Coil coil load calculations
Coil coil load calculations
(OP)
Hi friends
Can someone please verify and clarify?
Application: Offshore Rig
Area of operation: North Sea
System :DX
Ambient : 72*F/80%RH
Inside required in Summer : 75*F/50%RH
Loads/Airflows
Room Sensible Load : 187000 BTU/Hr
SHR : 0.89
Supply air: 15000 CFM
Fresh air : 6100 CFM
Return Air: 8900 CFM
Air flows are based on minimum air changes requirements as per offshore regulations
Mix air conditions : (6100x72+8900x75)/15000=73.78*F/68%RH
(RH for mix air is from psy chart)
Supply air temp
187000=1.1 x 15000 (75-Ts)
Ts = 60.7*F/68%RH
When RSHR line is extended on saturation curve it gives an ADP of 47.5*F
For simplicity I have neglected Bypass Factor/Fan heat gain etc..
My Questions are:
1. What is the meaning of ADP 47.5*F and supply temp of 60.7*F. Do we have to cool down the air to 47.5*F and then raise the temp to 60.7*F.
2. Coil capacity should be calculated based on Enthalpy difference for Mix temp and ADP or Mix and Supply Temp.
Thanks
Can someone please verify and clarify?
Application: Offshore Rig
Area of operation: North Sea
System :DX
Ambient : 72*F/80%RH
Inside required in Summer : 75*F/50%RH
Loads/Airflows
Room Sensible Load : 187000 BTU/Hr
SHR : 0.89
Supply air: 15000 CFM
Fresh air : 6100 CFM
Return Air: 8900 CFM
Air flows are based on minimum air changes requirements as per offshore regulations
Mix air conditions : (6100x72+8900x75)/15000=73.78*F/68%RH
(RH for mix air is from psy chart)
Supply air temp
187000=1.1 x 15000 (75-Ts)
Ts = 60.7*F/68%RH
When RSHR line is extended on saturation curve it gives an ADP of 47.5*F
For simplicity I have neglected Bypass Factor/Fan heat gain etc..
My Questions are:
1. What is the meaning of ADP 47.5*F and supply temp of 60.7*F. Do we have to cool down the air to 47.5*F and then raise the temp to 60.7*F.
2. Coil capacity should be calculated based on Enthalpy difference for Mix temp and ADP or Mix and Supply Temp.
Thanks





RE: Coil coil load calculations
Even if the ADP is 47.5*F you will not get there because at 61*F DB leaving air you will still be above the dew point of the entering mixed air of 59.73*F or a dry coil. Sensible Cooling Btu/hr = 214,331 or about 18 tons
1. "What is the meaning of ADP 47.5*F and supply temp of 60.7*F. Do we have to cool down the air to 47.5*F and then raise the temp to 60.7*F". (NO)
2. Coil capacity should be calculated based on Enthalpy difference for Mix temp and ADP or Mix and Supply Temp.
Mixed and Supply Temp.
RE: Coil coil load calculations
If we use only supply air temperature and still we can get room RH 50% if the process follow the SHR line, then, what is the significance of ADP.
Thanks
RE: Coil coil load calculations
The supply air temperature is a mixture of the air that contacts the coil with the air that does not make contact with the coil
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Coil coil load calculations
I have to give this info to a coil supplier for coil selection. would it be usefull if I give them the Supply air temperature as well as ADP info.
Does ADP plays any role in coil selection?
Thanks
RE: Coil coil load calculations
RE: Coil coil load calculations
Cool air down to the supply dewpoint you need and reheat it
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Coil coil load calculations
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Coil coil load calculations
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Coil coil load calculations
What could be the issues if I keep the system as it is. (for room temp and room RH)
As I understand (theoretically). If the procees starts at with a supply air of 15000 CFM, @61*F/68% RH, then follow the RSHR line, absorb 187000 BTU/Hr of sensible load and will give 75*F DB/50% RH
I have uploaded the Psy Chart and Report. Please have a look. Is this thing really going to work.
Thanks
RE: Coil coil load calculations
Extending the line from Mix to CC will not cut the saturation curve, there is no ADP that will work. This means a cooling coil by itself cannot convert the Mix Condition to the CC condition.
Why move all that air?
Your supply dry bulb is too low for 15000 CFM and 187000 sesnible room load, it would be more like 75-187000/(1.08x15000)= 63.5, the dewpoint of the supply air is going to be about 54 or os in that ball park.
Just cool off the outside air to 54F, or whatever your required supply air dewpoint is.
187000/(1.08 x ( 75-54)) = 8245 CFM
fan power will be about (8245/15000)^3 = 17% of what you will use for 15000 CFM, 15000 CFM could be a 10 to 15 hp motor, 8000 could be 5 hp.
You wind up 15000 CFM, you will see a couple degrees of fan heat.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Coil coil load calculations
But now I understand that if I keep the system as it is, I can get 75*F but there could be problem in getting 50% RH. Right?
RE: Coil coil load calculations
With your present scheme I do not see any problems controlling the temperature, but I do see a problem controlling humidity.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Coil coil load calculations