HVAC System Design - Comprehensive Engineering Course

<h3>Learning Objectives</h3><ul><li>Identify and describe the major categories of HVAC systems</li><li>Understand the advantages and limitations of each system type</li><li>Select appropriate system types based on building requirements</li></ul><h3>1.1 All-Air Systems</h3><p>All-air systems condition spaces using only air as the heat transfer medium. These systems centralize heating and cooling equipment, providing excellent filtration and humidity control.</p><h4>Constant Air Volume (CAV) Systems</h4><p>CAV systems deliver a fixed airflow rate to each zone, varying the supply air temperature to meet load changes. Key characteristics:</p><ul><li><strong>Single-Zone CAV:</strong> One thermostat controls one AHU serving one zone. Simple but limited flexibility.</li><li><strong>Multi-Zone CAV:</strong> Hot and cold decks mix air for multiple zones via zone dampers at the AHU.</li><li><strong>Terminal Reheat:</strong> Cool air is reheated at zone terminals - energy intensive but provides precise control.</li></ul><h4>Variable Air Volume (VAV) Systems</h4><p>VAV systems vary airflow to each zone while maintaining relatively constant supply air temperature. This approach offers significant energy savings over CAV systems.</p><ul><li><strong>Pressure-Independent VAV:</strong> Boxes with integral flow controllers maintain setpoint regardless of duct pressure fluctuations.</li><li><strong>Pressure-Dependent VAV:</strong> Simpler boxes where airflow varies with duct pressure - requires careful system balancing.</li><li><strong>Fan-Powered VAV:</strong> Series or parallel fan configurations maintain minimum airflow during low-load conditions.</li></ul><p>VAV terminals typically modulate from 100% to 30% of design airflow. Below minimum airflow, reheat may be required to prevent overcooling.</p><h4>Dual-Duct Systems</h4><p>Two parallel duct systems - one hot, one cold - supply mixing boxes at each zone. Provides excellent control but requires double the duct space.</p><h3>1.2 Air-Water Systems</h3><h4>Fan Coil Units (FCUs)</h4><p>Local fan-coil units receive chilled/hot water from a central plant. A separate DOAS provides ventilation.</p><ul><li><strong>Two-Pipe:</strong> One supply, one return - switchover between heating/cooling seasonally</li><li><strong>Four-Pipe:</strong> Separate heating and cooling coils - simultaneous heating/cooling capability</li></ul><h4>Active Chilled Beams</h4><p>Primary air induces room air across a chilled water coil. Critical: supply air must be dehumidified to prevent condensation.</p><h3>1.3 Unitary Systems</h3><h4>Variable Refrigerant Flow (VRF)</h4><ul><li><strong>Heat Pump VRF:</strong> All indoor units in heating or cooling mode simultaneously</li><li><strong>Heat Recovery VRF:</strong> Simultaneous heating and cooling in different zones</li><li><strong>Design:</strong> Refrigerant charge limits per ASHRAE 15, piping up to 540 ft, vertical lifts up to 160 ft</li></ul><h4>Water-Source Heat Pumps (WSHP)</h4><p>Individual heat pump units connected to common water loop at 60-90 deg F. Boiler adds heat when cold; cooling tower rejects when warm.</p><h3>1.4 System Selection</h3><table border="1" style="width:100%; border-collapse:collapse;"><tr><th>System</th><th>Best For</th><th>Pros</th><th>Cons</th></tr><tr><td>VAV</td><td>Offices, schools</td><td>Energy efficient, good zoning</td><td>Min ventilation at low loads</td></tr><tr><td>FCU+DOAS</td><td>Hotels, hospitals</td><td>Individual control</td><td>Maintenance in spaces</td></tr><tr><td>VRF</td><td>Retrofit</td><td>No ductwork, efficient</td><td>Refrigerant concerns</td></tr><tr><td>WSHP</td><td>Mixed loads</td><td>Heat recovery</td><td>Loop maintenance</td></tr></table>

