Sensible Heat ratio

[lh.ahn84]

Hi Gents,

I am quite new in this field and would like to request your kind advise.
I am in the Marine & Offshore HVAC field
I am now calculating one project by the following methods, Please correct me if i am wrong.

1) Calculating the supply air quantity by rooms' air change rate, to remove the sensible load ,fresh air requirement.
2) Calculating the cooling capacity by manually.
3) Cross checking by using ashrae psychrometric analysis CD version software.

The load is most likely the same in both calculation
*The problem is that sensible heat ratio that software provide and manul calculation is different in tons.And I cant put SHR line in chart according to my calculation. Let say on coil is 32'C @50%RH (32'C@50%RH), Off coil to be 11'C@8.1g/kg. SHR is 0.8. Software SHR is about 0.4


Kindly advise me in this issue

[Magoo]

Air on at 32' C at 50% RH and off coil dry bulb at +11 C is a dramatic change in wet bulb temp condition, hence SHR of 0.4. 60 % of coil duty is latent cooling, de humidification. Most off the shelf air conditioners have a SHR factor of average 0.80 > 0.85. All dependent on air flow versus coil surface area and saturated suction condition in the coil

[lh.ahn84]

Thanks Magoo for your advice. This is for the marine project which the ship will be operate in gulf of persia and spec call for the 30% Fresh air ratio.
But I am still in the grey area that the reason of SHR is different between the chart and manual calculation.Which one is correct to size up the DX Coil. BY the way, the air flow is 18,00 CMH and coil surface area is 2.2m2

[Magoo]

Try www.thePetroStreet\Psychro shop (http://www.thePetroStreet\Psychro shop)

[lh.ahn84]

Hi Magoo,

Thanks again for ur advice.
By the way I am currently using ASHRAE psychrometric analysis, CD version.

[Magoo]

Basically you have to play around with off coil conditions to increase SHR and lift the WB and dew point conditions, which will mean a larger coil surface area and limit/ control of SST higher. The off coil RH has to be high to increase SHR.