Not enough is being done to optimise the performance of boiler plant and some very obvious measures are being overlooked, argues Tony Willis of Sabien Technology.
Many legislation-driven energy-saving measures are designed to improve the energy performance of new buildings and major refurbishments - Part L being an obvious example.

Consequently, there is also a strong case for a closer look at the performance of existing plant.

As an industry, we have a responsibility to our end customers to make them aware of these issues and help them save as much energy as possible. However, there are some very obvious measures that are currently being ignored - usually through a lack of awareness or misconceptions about how such systems are controlled.

Boiler plant is a case in point. All of us in the industry know that around 80% of commercial boiler plant is oversized and subject to frequent cycles of operation. Many of us are also aware of the problem of dry cycling. This is where the boiler frequently fires just to compensate for standing heat losses of the boilers rather than actually contributing to the building heating load. The trouble is we're not doing enough about it.

Part of the reason is a common perception that the BMS will take care of this. The reality, though, is that a BMS is designed to control building comfort levels by zone control and weather compensation via mixing valves - it doesn't address the specific issue of standing losses from the boiler plant itself. And these standing losses can be significant.

When a boiler is standing idle, it acts like a large radiator and even a modern well-insulated boiler will lose 1-2% of its heat to the surroundings. A further 2-3% may be lost because of draught conditions in the flue drawing ambient air through the boiler. And this situation is exacerbated further when pressure jet burners purge the combustion chamber before firing.

Clearly, then, significant savings can be achieved by addressing this issue of standing losses - and this has to be done without compromising on comfort levels in the building. The thermostat/BMS set-point still needs to be the key reference point for system design.

For example, one traditional remedy has been to introduce a simple time delay so that boiler firing is delayed for a pre-set time when the system calls for heat. The trouble is this will happen whether the call for heat is the result of a genuine need for more heat (true call for heat) in the building or the result of standing losses (false call for heat).

A smarter and far more adaptable approach is to introduce intelligent boiler load optimisation that analyses the temperature differentials of the flow and return water, references the thermostat set point and determines the underlying reason for the call for heat.

Applying this approach to more than 1,500 units in the last few years, we have found it is possible to achieve energy and emissions savings of 10-25%, depending on conditions, while maintaining existing comfort.

The principle is simple. The system measures the boiler flow and return temperatures directly on each boiler. This will monitor and record the boiler thermal response to changing loads.

By measuring the call for heat signals and set point satisfied, the M2G will constantly identify and remove wasteful boiler firings during dry cycle conditions.

Crucially, the system also references the boiler thermostat/BMS set point each time it takes measurements, so it will constantly adapt to changes made to the system parameters.

In this respect, the practice of boiler load optimisation is wholly complementary to the BMS, rather than duplicating any of its traditional actions.

As with any complex building services system, there is a need to take a holistic view of all of the interacting elements of that system to achieve maximum boiler efficiency. So, rather than being a stand alone issue, dry cycling is just one example of how we, as an industry, can still do more to reduce energy costs and CO2 emissions for our customers.