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Technology OverviewCTV008

Low temperaturehot water boilersIntroducing energy saving opportunities for business

Contents

Introduction 01

Energy consumption 02

Summary of key areas 03

Technology overviewHow does a boiler work? 04

Identifying your heating system 05

Identifying your boiler 06

Improvements to existing boiler plant 08

Boiler controls 10

Maintenance 14

Replacing boilers 16

Energy monitoring and targeting 20

Next steps 21

Glossary 22

Front cover image (top right and bottom): courtesy of Future Energy Solutions, from AEA Technology

01Low temperature hot water boilers

Reducing energy use makes perfect business sense;it saves money, enhances corporate reputation andhelps everyone in the fight against climate change.

The Carbon Trust provides simple, effective adviceto help businesses take action to reduce carbonemissions, and the simplest way to do this is touse energy more efficiently.

This technical overview of low temperature hotwater boilers introduces the main energy savingopportunities for businesses and demonstrates howsimple actions save energy, cut costs and increaseprofit margins.

Technology Overview

Energy consumption

About a third of the UK’s energy consumption is used forheating or producing hot water. A significant proportion ofthis is provided by commercial boiler plant, so it should beincluded in any energy reduction strategy.

Typically, energy improvements of 10% or more can bemade relatively easily through maintenance and low cost,straightforward improvements. The financial rewards ofthese are often immediate or have a very short payback.

Longer-term measures are also well worth considering.Many buildings may still be using very old hot water boilers that had an operating efficiency of only about 70%when first installed and which will now be worse due topoor maintenance. New condensing boilers can achieveefficiencies of over 90% and consequently it can be worthconsidering replacement.

This overview covers some of the simple steps to saving on boilers, as well as the best approach to choosing a new boiler.

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About a third of the UK’s energy consumption is used for heating or producing hot water.


Boilers offer many energy saving opportunities, rangingfrom replacement of the boiler itself to retrofitting ofcontrols and other equipment.

The most appropriate solution will depend on what type of boiler and heating system you have, your business needsand your budget.

Savings in existing systems

These can range from the addition of boiler and pipeworkinsulation to retrofitting of new controls or flue gas heatrecovery systems. See page 8.

Maintenance and monitoring

Both new and existing boilers require an effectivemaintenance programme to ensure that they operate to peak efficiency. See page 14.

Selecting a new boiler

Not just as simple as replacing like for like, going through a careful analysis of what you really need can save a fortune.See page 16.

There are also significant opportunities to save byconsidering improved boiler controls (see page 10) and by monitoring your energy use (see page 20).

Summary of key areas

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A knitwear manufacturer in Hawick, Scotland,replaced their old, inefficient oil-fired boiler withtwo new high-efficiency gas-fired boilers that weresized to match more accurately the actual heatingdemand of the site. In addition, the new boilers had improved burner controls linked to a BuildingManagement System. The resulting savings were£13,200 and 276 tonnes CO2 per year, with an overallpayback time of under five years. The company alsoreported improved productivity and staff workingconditions following the retrofit.

Effective boiler replacement

ergy consumption cing hot water.

Technology Overview

Technology overview

04

Low temperature hot water (LTHW) boilers produce hotwater at around 90ºC and are the type most commonlyfound in houses and commercial premises. The hot waterproduced is distributed via pipework to ‘wet’ heatingsystems and hot water storage tanks.

LTHW boilers are usually gas-fired, but can also be run on oil or LPG models particularly in areas with no naturalgas supply. Oil and LPG are more expensive than gas andemit more carbon dioxide to the atmosphere. Biomassboilers which use wood, specially grown ‘fuel crops’ ororganic waste as the fuel, are becoming more popular.These create very little net carbon dioxide, but are moreexpensive and the availability and storage of fuel can be difficult. Only gas-fired boilers are discussed in thispublication; however, most of the energy saving advice is applicable across all models.

How does a low temperature hot water boiler work?

The diagram below shows the major components of a gas-fired LTHW boiler.

The controls on the boiler set the required temperatureand pressure of the water. If the water in the feed(the return water) is at a lower temperature than required,the boiler must ‘fire’ to produce heat, i.e. it must burnfuel. The gas burners ignite a mixture of gas (from the gas inlet ) and air (from the boiler surroundings) to producehot combustion gases. The precise mixture of gas and air iscontrolled by the gas valve and burner controls (this iscovered in further detail later). The hot combustion gasespass over the heat exchanger (a network of pipes) toheat the circulating water within. This water is circulated by a pump . The resultant hot water is distributed to theheating system via the hot water outlet and the exhaustgases escape to the atmosphere via a flue or chimney .Any condensate leaves the boiler via a drain . To preventheat loss from the boiler, the whole mechanism is containedwithin an insulated metal enclosure .

Low temperature hot water boilers produce hot water for spaceheating, general hot water demand or, occasionally, industrialprocesses.

Exhaust gases

Heat exchanger

Flue

Gas valve andburner controls

Gas inlet

Draft hood

Water feed

Hot water outlet

Temperature andpressure controls

Circulating pump

Drain

Insulated metal enclosure

Gas burners

Major components in a typical gas hot water boiler

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05Refrigeration


Identifying your heating system

There are a variety of heating systems that can be usedwith LTHW boilers, offering different opportunities forsavings. Understanding your type of heating system willhelp in identifying what kind of boiler you have, and where the best chances of saving are.

