Selecting HVLS Fans

 

Selecting HVLS Fans


What is an HVLS Fan?

HVLS stands for High Volume, Low Speed. The HVLS fans are becoming increasingly popular replacing conventional fans in spaces such as auditoriums, schools, factories, warehouses, greenhouses, hangars, churches, large commercial units etc. Typically, they come in sizes ranging from 7 to 24 ft diameter. Although less common, the term HVLD (High Volume Large Diameter) is also sometimes used.


Considerations while opting for HVLS fans

  1. Site Conditions

  • These fans are meant for circulating air in large spaces.  For a 7 ft fan, approx. 24 ft width and length is desirable for efficient and effective use. 

  • Building height is important while choosing HVLS fans. Typically, these fans are mounted at a height of 20 to 22 ft from the ground. Mounting the fan too high may cause the air to get dispersed before it reaches the required cooling area and conversely if it is mounted too low, it may fail to cover the required cooling area.

  • Shape of the circulation area can have an impact. A square or circular shape is more suitable compared to rectangular shape.

  • The ceiling or the girder should be suitable to support the weight of the fans, which can range from 45 to 75 kg for gearless fans and almost double for geared fans. The mounting hardware may add to this weight.

  • Obstructions below the fan can considerably affect the airflow. This becomes a key consideration in warehouses having storage racks, offices having cubicles. The furniture at the ground level can also cause obstruction to the airflow as the airflow in HVLS fans is a vertical column coming down, hitting the floors, dispersing away horizontally and moving up in a vertical column.

  • The placement of lights should be such that they do not cast strobing shadows of blades when the fan is rotating.

  • Direct hot air flow or radiated heat from outside should be minimal.

  • Although conventionally we think of ceiling mounting of fans, there are manufacturers offering floor mounted HVLS fans, where the fans are inverted and mounted on rigid poles.

  • The fans may be used in fully enclosed or semi-enclosed areas

  • There should be no hanging objects nearby that can swing and come in contact with the rotating fan blades

  • The fan control cables must be placed away from any audio-visual or communication cables and equipment to avoid signal interference


  1. Application

  • For auditoriums, factories, showrooms, event venues etc. that have large spaces requiring air circulation

  • The space usage of the building is an important aspect to be considered while deciding to use HVLS fans. If the space is used generally to its full capacity, the HVLS is ideal. If most of the time only a small portion of the space is used and the portion used is not fixed, a distributed fan system is a better option, in which only the fans in the required zone can be switched on and off as per the requirement.

  • Where a low noise level is required, the HVLS fans is a better option as the noise created by several conventional fans running simultaneously is very high. There are HVLS fans with noise levels less than 40db.

  • The HVLS fans may also be used in conjunction with the air conditioners for energy saving. The circulating air can provide nearly the same thermal comfort level at five degrees higher temperature setting in the AC. Same is true of heating. Using HVLS fans with heating can provide better comfort at lower energy costs by destratification.

Advantages

  • High volume of air flow - usually in the range of 300,000 to 600,000 cmh (cubic meters per hour) is common in HVLS.

  • High area coverage – as a thumb rule, the coverage is usually 3 to 3.5 times the diameter of the fan.

  • Most of the HVLS fans are very silent. There are few with noise level <35db, in which case you can hardly hear the fan rotating. During concerts etc. this low noise level certainly adds to the quality of performance and in prayer places it can help in creating a prayerful ambience.

  • Better cooling compared to conventional fans. With HVLS fans one can expect the thermal comfort level of about five-degree differential compared to ambient temperature. It  must be understood that the fans do not cool the air like air conditioners do. The feeling of cooling is by taking away skin temperature through convection and evaporation. The level of cooling depends on various factors such as type of clothing, relative humidity, activity being conducted etc.

  • Lower speed results in reduced maintenance.

  • Due to high efficiency and high volume of air flow, the overall energy cost is reduced. A 25 to 30% cost reduction can normally be expected.

  • The airflow is smooth without breaks, giving a feeling of pleasant three dimensional natural breeze. Manufacturers have their unique blade designs to achieve this smooth airflow.

  • HVLS fans help in reducing the humidity by evaporation, making them more suitable for high humidity areas.

Disadvantages

  • High investment cost compared to conventional fans. For a given area, the initial investment can be anywhere between 6 to 8 times that of conventional fans.

  • Maintenance turnaround time is high compared to conventional fans. MTR (Mean Time to Repair) is an important parameter to be taken into consideration in asset procurement. This is one of the important factors to be considered where the asset in question has a direct bearing on the revenue. For example, for an event venue, seven days for repair may mean loss of seven days revenue. If a conventional fan breaks down, you may buy a new one and replace the defective fan within a few hours. These can be easily accessed using a ladder and are locally available. Even a spare fan may be available. HVLS fans on the other hand may not be readily available in most of the locations and also a factory trained technician, necessary spares etc. may not be available. The turnaround time or the time to put a faulty fan back into service may take around a week.

