I will add another comment! Usually i place the fresh air to the residents, in the bedrooms to help the occupant get oxygen while they are sleeping instead of allowing the CO2 to linger around. Maybe i should be venting this area and allow the fresh air to come into the room by either the door or a well placed duct. Now, duct sizing and infiltration rates will be tampered with and will cause another manual J to be calculated. Oh well, what do you guys think?

 

You should exhaust enough air from the space the person is in to make the space negative. For existing areas like you have you may have to add temporary heating and or cooling. It doesn't matter where the makeup air to the room comes from as long as it is good quality. Most residences have enough leakage to compensate for the comparatively small amount of air exhausted from the room. If you want to go with an ERV just make sure you exhaust more air than you bring in to make the room negative.

I almost forgot WELCOME TO THIS SITE you will love it and we look forward to your comments.

 

Thanks Wayne,
That was my fathers name.
How much negative? Just until a magnihelic goes negative between inside the room and outside the room door?


thanks
M2cool

 

I would want about 0.02 negative with the worse case HVAC operation. You just need to make sure the room pressure never goes positive.

 

Put the clean air in to the cleanest partsof the home and remove air from the dirtiest parts. Into the bedrooms and exhaust from the baths/kitchen. Forget about negative and positive pressure. Wind, stack effect, kitchen hood, and the clothes drier will control pressure on the different parts of the home.

Keep the home below 60%RH as much as possible. Avoid continuous damp spots to prevent mold/dust mites in the home.

Regards Teddy Bear

 

In this case the main thing needed is to prevent contaminating any portion of the house with the virus. To do that pressure gradient is absolutely crucial and the affected area can only be isolated by being at a negative pressure relative to the rest of the house. This is not a comfort issue it is a health issue. I have recently consulted with old folks homes regarding this issue.

If you have any doubts M2 contact the health professionals immediately.

 

I am with Wayne on this one. One easy way to tell the room is negative is to get a strip of toilet paper four feet long and hold it close to the doorway to the bedroom. Crack the door 2 or 3" open and watch which way the toilet paper goes.

 

Seems to me that the issue is not the ERV but the house return. All the ERV's that I have seen have a wheel that air blows through front to back in and back to front out so the wheel spins and in one section of the unit the air is blowing one way though the media then as it spins to the other have it passes back the other way. Anything blown into the wheel on one side gets blown out on the other. Yes there are screens/filters to protect the wheel from a lot of dirt but I don't think they would catch very many viruses, so a virus that gets past the filter on the exhaust air gets put into the incoming air stream. Maybe there are other types but this is what the ERV's I have seen are like.

 

In theory, I don't think an ERV would change the Room pressure.

 

I'm familiar with a couple rural hospital isolation rooms. These are single story structures with the isolation room at the end of a wing of the building. They are simply using a roof mounted mushroom style exhaust fan that serves the room with a dedicated (Occupied) fan switch.

The fan is designed to move enough air to keep the room negative no matter what the variable volume air handling unit is supplying, or the position of the entry door. Nothing fancy, no anti rooms, no special air valves, just a simple system.

They use a smoke candle periodically to confirm proper operation.

Something like this might very easily be adapted for residential. You could also run the room exhaust through an energy recovery unit that maintains airflow separation. (no paper wheels).

A system like this will increase energy usage, and with the addition of the ERU, even more so, but for certain situations, it might be worth the cost.

 

The pressure in hospital isolation rooms depends on who is being protected the patient or everyone else. Protecting everyone else is easy because a negative room pressure does the trick. Protecting the patient from everyone else is a little harder.
Almost all hospitals now monitor the pressures via the HVAC controls and include alarm if the design pressure is not within tolerance.

 

I have a lot to learn




I know how important air balance is. I also know how closed doors and vent fans can effect overall performance of a home. My thoughts on this subject matter are just hypothetical. I am not sure if I know how to experiment with this other than the ol toilet paper and smoke tricks to see what the room actually does. Im just trying to figure out how to make the rest of the house hold safe if someone was quarantined to their bedroom for an illness. I could be overthinking this, but the pandemic does have me trying to better the systems that i install today. Wayne and Teddy Bear, wished i could hang out with you to for a while, i might just actually learn something. Thanks for the responses. Ive enjoyed them.

 

You could just get a 6" axial fan and put in a window. Blank the rest off with cardboard. Guess that might depend on what type of windows you have and how safe your neighborhood is.

 

I gave you the 0.02" negative because from your post #4 I thought you had a magnehelic gage. For troubleshooting I use a cigarette lighter. There are a lot of other ways such as BBeerme's toilet paper which also works well.
There is a lot of expertise on this site and everyone here is willing to share their area of expertise. The guys here will amaze you at how fast they zero in on the cause and fix of problems. You can hang out here with everyone. I'll be 80 this year and these young squirts here come up with stuff on a regular basis I never heard of.

Your scenario hit home with me because less than two weeks ago my cousin died from covid 19.

 

As you said Artrose protecting the patient is a whole new ball game. The main problem I had with them was the system design rarely had enough static to make it easy. The biggest problem I had was with the anti room.

 

So maybe, i just make the bedroom as normal as i can, and when the time arises with an occasion of a sick bed dweller, no matter the sickness, i evacuate that area with a simple bath vent fan, that i have pre installed in the room and only turn on when this occasion happens. Might be once a year, might be for a long length of time. The thought was to get that contaminated air out of the space and replace it with fresh air, which would come from the house. I would need to make sure that the house's air balance wasnt too negative.

thanks for the input.

M2cool

 

In regards to an ERV creating negative pressure in a home or room, what ways are you testing to see if you have negative pressure?

 

I thought an ERV moved the same amount of air in as out (?).

 

I'm happy you guys were able to help M2 with this specific issue.

I would also like to learn more on best practices for ERV installations. Teddy Bear summed it up nicely.

In my experience with a register at the peak of my cathedral ceiling (supply) and at 2 more at baseboard height the bedrooms (exhaust), the air is comfortable and healthy. I've played with swapping the ductwork at the ERV and discovered that just 100cfm does a much better job than I expected to push the heat out of the loft and into the bedrooms (which is good in Colorado with no ceiling fans). Mixing the air up there before it blows on anyone is ideal and the dog bed on the floor by the exhaust is so perfect if she stinks. Conversely, anyone who likes a colder bedroom could swap ducts the other way. Consider that if you have a comfort complaint and the ERV is ducted in a dedicated way that could work in reverse. Depending on the ERV design, you could also swap the ducts to outside to achieve this if it's simple and symmetrical like my EV90 is. I only suggest this as an option for those of us who like to tinker and test. BEST practice of course is to follow the f'n manual.

 

My new house has air returns in each room(far cry from 25 YO previous house with ONE return air vent. (shameless plug to get enough post to post my own question)