Radiators are metal units which exude the heat from thesystem’s hot water pipes. Effective temperature controland low maintenance make radiator systems a popularchoice, and they are the most common type of systemfound in the UK.

Convectors draw room air through a casing and push outair warmed by a covered hot water pipe. They have a lowsurface temperature making them popular in schools andhospitals, where otherwise there may be a burning risk tooccupants. Compared with radiators, they have a greaterheat output per unit size and a faster heat-up time;however, their maintenance costs are greater. The runningcosts are further increased when the convector has a fanwithin the casing.

Under floor heating consists of a network of hot waterpipes that is embedded between the floor finish and themain concrete floor slab. These pipes heat the whole floorsurface and cause heat to rise throughout the space. Themain advantage of under floor heating over radiators andconvectors is that it is ‘invisible’ and can give greaterflexibility in the use of a space (for example, positioning of furniture). However, these will not be found in buildingswhich require under floor electrical services or in olderbuildings with wooden floors.

While all systems can work with any type of LTHW boiler,some applications are more efficient with certain types of boiler. The next section covers these in more detail.

For more information on heating and heating systems, see the Carbon Trust’soverview on Heating, ventilation and air conditioning (CTV003).

Medium/high temperature hot water boilers and steamboilers tend to be found on large multi-building sites or industrial premises. They produce water or steam at high temperature and are not suitable for smallercommercial premises (for example, in offices) due tosafety risks. The Carbon Trust has further informationabout these boiler systems.

Technology Overview

Identifying your boiler

There are three main types of boiler: conventional, high-efficiency and condensing. These can be used alone or combined together within systems.

Conventional boilers

If your boiler is more than 12-15 years old, it is likely to bea conventional type, sometimes called ‘standard’ boilers.They are often cast iron and larger than other boilers. Most use atmospheric burners, where the air required for combustion is drawn from around the boiler throughnatural convection. Flues tend to be larger on standardboilers as they are sized according to the air flow at peak load.

Some conventional boilers and most other boiler types will use forced/induced draught burners. These use a fanto force/induce air into the boiler and up the flue. Whilstthis can give greater flexibility to flue design and result insmaller flues, they are noisier in operation. Forced/induceddraught boilers are easy to identify since the fans are fittedto the front of the boiler.

Conventional boilers are no longer available to buy due totheir lower efficiency. Businesses with one of these boilersshould consider replacement with either a high-efficiencyor a condensing model.

High-efficiency boilers

Since 1997, high-efficiency boilers have been the requiredstandard for new and replacement models. So if your boilerwas installed from 1997 onwards, it is likely to be thistype. These boilers have a low water content, a large heatexchanger surface area and increased insulation to the boilershell. They tend to be smaller than standard boilers.

High-efficiency boilers work with all heating systems. Theyare particularly suited to applications where a higher watertemperature is required, for example radiators at peak load(typical flow temperature of 80ºC). Businesses with a low-temperature application, for example, under floor heating,will find that a condensing boiler is a better option.

Condensing boilers

Even in modern high-efficiency boilers, waste heat in the exhaust gases is lost to the atmosphere via the boilerflue. Water vapour makes up some of these exhaust gases.In condensing boilers, a second heat exchanger is used to extract much of the waste heat and return it to thesystem. The temperature of the exhaust gases is reducedcausing the water vapour to condense, and this is drainedaway. Condensing boilers are the most efficient on themarket and since April 2005, legislation states that theymust be considered as the first choice for all new orreplacement installations.

Condensing boilers work best with low-temperatureapplications, such as under floor heating. However,efficiencies will still be increased when used with radiatoror convector circuits.

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QUICK TIP

You can find out things like your

boiler’s rating, age and settings

from the manufacturer’s plate.

This is usually found on the side

of the boiler casing.

Combination boilers

In a combination (or ‘combi’) boiler, there is a secondaryheat exchanger integrated within the boiler housing thatis used to provide hot water instantaneously. There is noneed for a hot water storage cylinder and associated coldwater feed tank and pipework. They can be particularlyattractive options in properties where space is limitedand are used mainly in domestic buildings.

Combination boilers are limited to smaller applicationsso will not be appropriate for most businesses. However,if your business is run from a very small building and hotwater demand is limited to taps, they may be an option.

07Refrigeration


Modular boiler systems

A modular boiler system is where a series of boilers arelinked together to meet a variety of heating demands.Modular boiler systems are best suited to businesses with a large heat demand that varies.

Because LTHW boilers work best when operated at full load, it makes sense to have a series of boilers tomatch the varying heating demands which UK businessesexperience. For example, consider a building with a peakwinter heating demand of 100kW. If a single boiler were to be used, it would operate at full capacity, and peakefficiency, for only a few weeks of the year. If five modularboilers of 20kW each were used instead, lower heatingdemands experienced at other times of the year could be met by a reduced number of boilers operating at full capacity.

The system can be a mix of condensing and conventionalboilers, but the condensing boilers should always be the‘lead’ to maximise efficiency.

Boiler efficiency

No boiler is 100% efficient. Energy is lost via the flue gases and through the main body of the boiler itself. Poor maintenance will exacerbate these losses.

