2012-Ctv051 Low Temperature Hot Water Boilers

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Low temperaturehot water boilersIntroducing energy saving opportunities for business

Technology Overview

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2Low temperature hot water boilers

Preface

Reducing energy use makes perect business sense; it saves

money, enhances corporate reputation and helps everyone in

the fght against climate change.

The Carbon Trust provides simple, eective advice to help

businesses take action to reduce carbon emissions, and the

simplest way to do this is to use energy more efciently.

This technical overview o low temperature hot water boilers

introduces the main energy saving opportunities or businessesand demonstrates how simple actions save energy, cut costs

and increase proft margins.

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Contents




enrgy consumption

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

A significant proportion of this is provided by

commercial boiler plant, so it should be included

in any energy reduction strategy.

Typically, energy improvements of 10% or morecan be made relatively easily through maintenance

and low cost, straightforward improvements. The

financial rewards of these 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 to poor

maintenance. New condensing boilers can achieve

efficiencies of over 90% and consequently it

can be worth considering 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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Summary of ky aras

Boilers oer many energy saving opportunities, ranging rom replacement o the boileritsel to retroftting o controls and other equipment.

The most appropriate solution will depend on what type of boiler and heating system you have,

your business needs and your budget.

Savings in existing systemsThese can range from the addition of boiler

and pipework insulation to retrofitting of new

controls or flue gas heat recovery systems.

See page 12.

Maintenance and monitoring

Both new and existing boilers require an

effective maintenance programme toensure that they operate to peak efficiency.

See page 19.

Selecting a new boilerNot just as simple as replacing like for like,

going through a careful analysis of what you

really need can save a fortune. See page 22.

There are also significant opportunities to save

by considering improved boiler controls (see

page 14) and by monitoring your energy use

(see page 28).

Cas studyEffective boiler replacement

A knitwear manufacturer in Hawick,

Scotland, replaced their old, inefficient

oil-fired boiler with two new high-

efficiency gas-fired boilers that were

sized to match more accurately the actual

heating demand of the site. In addition,

the new boilers had improved burner

controls linked to a Building Management

System. The resulting savings were£13,200 and 276 tonnes CO2 per year, with

an overall payback time of under five

years. The company also reported

improved productivity and staff working

conditions following the retrofit.

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Tchnology ovrviw

Low temperature hot water boilers produce hot water or space heating,general hot water demand or, occasionally, industrial processes.

Low temperature hot water (LTHW) boilers

produce hot water at around 90ºC and are the

type most commonly found in houses and

commercial premises. The hot water produced

is distributed via pipework to ‘wet’ heating

systems and hot water storage tanks.

Most LTHW boilers are designed to use natural

gas, but there are also designs that use mineral

or bio-oils or LPG. These are used particularly in

areas with no natural gas supply. Dual fuel

designs that can use oil or biomass and gas are

also available. Oil and LPG are more expensive

than gas and emit more carbon dioxide to the

atmosphere. Biomass boilers which use wood,

specially grown ‘fuel crops’ or organic waste

as the fuel, are becoming more popular. These

create very little net carbon dioxide, but are

more expensive to buy. The availability and

storage of fuel can be more difficult although

the supply chain has developed significantly.

Gas-fired boilers are the main focus of

discussion in this publication; however, much

of the energy saving advice is applicable to

boilers using other fuels.

There are numerous types of biomass boiler,

many of which are based on concepts used in

the past for coal fired boilers. For more

information about the types of biomass boilers

available, order or download the Carbon Trust’s

in depth guide, A practical guide for potential

users: Part 2 – Technical manual (CTG014).

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http://www.carbontrust.co.uk/Publications/pages/publicationdetail.aspx?id=CTG014







How does a low temperaturehot water boiler work?

The diagram in Figure 1 shows the major

components of a gas-fired LTHW boiler.

The controls on the boiler set the required

temperature and 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 burn fuel. The

gas burners ignite a mixture of gas (from the

gas inlet ) and air (from the boiler surroundings)

to produce hot combustion gases. The precise

mixture of gas and air is controlled by the gas

valve and burner controls (this is covered

in further detail later). The hot combustion gases

pass over the heat exchanger (a network of

pipes) to heat the circulating water within.

This water is circulated by a pump . The

resultant hot water is distributed to the heating

system via the hot water outlet and the

exhaust gases escape to the atmosphere via a

flue or chimney . Any condensate leaves theboiler via a drain . To prevent heat loss from

the boiler, the whole mechanism is contained

within an insulated metal enclosure .

Figure 1 Major components in a typical gas hot water boiler

Exhaust gases

Heat exchanger

Flue

Gas valve and

burner controls

Gas inlet

Draft hood

Water feed

Hot water outlet

Temperature and

pressure controls

Circulating pump

Drain

Insulated metal enclosure

Gas burners

1

10

11

2

3

4

5

6

7

8

9

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Identifying your heating system

There are a variety of heating systems that can

be used with LTHW boilers, offering different

opportunities for savings. Understanding your

type of heating system will help in identifying

what kind of boiler you have, and where the best

chances of saving are.

