Medical Air for outside air?

[PagoMitch]

Have an interesting problem and trying to think outside the box.

Working in a hospital doing a replacement of about 100 old chilled water fan coils with new, but with the addition of hot water heat. These serve medical offices only, no patient rooms. They were installed 20-40 years ago and are pretty much beyond their functional life. Unfortunately, when they were installed there was no outside air provided. Some (maybe half) had openable windows, but the other do/did not. So I need to get OA to the units (around 50) without openable windows.

Also unfortunaely, there is no reasonable menas to get OA to these units.
a. Corridor ceilings are packed. A 2" pipe may be able to be installed, but no way an OA duct.
b. Most of the problem rooms are interior spaces, so no exterior wall.
c. No room in corridor to duct OA across to get to an exterior wall.
d. The only option is to create an OA fan room in the basement, run OA duct horizontally around 400 liner feet, then branch off into OA risers appx 12 times, and come through 3 floors of occupied space to get to our floor with the OA risers. IMHO this is unreasonable, and will be extremely expensive.
e. Could also go up and do the same thing from the roof, but would have the same issues of risers through 3 floor of occupied space.

Had another idea this weekend when out in the garage working on stuff. Why not use the Medical Air system to provide OA? I can easily get 100 cfm through a 1.5" pipe. Expensive? Yes, but not compared to a new ducted system in the basement, risers, coring holes, fire dampers, furring out shafts, etc. I believe this is actually a "relatively" economical solution.

Other than apparantly never having been done before (at least according to my googling), does anyone see any downsides other than cost? This would be off of an existing oversize bonafide Medical Air system, with testing and alarms, so I am not worried about quantity or quality of air.

And no, this is not a late April Fools joke...

 

[MintJulep]

I would think the operating costs would be unpalatable for the owner.

 

[DRWeig]

Agree with Mint. Calculate the medical air compressors' energy cost for your outside air quantity on a continuous basis. I think it will turn out huge, but I don't have time today to make an estimate. The cost of your nightmarish ducted system may well be worth it.

Best to you,

Goober Dave

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[PagoMitch]

Hm. I was looking more for technical comments, but here is what I have for a first pass at economics:

Air Compressor:
Well, there is an existing good sized ((2), duplex 300 SCFM units each)) with a 250 gallon receiver. So initial costs are nothing. There will be some added maintenance, but I am going to ignore that for now.
For sizing, figure 1 person/room, 50 rooms = 5 cfm each, maybe a bit less, = 250 cfm.
From info I have readily at hand, a 125 cfm 100 psi air compressor has a 10 hp motor.
So allowing 1 hp = 1 kw, and with power at $0.10/kwh = $1.00/hr for 100 cfm. At 250 cfm = $2.50/ hr. x 8 hours/day = $20/day
At 2080 hours/year = 260 occupied days/year = $5200/year.
This would be worse case, as the equipment is existing and there is considerable economy of scale that I have not taken into account.

Ductwork:
1. Fans: assumed 2, as I cannot run 400 feet in the basement un-impeeded = 2 at 125 cfm ea, prolly 3" ESP say $1000 each installed = $2000.
2. Ductwork 400 Lf at $5/ft installed = $2000
3. Risers = assumed 12 in order to group rooms together and avoid horizontal ductwork in the occupied floors. Core drilling/clean up in occupied areas = $1000/hole x 12 risers x 3 floor = $36,000
4. Fire dampers = 36 at $1000 each = $36,000
5. Constructing and finish of shafts in occupied spaces for risers. Figure $1000/room disturbed = 12 risers x 3 floors = 36 shafts @ $1000 ea = $36,000
6. Distribution ductwork from risers to new Fan Coils = 50 rooms x $500 ea = $25,000.
Add it all up and I get 2000 + 2000 + 36000 + 36000 + 36000 + 25000 = $137,000.
As this is working in a fully occupied hospital setting, dust and noise control is a BIG issue. Probably add 20% = +27400 = $164,400. And this price is probably low.

So. $164,000 now or $5200/year for the next 20 years. A simple payback analysis yields 31 years... When it is all said and done, $5200/year in additional operating costs is acceptable. A $164,000 additional capital cost is probably not...

So economics aside, any other comments on engineering issues?

 

[IRstuff]

100 cfm is roughly 140 mph through a 1.5" pipe. If you tune your registers, you might be able to get them to play music and save on the Muzak...

TTFN
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[PEDARRIN2]

You need to look at NFPA 99.

I seem to remember that medical air cannot be used for anything other than medical purposes.

Not having patients might enable you to do it, but it would require verification.

