Reduce Cycling with Boiler Replacement

Boiler Replacement

A corporation in New Hampshire was operating with two (2) 200 HP Cleaver-Brooks firetube oil-fired boilers, with natural gas, however, the natural gas was never hooked up so they only used oil to operate the boilers to supply building heat.

The problem:

The building’s hydronic system consists of two zones, each with its own mixing valve controlling the radiation and air handler supply water temperature based upon load and outside air temperature.  The system distribution pumps did not have variable speed drives on them and ran at full speed.

The boilers operated at the normal 180-degree outlet and 160-degree return at full GPM flow.  The mixing valve zones can operate as low as 140 degrees on the first day of heating, so the boilers put out a lot more heat than needed at that design point. Resulting in a lot of return bypass hot water that was never used, and as a consequence, the boilers cycled frequently.

The solution:

Replace the firetube boilers with a new system design that is intended to use natural gas as the primary fuel and propane as the backup fuel. The idea was to improve the system hydronics in both supply water temperature and GPM flow rate, to improve the “System Turndown” at the “how low can you go” point on the first day of heating.

To address the new dual-fuel consideration, (1) one Cleaver-Brooks 5.0 MBTU ClearFire (model CFCE) condensing boiler and (2) 6.3 MBTU Flexible Watertube Boilers (model FLXPM) non-condensing boilers were selected to provide that capability. 

The next design consideration was to improve the hydronic “System Turndown”.

Using the CFCE in near condensing mode on the first day of heating, 150-degrees supply water outlet temperature with a 140-degree return temperature, and varying the flow from minimum to maximum allows very low BTU input.

As the building load increases, the CFCE boiler elevates the supply water temperature to 160-degree, with a 150-degree return water temperature.  At that point, the FLXPM’s now enter into the boiler rotation provide the supply water temperature to meet the coldest day requirements of 180 degree supply water temperature and 160-degree return water temperature.

The Cleaver-Brooks Hydronic System Control (HSC) runs the boilers and takes a command and control signal from the BMS for the most optimal, efficient boiler system operation. The HSC then communicates that information back to the BMS with a Protocol Translator

Thank you to Corporate Mechanical of New England who performed the equipment installation.