I was asked recently to explain just what a boiler is, so if you will forgive my starting with first principles, quite simply a boiler is a vessel for converting the heat produced by the combustion of a fuel into hot water or steam.  Boilers come in a massive variety of sizes and shapes with different capabilities depending whether you are just trying to heat a small office or raising steam to generate electricity for the national grid.  Whatever size and type of boiler you have, its operating efficiency impacts on your bottom line.  The boiler is where fossil fuel is converted to heat for use in heating or hot water and a small increase in efficiency can give a marked boost to profits.  Boiler design has come a long way over the past 20 years and with new technology comes improved efficiency and performance.  If your boiler is 20 or more years old it is time to start looking at options for your future heat generation strategy.

Older boilers used for heating and hot water were generally what we call "cast iron sectional" and they are very large compared to modern boilers as a result of which the eradiated heat from the boiler casing was much greater, increasing what we term "standing losses".  These boilers also had large passages for the hot gases to pass through which led to inefficient heat transfer - indeed losses from this type of boiler were often 30% and higher.  Some of these boilers were designed to burn coal or oil and have subsequently been converted to run on natural gas, but dependent on the design of the firing  chamber some of these conversions have decreased efficiency and output capacity of the boilers.

Modern boilers are compact, well insulated (as a rule) and designed to provide high heat transfer rates.  Boiler efficiency is much improved with typical losses running at 16-20%.  Heat from the boiler is used directly in the heating system and is often also passed through a tube bundle within a storage vessel (a "calorifier") in order to generate domestic hot water (DHW).  Some boilers generate DHW internally ("combination" boilers) and this provides additional reductions in standing losses from the calorifier.

Another development is the "condensing boiler" - where the boiler is equipped with additional heat exchanger surfaces to remove more heat from the flue gases before they are exhausted reducing losses even further to between 5-10%.   I shall deal with this in greater detail below.

In conventional boiler plant the combustion system will be a pressure jet burner or a series of atmospheric burner bars.  The setting and control of these combustion systems requires skilled knowledge in order to ensure peak system efficiencies.

return to top of page

return to top of page

return to top of page

Under Construction

return to top of page

Under Construction

return to top of page

Now here is a subject that - how shall I put it - has been prone to some "over-zealous" sales effort from various parties over the years.  I have seen claims for boiler economisers guaranteeing 40-50% savings and frankly all you can do is laugh!  The fact is that no boiler is ever 100% efficient (if you know otherwise please send me details) and there are several measures you can take to save money, from simple good housekeeping as shown above to the retro-fitment of various boiler controls (some called Economisers) - when appropriate.

In the early '90's several of these systems were marketed in the UK and at that time they were all based on simple delay timers wired in series with the burner circuit such that whenever the boiler stat demanded the burner come on the economising device inhibited the burner for a pre-determined period.  The delay varied from 2 minutes up to 15 minutes on most units and selection of delay was usually at the discretion of the installer.  The operating principle was simply that most boilers were set too high and as a result there was often plenty of hot water circulating in the pipes and radiators to allow a greater degree of cooling and the short delay simply ensured that no-one noticed. I have seen units with delays available of 45 minutes - I just hope that this was never utilised as the boiler must have almost cooled to ambient between each firing - no doubt saved a lot of gas but guaranteed it also led to some comfort problems.

And guess what - some of them worked when the delay was applied sensibly but it was pretty much hit or miss, dictated by the experience of the installer and the quality of instruction given to the home-owner.  As with most things the science has moved on - a little bit - and Automatic Load Compensation has arrived to take away a bit of the guesswork.

So what is Automatic Load Compensation?  How does it work?  Keeping things simple, when a boiler is in maximum demand (starting up first thing in the morning, for example) there will be no opportunity to make a saving as the boiler must achieve its maximum set-point to give you comfort heating and hot water.  However, at any other time when a full load condition does not exist (e.g. when the room temperature is near its set point) load compensating controls can achieve useful savings by adjusting the boiler operating temperature in relation to the reduced load.  It brings a degree of "intelligence" - perhaps common sense is better - to the response of the boiler's internal thermostat that can provide 10-15% fuel savings.

These controllers require a thermistor (very accurate temperature sensor) strapped to the return flow pipe-work to measure the rate of temperature decay and using a level of 'intelligence' or 'fuzzy logic' prevent the boiler from firing wastefully.  This does not affect comfort conditions because the controls should never prevent hot water being delivered to the radiators or other heat emitters.

These controls are purpose built for retro-fitting into existing systems.  Installation is completed without disruption to the occupiers.  Draining of the system is unnecessary and each boiler is out of service for no more than a few minutes.  After installation and commissioning the controls are self-regulating to give automatic year round performance and require no action by the user.  There are quite a few on the UK market and I have experience - good and bad - of most of them.   

Single Boiler Installation

Multiple Boiler Installation

Our thanks to Savastat for these diagrams

My personal advice is to think long and hard about the way they are sold to you.  I have included diagrams above from Savastat who are one of the good guys - good because they do not try and baffle anyone with science and - most importantly - they have a fixed price structure - in other words the price does not change to suit your fuel bills, the price is fixed whether it will save you £100 a year or £1,000 a year and I like that honest approach to the market.  

Beware the man who happens to have a  device that costs exactly 2 years worth of savings!

Controls are available with fixed temperature parameters for domestic boilers,  reference slope adjustment for small commercial boilers and as fully adjustable units to match system conditions for any Low Temperature Hot Water commercial / industrial boiler.  If you are sceptical don't just take my word for it.  Consultants WS Atkins (the guys who run the Carbon Trust scheme) conducted a trial in a Fire Station controlled and monitored by an Ambiflex 1000 BEMS unit, which confirmed that the system remained in control throughout the trial. Several tests were conducted with the Savastat unit switched to SAVE or BYPASS and a 23% saving was confirmed.

Full trial report available - also direct contact to WS Atkins consultant - 

Mr. Ed Zacchi   on Tel: 01865 734 201

or email     edo.zacchi@wsatkins.com

Alternatively email Stewart King for a copy to be sent direct to you by reply

return to top of page