Yet another home ventilation query

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110 posts

Master Geek
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#3295738 10-Oct-2024 21:33

tweake:

CrazyM:

Nah I dont agree. The fresh air temperature coming in from a BPV is always close to your exhausted air temperature so you can have it running all the time.

while thats true its only part of the story. what your not factoring in is the heat loss/effects etc from the air leakage. in a typical nz house you will be leaking as much, or quite easily up to double, the ventilation airflow. so the air thats going into the house and being filtered etc by the bpv is actually less than 50%. with a PPV your filtering a whole lot more of it because your using the house leakage as the exhaust instead of an inlet. yes there is no real heat recovery with ppv but the amount of energy it takes to heat air is pretty minimal and a bpv is only recovering from 50% or less of the airflow. so the difference between the systems is very little.

if you have an air tight house thats got very little air leakage then the bpv is handling 90% or more of the air going into the house and then its very effective.

the other interesting thing is that bathroom fans don't really work in air tight homes because they can flow more air out than the air leakage rate lets air in (also range hoods). this is why you use the bpv as the bathroom fans. conversely if you have bathroom fans, you may not have a house air tight enough to make a bpv worth while.

a house (especially kiwi homes) need to be build specially to be air tight. its fairly rare for standard kiwi homes to be air tight enough that a bpv is required.

I dont know how your "typical NZ house" is calculated but if its is leaking double your ventilation airflow then there is no point having any BPV, PPV, or probably even heating if not a roaring fireplace. And you wont have crying windows as a problem either...

A BPV by design should result in a negligible pressure difference between inside and outside so your amount of air leakage will not increase. For my house (unsure how 'typical' it is) it works very well. Using the rangehood or extract fan is enough to overpower the brush strips of the ranchsliders so the house doesnt pull vacuum, but when not on there is no noticeable drafts.

Not saying that a BPV is required, but for 20% additional cost i'd take it every day and have the year round ventilation that may not be as efficient as it could be. And I also dont want the roof space air pushed into my house, filtered or not :)

tweake

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#3296174 11-Oct-2024 16:29

CrazyM:

I dont know how your "typical NZ house" is calculated but if its is leaking double your ventilation airflow then there is no point having any BPV, PPV, or probably even heating if not a roaring fireplace. And you wont have crying windows as a problem either...

A BPV by design should result in a negligible pressure difference between inside and outside so your amount of air leakage will not increase. For my house (unsure how 'typical' it is) it works very well. Using the rangehood or extract fan is enough to overpower the brush strips of the ranchsliders so the house doesnt pull vacuum, but when not on there is no noticeable drafts.

Not saying that a BPV is required, but for 20% additional cost i'd take it every day and have the year round ventilation that may not be as efficient as it could be. And I also dont want the roof space air pushed into my house, filtered or not :)

I dont know how your "typical NZ house" is calculated

branz study many decades ago where they blower door tested houses.

but if its is leaking double your ventilation airflow then there is no point having any BPV, PPV, or probably even heating

leakage is kinda of an average as its dictated to by the wind. the advantage a ppv gives is its more consistent than the weather. even i noticed that going from opening windows to a ppv, the ppv is far better. its not that bad for heating, air doesn't actually hold a lot of heat. eg ventilation airflow is a whole lot less airflow than a heat pumps airflow.

the catch22 is that ventilation also brings in moisture. old homes use air movement to dry, which requires huge amounts of airflow. hence why grandma still opened windows even tho the old houses leaked 3-5 times the ventilation rate.

A BPV by design should result in a negligible pressure difference between inside and outside so your amount of air leakage will not increase.

well actually it does, sort of. the bpv itself is air leakage, its a couple of holes in the envelope which air goes in/out of the house. just like opening a window or door. as i mentioned before, your adding its airflow to the air leakage airflow. great for a house with no air leakage, terrible when you have a house with air leakage.

