District heating network designs for greater energy efficiency at Wembley Park

Crispin Matson, Director, Ramboll

Installing energy solutions that are not only efficient, but are also environmentally friendly, is becoming a priority across building developments within the UK. District heating networks have become more popular than ever before, especially in cities where buildings are far more densely populated. District heating is a unique solution that provides heating a number of houses or buildings form one central energy source. Using a singular source of energy removes the need for individual gas boilers, and provides a far more efficient and economically friendly solution that also reduces carbon emissions.

The Wembley Park regeneration project is the UK’s largest Build-To-Rent development to date, providing over 5,500 new homes along with commercial spaces in an 85-acre complex around Wembley Stadium. In May 2016, we were approached by Quintain to help with the design and delivery of a district heating network to serve the new development – one of the largest district heating networks in London. The regeneration project was designed to offer residents accommodation for rent by paying an all-inclusive charge, including all utility bills, within a single monthly payment.

The original planning permission outlined the development of two separate district heating networks across the site, each connected to approximately 20 separate buildings. However, an in-depth review from the design team led to these two networks being merged into one network with a single energy centre. Located underneath the residential tower of the largest development, the energy centre contains the main heat generating equipment: gas fired Combined Heat and Power (CHP) plant and gas fired boilers, and the primary distribution pumps.

We used energy analysis software to gain detailed data for the predicted energy demand, which allowed for the calculation of the optimum size of the CHP plant to work in conjunction with the optimum size of thermal stores. The CHP plant was able to achieve the maximum carbon savings by producing both heat, which is fed into the district heating network, and electricity, which is fed back directly into the electricity grid. The optimum size of the CHP was calculated to be 2 No 1.5 MWe gas fired engines, and the corresponding thermal store size was calculated to be 150m3. This was achieved by installing 2 No 75m3 tanks each 4 metres in diameter and 7 metres high. 3 No gas fired boilers (rated at 9MW capacity) provide additional heating capacity for peak and standby scenarios.

The district heating pipework network connects 20 separate individual buildings, through one main energy centre. The network route is approximately 2.5km in length, spanning across the site to buildings on three sides of the existing Wembley Football Stadium. Through the use of ‘System Rornet’ hydraulic analysis software, we were able to augment the district heating pipework size and determine the size of the most economical circulation pumps. The final route of the district heating pipework threads in a complex pattern which has been coordinated to avoid the multitude of other existing and new utility services (including, but not limited to, power cables, telecommunications services and gas services), stretching across both public and private land in the area. We were tasked with producing detailed pipework drawings to enable the installation of the pipework in independent construction phases. Therefore, the heating network could be installed during periods in the programme where there was greater access to the site, depending on the stadiums event schedule.

Common practice for district heating networks within the UK is to connect the network into an individual building block from a secondary heat exchange substation, typically located in the basement. From there, a secondary heating distribution system feeds into Heat Interfaces Units (HIUs), located in each individual apartment. However, given that the Wembley Park flats were to be rented rather than sold, it was decided that the HIUs were to be omitted. Instead, centralised heating and water systems would be installed in each building, feeding into the apartment separately. This meant the site would be able to benefit from a reduction in capital costs and an increasingly energy efficient heating system, as a result of lower district heating return temperatures from the omission of an additional heat exchanger, typically located within HIUs.

Within each building the two separate circuits were connected by two distinct heat exchangers – one for the buildings’ centralised heating circuit, and one for the centralised hot water system. Both heat exchangers are uniquely integrated into a single building substation to maximise their thermal efficiency by utilising the return water from the secondary radiator heating circuit’s heat exchanger to preheat the cold-water feed for the hot water domestic use. This allows the return water temperature of the dh network to be kept to an absolute minimum, which reduces the amount of heat that is lost through the network.

The project presented a number of unique challenges. The space that was allocated to the energy centre was predetermined, which made the designing process for the complex pipework route all the more difficult. In addition, working within a phased construction plan limited how much work could be completed at any given time. However, we were able to overcome these challenges by completing design work using software that could account for these issues, and by integrating heat exchangers in a unique manner.

The network and the associated energy centre are now in construction, whilst the majority of the pipework has already been installed. The installation of the energy centre is also rapidly progressing. The initial installation included the thermal stores, whilst the other major items of equipment, including the CHPs, boiler and pumps, are due to be installed later this year. The plan is to have the entire district heating network installed and running by late summer 2019. The project adds thousands of houses to the growing district heating network. District heating networks could be set to become the norm for new large-scale residential developments.