Redeveloped leisure centre at Watford outperforms Building Regulations

One of the largest energy loads in the redeveloped Woodside Leisure Centre at Watford is this 50 m competition swimming pool containing 1000 m3 of water.
The redeveloped Woodside Leisure Centre at Watford exploits a range of technologies to reduce its energy requirements — and then meet much of them usable renewable energy — as Ken Sharpe discovered. Leisure centres can be very high consumers of energy, especially if they have a large air-conditioned fitness suite and also a large competition swimming pool. But being such large users of energy offers scope for imaginative engineering to reduce consumption. Such is the case at Watford Borough Council’s redeveloped leisure centre at Woodside, where a range of low- and zero-carbon technologies have been incorporated into a building-services design by Matt Dickinson of Max Fordham & Partners. Overall, the low- and zero-carbon technologies are expected to outperform the requirements of the 2006 Building Regulations by at least 35%. The new facilities at Woodside include:
• 8-lane, 25 m competition swimming pool and a learner pool.
• 8-court sports hall.
• All-weather pitches.
• 100-station fitness suite and a dance studio.
• Squash courts.
• Cafe, function room and crèche. 400 000 visitors a year are expected.

Reusing much of the fabric of the previous building and adding a new area to house two swimming pools adds to the sustainability credentials of Woodside Leisure Centre.

Meeting the strict temperature and humidity controls of indoor swimming pools traditionally requires lots of energy. Associated facilities such as air-conditioned fitness suites and showers present additional loads. However, such high energy demands also offer the opportunity to deliver significant energy savings. Renewable energy is an important part of the engineering strategy. There are two main sources of renewable energy — a ground-source heat-pump installation and a solar thermal array. However, with such a project it is vital to first reduce the energy requirement by passive and best-practice measures and then meet much of the remaining requirement with renewable energy. For example, energy demand from the pool is reduced by a combination of factors. They include a rooflight, high-efficiency heat-recovery ventilation, optimum control of relative humidity and a system to transfer heat from the backwash to the pool water. This heat-transfer system also extracts heat from used shower water and significantly reduces the energy required to generate domestic hot water, which is always a substantial load in a leisure centre. 

One of the main sources of renewable energy for Woodside Leisure Centre is an array of 49 boreholes sunk 90 m into the ground.

Backwash water from the pool is at 28°C, and 30 m3 is lost every week. A Menerga heat-recovery unit incorporating a shell-and-coil arrangement recovers much of the energy that would otherwise be lost and transfers it into the incoming replacement water. Another heat-recovery system recovers 30 to 40% of the energy in waste domestic hot water and transfers it into the incoming cold water — the first time that Matt Dickinson has used this technique. The energy requirement for domestic hot water is reduced using PIR proximity sensors to activate showers in the pool changing room and automatic sensor-controlled taps in toilets. The Menerga air-handling units serving the pool recover energy using double-pass cross-flow plate heat exchangers. They can recover both sensible and latent heat from the pool-hall air which, at 29°C, is 1 K above the pool temperature. Further reductions in energy demand are achieved by mixed-mode ventilation in the pool hall. Quite simply, when the outdoor temperature in summer rises above 22°C, the air-handling units are turned off. The windows are operated by automatic window openers from SE Controls under the control of the Trend building-management system. Energy consumption elsewhere in Woodside Leisure Centre is reduced by techniques such as demand-led ventilation to the air-conditioned gyms based on carbon-dioxide concentration.

Thermal storage is an important part of a renewable energy strategy. These two buffers store heat recovered from hot water going to drain and from solar thermal collectors.

