Saturday, June 7, 2014

The Future of Residential Heat Recovery is Ductless

I just took ownership of the first ERV to be sold at Home Depot
Price $475
Extra stuff I learned about it once I got my hands on it:
1. The 16cfm mode, medium, (perfect for a 2 person bedroom) is only 0.3 sones at 4 watts. Almost inaudible.
2. Low speed is 8cfm (the one person setting) is 0.1 sones which is TOTALLY inaudible.
3. It can cycle on humidity if desired. That is, it will come on when the humidity reaches 45%RH (low), 55% (medium), or 65% (high). If the indoor humidity exceeds the set point, the unit is switched to high speed.  If the indoor humidity is within 5% of the set point, the unit operates at medium. If humidity is 5% below the set point, the unit switches to minimum speed.  This sounds like a reasonable control strategy for winter, but in the dry Mountain West, it would always be on low speed.  It sounds like the wrong control strategy for summer.
4. It pretty much is a ripoff of the Lunos design, but I don't know if either design is patented anyway.
It's not synchronized like the Lunos but I believe synchronization is unnecessary, and actually reduces the total house airflow.
5. The US distributor, Zoltan, will give a quantity discount, which gets it down to a price I can justify in new construction spec homes and rentals.  With a name like that, he knows all about predicting the future
6. The exterior vent cover is an elaborate, good looking, bomb proof fabrication of stainless steel.

7.  When the unit is off, it has a high quality, very tight powered plastic damper.

In my opinion, if the bedroom doors are left open except at bedtime, Fick's Law of Diffusion will ensure that fresh air will reach the rest of the house.   (The average speed of an air molecule flying around the room is 500m/s)  That means a three bedroom house may only need 3 total units.

Other important things that should be mentioned:
A.  Perfect zoning
B  Dead simple commissioning.
C.  Wires are easier to run than ducts.
D.  More total holes in the walls. (Bad)
E.  Inherent frost protection.

1 comment:

  1. Here's why I don't think two fans need to be synchronized:

    I did a quick thought experiment on the issue:
    In a Pretty Good House (PGH), total airflow would be nearly double if the two fans are "fighting" each other instead of synchronized. That's because a PGH isn't nearly tight enough to prevent these fans from pushing and pulling 64 cfm through its walls and ceiling.
    Q. But isn't all that flow is coming through cracks in the house?
    A. Yes.
    Q. Doesn't that affect the amount of heat recovery?
    A. Probably not, because the materials in the walls act as a regenerative heat exchanger when subjected to a cycling air flow regime.
    Q. Isn't that 64 cfm going to cause problems in the walls?
    A. No. It's only 64 cfm. In a PGH, that much air cruises through whenever it gets slightly windy. But when it's forced and cycled, at least you get that fresh air where you want it (bedrooms), when you want it (while sleeping).

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