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Millis team favors natural‑gas boilers, leaves electrical capacity for future electrification
Summary
Design team recommended high-efficiency natural‑gas boilers, chilled-beam classrooms and dedicated rooftop energy‑recovery units; the committee directed the team to design a single main electrical service sized with spare capacity for future all‑electric conversion and to make the roof PV-ready.
The design and engineering team told the Millis School Building Committee on May 7 that the mechanical and electrical approach for the middle–high school will rely on high-efficiency natural‑gas boilers, chilled beams for classrooms, dedicated rooftop energy‑recovery units and an open‑protocol building controls system. The committee agreed to a single electric service sized with spare capacity and to provisions to support future solar and electrification work.
Mechanical engineer Wayne Masson (Griffin/Varian) described the HVAC approach for a phased renovation: high‑efficiency natural gas boilers (approximately 96% thermal efficiency) to serve hot‑water heating, induction-style chilled beams for classroom heating/cooling, and dedicated packaged rooftop units with energy‑recovery for each wing, gym, auditorium and dining area. The systems are planned for zoned, flexible operation so a single wing can be conditioned for after‑hours use.
On electrical strategy, the electrical engineer described two options: remain a gas‑served building with one service (a ~3,500‑amp switchboard and a ~900 kW generator) or design now for an all‑electric building (which would likely need two services and larger generators). The engineer recommended designing for the gas option with an increased service buffer (up to 4,000 amps) and leaving conduit and space (PV‑ready pathways and spare raceways) so the building can be converted later without major demolition.
Committee members discussed lifecycle, reliability, maintenance and cost. Engineers noted that air‑to‑water heat pumps and large-scale all‑electric heat‑pump plants are currently more expensive, less established in local service markets and have less long‑term operational data in New England climates; they also said heat pumps can lose efficiency at very low outdoor temperatures. The team recommended gas now for budget and reliability reasons while keeping the design flexible for an eventual switch to electric heat pumps.
The committee did not take a formal roll‑call vote on the mechanical/electrical approach but directed the design team to proceed with the recommended gas‑primary, PV‑ready approach and to size electrical infrastructure with some additional capacity for future electrification.