For my house (unsure how 'typical' it is) it works very well.

so how do you know? most people who spend the money on something will always tell you it works, even tho they have no way to show it works. hand over the outlet, feeling the warm air coming out and claiming it works, is the same as tenants putting a hand over a ppv outlet, feeling the cold air then saying its making the house cold so they block the vents and wonder why the house goes moldy. sales people love it because most people don't test that it works, so they can talk complete bs.

most homes ranchsliders leak air like crazy when its windy. it takes so little wind to make the door move and you can see right past the seals. you need to go to the expensive passive house rated ones to get them air tight.

Not saying that a BPV is required, but for 20% additional cost

i'm not up on current pricing. last time i looked they where something like 3-5 times the price. the other thing is if the system is actually a full system or did they cut corners like leave the filter box out to make it cheaper.

neb

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#3296554 12-Oct-2024 18:19

wellygary: But, with underfloor waterproofing already installed. there has to be reasonable water ingress occurring somewhere?

With the windows open 95% of the time the moisture is coming straight back in again through them. For a dehumidifier to work properly you need to have it in a buttoned-up area so it can suck all the moisture out over a period of days.

In terms of ventilation + drying, the OP could look at a Dry Living system which is a positive-pressure dry air system.

tweake

2391 posts

Uber Geek

#3296579 12-Oct-2024 19:17

neb:

In terms of ventilation + drying, the OP could look at a Dry Living system which is a positive-pressure dry air system.

most likely its a ventilating dehumidifier. quite common feature with whole home dehumidifiers. (something you should have if you have an erv.)

their site doesn't show a whole lot, its seams to suggest a few things that are not shown and the install diagram is somewhat iffy. dehumidifiers require the air to go through multiple times. typically circulated the air in one big room and then move some of that air to the rest of the house. ie 200mm in/out of the lounge and then branch the out off to the other rooms.

there is another crowd that has one and a much better diagram.

CrazyM

110 posts

Master Geek
Inactive user

#3297053 13-Oct-2024 21:43

I dont know how your "typical NZ house" is calculated

branz study many decades ago where they blower door tested houses.

Blower door test by definition is pressurizing the house so will be a good estimate of leakage with a PPV. A BPV will with the same airflow will not be pressurizing the house so your leakage will be less.

I am using the term 'leakage' as airflow from the interior of the house going out through doors, windows, paths with no heat recovery.

but if its is leaking double your ventilation airflow then there is no point having any BPV, PPV, or probably even heating

Not following your logic here. You say ventilation brings in moisture but also huge amount of airflow is required to dry? Houses leaking 3-5x more than the ventilation rate (pulling a vacuum?)?

I feel like you are on both sides of the argument. i.e. A PPV of nominal airflow which is ALL leakage = good. But a BPV with same nominal airflow but less leakage = bad

A BPV by design should result in a negligible pressure difference between inside and outside so your amount of air leakage will not increase.

All air pushed in by a PPV will leave the house as leakage with no heat recovery.

Some air pushed in by a PPV will leave the house as leakage with no heat recovery, and a proportion (depending on the house) will be extracted and heat recovered (efficiency depends on heat exchanger, insulation etc...)

For my house (unsure how 'typical' it is) it works very well.

How do I know? Analytically I can measure the inlet and outlet temperatures. I can measure the airflow from the intakes and exhausts and know how many ACH my house is getting through the BPV. I can track the temperature in the lounge through the night from the Sensibo and see the difference with the BPV on/off. I can turn on the heatpump in the lounge in the morning and watch the temperatures rise in the kids bedrooms at the other end of the house and see the difference with BPV on/off. Experientially my windows are now dry on frosty mornings, my house is consistently warm and fresh throughout, and does not smell musty when locked up and gone away for the weekend.

