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Re: Sharp Bypassing and KC-Z40-W (Japan) Room Size

A Reader writes:

In one of your answers to inquiries you (it was actually a reader who contributes frequently) found information from Sharp about bypassing.

You wondered why it wasn't easier to find.

Sharp have told me this info isn't available. This is a good example of the refusals to answer my questions and delayed answers from Sharp's so called service center in Japan that I have been receiving for the last 3 months.

I have been trying to find out about Sharp's Plasmacluster series because they have HEPA filters which reduce the hot particle radiation from the Fukushima nuclear incident.

I have the KC-Z40-W which is not sold overseas (outside Japan). The brochure says it can clean the air in a 30 square meter room in 15 minutes.

My living room is 20 square meters and has 2 entrances which cannot be closed.

Do you think the KC-Z40-W is the right machine for the space involved?

Could you tell me where I can find information about bypassing in Sharp machines?

A Reader.

Ed's Reply

Hey Reader;

Sharp Electronics is a global corporation, with many products other than air cleaners.

Despite the good quality of their air cleaners, and the genius of the plasma-ionizer as a replacement for the ozone which preceded it in the market, Sharp has a number of issues.

As you have observed, customer service does not have first hand experience responding to air cleaner questions of a technical nature.

Sharp's regional divisions result in market specific products, with different names and specifications, in every part of the world.

The resulting confusion combines with a planned-obsolescence marketing strategy to make product evaluation difficult and replacement filters sometimes scarce.

Bypassing is designed into almost every air purifier, only the very best are exempt.

Bypassing cannot be measured easily, and changes with filter loading and fan power setting.

Bypassing is incorporated into many cheaper designs to reduce warranty claim costs and allow cheaper motors and fans in lower quality machines.

Clogged filters will overheat these motors, so enough space must be left around the filters for some cooling air to slip by.

Premium units, like IQAir, have almost zero bypassing.

Low cost air cleaners will almost always leak air.

The Sharps, and others in the mid-priced group, inevitably have some bypassing. But measuring it is a very difficult engineering problem.

While we can use a particle counter to test exhaust air particle counts, it is very difficult to actually measure bypassing in the context of overall efficiency.

Again, different filter loads will have different back-pressures and therefore more or less bypassing.

So Sharp, while obviously being evasive, is really avoiding saying "We really don't know."

The best test I have devised for bypassing, and air cleaner quality in general, is to run the machine for a year, then remove filter train and run a finger tip across the interior of the air cleaner near the fan.

If you can see fine dust there, your air cleaner is bypassing. Good air purifiers will not accumulate particles behind the filter or on the fan.

For more on bypassing, including a photographic example of a cheap machine which accumulated an internal dust load over several years, see; HEPA Air Filter Efficiency; backpressure and bypassing

I inspect my family's 4 Sharps interiors each time I wash the prefilter screens. There is never a large fine dust load.

Problems with the Sharps, in my opinion, stem from marketing strategy, customer service, and filter re-supply, NOT from design flaws like excessive bypassing.

KC-Z40-W, with 4.0 cubic meters per minute (141 cu ft/min), is a bit weak.

In the US this would be a 125 CADR machine.

Your 20 square meter (215n sq ft) room, assuming an (American-style) eight-foot ceiling, has about 1720 cubic feet to clean. One air change would take about 12 minutes on high speed

This is roughly consistent with the 15 minutes advertised by Sharp for the larger 30 sq meter room.

But you will likely not run the KC-Z40-W on high all the time. Sharps Plasmacluster oxidizers do extend the room size some, so with the open entrances, the "40" series is at the lower end of the range for your application.

I personally find the chore of refilling the water tank onerous, and so the room size rating would depend on the user's willingness to keep the tank filled and the unit running on high/humidifier mode.

Best wishes,

Ed

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