Designing ERV, kitchen and bathroom ventilation in concrete dome home without any ducting

I would NEVER use an ERV system in a house. I would strongly recommend an HRV in a new, very tight house (and yes, I have dealt with both).

OK. What's the difference? An ERV recovers both sensible and latent heat (the latter primarily from water vapour). Therefore, it recovers more heat — is more efficient — than an HRV. The problem is very simple: it also recovers most of the contaminants in the air along with the water vapour. These contaminants are not only things like moulds and bacteria and the like — which, to a certain extent, can be reduced or eliminated with a combination of UV and filtration — but also any chemical contaminants, such as from cooking, off gassing from carpets and furniture, odours, whatever.

An HRV doesn't do that. Rather, it strictly transfers heat from warm exhaust air to cool fresh air drawn in from outside, and nothing else — there is a barrier between air coming in and air going out. Since the objective of the exercise is to ensure enough fresh air for the occupants health and comfort, this works.

Therefore we need an HRV in newer tight houses.

Now. How much fresh air? Opinions differ, but somewhere around 6 air changes per day, or 3 cfm per 100 square feet of floor area, seems to be a sort of sweet spot for various opinions. That would work out to around 90 cfm for the main space and 50 cfm for the basement unit.

You mention joining various exhaust vents together. Well… I'd never run a kitchen vent together with anything else. Just not a good idea. Bathroom vents could be trunked together, but only if the exhaust fan is downstream of the junctions. Otherwise you will push air from one bathroom into another as well as — or even instead of — outside, which really isn't a good idea either.

You also enquire about filtration systems. One assumes that there will be good quality filtration on the intake from the HRV, to reduce (if not prevent) pollen and dust and the like — and squirrels — from getting in. If there are any recirculating units — such as a furnace, air conditioner, heat pump etc. — they should also have quality filtration. However. While it is possible to design systems which restore indoor air quality in a closed loop — think submarine or space station — it's very expensive to build, never mind maintain.

ERVs have filters but they bring moisture across a membrane which brings some other things with it.

OK thanks you did say filtration but you took away all my focus with "it also recovers most of the contaminants in the air along with the water vapour"

So you really didn't mean "most", right?

And sorry to pick nits, but they pass water vapor, not all stuff soluble in water, no?

An erv isn't removing moisture, it recovers the moisture to recover the latent heat of vaporization.

It would be nice if they didn't — but my experience with them is that any of the soluble gasses pass right back into the house. The two which we installed (two different houses) we tore out pretty soon and replaced with heat recovery units.

There are dampers for multiple fans in a common vent but none of them will seal completely so you will get odors in areas where fans are not running when other fans are running. that is why this will only work if you have an inline fan after they join. I would make each kitchen separate both because of the higher airflow needed and the grease that will collect in the duct.

Since the airflow for the hrv is low the ducts can be small which should make them easier to conceal.

Not sure how the hrv deals with unbalanced airflow to add makeup air for exhaust fans and clothes dryers.

Here?

https://www.greenbuildingadvisor.com/question/improving-air-quality-during-rehab-of-tight-home-with-no-ducting

Look at a product called Lunos. No duct work needed.

https://www.lunos.de/en

An ERV is not like a heating system. If you get it wrong, flows are a bit low, might be a bit loud and distributions is not that even but it will still mostly works. Important items is to go for autobalance unit as these are much easier to set up and stay in balance as filters clog.

For an ADU you can share the ERV but you need fire dampers. I think the simpler option is to install something like:

https://iaq.na.panasonic.com/erv/whispercomfort-60

And mount in the hallway. You can get the tandem vent kit for it for a simple install. No need for all the ducting, think of it as a good enough solution.

For the main unit, stick with the largest size duct your ERV can take. This is usually 6" for 100CFM units and 7" for 200CFM. Some big units come with only 6" ports, these need to be stepped up as 6" duct is way too loud at 200CFM.

Outdoor ducting to each unit needs to be insulated with a well sealed poly sleeve. The indoor ducting can be bare pipe.

An insulated pre-filter on the outside fresh air feed to the ERV is a good idea if you have the space. This would save you the cost of the expensive OEM intake filters plus you can oversize it so it lasts much longer (my external filter is good for a year).

Any filters should be easily accessible, you want the least amount of friction (in terms of effort) when it comes to swapping them.