<h3>Learning Objectives</h3><ul><li>Understand supply, return, and exhaust air distribution principles</li><li>Calculate air change rates and room air distribution effectiveness</li><li>Select appropriate diffuser types and layouts</li></ul><h3>2.1 Room Air Distribution</h3><h4>Air Changes Per Hour (ACH)</h4><p><strong>ACH = (CFM x 60) / Room Volume (ft3)</strong></p><p>Typical values: Offices 4-6 ACH, Conference rooms 8-12 ACH, Labs 6-12 ACH, ORs 15-25 ACH, Cleanrooms 20-600+ ACH</p><h4>Air Distribution Effectiveness (Ez)</h4><p>Per ASHRAE 62.1: Ez = 1.0 (ceiling supply cool air), Ez = 0.8 (ceiling warm air), Ez = 1.2 (displacement ventilation)</p><h3>2.2 Supply Air Distribution</h3><h4>Ceiling Diffusers</h4><ul><li><strong>Square/Rectangular:</strong> 1-4 way throw patterns. Use perforated face for VAV.</li><li><strong>Linear Slot:</strong> 1-4 slots, architectural appearance</li><li><strong>Perforated Face:</strong> Even, low-velocity - ideal for VAV, no dumping at low flows</li></ul><h4>Displacement Ventilation</h4><p>Low-velocity (50-70 fpm) supply at floor level, 63-65 deg F. Thermal plumes carry air to ceiling exhaust. 10-20% energy savings.</p><h3>2.3 Throw and Drop</h3><p>Throw (T) = distance to reach terminal velocity (50 fpm)</p><ul><li><strong>Cooling:</strong> T50 = 0.75-1.0 times distance to wall/adjacent diffuser</li><li><strong>Heating:</strong> T50 = 0.5-0.75 times characteristic length</li><li><strong>VAV:</strong> Select diffusers for 50% design airflow to prevent dumping</li></ul><h4>ADPI - Air Diffusion Performance Index</h4><p>Percentage of occupied zone within acceptable velocity and temperature. Target ADPI >= 80%.</p><h3>2.4 Return Air</h3><ul><li><strong>Ducted Return:</strong> Best sound control, required for labs/healthcare</li><li><strong>Plenum Return:</strong> Ceiling plenum as duct - lower cost, fire/smoke concerns</li></ul><p>Size return grilles for 300-500 fpm face velocity.</p><h3>2.5 Exhaust Systems</h3><ul><li><strong>General:</strong> Restrooms 75-100 CFM/fixture or 2 CFM/SF</li><li><strong>Lab:</strong> Fume hoods 100-150 fpm face velocity, total 10-15 ACH</li><li><strong>Kitchen:</strong> Type I hoods 150-550 CFM/linear foot</li></ul><h3>2.6 Pressure Relationships</h3><ul><li>Labs: -0.03 to -0.05 in. w.g. (negative to corridor)</li><li>Cleanrooms: +0.03 to +0.05 in. w.g. (positive)</li><li>Operating rooms: +0.01 to +0.03 in. w.g.</li><li>Isolation: Negative pressure with anteroom airlock</li></ul>

<h3>Learning Objectives</h3><ul><li>Apply equal friction, static regain, and velocity methods</li><li>Calculate friction losses in duct systems</li><li>Size supply, return, and exhaust ductwork</li></ul><h3>3.1 Equal Friction Method</h3><p>Most common method - maintains constant friction rate throughout system.</p><h4>Friction Rate Selection</h4><ul><li>Low-pressure (under 2 in. w.g.): 0.08-0.10 in./100 ft</li><li>Medium-pressure (2-6 in.): 0.10-0.25 in./100 ft</li><li>High-pressure (over 6 in.): 0.25-0.40 in./100 ft</li></ul><h4>Procedure</h4><ol><li>Determine CFM for each section from loads</li><li>Select friction rate based on system type</li><li>Use friction chart to find duct size</li><li>Verify velocity limits not exceeded</li><li>Calculate total pressure for longest path</li></ol><h3>3.2 Static Regain Method</h3><p>Sizes ducts so static pressure gain from velocity reduction equals friction loss in next section.