HIUs: Unlocking the Potential of Low Carbon Heat Networks

Mike Shaw, Commercial Director at Evinox Energy, takes a look at the advances in heat interface unit (HIU) technology and identifies some of the key technical considerations, which are fundamental to improving user satisfaction levels and the overall efficiency of the network.

Residents of district heating developments expect consistent and safe hot water at the tap. To achieve this, we here at Evinox Energy have developed a sophisticated HIU control logic, which uses a self-learning function to accurately match the required load, based on scheme specific operating conditions. This has greatly improved the HIU control valve opening and closing time and the control of output temperature. This proportional integral derivative (PID) control logic, in combination with accurate equipment sizing, pressure independent control valve and fast acting actuator, enables the HIU to deliver the hot water with minimal delay.

Our latest in-house test results show the delivery of domestic hot water at 55°C within 15 seconds of opening the tap. Not only does this provide user comfort, but also significantly contributes to increased network efficiency by reducing energy waste, minimising network return temperature, reducing heat loss and reducing water consumption.

Eliminating HIU heat losses
Instantaneous HIUs generally include a stand-by mode keep warm function, which keeps the domestic hot water plate warm to ensure quick hot water response. It’s important that this is thermally controlled so that it uses a minimal amount of heat network energy. The amount of energy used to maintain this function is often underestimated and in many cases not even considered.

If the keep warm function cannot be switched off, the system is using energy even when there is no potential demand, for example at night. The advantage of using electronically controlled HIUs is that the keep warm function can be programmed by the resident and switched off during periods of no demand. In addition, the advanced control feature ensures that the minimum amount of primary flow is used to accurately match the hot water plate set point. 

Heat Network Weather Compensation
One of the biggest issues with heat network performance, for residential developments, is that the peak demand only occurs for a short period, and for most of the year the heating demand is relatively low. This can be overcome using weather compensation.

This also allows for a greater network supply and return temperature difference – network delta T – at peak load, therefore reducing the pipework and equipment size required. The supply temperature can thereby be reduced as the demand decreases due to warmer outdoor conditions.

Modern HIUs should operate with the heating supply temperature being automatically adjusted depending on the outdoor temperature. This enables the network temperature to be weather compensated, resulting in minimised energy use and heat loss.

A New UK Test Standard for Heat Interface Units from BESA
A new HIU test regime has recently been published by the Building Engineering Services Association (BESA), developed under the auspices of an industry led steering group. Results from the new, independently performed tests will enable specifiers to benchmark HIU performance under typical UK operating conditions, in some ways, similar to the SEDBUK boiler rating scheme.

The UK HIU test regime has the full weight of industry behind it and is an initiative fully supported by Evinox Energy.  For the first time, the tests will allow manufacturers to evaluate the performance of HIU’s under typical UK conditions and will give designers the opportunity to see the impact of a particular HIU on their network.  The latest Evinox ModuSat HIUs are currently being tested and we look forward to results being published over the coming months.

Continuing innovation in modern HIU technology will allow us to achieve ever higher heat network efficiency, and at the same time enable system performance to be analysed with visibility of live data. At Evinox Energy we continually invest in innovation and development, always aiming to deliver the most energy efficient solution and are passionate about unlocking the potential of low carbon heat networks.


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