Summary

Challenge: In 2017, the steam district heating plant serving multiple building blocks in downtown Concord announced its closure at the end of the 2018 heating season. The closure affected several State-owned buildings that needed an alternative heating source.

In addition to the time-constraints due to the imminent plant closure, it was required that several heating options were evaluated before moving forward with the final design documents. Furthermore, limited mechanical space availability within the buildings, pollutant emission threshold requirements that needed to be adhered to and the buildings’ age and historic nature added an extra layer of complexity to the project.
Solution: It was decided that a central plant option was not feasible due to budgetary and spacing constraints. The alternative solution was to provide smaller individual heating plants for groups of buildings, within the existing building’s footprint. The buildings were grouped in categories, ranked by distance to each other and complexity of each building’s heating systems, and ultimately four separate bid packages were generated. Most buildings retained the steam heating source, while some were converted to hydronic heating (high efficiency condensing boilers).

Building height limitations necessitated lowering the existing floors sufficiently enough for the new boilers and associated piping to be installed. Extensive coordination with the contractor was required because there were no existing building structural drawings.

Aside from space height limitations, another challenge for each boiler plant was finding a suitable solution for venting the new boilers without disturbing the existing spaces and functions on the floors above. In maintaining the historic appearance of the buildings, and satisfying the New Hampshire Division of Historical Resources requirements, brick chimney facades were provided that enclosed the boiler flues running up the side of the buildings.

The State required heating part of the buildings with an alternative fuel source. It was met by providing biomass (wood pellet) boilers for one of the four groups of buildings. The location of appropriately sized wood pellet storage bins (or silos) was a challenge in itself, as it had to either be located indoors or be in an exterior location that does not aesthetically affect the appearance of the buildings. To that end, rather than providing tall, unsightly silos, three smaller square hoppers were provided and concealed in an appropriate low traffic location in close proximity to the building.

Additional considerations during design/construction:

  • Age of existing steam piping network. Leaks, corrosion and failing pipe sections.
  • Locating and tying in existing steam condensate lines (more than 600,000 s.f. of building stock) to new condensate return system.
  • Coordination of gas service requirements with utility company. Campus had very limited natural gas service availability.
  • Hoisting / rigging of very large boiler equipment in existing buildings. Roof removal was necessary at one location, wall removal at another.
  • Maintaining existing heating system active while new heating plants were being constructed. Existing system not removed until new plant construction was complete, and systems were commissioned.