Modelling of an open loop ground source energy design

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Courtesy of ESI Ltd - Environment Specialists

Client: Max Fordham Consulting Engineers

Location: London

Services: Ground Source Energy Modelling

Summary: An open loop ground source heating/cooling scheme is being developed for the redevelopment of the Tate Modern, located close to the River Thames.  ESI Ltd was instructeded by Max Fordham to construct a FEFLOW groundwater flow model to support the design

The geology at the Tate Modern site comprises Made Ground, Drift and River Terrace Gravels overlying a substantial thickness of London Clay.

To model the proposed open loop Ground Source Energy (GSE) scheme in the River Terrace Gravels, a single layer model was developed using the FEFLOW hydrogeological finite element modelling software. The model simulates groundwater flow in the River Terrace Gravels and overlying Alluvium and Made Ground and extends over an area approximately 2km by 1km, adjacent to the River Thames.

A steady state model was first used to assess the maximum abstraction rates that might be achieved and the likely impact on local groundwater levels. It also assessed the sensitivity of the GSE scheme performance to the borehole locations and uncertain hydrogeological parameters. A transient model was also used to investigate the feasibility of abstraction / injection at higher flow rates for limited periods of higher demand. The model was run to simulate a period of 24 hours, with increased abstraction.

The results indicated that it would be possible to double the abstraction rate relative to the designed flow for up to 12 hours without excessively dewatering the aquifer. However, if abstraction was continued at this rate, it became unsustainable with an increased risk that the groundwater levels would fall too low to continue operation.

It was concluded that the design represented the maximum sustainable flow rate for the boreholes, but that there was a degree of operating flexibility to meet short term peak energy demands. On the basis of the modelling carried out the client went on to commission the initial pumping and injection test at the site. The scheme is now being installed, and will make a renewable and efficient contribution to the building’s energy use.

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