Radiators are metal units which emit the heat

from the system’s hot water pipes. Effective

temperature control and low maintenance make

radiator systems a popular choice, and they are the

most common type of system found in the UK.

Convectorsdraw room air through a casing across

a hot water to air heat exchanger and direct hot air

back into the room. They have a low surface

temperature making them popular in schools and

hospitals, where a high temperature radiator-based

system could present a burning risk to occupants.

Compared with radiators, they have a greater heat

output per unit size and a faster heat-up time;

however, their maintenance costs are greater. The

running costs are further increased when the

convector has a fan within the casing.

Under floor heating consists of a network of

hot water pipes that is embedded between the

floor finish and the main concrete floor slab.

These pipes heat the whole floor surface and

cause heat to rise throughout the space. The

main advantage of under floor heating over

radiators and convectors is that it provides muchmore even heat distribution and operates at

lower temperatures. Both of these can

contribute to a more efficient system with lower

energy use. It is also ‘ invisible’ and can give

greater flexibility in the use of a space (for

example, positioning of furniture). However,

these will not be found in buildings which require

under floor electrical services or in older

buildings 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.

Identifying your boiler

Since the end of 1997, legislation has imposed

minimum efficiency requirements for boilers with

outputs of up to 400kW. Current UK boiler

efficiency regulations recognise three types of boiler

“standard”, “low temperature” and “condensing”.

The UK Building Regulations recognise only twotypes “standard” and “condensing”. These can be

used alone or combined together within systems.

Conventional boilers

If your boiler is more than 15 years old, it is

likely to be a conventional type of standard

boiler, designed to operate with an average

water temperature of 60 to 70°C. They often

have a cast iron heat exchanger and use

atmospheric burners, which draw the air

required for combustion from around the boiler

by natural convection. They tend to be larger

than boilers of more modern design.

Medium/high temperature hot water

boilers and steam boilers 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 smaller commercial premises

(for example, in offices) due to safety

risks. For information about boilers which

operate at higher temperatures , order or

download the Carbon Trust’s technology

overview, Steam and high temperature

hot water boilers (CTV008).

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http://www.carbontrust.co.uk/Publications/pages/publicationdetail.aspx?id=CTV008







Some standard boilers and most other boiler

types have forced draught burners. These use a

fan to force air into the boiler and up the flue.

These burners enable the amount of combustionair to be controlled more closely, producing lower

flue gas volumes than for atmospheric burners

and allowing narrower flues to be used. The

operation of the fan may give rise to additional

noise. Boilers which use separate forced draught

burners are usually easy to identify by the fan

and controls fitted outside the boiler case.

Standard boilers which do not meet the

minimum efficiency requirements are no longeravailable to buy new. Businesses using such

boilers should consider replacing them with

models that comply with current regulations.

High-efficiency boilers

Standard and low temperature boilers that meet

the minimum efficiency requirements of the

current regulations are generally marketed as

high-efficiency boilers. So if you have a standard

boiler which was installed from 1997 onwards, it

is likely to be this type. These boilers have; a

lower water contents, larger heat exchanger

surface areas and greater insulation of the boiler

shell compared to conventional designs.

High-efficiency boilers can work with all types of

heating system. They are particularly suited to

applications where a higher water temperature

is required, such as space heating systems usingradiators designed to operate at typical flow

temperatures of 80°C or, some process heating

applications. However, they are not well suited

to low temperature applications, such as, under

floor heating, where 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 boiler flue. Water vapour makes up some of

these exhaust gases. Condensing boilers have

extra heat exchanger surfaces to extract much of

the waste heat and return it to the system. The

temperature of the exhaust gases is reduced

causing the water vapour to condense, and this is

drained away. Condensing boilers are the most

efficient on the market and since April 2005,regulations require that they must be considered

as the first choice for all new or replacement space

heating installations. However they may not be the

appropriate choice for businesses with applications

with continuous full load demands for water at

higher temperature (up to 90°C).

Condensing boilers work best with low-

temperature applications, such as under floor

heating. However, efficiencies will still be increased

when used with radiator or convector circuits.

Combination boilers

In a combination (or ‘combi’) boiler, there

is a secondary heat exchanger integratedwithin the boiler housing that is used to

provide hot water instantaneously. There

is no need for a hot water storage cylinder

and associated cold water feed tank and

pipework. They can be particularly

attractive options in properties where

space is limited and are used mainly in

domestic buildings.

Combination boilers are limited to smallerapplications so will not be appropriate for

most businesses. However, if your

business is run from a very small building

and hot water demand is limited to taps,

they may be an option.

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.

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Modular boiler systems

A modular boiler system is where a series of

boilers are linked together to meet a variety of

heating demands. Modular boiler systems are

best suited to buildings or processes with a

significant, variable heat demand.

