The NXM2G- Intelligent Boiler Flame Controls

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Integrating M2G with High/Low Burners

Subject:  M2G Integration with and without high/low burners

 The main advantages of high low burners are as follows:

  • The burner would always start at a lower capacity (low flame) giving less thermal stress to the boiler. Sometimes known as soft start or sliding two stage.
  • The boiler can operate over a higher turn down ratio, giving matched firing capacity for the required boiler demand and avoid excessive firing operations.
  • The burner combustion efficiencies will be increased at the low firing stage, due to the lower exhaust gas temperatures (BET) and the stoichiometric CO2 levels in relation to the heat release rate.

Normal High / Low operation without M2G

The boilers are fitted with two thermostats, known as the “working stat” or control stat and a high/low or second stage stat. A further stat is also used for high temperature limit.

The control stat would be set for the desired boiler temperature typically 180°F; this stat has overall control of the burner operation. The high/low stat would normally be set 15 degrees lower i.e. @ 165oF

A typical burner sequence would as follows:

1. Cold start first operation of the day

Current boiler temperature @ 90oF, boiler control stat set @ 180oF and high/ low set @ 160oF. The burner would purge and fire at low flame, after a short time the burner would increase the firing rate to high fire. The boiler temperature will increase to 160oF, at this stage the burner will reduce the firing rate to low fire and remain on, until the desired set point of 180oF has been reached. At this point the burner will be turned off until the control stat “calls for heat” again typically @ 160oF, the burner will purge and fire at low fire only until the set point of 180oF has been reached, please note, the burner will not normally fire at high fire again, unless the boiler temperature has dropped to below 160oF due to a large increase in system demand.

2. Subsequence burner operations, boiler at or near to set point

Under normal circumstances and when the system has reached stable thermal conditions, the burner will start and stop without the burner going to high fire, as the boiler temperature is with the 20 degrees of the control stat and the high/ low stat.

Normal High/low operation with M2G

1. Cold start first operation of the day or “first fire

The M2G has “first fire” mode control for both low and high firing stages of the burner, in this way the boiler always maintains the required set point as the “save mode” is not invoked.

Current boiler temperature @ 80oF, boiler control stat set @ 180oF and high/ low set @ 160oF. The burner would purge and fire at low flame, after a short time the burner would increase the firing rate to high fire. The boiler temperature will increase until the boiler temperature has reached 160oF; at this stage the burner will reduce the firing rate to low fire and remain on until the desired set point of 180oF has been reached. At this point the burner will be turned off until the control stat “calls for heat” again typically @ 160oF, At this point the M2G will sense “call for heat” and check the memorized boiler temperature profile and inhibit the burner to fire until the true system load demand has been measured. After a maximum of 15 minutes or temperature profile has been lapsed, the burner will purge and fire at low fire only until the set point of 180oF has been reached, please note, the burner will not normally fire at high fire again, unless the boiler temperature has to drop below 160oF due to an large increase in system demand. Should the boiler demand be increased and the boiler temperature is below 160oF the second stage input will invoke the second stage “save” mode and select the best firing conditions for the system requirements.

Notes:

  • The above also assumes that the boiler high /low thermostat has been correctly adjusted. The burners have been correctly commissioned to give a typical 60/40% spilt on fuel inputs i.e. low fire would give the required gas/oil volume for 60% of the boiler capacity.
  • It would also be assume from the above, that the boilers have been commissioned correctly with the correct flow rates and hydraulic controls.

M2G is suitable for the following applications:

  • Commercial boilers with a maximum temperature of 257oF
  • Suitable for all fuels i.e. Gas, Oil, and LPG etc.
  • Compatible for Atmospheric and Forced draught boilers.
  • Interfaces with On/off burner, high/low burners, fully modulating burners.
  • Full compatible for BMS, BEMS, Weather Compensation Control, Building Optimization and Boiler Sequencing Controls.

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