  • Due to the height of installation, the accessibility for cleaning of the blades and maintenance can be challenging. 

  • The advantage of switching-on fans only in the required zone is not available in HVLS fans. The fan must be switched on even if only a small portion of the space is being utilised.

  • Not suitable for work areas where light materials are used, which can be easily blown away by high volume of air flow.

  • Not suitable for areas where certain rituals using fire or candles are performed.

  • The conventional fans can be installed and maintained by local electricians but the HVLS fans need to be installed and maintained by a professional technician, usually trained by the manufacturer.

  • Due to the risk associated with their large size, weight and mounting height, ongoing safety monitoring may be necessary.


Selection Criteria - Technical

The selection of fans must be done using techno-commercial evaluation. For asset procurement the life cycle cost is generally taken into consideration which includes not only the cost of initial procurement, but also the  operational costs such as energy consumption, cost of maintenance, cost of any consumables. Other factors to be taken into account for decision making are residual value at the end of useful service life and the disposal recovery value (or in some cases disposal cost) etc. 


For a fair comparison, a common unit should be used for comparing technical parameters. The grade of aluminium used for the blades may be stated in different standards, in which case a common standard equivalent may be derived for comparison. The volume of airflow for one manufacturer may be stated in cfm (cubic feet per minute) and the other in cmh (cubic meter per hour). They should be converted to one common unit. 


Some of the technical features to be considered are discussed briefly below.

  1. Type of Motor

Two common types of motors found in HVLS fans are BLDC (Brushless DC) and AC Synchronous Motor. 

BLDC (Brushless DC) motors can be of two types – with embedded sensors or sensor less. Due to its height, in case of any failure of the sensors due to lightning surge etc. the whole fan unit needs to be taken down and therefore sensorless BLDC are preferable. 


The electromagnetic interference of BLDC motors with other electronic circuitry, especially the audio visual is very low due to which one need not worry much about the placement of the controls and wiring with respect to other equipment and wiring. 


AC Synchronous motors can be with permanent magnets or without permanent magnets. The permanent motor synchronous motors (PMSM) use permanent magnets in the rotor and winding in the stator. The speed is regulated by varying the frequency using a variable frequency drive (VFD). 


Motor cooling – Generally the motors are air cooled. However, some manufactures offer liquid cooled versions as well. From a maintenance point of view, air cooled are preferable. The normal operating temperature of the motor should be taken into account.


  1. Geared or gearless (direct drive)

The gearless motors are better as there is no lubrication, no annual maintenance, no AMC, low noise, no leakages etc. Within the geared category, there are some fans with integral geared motors and some where the fan, reduction gear and the motor are separate units, which are then assembled. Alignment of the three can pose a challenge and any misalignment can result in reduced MTBF (Mean Time Between Failure), increased maintenance cost. In any rotating equipment, the lesser the rotating parts, the lower is the maintenance cost related to wear and tear and lubrication, which means compared to gearless fans, the cost of maintenance of geared fans is much higher. 

Gearless motors are also lighter, making the mounting fittings and hardware more cost effective. For old buildings, due to their lighter weight, gearless fans are recommended. The lighter fan also means less wear and tear.

  1. Fan blades, material, finish

Number of blades – higher the number, lower can be the speed for the same volume of airflow.

The material must be suitable for withstanding corrosion and any effect of fumes in the work environment. The blade finish may be anodized or powder coated. In case of powder coating, a glossy finish can mean reduced dust accumulation and easy cleaning. While the powder coating can offer different shades to match the decor, the anodised finish offers ease of maintenance. Aerofoil type blades offer more rigidity compared to sheet formed blades.

  1. Safety

Due to the weight and height of mounting, safety becomes one of the prime considerations. The mounting components, material, guy wire etc. are important from safety considerations. The number of guy wires, their material and size should be taken into consideration

  1. Air flow

The volume of air circulated for one hour is an important consideration because ultimately this measure indicates the effectiveness of the fan. Some manufacturers provide this data in cfm whereas others give this in cmh. The data must be converted to one unit for a consistent comparison.

Selection Criteria - Commercial

Some of the commercial parameters to be considered for selection are:


  • Basic price

  • Taxes

  • Packing & shipment

  • Transit insurance

  • Availability of local representative

  • Installation and commissioning cost

  • Number of fans installed

  • Years in business (for fans)

  • Annual maintenance cost

  • Breakdown response time

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