Castle Park Water Source Heat Pump Project

Vital Energi received the RIBA stage 3 design and worked with the client’s professional team to evolve it into a solution which would fit onto an extremely constrained site, whilst delivering optimal performance and eligibility for the Renewable Heat Initiative.

One of the biggest constraints on the Castle Park project was the tight site which also had limited access. This meant there was limited room for deliveries and no possibilities for storage. This resulted in waste material from groundworks, such as shrubs and topsoil, needing to be removed from the site immediately and deliveries being done on the day the items were needed.

We oversaw all piling and created an innovative concrete slab foundation which anchored the steel beams that supported the abstraction platform.

Other significant facilitating works included undertaking a full unexploded ordinance survey and dredging the harbour after investigations revealed significant submerged debris and the discovery of a 3m void which needed to be backfilled before construction could begin.

Because of the congested nature of the site, we were forced to build the project “from left to right”.  This was due to the fact that the energy centre filled a considerable proportion of the building footprint.

This called for works to be scheduled so that they wouldn’t block access to parts of the project scheduled for later.  We therefore delivered the abstraction platform, followed by the main energy centre and finally, took delivery of the containerised plantroom.  As each aspect was delivered, we lost significant access to that part of the site, making deliveries of large plant, or use of construction vehicles difficult.

An additional restriction was that the site straddles a drainage culvert.  We worked closely with the Environmental Agency to ensure construction work didn’t affect the structural integrity of the culvert.  To achieve this we undertook extensive sonar surveys and the design of the energy centre was tailored to meet the Environmental Agencies needs for future access.

The Castle Park project takes water from the nearby floating harbour, pumping it from the river into the energy centre. To achieve this we needed to create an abstraction platform to support the equipment.  The original design had the platform attached to the harbour wall in a cantilevered solution, but structural surveys of the 100-year-old wall identified that it would not be able to take the weight.

To achieve a viable solution we had to work closely with multiple external bodies (MMO, Environmental Authority, Harbour Master, Bristol City Council Bridges & Highways Structure department) to create a design which met the needs of the project without impacting on the surrounding structures.  To solve this our designers ran a steel beam from the foundations of the energy centre over the harbour wall.  This supported the abstraction platform without putting any strain on the wall.

As the installation of the platform was over water, it became a major logistical operation involving multiple crane lifts, a barge platform and several working boats.  The final result was an optimised solution which could safely support the weight of the equipment without putting a strain on the harbour wall.

The Castle Park location brought with it the need for a considerate construction programme and we were able to reach out to our nationwide network of experts to assist with specialist areas.  By bringing this team together we were able to use the experience of marine specialists, ecologists, tree surgeons, asbestos consultants, experts in Japanese Knotweed and many more to ensure all aspects of the project were delivered to the highest standards.

One clear example of this was found when groundworks uncovered the original walls of Bristol Castle and our archaeologist was on hand to stop works and explore the site, ensuring nothing of historical interest was damaged.

Due to the number of agencies involved with the harbour, and the sensitive nature of the project this scheme came with some of the most stringent planning conditions we had encountered.  In all, there were 26 separate conditions attached, all of which needed to be discharged through the construction phase.

Ensuring the heat pump project does not damage the ecology of the harbour was paramount to both Vital Energi and the client.  To achieve this, we worked with environmental specialists to ensure the harbour was unharmed.

Our solution sees water taken from , and returned into the harbour, without coming into contact with any chemicals.  The system will also only take 3°C of heat from the water so there is no adverse effect on wildlife.  Additionally, we have calibrated pump speeds so that fish and eels will not be caught in the abstraction flow.

Water is taken from the river via the abstraction pipework which is submerged below the waterline.  The water is filtered at this stage to prevent debris from entering the system.  From here it is pumped through a second filter which removes smaller particles which include mussel eggs which can hatch and grow in the pipework.

Once the water is filtered it passes through the water source heat pump where the ambient heat reacts with ammonia and creates low pressure vapour which can be compressed to a high-pressure vapour of around 110°C.  This is an extremely efficient way of generating heat and the system has a COP of 3.18.

Heat from the water source heat pump is directed into a thermal store which then feeds into the Bristol Heat Network where it contributes to heating 1,000 homes and businesses.

To ensure continuity of supply, and that peak demand could be met efficiently, the design incorporates back up gas boilers.  The heat pump will deliver approximately 80% of all heat from the energy centre and the gas boilers will be used during routine maintenance and times of exceptionally high demand.

The decision to make the 32-tonne plant room off-site enabled us to have fewer people, and fewer construction works on the crowded site.  The finished pre-fabricated energy centre was then craned into position and connected.  This part of the project was completed last as the plantroom significantly restricts access to the rest of the site once in place.

Due to the size of the plantroom and the thermal store, deliveries were major logistical operations and involved temporary road closures in the city centre and police escorts, all of which were delivered to reduce disruption to locals.

The existing Bristol Heat Network runs next to the border of the Castle Park construction site and it had been installed with a valve, which enabled easier connection.  Vital Energi installed a district heating from the energy centre, to the main network where it reaches 1,000 homes and businesses.

The water source heat pump at Castle Park uses Ammonia as a refrigerant and we needed to create a safe emergency system to handle any unlikely leaks.  Rather than a dispersion solution, which would release the ammonia safely into the atmosphere, we created an ammonia dispersion tank, which would pump it into a water-filled container which could then be safely disposed of by licensed professionals.

As the project was scheduled to be finished before we could connect a full load, we brought temporary load banks in during the commissioning process.  This allowed us to run the full plant and equipment, as needed, to complete the full commissioning schedule.

Since we began constructing the Castle Park heat pump project it has been on of the UK’s most high-profile renewable energy projects, attracting visits from the likes of London Mayor, Sadiq Khan and Shadow Secretary of State for Climate Change and Net Zero, Ed Miliband and most recently won the European Heat Pump Association’s “Heat Pump City of the Year” award.