 

[PagoMitch]

Thanks guys,

I actually thought about the noise problem, but only in the "discharge into the fan coil plenum" aspect. Have never had a problem with air piping noise in transmission; although I liked the thought of tuning the register ... That said, when you crack open a valve on a compressed air system, it is noisy. Unless no one can shoot my idea down for another reason, next step is to find a silencer; kind of like a muffler on a car.

I believe the limitations on Medical Air were to thwart folks wanting to utilize it for Dental Air, or Shop Air. As the facility has a giant Med Air system that is significantly under-utilized, I was thinking to isolate their duplex systems back at the source. One Med Air compressor to remain providing Med Air, and the other re-purposed to OA needs.

This whole thing is really nuts. The building and the systems have been in place and in service for decades. Does the OA meet current code? No. Did it when the building was built? Yes. And no one has yet suffocated from lack of OA in the building. Yet to comply with current code (by installing a ducted OA system) we have to spend almost 50% more for the project, or dream up goofy solutions such as piped OA... (Sigh)

 

[IRstuff]

One major objection might be analogous to my yearly ritual of getting the D@#$%@#$@#MN water main backflow valve tested, as required by the city. The back flow valve prevents any flow from my house back into the water mains.

I can imagine that one could argue that there's a similar risk of an active air leg sucking stuff out of a dead leg, and if the dead leg was somehow contaminated, say, with Legionella, because of its connection to the A/C, that would be a serious health issue for which no sane inspector would allow.

TTFN
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[miningman]

Personally I think theres an issue with your preliminary economics. A 600 cfm compressor needs a 125 HP motor so I dont see your 125 cfm needing less than a 25 HP motor. Theres a 250% increase in power costs. Then I have to query your idea of only running the system 260 days per year, 8 hours per day. Most hospitals I am aware of funcion 24 hours per day, 365 days per year. Thats almost 8800 hours per year. I accept that SOME offices will only be occupied during the day but many will be in use 7 days a week, at least 16 hours per day. I wouldnt use less than 5000 hours annually if these were my calcs....another 240% increase.

Then I would severely question your estimate of 5 cfm per room ..... thats pretty close to laminar flow and in an older building I suspect variations in external temperatures would generate sufficient natural ventilation pressures to totally overwhelm a 5cfm make up air scenario.

Just my thoughts.. luckiliy I have almost zero knowledge of the interiors of hospitals.

 

[Drazen]

If I understand well, these spaces are administrative offices or similar? Would you try with transfer air, putting two grills, one at the top, the other at the bottom of room doors, and ventilate corridors to say 0,5 ACH suply, without exhaust, using axial wall fans?

Maybe not the best solution, but maybe the only one in conditions you described. Some transfer grills on market are offered with filters.

 

[PEDARRIN2]

I did a little digging and think you will want to consult NFPA 99, 5.1.3.6.2.

I would copy/clip the section, but that might get my post red flagged for copyright infringement.

Even if the MA system is oversized and underutilized, I do not think repurposing one of the compressors for non medical use would be allowed.

 

[317069]

The question is not NFPA allow or not, but this idea is a feasible from engineering side or not, forget about standards for now. NFPA is not applied everywher on the earth.

 

[chicopee]

I like Drazen idea about interconnecting the rooms with registers and if lucky, one or several of these rooms that have windows can be incorporated in the interconnecting plan. Another possibilit, is to build shaftways thru the tree upper floors to bring in OA. Note, compressed air is not breathable air due to oil contaminants so the compressors would be of the type that provides breathable air; such compressors are available but the type that I have delt with in the past were for spray painters.

 

[annu777]

Also unfortunately, there is no reasonable means to get OA to these units.
a. Corridor ceilings are packed. A 2" pipe may be able to be installed, but no way an OA duct.
b. Most of the problem rooms are interior spaces, so no exterior wall.
c. No room in corridor to duct OA across to get to an exterior wall.
d. The only option is to create an OA fan room in the basement, run OA duct horizontally around 400 liner feet, then branch off into OA risers appx 12 times, and come through 3 floors of occupied space to get to our floor with the OA risers. IMHO this is unreasonable, and will be extremely expensive.
e. Could also go up and do the same thing from the roof, but would have the same issues of risers through 3 floor of occupied space.


Solution,
a.b.&c the corridor not directly exposed to the outside door? or interconnected too main lobby? if its connected you can used the ceiling as plenum of OA make sure that the ceiling air tight & make sure the FCU unit installed filter, installed intake air louver in external wall where the OA access. Return air control damper installed in fan coil to make sure the mixing of the air is right ratio to the OA.

d.&e. will proceed if there is no option and try to explain well to the client as consultant i think they can understand the situation. I think they are deserve to invest amount rather than to sacrifice their facilities.