And if I decided that a PPV was a better system I can just turn off the exhaust fan, close the extract vents, and enjoy all the benefits of the additional leakage :D

In my experiences in homes with a PPV is that if you want airflow then you are at the mercy of whatever the temp is in your roof/outside, and if you dont want that temp of air all you can do is turn it off. And that is fine most of the time, but I have had unpleasant nights under a PPV outlet pouring freezing air down on me, and also had PPV outlets pumping hot air into the house on a summer day. Both those situations can be fixed with temperature control turning off the system at the expense of turning off the airflow (I assume most PPV's have a check valve in the ductwork? or do they vent your house/heat into the roofspace when turned off)

Never noticed draftyness at home on a windy day. The house is well sheltered.

Not saying that a BPV is required, but for 20% additional cost

Prices on second page of the thread.

Anyway, I think I'm done here. That is my experience, YMMV depending on a myriad of factors :)

tweake

2391 posts

Uber Geek

#3297138 14-Oct-2024 11:49

no.

blowerdoor is done at high pressure to compare one house to another. we can estimate real world leakage rates by comparing that to the weather. for eg roughly 5ach@50 pascals = 0.35ach air leakage. 0.35ach is the required ventilation airflow rate.

while a ppv slightly pressurizes a house (you always need pressure to get flow) your turning some of the inlets into outlets. think of a box with 2 holes, 10 liters in and 10 liters out. then add a ppv with a third hole pushing air in 10 liters, which goes out at 5 liters through both holes. now with a bbv you have 10 liters in/out through the two holes and also 10 liters in/out though the bbv, making it 20 liters through the box. (thats very rough and ignores a few things).

Not following your logic here. You say ventilation brings in moisture but also huge amount of airflow is required to dry? Houses leaking 3-5x more than the ventilation rate (pulling a vacuum?)?

air flow dries. just like drying clothes on a sun less day with wind they dry fast, where as a day with no wind takes forever to dry the clothes. also ventilation crowds blow air over the window glass to remove the moisture from the glass.

as above 5ach@50 house is about the same as the ventilation rate (climate depending). nz homes are typically 5ach@50 up to 15ach@50 some worse some better. so roughly 0.3 to 1.5 ach natural airflow. thats the amount of air going through the home.

and air brings in humidity, especially in auckland/northland. this is why its important to know if you have an hrv or erv core in your bbv. with hrv core your relying on climate humidity to be reasonably good.

How do I know? Analytically I can measure the inlet and outlet temperatures.

but your only measuring the air flow thats going through the bbv, not whats going though the house. you cannot measure the natural air leakage temps. the only way to know is to blower door test the house and work out how much natural leakage it has. even then natural leakage varies with the weather. if no wind then no leakage, if windy then lots of leakage.

ppv normally turns off at high temps or switches over to a outside air source (summer vent). they slow down in cold weather but must keep going otherwise hot air will go back up in reverse and cause problems.

outlet pouring cold air onto you means they put the vent in the wrong place. it should never be above seating/beds etc. however they put them within range of windows to blow air over the ceiling and down the wall behind the curtains to give you moisture free windows. this is why they often put a lot of vents in lounges. far more than they need for airflow.

and yes ppv turning off is not good for airflow and bbv is far better in that regard. tho ppv compensates that a bit by blowing in far more air in during times when temps are better, to make up for when it slows down or stops.

despite the salesman claims, you really need an airtight house to make effective use of a bbv. the way standard nz houses are built, you have to deliberately build an air tight house. its rare you will get one thats air tight enough. which is why most people on here with bbv's have been ripped off by sales people. bbv is the new "hrv".

tweake

2391 posts

Uber Geek

#3298890 18-Oct-2024 15:38

talking of bbs and sales people, stuff have a new "article" (ad) from Damien McGill of Healthy Home Cooperation Consider this overlooked measure of how healthy your home is - or isn’t

"I don’t understand why you’d need a coffee to wake up or function in the morning: Why isn’t your sleep restful enough? Could it be something to do with the air quality in your bedroom?