Take care when considering boiler efficiencies.Manufacturers often quote instantaneous efficiencies which do not take into account the actual operation of the boiler or its practical use. A more accurate measureis the ‘seasonal efficiency’. This takes into account allcharacteristics of a boiler and is averaged over a season or year of true operation. It will therefore account for its performance under part-load conditions.

The table below shows the seasonal efficiencies for thedifferent boiler types discussed above and how this wouldaffect the energy input required to meet a heating demandof 100kW. Note that the boiler efficiency is also affectedby the heating system type.

Boiler type Typical seasonal Power input required to meet efficiency 100kW* heating demand

Standard, old, poor condition 45% 222kW

Standard, good condition 70% 143kW

High-efficiency 82% 122kW

Condensing (used with fixed temperature radiators) 85% 118kW

Condensing (used with variable temperature radiators) 87% 115kW

Condensing (used with under floor heating) 90% or more 111kW or less

*As a general rule of thumb, most commercial buildings will require a heating demand of around 70-90W/m2. So, a 100kW boiler would be sufficient to heat a building of 1,100-1,400m2. Retail and educational buildings will have a bigger heat demand (100-110W/m2) and so a 100kW boiler would be sufficient to heat a space of 900-1000m2.

Seasonal efficiencies

Technology Overview

Insulate boilers, pipework and valves

Heat loss through the boiler, pipework and valves leads to poor efficiency. All businesses should check theirsystems’ insulation.

Most modern boilers are well insulated to reduce heatlosses from the body of the boiler and these can accountfor less than 1% of the total energy input. However, onolder boilers, the insulation may be in poorer conditionand can account for heat losses of as much as 10% of the energy input. The boiler insulation should be assessed and replaced where it is insufficient or showing signs ofdegradation. Similarly, the insulation on the associatedboiler pipework and valves should be assessed and replacedif necessary. This can result in additional savings of up to10% of the boiler energy input.

Particular attention should be paid to valves as these areoften left uninsulated because of access concerns. Modernvalve-wraps solve this problem by providing suitable levelsof insulation but allow easy access to the valve throughquick-release fastenings.

Fit flue dampers

On larger boilers, the flue can cause a flow of air throughthe boiler, even when it is not firing. This cools the boilerand valuable heat is lost to the atmosphere — known as‘standing losses’. A flue damper can be used to close offthe flue automatically when the boiler is not firing, thuspreventing this energy loss.

Since 1998, regulations have required boilers to haveimproved efficiencies at both full and part-loads, and this has led to lower standing losses in modern boilers.Retrofitting flue dampers is therefore applicable to older,conventional boilers with a large load (typically >100kW).The advice of a qualified technician is essential.

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It may not be cost-effective to replace boilers that are relativelynew. However, there are still opportunities to make substantialsavings through improvements to other items of the boiler plant.Many of these measures will need specialist help. If in doubt, always consult a qualified technician.

Improvements to existing boiler plant

09Refrigeration


Install variable speed drives and pumps

On forced/induced-draught boilers, a variable speed drivecan be installed on the fan. The enables the fan to operateat lower speeds when less air flow is required. A reductionin fan speed of just 10% can result in fan energy consumptionsavings of around 20%, and a reduction in fan speed of 20%will save up to 40%. This is particularly relevant for bigboiler systems.

Variable flow control works on a similar principle. Most heating systems use the same amount of energy for pumping, regardless of the load on the system, butthey normally require maximum flow for only a limitedtime. This is usually during the ‘boost’ period when tryingto raise the temperature of the building to a comfortablelevel. Variable speed pumps can be fitted which decreasethe flow in the system to match demand. This can save 25-50% of the annual pumping energy consumption.

Retrofitting of variable speed drives and pumps is bestsuited to larger systems with variable loads. If the load onthe fan/pump is constant, energy consumption may actuallyincrease through the installation of a VSD. The advice of a qualified technician is essential to assess the economicfeasibility of this option.

Recover heat from exhaust gases

In conventional boilers, the heat contained within theexhaust gases is lost to the atmosphere. If replacementwith a condensing boiler is not possible, this heat can berecovered through the use of a heat exchanger. The heatcan be used to pre-heat the return water or the combustionair. Increasing the temperature of the combustion air by20ºC can improve the overall efficiency of the boiler by 1%.

This technology is best suited to conventional and high-efficiency boilers with flue gases of a sufficient temperature.It is important that the economics of retrofitting such asystem are assessed as the potential savings are relativelysmall. They will be most economical when applied to alarger system. Always consult a qualified technician.

Technology Overview

The first step is to assess what controls already exist, findout if they are calibrated accurately, and check that theirsettings match the business’s requirements. If they do not,adjust them either by asking for help from a qualifiedprofessional, or referring to the operating manual (usuallydownloadable from manufacturers’ websites if they havebeen lost).

The next step is to decide whether additional controlswould be beneficial. Again, installation of new controlsshould be carried out by a professional.

A brief description of a number of different control optionsis given below, with details on the optimum settings forthese controls. Manufacturers will be able to give moreadvice on the best control options for particular boilers.

Please refer to the Carbon Trust‘s technology guideHeating control (CTG002) for more in-depth information.

