Journey to low carbon development and achieving net zero carbon on a social scheme
Housing providers across the country are facing the same issues when it comes to creating sustainable homes for the future. While retrofitting existing stock is a hurdle in itself, new builds presents its own challenges.
One Manchester’s early ambition was to deliver homes that were warmer, healthier and cheaper to run for our residents. Even five or six years ago when our retrofit Passive House (PH) scheme was completing and our first PH new build scheme, Stoneygate, was in design stages, low carbon was not our chief goal – dramatically reducing the amount of energy needed was.
I wanted to obtain most of the benefits of a fabric first approach but believed that achieving that last 10% of performance came with too much cost. We settled on the PH Low Energy Building Standard (not classic) and let orientation of plots on the site deal with that last performance step. We achieved an 80% reduction in space heating energy demand at Stoneygate and homes that are ‘low tech’, naturally warm and cheap to run.
As we understood the climate emergency, we found that the energy reduction at Stoneygate wasn’t matched by the reduction in carbon emissions. Carbon had reduced by c.40-50%, not enough to hit the low carbon/zero carbon benchmarks, because we had installed gas boilers for remaining space and water heating and cooking.
We realised that gas ‘needed to go’ in our new builds and took the decision to work up three more sites. Simply replacing gas with electricity increases the running cost for residents, so we spent a long time modelling options for space, water and other energy requirements.
We considered air source heat pumps (ASHP), solar thermal, Photovoltaic Panels (PV), batteries and spent time worrying when the electricity and/or gas grids will be decarbonised and when battery technology will be mature.
We had comparison data covering capital cost, running cost, energy and carbon. We settled upon ASHP for water heating which with the fabric performance, gets us to a ‘low carbon/zero carbon ready’ position.
It achieves the energy and carbon reduction targets at a capital cost that we could afford – and with clearly benchmarked costs in use for customers. Adding a 4kWp PV array lifts the homes to net zero carbon (NZC), but the plan is to review this in in the future.
The same decision hierarchy was used to define our next retrofit project – tackling heat loss, damp, cold bridging and reducing space heating demand through fabric improvements; then replacing the next biggest call on energy with ASHP. We looked at running costs to residents, capital cost and carbon emission reductions and decided that we should stop at low carbon. That future step to net zero carbon will again require either future PV panels, a decarbonised grid, or there may be potential for a local energy network.
There’s a lot more to say about One Manchester’s journey– we have whole life net zero carbon homes on site and we have used a panellised system on several on-site developments.
We’re learning and improving with resident feedback on the practicalities of managing the homes, and we know we need to monitor and test the performance gap over time.