‍‍Harvard researcher Joseph Allen and colleagues found a link between indoor air quality and cognitive performance in a study of working professionals (Allen et al. 2015). They found diminished workplace performance with a 15 and 50% reduction in decision-making performance at 945ppm and 1400ppm respectively, compared with the 550ppm control group."

thats has actually been debunked. its been found that there is no loss in cognitive function when exposed to only high co2 levels. cognitive loss is most likely caused by other factors that can be fixed by ventilation, hence why co2 is actually a good indicator of lack of ventilation.

"‍‍What you need is filtered fresh air from outside pumped into your bedroom. This will push the stagnant stale stuffy air under your door, if and only if the door has been undercut sufficiently. That stuffy air needs to go somewhere, otherwise your house will blow up like a balloon. It’s better if it doesn’t find its way out through all the cracks and crevices in your home. That could cause condensation inside your walls, leading to decay."

false.

air will go outside via all the gaps as well as under the door. your house is never going to blow up like a balloon, unless its specially built to be air tight. there has been no evidence of it causing condensation inside walls. if air is going from inside to out, then humid outdoor has already been going from outside to inside, and your house hasn't rotted out. in nz climate its a non-issue. i would also argue that warm dry indoor air is through a wall is better than damp outdoor air going through the wall.

incidentally condensation does happen in the walls even without air being forced through them (see branz testing).

there is also no mention that your house is leaking air in/out as well and how that impacts things. simply ignoring that bbs systems don't work well on high air leakage houses (which is typical for nz). also they are using mvhr (heat recovery) which means indoor humidity is dictated by outdoor humidity.

just another example of a sales pitch to get people to buy a cure all device and ignoring how homes and ventilation actually work.

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Kickinbac

427 posts

Ultimate Geek

#3298961 18-Oct-2024 18:08

tweake:

talking of bbs and sales people, stuff have a new "article" (ad) from Damien McGill of Healthy Home Cooperation Consider this overlooked measure of how healthy your home is - or isn’t

"I don’t understand why you’d need a coffee to wake up or function in the morning: Why isn’t your sleep restful enough? Could it be something to do with the air quality in your bedroom?

‍‍Harvard researcher Joseph Allen and colleagues found a link between indoor air quality and cognitive performance in a study of working professionals (Allen et al. 2015). They found diminished workplace performance with a 15 and 50% reduction in decision-making performance at 945ppm and 1400ppm respectively, compared with the 550ppm control group."

thats has actually been debunked. its been found that there is no loss in cognitive function when exposed to only high co2 levels. cognitive loss is most likely caused by other factors that can be fixed by ventilation, hence why co2 is actually a good indicator of lack of ventilation.

"‍‍What you need is filtered fresh air from outside pumped into your bedroom. This will push the stagnant stale stuffy air under your door, if and only if the door has been undercut sufficiently. That stuffy air needs to go somewhere, otherwise your house will blow up like a balloon. It’s better if it doesn’t find its way out through all the cracks and crevices in your home. That could cause condensation inside your walls, leading to decay."

false.

air will go outside via all the gaps as well as under the door. your house is never going to blow up like a balloon, unless its specially built to be air tight. there has been no evidence of it causing condensation inside walls. if air is going from inside to out, then humid outdoor has already been going from outside to inside, and your house hasn't rotted out. in nz climate its a non-issue. i would also argue that warm dry indoor air is through a wall is better than damp outdoor air going through the wall.

incidentally condensation does happen in the walls even without air being forced through them (see branz testing).

there is also no mention that your house is leaking air in/out as well and how that impacts things. simply ignoring that bbs systems don't work well on high air leakage houses (which is typical for nz). also they are using mvhr (heat recovery) which means indoor humidity is dictated by outdoor humidity.

just another example of a sales pitch to get people to buy a cure all device and ignoring how homes and ventilation actually work.

Tweake - You seem really determined on debunking the benefits of MVHR systems and ignore building science. I'm concerned you are a PPV salesperson and if so should declare any conflict of interest.