Burner controls

Burner controls manage the fuel-to-air ratio which iscritical to the efficient operation of the boiler: too littleair and there will not be enough oxygen for completecombustion to occur resulting in a build-up of potentiallydangerous carbon monoxide in the flue; too much air andenergy will be wasted in trying to heat the excess. Thefuel-to-air ratio is normally set on the burner controls andwill be based on the boiler manufacturer’s recommendations.Proper control of this ratio will ensure that the boiler is asefficient as possible.

As part of routine servicing, a qualified technician willmeasure the fuel-to-air ratio of a boiler. This can then becompared with the manufacturer’s recommendations and,where necessary, the appropriate remedial actions taken.In some cases, the boiler technician will simply adjust the burner as part of the service but for more complexsystems, particularly those operating at part load for muchof the year, it may well be cost-effective to consider areplacement burner control that will improve efficiencyand result in energy savings.

Types of burner control

The simplest form of burner control is single-stage or ‘on-off’ control and is the type of control found on mostolder, standard boilers. With this type of control, theburner fires at full capacity when heat is required and is off otherwise. Air purges immediately before the burner isswitched on and after the burner is switched off to ensurethat no residual fuel or combustion vapour remains in theboiler, but this also causes heat to escape via the flue.

An improvement to the above is two-stage or ‘high-low’control. With this type of control, rather than beingcompletely switched off, the burner has the option ofgoing to a low firing rate, typically 40% of full capacity.This reduces the number of times the burner switches off and the number of air purges, and improves boilerefficiency under part-load conditions.

A further improvement is modulating control. With thistype of control, the fuel and air supplies are regulated to exactly match the required heat demand. This ensuresgood efficiency across the whole heat output range ofboilers. Modern burners use micro-processors fitted to fuelvalves and air dampers to monitor flue gases continuallyand control fuel-to-air ratios accurately.

Retrofitting of burner controls is best suited for older,conventional boilers with large, variable heat loads.

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The most effective way to improve boiler performance is through controls.

Boiler controls

Refrigeration


Boiler interlock

Boilers can continue to fire even when there is no demandfor heat (called dry-cycling) and so all the heat energy is lost to the flue. Find out whether this is happening byturning off the heat distribution system and then observingthe boilers themselves. If they continue to fire when no load is required, dry-cycling is occurring. Clearly thisshould be avoided.

Linking the boiler controls with the heating system controls(such as room thermostats) via a boiler interlock will ensurethat the boiler does not operate when there is no heatdemand and will prevent dry-cycling. This can be done usingstandard wiring between the boiler control and the mainheating control, or can be achieved through the installationof a specialised integrated controller. The best option willbe determined by the size of the system and location ofthe boiler and controls. A qualified technician should beconsulted for advice.

Interlock control is appropriate for all types of boiler.

Sequence control

If there are two or more boilers, it is a good idea toconsider sequence control if it is not already installed.Find out whether or not sequence control is operating by observing the boilers during part-load conditions, such as in spring or autumn. If all boilers are firing undermild conditions, it is likely that they are operating only at part-load and do not have sequence control.

Good sequence control ensures that only the minimumnumber of boilers required to meet the heat demandactually fire and that these boilers are used to full capacityrather than part-load. Also, sequence controllers ensurethat the order in which the boilers fire can be rotated to minimise maintenance costs. Note that where there are both condensing and standard boilers installed, the condensing boiler should always take the lead. Good sequence control could save 5-10% of the overallenergy consumption of the boiler plant.

Where not already installed, sequence control should beretrofitted to multiple boiler applications with a variableload pattern.

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DID YOU KNOW?

A poorly maintained boiler can use

10% more energy than one that is

well-maintained.

Technology Overview

Optimised start/stop control

Most heating systems will be controlled via a timeswitch.This will be set to switch the heating system (and hencethe boiler) on and off at pre-set times in the morning andevening, corresponding to building occupancy patterns. An optimiser is a sophisticated timeswitch linked to theinternal and external thermostats that switches the boileron at exactly the right time to ensure that the buildingreaches the required internal temperature in time foroccupation. Similarly, the boiler is switched off early sothat the internal temperature is maintained only whenrequired. Savings of 5-10% of the overall energy consumptionof the boiler plant could be achieved.

Most buildings with standard operating hours would benefitfrom installing optimised start/stop control.

Direct weather compensation control

To achieve more savings, the temperature of the water canbe regulated according to outside temperature. In milderweather, the flow temperature is reduced, thus saving energy.This is done through the use of a compensator linked tointernal and external thermostats.

This form of control is particularly useful in condensingboilers as lower return water temperatures can beachieved, thus ensuring that maximum condensation occurs within the boiler and increasing efficiency.

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Building Energy Management Systems

Controls work best when their operation is integrated and linked to the actual requirements of the building. A Building Energy Management System (BEMS) is a computer-based control system which automaticallymonitors and controls a range of building services.Installing a BEMS means that control options such assequencing, optimisation and compensation can be carried out by one system. It allows various environmentalparameters to be taken into account and provides logs of useful data that can be used in maintenance, energymonitoring and assessing further improvements to the system. 10-20% of heating energy can be saved byinstalling a BEMS in place of several independent controloptions. However, they are expensive and may only becost-effective for larger boiler plant. They will also beeffective only if operated by trained staff and maintainedand calibrated regularly. Manufacturers can advise on themost suitable BEMS for their boiler plant.

