Why dry cycling is best prevented by M2G boiler controls to cut boiler energy costs

Industry comment

Published: 17 November

Type: Industry comment

Year: 2014

When boiler dry cycling hasn’t been addressed in a non-domestic building it can cause significant energy waste and is a costly problem that needs to be addressed. Yet, unfortunately, it still goes unnoticed in many buildings and typically it will not be prevented by a Building Energy Management System (BEMS).

In the past, products have been developed or re-engineered to prevent it but, ultimately, these control strategies have failed and caused problems for the building operators. These old-style controls, some of which have re-emerged in recent years, either use a fixed time delay with no temperature sensors, or they lower the boilers’ operating temperatures. Neither of these strategies is satisfactory as they can compromise comfort conditions or existing control strategies – consequently they have been dubbed ‘black box’ controls.

Since 2004 though, there has been an alternative in the form of Sabien’s patented M2G. This was the first boiler control to use flow and return temperature sensors to monitor, analyse and control the flow and return temperatures of the boiler.

As such, it is the only retrofitted control which is able to determine the actual heating demand on the boiler and prevent it from dry cycling without lowering the system temperature or using a fixed time delay. Furthermore, all of the verified savings delivered by the M2G are actual kWh savings in gas consumption – not the reduction in firing time that some manufacturers promote. The latter has no relation to the money spent when high/low or modulating burners are used.

Since 2004 M2G has established itself as the market leading advanced boiler load controller. Sabien has delivered million pound contracts to install M2G into the estates of BT, Lincolnshire County Council, the MOD and many others – and M2G is now available worldwide.

Why not use a BEMS?

During initial discussions with clients it is often assumed the existing BEMS is already doing what M2G does, or that we can simply add to the client’s existing BEMS. Indeed, we have explored this possibility with clients and found that trying to deliver this functionality via the BEMS becomes very problematic - and that a separate retrofit solution proved to be the most practical and cost-effective option.

There are several reasons for this.

Retrofitting advanced boiler controls such as M2G involves minimal disruption, typically taking less than 2 hours per boiler to install with no downtime to the boilers’ operation. Most importantly, there is no requirement for site or boiler specific programming, which is likely to be the case if attempting to deliver control of dry cycling through the BEMS.

Furthermore, given that each site will often have a different control system, considering the varying requirements of each site individually will be very time-consuming and hardly the best use of your time and money.

In contrast, using advanced boiler controls that can be deployed estate-wide and do not rely on the existing control strategies and hardware will result in greater financial benefits being realised - and within a shorter timeframe.

Of course a BEMS will deliver significant savings within a building – however for these savings to be delivered year-on-year, continued commissioning and maintenance is required. Unfortunately it is often the case that organisations do not have the budget to maintain their BEMS systems at a level that ensures they continue to deliver optimum performance.

Another major benefit of M2G is its ability to self-learn, continually adapting to the changes in heating load on the boiler. Furthermore it requires no servicing, maintenance or continued commissioning and will work in harmony with any make or model of BEMS.

Demand Control Strategy

A demand-led control strategy within a building makes perfect sense, whether determined by temperature, occupancy or a combination of the two. However buildings are dynamic and typically accommodate multiple uses and, in most cases, will use their boiler plant for both space heating and hot water.

Where boilers are only providing space heating the likelihood of all heating zones being satisfied at the same time is highly unlikely. Therefore one or more of the boilers will be on standby and dry cycling.

If the boilers are providing constant temperature hot water then a demand-led control strategy will not be appropriate. This is because the hot water will need to be maintained at the required temperatures and its use may be sporadic throughout the day.

Installing M2G boiler load optimisation alongside your demand led control strategy will ensure that boiler dry cycling is prevented during periods of the day when the boiler(s) are on standby to meet those transient, short burst heating requirements.

Installed alongside your BEMS demand control strategy the M2G will ensure the boiler(s) are only ever firing in response to a genuine heating requirement from the building. In fact, M2G will work effectively alongside any BEMS control strategy, be it sequencing, weather compensation or demand-led control.

Another important point to bear in mind is that boiler dry cycling occurs in each individual boiler - not within the system of combined boilers. As BEMS are not typically configured to monitor individual boilers (typically they are designed to monitor the blended temperature from all of the boilers), preventing dry cycling using a BEMS would require sensors to be attached to the flow and return pipework of each boiler. Without that, boiler dry cycling will not be detected or prevented.

Lower heat loads = increased risk of boiler dry cycling

As the thermal performance of buildings improves and internal heat loads from people and machines increase there is a lower requirement for space heating. However, in most cases, the boilers have not reduced in size. This means they fire for short periods so that standing losses – and therefore dry cycling – during non-firing times increase.

Return on investment

It is also important to bear in mind that to upgrade an existing BEMS, or install a new one, in a building that has undergone many changes over the years will require significant investment. This will result in a long payback period, potentially outside your organisation’s return on investment criteria. It may even not pay for itself within your lease/tenancy period.

Nor is this something that can be delivered overnight; it is a lengthy process of programming, installation and commissioning.

This is another advantage of M2G boiler controls, insofar as they will typically deliver a payback in less than 18 months. Indeed, recent business cases have shown the ROI on M2G projects to be in excess of 300%.

As a result, the M2G will recover its costs very quickly. Furthermore, it can be re-installed to any new boiler plant that is introduced as part of your lifecycle programme.

Freeing-up cash flow

As part of a long term energy strategy the savings delivered by M2G can be recycled and used to fund longer term initiatives such as BEMs upgrades or other projects which have longer payback periods or do not meet your organisation’s investment criteria. Over and above the percentage savings and payback the M2G is a sustainable and future proof investment.

Nor is installing M2G a leap of faith or a short term strategy. The common reference of ‘black box control’ applies to the outdated time delay controls all those that simply lower the boilers’ set point temperature.

It is also interesting to note that one of the leading BEMS manufacturers has recently described a control “that monitors a boiler’s flow and return temperatures and calculates the latter’s rate of decay” as an effective approach that can be used to good effect.

 

Considering all the options

 

When looking at your control strategies you will of course explore what is feasible with your existing BEMS or the cost of deploying a new one.

Having installed over 8,500 M2Gs worldwide, 95% of them in buildings with an existing BEMS, we have worked with many building owners and operators who have compared the options of a retrofit solution to adding to their existing BEMS. In every case their investigation showed that the cost of going down the BEMS route greatly exceeds the cost of deploying M2G.

Rolling out a BEMS solution is also very time-intensive and is not something that can be achieved across a multiple property estate within weeks, unlike M2G. This is clearly exemplified by the fact that many leading FM companies, responsible for managing some of the largest estates across the world and some of the world’s most iconic buildings, are recommending the use of M2G alongside BEMS.

For more information call us on 0800 082 18 18 or email reduceco2@sabien-tech.co.uk