ARE HVAC Systems Cheat Sheet

HVAC Systems Quick Reference

This cheat sheet compares HVAC system types tested on the ARE 5.0 PDD exam. See the HVAC Systems topic guide for detailed study.

System Types Comparison

System	Type	Best For	Pros	Cons
VAV (Variable Air Volume)	All-air	Large commercial offices, multi-zone	Energy efficient; individual zone control; single duct	May have poor ventilation at low flow; requires VAV boxes
CAV (Constant Air Volume)	All-air	Single-zone spaces, warehouses	Simple; low first cost	No individual zone control; energy waste at part load
Fan Coil Units (FCU)	Air-water	Hotels, apartments, hospitals	Individual control; low ductwork; 2-pipe or 4-pipe	Maintenance in occupied space; drain pan required
VRF (Variable Refrigerant Flow)	Direct expansion	Multi-zone commercial, retrofits	Very efficient; no ductwork; simultaneous heating/cooling	High first cost; refrigerant piping limits; ASHRAE 15 compliance
WSHP (Water-Source Heat Pump)	Water loop	Multi-tenant offices, schools	Individual metering; heating and cooling simultaneously	Maintenance in occupied space; boiler/tower required
DOAS (Dedicated Outdoor Air System)	Air (OA only)	Paired with radiant, VRF, or FCU	Excellent ventilation control; energy recovery	Requires separate terminal heating/cooling
Radiant (floor/ceiling)	Water	High-ceiling spaces, lobbies	Quiet; uniform comfort; lower air volume	Slow response; condensation risk; limited cooling capacity
Chilled beam (active/passive)	Air-water	Offices, labs	Energy efficient; quiet; low floor-to-floor height	Cannot handle high latent loads; no condensation allowed on passive
Packaged rooftop (RTU)	All-air	Retail, single-story commercial	Low cost; easy maintenance; self-contained	Less efficient; limited zoning; requires roof structure

Efficiency Ratings

Rating	Stands For	Applies To	Benchmark
SEER / SEER2	Seasonal Energy Efficiency Ratio	Central AC, heat pumps (cooling mode)	Code min: 14–15 SEER; high-efficiency: 20+
EER	Energy Efficiency Ratio	AC equipment at single condition	Typically 10–13 for commercial
COP	Coefficient of Performance	Heat pumps (heating mode), chillers	GSHP: 3.0–5.0; ASHP: 2.0–4.0
HSPF / HSPF2	Heating Seasonal Performance Factor	Heat pumps (heating mode)	Code min: 8.2–8.8; high-efficiency: 10+
AFUE	Annual Fuel Utilization Efficiency	Furnaces, boilers	Standard: 80%; high-efficiency: 90–98%
IPLV	Integrated Part Load Value	Chillers at part load	Better indicator of real-world chiller performance

Central Plant Equipment

Equipment	Function	Key Facts
Chiller (centrifugal)	Cools water for distribution	Largest capacity; 200–2000+ tons; most efficient at full load
Chiller (scroll/screw)	Cools water	Smaller capacity (10–400 tons); better part-load
Cooling tower	Rejects heat to atmosphere	Evaporative; requires water treatment; can transmit Legionella
Boiler (hot water)	Heats water for distribution	Gas-fired most common; condensing type = 90%+ efficiency
Air handling unit (AHU)	Conditions and distributes air	Contains filters, coils, fan, mixing box, dampers

Ductwork Sizing Basics

Method	Description	Use
Equal friction	Maintain constant pressure drop per 100' of duct	Most common for low-pressure systems
Static regain	Size each section to regain static pressure lost at previous takeoff	Long duct runs, high-velocity systems
Velocity reduction	Reduce velocity progressively along trunk duct	Simple method, less precise

Typical velocities: Main ducts: 1000–2000 FPM. Branch ducts: 600–1000 FPM. At diffusers: 500–700 FPM. Occupied spaces (NC criteria): keep noise below NC-35 for offices.

Ventilation Quick Facts (ASHRAE 62.1)

• Outdoor air is required for all occupied spaces
• Rate based on: per-person (R_p) + per-area (R_a) components
• Office: 5 CFM/person + 0.06 CFM/sf
• Retail: 7.5 CFM/person + 0.06 CFM/sf
• Classroom: 10 CFM/person + 0.12 CFM/sf
• CO2 sensors can be used for demand-controlled ventilation (DCV)

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