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Hol Church solar retrofit (Norway)

Credits: ©2009 EcoBuildings

The Hol Church project in Norway uncovered big challenges that were met when dealing with a historic, protected buildings in Europe. As this building remained for decades and centuries, the challenge was to show how energy efficient solutions could be applied to a listed building under the authority of protective antiquarian wings; therefore no structural changes were allowed. To achieve energy need reductions in an existing buildings, AA restrictions (Antiquarian Authorities) had to be reconsidered when retrofitting installations, and innovative methods had to be applied in order to preserve this rich architectural heritage.

The Hol Church project shows that steadfastness and endurance coupled with innovation can lead to success


Hol Church Exterior

Renovation was centered around energy retrofits (insulation, air leaks and energy supply). An innovative energy supply was proposed: solar pre-heated air. ©2009 Brita in Pubs

The church, built in 1924, is located in a mountain valley in Norway's Southern part of the country; half way between Oslo and Bergen and only minutes from the popular winter ski resort Geilo. This church has a timber construction with steep roof indicating elements from the stave-church era. Its built on a stone foundation raising only slightly from the ground. It's extremely high interior of 20 metres equals the height of eight standard dwelling storeys, which is an energy challenge in itself since hot air rises and stay of comfort is hence a crucial element of this project. The un-insulated timber floor was not covering a full-scale cellar, only a crawl space with varying height up to one meter. The timber roof construction and walls were also un-insulated. Windows and doors were not closing properly, had no gaskets and were letting extremely cold draughts into the building. All this caused considerable comfort problems and the energy need was high. Regardless of the energy being used, it often felt cold when the outdoor temperature fell down to minus 20-30°C. No drawings of the church were made available to the project team. All studies, measurements and drawing plans needed had to be done on site. With the Antiquarian Authorities sitting 300 kilometres away in Oslo, and with low travelling budgets, proper communication really was a challenge.

Building constructions
After having received refusal from the Antiquarian Authorities (AA) for insulation works, appeals have led to compromises. The floor was insulated from below through the crawl space, which indeed was a difficult job. The details for the chosen insulation method were worked out with the AA to avoid dampness leading to rotting of the construction. A similar refusal/acceptance procedure was carried out for the flat part of the roof. Arguing that the existing ceiling, with a very dry sawdust covering, was a fire risk. Finally, the AA accepted that argument. The ceiling was insulated from above. This was also an extremely complicated work task, as bringing in materials could damage the church interior. Materials were instead crane-lifted into the building and through an upper window. The windows consist of two layers of glass with a 70 mm gap. The windows and doors were adjusted to close properly and they were equipped with rubber gaskets.

The existing heating system was a typical Norwegian one. Due to the huge hydropower production, electric resistance heating is common. The system has a total capacity of 70 kW and heaters are positioned under the benches. Due to the draughts, it took three days to reach a comfortable temperature in wintertime. This happened every time again with typical activities like approximately 21 services a year, 15 funerals, 5 weddings and 10 choir and other cultural events. The solar radiation normally gained passively through windows does not help either, since the church has only very small windows.

The heating solutions sought, can be split into three main categories:
-  Insulation reducing heat loss through the envelope, coupled with improved gaskets to avoid drafts from windows and doors. This has proven to be comfort level raise without it necessarily having a huge impact on energy need since the system before the retrofit was going full speed and still not managing to raise the comfort level to an acceptable level.
-  A vertical two metres high, 75 cm diameter round air canon of 4.200 m3/hour (drawing only 160 W) "shoots" unheated air upwards to replace the heated air under the ceiling. This process is normally started an hour before the service and it moves the warm air under the ceiling down to where people are seated. It has proven to be an efficient comfort measure that improves the feeling of comfort.
-  In this region of Norway, when it is cold, it is normally sunny and not windy. There is also a lot of white reflective snow in this region. That's why an air based solar thermal system has been selected.

