DX - EVAPORATOR COIL FACE VELOCITY IS 250 FPM

[Rastogii]

Hi,

we are using DX- Ducted split units and the data sheet I received from manufacturer shows the evap. coil face velocity 250fpm. As per our requirement cooling demand is high with less air flow- T.C.C - 68 TR - Airflow 15600 cfm

My question is;

At this fpm the air passing over the cooling coil will be relatively low will this cause any problem on coils for long run? What is the range allowed as per ASHRAE for DX Coil face velocities I have seen the face velocity must not exceed 550 fpm but min range not available.

As per our design and requirement-
Air flow requirements across the evaporator coil is very low - 1TR = 229 CFM does this cause the evaporator coil icing/shorten compressor life and reduce typical AC system EER.

Thanks,

 

[ZDR1985]

How did you come up with 15600 CFM? Looks like delta T is too high.

 

[Rastogii]

Design Ambient is 50Deg C
With Air On Coil Db/Wb Deg C-30.9 / 21.6
Air Off Coil Db /Wb Deg C - 12.9/12.6

 

[willard3]

A web forum is not a place to check ASHRAE tables. Take down the ASHRAE volume and READ.

 

[Rastogii]

Hi Willard,

I did read and checked the ASHRAE volume but only max allowable face velocity included which must exceed 550 fpm.

 

[dbill74]

What is up with people mixing unit systems? Velocities in FPM (Imperial) with temperatures in deg C (SI), opening yourself up to make errors.

Sorry for the vent there Rastogii, seen too many posts and questions where unit systems are mixed.

As for you question about velocity, 250 fpm does seem low. My main concern with having velocities too low would be coil freezing, especially with coils containing 4 rows or more. As for a "minimum" velocity, I think it would really depend on the manufacturer and coil specifications.

The 500-550 fpm maximum is a "rule-of-thumb" figure and again depends on actual coil construction. But is good for 90% of the coils out there.

Could always go back to the manufacturer and have them verify the coil face velocity is within their normal operating conditions.

PS)Where are you that has a design ambient of 50 deg C/122 deg F?

 

[Rastogii]

Hi dbill74,

Coil icing up at such low velocity which will greatly shorten compressor life as well.
Evap Coil const Cu/Cu- 8 rows /12 fins/inch ?
Design ambient is for Middle East-Kuwait.

I will again discuss this with the manufacturer.

Thanks,