SimScale CAE Forum

COVID Help!: Nursing Home Neg Pressure Floors

I need help designing a flow model for a wing of a nursing home. I want to make the wing negative pressure using HEPA filtration remediation fans and alter the HVAC system to keep infection down. I want to model the air flow and decrease it to decrease transmission. Project would involve multiple rooms connected to a hall and 3 units moving air and air supply. I will supply a blue print and specs on the equipment. At this point I need -30pa of pressure inside unit(which doesn’t seem like much), and low movement of air that decreases transmission particularly around patients. We are currently being told 2m is a contact range I want to be able to show results. Currently in NJ 93/93 residents were infected in a home and in MD 66/100 were infected (at this location it looks like they were following CDC protocols). It is considered droplet precaution at this time but all major hospitals are operating under some circumstances as though COVID is aerosolized (hoods, no bagging etc.).

Hi @csteiner!

Wrote you an email!



Hi @csteiner, I’ve been curious how difficult it is to modify an HVAC system to create a zoned negative pressure scenario. While I’m no HVAC expert, when you talk differential pressures in a contained environment I wouldn’t jump to flow modeling but rather simple ideal gas laws like Boyle’s. Even then I have to think the challenge is in modifying the HVAC system to do what you would like.

If the rooms have an exterior window, you could achieve this easily by installing a window-mounted exhaust fan. Room pressure could be adjusted by varying fan speed (no math models required!). I read somewhere this was being implemented successfully with HEPA filters mounted to bed headboards. It’s not clear from your post if you are looking for pro or fast, but assuming fast I know that very high efficiency furnace filters are still available at hardware stores and a functional plenum could be constructed with simple materials like cardboard or foamboard, tape, and hot glue. Dryer hose would make an excellent temporary duct.

Modeling-wise, if this was attractive to you I would work on sizing the fan to overcome the static pressure of the HEPA filters and ducting, depending on how many beds it would need to service.

With this solution, your HVAC system will be working harder because you’re exhausting the conditioned air, but it’s down, dirty, and fast. You could also consider fans that push air back into the hallway, but this would be more difficult to install and you would have more risk of contamination.

In either case you’ll need to make the rooms as airtight as possible by sealing the large gap that’s usually under the door. Hardware stores have a variety of sweepers for just this purpose.


I was just thinking about HVAC systems again. If the HVAC system has a dedicated air return in each room, you could achieve a negative pressure by simply installing a choke (such as a HEPA furnace filter) over the air vent inlet. This would tend to create a negative pressure compared to the rest of the building, however I think most large HVAC systems have only a few returns and rely on flow through the building.

I wrote you back an email. We had Servpro out today to talk volume of air and setup. I believe I have a group that will model the wing (ward). Stay posted I think it’s going to be cloud sourced here.

Looks like we are going to be working modeling this stay posted.

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Okay I’ll be interested to learn more about their solution.

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Tomorrow we in stall 2 motors in HVAC system that are on the returns.