Boiler House Efficiency


There have been energy efficiency initiatives since the industrial revolution, and certainly since Oliver Lyle wrote his book ‘Efficient Use of Fuel’ in 1944. There have also been initiatives from the previous Department of Energy going back to the 1970’s with the Boiler efficiency grant scheme and the Energy Survey grant scheme. An analysis of the latter scheme indicated that there was very little take up of the conclusions and recommendation of the Survey Reports to realise the savings predicted.

The proposed changes in the Building Regulations in terms of sealed buildings and energy efficiency is at least offering teeth to the requirements for all new buildings and refurbishments. However, the existing building stock in the UK is by far the biggest producer of carbon dioxide and greenhouse gases that the government have committed to reduce over the forthcoming years.

There is considerable concentration on almost every aspect of energy efficiency except one very important facility, The Boiler House.

Survey Results

Boiler House and Energy Surveys carried out by the author over the period 1978 to 1996 almost conclusively show failure to ensure that the initial energy consuming plant is working to optimum efficiency, and generally fuel savings of 15 – 25 percent can be achieved with very little capital expenditure.

The captains of industry and their accountants, who now appear to be running industry financially, are concerned with capital and operational costs to reduce company overheads and improve the bottom line. Although fuel and energy used in industry is approximately around 1 – 2 percent of turnover they view any savings as insignificant. However commitment to the Kyoto treaty does place a responsibility on those who have the authority to achieve results and dramatically reduce carbon emissions.

How, where, when

The ‘How’ is ensuring the boiler plant is maintained in correct working order, regular testing and adjustment, correct attention to maintenance and cleaning of the combustion chamber, correctly kept log book data to assist future interrogation for changes in performance. Losses in performance can result in substantial additional fuel and carbon dioxide emissions

The ‘Where’ will be all major plant items, not only boilers but air compressor plant, refrigeration and chilled water plant etc to ensure operation at maximum efficiency.

Multiple plant items such as boilers are usually all left running under the control of their individual boiler thermostats. All plant items should be operated up to full load before switching on the next unit otherwise substantial losses accumulate over the season..

The ‘When’ is at the regular intervals to maintain the plant at optimum efficiency and this can be determined from correctly maintained records of operating efficiency throughout the life of the plant, where additional expenditure for maintenance can be offset by increased efficiency and fuel cost savings.

It is strange that the company cars are put into the garage at regular service intervals, but major plant and system maintenance appears to be the one item in the expenditure that the accountant can disregard and eliminate.

Boiler house efficiency

There are statutory regulations for the safe and efficient operation of boiler plant, and a safety audit at yearly intervals would be the order under the Health and Safety at Work Act and successive Regulations.

The maintenance of the boiler plant should be taken seriously and carried out properly in all respects. This is where the greatest savings in fuel and greenhouse gases can and should be made at the initial development of the building energy.

Thorough cleaning to remove all carbon, scale and other deposits from the combustion chamber and the flueways at least at yearly intervals. Checking all possible leaks and holes in the fabric of the boiler to ensure additional air is not drawn in to change the combustion efficiency and create high chimney/stack losses.

The water side should be regularly inspected for water scale build up indicating the introduction of fresh water into the system, bringing in calcium/magnesium salts and air. The boiler body/casing should be regularly inspected for radiation and convective losses. If your boiler house is hot then it is likely that boiler losses are the cause. This is additional fuel costs.

The key piece of information could be the original commissioning certificate to provide the data for setting up the boilers after cleaning and re-assembly, which when used with the log book historical data can provide the level of losses. It is possible to determine optimum maintenance periods and the fuel savings achieved from this information.

Combustion testing and taking account of the boiler operating pattern and the thermal insulation of the boiler body will provide the instantaneous efficiency at that moment in time. By adding factors of maintenance and seasonal variations in load an overall annual efficiency is attainable, which will include a factor for system type and operation.

From the collected data of boiler testing over the years, I have developed a ‘Plant Utilisation Factor’ that will explain the difference between the expected and initially calculated fuel consumption and the actual fuel consumption.

The standard formula for fuel consumption:

Boiler load x hours of operation x system/weather Factor

Fuel Consumption = ———————————————————————-

Calorific value of fuel x Boiler efficiency.

It is possible to establish with reasonable accuracy the data for the formula and so calculate the fuel consumption, where:

• The Boiler load is usually taken as the boiler output duty, which is not necessarily correct and should be more related to the system load requirements.

• The hours of operation is relatively straight forward related to the time clock control of on/off times including the early start up time.

• The system/weather factor relates to the annual seasonal changes. All systems will have an operational factor based on performance and operation.

• For a heating system it is the Weather Factor based on actual degree days for the geographic location divided by total possible degree days and can be seen from an old copy of the IHVE Guide 1957, which is still sound data using up to date ‘degree days’.

• The calorific value will be as given by the fuel supplier or by reference to standard data for fuels.

The boiler efficiency is another difficult one to identify and can be the instantaneous Combustion Efficiency from CO2 and O2 flue gas temperature readings of a combustion test and will be at Maximum Continuous Rating, MCR.

It should however include the operating losses based on on/off switching of the boiler/burner unit, and radiation and convection losses to achieve an actual instantaneous Boiler Efficiency.

My version of this formula would include a PUF (Plant Utilisation Efficiency) to allow for seasonal operation and maintenance factors and the effect of operational control and load.

I derived this method from the collected data of the survey carried out, calculating back from the actual fuel consumption and working through the formula to find the further loss of efficiency that occurs in practice.

Boiler load x hours of operation x system/weather Factor

Fuel Consumption = ———————————————————————-

Calorific value of fuel x Boiler efficiency x PUF.

The resultant calculated Plant Utilisation Factor will show the available savings that can be achieved, i.e.

Calculated P.U.F 0.9 – 0.95 Very efficient.

0.8 – 0.9 Savings of 5 – 10 percent are possible, dependant upon system.

0.7 – 0.8 Savings of 10 – 20 percent

0.6 – 0.7 Savings of 25 percent plus

Below 0.5 Serious energy and fuel waste.

The potential items that can be identified from the P.U.F. are the state and condition of the plant and systems.

The P.U.F. can also include information on the following:

• Operating procedures of time and temperature.

• The effect of maintenance or lack of maintenance.

• Boiler running un-necessarily.

• Low efficiency heat exchange processes.

• Leaking valves, blowing steam to waste, condense losses.

Therefore a list of possible energy losses can be compiled from a full and detailed survey of the building and systems and the un-acceptable losses apportioned from data collected.

By consulting the British Standard BS 845:1972 the details of a combustion and boiler efficiency can be identified. The CIBSE Guide 1987 section B13-45 also gives a valuable commentary on Boiler Efficiency.

Summary

By correcting the combustion and boiler efficiency throughout the existing building stock, including industrial and commercial buildings, suitable savings of fuel and more importantly greenhouse gases can be made for future generations.

David J. Bradshaw MSOE,MIPlantE is a Building Services Engineering Lecturer

At the City of Bath College, Centre of Technology.

Can you help?

David is participating in a project to establish the average boiler plant efficiency across the existing building stock and therefore provide information into energy efficiency and global warming and potential reductions in both. If you are willing to submit details of your plant operation please contract David at: BradshawD@CityBathColl.ac.uk

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