HVLS Fan Selection Tool

Building & Environment Inputs

Ambient Temperature (°C)

Valid range: 25 – 42°C

Building Width (m)

Building Length (m)

Building Height (m)

Desired Cooling Effect (°C)

Range shown is min (90% RH) to max (10% RH). Select based on your humidity conditions.

@ 90% Humidity (min)

—

@ 10% Humidity (max)

—

Heating Season — Destratification Savings

If used in a Heated Building (Destratification)

Building height 5 m

Temp diff floor–ceiling 7.0°C

Destrat energy savings 15%

Destratification: For heating season, blow air towards the floor at 10% of full speed for excellent destratification. This will achieve at least the recommended 1 AC/hr required for good destratification under all conditions.

Fan Selection Results — GOR-DCI Series

Model	Coverage Ø (m)	No. of Fans	Fans (W×L)	Spacing – Width (m)	Spacing – Length (m)
Calculating…

Click a row to select a fan model and view the floor plan layout below. N/A indicates the selected velocity is outside the effective range for that model.

Floor Plan Layout

↑ Click a fan model row above to generate the floor plan

Introduction

The Elta Asia HVLS selection tool is designed to help select Gorilla HVLS fans. These fans improve thermal comfort in an indoor environment by assisting with the cooling and heating of building occupants.

The tool is available in two versions: Basic and Advanced. Both use the calculation methodology from ASHRAE 55-2017 Thermal Environmental Conditions for Human Occupancy to predict the cooling effect of air velocity.

Background Information

Cooling Effect

Air movement does not reduce the air temperature — it cools the skin through evaporation and convection. The amount of skin cooling (the cooling effect) depends on several factors:

Air temperature
Relative humidity — higher humidity reduces the evaporative cooling effect
Occupant activity level — higher activity generally produces more perspiration and more cooling
Clothing — more clothing means less skin exposed for cooling
Air velocity

Destratification

In a heated building, hot air rises and a temperature gradient forms between floor and ceiling. The temperature difference increases by approximately 1.4 °C for every 1 metre of building height. In a 10 m building, the ceiling could be ~14 °C warmer than the floor.

HVLS fans can bring the warm ceiling air down and mix it — a process called Destratification. For good destratification, the building requires at least 0.5 air changes per hour, and velocities must remain below 0.2 m/s to avoid occupant drafts.

Elta Asia recommendation: Select fans for cooling effect. Fans selected this way will also provide excellent destratification when run at 10% of full speed blowing downward — delivering >0.5 AC/hr and keeping ground-level velocities below 0.2 m/s.

We recommend blowing air downward in most scenarios. Running in reverse (blowing up) at higher speed risks warm air not reaching the floor due to structural obstructions such as purlins, and uses more energy.

About the Basic Selection Tool

The basic tool makes the following assumptions about occupants:

CLO (Clothing level) = 0.57
Trousers and a short-sleeve shirt

MET (Activity level) = 2.0
Walking at 3.2 km/h on a level surface

It also assumes standard atmospheric pressure, no external heat sources, and no hot radiant surfaces nearby.

Because the cooling effect depends on relative humidity, the tool calculates at both extremes. The lower value in the dropdown corresponds to 90% RH (worst case) and the higher value to 10% RH (best case).

For full control over these variables — including exact humidity, MET, CLO, mean radiant temperature, and atmospheric pressure — use the Advanced Calculator.

How to Use This Tool

Enter the building width, length, and height in metres. The tool works for simple rectangular buildings only.
Enter the ambient air temperature. This updates the Desired Cooling Effect dropdown with values calibrated to that temperature.
Select the desired cooling effect from the dropdown. The range shown (e.g. 2.0 – 3.5 °C) reflects performance at 90% and 10% relative humidity respectively.
The tool calculates the coverage diameter for each fan model needed to achieve the selected cooling effect.
Based on coverage, it determines the number of fans and their spacing across the floor plan.
Click a fan model row to generate the proportional floor plan below, showing fan positions and coverage circles.

The coverage diameter represents the average cooling effect between floor level and 1.5 m height within that zone. The actual cooling effect inside the coverage circle may be greater than predicted, provided there are no obstructions.

Energy Savings

Heated Buildings

For heating season, the tool estimates the percentage heating energy saving from destratification, based on the temperature gradient created by the building height.

Frequently Asked Questions

Does the fan mounting height change the cooling effect?

Elta Asia CFD analysis has shown that, unless a fan is positioned very close to the floor, the distance between fan and floor does not significantly affect ground-level velocity. All fans mounted between 4 m and 15 m produce almost identical ground air velocity. The only exception is a large fan mounted less than 3 m above the floor, which may slightly increase ground velocity. In summary: fan mounting height does not impact cooling effect for typical installations.

I change the temperature but the coverage diameter doesn't change. Is something wrong?

No — this is by design. The selection programme applies minimum and maximum limits to coverage diameters to ensure reliable real-world performance. For example, a larger fan could technically cover a greater area for a 1 °C cooling effect, but real-world obstructions would reduce velocity at large distances. The limits ensure the system will perform as predicted. You may therefore see the same coverage diameter across different temperature inputs.