Damien McGill is doing good work try to improve the quality of the housing in New Zealand based on good building science and research.

tweake

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#3298968 18-Oct-2024 18:45

Kickinbac:

Tweake - You seem really determined on debunking the benefits of MVHR systems and ignore building science. I'm concerned you are a PPV salesperson and if so should declare any conflict of interest.

Damien McGill is doing good work try to improve the quality of the housing in New Zealand based on good building science and research.

as i have said before, i'm an amateur, so no products to sell, no loyalties to brands/companies. i do not sell ppv or anything else.

feel free to argue against the points i've raised. this is not new, we have had several members here who have been sold erv's in homes that don't require them and owners that have not ben informed of the problems they can cause. thats most certainly not "good building science and research".

neb

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#3298973 18-Oct-2024 19:22

This should be interesting. The guy whose research "has been debunked" as you put it is Joseph Allen, the director of Harvard's Healthy Buildings program and, as a side-comment, the person who introduced the term "forever chemicals" to the world. He's a world authority on healthy buildings, so you're going to need a bit more than "oh, I don't believe that stuff" as an argument.

tweake

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#3298989 18-Oct-2024 20:59

neb:

This should be interesting. The guy whose research "has been debunked" as you put it is Joseph Allen, the director of Harvard's Healthy Buildings program and, as a side-comment, the person who introduced the term "forever chemicals" to the world. He's a world authority on healthy buildings, so you're going to need a bit more than "oh, I don't believe that stuff" as an argument.

have a quick look at the study. its not really about co2 causing impairment, its the difference between a green building and normal. using different ventilations rates. the research is not testing co2 effects on people but rather the effects of ventilation rates or lack of ventilation in a building (and the building part is important). its actually correct. "Exposure to CO2 and VOCs at levels found in conventional office buildings was associated with lower cognitive scores than those associated with levels of these compounds found in a Green building. " but the article is making the claim that they tested for direct co2 effects, not the differences in buildings.

in other studies where they use large amounts of co2 (far higher and not using ventilation) they found no change. (i'll see if i can dig up the actual study). ie when they tested ONLY co2 there is no change. therefore its not really the co2 thats doing impairment but rather something else in the building.

as i mentioned, co2 is a good marker for ventilation but its not the direct cause of the problems.

neb

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#3298990 18-Oct-2024 21:03

Ah, so the problem is Stuff's mangling of the actual results (not surprising), not the original work.

tweake

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#3298992 18-Oct-2024 21:15

CO2 Mythbusting: 20,000 ppm Tested for Cognitive Effects with NO concrete results w/ Jeffrey Siegel

interview with jeffery siegal (scientist). he co-authored a paper that looked into the studies. as he mentioned in the video, "there is no unsafe levels of co2"

btw the study the stuff article refers to only tested to 1400ppm. if i recall correctly you can hit 2000-3000 ppm in planes or even big indoor events.

tweake

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#3298993 18-Oct-2024 21:18

neb:

Ah, so the problem is Stuff's mangling of the actual results (not surprising), not the original work.

more likely the author of the article. more of a sales pitch than science, which is why i object to it. remember in the early days hrv (the company) claims of heating your home with the ventilation system.

neb

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#3298994 18-Oct-2024 21:27

Yeah, I had a quick look at the original study by Allen and even the title "Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments" tells you it's not just CO2. This is why I read the Guardian and not Stuff, they make it clear when something is an opinion piece (in Stuff's case, advertorial) by changing the background colour of the page rather than a single word "opinion" down in the text, and would probably never publish something like this even as an opinion piece since it's just advertorial. Here's the Guardian's take on the same thing:

The research indicates that better ventilation, lighting and heat control improves workers’ performance and could boost their productivity by thousands of dollars a year. It also suggests that more subjective aspects, such as beautiful design, may make workers happier and more productive.

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