REDUCING THE CARBON IMPACT OF HOUSING

Swansea Council and the Welsh School of Architecture won the Domestic Project of the Year category at this year’s CIBSE Building Performance Awards for an energy-efficient retrofit of six bungalows. Juliet R ennie of CIBSE explains how the team set about the work and why the methodology is relevant to other energy-inefficient homes.

As retrofit residential projects go, the results are exceptional: carbon emissions down 94%; Energy Performance Certificate rating up from G (the worst) to A (the best); and Standard Assessment Procedure (SAP) rating up from 12 to 95.

This impressive outcome is the result of a collaboration between Swansea Council and Cardiff University’s Welsh School of Architecture (WSA) on a project to retrofit six retirement bungalows. This outstanding scheme won Project of the Year – Domestic at this year’s Chartered Institute of Building Services Engineers (CIBSE) Building Performance Awards. The judges said the project “will have farreaching impacts in Wales and beyond”.

The terrace of six council bungalows selected for this project are representative of many Welsh homes in that they are off the gas grid and have been constructed with poorly-insulated windows, walls and roofs, making them expensive to heat. Consequently, many of the homes also had damp and mould problems.

This project builds on WSA’s learning from earlier residential projects where it developed its holistic approach to delivering retrofits as opposed to focusing on improvements to individual elements.

Professor Joanne Patterson, Professorial Research Fellow at WSA,

terms this “a whole-house approach”. She says its success depends on data-driven decision making.

The starting point for the bungalows’ retrofit is what Patterson calls a Practical Retrofit Early Stage Survey. Developed by the WSA, this is a formalised way of collecting accurate data from each dwelling. The survey helps the school understand how residents use their homes, which then informs its choice of retrofit measures.

In addition to questioning the residents, the WSA also undertook comprehensive preretrofit monitoring of the building fabric. This included airtightness testing, U-value measurements and thermal imaging to help identify problems with the building fabric that would also need to be addressed.

The decision-making process is supported by thermal and energy modelling of each home. This enabled different combinations of retrofit measures to be tested and the energy use and carbon emissions to be assessed for each mix.

Using the monitored data, the WSA first set about reducing the bungalows’ fabric energy demand before maximising the use of renewable technologies. The school’s approach is to use efficient and replicable solutions to help the local authority in its drive towards zero carbon.

The teams from Swansea Council and WSA worked with the residents and their supply chain to plan, design and enable installation of the proposed measures while the residents remained in place. To minimise disruption, it was decided to undertake the retrofit work over two phases. Fabric efficiency improvements, which included external wall insulation, a reduction in the glazed area and installation of highspecification, double-glazed windows and the addition of loft insulation, took place over the winter of 2018/19.

Installation of the energy supply and storage technologies took place the following year. These interventions included installation of an electric ground-source heat pump (GSHP) in each dwelling along with photovoltaic panels and a large battery to store surplus electricity generated by the PVs. The properties were also fitted with a mechanical ventilation and heat recovery (MVHR) system to provide constant energy-efficient ventilation.

To ensure interventions performed as intended, residents were given a simple user guide. Swansea Council’s energy manager also spent time explaining the technologies to the residents. In addition, post-retrofit monitoring by the WSA ensured the technologies had been commissioned correctly and that operation of each system had been optimised. Semi-structured interviews were used to gather residents’ perceptions of the impact of the retrofit interventions. These show that:

Thermal comfort in both winter and summer scored top marks with all rooms comfortably reaching the temperature set by the resident

Despite the installation of external insulation that increased the depth of the window reveals, availability of daylight and artificial light from new LED lighting also received top marks

The issue of noise from the new GSHP and MVHR systems was identified as audible but was not considered intrusive www.cibse.org

Occupants are also very satisfied with their ability to control all systems.

Post-retrofit monitoring by the WSA showed the improvements had a major impact on both operational energy and carbon emissions. The results after two years of monitoring showed that out of the heating season, 95% of the home’s energy was provided by the PVs and battery. Consequently, residents’ electricity bills dropped to £3.00 per month (excluding standing charges) for the supply of electricity, heating and hot water from March to September when it is warmer, and the days are longer.

Average energy consumption was found to be 5MWh, significantly lower than the UK average of 15MWh, of which 2.8MWh was provided by the PVs and battery, with 2.2MWh supplied from the electricity grid. In addition, without the need to burn oil or LPG for heating and hot water, the homes’ carbon emissions post retrofit are significantly lower. No wonder the CIBSE judges were impressed.

The WSA won a second CIBSE award for its collaboration with Wales and West Housing to deliver a series of whole-house retrofits on a variety of different house types across south and west Wales. The project used the same systematic approach to prove that it was possible to use off-the-shelf systems to significantly reduce energy consumption and improve occupant comfort.