003-07-01 2003-09-01-20

-10

0

10

20

30

40

50

60

70

80

90

100

Date

Pöide St Mary’s Church

Introduction Pöide St Mary's church is situated at the eastern shore of Saaremaa. At first a small Romanesque two-bayed church was erected in the second quarter of the 13th century. Its walls form part of the body of the present church. Probably on the first half of the 14th century the church was enlarged by adding two bays on the eastern and western sides of the previous building and the walls were built higher. Later, apparently in the late Middle Ages the tower was added above the western bay. In 1940 lightning struck the tower and caused a fire. The church was roofed again 1958-1960. In the 1990s the conservation works started again. 1995-1998 the choir and the sacristy were conserved. The congregation of the church is very small and it is in use very seldom. The church is unheated.


Graph 5 Relative Humidity and Temperature in Pöide Church

DRAFT

15


Relative

humidity.

82,8 % 13,8 100 36 %

Temperature 6,2 °C 9,1 24,4 °C -11,7 °C

Table 5 Average values and standard deviations for Pöide Church

Analysis The indoor temperature varies with the outdoor temperature with a very big seasonal temperature span; from –11 °C to 24 °C. The humidity level is extremely high, with an average of nearly 83%. The relative humidity has no distinct seasonal variation but there are fairly rapid variations up to 50 percentage points. The standard deviation is 13 percentage points.

The main problem in this church is the constantly high level of humidity. This is likely to cause biodeterioration from mould, algae and insects. The extreme variation in relative humidity poses a high risk to wooden objects.

Measures to control moisture transport and leakage should be taken as a first step. Conservation heating and appropriate ventilation should reduce both the level and the variations of relative humidity.

DRAFT

16

2002-11-01 2003-01-01 2003-03-01 2003-05-01 2003-07-01 2003-09-01-20

-10

0

10

20

30

40

50

60

70

80

90

100Valjala

Date

Valjala St Martins Church

Introduction Valjala St Martin's church is situated in the centre of Saaremaa. At first a small chapel-like building was erected in 1230s. On the second half of a 13th century chapel was rebuilt into a parish church - a nave was added to the western side of it. Probably on the 17th century a tower was added on a top of a sanctuary on the southern side of a church. The church is still in use as a parish church. The church is unheated.

Measurements The measurements were made from November 2002 to October 2003. The datalogger was placed centrally in the church. The results are shown in the graph 6 below. Average values and standard deviation are shown in table 6.

Graph 6 Relative Humidity and Temperature in Valjala Church

DRAFT

17


Relative

Humidity.

86,6 % 9,8 100 58,8 %

Temperature 6,3 °C 8,6 23,4 °C -7,5 °C

Table 6 Average values and standard deviations for Valjala Church

Analysis Typically for the unheated church, the indoor temperature varies seasonally with the outdoor temperature. The temperature difference between summer and winter is quite large, the span is –7 °C to 24 °C. The humidity level is extremely high most of the year, with an average of more than 86 %. In relation to the other Estonian churches, the variations in relative humidity are considerably smaller providing a more stable indoor climate. The standard deviation is around 10 percentage points and the short-term variations are limited to 30 percentage points.

Again, the main problem in this church is the high level of humidity. Measures to control moisture transport and leakage should be taken as a first step. Conservation heating and appropriate ventilation should reduce both the level and the variations of relative humidity.

DRAFT

18

Kandava Lutheran Church

Introduction

The current stone church was finished in 1736. There are dark wooden sculptures from the 17th century, an altar painting from the middle of the 19th century and organ from 1864 and two lanterns from the 19th century. Two wood stoves situated near the altar heat the church. The church is heated from October to May; 2-3 hours on Saturdays and around 5 hours on Sundays. In summer time the floor and walls (~ 11,5 m in height) are sweating because of humidity.


2003-11-01 2004-01-01 2004-03-01 2004-05-01 2004-07-01 2004-09-01 2004-11-01-10

0

10

20

30

40

50

60

70

80

90

100


Date

Graph 7 Relative Humidity and Temperature in Kandava Church

DRAFT

19


Relativ

Humidity.

80,9 % 6,1 90,9 50,9 %

Temperature 8,7 °C 5,8 19,8 °C -3,5 °C

Table 7 Average values and standard deviations for Kandava Church

Analysis The temperature in between services varies seasonally with the outdoor temperature. The church seems to have none or very little heating when it is not being used. Intermittent heating typically raises the temperature by 7-9 °C in 5-6 hours. In the wintertime, the temperature at service will be less than 10 °C. The humidity level is high, with an average of more than 80 %. The humidity variations, both short term and long term, are less compared to the unheated churches described in the previous sections. The standard deviation is around 6,1 percentage points and the short-term variations are generally limited to 10-15 percentage points. One exception is the Easter holiday in April when the church is heated long enough to significantly reduce the relative humidity.

Even though comfort is limited in the wintertime, this church seems to have a reasonable indoor climate. It would be favourable to have some background heating in order to lower the general humidity level.

DRAFT

20

Tukums St Trinity Lutheran Church

Introduction The first stone church in Tukums dates to 1644. In 1788 and 1789 additions were made to the church. The current altar painting “Kristus pie krusta” (Christ on the Cross) was acquired in 1859 and in the 1935 town citizens presented four stained glass windows to the church. The church is intermittently heated every week.


2003-11-01 2004-01-01 2004-03-01 2004-05-01 2004-07-01 2004-09-01 2004-11-010

10

20

30

40

50

60

70

80

90

100 Tukums


Date

Graph 8 Relative Humidity and Temperature in Tukums Church

DRAFT

21


Relative

Humidity.