LTHW boilers give optimum efficiency at a

particular load point (standard boilers at full load,

condensing boilers at part load) so, it makes

sense to have a series of boilers operating at

around their peak efficiency loads and together

matching the range of heating demands that

may be experienced in one of the UK’s

commercial buildings. For example, consider a

building with a peak winter heating demand of

100kW. If a single standard boiler were to be

used, it would operate at full capacity, and peak

efficiency, for only a few weeks of the year. If

five modular boilers of 20kW each were used

instead, lower heating demands experienced at

other times of the year could be met by a

reduced number of boilers operating at full

capacity. Modular systems are generally

composed of several identical boiler units

although a mix of condensing and conventionalboilers could be used. The condensing boilers

should in general be the ‘lead’ to maximise

system efficiency. To gain the maximum benefit

from arrangements of this type appropriate

sequence control needs to be implemented –

see section ‘Boiler Controls’.

Boiler efficiency

No boiler is 100% efficient. Energy (heat) 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 provides a means of

comparing the relative performance of different

boiler models. However, it does not take into

account the actual operation of the boiler or its

practical use. For a more meaningful indication

of performance in space heating applications a‘seasonal efficiency’ can be calculated and is

often quoted by manufacturers targetting this

market. This takes into account the efficiencies

of a boiler meausured at full and part load. It is a

weighted average of a defined number of hours

of full and part load operation which represents a

full year of operation.

The table on page 11, shows the seasonal

efficiencies for the different boiler typesdiscussed above and how this would affect the

energy input required to meet a heating demand

of 100kW. Note that the boiler efficiency is also

affected by the heating system type.

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Table 1 Typical seasonal efficiency

Boiler type Typical seasonal efficiency Energy input rate required to meet

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.

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Improvmnts to xisting boilr plant

It may not be cost-eective to replace boilers that are relatively new.However, there are still opportunities to make substantial savings

through improvements to other items o the boiler plant.

Many of these measures will need specialist help.

If in doubt, always consult a qualified technician.

Insulate boilers, pipeworkand valves

Heat loss through the boiler, pipework and

valves leads to poor efficiency. All businesses

should check their systems’ insulation.

Most modern boilers are well insulated to

reduce heat losses from the body of the boiler

and these can account for less than 1% of the

total energy input. However, on older boilers, the

insulation may be in poorer condition and 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 of degradation. Similarly, the

insulation on the associated boiler pipework and

valves should be assessed and replaced if

necessary. This can result in additional savings

of up to 10% of the boiler energy input.

Particular attention should be paid to valves asthese are often left uninsulated because of

access concerns. Modern valve-wraps solve this

problem by providing suitable levels of insulation

but allow easy access to the valve through

quick-release fastenings.

Fit flue dampers

On larger boilers, the flue can cause a flow of air

through the boiler, even when it is not firing. This

cools the boiler and valuable heat is lost to the

atmosphere – known as ‘standing losses’. A flue

damper can be used to close off the flue

automatically when the boiler is not firing, thus

preventing this energy loss.

Since 1998, regulations have required boilers to

have improved 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.

Install variable speed drivesand pumps

On forced/induced-draught boilers, a variable

speed drive can be installed on the fan. The

enables the fan to operate at lower speeds whenless air flow is required. A reduction in fan speed

of just 10% can result in fan energy consumption

savings of around 20%, and a reduction in fan

speed of 20% will save up to 40%. This is

particularly relevant for big boiler systems.

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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, but they normally requiremaximum flow for only a limited time. This is

usually during the ‘boost’ period when trying to

raise the temperature of the building to a

comfortable level. Variable speed pumps can be

fitted which decrease the 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 best suited to larger systems with variableloads. If the load on the fan/pump is constant,

energy consumption may actually increase

through the installation of a VSD. The advice of a

qualified technician is essential to assess the

economic feasibility of this option.

For further information about Variable speed

drives, please download the Variable speed

drives technology overview (CTG070).

Recover heat from exhaust gases

In conventional boilers, the heat contained

within the exhaust gases is lost to the

atmosphere. If replacement with a condensing

boiler is not possible, this heat can be recovered

through the use of a heat exchanger. The heat

can be used to pre-heat the return water or the

combustion air. Increasing the temperature of

the combustion air by 20ºC can improve the

overall efficiency of the boiler by 1%.

This technology is best suited to conventional

and highefficiency boilers with flue gases of a

sufficient temperature. It is important that the

economics of retrofitting such a system are

assessed as the potential savings are relatively

small. They will be most economical when

applied to a larger system. Always consult a

qualified technician.

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Boilr controls

The most eective way to improve boiler perormance is through controls.

The first step is to assess what controls already

exist, find out if they are calibrated accurately,

and check that their settings match the

business’s requirements. If they do not, adjust

them either by asking for help from a qualified

professional, or referring to the operating manual

(usually downloadable from manufacturers’

websites if they have been lost).

The next step is to decide whether additional

controls would be beneficial. Again, installation of

new controls should be carried out by a professional.

A brief description of a number of different

control options is given below, with details onthe optimum settings for these controls.

Manufacturers will be able to give more advice

on the best control options for particular boilers.

Please refer to the Carbon Trust‘s technology

guide Heating control (CTG065) for more

in-depth information.

