Equipment selection for Hvac Design such AHU Cooling Towers chillers etc..

  let’s go step-by-step through the complete HVAC equipment selection procedure (AHU, chiller, cooling tower, etc.) using a commercial building project as an example.

🔷 Example Project Summary

Building: 10-story commercial office tower

Built-up area: 20,000 m² (approx. 215,000 ft²)

Location: Hot & humid climate (e.g., Dubai / Mumbai / Houston)

Function: Office spaces, meeting rooms, cafeteria, lobby, data room

System type: Central chilled water system with Air Handling Units (AHUs), Fan Coil Units (FCUs), chillers, cooling towers, and pumps.

🧩 Step-by-Step HVAC Equipment Selection Procedure

Step 1: Load Estimation

Objective: Determine the total cooling (and heating, if required) load for the building.

Procedure:

Collect Architectural & Engineering Data:

Floor plans, elevations, sections

Wall, roof, and glass types (U-values, shading)

Occupancy, lighting, and equipment density

Orientation and location (for weather data)

Ventilation & fresh air requirements (ASHRAE 62.1)

Calculate Cooling Load Components:

External Loads: Solar, walls, roof, glass, infiltration

Internal Loads: People, lights, equipment

Ventilation Load: Fresh air latent & sensible

Miscellaneous: Elevator machine rooms, server rooms, etc.

Software Tools:

HAP (Carrier), Trace 3D+, Elite CHVAC, or manual (CLTD/CLF or RTS method)

Example Output:

Total Cooling Load = 1400 TR (Tons of Refrigeration)

Sensible heat ratio (SHR) = 0.78

Step 2: System Selection

Objective: Decide what type of HVAC system best suits the project.

Options:

All-air system (central AHU + ducting)

Air-water system (AHU + FCU)

Water system (chilled beams, etc.)

Packaged or split systems (for smaller areas)

Example Decision:

Use a Chilled Water System with:

Central Chiller Plant (water-cooled chillers)

AHUs for each floor zone

FCUs for cabins/server room

Cooling towers and primary-secondary pumping

Step 3: Zoning

Objective: Divide building into zones based on orientation, usage, and load patterns.

Example:

Zone Description Load (TR)

Zone 1 North-facing floors 200

Zone 2 South-facing floors 300

Zone 3 Interior zones 400

Zone 4 Lobby, cafeteria 150

Zone 5 Data room & misc. 50

Total 1100 TR (with diversity)

Step 4: Equipment Selection

A. Chiller Selection

Input Data:

Total cooling load: 1100 TR

Diversity factor: 0.9 → Design load = 990 TR

Chilled water: 44°F (6.7°C) supply / 54°F (12.2°C) return

Condenser water: 85°F (29°C) supply / 95°F (35°C) return

Select Chillers:

Type: Water-cooled centrifugal chillers

No. of chillers: 2 working + 1 standby

Capacity per chiller: 500 TR

COP ≈ 6.0 (or IPLV ~ 6.5)

Manufacturer: Trane / Carrier / Daikin / York

Power Requirement:

500 TR × 2 = 1000 TR actual

Power ≈ 0.6 kW/TR → 600 kW total

B. Cooling Tower Selection

Heat Rejection = Load + Compressor Work

 

= 1000 TR + (1000 / 6.0) = 1167 TR ≈ 4.1 MW

Select Cooling Tower:

Type: Induced draft counterflow

Water flow rate: 3 gpm/TR → 3000 gpm

Temperature range: 95°F → 85°F

Approach: 7°F

No. of cells: 3 (each 400 TR)

Material: FRP or galvanized steel

C. Pumps Selection

Chilled Water Pump:

Flow rate = 2.4 gpm/TR → 2400 gpm

Head loss (estimated) = 70 ft

Power ≈ 60 HP per pump

Configuration: Primary (2 duty + 1 standby), Secondary (2 duty + 1 standby)

Condenser Water Pump:

Flow rate = 3.0 gpm/TR → 3000 gpm

Head loss = 60 ft

Power ≈ 75 HP per pump

D. Air Handling Units (AHUs)

Determine AHU requirements per zone:

Based on floor-wise loads.

