Converting to Negative Pressure Rooms?

RayWohlfarth

I just received a call from a real estate customer saying the physician and dentist tenants told him they received a notice from the government that all medical and dental suites have to be negative pressure. Have you heard that? This could be a game changer on design and maintenance. Are there others that would fall under the same rule?
Thanks
Ray

SlamDunk

We use negative pressure in pharma all the time. I suspect hospitals do too.

In pharma,Outside air makes one pass thru ahu, gets pre filtered, conditioned to temperature, pushed thru HEPA filters into rooms. Rooms are tied in to exhaust fans and air is pulled out thru HEPA's faster than it is pumped in and back to atmosphere outside the building. All rooms have DP sensors to common areas. If negative differential is lost, a light above the door flashes.

Could be done less expensively in doctors offices but, you will likely need HEPA's for air coming in and going out if the name of the game is to protect.

That is why ventilation system on boats and assisted living facilities are being blamed for the spread of COVID. There are air returns recirculating contaminated air and re-distributed to other rooms. Like in your house! If someone in the house is in quarantine, best to isolate supply and return air from that room.

During winter cold and flu season, this is a good reason to keep your steam systems !

Jamie Hall

May I respectfully point out that in order to operate negative pressure spaces, two things are essential: first, the space must be sealed other than ventilation supplies and returns -- and I do mean sealed. This is feasible in new construction, although it isn't cheap. It is, in general, not feasible in older construction or in a retrofit situation. Second, the air supply and exhaust must be coordinated. You can't just casually stick a few fans in there and some ductwork. As @SlamDunk said, you will certainly need HEPA filtration on the inlet ducting, and very likely on the outlet.

An alternative -- commonly used in fabs (semiconductor fabrication) -- is positive pressure. The principle is somewhat similar, in that you have incoming air which is highly filtered (HEPA or HEPA plus), but instead of being held negative by the exhaust fan, they are held slightly pressurized relative to ambient. Pressure differential is maintained by throttling the outlet air. The big advantage is that you don't have quite the demand on the space being absolutely sealed, as if the inlet fans are adequate you can tolerate some leakage. Another advantage is that if there are humans in the space (there often aren't, in fabs) and they are in moon suits as they must be, all that is necessary is that the moon suits are maintained at a slightly lower pressure than the space, eliminating concerns about the almost inevitable slight leakage (note that moon suits in a hazmat environment are maintained at a slight positive pressure, to prevent outside contaminated air from getting in).

SlamDunk

They do not have to be tightly sealed. Weather stripping would work. Leaks are inevitable. Doors will open and close all day long. Even while procedures are taking place. Like Purell, negative pressure is 99.99% effective

Jamie Hall

I guess I'm conditioned -- if that's the word -- to fab clean rooms, where an outside air leak is simply unacceptable -- one speck of dust (just one!) can ruin a hundred thousand dollar wafer.

SlamDunk

Yeah, those places are extreme.

RayWohlfarth

Thanks @SlamDunk and @Jamie Hall The doctor said he thinks the CDC will mandate this on all existing doctor and dentist offices but maybe its not true. I would imagine they would need more outside air and higher operating costs. I appreciate the expertise

SlamDunk

It is a tall order to do for existing offices. A good idea, but not really affordable.

But then again, it is the CDC. One minute masks are not recommended, then the next they are! Who knows?

Larry Weingarten

Hi, So would it be correct to say that in these places, only direct vent combustion appliances could be used... no more atmospheric?

Yours, Larry

Jamie Hall

Larry Weingarten said:

Hi, So would it be correct to say that in these places, only direct vent combustion appliances could be used... no more atmospheric?

Yours, Larry

I would think so, @Larry Weingarten -- whether it's positive or negative one is looking at. It's a matter of control. But if the combustion appliance is outside the controlled space, no -- you could probably use pretty much anything.

And as to whether you are going to go positive or negative -- it's really a matter of what are you trying to do? Positive spaces you are trying to make sure that nothing from outside gets in. Negative spaces you are trying to make sure that nothing from inside gets out.

And as for the CDC -- it's the classic "ask five people and you'll get ten answers".

SlamDunk

Another idea that is affordable is ultra violet light in both supply and return ducts. Then, balance room pressure by choking down supply air in examining rooms...an idea that needs work.

clammy

I would believe that to be a tall order . In my area there are a lot of small offices and tons of older homes that where converted ions ago to medical and dental offices . I don’t know how it could be done with out just about a total renovation and in a lot of cases the practices would have to re locate plain and simple . All the clean room systems I ve worked on where all 2 door airlock and besides the hepa supply and return filter grills they seemed to use just standard rooftops w ecomizer on them . Ceilings where just drop but all walls ran to the ceilings and all penetrations sealed .most where for medical equipment manufacturing mostly For heart catheters and knee and hip replacement stuff . Laboratories and production are a different story and most have seperate vented work booths that operate independent of the main hvac systems and a lot depends on what there doing most try to fly under the radar being unless there trying for some iso rating which I ve seen and was not overly confident that it’s standard where up to stuff . Either way if that does go into effect I would image the money gotta come from some where and wonder where and who s gonna pay in the end . sounds overly paranoid and a cover all bases without some real testing and true research from the field ,not just some Politician or government appointee shooting their mouths off to cover their butt . Tall order $ either way . Peace and good luck clammy

motoguy128

I agree... as usual policy makers are mostly accustomed to larger metro areas with huge overdeveloped medical office suites. We are assuming these businesses have proper commercial equipment, RTU;s with economizers, etc. Most dentists I’ve been to are residential split systems not MUA.

However, you may be able to meet the intent by isolating rooms with curtains or tight doors, and installing exhaust fans in each room. Then increase heating and cooling system sizes and add passive MUA ducts to media filters. May need to increase the size of heating system in cold climates, within the ductwork limitations. And add a minisplit if needed for more cooling capacity in lobby areas that get all the fresh air.