Electrifying Somerset Passivhaus Plus Primary completes

The all-electric Two Rivers Primary School in Somerset sets a new benchmark for future Passivhaus schools. On-site renewable energy generation is predicted to surpass its annual energy consumption.

The commitment to Passivhaus Plus was implemented during the design phase, aligning with the local council's commitment to tackling the climate emergency.

A clear airtightness strategy and a centralised air handling plant were crucial to delivering Passivhaus Plus. Certification was awarded by PHT Patron WARM with PHT Patron Max Fordham, acting as Passivhaus consultant.

Key stats

Construction: Steel frame
TFA: 1821 m²
Number of occupants: 420 pupils
Build start date: 2021
Completed: 2022
Certified: Passivhaus Plus

Two-Rivers-Passivhaus-Primary © Bhagesh Sachania Photography

Two Rivers Primary School Quote Card Max Fordham © image Bhagesh Sachania Photography

Construction

Two Rivers Primary School is built using a traditional steel frame, concrete floor slabs and brickwork external walls. The ground floor is built from light buff brickwork, with white render above. High-quality dark grey aluminium windows and a dark grey roof are off set by strategically placed walls of local blue lias stone.

U-values

Ground Floor Wall: 0.146 W/m²K

6mm Render, 230mm Mineral wool, 10mm Adhesive, 13mm Siniat weather defence, 250mm Steel frame void, 15mm plasterboard

First Floor Wall: 0.213 W/m²K

Brick wall, 175mm Mineral wool, 13mm Backing board, 250mm Steel frame void, 15mm plasterboard

Two Rivers Primary School under construction - Concrete planks, steel frame, blue lias stone, render base

Building performance

Designed energy performance

Airtightness n₅₀ (≤ 0.6ACH @ 50 Pa)

0.391 ACH

Space Heating Demand (≤ 15 kWh/m².a)

7 kWh/m².a

Heating Load (≤ 10 W/m²)

7 W/m²

Primary Energy Demand (≤ 120 kWh/m².a)

149 kWh/m².a

Primary Energy Renewable (PER) Demand (≤ 60 kWh/m².a*)

59 kWh/m².a

Primary Energy Renewable Generation

87 kWh/m².a

*+/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.

Services

Department for Education (DfE) schools typically have mechanical air handling units installed in every classroom, but modelling revealed that this would result in too much heat loss to achieve Passivhaus Plus. As such, the school has an intelligent MVHR composed of a single large centralised air handling unit that promotes the natural movement of air throughout the school within a carefully curated system of ducts.

The design ensures a comfortable temperature of 20 degrees Celsius with air source heat pumps (ASHP), underfloor heating, and 'kiddie watts' - body heat from 420 pupils. It is complemented by on-site electricity generation from over 200 PV panels on the roof.

Two Rivers Primary School services

Lessons learned

Over 500 hours of training were delivered, successfully upskilling the supply chain on Passivhaus accreditation. It will influence further DfE school design. Collaboration between all stakeholders and the supply chain partners was the key to successfully achieving air tightness of 0.391m3/h/m3.

The architects highlighted the transferable nature of Passivhaus requirements and better detailing to other projects. They are working closely with the contractor to incorporate the enhanced design & detailing of the project into all future schemes in line with their net zero-strategies.

Two Rivers Primary School Quote Card Hatcher Prichard © image Bhagesh Sachania Photography

The contractor praised a greater degree of cost certainty early in the project than they would usually have, spurred by the detailed Passivhaus design. All parties working toward a shared goal and measurable targets facilitated a highly collaborative environment.

Two Rivers Primary School Quote Card ISG © Image Bhagesh Sachania Photography

Key team

Client: Department for Education (DfE)
Architect: Hatcher Prichard Architects
Passivhaus Consultant: PHT patron members Max Fordham
Contractor: ISG
M&E consultant: Hydrock
Passivhaus Certifier: PHT patron members WARM

This was the first Passivhaus project for the many of the stakeholders involved. Congratulations to the whole team & Hatcher Prichard Architects for embracing Passivhaus and delivering this wonderful Passivhaus Plus Primary School.