</p><p><strong>Delta SP (regain) = R x (VP1 - VP2)</strong> where R = 0.5-0.75</p><p>Best for long runs, high-velocity systems, many branches at different distances.</p><h3>3.3 Velocity Method</h3><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Application</th><th>Main</th><th>Branch</th><th>Risers</th></tr><tr><td>Residence</td><td>600-900</td><td>500-700</td><td>500-700</td></tr><tr><td>Hotel</td><td>1000-1300</td><td>600-900</td><td>800-1200</td></tr><tr><td>Office</td><td>1200-1800</td><td>800-1200</td><td>1000-1600</td></tr><tr><td>Industrial</td><td>2000-3000</td><td>1500-2200</td><td>1500-2200</td></tr></table><h3>3.4 Duct Sizing Calculations</h3><h4>Equivalent Diameter (Rectangular)</h4><p><strong>De = 1.30 x (axb)^0.625 / (a+b)^0.25</strong></p><h4>Aspect Ratio</h4><ul><li>Optimal: 1:1 to 3:1</li><li>Maximum: 4:1</li><li>High ratios increase friction and cost</li></ul><h3>3.5 Example Problem</h3><p>Given: 5,000 CFM, 100 ft main, branches at 30/60/90 ft, 0.10 in./100 ft</p><p>Solution: Main 24 in. (1,590 fpm), After Branch 1 20 in. (1,375 fpm), After Branch 2 16 in. (1,075 fpm)</p><h3>3.6 Return/Exhaust Sizing</h3><p>Return: 80% of supply velocity (mains), 60-80% (branches)</p>

<h3>Learning Objectives</h3><ul><li>Select appropriate duct materials</li><li>Understand SMACNA construction standards</li><li>Specify proper insulation and liner</li></ul><h3>4.1 Galvanized Steel</h3><p>Most common commercial duct material. G60/G90 galvanized coating.</p><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Pressure Class</th><th>Gauge</th><th>Application</th></tr><tr><td>1/2 in.</td><td>26-24 ga</td><td>Low-pressure</td></tr><tr><td>1 in.</td><td>24-22 ga</td><td>Standard commercial</td></tr><tr><td>2 in.</td><td>22-20 ga</td><td>Medium-pressure VAV</td></tr><tr><td>3 in.</td><td>20-18 ga</td><td>High-pressure mains</td></tr></table><h4>Spiral Round Duct</h4><p>Lock-seam spiral: 3-14 in. = 26 ga, 16-26 in. = 24 ga, 28-50 in. = 22 ga. Lower leakage than rectangular.</p><h3>4.2 SMACNA Seal Classes</h3><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Class</th><th>Sealing</th><th>Application</th></tr><tr><td>A</td><td>All joints, seams, penetrations</td><td>Over 3 in. w.g.</td></tr><tr><td>B</td><td>Transverse joints, penetrations</td><td>2-3 in. w.g.</td></tr><tr><td>C</td><td>Transverse joints only</td><td>1-2 in. w.g.</td></tr></table><h4>Leakage Classes</h4><p>CL 6: Class A sealing, CL 12: Well-sealed, CL 48: Unsealed</p><h3>4.3 Fiberglass Duct Board</h3><p>Self-insulating R-4.2 to R-8. Max 2 in. w.g., 2,500 fpm. Not for hospitals.</p><h3>4.4 Flexible Duct</h3><ul><li>Max 5-6 ft length, fully extended</li><li>Support every 4 ft</li><li>Friction: 1.5x extended, 3x at 15% compression, 6x at 30%</li></ul><h3>4.5 Specialty Materials</h3><ul><li><strong>Stainless:</strong> Kitchen/lab exhaust, cleanroom (304/316)</li><li><strong>Aluminum:</strong> Cleanroom, food processing</li><li><strong>PVC/FRP:</strong> Chemical exhaust</li></ul><h3>4.6 Insulation</h3><h4>Exterior (Duct Wrap)</h4><p>Fiberglass R-4 to R-8 with FSK vapor barrier. ASHRAE 90.1: R-6 to R-8 in unconditioned spaces.</p><h4>Interior Liner</h4><p>1/2 to 2 in. fiberglass for acoustics. Must withstand velocity without erosion.</p><h3>4.7 Fire/Smoke Dampers</h3><ul><li><strong>Fire Damper:</strong> Fusible link (165 deg F) at fire barriers</li><li><strong>Smoke Damper:</strong> Detector signal at smoke barriers</li><li><strong>Combination:</strong> Both functions in one</li></ul>