Burner controls

Burner controls manage the fuel-to-air ratio

which is critical to the efficient operation of the

boiler: too little air and there will not be enoughoxygen for complete combustion to occur

resulting in a build-up of potentially dangerous

carbon monoxide in the flue; too much air and

energy will be wasted in trying to heat the

excess. The fuel-to-air ratio is normally set on

the burner controls and will be based on the

boiler manufacturer’s recommendations. Proper

control of this ratio will ensure that the boiler is

as efficient as possible.

As part of routine servicing, a qualified

technician will measure the fuel-to-air ratio of a

boiler. This can then be compared 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 complex systems, particularly

those operating at part load for much of the year,

it may well be cost-effective to consider a

replacement burner control that will improve

efficiency and 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 most older, standard boilers.

With this type of control, the burner fires at full

capacity when heat is required and is off

otherwise. Air purges immediately before the

burner is switched on and after the burner is

switched off to ensure that no residual fuel or

combustion vapour remains in the boiler, but this

also causes heat to escape via the flue.

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An improvement to the above is two-stage or

‘high-low’ control. With this type of control,

rather than being completely switched off, the

burner has the option of going to a low firingrate, typically 40% of full capacity. This reduces

the number of times the burner switches off and

the number of air purges, and improves boiler

efficiency under part-load conditions.

A further improvement is modulating control.

With this type of control, the fuel and air

supplies are regulated to exactly match the

required heat demand. This ensures good

efficiency across the whole heat output range ofboilers. Modern burners typically use micro-

processors based controls. These adjust air and

fuel flows continuously, compensating for

changing conditions to ensure that the correct

fuel-to-air ratios are maintained accurately.

Retrofitting of burner controls is best suited for

older, conventional boilers with large, variable

heat loads.

For information about boiler controls in the

context of heating systems download the

Carbon Trust’s technology overview, Heating,

ventilation and air conditioning (CTV046).

Boiler interlock

Boilers can continue to fire even when there is no

demand for heat (called dry-cycling) and so all the

heat energy is lost to the flue. Find out whether this is

happening by turning off the heat distribution system

and then observing the boilers themselves. If they

continue to fire when no load is required, dry-cycling

is occurring. Clearly this should be avoided.

Linking the boiler controls with the heating system

controls (such as room thermostats) via a boiler

interlock will ensure that the boiler does not operate

when there is no heat demand and will prevent

dry-cycling. This can be done using standard wiring

between the boiler control and the main heating

control, or can be achieved through the installation

of a specialised integrated controller. The best

option will be determined by the size of the system

and location of the boiler and controls. A qualified

technician should be consulted 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

to consider 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 and shutting

down simultaneously, it is likely that they are

operating only at part-load and do not have

sequence control.

Good sequence control ensures that only the

minimum number of boilers required to meet the

heat demand fire and that these boilers are used

at their optimum efficiency load. Also, sequence

controllers ensure that 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

overall energy consumption of the boiler plant.

Where not already installed, sequence control

should be retrofitted to multiple boiler

applications with a variable load pattern.

Did you know?

A poorly maintained boiler can use 10% more

energy than one that is well-maintained.

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Optimised start/stop control

Most heating systems will be controlled via a

timeswitch. This will be set to switch the heating

system (and hence the boiler) on and off at pre-set

times in the morning and evening, corresponding

to building occupancy patterns. An optimiser is a

sophisticated timeswitch linked to the internal and

external thermostats that switches the boiler on at

exactly the right time to ensure that the building

reaches the required internal temperature in time

for occupation. Similarly, the boiler is switched off

early so that the internal temperature is

maintained only when required. Savings of 5-10%of the overall energy consumption of the boiler

plant could be achieved.

Most buildings with standard operating hours

would benefit from installing optimised start/

stop control.

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E x t e r n a l t e m p º C

Boilers firing

ON

ON

ON

ON

ON

OFF Mild weather

Cold weather

Deep winterON

OFF

OFF

20

24

12

16

8

04 5 6 7 8 9 10 11 12

I n t e r n a l t e m p º C

Time (hours)

Potential energy savings

Timeswitchset for 6am

Optimisedstart

Typical settingsMaximumheat-up periode.g. 6am to 9am

Normaloccupancy periode.g. 9am to 5pm

Figure 2 Sequence control

Figure 3 Optimised start/stop control

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Building EnergyManagement 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 automatically monitors and

controls a range of building services. Installing a

BEMS means that control options such as

sequencing, optimisation and compensation can

be carried out by one system. It allows various

environmental parameters to be taken into

account and provides logs of useful data that can

be used in maintenance, energy monitoring and

assessing further improvements to the system.

10-20% of heating energy can be saved by

installing a BEMS in place of several

independent control options. However, they are

expensive and may only be cost-effective for

larger boiler plant. They will also be effective

only if operated by trained staff and maintained

and calibrated regularly. Manufacturers can

advise on the most suitable BEMS for their

boiler plant.