Rather than being just another energy load, the VRF air-conditioning serving the fitness suite contributes to the thermal requirements. Instead of rejecting heat to atmosphere, this VRF system rejects energy to the water loop that is the heart of the low-carbon energy strategy. This water loop operates at 40 to 45°C to heat the pool water and heater batteries in the pool hall. If there is no demand for heating, energy from this VRF system is rejected to the ground, increasing its COP. Lighting is controlled by a mixture of PIR (passive infrared) sensors and photocells as appropriate. Also important from the sustainability viewpoint is that much of the existing leisure centre on the site was reused, reducing the embodied energy and cost of the project. The pool halls are an extension to the existing building, which was substantially refurbished with new cladding and high levels of thermal insulation. The external cavity walls previously had no thermal insulation. The cavity is now filled with insulation up to a height of 3 m, with insulated external render above that height to give a totally new external appearance. Without this redevelopment of the existing building, cost issues would have limited the facilities. The main sports hall, for example, would have had only four courts, not eight. The main source of renewable energy is from 49 boreholes under the main car park linked to a ground-source heat pump. These boreholes are 90 m deep in a 7x7 array on an 8 m pitch. This form of renewable energy was chosen over CHP and biomass as offering the best payback. The ground is chalk, which tends to contain lots of fissures and flints and be saturated with water — making a good source of energy for a heat-pump installation. The water table is about 10 m below the surface, so an 80 m depth of each borehole is exposed to groundwater. Energy from the ground is extracted using a closed-loop system, which can also reject heat if required. The boreholes for this project required planning permission and approval from the Environment Agency, but Brian Kennelly, managing director of EarthEnergy, which was responsible for the geothermal installation, tells us that neither have been required since 1 April 2008 — when ground-source heat pumps became permitted development. He further tells us that the ground temperature in Watford is about 14°C. A few miles south in London, it can be as high as 16°C because of the Tube. Over the country as a whole, 12°C can be generally expected. The boreholes are grouted with a high-thermal-conductivity grout to optimise heat conduction into the closed-loop collector tubes. A Ciat Dynaciat heat pump upgrades the temperature of the water-glycol mix that has already drawn heat from the ground and returns it 3 K cooler. The heat pump can deliver 200 kW of heat. For preference, it is run at night to take advantage of cheaper electricity tariffs. Renewable energy is also supplied by 140 m2 of solar collectors with flat panels. The heat collected is mainly used to pre-heat domestic hot water, but it can also be added to the general heating network. 55 kW is available from the solar thermal array. It is estimated that the heat available from the heat pump and solar thermal panels will amount to 350 MWh a year. Heat rejected from the VRF air-conditioning system that serves the fitness suite will amount to a further 108 MWh a year, taking the total available heat energy from these three sources to 458 MWh a year. The heating requirement is supported by two Viessmann gas-fired condensing boilers of 250 kW each, which are not required during the summer. These boilers are run at lower temperatures than usual, increasing their efficiency by 5 to 10%. Support for the solar thermal DHW system is provided by three Andrews Maxxflo water heating, each with 300 l of storage. They have a net heat input of 112 kW, modulating down to 24 kW. Thermal storage is an important part of a renewable-energy strategy, and the pool itself plays a major role. Its normal temperature is 28°C, but this can be raised to 29°C before swimmers become too aware. About 1 MWh of heat can be stored. There are also thermal buffers in the plant room to store heat recovered from DHW going to waste and energy from the solar thermal system. The various technologies are carefully controlled an optimised by the Trend BMS, which also monitors the energy use of the building.

The Ciat ground-source heat pump has a thermal output of 200 kW.

Sustainability continues with harvesting of rain water from the roof. It is stored in a 70 m3 tank and used to flush toilets, including urinals — of which there are only six. Max Fordham LLP was appointed M&E consulting engineering for this project from a competitive design tender. Matt Dickinson tells us that the client, Watford Borough Council, was committed to the best energy strategy from the outset and was prepared to pay for it. He says, ‘This was a very interesting project. Watford Borough Council was looking for the best in sustainability from the outset and true sustainability, not fads.’ Woodside was formally opened earlier this year with the help of sports personalities Sharron Davies, Olympic and Commonwealth swimmer, and Richard Haughton, Saracens rugby player. Matt Dickinson and Max Fordham LLP will continue to be involved to monitor the effectiveness of their systems and learn for the future. Contractor J S Wright was commissioned by Pellikaan Construction to install eco-friendly mechanical services for the new Woodside Leisure Centre in Watford. Andrew Smith, J S Wright technical director, said: ‘This was one of our most unusual projects and one that provided a learning curve for us all in maximising the use of heat-recovery and heat-exchange systems. It also provided an opportunity to apply further cost savings through value engineering as we went along and has put us in good stead for carrying out similar projects of a highly environmental nature.’ Reusing much of the fabric of the previous building and adding a new area to house two swimming pools adds to the sustainability credentials of Woodside Leisure Centre. One of the main sources of renewable energy for Woodside Leisure Centre is an array of 49 boreholes sunk 90 m into the ground. Thermal storage is an important part of a renewable energy strategy. These two buffers store heat recovered from hot water going to drain and from solar thermal collectors.
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