A chilled water plant instead of packaged cooling
Every district with an aging chiller gets offered the same alternative: abandon the plant, put packaged DX or split systems on the roof, and never rebuild a mechanical room again. It is a reasonable answer for some buildings. For a high school with a working glycol loop, distribution already in place and staff who maintain it themselves, it is usually the more expensive answer wearing a smaller first number.
The case for the plant here is capacity turndown. Two 160-ton machines give 320 tons at design, and a school in Ohio sees design conditions for a handful of afternoons a year. Splitting the plant in two means one machine carries the shoulder season by itself while the other sits idle, and rotary screw compressors with variable speed condenser fans hold their efficiency well down the load curve. The packaged alternative spreads that same tonnage across a dozen small compressors, each cycling on its own thermostat, each with its own roof penetration and its own end of life.
The second argument is where the equipment lives. Two chillers at grade and four pumps in one mechanical room means every filter, strainer, gauge and valve a technician touches is in two places. That is a plant a district maintenance staff can actually keep on a schedule, which is the difference between equipment that reaches its service life and equipment that does not.
Refrigerant matters on a purchase with this kind of horizon. The existing machines ran R-134a, which was recovered and turned over to the district; the new ones run R-513A. A district buying a chiller now is buying into a refrigerant supply chain for the next twenty years, and that belongs in the decision alongside tonnage.
Tying the new plant in without closing the building
The constraint on a plant replacement is rarely the equipment. It is that the plant is the building's only source of cooling, the building is a school, and the work has to land between one group of students leaving and the next arriving. Most of the decisions in this scope are sequencing decisions.
The glycol is the clearest example. A 25 percent ethylene glycol charge is not something to send down a drain and buy again, so the system was drained into owner-supplied drums — fourteen 55-gallon drums staged in the second floor mechanical room — held there through the demolition and the piping rework, then reinstalled, bled of air and rebalanced. That single decision sets the staging space, the drum count and the order of the whole job.
Reuse of what is already in the ground does the same work on the schedule. The chillers set in the existing chiller locations. The pumps mount on the existing housekeeping pads in the same general positions. The existing pump disconnects are reused with the new variable frequency drives installed between disconnect and pump. The underground electrical feed is intercepted and terminated at the new exterior disconnect rather than pulled back and re-run, and the new control wiring to the chillers is pulled through the conduit that is already there. Every one of those is a week of trenching, conduit and inspection that does not have to happen in July.
Two details are worth a facilities director's attention. A butterfly valve is installed on the system side of each triple duty valve, so a pump or a triple duty valve can be pulled years from now without draining the loop again. And the controls integration — BACnet wiring to four pump drives and both chillers, a Cat 6 run per chiller carrying status and critical chiller data, existing hardwired start, stop, status and alarm connections reused — is programmed offsite over district-provided VPN access. The plant comes up on the building's existing graphics, and one more trade stays out of the building during the tightest weeks.
