Controls
Controlling to the max
connectivity. They also need to present a simple interface to the people who will be commissioning the system, and to those who will be using the system on a day-to- day basis. This doesn’t mean that the level of control needs to be simple, it means the interface to the underlying sophisticated functionality must be user-friendly.
I
t will be apparent to anyone involved with the design or installation of heating systems that the plant at the centre of
the system needs to be inherently efficient if it is to meet the building operator’s expectations for energy efficiency. However, the efficiency of the plant is only part of the equation. It’s just as important to ensure that the plant is controlled effectively – or some of that inherent efficiency will be wasted. Historically, a constraining factor has been the complexity of the control systems available, making them quite difficult to commission, operate and maintain. Inevitably this increases risk of errors during commissioning and is a deterrent to fine-tuning of the system as building usage and thermal performance change. In recent years the situation has become even more complex with growing use of heating systems comprising multiple conventional and low carbon heat sources. These require a more sophisticated control strategy that has been challenging to deliver with old-style controls. It has also become apparent that simply tweaking traditional controller designs to try to address these issues has only been partially successful. This is why new designs of controller, re-engineered from the ground up, have been developed – and are proving their worth in a wide range of project types. To meet the requirements of modern heating systems (and their owners/operators) such controllers need to deliver new levels of modularity and
March 2017
Managing the mix Experience has shown that trying to control the multiple heat sources that are now commonly found in plant rooms with different controllers is extremely difficult and will usually compromise on overall performance. Consequently, controllers now need to have a ‘wider remit’, insofar as they can take effective control of a range of heat sources, with the ability to handle single units or operate cascades of heat sources. These heat sources might include boilers (gas, oil, biomass), calorifiers, heat pumps and solar thermal. When mixed heat sources are operated
in a cascade configuration, the controller needs to take account of the characteristics of each heat source. These mixed systems are very different from the more familiar cascades of modular boilers that have been in use for many years. For example, a system might make use of biomass for the lead boiler to meet base heat loads, supplemented by gas-fired boilers. In these cascade configurations it is essential the control strategy recognises that biomass boilers are not designed for rapid on/off firing. They require some time to stabilise, so the control parameters need to allow sufficient tolerances for the biomass boiler to meet the set-point temperature. Also, if the gas-fired back-up boilers are
brought in too quickly this may cause the biomass boiler to switch off, so that the full heat load is then being met by the gas- fired boilers. These issues can be addressed through correct commissioning of the control system.
Hoval supplied an STU boiler in a ‘plug and play’ skid-mount configuration complete with pumps, fans and fuel delivery augers as well as the company’s FlameTronix touch screen control system to Harrogate Grammar School
Hoval’s TopTronic E System Controller
For maximum efficiency of heating systems it is essential to combine inherently efficient plant with highly effective control. Hoval’s Steve Lalyk considers the key issues
Getting connected Connectivity through the internet is now also an expectation of many building operators, so that the system can be monitored remotely from a computer, tablet or smartphone, with alerts for routine or reactive maintenance. Similarly, integration with a building management system using OPC UA, ModBus or KNX interfaces, along with ‘smart grid’ readiness, are rapidly becoming ‘de rigueur’. There is also growing demand for
controllers that can operate within a heat network environment. Thus compatibility with ‘supervisor’ type controls will support real-time visualisation, monitoring and optimisation of district heating networks.
Efficiency of the plant is only part of the equation. It’s just as important to ensure the plant is controlled effectively – or some of that inherent
efficiency will be wasted
Changing requirements Equally, controllers need to make it easy to re-commission the system to reflect changing heat loads through the life of the building. This may be the result of a change of tenants or other changes to building usage or staff densities over time, as well as improvements to the thermal performance of the building fabric. In all these cases the control strategy needs to be updated accordingly and this is a far more straightforward process when using a control system that is easy to re- configure and re-commission. Thus it helps to ensure that the heating
system can be readily aligned with the building’s current usage and thermal performance, in line with the principles of the Government’s ‘Soft Landings’ concept. Ease of commissioning and re-
commissioning is underpinned by use of plain language and step-by-step guidance for the commissioning engineer, along with alerts for any issues detected by the system. Furthermore, ‘plug and play’ functionality will make it easy to extend the system in the future, if required, enabling further enhancements to efficiency as technologies improve or heat loads change.
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