Indoor air quality discussion

[AC_Hacker]

This is very useful information.

Originally Posted by JRMichler

Our house was... tested ... It came to 1.0 ACH50. That correlates roughly to 0.05 ACHnat (actual ACH under normal weather conditions).

I think that too many people underestimate what the Passive House target of 0.35 ACH50 really amounts to... it is almost a hermetic seal. 1.0 ACH50 is not Passive House, but is quite respectable.

So if your house is 1320 SF, and assuming 8 foot ceilings, its volume would be 10560 cubic feet, and your non-mechanical air exchange would be 528 cubic feet, and your 35 CFM (2100 CF/hour) for a total of 2628 CF/hr, which would translate to 0.25 ACH.

I did read some German research that measured improved academic performance if high school kids had ACH => 1.

Best,

-AC

[S-F]

Originally Posted by AC_Hacker

This is very useful information.



I think that too many people underestimate what the Passive House target of 0.35 ACH50 really amounts to... it is almost a hermetic seal. 1.0 ACH50 is not Passive House, but is quite respectable.



-AC

The passsivehaus blower door bust me 0.6 ACH 50. The recommendations for mechanical ventilation are something like 3-4 ACH for HRV blowers.

[Drake]

ASHRAE standard .35ACH ??? Passivehaus standard .35ACH50??? It was said that ACH50 is not same as ACH because under pressure. JRM's living .05ACH(using an HRV) is seven times less than ASHRAE's minimum .35ACH. Is he not getting enough fresh air?

[S-F]

Ok. Let's clear this up.

ACH 50 is a blower door measurement. ONLY. One of the passivhaus criteria is that the blower door measurement can't exceed .6 ach @ 50 pascals of depressurization.

The recommendations for HRV sizing is that it should provide a little more than 1 quarter air change per hour.

These are two completely different things we are talking about here.

[JRMichler]

HRV's come with defrost capability. Our unit goes into a defrost cycle every 30 to 60 minutes or so when the outside temperature is below freezing. It comes with a drain line for the melted frost.

We do not need a lot of outside air because our house does not have carpeting or smokers. In addition, we keep the humidity below about 55% so there is no mold.

We judge air quality by the lack of stuffiness when coming in from outside. In our case, 35 CFM from the HRV keeps the air clean. It's a total of about 0.25 ACH for the HRV plus leaks.

[Solaris]

I have taken the PassivHaus training, and the Germans have the design right. Make the home as air tight as possible with super-insulated building envelope, and you can heat a home with the top Paul HRV using a 1kw electric coil.

It is vital to have lots of fresh air while purging CO2 levels in a balanced way. It is critical to avoid moisture condensation inside the walls that result in mold and rot.

Air quality is not something to go cheap on. You can go 30 days without food, 3 days without water, and 3 minutes without air. Clean air is far more important than organic food - from a mass consumption view.

[Drake]

I am not in any way suggesting that a "safe" level of fresh air not be provide to ones living space. But what is wrong with doing it the "cheapest" method possible that adds the lowest net energy demand for that space or exploring ways or the amount of air exchange that is deemed safe is not questionable. I am surprised that individuals so proven to question experts and their standards on most everything are so, to the point of reverse engineering about anything they can are so reluctant to explore possible "fresh air" options. How to heat and the safe amount fresh air become the economic conundrum as no matter how much you insulate or how well you spot infiltration the amount of unheated air that needs to be provides to space for healthy human living with be the limiting factor in reaching zero energy demand. Heat recovery theory is a potentially valid solution to lowering the energy demand to provide the needed fresh air if it truly preformed to its theory but it doesn't every where. Frosty up in cold temps is a wrench thrown into it efficiency that only gets worse the more the HRV is needed even in ERV's which are not immune to frosty. So a solution to frosty is preheating(tempering) the incoming air to a temp above or near freezing(32F) in the cheapest, lowest energy demand way to make an HRV any net savings in cold climates over just letting your space "leak" fresh air. If a living space is/can be designed, built and be acceptable to its resident/s that is compact, low energy demand, indoor healthy to make a minimal footprint on our environment best maximized net expense with solution/methods that payback in energy eating McMansions. For me the saving has to out weight the cost for the remaining 20 or so yrs of my homeowner life or it is money poorly spent.

Having to replace all the air in my house 8 times a day to be healthy seems like a lot.

[AC_Hacker]

Originally Posted by Drake

I am surprised that individuals so proven to question experts and their standards on most everything are so, to the point of reverse engineering about anything they can are so reluctant to explore possible "fresh air" options.

I am glad that you are exploring fresh air options.

What are your finding in the research that you have conducted and the original work that you have done, so far?

-AC

[MN Renovator]

15 CFM per person

[AC_Hacker]

Originally Posted by MN Renovator

15 CFM per person

15 CFM would actually be 0.35 ACH if you lived alone in a 18' x 18' x 8' box.

...just don't have a party.

See: Human Comfort and Health Requirements

-AC