Details
Solution type
Topical area
Temperatures in the London underground have been steadily rising since it began operation in the 19th century, and to solve this problem, both heat exchangers and a heat pump have been installed.
The technological solution for recovering heat from the London Underground is to install a heat exchanger in the vents used to extract hot air from the network. A heat pump can create water hot enough to be used in a district heating network.
LO2 and LO3 are two of London's demonstrators. The demonstrated technologies are related to:
- The capture of waste heat from electrical transformers and tube ventilation shafts and integration of a thermal store. Removing heating from the tunnel system in winter, when it is mostly needed above ground, can help cool surrounding walls and, hereby, lower overall temperatures during summer. Heat extraction during winter enables more absorption capacity for the tunnel walls during summer.
- The extension of the Bunhill seed network. The Bunhill Energy Centre already, through a previous project in 2012, created a local district heating system to warm two leisure centres, three communally heated council houses and one private housing development, covering 805 units in total. The system comprises a 1.9MW CHP gas engine and 115m3 thermal storage with 1.5km of district heating pipework. The CELSIUS project aims to expand this network with 454 homes and include excess energy from the London Underground, potentially supplying 1000 homes.
Facts about the case |
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| Installed heat capacity: 1 MW heat pump Heat source: Excess heat from London Underground ventilation system Potential: 10% of heat losses from the London Underground is from ventilation. |
Support: FP7-supported CELSIUS project Organisation: Islington Council District heating network: +1000 units |
Idea and layout
The concept of the demonstrator foresaw the capture of heat from both:
- The transformers of the electricity substation, using an oil-to-water heat pump:
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Heat is generated from electrical transformers during normal activity due to losses incurred during voltage conversion. At the demonstrator’s site, the transformers are cooled using an oil system and the heat is currently lost to the environment. The feasibility study indicated that the expected available heat of the three transformers is approximately 160kW per transformer at full load, at oil temperatures assumed to be at least 48°C. Technical issues related to the age of the electrical transformers affected the project's feasibility, and at present, it will not be developed further.
- The tube ventilation shaft, using an air-to-water heat pump (integrating thermal storage)
- The ventilation shaft expels exhaust air at a rate of 30 m³/s at 22°C in winter and 28°C in summer. The feasibility study concluded that the mid-tunnel ventilation shaft's heat output would be around 0.4MW. To maximize the demonstrator's impact, it was decided to upgrade the extraction fan in the tube ventilation shaft. The new fan expels air at 70m³/s and increases the heat output to around 1MW.
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This will extend an existing district heating network using the heat from the identified waste heat sources. In addition, to maximise the impact, a new CHP plant will be installed at the London Underground vent site.
Impact
The overall demonstrator’s performance is summarized in the following table according to 5 evaluation criteria. It can be noticed that the assignment of all the scores is directly linked to the values calculated for the key performance indicators (KPI), except for socio-economic benefits, where a qualitative assessment is carried out based on this cluster’s indicators and separate interviews.
| Overall Impact | Fair/Medium | |||||
| Size [MWh/y] | 1-100 | 100-1000 | 1000-5000 | 5000-10000 | >10000 | |
| Primary Energy Savings | 0-10% | 10-20% | 20-40% | 40-60% | >60% | |
| GHG Emissions Reduction | 0-10% | 10-30% | 30-60% | 60-90% | >90% | |
| Pollutant Emissions Reduction | 0-10% | 10-30% | 30-60% | 60-90% | >90% | |
| Socio-Economic Benefits | Low | Fair | Medium | High | Extrem | |
Replication
Replication potential
| Replicability | Low | Medium | High |
| Authorizative easiness | X | ||
| Adaptability to different climate conditions | X | ||
| Easy-to-implement (No needs of specific technical requirements) | X | ||
| Easy-to-operate (No needs of specific technical requirements) | X | ||
| Opportunity of integrating waste energy sources | X | ||
| CAPEX needed for the deployment of the solution | X |
Technical requirements
Possible requirements for replicability for the demonstrator, related to heat extraction from the underground are:
- A ventilation shaft or a water source from the underground system should be present, and sufficient adjacent space should be available to install the necessary equipment.
