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| Table 1: Renewable energy analysis (based on 2006 prices) comparing standard B&Q system of heat pumps suspended from ceiling against underfloor heating and cooling | |||
| System | Rooftop warm-air AHU | Geothermal with suspended water to air heat pumps | Geothermal with water to water heat pumps and underfloor system |
| Heating | Gas-fired | Geo heat pump | Geo heat pump |
| Cooling | DX | ||
| Electricity | Grid | Geo heat pump | Geo heat pump |
| Grid | Geo heat pump | ||
| Annual energy cost | £192,000 | £168,000 | £158,000 |
| Scheme capital cost | £270,000 | £414,000 | £577,000 |
| Affected structure capital cost | £107,000 | £57,000 | £205,000 |
| 25-year energy costs | £2,689,000 | £2,357,000 | £2,220,000 |
| 25-year lifecycle/replacement costs | £401,000 | £344,000 | £240,000 |
| 25-year planned preventive maintenance | £989,000 | £989,000 | £329,000 |
| 25-year TOTAL | £4,445,000 | £4,161,000 | £3,571,000 |
| Simple payback based on year 1 costs | 3.99 | 12.13 | |
| Savings compared with base system (based on 25-year total) | £294,000 | £884,000 | |
| Summary of renewable technologies | ||
| Feature | Performance | Proportion of total energy |
| Geothermal heat pumps | 650kW heating, 440kW cooling using five heat pumps | 14.19% |
| Wind turbine | A 20kW wind turbine will provide up to 30,000 kWh | 1.52% |
| Photovoltaic panels | 49m2 predicted to give 4900kWh per annum | 0.17% |
| Solar water heating | 50m2 solar panels provide preheat water heating for domestic purposes | 0.80% |
| Rainwater recovery | 20,000 litre underground tank provides 92% of water required for water plants in garden centre and toilet flushing | |