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St. Sidwell's Point

Location: Exeter
Completion Status: Completed Occupancy: Occupied April 2022
Architect: Space and Place Architects Consultant: Gale & Snowden Architects
Contractor: Kier Client: Exeter City Council
Certification: November 2023 Certifier: Passivhaus Institute (PHI)
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Exeter City Council’s bold and trailblazing St Sidwell’s Point project  - the first leisure centre and public pool to achieve Passivhaus certification in the UK, opened its doors in April 2022.

St Sidwell's Point. Image credit: Exeter City Council

Conventional leisure centres are high energy consumers and costly to run as they operate at consistantly high temperatures and high humidity all year round.  Of all building types leisure centres make the most sense to be optimised to the Passivhaus standard. Pool halls operating at high temperatures need heating all year round therefore building to the Passivhaus standard with high insulation levels, triple glazing, high levels of airtightness, and thermal bridge free design significantly reduces this load.

Designed by PHT member Gale & Snowden Architects and Space and Place Architects, and built by PHT member Kier, St Sidwells Point, a £44 million leisure centre is one of only a handful of such projects in the world. Germany currently has two Passivhaus swimming pool buildings, however the St Sidwell’s Point includes multiple facilities such as a 150-station gym, studios, spin studio, creche, and health suite with spa facilities.

The differing thermal zones operating at a range of different temperatures, gym suites at 18oC and pool zones at 30oC, coupled with high humid zones competing with dry zones, St Sidwell’s Point is one of the most complex Passivhaus schemes in the UK to date.

St Sidwell's Point | Image credit: Tom Hargreaves
St Sidwell's Point | Image credit: Tom Hargreaves St Sidwell's Point | Image credit: Tom Hargreaves

 

As a result of its fabric first Passivhaus design, the flagship project for Exeter City Council is expected to achieve a 50-70% saving on annual energy costs, achieve 50% water savings compared to conventional leisure centres, has been designed to be climate resilient to 2080 and also incorporates building biology healthy design principles.


Quote card | There is now no excuse not to go Passivhaus even for complex buildings such as St Sidwell’s Point. It makes both financial and environmental sense for buildings that traditionally consume high quantities of energy. Passivhaus just got a bit sexier. | David Gale, Architect Director, Gale & Snowden Architects

 

Key Stats


  • Project cost: £44m

  • Construction: Reinforced concrete, blockwork, CLT, lightweight steel frame with sheathing boards

  • Construction started: 2021

  • Completed: 2022

  • Certification: 2023

St. Sidwell's Point | Image credit: Tom Hargreaves

 

Due to the prominent city location, the Council desired the new building to act as a landmark destination. Cascading curved forms step back at each level to maximise natural daylight that penetrates into the deep floor plan of the building. The result is an uplifting and healthy interior in the pool halls with striking geometric external shapes that still meets the Passivhaus criteria.

 

St Sidwells Point | Image credit: Gale & Snowden

 

Construction

The project has been built using a blend of structures including reinforced concrete, blockwork, CLT and lightweight steel frame with sheathing boards.  The building foundations include a 250mm-thick high-density expanded polystyrene insulation which extends around pile caps and 1000mm down the side of foundation piles to prevent thermal bridging. 

Thermal zoning

The first stage to realising Passivhaus energy optimisation was to set out the building and its thermal zones in context with the site identifying the ‘free’ energy savings.  Zones requiring cooling are placed to the north, hot zones which can harvest solar gain to the south, with buffer zones in between, so that there is a cascade affect between the temperature zones.

The next stage was to ensure that the separate temperature zones are sufficiently thermally separated between each other – buildings within a building. For example, placing a cooling zone at 16oC right next to a pool zone at 30oC was avoided, as this would increase energy transfer and also capital costs. The internal thermal barrier would have to be as good as the external fabric to deal with the issue or other elements would have to work harder to make up for the shortfall. By optimising in this manner, the thermal barrier between temperature zones is made simpler. 

Glazing ratios

Once the optimum layout and orientation is achieved, the next step is to arrive at the optimum glazing ratios. This involved detailed dynamic thermal modelling by Gale & Snowden to ensure the optimum for energy savings, to limit overheating and to achieve optimum daylight levels. Thermal modelling was carried out into 2080 future climate scenarios.

Giles Boon, Technologist and Passivhaus Designer, Gale & Snowden Architects commented: "These first steps are key to Passivhaus optimisation, once realised all other energy savings measures follow.  Without it you are simply driving up capital costs as other elements will have to work harder to meet the Passivhaus criteria."

St Sidwell's Point construction. Image credit: Exeter City Council
St. Sidwell's Point Construction. Image credit: Gale & Snowden Architects St. Sidwell's Point Construction. Image credit: T Clarke

Airtightness

The airtightness layer is formed as a composite between the sheathing board and fully adhered membrane. These are located on the outside of the structure to minimise disruption to internal work and reduce the risk of the airtightness layer being punctured from the internal works. This meant exceptional site control was needed to monitor perforations in the airtightness layer before it was covered up by follow on works.

