Skanska central nottinghamshire jv

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Introduction

The Skanska Central Nottinghamshire JV project embraces the redevelopment of the existing Kings Mill Hospital, located on the A38 between Sutton in Ashfield and Mansfield. The Hospital is bounded by the A38 road and Kings Mill Reservoir to the southeast and the A6075 and outskirts of Sutton in Ashfield to the southwest. To the north and east are fields including the East field and to the east is a supermarket.

As part of the development of the main hospital project a lake source geothermal scheme has been developed using the Kings Mill Reservoir to primarily provide cooling and some heating if the capacity is available. It will provide all the hospitals current cooling requirements rated at about 5.4 Mw. This scheme involves the pumping of warm water from the energy centre via a lakeside manifold to a series of underwater heat exchangers or radiator panels arranged in banks Fig1.

Background

The original aim has always been to reduce the overall energy consumption of the hospital estate. A number of schemes were originally considered including:-

  • Onsite electricity generation using mines gas - Methane
  • Combined heat and Power plant (CHP)
  • Ground source heating using conventional or a piled solution
  • Photovoltaics.

The feasibility studies at the time selected both photovoltaic in a limited capacity and ground source heating, a lake source system was dismissed as being un-economic and Wind was not permissible under the planning permission.

As the scheme developed it became clear that a piled ground source cooling option had some risks as well as being expensive and the lake was revived as an option. The final options for comparison in order of preference were.

  • Closed loop Lake source cooling
  • Open loop ground water cooling - pumping up groundwater from a borehole using it to cool site water then re-injecting into another borehole
  • Closed loop piled geothermal option - pipes built into the piles using ground water flow to provide cooling

The proposed ground source heat pump or geothermal solution will replace the conventional equipment with a system using heat pumps, located within the buildings, and a network of heat exchangers sunk into the near by lake. This system will move heat between the buildings and the lake rather than consuming fuel on site providing cooling via forced air cooling. Please note that some electrical energy is required to run the system but this is a small amount compared to the amount of heat exchanged with the lake.

Background

  1. The UK Government has set itself on a course to create a low carbon economy. It has set a target to cut the UK's carbon dioxide emissions - the main contributor to global warming - by 60% by about 2050, with real progress by 2020. The UK Government's Energy White Paper, published in February 2003, concludes that if the UK is to achieve a reduction in carbon emissions of that order, then renewables will need to contribute at least 30-40% of our electricity generation and possibly more. The UK Government has therefore set a target of supplying 10% of UK electricity from renewables by 2010, subject to the cost to consumers being acceptable, and aspires to double that amount by 2020.
  2. In order to help deliver the Programme for Government commitment to make an equitable contribution to the UK effort, the Scottish Executive set targets that 18% of electricity generated in Scotland should come from renewable sources by 2010 rising to 40% by 2020. It seems likely that the renewable energy capacity already installed, plus capacity that has been consented but not yet built, will be sufficient to meet the 2010 target. FREDS believes, therefore, that this would be an opportune time to take stock of progress, and to consider in particular how the 2020 target might be met, both in terms of technologies and the installed capacity that might be necessary. In doing so, FREDS believes that issues such as security of electricity supply, transmission infrastructure and Scotland's contribution to the UK renewable electricity targets, should be taken into account.

Description

The system uses banks of stainless steel radiators called slim Jims Fig 2 submerged in the neighbouring Kings Mill Reservoir connected via pipes to the hospital plant where heat pumps extract or add heat.

It will be the largest geothermal lake loop installed in Europe offering a total of 10MW (5.4 MW of cooling and 5MW of heating). When the water flows back through the plates in the reservoir the temperature imbalance is partly restored by the water without contaminating it because the system is entirely sealed off. This heat exchange is much more efficient than other renewable energy technology and conventional gas or oil heating. For every 1kw of energy used, 4kw is produced by the system, which means that not only will 1,700 Tonnes of CO2 be saved but energy bills will also be cut by around £120,000 every year. That is equivalent to saving 7 million miles of driving, or taking 600 cars off the road every year. The system will be used to cool the air in the hospital by reducing the temperature of the water flow, a distinct advantage over other energy sources like biomass and combined heating and power.

The scheme will significantly reduce the running costs and environmental impact of the hospital site as the heat exchange process is considerably more efficient than conventional heating and cooling equipment.

