Energy Saving in the Park

St.James’ Park benefited from major restoration and improvement works in 2010‑2011 under a Parks for People project funded jointly by the Heritage Lottery Fund, the Big Lottery Fund, Southampton City Council, and the Friends of St.James’ Park (FoSJP).

Several of the design elements of the improvement works focused on energy conservation. We hope that as well as reducing the environmental footprint of the Park, these energy conservation measures will also be a feature for educational activities such as visits from local schoolchildren. St.James’ Park is one of a very few public spaces in Southampton to have renewable energy in the form of photovoltaic cells.

Air Source Heat Pump
Air Source Heat Pump—up to 300% efficiency!

Rather than using a conventional gas‑powered water boiler to heat radiators, the ParkLife Building is heated via an external air source heat pump.

The air source heat pump extracts low grade thermal energy (at ambient temperature) from the environment (i.e. heat freely available in the outside air), upgrades the heat to a higher temperature, and via an internal heat exchanger releases that heat into water running through underfloor pipes throughout the building.

Each building zone is separately controlled

The underfloor pipes are used to divide the building into 7 heating zones, each of which can be separately temperature‑controlled for its needs: for example, store rooms can be maintained at a lower temperature than occupied rooms, and the Café can be maintained at a different temperature than the Community Room if required.

The energy efficiency of this system is estimated at up to 300% i.e. for every 1 kW of energy spent on running the system—pumping air and water around, upgrading heat—up to 3 kW of thermal energy can be extracted from the environment, giving 2 kW of surplus energy for heating the building.

In order to work efficiently, a large air gap is needed around all sides of the externally located heat pump. This is provided inside an external enclosure which also provides storage for the ParkLife Café’s waste and recycling bins.

One advantage of using an underfloor heating system rather than conventional radiators is that it increases usable space within the building, increasing flexibility within each room as there are no wall‑mounted radiators to be avoided. Hot water is provided separately to the kitchen, Community Room, and toilets via small electrical heaters.

Photovoltaic Cells
Photovoltaic cells on the Gazebo

The Gazebo at the end of the Botanical Walk has an array of 12 photovoltaic (PV) cell modules, which can produce up to nearly 3 kW of electricity.

Early designs considered installing PV cells on the roof of the building; however, the required angles and positioning compromised the overall design of the building, and output from the PV cells would have been reduced by shade from the nearby mature trees. It was decided instead to locate the PV cells on top of the new Gazebo which was to be built as a focal point at the north end of the Botanical Walk. The Gazebo, which is located away from the shade of any mature trees, was re‑designed to accommodate the PV cells at the optimum angle for their operation.

Cables in underground ducting takes generated electricity back to the building, where it can either be used to reduce local energy usage or fed back into the national grid under a Feed In Tariff scheme to provide additional income for ParkLife, the community interest company set up by FoSJP to operate the Café and Community Room as a social enterprise.

Café Kitchen Heat Exchanger
Inside the ParkLife Café kitchen

As a side effect of the Café kitchen being upgraded from “heat and serve” to full catering standard, its energy usage naturally increased. To counteract the effects of a full range of kitchen equipment—a 6‑burner range, deep fat fryer, grills, etc.—all being used at once, large amounts of fresh air need to be supplied to the kitchen to replace extracted air: up to 0.76 m3 per second. On cold days, supplied air needs to be heated up to internal temperatures to avoid excessive draughts in the kitchen and the Café.

Three solutions were proposed:

Electric Heating—electrically heat supplied air. This would require a unit of 0.65 m3 and would need 21 kW of electricity to heat the supplied air.
Partial Heat Recovery—a heat recovery unit to partly recover heat from extracted air to warm up supplied air. This would require a slightly larger unit of 0.76 m3 but would only need 16 kW of electricity to partially heat the supplied air.
Full Heat Recovery—a larger heat recovery unit to recover all heat from extracted air to warm up supplied air. This would require a much larger unit of 7.6 m3 but would not need any energy to heat the supplied air.
Kitchen Heat Exchanger

All three solutions would also need electric fans to drive large volumes of air for both extraction and supply: typically 5 kW each on maximum settings (so even option #3 would not be completely “zero energy”).

Option #3 was selected on the grounds of minimising energy usage. The large full heat recovery unit was installed immediately outside the kitchen wall, rather than roof‑mounting it which would have required additional roof strengthening and would have been unsightly.

The reason the unit is so large is in order to maximise the surface area shared between the outgoing used air and the supplied fresh air, so that as much heat as possible gets transferred to the supplied air.

The rooflights on the ParkLife Building
(all photos on this page – Martin Gardner)

Electrical lighting needs in the ParkLife Building have been significantly reduced by the five large rooflights.

Originally these were designed to be representative of World War II searchlights; only two were to be actual rooflights, the others being dummy lights on top of the original concrete slab roof. It was later decided to replace the entire concrete slab roof, as a side effect of which all the rooflights could be made to bring light into the building. However, it was found that the proposed material – glass‑reinforced plastic – would not admit sufficient light, so the rooflight design was changed to use thermally efficient double glazing, with the basic “inverted searchlight” shape retained, but with much better light efficiency.

During the daytime, no electric light is needed in those rooms – including the Community Room – that have these rooflights installed.
The ParkLife Café area has large areas of double glazing which both keep heat in and let light in, reducing both heating and lighting energy needs.

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