<h3>Learning Objectives</h3><ul><li>Calculate pressure losses through fittings</li><li>Apply equivalent length and loss coefficient methods</li><li>Design efficient duct layouts</li></ul><h3>5.1 Fitting Loss Methods</h3><ol><li><strong>Loss Coefficient (Co):</strong> Delta P = Co x VP</li><li><strong>Equivalent Length:</strong> Delta P = (Leq/100) x friction rate</li></ol><h3>5.2 Elbows</h3><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Elbow Type</th><th>Co</th><th>Eq. Length</th></tr><tr><td>90 deg square (no vanes)</td><td>1.2-1.5</td><td>75D</td></tr><tr><td>90 deg w/ single vanes</td><td>0.22</td><td>10D</td></tr><tr><td>90 deg w/ double vanes</td><td>0.15</td><td>7D</td></tr><tr><td>90 deg radius (R/W=1.5)</td><td>0.22</td><td>12D</td></tr><tr><td>45 deg</td><td>0.15-0.25</td><td>8D</td></tr></table><h4>Round Elbows</h4><p>5-piece 90 deg: Co=0.12, 3-piece: Co=0.14, Mitered: Co=1.2, 45 deg: Co=0.08</p><h3>5.3 Transitions</h3><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Type</th><th>Angle</th><th>Co</th></tr><tr><td>Converging (gradual)</td><td>15-30 deg</td><td>0.02-0.05</td></tr><tr><td>Converging (abrupt)</td><td>90 deg</td><td>0.50</td></tr><tr><td>Diverging (gradual)</td><td>15-20 deg</td><td>0.15-0.25</td></tr><tr><td>Diverging (abrupt)</td><td>90 deg</td><td>0.80-1.0</td></tr></table><p>Max angle: 20 deg expansion, 30 deg contraction</p><h3>5.4 Branch Fittings</h3><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Type</th><th>Straight Co</th><th>Branch Co</th></tr><tr><td>Tee straight-through</td><td>0.25-0.50</td><td>-</td></tr><tr><td>Tee branch</td><td>-</td><td>0.80-1.5</td></tr><tr><td>Tee w/ vanes</td><td>0.20</td><td>0.35</td></tr><tr><td>45-deg wye</td><td>-</td><td>0.30-0.50</td></tr></table><p>Wyes more efficient than tees.</p><h3>5.5 Other Fittings</h3><p>Dampers (open): Co=0.05-0.10. Entry from plenum: Co=0.50. Bell-mouth: Co=0.03-0.05. Exit to plenum: Co=1.0</p><h3>5.6 Total System Pressure</h3><ol><li>Identify longest/most restrictive path</li><li>Calculate straight duct friction</li><li>Add fitting losses</li><li>Include equipment (coils, filters, dampers)</li><li>Include terminal devices</li><li>Sum for total external static</li></ol><h3>5.7 Best Practices</h3><ul><li>Minimize fittings</li><li>Always use turning vanes in square elbows</li><li>3-5 diameters straight duct between fittings</li><li>Use wyes over tees</li><li>20 deg max expansion angle</li><li>4:1 max aspect ratio</li></ul>

<h3>Learning Objectives</h3><ul><li>Read and apply fan performance curves</li><li>Select fans for CFM and static pressure requirements</li><li>Apply fan laws for speed, flow, and pressure changes</li><li>Calculate fan power and efficiency</li></ul><h3>6.1 Fan Types</h3><h4>Centrifugal</h4><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Blade</th><th>Efficiency</th><th>Application</th></tr><tr><td>Forward Curved</td><td>60-70%</td><td>Residential, small AHU</td></tr><tr><td>Backward Inclined</td><td>80%+</td><td>Commercial AHU</td></tr><tr><td>Airfoil</td><td>85%+</td><td>Large AHU, hospitals</td></tr><tr><td>Radial</td><td>Lower</td><td>Industrial, dirty air</td></tr></table><h4>Axial</h4><ul><li><strong>Propeller:</strong> High flow, under 0.5 in. w.g.</li><li><strong>Tube Axial:</strong> 1-3 in. w.g.</li><li><strong>Vane Axial:</strong> 2-6 in. w.g.