Kellogg College is Passivhaus first for University of Oxford
The Kellogg Hub is the first Passivhaus project for the Oxford College & the University of Oxford. Occupied in April 2017, and certified the following month, the newbuild provides informal open space for college students and staff for study and socializing. It accommodates approximately 80 people and comprises a common room, cafe, toilets, vending facilities, and a commercial kitchen that provides catering for larger events.
Kellogg College Hub, CBG Consultants
The decision to adopt the Passivhaus Standard was made initially by Kellogg college, and supported by the University. The whole design team got behind the Passivhaus targets, and this is what made it a success.
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The University of Oxford has a commitment to sustainable buildings, which has typically required the application of BREEAM as an assessment methodology. However, the view was that this would be less appropriate given the size of the building, and its bespoke nature. There was also a concern that this building should try and avoid the ‘performance gap’ associated with many modern buildings. Passivhaus is the only standard that has been shown to deliver predicted energy use. A sustainable building was also high on the priorities of the college, who were interested in real performance more than achieving a ‘badge’. With a few tweaks to the initial concept, a simple-formed, south-facing building emerged, which presented an opportunity to adopt the Passivhaus standard.
Chris Swinburn, PHT member CBG Consultants
Key StatsTFA: 297m2 Form factor: 3.77 Completed: April 2017 Certified: May 2017 Airtightness: 0.58 ACH |
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Construction
Having a simple form, and the use of cast in-situ concrete greatly reduced the number of complex junctions, and played well to air tightness strategy. Initial air tests were well inside the Passivhaus limit, which gave confidence for the final test.
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Wall |
Type 1: Cast in-situ concrete + PIR Insulation (250mm) + Cavity + Brick single leaf Type 2: Timber cassettes with PIR infill |
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Roof |
Concrete planks + Screed + Bauder roof system with PIR insulation + Green roof |
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Floor |
EPS Insulation + Concrete + Screed |
Predicted Performance
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Thermal Energy demand (≤15kWh/m2.yr) |
12 |
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Thermal Energy load (≤10W/m2) |
11 |
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Primary E demand (≤120kWh/m2.yr) |
106 |
The performance of the building in summer was modelled in detail, with concerns that the highly glazed southern façade could create excessive solar gains. The external canopy was optimized for overheating versus winter solar gains and daylight. Results so far have been encouraging - during the latest heat wave the building’s thermal mass was able to moderate temperatures and stay consistently 2 degrees below the outdoor air temperature- without any cooling.
Main Challenges
- Finding a Contractor: It was not easy to find contractors for this project, and even harder to find one with Passivhaus experience, due to limitations of the local contractor pool and scale of the project.
- Building Form Factor: Although the building has a simple form, being single storey means that it has a high heat loss form factor of 3.8. Therefore, to hit the Passivhaus heating criteria, required much higher levels of insulation. High performance PIR boards meet the u-values, but are labour intensive to install, with high potential for thermal bypass issues if not installed carefully. The installation required close inspection and was photographed extensively to demonstrate that sufficient quality was achieved.
- Reliable Window Performance: Window suppliers were not well set up for the thermal performance requirements of Passivhaus, and struggled to provide the required document evidence to prove their claims. Data often differed from earlier claims, which affected PHPP calculations for the worse, and resulted in extra measures to rectify the numbers, such as increasing insulations where possible and a more detailed analysis of thermal bridges.
- Addition of Commercial Kitchen: A commercial kitchen was introduced to increase the overall on-site catering provision of the cafe. This presented several challenges; Finding locations for the ventilation plant in a small plan, and providing heat recovery for the canopy extraction, which is unusual for kitchens, making it difficult to find suppliers who would support it. The primary energy associated with the kitchen was difficult to maintain below the 120kWh/m2 Passivhaus limit.
- Vending Machines: Proposals for vending machines presented a further challenge to the primary energy target. Based on manufacturer’s data, it was estimated they could account for a third of the total. As with the windows, obtaining reliable performance data and identifying the most efficient units was extremely difficult.
Key Team
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Client: Kellogg College, University of Oxford Architect: Feilden Clegg Bradley Studio Landscape architect: Anna Benn Planning consultant: JPPC Main contractor: Speller Metcalfe Structural engineer: Price & Myers Passivhaus, & M&E consultant: CBG Consultants Quantity surveyor: Turner & Townsend Project Managers: Ridge & Partners Certifer: WARM |
The design team, client and contractor worked extremely well together, and we feel this was key to the building’s successful completion as a Passivhaus. The Passivhaus methodology at times created constraints for the client and designers, requiring close cooperation and flexibility, while maintaining a compliant design.
Chris Swinburn, PHT member CBG Consultants
This was the first Passivhaus for all the team except for the structural engineers, PHT member, Price & Myers. Crucially, this was the first for the client. Going forwards the University of Oxford intends to consider Passivhaus for all projects, and as a minimum to pursue the Passivhaus methodology.
Further Information
Previous PHT story: Kellogg College Hub aims for Passivhaus – 23 March 2017
