WC ENGINEERINGBuilding Specifications
Location: Jacksonville, FL
Facility type: electronic casino
Conditioned floor area: 2,420 sf
Design occupant load: 59 persons
Heat gain from the building envelope, lighting, electrical equipment, and occupants determines the HVAC system’s cooling load
Design Conditions
Infiltration rate: 1–2 ACH (air changes per hour, typical range)
Breathing zone:
Between 3″ and 72″ above finished floor (AFF)
At least 24″ from walls or air supply openings/equipment
Indoor relative humidity (per ASHRAE & ACCA):
Recommended comfort: 30%–60% RH
Cooling design: ~50% RH (40–60%)
Heating design: ~30% RH (often 30–40%)
Note: <20% RH may cause dryness/discomfort; >60% RH may promote mold and IAQ issues
Indoor design temperature (heating, DB):
70°F per ACCA Manual J
68˚F–72°F per ASHRAE 55 / Fundamentals (commonly 72°F)
Indoor design temperature (cooling, DB):
75˚F per ACCA Manual J
72˚F–76˚F per ASHRAE 55 / Fundamentals
Outdoor design dry-bulb temperature: 92.8˚F (1% cooling), 28.6˚F (99.6% heating) per ASHRAE Climatic Data
∆T (cooling) = Tₒ – Tᵢ = 92.8°F – 75°F = 17.8°F
Heat Gain
Basic formula: Q_dot (cooling) = U × A × ∆T
More accurate method: use Cooling Load Temperature Difference (CLTD) instead of ΔT
CLTD (°F) selected for light construction and a 95°F outdoor design dry-bulb (DB) temperature
Note: Even with CLTD, a ~15% error may still occur
Rough Estimation
Cooling load ≈ 0.25 to 0.35 tons per 100 sf of conditioned floor area
Q = 2,420 ft² × 0.30 tons / 100 sf = 7.26 tons
Outdoor Ventilation Air: Sized per ASHRAE 62.1 (~15%–25% min. outdoor air intake)
Roof Heat Gain
A = 2,420 ft² with 3 ft attic air space
R-values: 1.79 (½" acoustical ceiling tile), 30 (9¼" R-19 insulation)
Overall U-value = 1 / R_total = 0.03 Btu/h·ft²·°F
Q_roof (cooling): U × A × CLTD = 0.03 × 2,420 × 28 = 2,033 Btuh
Doors Heat Gain
(2) insulated 1-¾″ metal doors, east wall
A_door: 80″ × 36″ × 2 = 40 ft²
Q_doors (cooling) = 0.40 × 40 × 16 = 256 Btuh
Concrete Slab Heat Transfer
Thickness = 4" (0.333 ft)
∆T = 5°F
A_face = 2,420 sf
A_exposed_edges = 0.333 ft × (41 ft × 2) = 27.3 sf
U_face = 0.05 Btu/h·ft²·°F
U_edge = 0.81 Btu/h·ft²·°F
Q_slab = [(0.05 × 2,420) + (0.81 × 27.3)] × 5 = 716 Btuh
East Wall Heat Gain
A_wall_gross = 128″ (10.67 ft) × 41 ft = 437 sf
A_wall_net = gross wall area (437 sf) – windows (80 sf) – doors (40 sf) = 317 sf
R-values (wall assembly):
Outside air film (7.5 mph wind): 0.33
Concrete block (lightweight, 12" CMU): 2.04–2.56
Plywood (¾″): 1.08
Gypsum board (½″): 2.22
Inside air film (vertical): 0.68–0.69
Q_E_wall = U_total × A_wall_net × CLTD = 0.15 × 317 × 16 = 761 Btuh
West Wall Heat Gain
The wall assembly matches the east wall, with a 1″ stucco finish (R = 4.76)
Total wall area = 82 sf + 36 sf = 118 sf
Wall above windows = 24″ × 41 sf = 82 sf
Wall between windows: 16.5″ × 104″ × 3 = 36 sf
Q_W_wall = 0.09 × 118 × 16 = 170 Btuh
Windows Solar Heat Gain
Concepts & Factors
Solar radiation through glazing significantly affects space heat gain, especially during peak sun hours (~ 3–5 hrs/day).