</li></ul><h3>6.2 Fan Curves</h3><p>X-axis: CFM. Y-axis: Static Pressure and BHP. Efficiency contours show BEP.</p><h4>Selection Steps</h4><ol><li>Identify required CFM and SP</li><li>Add 10-15% for fouling/future</li><li>Select fan meeting requirements</li><li>Verify stable operating region</li><li>Confirm efficiency within 10% of peak</li><li>Check motor size</li></ol><h3>6.3 Fan Laws</h3><h4>Law 1: Flow</h4><p><strong>Q2/Q1 = N2/N1</strong> - Flow varies directly with speed</p><h4>Law 2: Pressure</h4><p><strong>P2/P1 = (N2/N1)^2</strong> - Pressure varies with speed squared</p><h4>Law 3: Power</h4><p><strong>HP2/HP1 = (N2/N1)^3</strong> - Power varies with speed cubed</p><h4>Example</h4><p>At 1,200 RPM: 10,000 CFM, 4 in. w.g., 15 HP</p><p>At 1,000 RPM (0.833 ratio): 8,330 CFM, 2.78 in. w.g., 8.7 HP</p><p>20% speed reduction = 49% power reduction!</p><h3>6.4 Fan Power</h3><p><strong>AHP = (CFM x SP) / 6356</strong></p><p><strong>BHP = AHP / efficiency</strong></p><h3>6.5 System Effect</h3><ul><li>Elbow at inlet: 10-25% capacity loss</li><li>No inlet duct: 5-15% loss</li><li>Elbow at discharge: 10-30% loss</li><li>Min 2.5 diameters straight duct at discharge</li></ul>

<h3>Learning Objectives</h3><ul><li>Understand two-pipe, four-pipe, primary-secondary arrangements</li><li>Calculate water flow rates from loads</li><li>Design for efficiency and controllability</li></ul><h3>7.1 System Configurations</h3><h4>Two-Pipe</h4><p>One supply, one return. Changeover or non-changeover. Cannot simultaneously heat and cool different zones.</p><h4>Four-Pipe</h4><p>Separate heating and cooling pipes. Higher cost but full flexibility. Required for hospitals, labs.</p><h3>7.2 Primary-Secondary Pumping</h3><p>Decouples production from distribution via common pipe.</p><ul><li><strong>Primary:</strong> Constant flow through chillers/boilers</li><li><strong>Secondary:</strong> Variable flow to loads</li><li><strong>Common pipe:</strong> Under 1 ft pressure drop</li></ul><h4>Variable Primary Flow</h4><p>Modern chillers handle variable flow directly. Min 33% flow. Bypass maintains minimum during low load.</p><h3>7.3 Flow Calculations</h3><p><strong>GPM = Q / (500 x Delta T)</strong></p><p>Where 500 = 60 min/hr x 8.33 lb/gal x 1.0 BTU/lb-F</p><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>System</th><th>Supply</th><th>Delta T</th><th>GPM/ton</th></tr><tr><td>Chilled</td><td>42-45 F</td><td>10-14 F</td><td>2.4</td></tr><tr><td>Condenser</td><td>85 F</td><td>10 F</td><td>3.0</td></tr><tr><td>Hot Water</td><td>140-180 F</td><td>20-40 F</td><td>varies</td></tr></table><h3>7.4 Piping Arrangements</h3><ul><li><strong>Direct Return:</strong> Shortest path - unbalanced unless balanced</li><li><strong>Reverse Return:</strong> Equal path lengths - self-balancing</li></ul><h3>7.5 Expansion and Air</h3><h4>Tanks</h4><ul><li><strong>Compression:</strong> Air over water, larger</li><li><strong>Diaphragm:</strong> Membrane separates, smaller</li></ul><h4>Air Elimination</h4><p>Separators at pump discharge, auto vents at high points, manual vents at terminals.</p><h3>7.6 Valves</h3><ul><li><strong>Two-way:</strong> Variable flow, modulate to terminal</li><li><strong>Three-way:</strong> Constant flow, bypass when not needed</li><li><strong>PICV:</strong> Pressure-independent, maintains flow regardless of pressure</li></ul>

