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How to calculate TMBH & SMBH for FAHU selection if know supply fresh air & return air capacity?

for an example if supply air is3000 l/s or6000 cfm and return air is2700 l/s or5400 cfm how caan we find out TMBH (TOTAL MEGA BRITISH THERMAL UNIT PER HOUR) and SMBH (SENSIBLE MEGA BRITISH THERMAL UNIT PER HOUR )

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تاريخ النشر: 2015/08/27
Muhammad Arsalan Siddiqui
من قبل Muhammad Arsalan Siddiqui , Associate Director (MEP) , JLL

You can find this through HAP or if you know the air condition i mean temperature DB and WB and RH and Humidity then you can find by Psychometric Chart

SI-Units

The sensible heat flow can be expressed in SI-units (metric) as

Qs = cp ρ q Δt /3600         (1)

where

Qs = sensible heat flow (kW)

cp = specific heat of air (kJ/kg K)

ρ = air density at standard conditions (kg/m3)

q = air flow (m3/hr)

Δt = temperature (oC)

English (Imperial) units

In English (imperial) units the sensible flow heat can be expressed as

Qs=60 cp ρ q Δt =1.075 q Δt         (2)

where

Qs = sensible heat flow (Btu/hr)

cp =0.2388 - specific heat (Btu/lboF)

ρ =0.075 - air density at standard conditions (lb/ft3)

q = air flow in (ft3/min)

Δt = temperature difference (oF)

 

LATENT HEAT

English (Imperial) units

The latent heat flow can be expressed in English (Imperial) units as

Ql =60 hwe ρ q Δx         (1)

where

Ql = latent heat flow (Btu/hr)

hwe =1060 - latent heat of vaporization of water (Btu/lb)

ρ =0.075 - air density at standard conditions (lb/ft3)

q = measured air flow (ft3/min)

Δx = humidity ratio difference (lb water/lb dry air)

SI-Units

The latent heat flow can be expressed in SI-units (metric) as

Ql = hwe ρ q Δx /3600         (2)

where

Ql = latent heat flow (kW)

hwe =2465.56 - latent heat of vaporization of water (kJ/kg)

ρ =1.202 - air density at standard conditions (kg/m3)

q = air flow (m3/hr)

Δx = humidity ratio difference (kg water/kg dry air)

 

And by adding both you will find total Heat

also u can use enthalpy instead of temperature or humidity in the same formula and it will give same result

 

Abdu Samad
من قبل Abdu Samad , Mechanical Project Engineer , Tech Engineering L.L. C

 TMBH= 4.5* CFM* (HI-H2)

WHERE H1= ENTHALPY AT COOLING COIL INLET

H2= ENTHALPY AT COOLING COIL OUTLET

ENTHALPY VALUES  WE CAN CALCULATE FROM PSYCHOMETRIC CHART BY DRAWING GSHF AND RSHF LINES FOR SPECIFIC AIR CONDITIONING SYSTEM

SMBH= 1.08*TOTAL ROOM AIR CFM(T1-T2)

T1= ROOM SUPPLY TEMP

T2= ROOM DESIGN TEMP

Sherif Mohammed Ibrahim
من قبل Sherif Mohammed Ibrahim , Senior Mechanical Technical engineer , Al-Latifia Trading & Contracting Company

SMBH = sensible cooling capacity in thousands of BTU's per hour.

TMBH= total cooling capacity in thousands of BTU's per hour.

Sensible Heat Calculation (at sea level): SMBH =1.* (CFM/) * (∆T air)

Total Heat Calculation (at sea level): TMBH =4.5 * (CFM/) * (∆h air)

as shown in equations and as per eng Muhammad Arsalan Siddiqui you have to get inlet and outlet air condition to use Psychometric Chart to get ∆h air then you can use the equation

as an estimation: (this calculation not accurate don't use it as final)

usually for FAHU one ton =toCFM take it asCFM that means total cooling load is around.5ton

for sensible load take outdoor temp. as.8F and the outlet temp..4F then ∆T air =.4F

the sensible heat will beBTU/HR =.1MBTU/HR which equal.ton

 

NABEEL  AJMAL T K
من قبل NABEEL AJMAL T K , HVAC Design engineer , C and T engineers

SMBH=(1.08)*OACFM*(TEMP OUT SIDE-TEMP ROOM )/1000

TMBH=4.5*CFM*(ENTHALPY OUTSIDE-ENTHALPY ROOM)/1000

 

 Enthalpy values corresponding to the temperatures will get from the psychrometric chart...

chetan sharma
من قبل chetan sharma , Senior project engineer , trinity engineering services

if you know the cfm the simple formula is Q=M. X DELTA H

DELTA H can be obtained from psychometric chart that is H at inside temperate and H at out side temperature

and M. is the flow rate in m3 /hr

REHANA JAMAL
من قبل REHANA JAMAL , Sr. Application Engineer , CURRICULUM VITAE Rehana Jamal 4 II. Name of Employing Agency Zelin (Pvt) Ltd Karachi

We know the ambient and room temperature as well

We can caiculate by using psychrometric chart and caculating the entalpy.

FADEE ALTRH
من قبل FADEE ALTRH , MEP PROJECT ENGINEER , ARTAR: Abdul Rahman Saad Alrashed CO

you shuld care about recovery by heat wheel or heat pipe and the equation above is right answer and final for calculat fresh air load we give 1 ton to each 200 CFM ( nearly )

Afzal Hussain
من قبل Afzal Hussain , ELECTRICAL DESIGN ENGINEER , Al Hamra Engineering Consultants co ,Sharjah

Sir I have much need calculate cfm and smbh but how

 

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