Thursday, October 13, 2011

Lifestyle compromises in an ultra-energy efficient home (or welcome to the world of ventless dryers)

Autumn at our patch of dirt
(This blog entry was written by Paul)

A Passive House uses 10% of the heating energy of a traditionally built house.  Once you spend the extra time, effort and money on designing and building a home to the Passive House standard are you done?  Is it business as usual living in a Passive House or do you need to make some compromises?

So far, we’ve been asked to get comfortable with two things that are a little different from our current way of doing things, tilt-turn windows and ventless dryers.

Double or hung or sliding windows don’t cut it in terms of energy efficiency.  They just don’t seal well enough at the seam where the windows on different tracks meet.  In the US, we have casement windows which create a much better seal, but the most energy efficient windows being made are from Europe.  These European windows use a tilt-turn system.

After searching the web to learning about tilt-turn windows, I only had one concern.  Because the windows open by tilting inwards, I was worried about being able to close a blind or shade with the windows open.  Since our house is going to have one foot thick walls, the windows can be installed such that there is a very deep window sill.  This will allow the windows to tilt in without breaking the plane of the inside walls.  Having spent the last several winters up here in northwest CT with less efficient sliding windows, I look forward to having tilt-turn windows that really keep the heat inside the house.

Ventless dryers were a different story.  The problem with a vented dryer is that it pumps quite a bit of air from the room where the dryer is located directly out of the building envelope.  One of the fundamental principals of a Passive House is air tightness.  The only air that enters or exits the envelope should be through the energy recovery ventilation (ERV) system.  Vented dryers are inconsistent with this principal.  (Dear ERV designers, it would be really cool if one could vent their dryer through the ERV system)

So, vented dryers won’t work with a Passive House.  What’s so bad about a ventless dryer? 

  • Might be slower than vented dryers:
  • Are smaller than vented dryers (7.3 c.f. vs 4.2 c.f.)
  • Are much more expensive than vented dryers.
  • Are reportedly less energy efficient (excluding venting issues, but this is difficult to confirm since no dryers have an EnergyGuide).
  • Require periodic cleaning of the condenser
  • Air cooled condensers heat up the room they occupy (I think that all the ones I’ve seen on the market are air cooled)
  • Water cooled condensers use additional tap water
  • A bunch of lint that gets through the lint trap to the condenser seems like it will be making it’s way to the septic system.
  • No need for a vent that forces hot air out of your house at > 100cfm which must be replaced with cold air from outside.
  • Air cooled condensers heat up the room they occupy (nice in the winter)
There are not a ton of models available in the US:

Cubic Feet

 4.2                  LG       DLEC855W
3.95                 Bosch  WTE86300US
4ish                  Miele   T8013C
4ish                  Asko    793C

In Europe and Asia, they also have heat pump dryers which are just like condenser dryers but 40% more efficient.  Bosch apparently has a model, the EcoLogixx 7 that uses the condensed water to clean itself reducing maintenance.  But in the US, the vast majority of dryers sold are vented, so we don’t have access to the latest and greatest in ventless dryer technology.

The main issue is that the ventless dryer is going to make doing laundry take twice as long to do.  We’ll need to do two dryer loads for every one that we currently do.  We’ve decided that we can live with this.  We might try to get around this by buying a second dryer for the laundry room.

So, as far as I can tell, apart from issues with the clothes dryer, living in a Passive House shouldn’t require much in the way of lifestyle compromises.

If you’re interested in reading more about ventless dryers in a Passive House check out