<h3>Learning Objectives</h3><ul><li>Apply Hazen-Williams and Darcy-Weisbach equations</li><li>Understand velocity limits</li><li>Calculate friction losses and select sizes</li></ul><h3>8.1 Hazen-Williams</h3><p><strong>h_f = 10.44 x L x Q^1.85 / (C^1.85 x d^4.87)</strong></p><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Material</th><th>C (new)</th><th>C (aged)</th></tr><tr><td>Copper</td><td>140-150</td><td>130</td></tr><tr><td>Steel</td><td>140</td><td>100-120</td></tr><tr><td>PVC</td><td>150</td><td>150</td></tr></table><p>Typical design: 4 ft/100 ft (about 1.5 psi/100 ft)</p><h3>8.2 Darcy-Weisbach</h3><p><strong>h_f = f x (L/D) x (V^2/2g)</strong></p><p>More accurate, applicable to all fluids.</p><h3>8.3 Velocity Limits</h3><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Service</th><th>Max fps</th><th>Range</th></tr><tr><td>Chilled water</td><td>10</td><td>4-8</td></tr><tr><td>Condenser</td><td>12</td><td>6-10</td></tr><tr><td>Hot water</td><td>8</td><td>4-6</td></tr><tr><td>Dom. hot</td><td>5</td><td>3-5</td></tr><tr><td>Dom. cold</td><td>8</td><td>4-6</td></tr></table><p>Min 2 fps to prevent stratification/settling.</p><h3>8.4 Sizing Procedure</h3><ol><li>Calculate GPM from load</li><li>Select friction rate (4 ft/100 ft typical)</li><li>Find size from chart</li><li>Check velocity</li><li>Calculate total head</li></ol><h3>8.5 Fitting Equivalent Lengths (ft)</h3><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Fitting</th><th>2 in.</th><th>4 in.</th><th>6 in.</th></tr><tr><td>90 std elbow</td><td>5</td><td>11</td><td>14</td></tr><tr><td>90 long radius</td><td>3</td><td>6</td><td>9</td></tr><tr><td>45 elbow</td><td>2</td><td>5</td><td>7</td></tr><tr><td>Tee branch</td><td>10</td><td>22</td><td>30</td></tr><tr><td>Gate valve</td><td>1</td><td>2</td><td>3</td></tr><tr><td>Check valve</td><td>12</td><td>22</td><td>30</td></tr></table><h3>8.6 Total Head</h3><p>Pipe friction + Fitting losses + Equipment (chiller 10-30 ft, coil 5-15 ft) + Control valves (3-10 ft)</p><h3>8.7 Materials</h3><ul><li><strong>Black steel Sch 40:</strong> Most common hydronic</li><li><strong>Copper Type L:</strong> Domestic, small hydronic</li><li><strong>CPVC:</strong> Domestic hot, some chilled</li><li><strong>PEX:</strong> Radiant, domestic</li><li><strong>Grooved:</strong> Large chilled water</li></ul>

<h3>Learning Objectives</h3><ul><li>Select pumps based on flow and head</li><li>Read and apply pump curves</li><li>Calculate NPSH</li></ul><h3>9.1 Pump Types</h3><ul><li><strong>End-Suction:</strong> Horizontal, most common</li><li><strong>In-Line:</strong> Same centerline, space-saving</li><li><strong>Split-Case:</strong> Double suction, large capacity</li><li><strong>Vertical:</strong> Motor above, compact</li></ul><h3>9.2 Pump Curves</h3><p>X: GPM, Y: TDH (ft), Efficiency contours, NPSH required</p><h4>Selection</h4><ol><li>Calculate GPM from load</li><li>Calculate total head</li><li>Select pump through duty point</li><li>Verify 80-120% of BEP</li><li>Check NPSHa > NPSHr + 2-3 ft</li></ol><h3>9.3 Total Dynamic Head</h3><p><strong>TDH = Static + Pressure + Friction + Velocity</strong></p><p><strong>Closed loop:</strong> TDH = Friction only (static cancels)</p><p><strong>Open system:</strong> TDH = Static lift + Friction</p><h3>9.4 NPSH</h3><p><strong>NPSHa = Hatm + Hs - Hf - Hvp</strong></p><ul><li>Hatm = 33.9 ft at sea level</li><li>Hs = Static suction head</li><li>Hf = Suction friction losses</li><li>Hvp = Vapor pressure head</li></ul><p><strong>NPSHa >= NPSHr + 2-3 ft</strong></p><h3>9.5 Affinity Laws</h3><ul><li>Q2/Q1 = N2/N1</li><li>H2/H1 = (N2/N1)^2</li><li>P2/P1 = (N2/N1)^3</li></ul><p>80% speed = 51% power!</p><h3>9.6 Parallel/Series</h3><p><strong>Parallel:</strong> Flow adds, head same. Capacity staging.</p><p><strong>Series:</strong> Head adds, flow same. High head needs.</p><h3>9.7 Efficiency</h3><p><strong>Eff = (GPM x TDH) / (3960 x BHP)</strong></p><p>Typical 70-88%</p><h3>9.8 Installation</h3><ul><li>10 diameters straight at suction</li><li>Eccentric reducer (flat up)</li><li>Flex connectors both sides</li><li>Check and isolation at discharge</li><li>Gauges at suction and discharge</li></ul>