- Set up clear lines of responsibility between infrastructure and district heating.
- High temperatures in the waste heat source (minimum 20-30°C).
- A failsafe system should be available to allow normal operation in case of district heating breakdown.
Possible requirements for the replicability of the demonstrator related to heat extraction from the electrical substation are:
- The presence of oil-cooled transformers with an oil-to-water heat exchanger and normal cooling systems.
- Sufficient load on the transformer requires cooling systems.
- Availability of sufficient space for the equipment to be installed.
- Set up clear lines of responsibility between infrastructure and district heating.
- The presence of a failsafe system allows normal operation in the event of district heating breakdown.
Stakeholders
| Stakeholders | Organization Name | Organization Type | Organization Domain | Benefits from demo |
| District heating network operator | Islington Council | Local authority | Local government | Expanded district heating system and cheaper heat source |
| Ventilation shaft operator | London Underground | Public transit authority | Transport in London | Increased ventilation capacity, potential for cooling in summer |
| Islington residents | N/A | N/A | N/A | Reduced energy bills |
Islington has a standard template contract that is used to supply heat. This forms the basis of discussions and aims to ensure that the council has the following guarantees - A guaranteed bulk heat price, which provides revenue certainty to both parties. - A maximum return temperature from connected buildings back into the network. This is required to ensure that the primary network operates as efficiently as possible and minimize thermal losses in the system. - A minimum amount of heat is required to connect loads to the network. This ensures that the connected development must operate their respective secondary systems with the primary district heating network as the lead.
The heat supply agreement/contract also has a clause which requires a review of the minimum take every 12 months.
Negotiations for heat supply can be broken into two sub-categories: 1) Planning application stage. As operators of our network, we must work closely with planning colleagues to mandate major developments within the vicinity of the network in which to connect. Islington has strong policy support from the 'London Plan' regional planning document and local planning guidance. These documents allow us to have planning and section 106 conditions, which lead the developer to connect. This is a two-way relationship as developers who connect to district energy networks can meet their mandatory CO2 targets for emissions reductions.
There are several ownership models which can be used for district heating networks. Most are either wholly public or wholly private, the Islington scheme is wholly public and is owned and operate by Islington council as a municipal scheme, other networks such as Citigen are wholly private and are typically owned by energy companies or energy service company providers (ESCO's).
Finance
The full procurement and preliminary stage is now completed for the project, and we have appointed Colloide Engineering Systems as the principal contractor. Details of the capital costs for the project are available from the project team.
Many public decentralized energy projects are developed as 'spend to save' with public bodies such as councils or NHS Trusts looking to recover their capital investment through reduced energy revenue savings.
Challenges and risks
Challenges
The project's complexity, coupled with the relatively small amount of space available at the energy center, has produced a number of specific challenges that the project team is working to overcome.
- Collaboration with London Underground Railway Authority (LUL). LUL is undertaking the works to demolish the existing building at the site and replace the existing ventilation shaft fan and other auxiliary mechanical plant. The level of detail required in planning and coordinating the works and respective contractors has been substantial. To ensure that a program suitable for both parties has been produced, a series of programming meetings have taken place.
- Obtaining expertise. Decentralised energy is a relatively small field, and there is a lack of expertise within the field, impacting project delivery. To ensure the project was a success, the council undertook a full public procurement exercise to appoint a specialist client engineer to develop specifications, manage the design process, act as clerk of works and generally provide technical guidance and expertise to the client. As the client, we also appointed a highly qualified project team to oversee the project for the council
- Obtaining support. The project's overall aim is to provide cheaper and greener heat to the residents of Islington and to obtain full support for the investment; the project team had to demonstrate with certainty that the project would generate a minimum saving. To do this we used a complex energy modeling program to replicate the operating conditions and variability in energy markets to produce outputs in the form of heat prices and values for connected buildings.
Risks
Some risks to the project could be categorized into financial, technical, and reputational.
