The Heat Network Efficiency Scheme (HNES) supports performance improvements to existing district or communal heat networks. But what are we funding exactly, and what do the technical terms mean?
HNES aims to increase the efficiency of heat networks by funding improvement measures for poorly performing heat networks that are causing issues for residents and network owners. Heat Interface Unit (HIU) upgrades, dynamic flushing or converting a 4-pipe system to a 2-pipe system are just some of the improvements HNES supports.
This article delves into some of these measures, what they are, and how they result in network performance improvements.
Primary, secondary, and tertiary system explained
When we talk about different sections of a heat network, and specifically which sections are being altered or improved, we often talk about the primary, secondary and tertiary systems.
In heat network terms, the primary system refers to the main pipework and infrastructure from the energy centre or plant room to the entry point of the buildings being heated. The secondary system refers to the distribution pipework within a building. Within an apartment block, this includes the pipework going through the building itself, but not the pipework within each flat.
The tertiary network refers to the infrastructure within each dwelling. The secondary system may connect to the HIU in each property, but the pipework after this, leading to radiators, hot water taps, or underfloor heating loops, is the final destination for the hot water, or the tertiary system.
HIUs, TRVs, and BMS: Explaining our most used acronyms
When we talk about a Building Management System (BMS), we’re referring to the systems often located inside the plantroom or energy centre. Appropriately named, the BMS is the hub for all components of a heat network system. It ensures the system is working correctly while providing centralised control and monitoring of the whole heat network.
From the BMS, heat network owners and operators can track flow and return temperatures, water pressure, and monitor various valves, sensors and controllers from a single digital platform. This also makes it easier for site managers and maintenance teams to identify and respond to any issues in real-time and make improvements more easily.
In HNES terms, projects often talk about ‘recommissioning’ the BMS. In this sense, projects are optimising, refreshing, and realigning the system to more effectively and efficiently monitor and communicate with the heat network, particularly when other improvements have been made across the system. This is an effective way of improving a network’s performance, versus replacing the system entirely.
Heat Interface Units (HIUs) and Thermostatic Radiator Valves (TRVs) work similarly to the individual gas boilers and radiator valves located in many homes across the country. HIUs are often considered as the replacement for the boiler unit you would normally install in your home. They’re located in each dwelling connected to a heat network.
HIUs are the heat exchanger acting as a bridge between the central heat network system and the end user. Like a traditional gas boiler, the HIU provides instant domestic heating and hot water for radiators, underfloor heating, taps, and more. HIUs also provide residents with good visibility over temperature and energy consumption.
Some of our projects also talk about dual- and single-plate HIUs. Single plate HIUs use the hot water from the main heat network to heat the radiators or underfloor heating in the home, but keep the hot water used for taps hydraulically separate. Dual-plate HIUs keep the heat network water separate from both the home’s heating and hot water systems. This allows heating temperatures within the home to be controlled separately and helps protect the home’s heating system from pressure changes in the wider network.
TRVs are the valves fitted to each radiator in a home, much like those fitted to homes with an individual gas boiler or heat pump. Thermostatic valves automatically adjust based on the room temperature, helping to keep a constant, comfortable temperature and minimise energy consumption. As a result, this helps with energy savings, overheating, and ultimately lowering energy bills for residents.
What is the flow and return temperature?
Flow and return temperatures don’t just apply to heat networks. They apply across all domestic heating systems, including those with standalone gas boilers, heat pumps, and other wet central heating systems. Not to be confused with your home temperature, the heat network flow temperature refers to the temperature of the water as it leaves the boiler or energy centre and travels to a radiator or underfloor heating system (essentially, the temperature the radiator itself reaches).
The return temperature is the temperature of the water flowing back to the boiler or energy centre after delivering heat to a home. The water is cooler because some of its heat has been transferred to the home.
The lower the return temperature, the more efficient the heating system is, provided the system can effectively transfer heat to the room (this can be affected by radiator sizes and pump circulation speeds). When radiators transfer heat effectively to the room, water returns significantly cooler than it arrived.
Lower flow temperatures reduce heat lost from pipes, helping to prevent corridors from overheating. They can also help slow corrosion and reduce stress on components caused by sudden temperature changes.
Dynamic flushing and improving water quality
When we say improved water quality, we don’t mean the water from taps that people are drinking, but the water that circulates within the closed system of a heat network, carrying heat from the energy centre to radiators and back again.
The main issues experienced are dirt and debris within this water, that can block or damage equipment, including pumps, valves, radiators and heat exchangers, reducing their performance and lifespan.
Some of our projects have implemented dynamic flushing procedures across their networks. This involves pumping water and chemicals throughout the system at high speeds, to help clear out the system by dislodging and carrying away any debris.
Improving the quality of the water circulating around a heating system helps it transfer heat more efficiently and can extend the life of the network’s pipes and equipment.
Conclusion
We’re continuing to publish the outcomes from some of our funded projects. Check out our case study page to find out more or follow us on LinkedIn to learn when we publish more outcomes and benefits created through the scheme.