Is it really optimised?

Industry comment

Published: 22 January

Author: Geoff Newman

Type: Industry comment

Year: 2014

When managing the energy consumed by a building’s services it is often assumed that all plant is optimised. However, this is isn’t always the case, leaving further cost savings to be achieved

Optimisation of a building’s energy use and in particular the optimisation of individual plant is a tried and tested approach to reduce energy costs - and there will always be varying levels of optimisation. However even in buildings where extensive optimisation has been delivered there are further opportunities to reduce energy costs, a case in point being the boiler plant.

It’s not uncommon for commercial boiler plant to have a number of control elements in place to optimise the boilers’ and heating systems’ performance. These may include boiler sequencing, weather compensation, demand control, modulating burners and even ensuring the correct air to fuel ratio is being achieved. Many of these are delivered through routine maintenance and commissioning, standalone controls or via a building management system (BMS). Each will be delivering significant cost savings and reduced carbon emissions. However, it is very likely the inherent problem of boiler dry cycling is occurring and going unnoticed, resulting in unnecessary energy costs – even with these sophisticated controls in place.

Why isn’t boiler dry cycling being addressed?

Firstly it is important to understand what dry cycling is and why it occurs. Boiler dry cycling is a symptom of standing losses (heat lost via the boiler casing and flue). Once the heating system is satisfied the boiler(s) will turn off. Naturally the boiler cools down, as the temperature drops below the setting on the boiler’s thermostat, the boiler will fire to recover its standing losses, yet the building requires no heat – this is boiler dry cycling. It will be a continuous occurrence throughout the period the boiler is operating. The unnecessary firings are not delivering heat to the system as there is no genuine heating demand and as a consequence, significant energy is being wasted.

Secondly, do not assume the latest boilers with modulating burners, sequencing and BMS control will not be suffering from boiler dry cycling. Typically the existing controls, including BMS, are configured to control the heating system as a whole from the common header (the blended temperature of all boilers), rather than monitoring and controlling each individual boiler. It is impossible to identify which boiler is dry cycling from the common header. Therefore dry cycling is present and causing you or your client unnecessary expense.

The issue of boiler dry cycling can be an expensive one if not addressed. Analysis illustrates that preventing boiler dry cycling will deliver average cost savings of 12% across an estate, with a typical payback under 18 months.

Many Facilities Managers and FM organisations are tackling dry cycling by installing discrete standalone controls specifically designed to identify and prevent boiler dry cycling. Furthermore these controls will complement and can be integrated with any existing controls such as BMS. One such control is Sabien’s M2G which has been evaluated and deployed by a number of FM service providers and end users. These include Interserve, Cofely, Vinci Facilities, Jones Lang LaSalle, EDF Energy, Schneider Electric, Babcock, Carillion, John Laing, G4S, Serco, BT, Aviva, Royal Mail, central government departments such as Defra, CLG and the MoD, along with many local authorities and universities.

Sabien’s M2G boiler load optimisation constantly measures and analyses the temperature profile of each boiler in real time. This enables the M2G to identify and prevent the boiler from dry cycling and, more importantly, allow the boiler to fire immediately if there is a genuine demand for heat. If a BMS is in place, the M2G integrates with it taking its signal from the BMS. Just as importantly, it recalculates the values every time the boiler reaches its required set point temperature. This means it adapts to BMS/optimiser variable set-points and does nothing to conflict with other existing controls such as weather compensation, demand control or sequencing. The boilers’ designed set points are never altered.

Crucially, M2G units require no maintenance or seasonal calibration and can be easily moved to new boilers if existing plant is replaced.

Savings will vary as dry cycling is a dynamic condition, determined by a number of factors including outside temperature, occupancy levels etc. However, it is important that savings can be verified to the client or your management team. Sabien Technology is believed to be the first UK retrofit boiler controls company to achieve certification for staff to the International Performance Measurement and Verification Protocol (IPMVP). The IPMVP defines a best practice framework for quantifying the results and benefits of energy efficiency investments. It ensures that there is total clarity and transparency for all parties in relation to the scope of work from initial planning, the measurement methodology, through to the validation of results.

Extensive analysis across many of the UK’s leading private and public sector organisations demonstrates typical savings of between 10% and 25% and payback of circa 18 months.