Proving replacement pays before the capital request.
Four large rooftop units, one question from the facility team: is replacement worth it? We answered with a unit-for-unit engineering analysis instead of an opinion.
Download the one-page PDFThe problem
Four 115-ton rooftop units were carrying an industrial facility at 9.0 EER and 1.33 kW per ton. The facility team needed to know whether replacing them would pay back, with numbers solid enough to support a capital request and a utility incentive application.
The solution
We compared the existing units to four 120-ton replacements with variable speed scroll compressors, VFD fans, enthalpy economizers and BACnet controls. We modeled capacity, power draw, annual kWh and annual cost for each unit, and identified utility incentive eligibility during scoping, before any money was committed.
| Per unit | Existing | Replacement | Change |
|---|---|---|---|
| Cooling capacity | 115 tons | 120 tons | +5 tons (+4.3%) |
| Efficiency (EER) | 9.0 | 10.7 | +19% |
| Full-load power draw | 153.3 kW | 134.6 kW | −18.7 kW |
| kW per ton | 1.33 | 1.12 | 16% lower |
| Annual energy use | 214,620 kWh | 188,440 kWh | −26,180 kWh |
| Annual energy cost | $30,047 | $26,382 | −$3,665 per year |
Estimates from the engineering analysis. Based on full-load EER, $0.14/kWh and 1,400 annual cooling hours, representative of Chicago-area commercial operation; excludes demand charge and part-load savings, which would be expected to add to real-world results. Incentives are subject to eligibility and approval.
| Item | Detail |
|---|---|
| Existing units | Four 115-ton rooftop units, 9.0 EER |
| Replacement units | Four 120-ton packaged rooftop units, 10.7 EER |
Replacement equipment specification
- Variable speed scroll compressors
- Factory VFDs on supply and return fans
- VFD condenser fan for head pressure control
- Enthalpy economizer with low-leak dampers
- Modulating stainless steel gas heat exchanger
- Factory unit controller with BACnet interface
Weighing repair vs. replace on aging rooftops?
Email sales@rabinemechanical.com or call 815.331.1035. Our own crews cover northern Illinois and southern Wisconsin; qualified service partners cover all other markets.