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0 20 40 60 80 100

E x t e r n a l t e m p º C

Flow temp ºC

Normally two settingsMinimum flow temperature

Ratio or slope of graph

Figure 4 Direct weather compensation control

Direct weathercompensation control

To achieve more savings, the temperature of

the water can be regulated according to outside

temperature. In milder weather, the flow

temperature is reduced, thus saving energy.

This is done through the use of a compensator

linked to internal and external thermostats.

This form of control is particularly useful in

condensing boilers as lower return water

temperatures can be achieved, thus ensuring

that maximum condensation occurs within

the boiler and increasing efficiency.

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Check controls

The benefits of improved controls will be

realised only if frequent checks are carried out

on control settings and their operation. This is

particularly important if business needs have

affected the controls. For example, controls are

set to cover a period when staff work out of

hours, but are not returned to their original

settings. A regular check will spot where

energy is being wasted in this way.

Simple control settings (such as timeclocks) can

be adjusted by non-professional building staff as

circumstances require, provided they have had

appropriate training and take care. More

sophisticated controls should be adjusted by a

qualified technician. Similarly, control operation

and calibration should be checked annually by a

qualified technician.

A simple way of assessing the effectiveness

of boiler controls is to plot heating energy

consumption on a graph and compare with

periods of building operation and outside weather

conditions. Does the building show a high energy

use out-of-hours? Is there a high heating load

when the weather is mild? These are indications

that control settings are inaccurate or that

additional controls are required.

Table 2 Summary of control options

Boiler size What are the minimum

controls you should have?

Minimum standard

Want to save even more

energy?

Good standard

For boilers up to 50kW Boiler interlock Minimum standard

PLUS

Optimisation

Direct weather compensation

For boilers over 50kW Boiler interlock

Sequence control

Minimum standard

PLUSOptimisation

Direct weather compensation

Building Energy Management

System (BEMS)

Sequence controls, optimised start/stop controls and direct

weather compensation controls can be purchased as a unit or

can be programmed as part of a Building Energy Management

System (BEMS).

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Maintnanc

Eective maintenance is essential in getting the best perormance rom your LTHW boilers.Without it, boiler efciency can drop signifcantly and equipment lie expectancy is reduced.

Effective maintenance can also highlight

potential problems quickly and enable remedial

action to be taken before there is a major impact

on performance.

Perform regular servicing

A full boiler service should be carried out by a

qualified technician on an annual basis, ideally

before the start of the heating season. This

service should include a flue gas analysis (to

check fuel-to-air ratio), an operational check,

controls calibration, burner cleaning and

limescale treatment.

Boiler maintenance should be carried out by GAS Safe or

OFTEC registered contractors ONLY.

Analyse flue gas

As mentioned in the previous section, the

fuel-to-air ratio is 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 determine

whether this ratio is correct and what

adjustments need to be made. Different ratios

will be required for different boilers and your

boiler manufacturer or maintenance technician

can give the appropriate advice.

Flue gas analysis should be carried out every

three months by a suitably qualified technician.

Ask for a report on the combustion efficiency

which includes measures for improving it.

Remove soot

If combustion conditions are not correct,

particularly if too little air is used, fuel combustion

will not be complete. So excessive amounts of CO

and particles of carbon (soot) will form. If these

particles build up on the fire side of the boiler’s

heat exchanger they will form an insulating layer,

inhibiting heat transfer to the water. More heat

input is required to meet the heat demand and

more heat energy will be lost to the flue.

All hydrocarbon fuels – gas, oil, coal – may create

soot. Properly controlled gas boilers create

insignificant amounts of soot and will rarely require

cleaning, although the manufacturer’s guidance

should always be followed. However, if combustion

checks show poor combustion then the heat

exchanger should be check and cleaned if necessary.

Oil, coal and biomass are more likely to form soot

and should be carefully monitored. Cleaning should

be carried out by a qualified technician.

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For very large boilers, typically used in industrial

application, integrated soot-blowers are often

installed in boilers to provide continual cleaning;

however, these will need to be checked regularly

to ensure good working.

Minimise limescale build-up

In hard water areas, limescale can build up on

the water side of the boiler’s heat exchanger.

This creates an insulating layer, inhibiting heat

transfer to the water in the same way as the

soot deposits above.

The most effective method of limescale removal

is through chemical treatment of the water. This

should be done annually by a qualified technician

to minimise limescale build-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 updated regularly. This manual should include:

•The maintenance plan.

•Block diagram of the boiler plant showing the

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

technicians and boiler manufacturers.

Particular attention should be paid to specific

instructions from manufacturers as these will ensure

the optimum performance of the boiler plant. Also,

failure to follow them may invalidate warranties.

A maintenance logbook should be kept giving

detailed records of maintenance tasks, includingwhich actions were taken, the person

responsible, and when they were completed.

This logbook will ensure that tasks are carried

out at the correct frequency and will highlight

ongoing problems.

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.

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

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Table 3 Summary of maintenance requirements

Maintenance task Frequency Responsibility

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

Full service Yearly Qualified technician

Flue gas analysis (combustion check) Quarterly Qualified technician

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

Limescale treatment Yearly Qualified technician

Check/adjust simple control settings Quarterly, or as changes to building operation

demand

Building staff

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

Check control operation Yearly Qualified technician

Calibration of controls Yearly Qualified technician

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Rplacing boilrs

I a boiler is more than 15 years old, or i it is showing signs o inefcient operation, itshould be replaced.

