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Back to basics

15 September 2011

Despite all the publicity for renewable energy sources, the actual figures for the uptake of renewables are much lower than many people realise. So there needs to be more emphasis on improving the efficiency of existing plant, such as boilers, using retrofit technologies, says Tony Willis of Sabien Technology.

Figures released recently by the Department of Energy & Climate Change (DECC) show that the contribution of renewable energy sources to the UK’s overall energy production rose by just 0.3% during 2010.This means that renewable energy still only accounts for 3.3% of all the energy used in the UK. Most of the rest still comes from fossil fuels – with gas continuing to be the predominant energy source for heating, followed by oil.

Consequently, the only realistic chance that the UK has of meeting its challenging emissions targets is to focus on improving the efficiency of plant that is already in use. Importantly, the cost of energy efficiency relative to renewable energy generation is lower and does not require government subsidy to make them economically viable.And the way to do this is to ensure that such plant is properly configured, maintained for optimum efficiency and controlled in relation to the demands of the building.

Boilers are a case in point – and an important one because heating buildings makes a significant contribution to the UK’s carbon emissions.

So using boilers as an example, the first thing to do is identify the cause of any energy wastage. Are the boilers firing unnecessarily or sequenced correctly, has weather compensation control been deployed and adjusted to the correct occupancy levels, has the building management system (BMS) been recently optimised or upgraded- or indeed maintained?

Or are the boilers firing wastefully to compensate for their own standing heat losses- rather than in response to a true demand for heat from the building load? In fact, standing heat losses are a major concern because they can lead to boiler dry cycling, a well-known phenomenon that can waste a lot of energy.

The fact is that even a well-insulated boiler loses heat to its surroundings (standing losses) when the boiler is off/ standing idle. The result is that the water temperature in the boilers can fall below the required current set-point of the boiler’s owninternal thermostat / load control. When this happens, the boiler may fire simply to recover this loss of temperature or wasted heat – even though this energy is not being used to meet a genuine system demand from the building. This unnecessary boiler firing isknown as “boiler dry cycling”.

Ironically, where renewable and other low-carbon heating technologies are introduced to an existing system, this can increase the level of “boiler dry cycling” and “boiler short cycling”, due to the available boilers now being over capacity for the system demand. This can introduce further standing losses and inefficient boiler operations.

Crucially, a BMS is not usually configured to manage boilers’ dry cycling directly. A BMS strategy is typically designed to optimise a building rather than individual items of boiler plant.

There have been other attempts in the past to control boiler dry cycling, but these either delay the boilers’ firing, or artificially reduce the boiler set points, both of which allow the boiler required set point temperatures to fall, reducing space / hot water temperatures within the building.. In addition, they can cause direct conflicts with the BMS strategy by artificially changing the BMS set points. All of which compromises workplace comfort and has the potential to generate complaints to the FM department.

In contrast, intelligent boiler load optimisation using modern, patented technologies – such as Sabien’s M2G - analyses each boiler’s temperature profile in real time to ensure the boilers only fire in response to a genuine demand for heat from the building’s load.This is achieved by constantly monitoring the boiler’s thermal response to changing loads, calculating the temperature decay over time and determining when the boiler should fire and when firing should be inhibited. Consequently, it is fully adaptive to changing boiler load/heating demand.

Crucially, the boiler set point has to be reached before these calculations can be made, so this technology cannot change the required set point. This ensures that it works in harmony with the BMS and other controls, such as weather compensation, rather than causing conflicts.

Intelligent boiler load optimisation, patented in Sabien’s M2G unit, also monitors each boiler individually to provide very precise control of the boiler plant at individual boiler level. In this way, it is designed to enhance and augment the performance of the BMS or other controls, providing the fine-tuning that is required to furtherreduce energy consumption.

Intelligent boiler load optimisation has been tried and tested in a wide range of applications. Average savings across an estate are typically around 12% to 15%, with paybacks ranging from a few months to two years. Current users include BT, Lloyds Banking Group, Vodafone, Hampshire County Council, Defra, and the Environment Agency.

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