ASHRAE 90.1 Table 6.8.3-1

ASHRAE 90.1 / ASME B31.9

Chilled water piping insulation must have a continuous vapor barrier (vapor retarder) on the exterior to prevent moisture from migrating through the insulation and condensing on the cold pipe surface.

ASHRAE 90.1 / IECC

Economizer operation using outdoor air for free cooling is not only allowed but required by energy codes for most commercial systems. Using enthalpy (temperature + humidity) control is the preferred method. The 55°F changeover and 100% OA capability are standard economizer settings. The 20% minimum OA ensures ventilation is always maintained.

ASHRAE 90.1 Section 6.5.1

This fails ASHRAE 90.1 requirements. ASHRAE Standard 90.1 Section 6.5.1 requires economizer systems for cooling equipment above certain capacity thresholds in climate zones with sufficient free cooling hours, and Climate Zone 5A (Chicago) easily qualifies with thousands of annual hours where outdoor conditions can provide free or assisted cooling. A PUE of 1.8 indicates that 44% of total facility energy is consumed by non-IT overhead, which is very poor by modern standards. With a properly designed air-side or water-side economizer, this facility could achieve a PUE in the 1.2 to 1.4 range, saving hundreds of thousands of dollars in annual energy costs. The economizer requirement is not optional regardless of cost justification arguments.

ASHRAE 90.1-2019 Section 6.4.3.4.2 (shutoff damper controls) / high-rise office Mechanical Specification

The high-rise office specification requires the motorized outside air damper to be interlocked with evaporator fan operation. The damper must open only when the fan is running and close when the fan stops. A timeclock-only schedule creates two problems: (1) if the fan trips or fails during occupied hours, the damper remains open, allowing unconditioned outdoor air into the space; (2) if the timeclock schedule does not match actual fan operation (overtime, holidays), the damper may be open with no fan running. The interlock ensures the damper state always matches the fan state, satisfying the project specification and the ASHRAE 90.1-2019 Section 6.4.3.4.2 shutoff-damper requirement that outdoor-air dampers automatically close when the system serving the space is not in use.

ASHRAE 90.1-2019 Section 6.5.3.4 (supply-air-temperature reset)

This passes. ASHRAE 90.1-2019 Section 6.5.3.4 requires multiple-zone HVAC systems to reset supply air temperature in response to either representative building loads OR outdoor air temperature, by at least 25 percent of the difference between the design SAT and the design room temperature. The scheduled reset from 55 degrees F at 90 degrees F OAT up to 65 degrees F at 60 degrees F OAT is a 10-degree reset driven by outdoor air temperature — an explicitly permitted method that meets the code minimum. Zone-based Trim-and-Respond reset (ASHRAE Guideline 36) is a voluntary best-practice guideline, not adopted code, so its preference cannot make an otherwise-compliant outdoor-air reset fail inspection. Only if the project specification specifically mandated G36 zone-based reset would the OAT method be non-compliant — and the spec would have to state that.

ASHRAE 90.1-2019 Section 6.5.4.2 (Hydronic Variable Flow Systems)

ASHRAE 90.1-2019 Section 6.5.4.2 (Hydronic Variable Flow Systems) requires that any HVAC pumping system with a total pump system power exceeding 10 HP that uses modulating control valves be designed for variable flow — capable of reducing pump flow to 50% or less of design — and three-way valves are explicitly not acceptable. The trigger is pump system power, not chiller tonnage, but a 500-ton plant's chilled water pumps are far above 10 HP, so the requirement plainly applies. The constant-flow arrangement with 3-way valves and no pump VFDs violates it. The system must be redesigned with 2-way control valves at all coils, variable frequency drives on chilled water pumps, differential pressure sensors for pump speed control, and a minimum flow bypass to protect chiller evaporators at low loads. Constant-flow systems at this scale waste enormous pumping energy, particularly at the part-load conditions that represent the vast majority of annual operating hours.