Publication - Progress report

Guardbridge geothermal technology demonstrator project: feasibility report

Published: 23 Mar 2016
Directorate:
Energy and Climate Change Directorate
Part of:
Environment and climate change
ISBN:
9781786521293

Report of the study exploring the potential of a geothermal district heating system accessing hot sedimentary aquifer resources underlying Guardbridge, Fife.

115 page PDF

17.3 MB

115 page PDF

17.3 MB

Contents
Guardbridge geothermal technology demonstrator project: feasibility report
7. Geothermal Heating Potential

115 page PDF

17.3 MB

7. Geothermal Heating Potential

A traditional heat network has its extent defined either by choice or by available demand, however the extent and capacity of a geothermal-based network is mostly defined by the heating potential of the target resource. This is determined by both the source temperature, which influences the achievable temperature drop, and extraction flow rates from the resource.

7.1 Initial Estimates of Output

Before the geological work had reached its final conclusions, this heating potential was quantified for a wide range of possible values which can be seen in Table 6.1. Due to the initial assumptions around the type of geothermal resource and target depths, it was known that the temperatures found would definitely be below the typical return temperature of a district heating network ( DHN), even a low temperature network with a return of 45 °C. This meant that the only possible heating solution would be to utilise a heat pump and to upgrade the geothermal heat to the required network flow temperature. This meant that a temperature drop of 5 °C could be assumed and the potential heat output calculated for a series of flow rates and coefficients of performance ( COP's) using the following equation:

Mathematical Equation

It should be noted that although the overall heat production does decrease slightly with a rising COP (Table 7.1), this is because a more efficient heat pump will draw less of its output from electricity. Given a fixed source input, this will therefore reduce the final heat output of the unit. However, the increased COP does reduce the cost of heat by a much more significant margin as can be seen to the bottom of Table 7.1. The range of COP values is based on supplier data (Fig. 7.1).

Table 7.1: Heat pump outputs for various flow rates and COP values, and the indicative cost of heat shown based on 12p/kWh for electricity.

Heat capacity of heat pump based on T of 5 ºC (kW)

Source Flow Rate (l/s)

COP of Heat Pump

3.0

3.5

4.0

4.5

5.0

5.5

6.0

5

157

146

139

134

131

128

125

10

314

293

279

269

261

255

251

15

470

439

418

403

392

383

376

20

627

585

557

537

523

511

502

25

784

732

697

672

653

639

627

30

941

878

836

806

784

766

752

35

1097

1024

975

941

914

894

878

40

1254

1170

1115

1075

1045

1022

1003

Cost of Heat (p/kWh)

4.0

3.4

3.0

2.7

2.4

2.2

2.0

7.2 Final Heat Production Estimates

The final temperature and flow estimates were obtained from Town Rock Energy and were given in the form of one high flow scenario that was more favourable and a low flow scenario with more conservative assumptions (Section 4.1.3). The potential heat outputs [1] of the scenarios were therefore defined as 418 kW for the high flow case and 139 kW for the low flow case.

Figure 7.1: GEA heat pump performance against source temperature, delivering at 75 oC.

Figure 7.1: GEA heat pump performance against source temperature, delivering at 75 oC.


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