Cambridge Net Zero Retrofit Pilot

This project was established as a Net Zero Retrofit Pilot to improve resident wellbeing through comfortable, warm and healthy homes, which are energy efficient and affordable to heat. The Net Zero (Operational Energy) pilot aims to develop a precedent methodology to be used for future projects across Cambridge City Council’s existing housing portfolio in their goal to be carbon neutral by 2030.

Understanding the existing performance was crucial to determining the retrofit measures. This included pre-work retrofit assessments, gathering bill data, calculating energy performance certificates and pre-works air tightness testing. SOAP retrofit also undertook pre-works monitoring studies to determine the heat transfer co-efficient (the rate at which heat was escaping from the homes), as well as temperature and humidity profiles to calculate the dwelling condensation and mould risk, which is a real concern for residents. A similar process of monitoring is planned for post-completion.

The design process has involved extensive and iterative energy modelling in PHPP (the passivhaus planning package) at each work stage. To target net zero operational energy, the EnerPHit approach was followed as it is recognised to deliver both at the design stage and construction stage. The result is a deep retrofit; measures include external wall insulation, cavity wall insulation, roof insulation, floor insulation, triple glazed windows, insulated doors, mechanical ventilation heat recovery, hot water units heated by air source heat pumps and photovoltaic panels. Calculations were also carried out to ensure residents will have cost savings from bills with the switch from gas to electricity.

Ultimately, the achievement of the net zero operational energy target will be dependent on the configuration and use of each individual dwelling. For example, the number of PV panels on each house varies from 2 to 13; homes with more panels are more likely to meet the net zero target. However, the most important priority is the residents’ health and wellbeing and to ensure all residents will benefit from deep fabric and MEP upgrades equally. This has been achieved by finding a balance between high performing retrofit measures, while ensuring the final design is affordable for the council to roll out across the housing stock.

Team:

• ECD Architects – Architecture
• Keegans – Retrofit Coordinators & Assessors
• Greengauge – Mechanical, Electrical and Plumbing Engineering
• Focus – Quantity Surveyors
• SOAP Retrofit – Monitoring and Evaluation