Floor Load (TR) Airflow (CFM @ 400 CFM/TR) AHU Size

1–3 150 TR 60,000 CFM 3 AHUs of 20 TR each

4–7 200 TR 80,000 CFM 4 AHUs of 20 TR each

8–10 150 TR 60,000 CFM 3 AHUs of 20 TR each

Total 500 TR 200,000 CFM 10 AHUs

Select AHUs:

Cooling coil: 6-row chilled water

Face velocity: 450–500 fpm

Filter: MERV 8 pre + MERV 13 final

Fan type: Backward-curved plug fans (VFD-driven)

Supply air temp: 55°F (12.8°C)

E. Fan Coil Units (FCUs)

Small zones / cabins / data rooms.

Typical capacity: 1–5 TR each.

Supply: 44°F chilled water.

Return air & fresh air through separate ducts.

Step 5: Ducting and Piping Design

Design air ducts based on velocity (main duct ~1500 fpm, branch ~800 fpm)

Calculate static pressure for fan selection

Design chilled/condenser water piping (use friction loss 2–4 ft/100 ft)

Include balancing valves, strainers, expansion tanks, etc.

Step 6: Controls & BMS Integration

Chiller sequencing

VFD control for pumps and fans

AHU temperature & humidity control

Differential pressure sensors

Energy meters and performance monitoring

Step 7: Equipment Schedule (Summary Example)

Equipment Quantity Capacity Remarks

Water-cooled chiller 3 500 TR each 2W + 1S

Cooling tower 3 400 TR each FRP type

CHW Pump 3 2400 gpm, 70 ft head 2W + 1S

Condenser Pump 3 3000 gpm, 60 ft head 2W + 1S

AHU 10 20 TR each VFD, CW coil

FCU 25 2–5 TR Ceiling mounted

Expansion tank 1 1000 L 

Chemical dosing & makeup 1 set — 

Step 8: Validation

Cross-check loads vs. equipment capacity.

Confirm flow rates, coil face area, air velocity, and noise levels.

Verify compliance with ASHRAE, SMACNA, and local energy codes.

Step 9: Documentation & Submission

HVAC Design Report

Equipment Data Sheets

Schedules and BOQ

Manufacturer Selections

Layout Drawings (plant room, AHU rooms, piping, ducts)

✅ Final Outcome:

A fully optimized HVAC system where each piece of equipment (AHU, chiller, pump, cooling tower) is selected based on accurate load, redundancy, energy efficiency, and maintainability.

A complete HVAC equipment selection record for a commercial project.

I’ve also included formulas and sample data for clarity.

🧾 HVAC Equipment Selection Template (Excel Format)

Sheet 1: Project Summary

Parameter Description Example

Project Name “ABC Commercial Tower”

Location Dubai

Total Built-up Area (m²) 20,000

Floors 10

Design Conditions Indoor: 24°C DB, 50% RH / Outdoor: 43°C DB, 28°C WB 

System Type Water-cooled chilled water system

Cooling Load Software HAP v5.13

Total Calculated Cooling Load (TR) =SUM(Zones!C2:C10) 1,400

Diversity Factor 0.9

Design Load (TR) =B9*B10 1,260 TR

Sensible Heat Ratio (SHR) 0.78

Sheet 2: Zone Load Summary

Zone / Floor Area (m²) Load (TR) Sensible Load (TR) Latent Load (TR) Airflow (CFM) =Load*400 Notes