Check controls

The benefits of improved controls will be realised only if frequent checks are carried out on control settings andtheir operation. This is particularly important if businessneeds have affected the controls. For example, controlsare set to cover a period when staff work out of hours, but are not returned to their original settings. A regularcheck will spot where energy is being wasted in this way.

Simple control settings (such as timeclocks) can be adjustedby non-professional building staff as circumstances require,provided they have had appropriate training and take care.More sophisticated controls should be adjusted by a qualifiedtechnician. Similarly, control operation and calibrationshould be checked annually by a qualified technician.

A simple way of assessing the effectiveness of boilercontrols is to plot heating energy consumption on a graphand compare with periods of building operation and outsideweather conditions. Does the building show a high energyuse out-of-hours? Is there a high heating load when theweather is mild? These are indications that control settingsare inaccurate or that additional controls are required.

For more advice and publications on energy monitoring, contact the Carbon Trust.

Sequence controls, optimisedstart/stop controls and directweather compensation controlscan be purchased as a unit orcan be programmed as part ofa Building Energy ManagementSystem (BEMS).

Boiler size What are the Want to saveminimum controls even more you should have? energy?

Minimum standard Good standard

For boilers Boiler interlock Minimum standard up to 50kW PLUS

Optimisation

Direct weather compensation

For boilers Boiler interlock Minimum standard over 50kW Sequence control PLUS

Optimisation

Direct weather compensation

Building Energy Management System (BEMS)

Summary of control options

Technology Overview

Perform regular servicing

A full boiler service should be carried out by a qualifiedtechnician on an annual basis, ideally before the start ofthe heating season. This service should include a flue gasanalysis (to check fuel-to-air ratio), an operational check,controls calibration, burner cleaning and limescaletreatment.

Analyse flue gas

As mentioned in the previous section, the fuel-to-air ratiois critical in ensuring efficient boiler operation. Analysis of the boiler’s flue gases for levels of carbon dioxide (CO2),oxygen (O2) and carbon monoxide (CO) will determinewhether this ratio is correct and what adjustments need to be made. Different ratios will be required for differentboilers and your boiler manufacturer or maintenancetechnician can give the appropriate advice.

Flue gas analysis should be carried out every three monthsby a suitably qualified technician. Ask for a report on the combustion efficiency which includes measures forimproving it.

Remove soot

If combustion conditions are not correct, particularly if toolittle air is used, unburnt fuel particles — soot — will buildup on the fire side of the boiler’s heat exchanger. This sootcreates an insulating layer, inhibiting heat transfer to thewater. More heat input is required to meet the heat demandand more heat energy will be lost to the flue.

All hydrocarbon fuels — gas, oil, coal — will create soot.Gas boilers create less soot and will require cleaning every six months. Oil and coal boilers should be cleanedmore regularly. Cleaning should be carried out by a qualified technician.

For very large boilers, typically used in industrial application,integrated soot-blowers are often installed in boilers toprovide continual cleaning; however, these will need to be checked regularly to ensure good working.

Maintenance

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Effective maintenance is essential in getting the best performancefrom your LTHW boilers. Without it, boiler efficiency can dropsignificantly and equipment life expectancy is reduced. Effectivemaintenance can also highlight potential problems quickly andenable remedial action to be taken before there is a major impact on performance.

DID YOU KNOW?

A 1mm layer of soot will cause a 10% increase in energy

input to the boiler to meet the same heat demand.

Boiler maintenance should becarried out by CORGI or OFTECregistered contractors ONLY.

Refrigeration


Minimise limescale build-up

In hard water areas, limescale can build up on the waterside of the boiler’s heat exchanger. This creates an insulatinglayer, inhibiting heat transfer to the water in the same wayas the soot deposits above.

The most effective method of limescale removal is throughchemical treatment of the water. This should be doneannually by a qualified technician to minimise limescalebuild-up and keep your boiler running at its most efficient.

Produce a maintenance plan, manual and logbook

To ensure effective maintenance is carried out, a maintenance plan should be put in place. This will detail what maintenance tasks are to be carried out, the frequency of these tasks and who is responsible.

A maintenance manual should be produced that is updatedregularly. This manual should include:

The maintenance plan

Block diagram of the boiler plant showing the location of key components and controls

Schematic diagrams of the heating system and the controls

Operating instructions and control settings

Emergency shutdown procedures

Contact details of installation/maintenance techniciansand boiler manufacturers.

Particular attention should be paid to specific instructionsfrom manufacturers as these will ensure the optimumperformance of the boiler plant. Also, failure to followthem may invalidate warranties.

A maintenance logbook should be kept giving detailedrecords of maintenance tasks, including which actions were taken, the person responsible, and when they were completed. This logbook will ensure that tasks arecarried out at the correct frequency and will highlightongoing problems.

Maintenance task Frequency Responsibility

Review boiler maintenance policy Yearly Energy/facilities manager with the advice of qualified technician

Full service Yearly Qualified technician

Flue gas analysis (combustion check) Quarterly Qualified technician

Remove soot deposits Six-monthly (more frequent Qualified technicianfor oil/coal boilers)

Limescale treatment Yearly Qualified technician

Check/adjust simple control settings Quarterly, or as changes to Building staffbuilding operation demand

Adjust/re-programme complex controls Yearly, or as changes to Qualified technicianbuilding operation demand

Check control operation Yearly Qualified technician

Calibration of controls Yearly Qualified technician

Summary of maintenance requirements

A 1mm layer of limescale willcause a 7% increase in energyinput to the boiler to meet the same heat demand.

