HVAC and Refrigeration Distribution and Systems

Getting air and fluids where they need to go, plus the refrigeration cycle: ductwork and diffusers, ventilation and air quality, hydronic/steam/fuel piping, control valves and dampers, and refrigeration systems. One of the heavier areas on the HVAC & Refrigeration depth.

What the problems look like

Sizing-and-selecting flow paths and working the vapor-compression cycle. Recurring shapes — duct sizing and friction loss → fan total/static pressure; ventilation/outdoor-air (minimum OA, economizer %OA, mixed-air temperature); piping pressure drop and pump head for a hydronic loop; control-valve authority; and the refrigeration cycle (refrigeration effect, mass flow, COP, condenser/evaporator duty). System-curve-ish and frequently multi-step.

By exam day you should be able to —

• size a duct / compute friction loss and the system's total pressure;
• compute minimum ventilation (per-person + per-area) and an economizer %OA / mixed-air temperature;
• compute piping pressure drop and pump head for a hydronic loop;
• evaluate control-valve authority;
• work the vapor-compression cycle — refrigeration effect, refrigerant mass flow, COP, condenser and evaporator duty.

Where people lose points

• Economizer %OA / mixed-air temperature by averaging the return and outdoor temps instead of flow-weighting them.
• Ventilation math: combining per-person and per-area terms wrong (Vbz = Rp·Pz + Ra·Az), or using people only.
• Water vs. air constant — using an air constant (1.10 or 4.5) on a hydronic flow, where water duty is Q = 500 × gpm × ΔT.
• Confusing total vs. static vs. velocity pressure in duct/fan work; pushing equal-friction past its range.
• Control-valve authority set against the wrong pressure drop.
• Refrigeration cycle: condenser load = evaporator load + compressor work (the equipment area tests the same relation); refrigerant mass flow ṁ = (tons × 12,000) / refrigeration effect.

Have these at your fingertips

The duct-friction chart, the outdoor-air/ventilation relations, and the refrigerant P–h diagram — plus where they live in the Handbook so you're navigating, not hunting.

Going deeper

• Duct design & air distribution
• ASHRAE 62.1 & ventilation
• Pipe flow & pressure drop
• Refrigeration cycle & COP

Part of the HVAC & Refrigeration depth. Practice this area with exam-real problems — the tutor walks any one you miss. → Start your 7-day free trial — no card. Or take the free practice exam first.