Equations
Q_fes = (A_s × SHGF + A_sh × SHGF_sh) × SC
Q_fs = Q_fes × CLF (accounts for time lag, space load)
Parameters
A_s = Unshaded glass area = [1 – (SL / window width)] × A_tot
A_sh = Shaded glass area = A_tot – A_s
SHGF = Solar Heat Gain Factor (Btu/hr·ft²), based on latitude (32°N) and hottest month (June)
SHGF_sh = Shaded SHGF, adjusted for orientation and month
SC = Shading Coefficient (depends on glass and shading device)
SL = Shade Line = SLF × shadow width from overhang
SCL (Solar Cooling Load) = SHGF × CLF
CLF = Cooling Load Factor (accounts for time lag effect)
GLF = Glass Load Factor = SCL × SC
Glass Area
Area of door (aluminum frame single-pane glass) = 72” x 104” = 52 sf
Area of (6) windows = 66” x 104” = 48 sf
Total glass area = 52′ + (48′ x 6) = 340 sf
Method 1 (less accurate)
U = 1.27 Btu/hr-sf-°F
Q_windows = 1.27 x 16 x 340 = 6,910 btuh
Method 2 (more accurate)
Overhang width = 101″ → SL = 0.8 × 101 = 81″
A_s = [1 – (81/104)] × 340 = 75 ft²
A_sh = 340 – 75 = 265 ft²
SHGF = 1,169 Btu/ft²·day ÷ 8 hrs = 146 Btuh·ft²
SHGF_sh = 142 W/m² × 0.0929 × 3.41 = 45 Btuh·ft²
SC (shading coefficient): 1.0 (no shade), 0.50 (blinds or translucent roller shades), 0.25 (white shades)
Q_windows = (75 × 146 + 265 × 45) × 0.50 = 11,438 Btuh (with shades)
Lighting Heat Gain
Method 1 (less accurate)
Common Space Type: Computer Room
Lighting Power Density (LPD): 0.94 (from 2021 ASHRAE Handbook Fundamentals, Table 2 Lighting Power Densities Using Space-by-Space Method)
Q = 3.412 × 0.94 W/sf × 2,420 sf = 7,762 Btuh
Method 2 (more accurate)
Equation
Q = 3.412 × W × BF × CLF
Parameters
3.412 = conversion factor from watts to Btuh
W = lighting power in watts
BF = Ballast Factor (accounts for heat loss in fluorescent lamp ballasts)
CLF = cooling load factor (accounts for heat storage in lighting fixtures, typical value = 1.0)
Lighting Fixtures
(25) 4′ × 2′ fixtures, each with (4) U-bend T12 lamps (48″ length), Ballast Factor: 0.92
(6) 2′ × 2′ fixtures, each with (2) T12 lamps (24″ length), Ballast Factor: 0.94
Lamp Power: 32 W
Q_lighting = 3.412 × [(25 × 4 × 32 × 0.92 × 1.0) + (6 × 2 × 32 × 0.94 × 1.0)] = 11,277 btuh
Occupant Heat Gain
Equations
Sensible heat: Q_s = qs x n x CLF
Latent heat: Q_l = ql x n
Parameters
Activity type: office work
Activity level: moderate
Sensible heat gain per person (qs): 250 btuh
Latent heat gain per person (ql): 200 btuh
Number of occupants (n): 59
Diversity factor: 0.9
CLF (capacity of space to absorb and store heat): 0.91 – 1.0
Q_occupants_undiversified = (qs + ql) x n = 450 btuh/person x 59 = 26,550 btuh
Q_occupants_diversified = 26,550 x 0.9 = 23,895 btuh
Equipment Heat Gain
Power Consumption
Computers: (59) with 21″ monitors, 130 W each (continuous)
Computer: (1) with 15″ monitor, 110 W (continuous)
Televisions: (2) 50″ (Westinghouse), 151.3 kWh/yr each
Refrigerator: (1) 15 ft³, 510 Btuh
Laser printer: (1) 240 Btuh
Coffee maker: (1) 2,590 Btuh
(1) 8-head soda machine: 2,185 Btuh
Other office equipment: 25% of nameplate power
Q_computers_21″ = 3.412 × (59 × 130 W) = 26,170 Btuh
Q_computer_15″ = 3.412 × 110 W = 375 Btuh
Q_televisions = 2 × 151.3 kWh/yr × 0.3895 (Btuh per kWh/yr) = 118 Btuh
Q_equip_undiversified = 32,188 Btuh
Q_equip_diversified = 32,188 × 0.7 = 22,532 Btuh
Total Load (roof + doors + slab + walls + windows + lighting + occupants + equipment):
Q_total = 2,033 + 256 + 716 + 761 + 170 + 11,438 + 11,277 + 23,895 + 22,532 = 73,078 Btuh
Ventilation Air
Basis: ASHRAE 62.1, Table 6.2.2 (Gaming Area / Casino)
Rp (per person): 15 CFM/person
Ra (per area): 0.06 CFM/ft²
Pz (occupant load): 59 persons
Az (conditioned floor area) = 2,420 ft2
Ez (distribution effectiveness): 1.00
Equations
Ventilation rate in the breathing zone outdoor air: Vbz_dot = Rp × Pz × Ra × Az
Zone outdoor airflow: Voz_dot = Vbz_dot / Ez
Voz_dot = (5 × 59 + 0.06 × 2,420) / 1.0 = 440.2 cfm
Design ventilation rate = 445 cfm (rounded up to the nearest 5 cfm)
Sensible Cooling of Ventilation Air
Sensible heat (h_s) = 1.08 × Voz_dot × ∆T = 1.08 x 440.2 ft3/min x 17.8°F = 8,462 btuh
Reference: https://engineeringtoolbox.com/cooling-heating-equations-d_747.html
Return duct leakage and return fan heat gains are assumed negligible.
Latent Cooling of Ventilation Air
Latent heat (h_l) = 4,840 × Voz_dot × dw_lb
Humidity ratio difference (dw_lb) = 0.0206 lb water/dry air
Mean coincident wet-bulb temperature (T_wb) = 25.4°C = 77.7°F
Latent heat (h_l) = 4,840 x 440 ft3/min x 0.0206 = 43,870 btuh
Total Cooling Load
Total heat (sensible + latent): h_t = h_s + h_l = 8,462 + 43,870 = 52,332 btuh
Q_t = Q_l+s_r + h_t = 73,078 + 52,332 = 125,410 btuh / 12,000 = 10.5 tons
Alternative Method
Total heat (h_t) = 4.5 x Voz_dot x dh
Enthalpy difference (dh) = h_o - h_i
h_o = 45.5 (using psychrometric chart at T_db = 92.8˚F and dw_lb = 0.0206)
h_i = 28 (using psychrometric chart at T_db = 75˚F and RH = 50%)
h_t = 4.5 x 440.2 x (45.5 - 28) = 34,666 btuh
Q_t = Q_l+s_r + h_t = 73,078 + 34,666 = 107,744 btuh / 12,000 = 9.0 tons