64,8 % 12,3 85,8 34,9 %

Temperature 13,8 °C 3,08 21,4 °C 8,0 °C

Table 8 Average values and standard deviations for Tukums Church

Analysis The church is kept at a basic temperature around 10 °C. Intermittent heating raises the temperature to somewhere between 16 and 20 °C. Heating time is typically between 4 and 6 hours in the winter time, the temperature at service will be less than 10 °C. The average humidity is much lower than the unheated churches. There is a strong seasonal variation with a difference of 40 percentage points between the winter and summer. The standard deviation is about the same as for the unheated churches; 12,3 percentage points. The short-term variations associated with intermittent heating are generally around 15-20 percentage points.

This church provides good thermal comfort most of the time. From a conservation point of view it would be better to decrease the background temperature in the winter in order to reduce the seasonal variation in relative humidity.

DRAFT

22

Dzirciema Lutheran Church

Introduction This stone church was built in 1879. This is one of the few churches in Latvia whose doors face north. The interior design dates to 1827 and it was transferred from the Livonian Castle Chapel in Ventspils. The famous woodcarver masters Nikolass Sefrens and Johans Mertens made the altar under pulpit and it was finished in 1711. Dzirciema church is unheated.


2003-11-01 2004-01-01 2004-03-01 2004-05-01 2004-07-01 2004-09-01 2004-11-01-10

0

10

20

30

40

50

60

70

80

90

100

Relative humidity (%)Temperature (C) Dzirciema

Date

Graph 9 Relative Humidity and Temperature in Dzirciema Church

DRAFT

23


Relative

Humidity.

84,5 % 6,9 100 58,8 %

Temperature 8,2 °C 6,7 20,2 °C -5,2 °C

Table 9 Average values and standard deviations for Dzirciema Church

Analysis The temperature varies seasonally with the outdoor temperature. The temperature span is from –5 °C to 20 °C. The humidity level is extremely high, with an average of more than 84 %. Through the cold season, the relative humidity is above 90% most of the time. With the exception of a few events, the variations in relative humidity are limited to 10-15 percentage points.. The standard deviation is 7 percentage points.

The main problem in this church is the high level of humidity. Moderate background heating and appropriate ventilation would decrease this problem.

DRAFT

24

Conclusion

The measurements are limited in scope and time. One should be careful not to draw too far reaching conclusions from the results. However there are some interesting observations that could lead to further investigations.

The measurements show that the indoor climates in the nine observed churches are quite different, but the differences can be explained and related to each other based on the history of use and heating strategy for each church.

The data obtained from the measurements can be used as a reference in future considerations about the heating and indoor climate in each separate church. As mentioned in the chapter Theory, the indoor climate history of the building serves as an important reference in determining the proper indoor climate for the future. In general, temperature and relative humidity should be monitored continuously in all churches to keep track of the present climate and to provide a document of the climate history. This will also provide a tool to conserve energy. The cost for monitoring is marginal in relation to the cost of conservation efforts, to repair damages, and the overall heating cost.

The table below gives a summary of the relative humidity variations in all observed churches. A specific analysis and comments for each church has been given in the previous sections. In order not to damage the building and the interiors, the relative humidity should be kept stable and one should avoid extremely high or low values. A simple, even though not complete, way to quantify the climate variations is to look at the standard deviation and the seasonal variation, i.e. the difference between the maximum and minimum value.

DRAFT

25

Type of heating

Average (%)

Std Dev (%)

Max (%) Min (%)

Lau None 69,9 9,4 100 41

Öja Intermittent 64,7 3,8 76,4 54,3

Väskinde Intermittent 66,6 7,6 83,0 47,4

Kaarma None 84,7 10,1 100 54

Pöide None 82,8 13,8 100 36

Valjala None 86,6 9,8 100 58,8

Kandava Intermittent 80,9 6,1 90,9 50,9

Tukums Intermittent 64,8 12,3 85,8 34,9

Dzirciema None 84,5 6,9 100 58,8

Table 10 Levels and variation of relative humidity in each of the nine churches

Clearly, the most stable indoor climate is provided in Öja church, where both the standard deviation and the seasonal variation are much lower than in the other churches. The relative humidity stays within an interval of 55 – 75% throughout the year. The heating in Öja is characterised by quick intermittent heating about every other week, moderate temperature during services and a relatively high background temperature. This requires high heating power and a high energy consumption, both of which are quite expensive.

The church of Tukums uses the same heating strategy as Öja church but the relative humidity is much less stable. This is due to higher temperature levels both during and between services and also more frequent use of the church.

The two churches with intermittent heating for services but no background heating, Väskinde and Kandava, provide an indoor climate less stable than that of Öja church but more stable than the unheated churches.

The natural, unheated, indoor climate of a church is sometimes presented as the ideal, optimal climate for conservation. However, in present study the unheated churches all have problematic indoor climates. There are considerable variations both in the long and short term and, with one exception, the levels are too high. This causes a risk for both biodeterioration and damages on wooden objects due to variations in relative humidity. The high levels of relative humidity may partly be explained by the fact that some of the churches have not been used or maintained

DRAFT

26

properly for a long period of time. With proper ventilation and conservation heating both the level and the variations can be decreased to a safe interval. Given that that the masonry constructions probably are saturated with moisture, this will take years.

The study gives some general information and advice for each church, but in order to better understand the indoor climate and the need for climate control in the specific case, one would have to make more extensive measurements.

The results indicate some relation between heating strategy. Most noteworthy is the relatively unstable indoor climate of the unheated churches. To learn more about this it would be valuable to study many churches with different heating strategies.

Documents

Baltic churches