River Thames is heat source for apartment development
Down at Kingston upon Thames, a huge heat-pump system is drawing heat from the River Thames to serve an innovative district-heating system for a residential development — a project that was facilitated by local MP and Secretary of State at DECC Ed Davey. Ken Sharpe has been finding out more.
It was about five years ago that Mike Spenser-Morris, managing director of NHP Leisure Developments, became aware of the potential of heat pumps for community heating in apartment blocks. He decided to look more closely at this technology as an alternative to the combination of gas-fired CHP and biomass that was then being considered for the Kingston Heights and River Walk development of residential apartments at Kingston upon Thames.
His enthusiasm was prompted by the computer -generated images produced to promote the development, which clearly showed the River Thames in the background (top photo).
The development includes 56 homes in Kingston Heights for Affinity Sutton, a national provider of affordable housing, and 81 luxury private apartments known as River Walk provided by Redrow London.
Mike Spenser-Morris had picked up some knowledge about water-source heat pumps, and decided that the River Thames, which is not tidal at this point, would be an ideal source of heat. Discussions with consulting engineer Chris White, managing director of White Associates, confirmed that the approach would be technically and economically feasible and cost little more than gas-fired CHP and biomass system.
One of the key problems was to find a similar installation elsewhere, for no-one really wants to be a pioneer for such a project.
There wasn’t one in this country, nor was there one in Europe. Eventually, one was found in Japan — which was duly visited, providing the confidence to go ahead at Kingston
But where this community/ district-heating system differs from most other systems is that there are no hot-water mains.
What happens instead is that water at about 9 or 10°C is piped to local plant rooms with Mitsubishi heat pumps in them. That circulating water is the energy source for the heat pumps and returns at a lower temperature — about 3 K lower. There are 41 heat pumps with a heat output of about 30 kW each.
The next stage resembles a VRF air-conditioning/heating system in that hot refrigerant gas is sent to a ‘heat-pump boiler’ in each apartment. That ‘boiler’ then heats water for underfloor heating systems and a hot-water cylinder, which has the support of an electric immersion heater. Water comes off the boiler at about 45°C. Every room in an apartment has its own thermostat.
|Two plate heat exchangers provide the interface between the River Thames and the main water-distribution pipework.|
And lest refrigerant circulating in a building sets off your personal alarms, there is no need for refrigerant leak detection because the quantity in any particular circuit is small and there is no refrigerant pipework in bedrooms.
The kit used throughout the project is quite standard — from the heat pumps to the heat-pump boilers, the inverter-controlled primary and secondary pumps, and the plate heat exchangers.
Because the main underground distribution pipework transports water at a temperature comparable with the ground, there are no concerns about heat loss, as there would be with hot water. Indeed, it is even possible that more heat might be extracted from the ground, but the effect should be small. Because the temperature of the water in the pipe is about the same as the surrounding ground, the main pipework does not need to be insulated. These pipework runs are plastic — MDP underground and ABS above ground.
The low temperature of the primary pipework will also not contribute to internal heat gains, a concern of the latest Part L which comes into effect in April 2014.
Primary water is drawn from the River Thames at up to 150 l/s. At the depth of abstraction, the temperature is a steady 9°C, with return water about 3 K cooler. The water is piped to a nearby plant room, where plate heat exchangers provide the interface with flow and return pipework to the building. The river-water circuit is thus open, and the circuit to the building is closed. Ultimately, the system will generate around 2.3 MW of heat.
It should be evident that water is not actually extracted from the river, used for a process and then returned. That perception, however, was not available to the Environment Agency, which had to consider the application for an extraction licence.
That was when Ed Davey, Secretary of State at the Department for Energy & Climate Change, became involved. He is MP for the neighbouring constituency, the boundary of which is a couple of hundred yards away across the railway line to Waterloo Station in London. Ed Davey was intrigued by the project, as was evident when the installation was officially turned on in October.
Mike Spenser-Morris went to one of Ed Davey’s surgeries and convinced him that the nature of this project was potentially of huge significance on a national scale. Levers were obviously pulled in the right places, and, presumably lessons learned for the future. Indeed, Mike Spenser-Morris admits that the project would not have succeeded without Ed Davey’s help.
|Project culmination — Ed Davey, Secretary of State at the DECC sets the district-heating system operating, watched by Mike Spenser-Morris of NHP Leisure Developments.|
Even the maximum draw-off from the River Thames is relatively minute — about 1 part in 2000 of the flow (0.05%). The 3 K lower return temperature has no discernable effect on the river itself just a short distance from the return point.
The safety of fish and eels in the river is protected by a fine mesh across the draw-off area. The mesh has a pitch of just 2 mm, so even elvers cannot be drawn in. The water velocity is also very low, about 0.2 m/s, so there is no risk of fish being pinned to the grille and unable to escape.
If the mesh becomes blocked, the flow can be reversed to clear obstructions.
The story could stop there, except that an adjacent 142-bedroom hotel will also be linked into the system — for heating and air conditioning. The idea is that heat from the hotel air conditioning will be rejected into the closed-circuit cold-water loop. An air-conditioning system rejecting heat into water at well under 10°C will achieve a very good EER (energy-efficiency ratio).
That heat rejected becomes available to the heating system for the apartments, for which it is preferentially used rather than being rejected to the River Thames. So we have the dual benefit of highly efficient air conditioning and highly efficient heating via heat pumps.
A COP of four to six for heating the apartments is expected, but the original calculations did not include this benefit of heat rejection from the hotel.
Heating costs for the apartments are expected to be some 20% less, than would otherwise be the case, with carbon emission reduced by 500 t a year. Carbon emissions will actually be zero as green electricity is supplied by Ecotricity
Given his support for the project, it was entirely appropriate that Ed Davey should formally switch it on. He said, ‘Kingston Heights is a great example of how sustainable solutions can help power entire communities. I want to see a community energy revolution where projects like this are the norm, not the exception.’
Donald Daw, commercial director with Mitsubishi Electric, said, ‘This project is one of the most impressive in Europe if not the world. This is a pioneering installation and hugely innovative.’
Mike Spenser-Morris is keen that the knowledge and experience should be shared. A company, Zero Carbon Partnership, has been set up to help encourage the application of open-water technology for district-heating systems.