Solar Thermal
An air based solar thermal system has been developed at a distance from the building. Since the AA has to approve everything within a radius of 65 metres of the church, this instalment was fully rejected, even through the appeal round. The only solution was to appeal to the Bishop, who has the authority to overrule the AA. The compromise was to reduce the height of the solar thermal system to 6 metres. Which also reduces the area and to increase the distance from the church to the absorber to 15 metres. The vertical system is connected to the church through an earthsheltered insulated duct bringing heated air to the church and sucking air from the church in a similar duct returning to the solar absorber. The air is moved through the solar absorber and from the absorber to the church by two small fans connected to a solar PV system that starts, stops and regulates air speed depending on how bright the sunshine is. It is in other words an autonomous and self-regulating system.

Solar PV
A minor solar PV system was initially planned. However, the confrontation with the restrictions from the AA have led to rethink this kind of solution for several reasons: The contribution per m2 is small compared to solar thermal which delivers 3-4 times more energy per m2 absorber at a lower cost. The cost of PV is high which leads to a high payback time (90 years). The AA would probably not allow the system to be implemented unless it was located at a minimum of 65 metres from the church wall. A final decision about this issue is now being taken.

Since the church has a very simple energy system, a complicated Building Energy Management System (BEMS) was not necessary to control the heating systems. Instead, a close dialogue, analysis and discussions with the caretaker has proved to be valuable in taking measures, checking routines and improving routines while continuously supporting the caretaker. It was the underlaying philosophy for this project. To assure optimum control of the building and thus save energy, a continuous process of dialogue between the planners and the caretaker has proved to be fruitful. This even resulted in a considerable awareness level that in itself turned out to lower energy bills. In order to bridge the huge distance between the caretaker's home and the church (25 km) an automated "Ring the church warm" system has been installed. Before, the caretaker always had to drive to the church each time to turn the heat on, days before a major church activity took place. Or when the caretaker stayed elsewhere, the heat was turned on even some days before. By installing the new "Ring the church warm" system, this was no longer necessary. It saved not only valuable heating days, but also reduced the energy consumption caused by the trips to and from the church, 51 times a year. Additional energy savings: 51 trips x 25 km x 2 = 2550 km, means annual petrol energy saving of approximately 255 litres and CO2 emissions of half a ton (500 kilos) a year.

User survey
A user survey under the regular Sunday church service visitors during the winter of 2006/2007 illustrated the increased comfort level: "Have you noticed improvements in the indoor climate since last winter as regards draught, temperature etc."
- Much better 55%
- A little better 35%
- No improvement 10%

Energy data and addistional results
These are the assumed savings calculated at the project initialisation phase (see website for energy saving table)

Assumed energy costs used for the payback calculation: E
lectricity: 0,15 Euro/kWh (1,20 NOK/kWh)

Measurements and evaluation:
All costs for the energy savings measures are within and some below budget. Although the final bills have not been received as yet it is clear that there will not be a cost overrun. Measurements were started 1 May 2007 and data are being registered every month. The one year monitoring result will hence be available immediately as the last month, April 2008, is ending.

First hand experiences
-  Existing, listed buildings are part of an architectural heritage that is well protected by the state through Antiquarian Authorities. They have an important job at protecting the valuable listed buildings and groups of buildings. This important job often is in conflict with the equally important job of reducing the energy need in existing buildings.
-  The processes described above are time- and resource demanding. One should be prepared for several rounds before an approval is possible - if ever.
-  In this instance, had it not been for the Bishop overruling the AA, there would have been no solar thermal system.
-  A motivated client and a motivated caretaker is a crucial element towards success.
-  Awareness building with the caretaker is showing positive energy need reducing results.
-  As the project developed the local energy utility Ustekveikja decided, contrary to our predictions, that the cost of electricity shall fall instead of rise. Whilst the electricity costs in Norway have risen over the last years and is now in the region of our predictions that is being used for our payback period calculations, Ustekveikja have reduced the costs of electricity down to between 1/2 to 1/3 of the average market price in the winter, for the inhabitants in the region as a gesture to them. Through this, Ustekveikja argues that the inhabitants in this way get their share of the valuable local hydropower plants. This undermines energy efficiency measures and the introduction of renewables as the savings are reduced and payback time increases. It is also contrary to the trends in all other parts of Europe and in Norway.
-  PV (solar electricity) is normally more costly per m2 installed modules compared to solar thermal. One m2 PV also delivers only 1/3 of the energy delivered by the same m2 solar thermal. PV payback time is so long that it brings up the overall payback time for the total building project to an unnecessary high level.