How to exhaust a conventional dryer and range hood in a passive house?

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Jonathan Kaplan

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Jan 3, 2014, 1:25:30 AM1/3/14
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What's the best solution for managing range hood and dryer exhaust in a tight SF passive house?
 
Here in California it appears that code requires the kitchen range hood to be exhausted to the exterior at 100cfm or more.  The lowest cfm hood I could find for a kitchen island hood  is 200-290 cfm.   The AirPohoda ERV I plan to use can kick in 20 cfm or so of surplus air, but I assume the rest will need to come from a rather large engineered opening with a motorized damper.
 
Similarly, the dryer must have an exhaust to the exterior unless its a condensing (vent-less) unit.  Condensing dryers seem to be smaller, less efficient, less convenient (slower)  and run on electricity which requires triples the source energy relative to my existing natural gas dryer when supplied by our utility here.    Do I really have to give up the conventional gas dryer for one that doesn't work as well and is less efficient?
 
In our moderate climate in San Francisco, heating the make-up air for these units is not a big deal, if I did the math right,  but adding lots of motorized dampers and large openings seems like a recipe for leaks and maintenance issues...
 
Huge thanks in advance for any advice....  Best, Jonathan

Cody Farmer

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Jan 3, 2014, 7:45:43 AM1/3/14
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Jonathan; depending on the number of bathrooms and exhaust points on ramp up you may have the CFM requirement for the kitchen available. If you can publish the link to your special San Francisco code. Does it say anything about continuous ventilation requirements? Hopefully your local code folks are friendly. We do a lot of personal time with our local code offices and it is helping. I love it when they get the ahh Ha! moment. (venting the dryer and including an exhaust fan..RUBBISH!!  Might as well leave the front door open for makeup air!)

My family recently came back from Ireland and was forced to use the condensing dryer...They said it was slower but worked very well.

I'm in the active search for one as well for the Travelers Rest passive house. The reviews have gone up in a positive way since I last shopped.  Our project is in the middle of gas land drilling. With-in eyesight you can see 5 to 6 drill rigs actively opening up mother earth. We like natural gas too, but the site of the drilling makes my belly churn.. The parody in our project is that we can't connect to any gas even though there are 5 new 15" lines running through the center of the 80 acre field Traveler's is being erected on.

Perhaps for your project run the gas line for back up, and try the condensing dryer and let us all know how the owners adjust. Hopefully your exterior finish will allow a hole later if needed for the dryer.

Happy New Year all--Cody


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Adam Cohen

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Jan 3, 2014, 8:21:02 AM1/3/14
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We have been using interlocked dampers for vented appliances.  Because the testing of the air tightness needs to be done with pressurized and depressurized motorized dampers are the only real solution.  You will need two dampers per appliance, one for intake air and one for exhaust, do not rely on your ERV for the additional air.  For a dryer, you put an intake under the dryer with a damper in that line and a damper on the exhaust line.  You will need to interlock the dampers with the dryer motor and DO NOT FORGET TO VERIFY that your code official will not have kittens with a damper in the exhaust line.  (Point out standard weighted backdraft dampers).

For an exhaust hood it is similar, but we dump the outside air right behind the range in a thin insulated duct that vents on top.  

Here are two:

Good Luck!
Adam Cohen
Certified Passivhaus Consultant - North America and Europe
Registered Architect, LEED AP, NAHB Green Professional
Design/Builder of the First US Passivhaus Public School Building
2012 VSBN Green Designer of the Year
2013 Green Builder Green Home of the Year


Structures Design/Build, LLC
5104 Bernard Drive
Roanoke, VA 24018

Web site: www.structuresdb.com
Commercial Passivhaus information: http://passivscience.com/
Passivhaus information: http://www.passivehousedesign.us/
More Passivhaus info: http://www.viking-house.us/

    

Jonathan Kaplan

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Jan 3, 2014, 10:13:08 PM1/3/14
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Steve Tjiang

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Jan 4, 2014, 7:34:17 PM1/4/14
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Jonathan,

I don't have a passive house but we did have to deal with some of these issues when we built our "near-passive" house.  I'm in Palo Alto.

Range hood:  At least in our city, a range hood that exhaust outside is not required by code.  We have a recirculating hood.  We boost our HRV (Zehnder Comfoair 350) when cooking and it is more than enough to keep the kitchen and house dry.  We also have an induction cooktop, not a gas one....so there are no combustion products or need for make-up air to worry about.  I highly recommend an induction cooktop for this and other benefits.  I would never buy anything but an induction cooktop from now on.

Dryer:  We opted for a condensing dryer (and am trying to convince the family to hang our clothes to dry).  It is a little less efficient but if you consider all the conditioned air you lose with an exhausting dryer it might not be a bid deal.  Also the condensing dryer heats up the house so that's a benefit on those cold SF summer nights, although I doubt this is necessary in a passive house.

