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Are boiler controls a good idea?

Boilers represent a key energy efficiency 3450_20-img-165x227-09 - - beckyopportunity as they frequently account for a significant proportion of energy wastage. Optimisation of their efficiency always results in worthwhile savings with a quick return on investment. However, as with all aspects of energy efficiency, choosing the best solution is not straightforward and requires site investigations to get it right.

This article explains why making better use of your Building Management System (BMS) is a much better way to improve boiler efficiency than bolting on extra boiler controls because it is likely to achieve far greater energy savings. It covers the following topics:

  • What are boiler controls?
  • Existing control systems – thermostats and building management systems
  • Oversized plant
  • Making better use of your BMS

What are boiler controls?

For many years a class of devices known as “boiler controls” has been promoted as an instant way to reduce the energy use of boiler plant. These controls, sometimes known as “Dynamic Boiler Management Units”, “dry-cycling controllers”, “intelligent boiler optimisers”, “boiler sequencers”, “anti-cycle” devices or similar, are specifically a retrofit item and completely different to the controls that will have been fitted as part of an original installation.

Broadly speaking, these devices make an assessment of the system’s thermal load by taking simultaneous measurements of the flow and return temperatures. If the load is assessed as being very small, they reduce burner operation to reflect that. In a multiple boiler installation they may prevent more than one boiler from operating at such times, and this could be beneficial.

Boiler controls are usually promoted as being capable of reducing energy use by 15-25% which may or may not be valid for a particular device in a particular set of circumstances. However, in our experience, a debate about such savings opportunities completely misses the point because much greater savings can almost alwaysbe achieved much more cheaply by other means – and so the following issues should be considered.

Existing control systems – thermostats and building management systems

The first consideration is the existing control systems. Most sets of boiler plant have at least two controls systems already. They will probably have two thermostats, one being used for “control” and the other as a high-limit ‘stat. The control ‘stat may also determine whether the boiler will operate at high or low fire or the degree of modulation.  On most larger installations there will also be an additional control in the form of a Building Management System (BMS or BEMS) or a smaller stand-alone system that provides limited control to just the boiler plant and heating circuits.

The first point to make is that the relationship between the existing control systems is often an unhappy one. For example, the control ‘stat on some boilers cannot exceed 75oC, but the BMS may be programmed to demand an 80oC flow temperature. This results in the BMS “enabling” all of the boilers in an attempt to achieve what is patently unachievable. The addition of a retrofitted boiler control system to the equation will not necessarily improve the situation.

Oversized plant

However, the main problem is that all boiler plant is oversized for the vast majority of its operation, and most boiler plant is oversized even in the most extreme conditions. The biggest radiators on a heating system are often the boilers themselves. If losses are to be minimised it is vital that the plant is sequenced correctly, and that non-firing boilers are hydraulically isolated. Whilst boiler controllers may assist with sequencing, this is a function that can be achieved using the existing controls if they are set up correctly.

Making better use of your BMS

A well set up BMS can do everything that a “boiler controller” can do and a lot more besides. For example, it can modulate the boiler flow temperature on the ambient temperature, and reduce this to as low as 30oC with a suitable “condensing” boiler. It will also control boiler isolation. Boiler controllers will do nothing for the isolation of the plant, and indeed if automatic isolating valves are fitted, they may actually interfere with their operation. This is because as the controller detects that there is no load on the system it will prevent the boilers from firing, and the circuit temperature will drop. The BMS will then enable additional boilers and restore the situation.

If the plant is used for the generation of hot-water as well as space heating, as is often the case, it is important that the primary circuit is maintained at a sufficiently high temperature to ensure that water storage temperatures are high enough to comply with the Approved Code of Practice (ACoP) on Legionella.

Your Independent RISK FREE Solutions

Green Consultancy Boiler Health Check investigate all of the above issues and more to ensure that the efficiency of your boiler plant is maximised. For an investigation of all equipment controlled by your BMS you might like to consider a BMS Health Check or a BMS Audit.

All of our energy/carbon reduction services are based on our unique rigorous and scientific methodology – for full details please see Energy efficiency methodology

Put us to the test NOW! To discuss your requirements please call John Treble on 01761 419081, or email John@GreenConsultancy.com

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BMS Audit for University of Lincoln

“The University of Lincoln was very pleased with the report that The Green Consultancy put together for us. The report has enabled us to re-focus how our Building Management System is used to manage energy consumption and control the environment in academic spaces.”

Daniel Clayton, Environmental Sustainability Manager

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University BMS Audit

The Green Consultancy carried out a BMS Audit of a university campus which identified over 70 opportunities to reduce energy consumption leading to a total reduction of over 2,000 tonnes of CO2.  Recommended BMS upgrades, adjustments and associated plant upgrades will reduce costs by £260,000 per year, and although there will be some implementation costs for plant upgrades, much of this can be achieved at low cost simply through improved management of the BMS. Maintenance issues accounted for £93,000 per year of the total annual savings identified.

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BMS Services for University of Worcester

Following a BMS Health Check we provided a new strategy and full tendering support for a replacement BMS.  These were some of the services delivered within a three year contract for energy management involving a consultant being on site for up to three days per week.

"The Green Consultancy have proved to be adept at understanding the requirements of a complex organisation across an extensive estate and have worked with colleagues in the University of Worcester to help us better understand our priorities in relation to carbon reduction.  Their support for the estates team is working extremely well and in addition to resolving issues and making efficiency gains, members of the in house team are also increasing their knowledge base. I would not hesitate to recommend them to others."

Mark Hughes, Director of Estates & Facilities

John Treble

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You need not take our word for it – hundreds of their comments are at the foot of these pages.

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