The key technical risks stem from the level of innovation in this project and the fact that heat recovery from an underground railway has never been done commercially. The main technical risk is around the coil (air-to-water heat exchanger) located in the ventilation shaft and the level of fouling due to dirty and contaminated air being extracted from the railway. To mitigate the risk, we are designing a coil with a wider-than-average spacing between the heat exchanger fins to reduce the ability of the coil to trap particulates, and we are also developing a washer system that will automatically wash the coil. The project team have worked closely with London Underground to undertake trials of heat exchanger coils within the Underground network.
We have specified the use of an ammonia heat pump to achieve flow temperatures in excess of 50c from the heat pump. This is a non-standard refrigerant and a full risk assessment and risk mitigation plan for the energy centre are required.
The other major technical risk is around return temperatures in the network.
There are also several commercial and financial risks to the project. A number of these would be generic and applicable to most building and engineering projects of this scale; however, there are still some specific risks that would apply to the Islington demonstrator.
1. Drop in wholesale energy prices. Our network relies on power sales, so any drops in electricity prices will affect the savings we can offer to heat customers.
2. Lack of commercial connections. We are going to be exporting heat to commercial developments within the Old Street area. The majority of these are office buildings, which have a more diverse and different load profile than council residential buildings. Without these loads, it will be harder to operate the plat at optimum conditions for as long.
3. Government support for renewable heat. The utilisation of the heat pump is classed as a renewable heat source and is therefore eligible for government subsidy in the form of the RHI (renewable heat incentive). The government has recently slashed the subsidy available to renewable power generators, so there remains uncertainty with renewable heat.
Lessons learnt
Demonstrator development
An important lesson learnt is related to optimizing the realization process: by twin-tracking the procurement processes with the planning/authorization process, it has been possible to move the project forward as efficiently as possible, preventing possible delays.
Demonstrator performance monitoring
Following the monitoring methodology set up for monitoring the Celsius demonstrators, relevant key performance indicators are identified for this technology to quantify and measure its impact for the specific baseline situation referred to the common mix of heating systems used in London, consisting of natural gas-fired boilers, oil fired boilers, electric heaters and electric heat pumps.
| Technical KPIs |
| Yearly amount of electric energy used by the installed heat pump system at ventilation shaft and thermal storage- MWhe/year |
| Seasonal COP of the heating pump system at ventilation shaft and transformer |
| Yearly amount of thermal energy recovered/provided by ventilation shaft and thermal storage- MWht/year |
| Thermal energy delivered to the buildings connected to the district heating system in the expansion of the network- MWht/yea |
| Environmental KPIs |
| Variation of emissions with reference to baseline situation- kg/year of PM10, PM2.5, TSP, NOx, SOx, CO, CO2 and % of variation |
| Yearly GHG variation- % of variation and kg/year of CO2e |
| Economic KPIs |
| Yearly cost for electric energy consumption at ventilation shaft and thermal storage(C)- €/year |
| Maintenance costs at ventilation shaft and thermal storage- €/year |
| Yearly savings for the end-user-€/year per end-user |
| Social KPIs |
| Additional buildings connected to the district heating system |
| Internal surface served by the new system- m2 |
| Number of residents benefitting of the new system |
| Number of workplaces benefitting of the new system |
Islington, London, United Kingdom
2019 - 2022
IVL Swedish Environmental Research Institute
Related Celsius content:
Making the underground cool again
Making use of excess heat: Assessment methodology for urban excess heat recovery solutions
References:
- Jamie Burn (2014) Cooling the Tube & Bunhill, Presentation given at the Celsius Conference, 11 November 2015
External links:
Greater London Authority (GLA), Islington Council, CELSIUS Talk: Putting pipes in the ground, Handbook – 25 cases of urban waste heat recovery
Replicability |
Low |
Medium |
High |
|---|---|---|---|
| Authorizative easiness | x | ||
| Adaptability to different climate conditions | x | ||
| Technology easy-to-implement (No needs of specific technical requirements) | x | ||
| Easy-to-implement (No needs of specific technical requirements) | x | ||
| Easy-to-operate (No needs of specific technical requirements) | x | ||
| Opportunity of integrating waste energy sources | x | ||
| CAPEX needed for the deployment of the solution | x |