The code however, does say a laundry room has to have a exhaust for future "upgrades" (LOL).  The inspector won't let us get away without an exhaust even though we are using a condensing dryer.  My contractor installed the exhaust and we just sealed it back up after inspection with a removable plug made from foam. I'll unplug it if we ever sell the house.

Hope that helps.

-- Steve

---- Steve (KZ6LSD)

Bronwyn Barry

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Jan 9, 2014, 5:16:08 PM1/9/14
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Hi Jonathan (et al)

This is a classic PH issue and there have been a number of solutions already implemented here in California to address this conflict between code and ideal PH theory. Some project teams have elected to work directly with the local code official to have them approve an 'alternate means and methods' use of the ERV/HRV as the exhaust vent system. That option is a lot of work, but it has been done. In the One Sky Homes projects I've worked on (one new, the other a retrofit) we've used a conventional direct vent kitchen exhaust hood and added a separate make-up air vent below the cooktop.  Neither the hood or make-up air vent are connected to the ERV/HRV. From the comfort and performance data that have been collected on both these projects, this solution doesn't appear to be adversely affecting either the internal temperature/comfort or overall performance of our projects.  That said, this is likely due to the fact that we're in California and don't (typically) have extreme temperature differentials to deal with.  (Sorry all you Northwesters!)

I do hope we'll see you at one of our upcoming PHCA events.  (Easiest way to keep up with us is on Meetup: http://www.meetup.com/Passive-House-California/ or via our website: www.passivehousecal.org. You'll be able to talk directly to many of the designers, architects and contractors working on PH projects here in California.

Happy 2014 everyone.

Best regards,
Bronwyn Barry


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Bronwyn Barry, CPHD, Assoc. AIA
Certified Passive House Consultant
Director - One Sky Homes
t: @passivehouseBB and @oneskyhomes

     

Tad Everhart

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Jan 13, 2014, 10:06:35 PM1/13/14
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Jonathan,
There are several passive houses in Portland with range ventilation hoods which do not exhaust to outdoors and rely on the hoods to filter the air and the HRV ventilation system to exhaust it.

I've used this since January 2010, and even with our gas range/oven, we've had no problem with city approval or IAQ.  

We have a sensitive CO monitor, and the only time it detects CO is when we use our gas oven.  That's rare, and we simply operate our HRV at its measured maximum 187 cfm exhaust (with 63 cfm measured exhaust from the kitchen exhaust).  We have a CO2 monitor nearby, and only the oven will push us over 1,000 ppm.  We're saving for a conduction stove top and electric oven.

Our commissioning test results are attached for our ZehnderAmerica CA350.  

Our kitchen exhaust is shy of 100 cfm, but it is sufficient as other air passes through the kitchen on the way to the nearby bathroom (with 34 cfm measured exhaust).  Also, I believe most people take the position that continuous kitchen exhaust allows a lower intermittent exhaust rate.

As you'll note from the attached report, when we want exhaust primarily from bathrooms (e.g, for peak moisture loads like my teenager's showers), we activate (from switches in any of the 3 bathrooms) a damper that increases the exhaust rate in all 3 bathrooms.  

We find this is essential to quickly remove most of the moisture from the bathroom when a person takes a long shower.  That reduces the exhaust from the kitchen, but we get nearly 60 cfm exhaust from each bathroom.  

This has not caused problems with kitchen ventilation.  Probably because the downstairs bathroom is pulls part of its exhaust air through the kitchen.  Also, most bathroom moisture loads are morning showers and kitchen ventilation needs are highest in the evening.  At any rate, we've had no problems.

Recently, PDX Living LLC and Green Hammer both separately obtained written approval from the City of Portland for substituting mechanical (HRV) exhaust system for range hoods vented to the outdoors.  Both relied on the fact that the kitchen exhaust was continuous. 

action=entry&appeal_id=10080


When we retrofit our home to be a passive house we moved our gas-fired clothes dryer to our garage.  However, since then I have reviewed condensing and heat pump dryers.  

Years ago, we elected to wait for a heat pump dryer even thought it would have less waste heat than a condensing dryer.  Another factor in my decision what learning that some condensing dryers use potable water to condense the moisture in the dryer air.  

I understand that heat pump clothes dryers may be available this year in the US.  However, they are complicated mechanically, and we hope we've found a solution for indoor winter clothes drying that has the virtue of simplicity and synergy.

Especially as our complex, technological living arrangement cause long-term damage to the Earth, I'm persuaded that our solutions must be as simple as possible.  I am indebted to Katrin Klingenberg for teaching that simplicity must always be a guiding design principle.