Technology Overview

When considering a boiler replacement, advice should besought from a qualified building services engineer or boilertechnician. To help them, consider the following information.

The building’s heating requirements

The most important aspect in selecting a new boiler isgetting the size right. It was once common practice tooversize boiler plant with the mistaken notion that thiswould provide greater flexibility in the future. However, it is now realised that this is unnecessary as the heatingdemand for many commercial buildings has fallen. This isdue to improvements in building fabric and an increase ininternal heat gains, such as from IT equipment, lightingand occupants. If a boiler has not been replaced for many years, the heating load of the building may havechanged significantly.

Start by reviewing the building’s internal environment andgeneral operation. What is the current internal temperatureof the building? Are employees happy with the internalenvironment? Are there any hot or cold spots within the building? Are there any areas of the building wheretemperature is critical? When is the building occupied?

Next, review your annual energy bills. What fuel do you currently use for heating? How much energy has thebuilding used over the last year and how much did it cost?How does this compare with other similar building types?To do this, divide the annual heating energy used by thearea of the building to gain a ‘benchmark’ in kWh/m2. The Carbon Trust and other organisations publish typicalbenchmarks for different types of building for comparison.Call the Carbon Trust to see if relevant benchmarks existfor your building type.

Smaller boilers cost less, so look for ways of reducing the heating demand. Can the insulation of the building be improved? Could draught-proofing be improved?

Replacing boilers

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If a boiler is more than 15 years old, or if it is showing signs ofinefficient operation, it should be replaced. This is not as simple as noting the old boiler’s rating and purchasing a new, condensingmodel. To find the best solution, thoroughly review the building’sheating demand and your business needs, and check these againstyour technical, financial and policy requirements.

Information Source How is this information used?

Floor area of building Property documents Energy benchmarksDirect measurement

Occupied hours Staff records Calculating heating demandSelecting boiler controls

Internal environmental data, Direct measurement Calculating heating demandsuch as temperature Control settings Assessing effectiveness of

Staff comments existing heating system

Annual energy use/cost for heating Utility bills Energy benchmarksEnergy monitoring and targeting system

Details of planned energy saving measures Company energy policy Calculating heating demand

Find out the building’s heating requirements

Refrigeration


Technical considerations

The choice of boiler will be dependent on a number oftechnical issues. A building services engineer or boilertechnician can give advice, but you can provide some basic information to help.

Fuels

Ultimately, the choice of fuel will be based on cost andavailability of supply. Ask which fuels are available on-site.Is there a natural gas supply? If not, are there issuesrelating to the supply or storage of fuels such as LPG.

Unless biofuels are a realistic option, natural gas is thebest choice where a supply is available as it is the mostversatile and has the lowest carbon emissions. Boilers aredesigned to operate with particular fuels and are rarelyinterchangeable.

Location

Where you have more than one boiler, find out if theexisting boiler plant is centralised or de-centralised.

Centralised plant (where all boilers are in one plantroom)may be easier to maintain and control, but heat lossesthrough long pipework runs will be higher. Combine thereplacement of boilers with upgrades to the pipeworkinsulation. Also take advantage of the central location toinstall upgraded controls or re-programme existing ones.

De-centralised plant (where a number of smaller boilers arelocated around the building) will reduce pipework losses,but you will not have the option of integrating controloperation and maintenance may be more problematic and expensive. This is because it costs more to carry outmaintenance checks on several smaller boilers than onelarge boiler.

Flue outlet

Where is the boiler flue outlet? Condensing boilers generatelower temperature flue gases and visible plumes of steam.This may cause problems if the flue outlet is close to otherbuilding surfaces.

Heating system

What type of heating system is currently used in thebuilding? Unless a major refurbishment is planned, it may not be cost-effective to replace the whole heatingsystem so the new boiler must be compatible with what is there already. Condensing boilers work best with low-temperature applications such as under floor heating, butwill still provide a higher level of efficiency when appliedto a radiator circuit. It may be necessary to upgrade theheating controls of the system to get the best from thenew boiler. Do not forget to account for these costs whenconsidering the purchase price.


Fuel supply available Utility companies Specification of boiler typeLocal authority

Centralised or de-centralised plant Observation Specification of boiler typeSelecting boiler controlsPipework insulation required

Location of flue outlet Observation Specification of boiler typeAssessing effectiveness of existing heating system

Type of heating system Observation Specification of boiler typeHeating controls

Find out the technical requirements

Technology Overview

Financial considerations

Consider the costs of the new boiler, including capitalexpense, fuel and maintenance. This is called life costing,that is, how much will the boiler cost over its actuallifespan. It is important to capture all the activitiesassociated with the ownership of a boiler if it is to last its normal life expectancy.

Capital expense

How quickly will the investment pay for itself throughreduced running costs? Will this influence the purchasingbudget?

Condensing boilers are more expensive than standard high-efficiency boilers, but they are more efficient and cost less to run. So the extra cost is often paid back within two years or less.

