Rooftop Unit Replacement and Economizer Applicability
A 9,000 ft² strip-mall tenant replaces a failed 10-ton packaged rooftop unit serving a retail sales area in CZ 4A. The like-for-like replacement is quoted at 11.0 IEER and 13.0 SEER2, with a factory economizer option deleted to save cost. The mechanical contractor states that because it is a 'replacement of an existing unit,' economizer requirements and the new-equipment efficiency minimums do not apply - only safety codes. The permit is a mechanical replacement permit. The existing unit had no economizer. The building has no central plant; each tenant has its own RTU.
1. Is the contractor's claim correct that replacement equipment is exempt from efficiency and economizer requirements?
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No. Replacement equipment must meet the efficiency minimums in effect for new equipment of that type and size at the time of permitting - 'replacement' is not an efficiency exemption. The reviewer should verify the quoted 11.0 IEER / 13.0 SEER2 against the applicable minimums for a 10-ton (≥65,000 and <135,000 Btu/h) packaged unit; if any rating falls short, the unit is noncompliant regardless of like-for-like intent.
Economizer applicability is a separate question governed by system capacity, climate zone, and the code's economizer thresholds and exceptions (e.g., where the system serves space with certain conditions, or where the added cost/feasibility exceptions apply). The contractor must document the basis for deleting the economizer - not merely assert it. A blanket 'replacement = exempt' statement is wrong on both counts.
2. What documentation should the plans examiner require before approving the economizer deletion?
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Require a written economizer exception justification citing the specific code exception relied upon, supported by:
- System capacity and type (10-ton packaged DX, single zone).
- Climate zone (4A) and the code's economizer requirement threshold for that zone.
- If claiming a feasibility/cost exception, a documented analysis showing the economizer's installed cost exceeds the threshold relative to the equipment, or that space conditions (e.g., humidity control, contaminant) justify the exception.
- If claiming a space-condition exception, evidence the served space qualifies.
Also confirm the unit's controls meet requirements (setback, fan control where applicable) and that the efficiency ratings meet minimums. If no valid exception is documented, the permit should be denied pending an economizer-equipped unit or an approved alternate.