The Fireye® NXM2G is designed to prevent boiler dry cycling which occurs when a boiler loses heat to its surroundings. The Fireye® NXM2G is fully compatible with existing control systems and building management. Designed for use with low & medium temperature water boilers, single stage burners, fully modulating burners and many more.
The inherent problem
- All boilers within an estate, no matter how modern, waste heat as a consequence of standing losses and poor temperature controls.
- Boilers often fire to only recover these standing losses
- This is known as “boiler standby cycling”
- Boiler standby cycling is an industry wide problem
- Other areas of inefficiency includes short cycling and short circuiting
What is standby cycling?
- The boiler fires to reach its set point, meeting the building’s heating demands (load).
- Once the set point has been reached the boiler stops firing. However, standing heat losses continue and the boiler cools down without transferring this heat to the system load the boiler will then fire unnecessarily to recover these losses even though the building requires no heat.
- Radiated heat losses whilst boiler is firing and during stand by
Additional Heat Loss
The heat loss is exacerbated when the boiler enters a pre-purge before the next firing to remove any residue of combustible gases. This is effectively blowing cool air across the combustion space therefore cooling the boiler down before it begins to re-fire.
Standby cycling throughout the year
Standby cycling occurs throughout the year, even if the boilers are just providing hot water generation during the summer months.
Annual profile of standby cycling
Results in continuous firing
As a result of the standing losses. Boilers will fire unnecessary to recover the standing losses resulting in wasted fuel consumption, costs and CO2emissions. Standby cycling can be removed by fitting Fireye® NXM2G – intelligent boiler load optimization to each boiler. Fireye NXM2G identifies and removes standby cycling therefore reducing energy costs and CO2 emissions.
Illustration of boiler firings with and without Fireye NX
This is caused when the boiler minimum firing/ boiler capacity exceeds the current system load, for example the boiler kW output is 100kW as a minimum value but the current system base load is at 50kW. This will cause the boiler to fire for very short periods, as the heat generated (100kW) cannot be used and the boiler will reach set point very quickly and cool down slowly. This “short cycling” can be wasteful on some types of boilers due to the increase in standing losses caused by increased burner purging. During this process the burner will blow cool air across the boiler combustion chamber each time the boiler starts and effectively cool the boiler that is being heated up.
This problem can also occur on fully modulating boiler/burners, for example boilers/burners with limited Turn Down Ratio.
The “turn down ratio” enables a boiler to dynamically match the current base load of the system. For example a 400kW boiler may be correctly sized for the application and at high fire will give an output of 400 kW (100%) and at low fire will give an output of 100 kW (25%). This would be referred to as a “turn down ratio” of 4:1.
If the above example is used and the base load remains at above 100 kW, the boiler will modulate without turning off and “short cycling ” will not occur. However, if the base load is below 100 kW the boiler will reach and exceed the set point and the burner will turn off and “short cycle”.
As a consequence of standby cycling and short cycling, boilers can suffer premature damage due to the increased thermal shock each time the boiler fires unnecessarily.
Illustration of Short Cycling
This is caused by some of the heat generated by the lead boiler being lost due to increased “standing loss” across the boilers not currently firing.
In this example the three boilers are being sequenced from a common header. The current system base load is 100kW with only the number 1 boiler firing. The stand-by boiler(s), often referred to as “lag boiler(s)”, are not being automatically hydraulically isolated via motorized “back end” valves. This will cause some of the heat generated by the lead boiler (number 1) to be pumped across the stand–by boilers thus increasing the “standing loss” across all boilers and diluting the overall common flow required temperature.
Illustration of short circuiting