The business may be able to take advantage of EnergyEfficiency Loans or the Enhanced Capital AllowanceScheme (see next page for information on the Carbon Trust’sfinancial products).

Fuel

Fuels vary in price. Consider your current and projectedenergy use and calculate the cost of running the boiler.

Maintenance

As stated previously, maintenance of boilers is important.Will the maintenance costs of the new boiler be higher?Will extra staff training be required to ensure efficientoperation? Can maintenance be done in-house or will it be contracted out? Make sure that all staff involved in theoperation and maintenance of the boiler plant have a sayin the choice of the new boiler.

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Purchase budget Finance/Company director Specification of boiler

Availability of loans/tax incentives Carbon Trust Changes to purchase budgetHM Revenue and Customs

Running costs of new boiler Building services engineer Calculating payback periodsBoiler technician Predicting future energy expenditureManufacturers Life costingUtility bills

Maintenance costs of new boiler Building services engineer Calculating payback periodsBoiler technician Predicting future energy expenditureManufacturers Assessing staff training needsFinance dept. Developing a maintenance plan

Life costing

Find out financial considerations

DID YOU KNOW?Replacing a conventional boiler with a condensingmodel can save 10-20% of annual energy costs — moreif the original boiler is in a particularly poor condition.Example: A building with a heating demand of 100kWhas an annual gas bill of £7,150.1 A new condensingboiler is installed at a cost of £2,000 with a seasonalefficiency of 90%. The new annual gas bill is £5,550 — a saving of 22% or £1,600/year. Maintenance costsare increased by £200 per year. Therefore, the cost of the new boiler is paid back within 18 months.1 Based on a 70% efficient boiler, 2,500 operating hours/year and 2p/kWh gas price.


Environmental considerations

As well as reducing running costs, condensing and high-efficiency boilers will have reduced emissions ofcarbon dioxide (CO2) and harmful pollutants such assulphur dioxide (SO2) and nitrogen dioxide (NO2). Does yourcompany have an environmental policy? Will this influencethe choice of a new boiler?

Preparing a detailed brief

Once this information has been gathered, use it to preparea detailed brief for a building services engineer or boilertechnician. They will use this information to select the bestboiler to achieve your needs within the proposed budget. A detailed brief will save time and money and ensure thatyour new boiler is both efficient and effective.

Environmental Company director Specification ofpolicy boiler to ensure

reduced emissions

Find out environmental considerations


Energy Efficiency Loans

The Carbon Trust can provide an energy efficiency loan to SMEs in England and Wales of up to £100,000*and for all businesses in Northern Ireland of up to£200,000 for investment in energy saving projects suchas the upgrading or replacement of lighting, boilers or insulation. The loans are interest-free, unsecured,repayable over a term of up to four years and with noarrangement fees. In Scotland, the Scottish Executiveoffers a similar scheme called ‘Loan Action Scotland’.

*Subject to terms and conditions and local funding.

Tax incentives

Enhanced Capital Allowances (ECAs) enable businessesto buy energy efficient equipment using a 100% rate oftax allowance in the year of purchase. Businesses canclaim this allowance on the investment value of energyefficient equipment, if it is on the Energy TechnologyList. The procedure for claiming an ECA is the same as for any capital allowance. For further informationplease visit www.eca.gov.uk or call the Carbon Trust on 0800 085 2005.

Technology Overview

The first step is to take regular meter readings — at leastmonthly, although weekly would be better for largerbuildings. If a BEMS is installed, it may be possible toautomate this process. This will be dependent on the typeof meter installed and advice should be sought from theBEMS manufacturer and/or the utility company. Dependingon the size of the building, utility companies may be ableto provide half-hourly energy data.

The meter readings should be recorded on a table and theenergy consumption for the period calculated. Graphs canthen be produced to show the energy consumption overtime and comparisons can be made to assess performance.

If the individual performance of a boiler is required, spotmeters should be installed on the individual fuel intakes.This may not be cost-effective for smaller boilers so shouldbe considered carefully.

It is important to assess heating energy use in the contextof weather conditions and building operation. For example,heating energy will increase when the weather is colderand heating energy should be minimal when the building is unoccupied.

If your heating energy use profile does not match weatherconditions or building operation, it may be an indication of poor control.

Set targets and monitor progress

Simply monitoring energy use will not result in savings.Targets for reduction should be set and measures put in placeto achieve those targets. A 10% reduction in heating energycan often be achieved through simple adjustments to existingboiler plant. Greater reductions can be achieved throughthe replacement of equipment, components or controls.

Keep a check on progress towards meeting targets. If progress is slow, carry out another review of the heatingsystem and look for additional measures that can be taken. Report progress to all building occupants — this will increase energy awareness and get everyone involvedin reducing the building’s energy use.

Energy monitoring and targeting

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If energy use is not monitored, it cannot be controlled. An energyefficiency strategy will be most effective when accompanied byappropriate energy monitoring and targeting. By monitoring theenergy used by the boiler plant, the effect of improvements can be assessed in both financial and environmental terms. In addition,unusually high energy consumption can be spotted quickly, problemsidentified and remedial action taken.

For more information on energy monitoring, contact the Carbon Trust.

