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Blueprint MechanicalDenver, Colorado
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DENVER, CO · 2025

Nine rooftop units replaced over four weekends

A 1998 campus with nine failing packaged rooftop units, non-functioning economizers and duct static pressure high enough to be eating the fan energy budget. Replaced unit by unit on weekends with shop-built curb adapters.

Measured result

Measured fan energy down 31 percent. No tenant lost a working day.

Client
Central Park flex office campus
Sector
Office, 96,000 ft2
Completed
2025
Rows of packaged rooftop HVAC units and ductwork on a commercial roof in Denver with the Front Range in the distance

The brief

  • Nine constant-volume packaged rooftop units, 7.5 to 20 tons, installed in 1998 and past economic repair.
  • Economizers on seven of the nine units were seized or disconnected, which in Denver climate zone 5B throws away most of the free cooling the weather gives you.
  • The facility team had measured 3.4 in. w.c. across two of the units and wanted to know why the fan energy line kept climbing.
  • Tenants on 24 month leases, none of whom would tolerate a weekday shutdown.

What we did

We measured before we specified

Two weeks of trend logging on supply and return temperatures, plus a full static pressure traverse on every unit. Six of the nine were moving 20 to 28 percent less air than the schedule claimed. Sizing the replacements from the original schedule would have repeated the mistake at a higher efficiency rating.

A fresh block load, derated for altitude

A new block load calculation against current occupancy and the actual glazing, with the 0.4 percent Denver design condition of 91 F dry bulb and 59 F mean coincident wet bulb. At 5,280 ft the sensible heat factor drops from 1.08 to roughly 0.90, so the replacements were selected on airflow at Denver density rather than sea level catalogue data.

Curb adapters built in our own shop

Nine different curb footprints, nine shop drawings, nine adapters cut on our plasma table. Generic adapters would have left transitions that add static pressure back into a system we were trying to take static pressure out of.

Weekends, with the roof protected

Crane picks on Saturday mornings from a single set-up point per weekend, roof membrane protected, tenants back on Monday. Four weekends, nine units, zero weekday outages.

The outcome

  • Total external static pressure across the nine units reduced from a measured average of 2.6 in. w.c. to 1.1 in. w.c., mostly by fixing transitions and filter racks rather than by buying bigger fans.
  • Fan energy down 31 percent against the trended twelve months before replacement, weather normalised.
  • All nine economizers commissioned with a differential enthalpy changeover, sensors calibrated against a reference, and fault detection enabled at the unit.
  • Every unit handed over with a startup sheet, a measured airflow reading and an economizer changeover setpoint recorded in the maintenance log.

Other case studies

Boulder, CO · 2025Heat recovery VRF for a laboratory with 19 zones and one budgetSimultaneous heating and cooling handled without a second plant.Aurora, CO · 2024A warehouse that finally holds 65 F at the floorFloor level temperature swing cut from 14 F to under 3 F.

Tell us what the building is doing wrong.

Send us the building, the equipment and the complaint. You get a written response with the load we would run, what we would measure first, and a range before anyone visits.

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