Replies

1. 
   Anon3 | Mar 21, 2017 06:22pm | #1

   Do you actually use the exhaust fan much to matter? An ERV exhaust from bathroom 24/7 is a much better idea.

2. GBA Editor
   Martin Holladay | Mar 22, 2017 05:07am | #2

   Lance,
   Panasonic's specs on the FV-05VK3 WhisperGreen fan claim 12.4 cfm/watt.

   So the 16.4 cfm/watt claimed by AirKing fan beats the Panasonic claim of 12.4 cfm/watt.

   Note, however, that these claimed efficiencies occur at a static pressure of 0.1 inches w.g. Once you connect a typical ducting system (usually including an elbow or two), your static pressure will go up and your efficiency will go down.

   -- Martin Holladay

3. 
   lance_p | Mar 22, 2017 06:21am | #3

   Agreed. I still find it very interesting to see the envelope being pushed.

   Interesting to note that, on the Energy Star listing they claim peak efficiency occurs at maximum airflow:

   130cfm = 19cfm/W
   80cfm = 18.2cfm/W
   30 = 9.7cfm/W

   I was going to post a link to the ES page but it's being blocked.

4. GBA Editor
   Martin Holladay | Mar 22, 2017 06:37am | #4

   Is this the link you tried to post?
   http://www.airkinglimited.com/page/m-energy-star-d4-exhaust-fan.html

   --Martin Holladay

5. 
   lance_p | Mar 22, 2017 08:08am | #5

   It was this link to the Energy Star site listing for the DL4S model.

   Thanks for posting the company's product page. It looks like they have yet to update their own specs to match the ES page. Their site claims 40-120cfm, ES lists it at 30-130cfm.

6. GBA Editor
   Martin Holladay | Mar 22, 2017 09:55am | #6

   Lance,
   Perhaps this is the link:
   https://www.energystar.gov/productfinder/product/certified-ventilating-fans/details/2261807

   -- Martin Holladay

7. 
   lance_p | Mar 22, 2017 09:58am | #7

   That's the one! Thanks Martin. There are many versions of this fan between all the lights and sensors available, but they all share the same airflow specs.

8. 
   lance_p | Mar 22, 2017 09:59am | #8

   In response to reply #1 (all I see is N/A N/A for a poster name?), there are many people who install exhaust only ventilation systems who would be very interested in the most efficient fan available for a 24/7 application. I personally would prefer a ducted ERV as you suggest, but that doesn't mean it's the most desirable solution for everyone or every situation.

   Look at it another way; how much more efficient would an ERV be with these fans installed running 24/7? If bathroom fans are getting this efficient the technology will soon spill into other ventilation products as well.

9. 
   Anon3 | Mar 22, 2017 11:19am | #9

   Nah, we pretty much reached maximum efficiency when it comes to fans. The reason ERV uses more watts is because of pressure loss(through the core, the bigger the core, the more pressure loss, but the better efficiency, but more watts) and the need to perform filtration. Did you know that filters are designed to be replace when 1" pressure loss is reached? Checkout the fan curve, it should be flat, and not decreasing.

   It's actually more important for the intake fan to maintain constant airflow over different pressure losses, like the panasonic one is doing, to prevent negative pressure happening once filter loading occurs.

10. 
    lance_p | Mar 22, 2017 01:59pm | #10

    Curious about duct losses, I found this site:

    http://www.freecalc.com/ductloss.htm

    I'm sure the "average" installation of a bathroom vent fan would be a hideous contraption compared to this proposal, but let's see what a semi energy conscious installer could accomplish. Let's face it, someone spending big bucks on an exhaust fan is more likely to insist on getting the details right.

    I modeled a 6" diameter galvanized duct 10' long with three "4-piece" 90 degree elbows at 1.5D, "none" for an entry (ideal since the fan connects directly to the pipe), and a 45 degree tapered contraction with a 4" diameter outlet (to simulate a reasonably restrictive exterior vent). The total duct loss on that configuration is 0.065" of water @ 80CFM, and that duct would cover a reasonably complicated install that covers 10 feet and goes up and over an obstacle (two elbows) before turning down (3rd elbow) through a soffit vent.

    A much more direct and efficient installation might look closer to this; a 6" diameter galvanized duct 5' long with one "4-piece" 90 degree elbow at 1.5D, "none" for an entry (ideal since the fan connects directly to the pipe), and a 45 degree tapered contraction with a 5" diameter outlet (to simulate a reasonably free-flowing exterior vent). The total duct loss on that configuration is 0.02" of water @ 80CFM, and would cover a more direct install going out over the wall and turning down (one elbow) into a reasonably efficient soffit vent.

    Both of these scenarios should, in the case of a flow-regulated fan, exceed the 80CFM @ 0.1" water specifications by quite a margin. This would have a reasonable impact on the fan's energy use over time, percentage wise if not in real $ saved due to the low overall power requirement.

    Yes, I'm splitting hairs, I get it. But as I said before, someone spending 3-4x what a basic exhaust fan costs would be far more interested in the install details I would think.

    Comments WRT use in ERVs noted, and likely 100% true at higher flow rates. At lower flow rates, however, the core and filtration restriction drops dramatically and at 24/7 usage could make a significant difference in yearly power consumption. A 2000sqft four occupant household ventilating at 50CFM continuously with a 100CFM capable ERV could certainly see some savings.

    I know, I know... small potatoes, but I think it's fun to look at the details as the envelope gets pushed further and further.