what is the factor (4.5) that you used to calculate the tonnage of cooling in Example 8 when you said (in min 48:12) the (tons of cooling) = difference in enthalpy times the constant 4.5 times the air flow rate of 5000 Cubic Feet per Minute = 34 tons of cooling? I'm not familiar with that 4.5 constant. However, I know that total heat removed by air conditioner, i.e. the sum of sensible heat of the dry air plus the latent heat due to presence of moisture = air flow (m3/sec) * moist air density (1.202 kg/m3) * enthalpy difference (kJ/kg), where multiplying the flow rate by air density gives the flowing air in kg / sec and multiplying this air flow in kg / sec by enthalpy difference in kJ/kg will give certain number of kJ / sec, i.e in kW 1 Refrigeration Ton (RT) = 12000 Btu/h = 3025.9 k Calories/h = 12661 kJ/h = 3.517 kW Thanks a lot.
Sorry for the delay in responding, Dr. Fahmy; I had to ask an expert about this one! According to the video's creator, 4.5 is the factor used to calculate total cooling load (at standard pressure and temperature). The equation is: 4.5 x CFM x Delta Enthalpy = total cooling load including both sensible and latent. The 4.5 factor will change as the elevation changes.
4.5 is the ratio to convert CFM to Mass/sec (at standard conditions in imperial units). The unit conversion is done by taking 60 seconds/min and dividing by specific weight 13.3. SO 60/13.3~4.5
Nobody in the world understands the imperial units these days outside the UK and the USA. You do better to re-make this video using the SI units. Thank you.
Dr. Fahmy - thanks for your suggestion! Because the Psychrometric Chart app includes both SI and I-P units, we should do everything we can to ensure measurements are accurately presented in our videos. I will pass your feedback along, and perhaps work can begin on an updated version of this video that includes SI.
Is there an free app for getting the psychrometric values
do we need to buy the app?
Here is the link with more information on how to buy the app: www.ashrae.org/technical-resources/bookstore/psychrometrics
Is there an app with SI (normal) units..?
what is the factor (4.5) that you used to calculate the tonnage of cooling in Example 8 when you said (in min 48:12) the (tons of cooling) = difference in enthalpy times the constant 4.5 times the air flow rate of 5000 Cubic Feet per Minute = 34 tons of cooling? I'm not familiar with that 4.5 constant. However, I know that
total heat removed by air conditioner, i.e. the sum of sensible heat of the dry air plus the latent heat due to presence of moisture = air flow (m3/sec) * moist air density (1.202 kg/m3) * enthalpy difference (kJ/kg),
where multiplying the flow rate by air density gives the flowing air in kg / sec
and multiplying this air flow in kg / sec by enthalpy difference in kJ/kg will give certain number of kJ / sec, i.e in kW
1 Refrigeration Ton (RT) = 12000 Btu/h = 3025.9 k Calories/h = 12661 kJ/h = 3.517 kW
Thanks a lot.
Sorry for the delay in responding, Dr. Fahmy; I had to ask an expert about this one!
According to the video's creator, 4.5 is the factor used to calculate total cooling load (at standard pressure and temperature). The equation is: 4.5 x CFM x Delta Enthalpy = total cooling load including both sensible and latent. The 4.5 factor will change as the elevation changes.
@@ASHRAEvideo Is there an free app for getting the psychrometric values
4.5 is the ratio to convert CFM to Mass/sec (at standard conditions in imperial units). The unit conversion is done by taking 60 seconds/min and dividing by specific weight 13.3. SO 60/13.3~4.5
4.5 is a constant used to get the BTUHr=CFM x 4.5 x Enthalpy difference. 4.5 = 0.075 the weight of a cubic foot of air x 60 minute
Nobody in the world understands the imperial units these days outside the UK and the USA. You do better to re-make this video using the SI units. Thank you.
Dr. Fahmy - thanks for your suggestion! Because the Psychrometric Chart app includes both SI and I-P units, we should do everything we can to ensure measurements are accurately presented in our videos. I will pass your feedback along, and perhaps work can begin on an updated version of this video that includes SI.
Thanks a lot for your very nice answer to my modest suggestion.