GF Lobby 2,000 150 120 30 60,000 High occupancy

Floors 1–3 6,000 300 240 60 120,000 South orientation

Floors 4–7 8,000 400 310 90 160,000 Mixed orientation

Floors 8–10 4,000 150 120 30 60,000 North orientation

Data Room 300 40 40 0 16,000 24x7 load

Cafeteria 500 50 40 10 20,000 High latent

Total 20,800 1,090 TR 870 220 436,000 

Sheet 3: Chiller Selection

Item Parameter Unit Formula / Value Example

Design Load TR =‘Project Summary’!B11 1,260

No. of Chillers Nos. 3 (2W + 1S) 3

Capacity per Chiller TR =B2/B3 420

Type Water-cooled centrifugal 

COP 6.0 

Chilled Water Flow gpm =TR*2.4 1008 

Condenser Water Flow gpm =TR*3.0 1260 

Power Input kW =TR*(0.6) 252 

Manufacturer Trane / Carrier / York 

Notes Include VFDs and BMS interface 

Sheet 4: Cooling Tower Selection

Parameter Unit Formula / Value Example

Heat Rejected TR =Load + (Load/COP) 1,260 + 210 = 1,470

Flow Rate gpm =Load*3.0 3,780

Temp Range °C 35 → 29 

No. of Cells 3 (2W + 1S) 

Cell Capacity TR =B2/B5 490

Type Induced Draft, FRP 

Approach °C 4 

Fan Power kW 15 per cell

Total Power kW =15*2 30

Notes Include drift eliminators & water saver

Sheet 5: Pump Selection

Pump Type Flow (gpm) Head (ft) Efficiency Power (HP) =FlowHead/(3960Eff) Qty Remarks

Chilled Water Primary 2,520 70 0.75 =252070/(39600.75)=59 2W+1S VFD driven

Chilled Water Secondary 2,520 60 0.80 =252060/(39600.8)=48 2W+1S VFD driven

Condenser Water Pump 3,780 60 0.80 =3,78060/(39600.8)=72 2W+1S Duty/standby

Sheet 6: AHU Selection

Zone/Floor Load (TR) Airflow (CFM) AHU Qty CFM/AHU Coil Type Fan Type Filter Supply Temp (°C) Notes

GF Lobby 150 60,000 3 20,000 6-row CW Plug Fan (VFD) MERV 13 13 With return fan

1–3 Floors 300 120,000 6 20,000 6-row CW Plug Fan MERV 13 13 Zonal AHUs

4–7 Floors 400 160,000 8 20,000 6-row CW Plug Fan MERV 13 13 –

8–10 Floors 150 60,000 3 20,000 6-row CW Plug Fan MERV 13 13 –

Total 1000 TR 400,000 20 AHUs      

Sheet 7: FCU Selection

Room Load (TR) Airflow (CFM) Type Coil Qty Remarks

Meeting Rooms 3 1,200 Ceiling 4-row CW 5 

Server Room 5 2,000 Floor 4-row CW 2 24x7 duty

Cabins 1 400 Ceiling 4-row CW 10 

Total 17 

Sheet 8: Summary of Equipment

Equipment Qty Capacity Flow (gpm) Power (kW) Type / Remarks

Water-cooled Chiller 3 420 TR 1008 252 Centrifugal, VFD

Cooling Tower 3 490 TR 1260 15 Induced Draft, FRP

CHW Pump (Primary) 3 2520 gpm 70 ft 44 Inline VFD

CHW Pump (Secondary) 3 2520 gpm 60 ft 36 VFD driven

Condenser Pump 3 3780 gpm 60 ft 55 VFD driven

AHU 20 20 TR each — — 6-row coil

FCU 17 1–5 TR — — 4-row coil

Expansion Tank 1 1000 L — — Bladder type

Chemical Dosing Unit 1 — — — For closed loop

Sheet 9: Notes & References

Section Standard / Reference

Load Calculation ASHRAE Handbook – Fundamentals

Ventilation ASHRAE 62.1

System Design ASHRAE 90.1, 2022

Ductwork SMACNA Duct Design Manual

Pumps Hydraulic Institute Standards

Water Quality ASHRAE 188 (Legionella)

Controls BMS integration, BACnet protocol

🧮 Optional Formulas (for Excel)

You can paste these directly into Excel:

=Load_TR*2.4 # Chilled water flow (gpm)

=Load_TR*3.0 # Condenser water flow (gpm)

=Flow_gpm*Head_ft/(3960*Eff) # Pump HP

=Load_TR*400 # Airflow (CFM)

=Load_TR*(1+1/COP) # Heat rejected (TR)

📦 Deliverables You Can Generate from This Template

Equipment data sheets (auto-fill from Excel)

BOQ (Bill of Quantities)

Schedules for drawings

Load reports

Selection justification sheets (for consultant approval)