Control as the key to reducing boiler energy consumption
Modern boilers are very different from those of 10 to 20 years ago — and so are their controls and their capabilities for maximising the efficiency of boilers that are inherently efficient. Bob Walsh has the full story.
Methods of controlling commercial boilers have improved almost beyond recognition in the last ten years. Microprocessors are, predictably enough, at the heart of this transition. But given that the service life of a quality boiler is at least 15 to 20 years, there is a strong possibility that many property owners and facilities managers are not fully aware of how things have changed.
The good news is that when heating systems are fully integrated with modern system controls, those responsible for managing nursing and care homes, mixed-use developments, leisure facilities and other large buildings can reasonably expect impressive efficiencies and fuel savings. Such savings were barely imaginable a decade ago when boilers came with on/off switches of varying degrees of sophistication — and that was that.
Now, it is possible to fine tune performance precisely — and save serious amounts of increasingly costly energy in the process.
There are two key elements to effective boiler control — the individual control capability built into the boiler and how multiple boilers are controlled in commercial buildings.
At Hamworthy we use the proven and superbly reliable Siemens LMU controls platform in our boilers. This provides a fully integrated controls solution, which is suited to both single boiler and multiple boiler installations.
Modern high-efficiency boilers have fully modulating burners, which allow the heat production to be closely matched to the heat demand in the building.
A common problem with old boilers or poorly designed systems is what is known as ‘dry cycling’, where a boiler is repeatedly firing and shutting down to satisfy signals from local sensors rather than to meet real demand. This creates unnecessary wear and tear on the boiler and wastes energy.
Modern boiler controls counter this dry cycling so that in the event of a poorly designed system, the in-built control can monitor the heating-temperature curve and hold off a boiler from firing, reducing the number of boiler operations and saving energy. Obviously it is better to improve the system and eliminate the problem; however that is not always possible, due to other constraints, so the boiler control comes to the rescue.
Multiple boilers in commercial buildings can be controlled either via a building-management system or in a stand-alone solution using a boiler sequence controller.
The introduction of products like our Merley boiler sequence controller, which uses the Siemens RVS platform with digital communications bus protocol, confirms that leading companies are committed to ongoing improvement in heating system control.
The secret of improved boiler efficiencies and achieving the associated savings lies in taking a big-picture view and installing a fully integrated system. This will comprise multiple modulating boilers, system controls to interpret demand and force the modulation, plus a range of sensors. The sensors provide real-time information on external and internal air temperatures for the building and will include a mixed-flow sensor for the water temperature within the heating system.
It is an unfortunate fact that retro-fitting new micro-processor controls onto an existing system will not, and cannot, have the same positive impact. This is because such systems are likely to be reliant on older boilers without a modulating function, so improved controls are better fitted as part of a boiler-replacement programme.
For both new build-applications and heating-system refurbishments, the starting point is to consider the lifetime cost of the installation. This will include the purchase and installation costs for multiple boilers in most instances, the control system, associated pipe work, and maintenance and fuel costs. Anyone who has not done the arithmetic could well be surprised by the fact that on a lifetime cost basis over 20 years, fuel will account for at least 95% of the total paid for a heating system. The logical conclusion must be to match performance to demand as precisely as possible, and this is where boiler sequence controller comes in.
Our Merley sequence controller, for example, can control up to 16 boiler modules with a 7-day time clock and three programmable periods per day. It can also vary the flow temperature in response to the room and outside temperature, providing increased comfort for the building’s occupants and saving energy by maximising the condensing performance of the boilers.
Obviously such control systems need to be linked to boilers that are capable of responding, which is why multiple modulating high-efficiency boilers are the other essential component of an economical modern heating system. Modulation means that boilers can be adjusted through the control system to work at, say, 20 to 100% of boiler output.
Modern boilers are more efficient when they are run at part load and not flat out. On a lifetime cost basis it is far more economical to have, for instance, three boilers operating at one-third of capacity rather than one boiler working flat out.
Such an installation of three boilers would also have plenty of additional capacity in the event of exceptionally cold weather and the associated higher demand. The boilers will not be worked as hard as a single large boiler, so they will be subject to less wear and tear.
In conclusion, I firmly believe that we currently have plenty of opportunities to contain the cost of heating despite expected rises in fuel costs. It is, however, essential for property owners and users to rethink their approach when briefing or consulting with specifiers and look at integrated systems.
We now have the advantage of Building Regulations that insist on new-build and refurbished properties being far more thermally efficient. At the same time, boiler manufacturers have been very willing to adopt new technologies and work closely with the consultants and contractors who design and install space-heating systems. With integrated controls we are establishing a new paradigm for heating systems based on lifetime costing for impressive economies, and with them valuable carbon reductions.
Bob Walsh is technical director with Hamworthy Heating.