The 3C's - how to increase the efficiency of your boiler plant

Boiler Dry Cycling

The boiler is currently at set point and is in stand-by mode as no further heat is required from the system load. at that time. Due to the ambient radiated heat losses, together with the flue draught heat losses (“standing losses”) the boiler will naturally cool down over time which may cause the boiler temperature controls to instruct the boiler to re-fire and return the boiler back to set point. In this case the heat is not being used by the system base load; it is only replacing the “standing heat loss” and therefore wasting energy.

Preventing boiler dry cycling

The inherent problem of boiler dry cycling can be prevented by retrofitting boiler load optimisation to your boilers. Our patented M2G boiler load optimisation control is proven to remove dry cycling and reduce energy consumption typically by between 10% and 25% (depending on the application). Dry cycling often occurs even with existing building controls such as BMS, boiler sequencing, and weather compensation and is often overlooked.

How does M2G boiler load optimisation remove boiler dry cycling?

M2G dynamically identifies the occurrence of boiler dry cycling by monitoring and analysing the individual boilers temperature every 10 seconds via digital sensors fitted to the flow and return.  M2G records the boiler's set point at the last genuine firing and is able to determine if the load demand is genuine or false i.e. dry cycling as a consequence of the standing losses. M2G will prevent the boiler from firing due to dry cycling only and does not delay the boiler firing under normal load conditions; further the boiler's designed set pints are always maintained.

Do I need boiler load optimisation if I have BMS?

Yes, it is very likely that boiler load optimisation will be required. Typically the BMS is designed to optimise the building  controls and not the boilers. The BMS is likely to be providing zone control, optimum start and stop, weather compensation and sequencing, not typically boiler load optimisation.

To find out how M2G integrates and complements BMS click here

Boiler Short Cycling

Boiler short cycling has increased due to better energy efficiency within the building i.e. better insulation and glazing, increased occupancy from property rationalisation and increased IT equipment and the related heat increase. Boiler short cycling 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”.

Doesn't my BMS prevent boiler short cycling?

For short cycling to occur the BMS/or local controls have enabled the boiler to fire under normal load conditions. However, it is extremely unlikely that the BMS is able to identify or determine if the boiler is over capacity in relation to the current system base load at this time. It is not common for the BMS to directly control the firing capacity of the burner/boiler (size of flame) directly.

How can M2G prevent short cycling?

The M2G was not specifically designed to control boiler 'short' cycling. However, the way in which M2G dynamically analyses the temperature decay over time can help in removing the boiler temperature 'over shoots' caused by the latent heat within the boiler under short cycling conditions. In this way the M2G will avoid unnecessary boiler firings during light load conditions and therefore increase the boiler efficiency.

Boiler Short Circuiting

This is caused by some of the heat generated by the lead boiler being lost due to increased “standing losses” across the boilers which are 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 motorised “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 losses” across all boilers and diluting the overall common flow required temperature.

Preventing boiler short circuiting

Ideally the boilers will be hydraulically isolated via motorised valves (i.e. back end valves) when not required to operate/fire, therefore preventing temperature dilution and increased standing losses across all lagged off/sequenced boilers. In applications where it is not possible or commercially viable to have motorised valves then M2G may assist in minimising the effect of short circuiting.

How does M2G minimise boiler short circuiting?

The most efficient boiler is the one that is not firing. We always recommend that boilers are correctly configured and commissioned, this includes boiler sequencing and back end valves for hydraulic isolation (to avoid boiler short circuiting). Although M2G was not specifically designed to eradicate boiler short circuiting, it will help alleviate it by controlling the effects of the increased standing losses.

M2G is constantly analysing the boiler load profile every 10 seconds, via digital temperature sensors and under different load and controls situations, with or without BMS control. In this way it is able to identify the effects and consequences of boiler operations listed above i.e. the 3C's.

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