Environmental Impact

There were a number of users of the lake including the local yacht club, a county activity centre, the Friends of Kings Mill Reservoir, a local preservation group, and the local angling group. The reservoir is used for recreational boating and for quiet pedestrian enjoyment of the wildlife and landscape. Therefore any scheme must take into account the users of the lake.

The lake itself is a eutrophic (nutrient rich) standing water with a high degree of siltation and associated fauna. The previous data suggests that the reservoir is hypertrophic given the loading of nutrients and algae. From an ecological point of view the reservoir remains a highly eutrophic body of water.

Key impacts include:-

  • Remobilisation of sediment causing release of nutrients - eutrophic condition.
  • Increase in temperature of the overall ware body leading to changes in ecology.
  • Restrictions to users.
  • Entanglement of sailing craft in Slim Jim heat exchanger units
  • Disturbance of wildlife.

The scheme was designed to minimise the impact with work carried during the winter months and a floating reed bed Fig 3 designed to site around the Slim Jim heat exchange units.

Consultation

There were a number of users of the lake including the local yacht club, a county activity centre, the Friends of Kings Mill Reservoir, a local preservation group, and the local angling club. There were also a number of ecological concerns from invertebrates to water voles.

Skanska Central Nottinghamshire JV consulted extensively with these local community groups along with Ashfield District Council, the local wildlife trust to assure them that the environmental impact of the system would be extremely low, and in some cases benefit the ecology of the body of water.

Mitigation

The floating Reedbed systems Fig 3 as supplied by the A.G.A Group are made up of single 2mx2m EcoIsland modules, these modules interlock to make up the extended floating reedbed. These modules are constructed on-site as they interlock with each other to form a floating Reedbed that is robustly secured. This will primarily provide mechanical protection to the heat exchangers but will also provide some extra habitat and offset additional nutrient build up.

The temperature of the system refrigerant will be monitored to ensure maximum temperatures submitted in geothermal calculations are not exceeded at the heat exchanger plates. An alarm will provide early warning of any temperature exceeding system design values.

Geothermal Lessons Learned

Description

Skanska Central Nottinghamshire JV has installed a lake based geothermal heating and cooling system for Kings Mill Hospital. The system will use a network of plates submerged in the neighbouring Kings Mill Reservoir connected via pipes to the hospital plant where heat pumps extract or add heat. Skanska central Notts JV, consulted extensively with the local community during the process, including Ashfield District Council and Friends of Kings Mill Reservoir, a local preservation group, to assure them that the environmental impact of the system would be low, and in some cases benefit the ecology of the body of water.

It will be the largest geothermal lake loop installed in Europe offering a total of 10MW (5.4 MW of cooling and 5MW of heating). When the water flows back through the plates in the reservoir the temperature imbalance is partly restored by the water without contaminating it because the system is entirely sealed off. This heat exchange is much more efficient than other renewable energy technology and conventional gas or oil heating. For every 1kw of energy used, 4kw is produced by the system, which means that not only will 1,700 Tonnes of CO2 be saved but energy bills will also be cut by around £120,000 every year. That is equivalent to saving 7 million miles of driving, or taking 600 cars off the road every year. The system will be used to cool the air in the hospital by reducing the temperature of the water flow, a distinct advantage over other energy sources like biomass and combined heating and power.

Specification - Kings Mill Hospital Geothermal

  • 65,000m2 lake
  • 140 slim jim units In 7 banks
  • 5,400kW cooling (all the cooling for the site)
  • 5,000kW heating (significant proportion of heating)
  • 42 EKW130 heat pumps
  • Saving 9,600MWh of Gas & Electricity annually
  • Annual savings of 1700 Tonnes of CO2
  • £120,000 Savings in Energy Bills Each Year
  • Savings equivalent to 7 million miles of driving or taking 600 cars off the road

Future Trends and Development

Summary

Specification - Kings Mill Hospital Geothermal

  • 65,000m2 lake
  • 140 slim Jim units In 7 banks
  • 5,400kW cooling (all the cooling for the site)
  • 5,000kW heating (significant proportion of heating)
  • 42 EKW130 heat pumps
  • Saving 9,600MWh of Gas & Electricity annually
  • Annual savings of 1700 Tonnes of CO2
  • £120,000 Savings in Energy Bills Each Year
  • Savings equivalent to 7 million miles of driving or taking 600 cars off the road

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