This is not as simple as noting the old boiler’s

rating and purchasing a new, condensing model.

To find the best solution, thoroughly review the

building’s heating demand and your business

needs, and check these against your technical,financial and policy requirements.

When considering a boiler replacement, advice

should be sought from a qualified building

services engineer or boiler technician. To help

them, consider the following information.

The building’s heating requirements

The most important aspect in selecting a new

boiler is getting the size right. It was once

common practice to oversize boiler plant with

the mistaken notion that this would provide

greater flexibility in the future. However, it is

now realised that this is unnecessary as the

heating demand for many commercial buildings

has fallen. This is due to improvements in

building fabric and an increase in internal heat

gains, such as from IT equipment, lighting and

occupants. If a boiler has not been replaced for

many years, the heating load of the building may

have changed significantly.

Start by reviewing the building’s internal

environment and general operation. What is the

current internal temperature of the building? Are

employees happy with the internal environment?

Are there any hot or cold spots within the

building? Are there any areas of the building

where temperature 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 the building 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

the area of the building to gain a ‘benchmark’

in kWh/m2.

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?

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Technical considerations

The choice of boiler will be dependent on a

number of technical issues. A building services

engineer or boiler technician can give advice, butyou can provide some basic information to help.

Fuels

Ultimately, the choice of fuel will be based on

cost and availability of supply. Ask which fuels

are available on-site. Boilers are designed to

operate with particular fuels and are rarely

interchangeable so it is important to make an

appropriate selection.

Of the fossil fuels natural gas is the best choice

where a supply is available, as it is the most

versatile and has the lowest carbon emissions.

Is there a natural gas supply? Remember that

the situation may have changed since the

current equipment was installed. If not, then

consideration must be given to which alternative

fuels are available such as LPG, mineral oils or

biomass. These fuels are delivered in batches

and careful consideration must be given to

issues relating to their long term availability,

supply routes and storage.

Table 4 Find out the building’s heating requirements

Information Source How is this

information used?

Floor area of building Property documents

Direct measurement

Energy benchmarks

Occupied hours Staff records Calculating heating demand

Selecting boiler controls

Internal environmental data,

such as temperature

Direct measurement

Control settings

Staff comments

Calculating heating demand

Assessing effectiveness of

existing heating system

Annual energy use/cost

for heating

Utility bills

Energy monitoring and

targeting system

Energy benchmarks

Details of planned energy

saving measures

Company energy policy Calculating heating demand

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If you think that biomass boilers may suitable for

your requirements and you need some more

information order or download the Carbon Trust’s

introductory guide, Biomass heating – An

introduction for potential users (CTG016).

Location

Where you have more than one boiler, find out

if the existing 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 losses through long pipework

runs will be higher. Combine the replacement of

boilers with upgrades to the pipework insulation.

Also take advantage of the central location to

install upgraded controls or re-programme

existing ones.

De-centralised plant (where a number of smaller

boilers are located around the building) will

reduce pipework losses, but you will not have

the option of integrating control operation and

maintenance may be more problematic and

expensive. This is because it costs more to carry

out maintenance checks on several smaller

boilers than one large boiler.

If you are considering changing to biomass

boilers the available space for the boiler and the

associated fuel store must be adequate and their

relative positions such that any automated fuel

transfer systems (from storage bunker to feed

hopper) can function effectively.

Flue outlet

Where is the boiler flue outlet? Condensing

boilers generate lower temperature flue gases

and visible plumes of steam. This may cause

problems if the flue outlet is close to other

building surfaces.

Heating system

What type of heating system is currently used in

the building? Unless a major refurbishment is

planned, it may not be cost-effective to replace

the whole heating system 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, but will still provide a higher level of

efficiency when applied to a radiator circuit. It

may be necessary to upgrade the heating

controls of the system to get the best from the

new boiler. Do not forget to account for these

costs when considering the purchase price.

Biomass boilers are best suited to steady

heating loads between 30% and 100%. Theymay need to be partnered with a heat store of a

gas or oil fired boiler to match overall output and

to meet peaking demands. They might also be a

suitable component for a decentralised system.

For information about biomass boilers in the

context of heating systems, order or download

the Carbon Trust’s in-depth guide, Biomass

heating – A practical guide for potential users

(CTG012).

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Condensing boilers are more expensive than

high-efficiency standard boilers, but they are

more efficient and cost less to run. So the extra

cost is often paid back in two years or less.

The business may be able to take advantage of

Energy Efficiency Financing or the Enhanced

Capital Allowance Scheme (see next page for

information on the Carbon Trust’s financial

products). The Enhanced Capital Allowance

Scheme covers the most efficient gas and oil

fired hot water boilers and biomass boilers.

