Comments on: Passive House Ventilation Design

By: STUART

STUART — Fri, 14 Oct 2011 02:05:44 +0000

I really liked your very informative webpage, including the “question and answer” format blog postings. I am hoping to build my retirement home in the next few years, and I am heavily researching every aspect of “green” construction in preparation. I have discovered that there is a world of eco-friendly information and construction supplies and components out there. I just have to find the right combination for my particular needs and wants. I’m sure that you know many good information resources on the internet. Feel free to suggest any or all of your favorites with me and your other readers. Thank you!

By: cgaff

cgaff — Thu, 14 Jul 2011 13:23:51 +0000

Great information here! Would you still use an ERV if you had operable windows?

By: shawn

shawn — Mon, 18 Oct 2010 13:57:59 +0000

ive been reading your house blogs for the last year. trying to incorporate passive designs into my new house. i am not an architect/engineer but did design our house that will be breaking ground in a month. i bounced my ideas off architects/engineers i know: fixed windows,sealing strategy’s,radiant heat in basement, rain water collection,solar water heat,superior walls,white metal roof,etc.

i was thinking about this all weekend – you are right. i am building in north carolina with humid summers and mild winters. i am more concerned with air quality and cooling rather than air quality and heating. ultimate stressed being concerned with just air quality. im also thinking that the erv will be pressurizing (pressuregaurd) the inside, for the few showers a day, its worth the few times id heat incoming air. versus pushing conditioned air out the vents all the time. jeez full circle on it – i have about 2 months to figure this out

By: Jim Wild

Jim Wild — Mon, 18 Oct 2010 10:59:12 +0000

Shawn,
Your post and the report makes interesting reading.
It is not always easy to put new kit and technology into old systems. The model shown by postgreen is very much the one we see in Europe, where we don’t have any other ducted HVAC. It’s all about fresh air and recovery of heat, not cooling.
HVAC solutions tend to be climate specific, though no matter where they are passive houses (not passivhaus) tend to need very little HVAC so perhaps look at how you can design out HVAC as much as possible with lots of insulation, thermal mass, moisture balancing materials, minimal solar gain, etc (it’s all out there as DIY guides) and then you may find you don’t need anything to complex to condition the space.
As an engineer I can design all sorts of HVAC to condition “poorly” designed buildings, but I love the challenge of proving that you can design a building to not need HVAC. ERV/ HVAC as the report on advancedenergy site kind of says is just too complex for domestic installers and home owners. Do you think they will ever be educated in these systems? I’m degree educated and 10 years in the job, it’s still a learning curve for me.
Jim.

By: shawn

shawn — Fri, 15 Oct 2010 16:15:32 +0000

i am looking at an erv for my new home. i contacted ultimateair – they recommend not using it to vent bathroom/kitchens. ive also found a best practices paper on ervs that also recommends not venting bathrooms/kitchens through the erv. (http://www.advancedenergy.org/buildings/knowledge_library/ventilation/erv.pdf)

whats your reasoning for venting through the erv.

By: Dan

Dan — Mon, 25 Jan 2010 13:59:12 +0000

Greenbuildingindenverdotcom,

Thanks. That makes a lot more sense. I’ve asked a lot of vendors selling these units a similar question. Not one has been able to answer how this was done. Glad I now know the “trick”.

By: greenbuildingindenverdotcom

greenbuildingindenverdotcom — Sat, 23 Jan 2010 06:30:53 +0000

Dan,

Your 50% calculations are correct based on a parallel (concurrent) flow heat exchanger. Most HRVs, including this one, are cross-counterflow. In units with large surface area, they perform like pure counterflow (countercurrent).

Counterflow heat exchangers theoretically CAN achieve 100% efficiency because the outlet temperature of the warm stream can equal the incoming temperature of the cold stream. For a picture, see http://en.wikipedia.org/wiki/Countercurrent_exchange

Chad, I was relieved that the PassivHaus rules changed just in time for you, and you didn’t have to use that goofy underground air inlet. I suspect Dr. Feist will eventually be browbeaten so badly he’ll relent on the “subslab overkill” as well.

By: Dan

Dan — Fri, 22 Jan 2010 16:05:56 +0000

First, let me correct my formula in the example I gave. The new air temp will be the equilibrium temp of the two, assuming perfect heat transfer, i.e. 100% efficiency. So in the example I gave, 40F = 0.5*(70-10) + 10 is what I should have typed.

Jim, the laws of thermodynamics say that heat always goes from hot to cold. That works to transfer the heat from the hotter outgoing air to the colder incoming air up until they reach the same temperature, 40F in the example above. That transfer stops once they are at the same temp! If you can get that incoming air up past 40F to anything approaching 70F without adding energy, you’ve rewritten the laws of thermodynamics, solved much of the world’s energy problems and are a shoe in for a Nobel.

Maybe efficiency is calculated in terms of this theoritical limit? I don’t know, but was hoping for clarification. However, it is often phased by the HEV/ERV vendors in a manor that definitely implies that 95% (or whatever) of the heat is saved. Sorry, but that is simply not possible according to the laws of physics/thermodynamics. At the very least, I think it’s important for each of us to be aware of this and not expect something that can’t be delivered.

For what it’s worth, I plan on putting an ERV system in my home that I’m building later this year. I think they are probably worth it despite the misleading claims. I hope others use them as well, but also hope they don’t have unrealistic expectations.

By: chad

chad — Fri, 22 Jan 2010 14:52:40 +0000

John – We use a recirculating range hood with a quality charcoal filter that handles all grease and smells. Good question.

By: Peter Troast

Peter Troast — Fri, 22 Jan 2010 13:28:12 +0000

All–Martin Holladay has a new post up this morning on Green Building Advisor on ERV vs HRV. It’s good.

http://www.greenbuildingadvisor.com/blogs/dept/musings/hrv-or-erv