The Gospel Oak project originated in 2012 when MITIE (now part of Utilyx) appointed Ramboll to carry out the detailed design of a district heating scheme in the London Borough of Camden.
MITIE's involvement with Camden started when it was appointed by the Royal Free NHS Trust to install and run a 5 MWe gas-fired Combined Heat and Power plant (CHP) in the Royal Free hospital. This was designed to achieve both energy savings and approximately 93,000 tonnes of CO2 reductions over a 15 year period. At the same time Camden council were separately investigating alternatives to upgrade the heating infrastructure to a number of large housing estates situated close to the Royal Free hospital.
These housing blocks had originally been built in the 1960s and their heating systems were nearing the end of their normal operational life. Camden explored a number of opportunities including replacing individual boilers through to estate wide district heating (DH) systems connected to a central CHP plant. Given the proximity of the housing estates with the hospital, a further option was investigated - taking surplus heat from the newly installed CHP and using it to supply heat to the housing block via a new district heating scheme. It was decided to move forward with latter option.
In addition to saving energy, this proposed scheme enabled MITIE to partner with Camden Council to help it achieve its declared borough-wide CO2 reduction target of 40% by 2020. The Gospel Oak CHP project would be a significant first step, with at least 2500 tonnes of CO2 saved annually (equivalent to insulating 4000 typical semi-detached homes).
The DH scheme therefore became a unique partnership between the Royal free NHS Trust, MITIE and Camden Council. It was also the first public private partnership of its kind aimed at alleviating fuel poverty as well as saving carbon. The project was funded via various sources including the (London) Mayor Targeted Fund Stream and the Community Energy Saving Programme. Savings realised from lower fuel costs will be used to set lower heating charges for residents.
In April 2011 the council cabinet members approved the direct award of the works and supply of heat to MITIE. In addition MITIE was awarded the contract to operate the district heating scheme for 14 years.
Ramboll was responsible for the Mechanical and Electrical engineering design (including controls), the structural engineering design, the acoustic design and the architectural design. In addition the company also oversaw the installation and the successful commissioning of the scheme. The design was carried out in both our London and Copenhagen offices with key engineering experts allocated to the project as necessary.
Project details
The heat source for this district heating scheme is the flue gases which are discharged from the hospital’s new CHP plant. By placing a heat exchanger or economiser in the 2m diameter exhaust flue, heat can be extracted from the 195°C gases and used to heat the district heating water from 40°C up to 90°C. At 90°C the water is hot enough to be used directly in the heating and hot water systems in individual dwellings without the need for it to be boosted by a heat pump or other form of heat. In this way up to 1.5MW of useful instantaneous heat can be recovered.
This heat is then used to provide energy for dwellings in the Gospel Oak part of Camden including both the Fleet and Dunboyne Estates. Specifically it was decided to connect into six of the existing blocks of community housing owned by Camden. The six blocks connected are Cayford, Dunboyne, Waxham/Ludham, Bacton, Wendham and Weedington, comprising a total number of 1449 dwellings or apartments. The blocks are varied in size between 100 to 300 dwellings and up to 22 stories high.
The route of the district heating pipework runs above ground from the hospital to a pumping station located adjacent to the first block served. The district heating circulation pumps were installed in the oil tank plant room which became redundant when the boilers in the Cayford block were changed to gas as fuel source. After connecting into the Cayford block, the pipe work is then routed below the streets for approximately 1km to connect into the remaining five blocks (see diagram). The size of the pipework varies, but is generally 200mm in diameter with branches to the individual blocks of between 80-125mm in size.
Within each block the DH plant room enters a ground floor or basement plant room to connect into a plate heat exchanger. The plate heat exchanger is in turn connected in parallel with gas-fired boilers to feed the hot water and communal heating systems within each block. In this way the district heating system is designed to provide the base-heating load with the boilers providing additional capacity required in times of maximum heating demand. As part of the works, each block also had its existing gas fired boilers replaced with new boilers, controls and heat meters.
The DH network system controls have been designed to effectively spread the available 1.5MW of heat equally between the six blocks depending on their combined heating demand. The variable speed circulation pumps work in conduction with two port automatic control valves to achieve this in an energy efficient manner.
Although the DH system initially delivers only the 1.5MW recovered from the hospital, the network has been designed to take a maximum thermal load of 3.5 MW. In this way it can be extended to connect to both future loads and also heat sources as the DH network grows.
The scheme was completed and constructed in less than six months (May - November 2012) and has been running successfully since then. It produces £320,000 of annual fuel savings per year in addition to the carbon savings. This equates to a saving of approximately 2.7p per kWh of heating energy used.
Since then Ramboll has carried out the detailed design of a number of further DH projects throughout the UK and is currently working both in Sheffield and in London on schemes connecting both new and existing buildings.
In the first of this series, Crispin Matson looked at the potential advantages of district heating for the UK, where the technology is expected to meet 20% of the country's heat demand by 2030.
ABOUT THE AUTHOR
Crispin Matson is Country Manager for Ramboll Energy UK.