Effective energy monitoringand targeting can highlightpotential problem areas andlead to swift, remedial actions.

Refrigeration


Next steps

The checklist below will help you to carry out an initial review ofthe boiler plant and assess what actions can be taken. Many suchactions can be taken in-house; however, you may need specialistsupport from your contractor or consultant for others.

Review Questions Actions to be considered Comments

Make, model, size, Is the boiler more Replacement Different improvement optionstype and age of boiler than 15 years old? will apply depending on

Is the boiler oversized? Replacement boiler type

Fuel consumption of How efficient is Assess through meter boiler plant the plant? readings. Estimate efficiency

based on consumption and rated output

Check physical Is there any corrosion? Get service done Poor physical condition will condition Is insulation adequate/ Replace/upgrade insulation cause poor performance;

in good condition? Replacement consider replacement

Assess controls What type? Install additional controls Improved control will reduce Are sequencers, optimisers energy consumptionor compensators used?

Check control settings Are they appropriate? Adjust settings Improved control will reduce Do they match building energy consumptionoperation patterns?

Review maintenance When was the last Establish a proper Poor maintenance can reduce history maintenance carried out? maintenance plan boiler performance by up

Is a proper maintenance Order service/maintenance to 10%plan in place? check

Technology Overview

Glossary

22

Atmospheric burner A burner where the air required for combustion is drawn in via natural convection.

Boiler A vessel for converting heat produced by combustion of fuel into hot water or steam.

Boiler efficiency A comparison of the energy output versus the energy input of the boiler.

Boiler interlock Where the boiler and system controls are linked to ensure the boiler does not fire when there is no heating demand.

Building Energy A computer-based system that operates all building controls and enables automatic Management System adjustment and monitoring of settings.(BEMS)

Burner The device producing the flame for combustion in the boiler.

Combustion The process of turning fuel into useful heat.

Compensator A device, or feature within a device, that adjusts the temperature of the water circulatingthrough the heating system according to the temperature measured outside the building.

Condensing boiler A boiler that reclaims heat from the exhaust gases to improve overall efficiency.

Convector A heat emitter that heats a room through either natural or forced convection.

Energy benchmark A measure of a building’s energy use that can be compared to other buildings of a similar type. Expressed in kWh/m2.

Flue The boiler’s chimney — used to transport exhaust gases to the atmosphere.

Flue damper A device that shuts off the flue, avoiding cold air penetrating the boiler when it is not firing.

Forced/induced A burner where the air required for combustion is drawn in via a mechanical fan.draught burner

Heat exchanger A network of pipes within a boiler whereby the heat from the burner is transferred to thecirculating water.

Modulating burner Where the fuel and air intake are controlled over the whole range of boiler output.control

Optimiser A sophisticated timeswitch linked to the internal and external thermostats that switches theboiler on at exactly the right time to ensure that the building reaches the required internaltemperature in time for occupation.

Radiator A heat emitter, made of metal, that heats a room through a combination of radiation and convection.

Sequencer A controller for multiple boiler systems that ensures the minimum number of boilers is used to meet the required heating demand.

Single-stage Where the burner is either ‘on’ or ‘off’ and fuel/air intakes are the same regardless burner control of heating demand.

Two-stage Where the burner can revert to a low-firing range under part-load conditions.burner control

Under floor heating A network of low temperature hot water pipes installed under the floor finish which heat a room from beneath.

Variable flow control Where the pump flow is regulated to match demand and flowrate.

Variable speed drive A device fitted to electric motors that regulates speed to match demand.


Notes

Technology Overview24

Notes

receive free publicationsThe Carbon Trust has a comprehensive library of energy saving publications.For more information on your sector, technologies within your sector and thetechnologies listed in this guide, please visit our website or phone us.

www.thecarbontrust.co.uk/energyAll of our publications are available to order or download from the Carbon Trust website at www.thecarbontrust.co.uk/energy. The site provides a range of information suited to every level of experience including top tips, action plans, forthcoming events and details of the range of Carbon Trust services.

For further information…

call the Carbon Trust on 0800 085 2005

You’ll find free advice on what your organisation can do to save energy and save money. Our team handles questions ranging from straightforwardrequests for information to in-depth technical queries about particulartechnologies and deals with all kinds of energy saving topics for people at all levels of experience.

The Carbon Trust works with business and the public sector to cut carbon emissions and capture the commercialpotential of low carbon technologies.

An independent company set up by the Government to help the UK meet its climate change obligations throughbusiness-focused solutions to carbon emission reduction, the Carbon Trust is grant funded by the Department for Environment, Food and Rural Affairs, the Scottish Executive, the Welsh Assembly Government and InvestNorthern Ireland.

Whilst reasonable steps have been taken to ensure that the information contained within this publication is correct,the Carbon Trust, its agents, contractors and sub-contractors, and the Government give no warranty and make norepresentation as to its accuracy and accept no liability for any errors or omissions.

Any trademarks, service marks or logos used in this publication are the property of the Carbon Trust and copyrightis licensed to the Carbon Trust. Nothing in this publication shall be construed as granting any licence or right touse or reproduce any of the trademarks, service marks, logos, copyright or any proprietary information in any waywithout the Carbon Trust’s prior written permission. The Carbon Trust enforces infringements of its intellectualproperty rights to the full extent permitted by law.

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