FuelFuels vary in price. Consider your current and

projected energy 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 berequired to ensure efficient operation? Can

maintenance be done in-house or will it be

contracted out? Make sure that all staff involved

in the operation and maintenance of the boiler

plant have a say in the choice of the new boiler.

Table 5 Find out the technical requirements


information used?

Fuel supply available Utility companies

Local authority

Specification of boiler type

Centralised or

de-centralised plant

Observation Specification of boiler type

Selecting boiler controls

Pipework insulation required

Location of flue outlet Observation Specification of boiler type

Assessing effectiveness of existing heating system

Type of heating system Observation Specification of boiler type

Heating controls

Financial considerations

Consider the costs of the new boiler, including

capital expense, fuel and maintenance. This is called

life costing, that is, how much will the boiler cost

over its actual lifespan. It is important to capture all

the activities associated with the ownership of a

boiler if it is to last its normal life expectancy. The

introduction of the Renewable Heat Incentive near

the end of 2011 provides a mechanism to

encourage the installation of renewable heat

equipment including biomass boilers.

Capital expense

How quickly will the investment pay for itself

through reduced running costs? Will this

influence the purchasing budget?

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Table 6 Find out financial considerations


information used?

Purchase budget Finance/Company director Specification of boiler

Availability of loans/

tax incentives

Carbon Trust

HM Revenue and Customs

Changes to purchase budget

Running costs

of new boiler

Building services engineer

Boiler technician

Manufacturers

Utility bills

Calculating payback periods

Predicting future energy expenditure

Life costing

Maintenance costs

of new boiler

Building services engineer

Boiler technician

Manufacturers

Finance department

Calculating payback periods

Predicting future energy expenditure

Assessing staff training needs

Developing a maintenance plan

Life costing

Did you know?

Replacing a conventional boiler with a

condensing model can save 10-20% of

annual energy costs – more if the original

boiler is in a particularly poor condition.

Example: A building with a heating

demand of 100kW has an annual gas bill

of £8,930.1 A new condensing boiler is

installed at a cost of £3,000 with a

seasonal efficiency of 90%. The new

annual gas bill is £6,940 – a saving of 22%

or £1,980/year. Maintenance costs are

decreased by £200 per year. Therefore,

the cost of the new boiler is paid back

within 20 months.

1 Based on a 70% efficient boiler, 2,500 operating hours/ year and 2.5p/kWh gas price.

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Tax incentives

Enhanced Capital Allowances (ECAs) are

a straightforward way for a business to

improve its cash flow through accelerated

tax relief. The ECA scheme for energy-

saving technologies encourages

businesses to invest in energy saving plantor machinery specified on the Energy

Technology List (ETL) which is managed by

the Carbon Trust on behalf of Government.

The ECA scheme provides businesses

with 100% first year tax relief on their

qualifying capital expenditure. The ETL

specifies the energy-saving technologies

that are included in the ECA scheme. The

scheme allows businesses to write off the whole cost of the equipment against

taxable profits in the year of purchase.

For further information please visit

www.carbontrust.co.uk/eca or call the

Carbon Trust on 0800 085 2005.


Environmental considerations

As well as reducing running costs, condensing

and high-efficiency boilers will have reduced

emissions of carbon dioxide (CO2) and harmfulpollutants such as sulphur dioxide (SO2) and

nitrogen dioxide (NO2). Does your company

have an environmental policy? Will this

influence the choice of a new boiler?

Preparing a detailed brief

Once this information has been gathered, use it

to prepare a detailed brief for a building services

engineer or boiler technician. They will use this

information to select the best boiler to achieve

your needs within the proposed budget. A detailed

brief will save time and money and ensure that

your new boiler is both efficient and effective.

Table 7 Find out environmental considerations

Information Source How is this information used?

Environmental policy Company director Specification of boiler to ensure reduced emissions

Energy Efficiency Loans

Investing in energy efficient equipment

makes sound business and environmental

sense, especially with the easy, affordable

and flexible Energy Efficiency Financing

scheme brought to you by Carbon

Trust Implementation and SiemensFinancial Services. To find out more visit

www.energyefficiencyfinancing.co.uk

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http://www.carbontrust.co.uk/eca

http://www.energyefficiencyfinancing.co.uk/


http://www.carbontrust.co.uk/eca




enrgy monitoring and targtingI energy use is not monitored, it cannot be controlled. An energy efciency strategy

will be most eective when accompanied by appropriate energy monitoring and targeting.

By monitoring the energy 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.

The first step is to take regular meter readings – at

least monthly, although weekly would be better for

larger buildings. If a BEMS is installed, it may be

possible to automate this process. This will be

dependent on the type of meter installed and advice

should be sought from the BEMS manufacturer

and/or the utility company. Depending on the size

of the building, utility companies may be able toprovide half-hourly energy data.

The meter readings should be recorded on a table

and the energy consumption for the period

calculated. Graphs can then be produced to show

the energy consumption over time and comparisons

can be made to assess performance.

If the individual performance of a boiler is required,

spot meters should be installed on the individual

fuel intakes. This may not be cost-effective for

smaller boilers so should be considered carefully.

