High density residential development of new low energy housing on a brownfield site
Located on the site of the former car park for Gurnell Leisure Centre in Ealing, this development of 295 new build flats and duplexes seeks to provide high quality new build accommodation to meet the aspirational sustainability standards set out by Ealing Council in their emerging Local Plan, as well as the requirements for major developments set out in the GLA’s London Plan.
Greengauge was part of the project team to planning, acting as M&E services engineer, providing Passivhaus design advice, carrying out energy modelling in both PHPP and SAP as well as dynamic thermal modelling in IES to assess likely overheating risk for Part O.
The project successfully achieved planning permission and is now under development.
Key data
- 295 units, in blocks of up to 10 storeys
- Predicted heating load of 15 kWh/m2/Yr
- Predicted EUI of 36 kWh/m2/Yr (32 kWh without cooling)
- London Plan definition net zero carbon, achieved 100% via on-site renewables
- Noisy brownfield site, requiring windows to be closed at night for Part O
- Individual heat pumps for heating and “peak lop” cooling if windows kept shut
- Ambient loop with boreholes as communal heat source/ sink
- Building fabric and services designed in line with Passivhaus
Project team
Architect: Mikhail Riches
Project Manager: Gleeds
Building physics: Greengauge
M&E Design: Greengauge
Structural Engineer: Expedition
Sustainability Consultant: Expedition
Planning Consultant: Tibbalds
Landscape Architect: Periscope
Key data
“It is always a pleasure to work on substantial new low energy housing projects, as these are definitely something that we need more of! Some quite challenging site constraints on this project, but we had an excellent design team to work alongside and I think the resulting scheme delivers well on the aspirational Client brief.”
Gerard Thacker, Associate Director, Greengauge
Key features
Building fabric and servicing designed to achieve Passivhaus levels of performance
The LETI-derived sustainability targets set out in the emerging Local Plan were based on achieving Passivhaus levels of thermal performance. The buildings were therefore designed from the outset to be able to meet the Passivhaus standard, with modelling in PHPP carried out by Greengauge from the early stages to inform the developing design. This helped to improve form factor and glazing ratios as well as ensuring appropriate space was planned in for insulation of sufficient thickness, influencing the specification of glazing, airtightness targets etc.
Each unit was also planned to have suitable plant-space and ducting routes for an efficient, PHI-certified MVHR system, as well as a centrally located hot water cylinder to enable efficient, small bore radial distribution.
Overheating control strategy
The development site was in a relatively noisy location, with a busy road to the front, nearby railway line and flight paths from Heathrow. Background noise levels were found to exceed the threshold above which windows have to be assumed shut at night for Part O (overheating).
A dynamic Part O model was therefore built at the early stages and used to inform the developing architectural design. Passive design features were prioritised with glazing areas minimised and balanced against the need for daylight and external balconies planned on South-facing facades to reduce unwanted solar gains in Summer.
However, with bedroom windows assumed to be shut at night as required by Part O, dynamic thermal modelling suggested that some facility for mechanical cooling would be required to maintain comfortable temperatures due to the ongoing internal gains overnight.
A reversible heat pump system was therefore planned in which would give the facility for some “peak lop” cooling when required and provide future resilience for the warming climate.
Ground Source Heat Pumps and a communal ambient loop with boreholes
It was established at the early stages that heat pumps would be required throughout the development, both to achieve the aspirational LETI-derived EUI targets and to provide the “peak lop” cooling required for Part O and climate resilience.
However, the relatively high density of the development and London Plan requirement to prioritise heat networks for major development made this challenging, effectively ruling out simpler options often employed on lower density developments, such as individual Air Source Heat Pumps.
After some optioneering with our Client at Stage 2, a strategy was agreed employing individual “shoebox” Ground Source Heat Pumps (GSHPs) within each unit to provide space heating, hot water heating or cooling as required and exchanging heat with a communal “5th generation” ambient heat network. This heat network was then connected to a series of boreholes to act as a passive heat source/ sink via the ambient environment outside the building without the need for further centralised plant.
Boreholes were planned into a landlord maintained servicing strip around the perimeter of each block and within the centres of the courtyards (outside the Tenant garden spaces) to allow these to be more easily maintained.
Lower network losses
As well as simplifying energy billing, locating the heat pumps within the units has the significant advantage of allowing communal pipework in the circulation spaces etc. to run at much lower temperatures, greatly reducing network heat losses and potential overheating from summer hot water generation. The common loop also allows units generating hot water to utilise waste heat from units generating cooling in Summer. This significantly reduces energy consumption compared to traditional “4th generation heat networks with centralised plant, reducing both energy costs for Tenants and the amount of on-site renewable energy generation required to offset this.
‘Heat as a utility’ funding model
A ‘heat as a utility’ funding model allowed capital costs for the ambient network to be kept manageable (similar to individual ASHP schemes) and hence kept the scheme financially viable. In this model the borehole installer funds the upfront installation of the boreholes and ambient network and then acts as an ESCO, maintaining the system and recouping their costs from tenants via a standing charge for their heat network connection (similar to the standing charge for a gas meter). Tenant running cost calculations produced for various different options showed that this standing charge would essentially be offset by the reduction in energy costs when compared to a traditional 4th generation heat network, or a 5th generation heat network using further centralised heat pumps as a source/ sink.
Large Solar PV arrays with direct connection to the dwellings
In order to achieve the London Plan net zero carbon objective, the large flat roof areas of top of each block were fully covered in Photo Voltaic (PV) panels to maximise on-site renewable energy generation
The energy generated by these arrays is then proposed to feed back to each dwelling via a load management system such as the Allume Solshare system. This allows Tenants to benefit directly from the generation, rather than the energy going back to a Landlord’s board, as is often the case.
The Solshare system also uses a smart algorithm and load sensors to change energy distribution depending on which dwellings have most demand at any given time, which significantly increases on-site consumption.