For years, we've hung damp clothes in the bathroom nearest our clothes washer.  Our washer has a high-speed spin, so they are not as wet as clothes from old washers.  They dry quickly on the portable drying racks we leave in the shower stall (another way that continuous HRV ventilation helps).  We find that clothes dry easily overnight. Then if you prefer your clothes softer, you can give them a short run in the dryer with a damp towel.

However, there are lots of things we don't want to hang up in our bathroom.  So, we recently purchased an Asko clothes drying cabinet which sits right next to our clothes washer (where our dryer was before we exiled it to the garage).  

It is a metal cabinet roughly 2 feet square and 6 feet tall.  It includes a 34-watt fan, 1,200-watt resistance heater, and 52 feet of clothes rods.  It is rated to dry a full load in 1.5 hours (with heat) or about 8 hours (without heat).  

Again, a mechanical, balanced whole-house ventilation system makes this possible since we can exhaust the moist air from the cabinet directly into the exhaust ducts and exhaust the moisture outside the house.  With heat recovery, we'll not only get dry clothes but heat our house with the 1,200-watt heater.

Our utility's source energy is 40% coal, and I'm working to change that.  However, we pay a premium to purchase 100% wind power so that at least we nudging our utility to a cleaner source.  And there is almost always plenty of wind at least somewhere in Oregon all winter. 

We haven't used the cabinet yet, but hope to soon.  Hope to have it operating by month's end.

Good luck!

Tad

Tad Everhart

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Jan 13, 2014, 10:10:35 PM1/13/14
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Jonathan,

Here's the attachment.

Tad

On Thursday, January 2, 2014 10:25:30 PM UTC-8, Jonathan Kaplan wrote:
2009-796 Everhart Residence HRV_rev010310.pdf

Steve Tjiang

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Jan 13, 2014, 11:59:49 PM1/13/14
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Tad,

In your reply, you said that heat pump dryers were coming to the US this year.  Can you direct me to more information?  I would love to find out more.  We went with the condensing dryer (Bosch which does not use any water to cool the air for condensation).  But having seen the heat pump dryers in Switzerland I would like to look into getting one.

---- Steve (KZ6LSD)


Tad Everhart

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Jan 14, 2014, 1:47:05 PM1/14/14
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Steve,

Thanks for the information on the Bosch condensing dryer.  

To my knowledge, the person with the most information about when HPCDs hit the US market is Christopher Dymond at NEEA (and note he does not like to be called Chris, but prefers his entire first name).  See http://neea.org/about-neea/staff?page=2  

I spoke with Christopher about two months ago, and he is helping bring HPCDs to market and can tell you his predictions.  NEEA's Conduit site doesn't appear to be updated on this particular technology.  See https://conduitnw.org/Pages/Article.aspx?rid=190

I've attached a study on HPCDs.

How does the Bosch condense the moisture out of the air in the drum?

Tad Everhart , Certified Passive House Consultant   
Green Building Consultant 


Earth Advantage // Better Buildings Now


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European Study of Heat Pump Clothes Dryers D3B64d01.PDF

Steve Tjiang

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Jan 15, 2014, 9:35:27 AM1/15/14
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Tad,
The condensing dryer has a heat exchanger that uses room air to cool the drum's air. It does heat up our laundry room good and it takes a long time, 2 hours per load.

Another downside of condensing dryer besides the long drying time is that since lint is not exhausted filter maintenance is important. More so than a regular electric dryer. There are several filters too.

Tad Everhart

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Jan 15, 2014, 9:57:41 AM1/15/14
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Steve,

Thanks for the explanation.  It explains why drying takes so long.  I expect that using 70 F household air through a heat exchanger for a condenser doesn't remove as much of the moisture as the systems which use cold water (50 F) in the heat exchanger condenser.  The heat pump dryer replaces the simple heat exchanger with a heat pump.  I believe an important part of the development of the HPCDs has been filters.

Thanks, again.

Tad

Tad Everhart , Certified Passive House Consultant   
Green Building Consultant 


Earth Advantage // Better Buildings Now


John O'Brien

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Jan 15, 2014, 1:34:13 PM1/15/14
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As someone with 3 cats, and 2 gian dogs. Filter maintenance is a pain
in the ass. Especially since in order to access the pump resevoir, one
needs to dismantle half of the dryer.

A clever engineer with dogs would have put a simple removeable panel
over the pump resevoir.
I will probably end up just dremeling out a hole the next time.

J

Jonathan Kaplan

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Jan 25, 2014, 12:07:59 AM1/25/14
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This is a very rich collection of thoughtful responses.  Huge thanks to all of you!
 

On Thursday, January 2, 2014 10:25:30 PM UTC-8, Jonathan Kaplan wrote:
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