Engineering Case Studies

Real-World Coil Selection Examples

See how ExCoil's calculation engine solves actual HVAC and refrigeration design challenges with rigorous thermal analysis and industry-standard correlations.

HealthcareCase Study #1

Hospital AHU: Chilled Water Coil Selection for Surgical Suite

Precise temperature and humidity control for critical healthcare environments

!The Challenge

A 200-bed hospital in São Paulo required a new air handling unit for its surgical suite complex. The design called for strict temperature control at 22°C ± 1°C with relative humidity maintained between 45–55% year-round. The existing chilled water plant operates at 7°C supply / 12°C return with a 30% propylene glycol solution for freeze protection.

Hospital AHU: Chilled Water Coil Selection for Surgical Suite

Design Requirements

Total cooling capacity: 120 kW (sensible + latent)

Air flow rate: 15,000 m³/h (face velocity ≤ 2.5 m/s)

Entering air: 32°C DB / 24°C WB (worst case)

Leaving air: 14°C DB / 13°C WB

Maximum air-side pressure drop: 250 Pa

Maximum water-side pressure drop: 45 kPa

✓Solution with ExCoil

Using ExCoil's Chilled Water calculator with glycol correction, we selected a 6-row coil with 3/8" (9.52mm) copper tubes and aluminum fins at 12 FPI. The coil face dimensions were set to 1200mm × 800mm to maintain face velocity at 2.3 m/s. The glycol correction factor reduced the water-side heat transfer coefficient by approximately 18% compared to pure water, requiring the additional rows.

Total Capacity

124.3 kW

Sensible: 89.7 kW | Latent: 34.6 kW

SHR

0.72

Adequate dehumidification for surgical suite

Leaving Air

13.8°C DB / 12.9°C WB

Within specification

Air ΔP

187 Pa

25% margin below 250 Pa limit

Water ΔP

38.2 kPa

15% margin below 45 kPa limit

Water Flow

4.2 L/s

30% glycol, ΔT = 5.0°C

Key Engineering Insight

The glycol correction was critical — an initial design without glycol adjustment would have been undersized by 15%. ExCoil's engine automatically applies ASHRAE-based glycol property corrections for viscosity, thermal conductivity, and specific heat, ensuring accurate capacity predictions.

Commercial RefrigerationCase Study #2

Supermarket Walk-In Cooler: DX Evaporator Sizing with R-449A

Transitioning from R-404A to low-GWP refrigerant in commercial refrigeration

!The Challenge

A major supermarket chain in Brazil needed to replace aging R-404A evaporator coils in their walk-in coolers as part of a fleet-wide transition to R-449A (Opteon XP40), a lower-GWP alternative. The challenge was to maintain the same cooling capacity while accounting for R-449A's different thermodynamic properties, particularly its temperature glide of approximately 5.5°C.

Supermarket Walk-In Cooler: DX Evaporator Sizing with R-449A

Design Requirements

Cooling capacity: 18 kW at -5°C evaporating temperature

Air inlet: 2°C DB / 1°C WB (cooler steady-state)

Air flow: 5,500 m³/h

Refrigerant: R-449A (GWP 1397 vs R-404A GWP 3922)

Superheat: 6°C minimum for TXV control

Maximum coil pressure drop: 15 kPa (refrigerant side)

✓Solution with ExCoil

ExCoil's DX Evaporator calculator was used with R-449A properties from the built-in refrigerant database. The temperature glide was handled by the segment-by-segment solver, which divides the coil into two-phase and superheated zones. We selected a 4-row coil with 1/2" (12.7mm) tubes and 8 FPI aluminum fins — wider fin spacing to minimize frost accumulation in the low-temperature application.

Total Capacity

18.6 kW

3% margin above requirement

SHR

0.94

Minimal latent load at low temperature

Superheat

7.2°C

Above 6°C minimum for stable TXV

Air ΔP

62 Pa

Low for energy-efficient fan operation

Ref ΔP

11.8 kPa

Within 15 kPa limit

UA Value

1,420 W/K

Effective heat transfer coefficient

Key Engineering Insight

R-449A's temperature glide actually improved evaporator performance by 4% compared to R-404A at the same conditions, because the glide creates a better temperature match with the air stream in counterflow arrangement. ExCoil's segmented solver captured this effect accurately, while simplified LMTD methods would have missed it.

Commercial HVACCase Study #3

Commercial Office: Hot Water Heating Coil for VAV System

Optimizing heating coil performance for variable air volume applications

!The Challenge

A 15-story commercial office building in Curitiba (climate zone 3 — cold winters) needed heating coils for its VAV air handling units. The design had to handle both full-load winter conditions and part-load operation down to 30% airflow. The hot water system operates at 80°C supply / 60°C return from a central boiler plant.

Commercial Office: Hot Water Heating Coil for VAV System

Design Requirements

Heating capacity: 85 kW at design conditions

Air flow: 12,000 m³/h (design), 3,600 m³/h (minimum)

Entering air: 5°C DB (winter design), 0% RH (sensible only)

Leaving air: 35°C DB minimum

Hot water: 80°C supply / 60°C return

Maximum water-side pressure drop: 30 kPa

✓Solution with ExCoil

Using ExCoil's Hot Water calculator, we designed a 2-row coil with 5/8" (15.88mm) tubes to maximize water-side turbulence at part-load conditions. The larger tube diameter ensures Reynolds number stays above 4,000 even at reduced water flow rates. Fin spacing was set to 10 FPI — sufficient for heating-only applications where condensation is not a concern.

Total Capacity

87.4 kW

2.8% margin above requirement

Leaving Air

36.2°C DB

Above 35°C minimum

Air ΔP

78 Pa

Low pressure drop for energy savings

Water ΔP

22.1 kPa

26% margin below 30 kPa limit

Water Flow

1.04 L/s

ΔT = 20°C as specified

LMTD

42.8°C

Efficient temperature driving force

Key Engineering Insight

The 5/8" tube selection was critical for part-load performance. At 30% airflow, the water flow drops proportionally, but the larger tubes maintain turbulent flow (Re > 4,000) down to 40% load. With 3/8" tubes, the flow would become laminar below 60% load, causing a dramatic drop in water-side HTC and potential control instability. ExCoil's Gnielinski correlation accurately predicted this transition.

Ready to Size Your Own Coils?

ExCoil uses the same rigorous correlations shown in these case studies — Chen (1966), Gnielinski (1976), Wang et al. j-factor, and Threlkeld wet coil method — all accessible through an intuitive engineering interface.