A Salt Lake City small office building owner contacted us about replacing aging rooftop HVAC equipment serving their 4,800 sq ft office space. Two original 2003-installed rooftop units (RTUs) were past service life with increasing repair costs and capacity issues. The customer wanted reliable replacement equipment with reasonable operating costs and proper commissioning for the commercial space.
While most of our work is residential, we handle small commercial projects like this one for established customers.
Customer Situation
- Building: 4,800 sq ft single-story office building in central Salt Lake City
- Existing equipment: Two 2003 Carrier 5-ton RTUs (10 tons total cooling)
- Symptom: Aging equipment with increasing repair costs, capacity decline during peak summer
- Customer priorities: Reliable replacement, reasonable operating costs, proper commissioning, scheduled maintenance program
Load Calculation
Commercial Manual N load calculation (commercial equivalent of residential Manual J):
- Conditioned area: 4,800 sq ft
- Occupancy: 18 people typical
- Equipment load: standard office (computers, lighting, etc.)
- Total cooling load: 87,500 BTU/h (7.3 tons)
- Total heating load: 110,000 BTU/h
Note: existing 10-ton total capacity was 37% oversized for actual building load — common scenario in older commercial installations producing short-cycling and poor part-load performance.
Equipment Selection
Right-sized replacement: Two 4-ton RTUs (8 tons total)
– Carrier 48HC-024 (4-ton package unit, 14.3 SEER2, 81% AFUE gas heat)
– Two units provide redundancy if one fails
– Closer to actual load while maintaining safety margin
– Better part-load efficiency
Installation
Duration: 2 days with crane scheduling
- Crane removal of old RTUs (one day)
- Crane placement of new RTUs (one day)
- Electrical connections updated
- Gas line connections verified
- Ductwork connection verification
- Smart commercial thermostats with scheduling
- Complete commissioning across both units
Commissioning
Both RTUs verified within manufacturer specifications across cooling and heating modes. Combustion analysis on gas heating sections. Refrigerant charge verified by subcool. Static pressure measurements confirm adequate ductwork. Smart thermostat scheduling programmed for business hours.
Final Cost
Customer’s project cost: $26,500 (includes both units, crane, electrical, commissioning)
Rebates:
– Rocky Mountain Power Wattsmart commercial cooling rebate: $480
Effective net cost: $26,020
Customer Outcome
Equipment operates reliably. Operating costs reduced approximately 22% vs. oversized old equipment (more efficient part-load operation). Comfort across office consistent throughout business hours. Annual commercial maintenance program enrolled for proactive service.
What This Case Study Demonstrates
- Commercial Manual N load calculation prevents oversizing common in older commercial installations
- Two-unit redundancy provides reliability for business operations
- Right-sized commercial equipment delivers better part-load efficiency
- Crane scheduling required for rooftop work
- Commercial maintenance program essential for business HVAC reliability
Commercial HVAC Needs?
If you have a small commercial building in Salt Lake City needing HVAC service, call (385) 250-0687.
- Phone: (385) 250-0687
- Address: 4454 Manhattan Ct, West Valley City, UT 84120