GROUND SOURCE HEAT PUMPS IN CHURCHES
Ground source heating
Ground source heat pumps are very rarely recommended for heating up churches. Retrofitting the heating system for ground source heating in a way that ensures that the church can be heated satisfactorily is usually very difficult and very expensive.
Periodically heated churches
A heating system in a church that is heated only periodically must have a considerably higher output than other buildings of the same size. This is because the Ministry of Ecclesiastical Affairs’ Heating Circular requires that the church can be heated from 6° C to 18° C in just 6 hours. An underscaled heating system extends the heating time thus increasing energy consumption. The risk of damages to the church's furnishings and décor also increases.
Heating a church using a ground source heat pump, typically requires an output of 30 to 80 kW, depending on the church's size and condition. The heating system must also be dimensioned to provide this output at a relatively low flow temperature, usually around 55° C. This requires many large radiators and convectors, which can be difficult to find room for in a church building.
Ground source heat pumps as partial solution for churches with base heat
Some periodically heated churches have a base heat, typically at 8˚C, which is the temperature prescribed by the Ministry of Ecclesiastical Affairs’ Heating Circular. Some churches, however, have a higher base temperature - and correspondingly higher energy consumption. Base heating typically accounts for 20-40% of the total energy consumption in the church. A small ground source heat pump, installed in combination with the existing heating system, could provide this base heating. This may be especially relevant if the church is heated by oil or gas, and if the conditions for installing a ground source heat pump are present.
Permanently heated churches
A permanently heated church needs relatively less heat output compared to a periodically heated church of the same size, but it still needs a large heating system compared to other buildings. Furthermore, permanently heated churches are often larger churches, which requires correspondingly larger heating systems. The output should normally be 65 to 70 kW for a permanently heated church with a volume of about 2,000 cubic meters.
In many of the largest churches, the heating distribution system is often considerably underscaled. This requires a very high flow temperature (70-80 ˚C), in order to raise the temperature inside the church within a reasonable timespan. This is not possible using a ground source heat pump.
In small permanently heated churches ground source heat pumps can sometimes be a solution, but it requires (among other things) an area in close vicinity of the church, which is suitable for placing water tubes. At the same time the heating distribution system (radiators or calorifiers) must be reasonably well-dimensioned.
Water tubes (ground collectors)
A ground source heat pump requires a reasonably sized ground area for burying the water tubes. The general rule is about 50 m of water tubes corresponding to 60 - 70 m2 land per installed kW heat pump. The recommended tube length also depends on the soil conditions.
Water tubes may not be buried in a cemetery, so an appropriate area available outside the cemetery is needed. Please note that the local museum must be notified before starting any digging work in the cemetery of a medieval church. There are likely remains of archaeological or historical interest close to the church. If the museum wants to make excavations, this will delay and increase the cost of the project.
Before the establishment of a ground source heat pump a permission from the municipality is always required.
An annual inspection is mandatory.
Typically, the annual heating bill is reduced by 50% or more using a ground source heat pump instead of an older oil-fired boiler. The payback time is typically about 10 years, but can vary between 5 and 15 years depending on local conditions.
Savings are only achieved if the ground source heat pump is properly dimensioned (following the recommendations of the Ministry of Ecclesiastical Affairs’ Heating Circular).
A ground source heat pump of 35 kW was installed instead of an older oil-fired boiler of 65 kW in a periodically heated church with a volume of 1,200 cubic meters. The Parish Council expected savings of about 50%, but it turned out that hardly any savings were achieved. The investment of approximately 500.000 kr. could not pay for itself.
The reason was, that the church is now more difficult to heat up and practice around heating the church has therefore changed. Previously, the church had no base heat, but now there must be a base temperature of about 12° C, otherwise it takes up to two days (and sometimes more) to heat the church to a comfortable temperature. The problems obtaining a satisfactory temperature in the church is partly due to the ground source heat pump being significantly underpowered. Also, the radiator system was not replaced and was dimensioned for a high flow temperature, which a ground source heat pump cannot deliver.
The church's total energy consumption increased by 80 to 100% due to the need for base heat. So even though the heat is produced cheaply, effectively and environmentally sustainably with a ground source heat pump compared with the old oil-fired boiler, no real savings were achieved.
Read more (in Danish):
List of heat pumps: http://sparenergi.dk/forbruger/vaerktoejer/varmepumpelisten
The heat pump system: www.vp-ordning.dk
The Ministry of Ecclesiastical Affairs’ Heating Circular: https://www.retsinformation.dk/Forms/R0710.aspx?id=72628