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BOILERS & HOT WATER BSEE
TAKE CONTROL OF YOUR BOILERS Controlling for maximum efficiency
Maximising the efficiency of heating plant requires a combination of efficient plant and efficient control. Steve Lalyk, Senior Applications Specialist with Hoval, takes a look at the key issues that need to be considered.
A
n essential component in any efficient heating system is inherently efficient central heating plant, be that traditional boilers, low
carbon heat sources or a mixture of both. Such plant will therefore be a key consideration for building services specifiers.
Equally, building services engineers will recognise the importance of effective control to take full advantage of plant performance. Failing to do so results in wasted energy – something that, sadly, has been the case in many older heating installations.
Such historical waste has, at least partly, been due to the limitations of the control options available. Control systems have tended to be quite complex, which makes them difficult to commission, operate and maintain. Inevitably this increases the risk of errors during commissioning so that the plant may not ever have been operating at optimum efficiency.
Even if the plant was initially commissioned to deliver optimum efficiency at the time, complex controls may make it difficult and expensive to re-commission the system to accommodate changes in the building’s thermal performance, its usage/occupancy – or both. 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.
uHarrogate Grammar School improved energy efficiency and reduced carbon emissions with a Hoval STU biomass boiler, backed by two UltraGas gas‐fired condensing boilers. Hoval supplied the 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.
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 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. Very often, the people using the system will not have specialist knowledge of heating controls, so their interactions with the system need to be intuitive. 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.
A wider remit for controls
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), combined heat and power (CHP), 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. The same principles apply but in such cases the boilers will typically be ‘topping up’ low carbon heat sources.
An example of this is when gas-fired CHP is used alongside gas-fired boilers. Here, the CHP will usually be used to meet base heat loads with the gas boilers providing a top-up at times of peak demand. This arrangement needs to maximise the run-times of the CHP, so it’s important that the base heat load is sufficient for the CHP to run for at least three hours each time it fires.
This has control implications, because if the gas-fired back-up boilers are brought in too quickly this may cause the CHP to switch off, so that the required run-times are not met and the system is less efficient and cost-effective than should be the case. These issues can be addressed
through correct commissioning of the control system.
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.
Changing requirements
Equally, as mentioned earlier, 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.
www.hoval.co.uk
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‘ It has 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.
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BUILDING SERVICES & ENVIRONMENTAL ENGINEER SEPTEMBER 2017 19
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