Junctions around curtain walls were particularly challenging and precise installation of insulation around pile caps also required numerous checks and attention to detail. Achieving high levels of airtightness given the complex geometry of the building was the biggest challenge of the job.

For example, to achieve an 'airtight' installation of a double door, the door should meet a specified air permeability class to EN12270 and the connection between the door and each of the adjacent elements must be sealed. If the door is glazed into a curtain wall, then similar attention to detail is needed at the transition between the curtain wall mullion and the threshold of the door. At St Sidwell's Point, much of this was subjected to product changes, critique, review, consultation and testing.

The general arrangement of thermal zones coupled with programmatic constraints meant that the scheme did not lend itself to interim whole building air pressure tests. To mitigate this risk, mock-up models of the airtight details were built on-site, temporary airtight zones were created, and thermal imaging cameras and smoke machines were used to identify leaks as an interim approach. The care and attention paid off when the final air test came in at 0.3m3.h/m2@ 50 Pa which for SSP equates to an airtightness of 0.1 air changes per hour at 50Pa - well within the requirements for Passivhaus certification.

 

Quote card | We were amazed at the buy-in we got from the supply chain.  Most of hte people on this site were coming up with ideas themselves and were proud of what they were doing. It’s almost unheard of in my experience | Joe O’Connell Senior Project Manager, Kier

 

Building performance

Complex leisure facilities incorporate multiple, often competing energy systems and processes. In all aspects of the St Sidwells design; fabric, ventilation, zoning, filtration, heat recycling, thermal zoning and controls - energy savings were realised.  In many instances, these could be implemented without additional cost.   

  • Reduced evaporation: With good building fabric performance, the risk of internal condensation in the pool halls is reduced, which allows the pool hall to operate at a slightly higher relative humidity (RH) (up to 64%) than the average pool building (normally between 50-60% RH).  Operating at a higher relative humidity reduces pool water evaporation rates uses significant quantities of energy due to the latent heat of evaporation. Subsequently, the pool water not only cools down, replacement water is then required th be heated before entering the pool.  In a non-Passivahus leisure scheme, pool water heating is easily 3 to 4 times higher than the space heating load in the pool hall.  The St Sidwells Passivhaus system is designed to just double the space heating load, while the hydro and confidence pools are drained overnight which reduces evaporation and energy further.
  • Ventilation savings: The higher relative humidity brought multiple significant energy savings.  With reduced evaporation, ventilation air change rates can be reduced as less dry air is required to deal with the latent load.  While typical pool hall air change rates are anything up to 4 - 6 per hour, St Sidwells were reduced down to arround 1.5 per hour.
  • Filtration energy usePool water filtration systems are another significant energy draw for a swimming pool.  There is no measure in the energy regulations to capture their impact and so little incentive to reduce their energy use.   Filtration systems account for around 1/3 of total electrical energy in a Passivhaus scheme.  The PHI set a challenging energy target of 40 Wh/m3  This was particularly challenging for the filtration specialists and required carefully planning and co-ordination of the pipework systems in order reduce pressure drops to meet the target.  In addition, the pipework had to sit within the thermal envelope adjacent the pool tanks in order to limit heat loss.  In typical schemes they are buried in the ground and uninsulated.
  • MicrofiltrationThe microfiltration system for the pool contributed to further energy savings.  Compared to traditional sand filtration systems, it requires less backwashing and can achieve water savings of up to 50% .  This has a big impact on the heating load of the pool water.   The microfiltration design also supported the building biology aspirations of the project.  With higher efficiency filtration coupled with UV sterilisation, chlorine levels are minimised to those better than drinking water.
  • Human-powered energy: Early stage dynamic modelling identified that there was a significant heat gain energy load in the gym and spin studios that needed to be dealt with.  Rather than cool this space down in the traditional manner with cooling systems that throw the heat away, it was decided to divert this useful energy into heating the pool water and other parts of the building.  This led to a change in strategy from CHP (which was originally proposed) to the innovative use of heat pump technology. 150 gym users working out on a daily basis, plus the spin studios will produce high levels of heat energy.  The use of a hybrid air source heat pump which can deliver heat and cooling simultaneously was adopted.  All of the’ waste heat’ from cooling these spaces will be used for a significant proportion of the water and space heating, resulting in a heat pump TER (target efficiency ratio) of 7! This is the sum of cooling plus heating outputs to total power input.
  • Reusing heat from waterA water source heat pump is used to recycle the waste heat from the back washwater to top up the water heating. Once the heat is taken out of it the backwash water is also being recycled to flush the building's WCs, contributing to the estimated 50% water savings.  

