Covid-19 Ventilation Control

We will describe below methods in improving the filtration aircon system to mitigage/reduce the risk.

Introduction: Air filters in AHU, PAU. HEPA filters

Most important factor is airchange and fresh air. Second, Better air filters which can increase airchange and or efficiency.

1.  Most buildings are equipped with secondary filters MERV13-15 air filters. Research showed the MERV13 filters control and removed the more highly contagious influenza and marked reduction for flu,rhinovirus and TB. Most commercial office AHU are NOT designed and not required to install HEPA filters which drastically reduce airchange, ventilation or fresh air which is most important. Many filters in market claim to be HEPA but infact misinterpreted  and not standards tested as "HEPA" as Secondary/Final high efficiency filters like MERV14,MERV16 SemiHEPA.

2. Increase airchange and fresh air which promotes ventilation. This can be done by replacing dirty air filters and shorter replacement frequency. Do not wash the air filters. Fresh air can also be done by opening windows and doors to allow outside air to mix. This is opposite to during Haze which has contaminated air outside. A fan blowing out can be used to exhaust room air for cross ventilation. Filters change to be timely. Do not wait till last minute to change air filters (no air). Always standby or store some air filters.

3. Use Better air filters means higher efficiency, better airchange and lower pressure drop which means higher airchange.

Action Plan Solution: Use of Air filters

1. Secondary filters min MERV13/14 is a must have in the AHU/PAU. C90 Ccell MERV14,15 and C90N, VH10 Vcell MERV16 (99%@1-3um) has higher efficiency and able maintain same airflow. Put back secondary filters if there is already slot.

2. Increase the efficiency of pre-filters. Recommended ES65 IF (MERV11) or ES13 IF (MERV13) or ES14 IF (MERV14) Pleated Box panel filters. They are low cost, interchangeable to existing prefilters and unlikely affect existing airflow except shorter replacement period and can be replaced disposed as sacrificial filter.

3. For FCU or areas without secondary filtration or no slot, C90 2in MERV14 (2,4" thickness), ES13 IF MERV13 or ES14 IF MERV14 (1,2,4" thickness) can be used. Sizes can be customised. Quick short term retrofit for old aircon or ducted FCU with no available slot.

4. ES65 Media Rolls 0.61x180mx3mm thickness (MERV10) can be used quickly to cover AHU. Note the filter frequency may increase.

Carbon filters are not required but it can help control the alcohol or smell. (unlike in haze)

 **  Do not attempt to use two layer of MERV14 filters, it does not mean high filtration but may decrease airflow, inhibit the airflow and airchange ventilation unless the aircon is designed to handle. It will far be better with higher airchange by use of  1st layer prefilters to capture bigger particles to protect the secondary filters instead.

Secondary, SemiHEPA filters

Most secondary filters like bag filters are (SH) Single header construction which will suit most AHU universal holding frames.

1. Vcell of 12" depth SH Model:VH10 MERV16, V98 MERV15, V90 MERV14

Pros: Higher Airchange, very low pressure drop, very high efficiency

2. Minipleat Ccell 2",3",4" depth/thickness available in Model: C90 of MERV14,15, CH10 of MERV16

No Header/Box (NH):      2" depth , Gi 4", 3"

Single Header (SH): Gi 4" depth

Pros: Slim 2",4" thickness, various sizes

Prefilters or Secondary filters

3. Model: ES65 IF, ES13 IF, ES14 IF ES Pleated 24x24x2" (595x595x45mm)

Depth: 1",2",4"  (Box, NH)

can Interchange with all prefilters in AHU, PAU, FCU

Pro: Slim 1-4" thickness, various sizes, long life


Being Manufactured in Singapore factory, we are churning out air filters as we give priority and allocation to priority services, existing customers, hospitals and prevent unnecessary stockpile by individual.

Please be patient to us, Please email to This email address is being protected from spambots. You need JavaScript enabled to view it. to facilitate queries. 


Other Information, Efficiency Chart for Removal of viruses

Efficiency increase when air filters are loaded with dust! This natural fundamental filtration mechanism may not apply to other filtration mechanism like electronic filtration. Virus like MS2 phage size is about 0.027um =27nanometers, particle size less than 0.1um(micron) or 100nm, the removal efficiency actually increases. So we expect SemiHEPA MERV16 99%@>1um (1000nm) is equivalent to 99%@<0.03um (30nm).

Removal Efficiency of MS2 phage virus size: 0.027um =27nanometers

 ASHRAE 52.2 

When loaded w dust

for MS2 Phage

When clean

for MS2 Phage


1-3um %  


3-10um%   Type of products
MERV16 99.6 99.3 >95


>95-99   VH10, CH10
MERV15 99 95 >85 


>95-99 V98, IP90,C90/98
MERV14 99 87 >75 >90-#96 >95-99 V90, IP90,C90,IFR90
MERV13 93 70 >50  >85-#92 >90-99 ES13,C80,IP80
MERV11 91 60 >20 >65 >85 ES65 IF
MERV 8 91 57 - >20-#50 >70 IF40 Pleated
MERV 7 90 50 - - (>#30) >50 IF30 Pleated
MERV6-8 79 40 - >35 Prefilter Roll T209,T350

 * Ours secondary filters V90,IP90,C90 are tested and expect to filtration efficiency of MERV15.

BFE:Bacterial Filtration Efficiency is typically used for mask and tested lower velocities for reference which expects the size of bacterial or virus due to filtration mechanism increase when mass size decreases below 0.3um or 30nm

# You will expect Higher filtration efficiency for our high quality air filter products as it meets more than the required standard.

HEPA air filters

"True" HEPA(High Efficiency Particluate Air) filters are removal efficiency >99.97%@0.3um also call absolute HEPA. Most consumer market or air purifiers "HEPA" operate at lower airflow, if tested to 2.5m/s, they could be in range of MERV14,15 or 16 air filters. Most commercial office AHU are NOT designed to use HEPA filters and may expect near or ZERO flow when installed, drastically reduce airchange ventilation. The recommended airchange is 12 per hour. Hospitals isolation wards,Biosafety labs usually design negative pressure (min-6Pa), Biosafety Cabinets uses HEPA 99.99% which are properly designed to protect the personnel and environment.

ES65 Media Roll or ES14 IF pleated for Smaller aircons cassette units: 

This unique permanent charged electrostatic product in roll form can be cut and used in smaller aircons as flat disposable media, ES65 Media can be used in lower airflow velocity achieves MERV10 like small unit Ducted FCU,Cassette units. Due to high efficiency, they need to be changed often 1-3mths and coil must be clean before use. A plus point is you will expect coil to be clean state after use for longer time.

Information: No products in roll forms for MERV13

Please note there is NO products in roll form for secondary aircon filtration of MERV13, 14 or typically above MERV8. The reason is the design pressure drop is too high and thus must be in panel pleated air filters. Many claim to achieve the MERV13 or 14 efficiencies are usually tested at very low velocities which is different from ASHRAE 52.2 MERV tests at rated face velocity 2.5m/s. Thus they will be irrelevant to use in commerical, industrial aircon and will have much low efficiencies. They often marketed as roll filter media in which they required to be constructed manufacture into pleated, bag, minipleat rigid filters for use in HVAC aircon.

** Note information are provided as accurate of our knowledge and limits any liability or consequences that could arise from using them.

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