<h3>Learning Objectives</h3><ul><li>Select AHUs based on airflow and coils</li><li>Specify cooling/heating coils and filters</li><li>Understand configurations and options</li></ul><h3>10.1 AHU Types</h3><ul><li><strong>Packaged:</strong> Factory-assembled, standard. Lower cost, faster.</li><li><strong>Custom:</strong> Built to spec. Double-wall, thermal break.</li></ul><h4>Component Sequence</h4><ol><li>OA/RA/EA dampers</li><li>Filters (pre + final)</li><li>Preheat coil</li><li>Cooling coil</li><li>Heating coil</li><li>Fan section (VFD)</li><li>Sound attenuator</li><li>Humidifier</li></ol><h3>10.2 Cooling Coil</h3><ul><li>EAT: DB/WB and CFM</li><li>LAT: 52-55 F typical</li><li>EWT: 42-45 F</li><li>Delta T: 10-14 F</li><li>Face velocity: 400-550 fpm (500 common)</li></ul><p><strong>Face Area = CFM / Velocity</strong></p><p>Example: 20,000 CFM / 500 fpm = 40 SF</p><h3>10.3 Heating Coil</h3><ul><li><strong>Hot Water:</strong> 140-180 F, 1-2 rows</li><li><strong>Steam:</strong> Distributing tube, vacuum breaker</li><li><strong>Preheat:</strong> Glycol or steam, freeze protection</li></ul><h3>10.4 Filters (MERV)</h3><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>MERV</th><th>Efficiency</th><th>Application</th></tr><tr><td>1-4</td><td>Under 20%</td><td>Residential, prefilter</td></tr><tr><td>5-8</td><td>20-35%</td><td>Commercial prefilter</td></tr><tr><td>9-12</td><td>40-75%</td><td>Commercial final</td></tr><tr><td>13-16</td><td>80-95%</td><td>Hospital, cleanroom</td></tr><tr><td>HEPA</td><td>99.97%+</td><td>OR, critical</td></tr></table><p>Initial: 0.15-0.30 in. w.g. Final (dirty): 0.50-1.0 in. Design for dirty.</p><h3>10.5 Fan Section</h3><ul><li>Centrifugal (FC, BI, Airfoil)</li><li>Plenum/plug fans</li><li>Fan arrays for redundancy</li></ul><p>VFD required over 5-10 HP per codes.</p><h3>10.6 Energy Recovery</h3><ul><li>Enthalpy wheel: 70-80%</li><li>Sensible wheel: 65-75%</li><li>Plate HX: 50-70%</li><li>Run-around: 45-55%</li></ul>

<h3>Learning Objectives</h3><ul><li>Select VAV boxes for VAV systems</li><li>Specify fan coil units</li><li>Choose unit heaters and other terminals</li></ul><h3>11.1 VAV Terminals</h3><h4>Types</h4><ul><li><strong>Cooling-Only:</strong> Modulating damper</li><li><strong>With Reheat:</strong> HW coil or electric heater</li><li><strong>Series Fan-Powered:</strong> Fan runs continuously</li><li><strong>Parallel Fan-Powered:</strong> Fan during heating only</li></ul><h4>Selection Parameters</h4><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Parameter</th><th>Range</th></tr><tr><td>Max CFM</td><td>50-5,000</td></tr><tr><td>Min CFM</td><td>20-50% of max</td></tr><tr><td>Inlet velocity</td><td>1,000-2,500 fpm</td></tr><tr><td>Pressure drop</td><td>0.2-0.5 in. w.g.</td></tr><tr><td>NC rating</td><td>25-35</td></tr></table><h3>11.2 Fan Coil Units</h3><h4>Configurations</h4><ul><li><strong>Vertical:</strong> Under windows</li><li><strong>Horizontal:</strong> Above ceiling</li><li><strong>Cassette:</strong> Exposed ceiling panel</li></ul><h4>Piping</h4><ul><li><strong>Two-pipe:</strong> Changeover seasonal</li><li><strong>Four-pipe:</strong> Separate H/C coils</li></ul><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Parameter</th><th>Range</th></tr><tr><td>Capacity</td><td>6,000-48,000 BTU/hr</td></tr><tr><td>Airflow</td><td>200-1,600 CFM</td></tr><tr><td>External SP</td><td>0-0.5 in. w.g.