It is important to assess heating energy use in the

context of weather conditions and building

operation. For example, heating energy will increase

when the weather is colder and heating energy

should be minimal when the building is unoccupied.

If your heating energy use profile does not

match weather conditions 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 place to achieve those targets.

A 10% reduction in heating energy can often be

achieved through simple adjustments to existing

boiler plant. Greater reductions can be achieved

through the replacement of equipment,

components or controls.

Keep a check on progress towards meeting

targets. If progress is slow, carry out another

review of the heating system and look for

additional measures that can be taken. Report

progress to all building occupants – this will

increase energy awareness and get everyone

involved in reducing the building’s energy use.Effective energy monitoringand targeting can highlightpotential problem areas andlead to swift, remedial actions.

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Nxt stpsThe checklist below will help you to carry out an initial review o the boiler plant and

assess what actions can be taken. Many such actions can be taken in-house; however,

you may need specialist support rom your contractor or consultant or others.

Review Questions Actions to be considered Comments

Make, model, size,

type and age of boiler

Is the boiler more than 15 years old?

Is the boiler oversized?

Replacement

Replacement

Different improvement

options will apply depending

on boiler type

Fuel consumption ofboiler plant How efficient is the plant? Assess through meter readings.Estimate efficiency based on

consumption and rated output

Check physical

condition

Is there any corrosion?

Is insulation adequate/

in good condition?

Get service done

Replace/upgrade insulation

Replacement

Poor physical condition will

cause poor performance;

consider replacement

Assess controls What type?

Are sequencers, optimisers or

compensators used?

Install additional controls Improved control will reduce

energy consumption

Check control settings Are they appropriate?

Do they match building operation patterns?

Adjust settings Improved control will reduce

energy consumption

Review maintenance

history

When was the last maintenance carried out?

Is a proper maintenance plan in place?

Establish a proper maintenance plan

Order service/maintenance check

Poor maintenance can reduce

boiler performance by up to 10%

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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 Management

System (BEMS)

A computer-based system that operates all building controls and enables automatic adjustment and monitoring

of settings.

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 circulating through 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.


Glossary

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3L h b il




Forced/induced

draught burner

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

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

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

Optimiser A sophisticated timeswitch linked to the internal and external thermostats that switches the boiler on at exactly the

right time to ensure that the building reaches the required internal temperature 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 burner control Where the burner is either ‘on’ or ‘off’ and fuel/air intakes are the same regardless of heating demand.

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

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.

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32L t t h t t b il




Go onlin to gt mor

The Carbon Trust provides a range o tools, services and inormationto help you implement energy and carbon saving measures.

Website – Visit us at www.carbontrust.co.uk

for our full range of advice and services.

www.carbontrust.co.uk

Publications – We have a library ofpublications detailing energy saving techniques

for a range of sectors and technologies.

www.carbontrust.co.uk/publications

Case Studies – Our case studies show that it’s

often easier and less expensive than you might think

to bring about real change.

www.carbontrust.co.uk/casestudies

Energy Efficiency Financing –Investing in energy efficient equipment makes sound

business and environmental sense, especially with

the easy, affordable and flexible Energy Efficiency

Financing scheme brought to you by Carbon Trust

Implementation and Siemens Financial Services.

www.energyefficiencyfinancing.co.uk

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CTV051

http://www.carbontrust.co.uk/publications


http://www.carbontrust.co.uk/casestudies








CTV051

The Carbon Trust receives funding from Government, including the Department of Energy and Climate Change, the Scottish

Government, the Welsh Government and Invest Northern Ireland.

Whilst reasonable steps have been taken to ensure that the information contained within this publication is correct, the authors,

the Carbon Trust, its agents, contractors and sub-contractors give no warranty and make no representation as to its accuracy

and accept no liability for any errors or omissions. All trademarks, service marks and logos in this publication, and copyright in it,

are the property of the Carbon Trust (or its licensors). Nothing in this publication shall be construed as granting any licence orright to use or reproduce any of the trademarks, services marks, logos, copyright or any proprietary information in any way

without the Carbon Trust’s prior written permission. The Carbon Trust enforces infringements of its intellectual property rights

to the full extent permitted by law.

The Carbon Trust is a company limited by guarantee and registered in England and Wales under company number 4190230

with its registered office at 4th Floor Dorset House, Stamford Street, London SE1 9PY.

Published in the UK: March 2012.

© The Carbon Trust 2012. All rights reserved.

The Carbon Trust is a not-for-profit company with the mission to accelerate the move to a low carbon economy.

We provide specialist support to business and the public sector to help cut carbon emissions, save energy and

commercialise low carbon technologies. By stimulating low carbon action we contribute to key UK goals of lower

carbon emissions, the development of low carbon businesses, increased energy security and associated jobs.

We help to cut carbon emissions now by:

• providing specialist advice and finance to help organisations cut carbon

• setting standards for carbon reduction.

We reduce potential future carbon emissions by:

• opening markets for low carbon technologies

• leading industry collaborations to commercialise technologies

• investing in early-stage low carbon companies.

www.carbontrust.co.uk

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