Recovery room 3

[grass22]

i need help on air change requirement in a recovery room. I have a room of 40x20x8 code says 6 ACH and no recirculation allowed.

CFM = 40x20x8 x(6ACH)/60 = 640 CFM

By my load calculation i need about 1200 cfm for this space. And i will have dedicated unit for this space.
My question is what size unit i should use and do i need to exhaust all the air i am supplying as no recircualtion is allowed. Or can i exhaust only 640cfm.
If i exhaust all the air 1200 cfm then i need a makeup air.

 

[quark]

No. of ACPH is the recommendation to maintain minimum flow required to keep the contaminants out. You should, however, go with the maximum cfm you get based upon your heat load calculation. If you input 1200 cfm and take out 640 cfm, your room will be pressurized to great extent and you will find uncontrolled leaks to the outer areas.

So, ideally you have to exhaust 1200 cfm if your area doesn't require pressurization. If you have to pressurize the area, then find the leak rate by using Q_leak = 2910xAxDP^1/2, where A is leak area in sq.ft and DP is differential pressure in inches WG. Then Q_return = Q_supply-Q_leak

If you are worried about energy wastage, go for heat recovery systems.

 

[grass22]

I guess i am little confused when you say 1200 cfm exhaust does it mean to outdoor. Or i will take 1200 cfm as return and exhaust 640 cfm. Then add 640cfm as fresh air to my 560cfm left over.

Will this 560cfm considered as recirculation which as i understand is not allowed by code.

 

[ChrisConley]

No recirculation means no return air. So if you need to supply 1200 cfm, you need to exhaust (to the outside) 1200 cfm.

The calculation quark lists is to allow you to calculated a differential airflow for pressurization, if you're required to pressurize.

If there is no requirement to pressurize, a 10% difference between supply air and exhaust air is generally acceptable to create a mild positive in the area.

Another thought, if you used colder air you would need less air to meet your loads. Could be much more energy efficient in the long run. (small DX or chilled water duct coil say to drop the air temp).

 

[lilliput1]

Fot Recovery Room, the 2006 AIA Guidelines for Design and Construction of Health Care Facilites Table 2.1-2 requires minimum 2 ACPH outdoor air, minimum 6 ACPH total air change, no recirculation by means of room units. It does not require that all air be exhausted directly to outdoors. The no recirculation requirement is only for fan coils that can not provide the MERV 8 (30% AHSHRAE) efficient initial filter and the MERV 14 (90% ASHRAE) efficient final filter, with the final filter downstream of the supply fan per Table 2.1-3 requirement.
You can use variable volume system to limit the minimum supply air to 6 ACPH while using minimum 2 ACPH of outdoor air using central system type AHU with the required filters.