Energy usage targets

Total energy targets

Typical leisure centre:  1,579 kWh/m2.yr

Best practice usage: 737 kWh/m2.yr

St Sidwell’s target: 375 kWh/m2.yr

 

Airtightness targets

Requirement: q50 ≤ 0.4 m3 /h per m2 envelope area

Recorded: q50 ≤ 0.3 m2 /h per m2 envelope area 

St Sidwell's Point Leisure Centre, Exeter. Image credit: Exeter City Council

 

Passivhaus energy breakdown targets

Heating demand for pool halls

40 kWh/m2.yr

Heating demand for all other areas

20 kWh/m2.yr

Total heating demand 

60 kWh/m2.yr

Pool water heating

73 kWh/m2.yr

Domestic hot water demand (changing rooms)

0.7 kWh / person

Equivalent to 56 kWh / m2TFA .yr     

Cooling demand for gym space areas

22 kWh/m2.yr

Total electricity demand

(All ventilation, lighting, appliances, pool water treatment and circulation)      

120 kWh/m2.yr 

Pool circulation / water treatment electricity demand)

40 Wh/m3

Ventilation

20 kWh/m2.yr 

Lighting

20 kWh/m2.yr

Other appliances

20 kWh/m2.yr 

 

One year of in-use energy performance

After a year of monitoring, the current analysis indicates that heating and cooling consumption are well aligned with expectations, whilst the electricity consumption is higher than anticipated. As expected and calculated with the multi-zone PHPP the highest energy consumption is caused by the space heating for pool halls, the pool water heating and shower water heating demand. High electricity consumption is not uncommon for projects of such size complexity, as it is difficult to capture all consumers and equipment runtimes during design stage energy modelling. A detailed analysis of the calculated energy demand and this in-use energy consumption data is yet to be completed for the different facilities and systems in the building. The energy assessment and post-completion support is ongoing and it is likely that energy consumption can be lowered even further by adjusting and optimising controls. Find out more on Passipedia 

St Sidwell’s Point Leisure Centre: One year of in-use energy performance

 

Training

The training of staff and the supply chain was integral to the success of the technically complex and pioneering project.

  • Strong efforts were made to engage and train up the supply chain, which was seen as preferential to employing an army of managers to supervise and check the work of the supply chain team.
  • Regular workshops were held with the supply chain to ensure they understood what was required and to get their feedback.
  • Throughout the construction process, more than 2,000 workers went through the training process, and received a 'Passivhaus passport'.
  • Mock-ups of construction details were built in advance to test them and give the building team the confidence that these would work on site. The mock-ups were also used as a training tool for the supply chain.

 

Quote card | The project involved a highly collaborative and co-ordinated effort from all parties involved. It is a reflection of all disciplines coming together, with a single goal of delivering the UK’s first Passivhaus Certified Leisure Centre | Jason Fitzsimmons, Passivhaus Designer & Mechanical Engineer, Gale & Snowden Architects

 


Key team

Client: Exeter City Council

Lead Architect: Space and Place Architects

Passivhaus Designer, Building Envelope Architect, Building Biology Consultant: Gale & Snowden Architects 

Cost consultant and employer’s agent: Randall Simmonds

Main Contractor: Kier

Structural & MEP engineerArup

Pool Filtration Specialist : FT Leisure

MEP Sub Contractor: T Clarke

Air-testing consultant: Jennings AldasWARM

CertifierPassivhaus Institute (PHI)


 

Funding & payback

The Leisure Centre had to pay for itself and the running costs and build costs for the building were not linked to council tax rates. The project has been built within budget. The predicted annual energy savings of the building will offset the extra building costs.  The building has been designed to last 80 years and, with 70% less energy use than a conventional centre, to have a payback period of just 8-9 years.

Quote card | The premium is more than covered by the long-term picture; it more than pays for itself over the life of the building |  Duncan Wood,  Councillor for Leisure & Physical Activities, Exeter City Council

 

 

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Further information

St Sidwell's Point

Large & Complex Passivhaus Masterclass 2024

Large & Complex Passivhaus Masterclass lecture series: On-demand

Previous PHT story: The UK's first Passivhaus Leisure Centre makes a splash  – 25 March 2022

Previous PHT story: UK's 1st Passivhaus pool progresses  – 1 October 2020

Previous PHT story: St Sidwell's Point targets world first  – 15 February 2019

Passivhaus Sports & Leisure case studies

PHI Guidance: Swimming with a clear conscience

BBC: UK's first energy efficient leisure centre to open in Exeter - 1 February 2022

BUILDING magazine: Take a dive into the UK’s first Passivhaus leisure centre - 16 February 2022

Gale & Snowden Architects: St Sidwell’s Point

Gale & Snowden Architects: Reflections on the UK's First Passivhaus Leisure Centre

Kier: Passivhaus Passports at St Sidwell’s Point