As part of the planned evolution of the King's Cross energy centre, Vital Energi were chosen to develop, deliver and operate the cooling energy centre and network. This was an important step in the development's progress as it allows the overall energy solution to become a trigeneration scheme and operate more efficiently.
“The Cooling Pod is capable of producing 12.4MW of cooling but as standard will deliver 9MW. The Cooling Pod plant comprises a 1.4MW absorption chiller, three 3MW water-cooled electric chillers, two 1MW dry air-cooled chillers and two 30m³ thermal stores. ”
Vital Energi have been involved in developing the King’s Cross energy strategy since 2009, creating an energy generation and distribution solution which evolved alongside the development, ensuring optimum performance at each stage.
One of the planning stipulations attached to the 67-acre London site was that the energy infrastructure would produce low carbon cooling, in addition to heat and power, making it a tri-generation scheme. Vital Energi were commissioned to perform a feasibility study and designed a solution which took waste heat from the CHPs in the existing energy centre, during the warmer summer months when it wasn’t being used, and converted it into cooling for the surrounding buildings via an absorption chiller.
The project was made challenging in several respects, with one being the unusual shape and size of the footprint the new “cooling pod” would be situated on and the second was the proximity to the HS1 train line which brings strict restrictions which are backed up by severe financial penalties.
The initial concept for the development would have seen traditional, individual cooling solutions set up in each building, but Vital Energi were asked to develop a proposal for a central cooling pod, which would fulfil the tri-generation requirement for the project. The site of the Cooling Pod was the last area to be designated in the plans and makes use of a crescent shaped piece of land situated between the HS1 Channel Tunnel Rail Link and an office development.
This irregular, curved 120m long space varied from 6-8 metres wide. Our designers created a two-story solution with an optimal plant layout which not only accommodated all the necessary equipment, but allowed for safe operation and maintenance going forward.
Overcoming restrictions to deliver the optimum energy solution
Proximity to the HS1 trainline brought many challenges to the project. This included routine issues such as working with Network Rail to ensure all nearby crane works were acceptable to more in depth concerns which needed design-led solutions. There was a concern from Network Rail, for example, that pluming from the plant could drift across the rail tracks and impair drivers’ sight lines. The concern was so great that it was agreed that substantial financial penalties would be imposed if trains were disrupted by pluming.
This restriction resulted in the need for a robust solution which could be relied on under all circumstances and weather conditions. The design of the energy centre includes three different types of chillers; absorption, water cooled and air cooled, which each produce chilled water. The absorption chiller, which converts waste heat from the T1 energy centre into cooling, only initiates when the external temperature reaches 17°C or above which eliminates the possibility of pluming. These three types of cooling are controlled by a sophisticated Building Management System which ensures the correct combination of cooling is in use at any time.
Where possible, the system utilises the excess heat from the T1 energy centre. If this heat is not available, as it is being used for heating in the colder winter months then the system will switch to the water source chillers as they are more efficient than the air chillers (during these colder environment conditions). When the temperature creates the possibility of pluming the system switches to the air chillers. All three of these types of cooling are extremely efficient and as the grid decarbonises, the air and water chillers result in lower carbon emissions.
The Cooling Pod is capable of producing 12.4MW of cooling but as standard will deliver 9MW. The Cooling Pod plant comprises a 1.4MW absorption chiller, three 3MW water-cooled electric chillers, two 1MW dry air-cooled chillers and two 30m³ thermal stores. Crucially, the solution also has two 2.5MVA transformers which gives added resilience, allowing cooling to be maintained should one fail.
A major benefit of the cooling solution is that it makes the overall energy scheme more efficient. An electric chiller operates during the majority of the year when the cooling demand is low, but in the warmer summer months, the waste heat which is generated by the CHP engine is transported to the cooling pod, converted into chilled water through an absorption chiller and then distributed via a network of district cooling pipework connecting office blocks, residential and the King’s Cross Coal Drops facility.
This not only makes use of the waste heat generated, but also allows the CHP engine to run more hours and closer to full capacity, which makes it more efficient and commercially beneficial. The electricity generated from the CHP also feeds the plant in the cooling pod which has an overall cooling capacity in excess of the peak load and can fully meet the anticipated peak cooling of the buildings it serves.
Energy efficient district cooling network
The hot water is produced by the CHP in the T1 energy centre and pumped through 80m of buried, pre-insulate, twin series pipework. Once the heat has been converted into cooling through the absorption chiller it is distributed through a district cooling network which is currently made up of 680m of Series 1 pre-insulated pipework.
This network currently connects two buildings, but this will expand to four commercial and three residential, with the Cooling Pod able to deliver 9MW of cooling overall. Whilst the installation of district cooling is the same process as district heating, it still encountered some substantial technical hurdles which required a 38m thrust bored tunnel which allowed it to avoid the High Voltage electric cables and gas mains in its path.
As on many large-scale projects there is a need to work closely with others and build relationships and the King’s Cross cooling network saw us liaise with four developers across multiple sites along the network route. As our work would impact on their developments we had to be in constant contact with these developers and meet extremely challenging timescales to ensure we did not cause them delays.
Meeting noise restrictions
One of the biggest restrictions for the project was noise, which severely limited the acoustic emissions from the plant and this called for the design of a specialist, bespoke solution. Our designers worked very closely with the project acoustic specialist to create a range of internal acoustic insulation to ensure noise emissions were acceptable to the planning conditions’ noise criteria. The most innovative part of this solution saw the creation of an acoustic green roof to attenuate the noise of the cooling towers and air cooled chillers. This ensured acoustic emissions fell within acceptable parameters, but also provided an attractive architectural feature for the structure.
Employing innovation & flexibility to commission the project
The commissioning process is an essential step to ensuring the energy installation will perform as designed. Vital Energi consider this to be one of the most important steps in designing an efficient and reliable energy solution and the King’s Cross Cooling Pod project presented several interesting challenges.
Firstly, the project was commissioned before the heat loads were connected to the network. This resulted in our Prefabrication department creating a custom made Heat Load Bank which enabled us to run the system as normal, thoroughly testing every aspect to ensure it was performing optimally.
Any pluming from the cooling towers could be dangerous to the nearby trains and would result in significant fines. Vital staff arranged to test the cooling emissions during overnight sessions when the trains weren’t running, negating the possibility of any issues. During the commissioning process the system performed as predicted meaning we could have full confidence that it would not interfere with the nearby train line.
Our involvement from the initial concept, through to feasibility study, detailed design and project delivery saw us produce a coherent solution which overcame many challenges and resulted in significant capital expenditure savings as well as reducing on-going maintenance costs.
Our solution met all legislation and planning conditions and restrictions while satisfying the client’s brief and resulted in a cost effective, energy efficient cooling solution which will benefit the surrounding development for years to come.