CASE STUDY – DHN SWAFFHAM

IWTM win Swaffham Prior DHN in UK first Recommended to the network developer IWTM won the project as it controls the causal elements for corrosion and bacteria and when at VDI2035 the system water does not have to be in circulation to protect the system.

NetZero strategy

The 300-home village is the first retrofit of a heat network into an existing community. With nearly 75% of homes not connected to the gas grid, most homes have oil fired boilers or other types of stored fuel. As part of its NetZero strategy, Cambridgeshire CC wanted to create a system where 100% of the thermal energy demand of the village was met by renewable energy. The project consisted of developing the energy centre (EC), the buried pipe heat network, heat interface units (HIU) to each home and a solar farm to create a renewable energy source to power the EC.

An initial study proved positive with half the village wanting to sign up to the new district heat network (DHN). The overall design and development engineer had full responsibility of the EC, whilst another contractor was responsible for the buried pipe heat network. The gradual take-up expected across the village to end customers meant there would be multiple non-flushable pipework sections that would contain stagnant water. This meant a conventional approach to pre-commissioning cleaning and treatment using chemicals was unlikely to reliably control bacteria levels and could result in poor water quality and bacterial growth.

One of the key contractors had been considering chemical-free water treatment on other projects and made the recommendation to the network developer. Following their evaluation of IWTM’s solution and consideration of the environmental and technical advantages, IWTM was awarded the project over traditional solutions.

The approach

Neither the M&E contractor or their water treatment specialist (WTC), had used chemical-free principles on previous projects. Both understood the advantages of the system and agreed the approach despite a reduction in the water treatment contractors quote by £30,000 as it removed the need of chemicals from the system. The solution consisted of an array of two IWTM Industrial T1000s and 3 PUROTAP Compenso 50s to cater for the 600,000l system volume and VDI2035 water quality standards were adopted across the project.

To achieve VDI2035 chemical-free principles were adopted across the project which eschews the use of chemicals from Pre-comm through the life of the of the project. For the pre-commission builders clean and fill a PureWater rig was selected to provide the initial fill. The raw water passes through an RO unit membrane and pre filter before passing through a PUROTAP Compenso.

The WTC then installed a side stream filtration unit via the flushing loops and use the energy centre pumps to circulate the water around the energy centre primary and secondary circuits. Side stream filters will be used until the system is-free of any builder’s debris whilst the installed IWTM T1000s works on controlling the residual dissolved oxygen as the water is circulated within the energy centre pipework. During this initial period the water will be continuously monitored using the onsite test equipment until the water stabilises, then re-checked 6-12 weeks after commissioning to ensure all is stable.

Ice pigging was used to clean through the network with IWTM supplying a twin unit Protector rig to give a final polish to the water. The Protector rig is designed to clean and filter system water and to accelerate the water quality to VDI2035 levels prior to its connection with the energy centre.

Benefits

Chemical-free offers long term benefits to the operators and owners as the solution adds a reliability of operation whilst removing the administration and labour of handling hazardous chemicals. Softer benefits are expected to add to the return on investment through fuller life of the network components and reductions in corrosion associated breakdowns.