</td></tr></table><h3>11.3 Unit Heaters</h3><ul><li><strong>Hot Water:</strong> 10,000-500,000 BTU/hr</li><li><strong>Gas:</strong> Direct or indirect, 80-93% eff, must vent</li><li><strong>Infrared:</strong> Radiant, heats objects not air, great for high-bay</li></ul><h3>11.4 Other Terminals</h3><ul><li><strong>Baseboard:</strong> Finned-tube, perimeter heating</li><li><strong>Radiant Panels:</strong> Heating 100-300 BTU/hr/SF, Cooling 15-40 BTU/hr/SF</li><li><strong>Chilled Beams:</strong> Induced air through coil. MUST control dewpoint!</li></ul>

<h3>Learning Objectives</h3><ul><li>Understand NC and RC noise ratings</li><li>Calculate sound levels in spaces</li><li>Specify vibration isolation</li></ul><h3>12.1 Noise Fundamentals</h3><ul><li><strong>Sound Power (Lw):</strong> Energy from source (manufacturer data)</li><li><strong>Sound Pressure (Lp):</strong> What we hear (depends on distance/room)</li></ul><p>Octave bands: 63, 125, 250, 500, 1000, 2000, 4000, 8000 Hz</p><h3>12.2 NC Curves</h3><p>Noise Criteria - max octave band levels for background noise.</p><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Space</th><th>NC</th></tr><tr><td>Concert hall, theater</td><td>15-20</td></tr><tr><td>Private office, bedroom</td><td>25-30</td></tr><tr><td>Conference room</td><td>25-30</td></tr><tr><td>Open office</td><td>35-40</td></tr><tr><td>Restaurant, retail</td><td>40-45</td></tr><tr><td>Mechanical room</td><td>50-60</td></tr></table><h3>12.3 RC Curves</h3><ul><li><strong>RC-N:</strong> Neutral - balanced</li><li><strong>RC-R:</strong> Rumbly - excess low freq</li><li><strong>RC-H:</strong> Hissy - excess high freq</li></ul><h3>12.4 HVAC Noise Sources</h3><ul><li>AHU: Fan, motor, casing radiated</li><li>Duct: Regenerated at fittings, breakout through walls</li><li>Terminal: VAV damper, diffuser turbulence</li></ul><h3>12.5 Noise Control</h3><h4>Source</h4><ul><li>Select quiet equipment</li><li>Larger, slower fans are quieter</li><li>Smooth airflow</li></ul><h4>Path</h4><ul><li><strong>Lining:</strong> 1-2 in. fiberglass</li><li><strong>Silencers:</strong> 3-10+ dB/band</li><li><strong>Plenum:</strong> Lined chambers break path</li></ul><h3>12.6 Vibration Isolation</h3><table border="1" style="width:100%;border-collapse:collapse;"><tr><th>Type</th><th>Deflection</th><th>Application</th></tr><tr><td>Rubber pads</td><td>0.1-0.3 in.</td><td>High-speed equip</td></tr><tr><td>Neoprene</td><td>0.2-0.5 in.</td><td>Fans, small pumps</td></tr><tr><td>Springs</td><td>1-4 in.</td><td>AHU, large pumps</td></tr><tr><td>Air springs</td><td>3-10 in.</td><td>Sensitive equip</td></tr><tr><td>Inertia base</td><td>w/ springs</td><td>Reciprocating</td></tr></table><h4>Guidelines</h4><ul><li>On grade: Springs for low-speed, neoprene high-speed</li><li>Upper floors: Springs required</li><li>Above occupied: Min 2 in. deflection</li><li>Reciprocating: Inertia base + springs</li><li>Flex connectors at isolated equipment</li></ul><h3>12.7 Specifications</h3><ul><li>Max NC/RC per space type</li><li>Require sound power data in submittals</li><li>Specify isolation type and deflection</li><li>Show lining/silencers on drawings</li><li>Field testing for critical spaces</li></ul>