Guide to efficient use - Boilers

Boilers

Table of Contents

1 Introduction

2 Is it for me?

3 How much does it cost?

4 What are the benefits?

5 Step by step guide

6 Case studies

7 Where Can I find out more?

Is it for me?

Boilers often provide many opportunities for improvement by applying simple saving measures with low pay back periods.

One of the most important parameters to be evaluated in a boiler is its efficiency, defined by the ratio of produced useful heat (taking into account the losses) and the input energy (fuel).

Efficiency is not constant with time. It decreases continuously over the years, until the boiler needs to be replaced due to malfunction and age.

Testing the efficiency of the boiler

A flue-gas analyser is requested to test the efficiency. It supplies the concentration of O₂, CO₂, CO and the temperature of the exhaust gases. A surface thermometer is needed to measure the temperature at the boiler walls.

The suitable values of O₂, CO and gases temperature depend on the sort of fuel and burner used and on the size of the boiler. Check the user manual for your equipment or consult the provider to get those values.

The following table shows some guiding values:

Analysed values	Cause	Solution
CO high and O₂low	Insufficient amount of air introduced into he boiler	Increasing the amount of air introduced by enlarging the burner door opening.
CO₂ low and/or O₂ high	Air excess	Reducing the opening of the door for air going to the burner.
CO high and O₂ high	Inadequate air-fuel mixture	Strip down the injector for cleaning or replacing it if neccesary.
Wall temperature>> room temperature	Old boilers or bad insulated boilers	Insulation materials replacement.
Gases temperature > 230ºC	Inappropriate heat exchange	Cleaning the interior of the boiler or installing a heat economizer.

Fuel	O2 max (%)	CO max (ppm)
Fuel oil	3.5	200
Diesel oil	3.5	200
Natural gas	2	50

Boiler replacement

All boilers have to achieve some efficiency parameters. Regular maintenance keeps it within the legal established values.

However, when the boilers become obsolete and the efficiency decreases to the minimum limit, replacing the boiler with a high efficient one is highly recommended.

A condensing boiler reaches its optimum performance when the system demands low temperature water (between 30 and 50°C). However high savings (about 15%) can also be obtained at greater temperatures (70-80°C).