Building - Sgoil Chrois
Our building was the former Cross Primary School, constructed in 1879. The school closed in 2011 and it was then that Comunn Eachdraidh Nis (CEN) took ownership of the building.
This building was redeveloped in 2019 to become an innovative and welcoming community hub with many community groups using it regularly for gatherings and events.
Public buildings of this era are notoriously costly to run. The renewable heating system is an integral part of the wider redevelopment of the centre. It aims to make the building as energy efficient and as cheap to run as possible, as well as increasing comfort levels for users.
The system incorporates underfloor heating and solar photovoltaic array in order to make the overall system as efficient as possible. Insulation and double glazing were also included within the main project works. The photovoltaic array is also now linked to an energy store that runs an immerser that powers some of the hot water demand for the building.
The evaporator, located at the rear of our building, collects energy from the air and feeds it via the refrigeration pipe to the heat pump or condenser.
OCHSNER heat pumps are manufactured exclusively in Austria where they regularly work in temperatures of -20⁰. Today, the company is recognised as one of the sector’s international technology leaders.
This heat pump is 400% efficient, given that every kw of electricity used yields 4kw of heat.
The condenser feeds the buffer tank which stores the energy from the heat pump typically at 35C and the underfloor heating has been designed to work at this temperature to maximise the efficiency of the system.
A smart control system is also in place, along with thermostats at various points, to ensure the optimal running of the system. The smart control system connects to the internet so that the system can be operated remotely. It also enables troubleshooting to be undertaken without having to visit the site.
The condenser then connects to the buffer tank which feeds in to the underfloor heating system. It also collects any excess heat from the main building which comes through the ceiling vent in the museum.
In order to optimise the system, we aim to run the heat pump at a higher temperature than would otherwise be the case during times where there is ‘spare’ electricity from the solar PV panels, or during the night when the electricity tariff is at the off-peak rate.
This will ensure that there is energy stored for use later in the day. The heat pump will also be able to operate at the usual, low temperature heat, providing heating for the wet underfloor and radiator heating system, and at a very high temperature during times when there is a requirement for more hot water in the hot water tank.
As part of the design, we have also introduced an innovative approach to maximise solar gain in the building where areas of floor exposed to the sun through south-east facing windows are tiled in slate to absorb heat more effectively. The ‘Green Ness’ floor has been expressed as islands within the timber flooring.
The underfloor heating system at this point has a higher-than-normal density of underfloor pipework in order that passive solar collection can be trialled. During times of solar collection, the heat pump can be turned off but the heating circulation pumps left on to distribute heat collected by the pipes beneath the dark floor throughout the rest of the system.
This allows for underfloor heating to be installed on a joisted floor with minimal impact on floor height and still running at a very efficient flow temperature. Utilising the floors as a thermal generator offers an exciting opportunity to test this simple technique, using standard construction products in an innovative manner. The principles of the idea are simple yet, when considered holistically, offer an effective method to harness renewable solar heat. It also benefits the museum by regulating temperature during periods of intense sunlight.
The hot water comes from a thermal store. Here the aim is to run the temperature much higher to provide ample hot water for service users and the café kitchen. Despite the higher temperature the system is still very efficient. It has two sources of energy.
The mini Europa DHW heat-pump recovers waste heat from the building and is able to use this to run at a high temperature. If you look above you in the main museum area you will see the vent which recovers the heat from the main museum. This allows a good regulatory air flow in the museum whilst also not wasting the heat accumulated in the space.
Sometimes there is excess energy from the PV system which can’t be readily used in the building. Normally this would just go back to the grid but it is far more efficient and cost-effective if that energy can be stored. Phase change heat batteries, such as this example produced by SunAmp, optimise the operation of renewable heat sources by storing excess energy, then providing heated water when required. During times of excess heat, the material ‘melts’, thus storing energy by changing phase. When heat is required, the material re-solidifies, giving the heat back out. The system can store the same amount of energy as a large hot water tank.
This project brought together experts in building design, architectural experience and energy to review which renewable system would be best for the building. As part of this work this specialist team has been able to incorporate innovation, in particular the storage of renewable energy, as a key element of the project. CEN is a good example of how old buildings can be enhanced and improved to allow for new technologies to be installed.