Boiler Efficiency

Boiler Efficiency is simply the ratio of the energy in to energy out. Basically high efficiency boilers use less fuel (Oil or electricity) as an input to produce the same amount of heat as lower efficiency boilers.  All boilers have heat losses.  Some boilers loose heat in the flue where combustion heat from the bolier is loss to the outside air.  Most boilers loose heat through conduction through the boiler’s casing into the boiler closet.

In an ideal world if the total amount of energy produced by combusting gas or utilizing electricity was converted into hot water than the efficiency would be 100%.

However in reality due to the losses mentioned above the efficiency of all boilers is less than 100%.

The boiler thermostat
The bolier thermostat is an important part of the boilers control system that measures the water temperature in the boiler. Usually set at around 70°C it will ensure that the boiler temperature will remain as close as possible to 70°C. In this case the terminology is called constant water temperature control.  For many boilers this is a requirement as if the temperature falls below threshold corrosion will occur.

Conversely the disadvantage of constant water temperature control is that because the temperature is constantly high, stand-by heat losses are high.  Therefore on an annual basis this form of control is less efficient, especially for older boiler applications where insulation is poor.

In larger installations an automatic 3-way valve can be used to control the temperature in the distribution circuit.

The outside temperature control
The outside temperature control consists of several parts:
A temperature measurement at the discharge side of the boiler
A thermostat temperature measurement of the outside air
A control unit that is capable of setting the heating curve.  The heating curve is the relationship between outside air temperature and the required water temperature.

When the heating curve is set, the control system will ensure just enough heat to see the boiler temperature will change constantly in relation to outside air temperature.

This is known as gliding water temperature.

Boilers that use the gliding water temperature principle usually have lower heat loss and therefore higher efficiencies than boilers on constant water temperature.  However boilers using gliding water temperature control are susceptible to condensation and therefore corrosion.

A room thermostat
A room thermostat is an important part that measures the room temperature to ensure that the heating will not heat beyond a certain set-point.  Typically a room thermostat is only installed to one room in the dwelling, usually the largest room such as the living room.  The room thermostat should only be installed at a height of approximately 1200mm out of direct sunlight and not near unnatural heat or cold sources.

Room thermostats tend to be electronic with time programming built in.  Time programming can allow people to set temperatures on an hourly, daily or weekly basis.

Thermostatic radiator valves
As the room thermostat is only in control of one room in the dwelling, thermostatic radiator valves make it possible to control other rooms individually within the dwelling.  Radiator valves are selected based on the characteristics of the particular radiator system and must be installed correctly.

Thermostatic radiator valves usually contain an expanding and contracting bulb based on room temperature.  Heat flow is controlled by the restriction caused by the bulb.

Since thermostatic radiator valves allow people to set different temperatures in different rooms energy savings can be realised if used correctly.
Manual controlled radiator valves also exist however constant interaction is required to ensure efficiency and energy savings.

Night set-back
Night set-back is a programmed lowering of room temperatures during the night when people are asleep.  This is usually set on the room thermostat control panel.  Night set-back can reduce energy costs significantly.