COMMENTS ON PROPOSED HEATING SYSTEM FOR THE NORTH STREET QUARTER
Technical Director of Ovesco
The proposals from Santon for the development of the North Street Quarter include the use of a district heating system based on water source heat pumps using the river Ouse as the heat source.
The use of rivers for heat pump sources has recently been surveyed by DECC and they have published, as part of their national heat map, a layer showing the potential for heat extraction from rivers by heat pumps:-
This shows the Ouse above Lewes with a capacity of 3.8 to 6.6 MW. Some measurements that I have personally taken would indicate that such a figure is not unreasonable and would be ample for the proposed scheme.
The district heating proposal is unusual in that instead of a central heat source producing hot water which is fed around the district in insulated pipes, a substantial number of small water-source heat pumps, each serving one or a small number of users, have their cold water intakes connected together to an uninsulated common loop of circulating cold water with a single inlet and outlet to the river. Although the scheme is unusual in this respect (two such are known), the use of open-loop water-source heat pumps is fairly common, and their performance is well known.
The scheme has a number of advantages:-
- By using uninsulated pipes, the pipes can be pushed through the ground, including under roads, requiring much less excavation, which is important as contamination of the ground is suspected.
- There are no heat losses from the pipes as is the case with circulated hot water. Indeed heat from the surrounding ground, leaking into the pipes to the water cooled by the distributed heat pumps is an advantage, making it a partly ground source system.
- By reversing the heat pumps, cooling can be obtained at very little extra cost. As global warming sets in, an ever greater proportion of domestic and light commercial energy use will swing from heating loads to cooling loads. This will be a particular problem if approval is given for techniques such as structural insulated panels that achieve high insulation values but give very low thermal mass so that buildings heat up rapidly during the day thus requiring cooling. Concentrating on insulation values alone is to solve yesterday’s problem, not tomorrow’s.
- To the extent that larger buildings may require cooling at the same time as smaller ones need heating, the shared water loop creates a form of thermal cross-subsidy, enhancing the efficiency of both.
- Although the heat pumps require an electrical input, 15 to 25% of the output depending on the coefficient of performance obtained, which has an external CO2 burden, this burden will gradually decrease as electrical generation is de-carbonised. The CO2 burden of gas heating will only increase as gas is obtained from evermore energy intensive sources.
When Ovesco was approached by Santon to enquire whether we would be interested in running such a scheme as an Energy Services Company (ESCO), it was stated that gas would not be supplied to the development. This was important, as it meant that it was unlikely that any customers would be tempted to take the short-term cheaper, but long-term more expensive option of installing a gas heating system. This helped to ensure the long term viability of the investment in such a scheme.
It is feared that by allowing the installation of a gas supply and not mandating the use of the heat pump scheme, that this innovative scheme will be used to aid acceptance of the development, but will be dropped after approval is obtained on the ground that no ESCO can be found to take it on as its long term viability is questionable.
It is urged that, if this proposal is accepted, and no comment is offered on other aspects of it, environmentally advantageous proposals are not approved as options with the possibility of them being dropped on economic grounds but made mandatory and that steps such as the installation of a gas supply that would damage the viability of the heat pump system be not approved. There is a depressing history of such behaviour by developers.
Nick Rouse, Technical Director of Ovesco
Chief Engineer of Telcon Ltd, manufacturer of electrical and energy monitoring equipment
BSc in electrical and electronic engineering
Graduating this year with an MSc in Renewable Energy from the Centre for Alternative Technology
Graduate Member of the Energy Institute