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cold.man
04-02-2012, 10:27 PM
the affects on a refrigeration system with high humidity.

i understand obviously your dry bulb and wet bulb temps for example

10 degC dbt and 4 degC wbt = 6 degC diff = 35% rh and if for instance if your dbt and wbt is the same you would have 100% rh.

what i dont understand fully is if the ( rh ) is high how and why does it affect the cooling capacity of the system or does it?

!!! what affect would high ( rh ) in a supermarket have on the cases on the shop floor for instance?

mad fridgie
04-02-2012, 10:43 PM
First thing to remember is the RH is "relative humidity", so on its own has very little meaning.
What you are really talking about is the actual mass of water vapour in the air.
If you have a lot of water vapour in the air, this will condense out when it becomes cold.
This takes a great deal of energy removal, (which adds load to an evap) but with little benefit to dropping the air temperature.
The term "Sensible Heat Ratio" is used to explain how much of the refrigeration capacity is used to chill air and how much is used to liquefy the water vapour

Tayters
04-02-2012, 10:49 PM
Hi Cold Man,

The way I see it a coil takes heat out the air, this air contains a certain amount of moisture depending on the RH.
Energy is taken out the air and the moisture, therefore the more moisture, more of the duty of the coil is used to cool the water down instead of the air. This cooling of the water wont help cool the space as much as the air.

In your example, the cases would effectivley have a smaller duty coil as they are cooling down air and more water.

Cheers,
Andy.

cold.man
04-02-2012, 11:09 PM
so if your actual mass of water vapour in the air is higher than normal this would put extra load on evap coils ie extra load on the system and inturn affect overall temps.

i would imagine high RH would affect water cooled condensors like it reduces cooling capacity of evaportive air conditioning systems.

i am just trying to understand the affect high RH or high actual mass of water vapour would have on a system, on my understanding the affect of high RH has more of an affect on water cooled evaps and condensors than it does on air cooled would i be right or wrong?

i have established from mad fridgie that high humidity levels puts more load on the evap coils is there any other affects on the system?

just for instance on a supermarket shop floor what would be considered an adaquate humitity level as to where it would not put more load on the refrigeration system.

obviously i would say the lower the better im i right or wrong can low humidity affect the system aswell?

cold.man
04-02-2012, 11:29 PM
cheers for your input mad fridgie and tayters !!!

from the posts !!!

lower the humidity higher the cooling capacity of the evap coils
higher the humidity the reduction of cooling capacity of the evap coils

so what is deemed an acceptable humidity level on a supermarket shop floor as it doesnt affect the refrigeration?

i understand when an air conditioning system is sized for a particular site the RH is taken into consideration on the sizing of the system.

i would imagine when the refrigeration plant is sized for a supermarket the RH would be taken into consideration aswell especially where you have multi deck cabinets as above would i be correct in saying this or incorrect?

this is why i am asking is there a level which is deemed acceptable i know obviously humidity levels change but if the humidity level is controlled on a shop floor this could in fact affect the refrigeration if not correct
putting more duty on the systems and use more energy etc.....

its just somthing i want to have more of an understanding of.....

cold.man
04-02-2012, 11:54 PM
obviously the higher the RH also the more frost build up you would have on the evap coils and the lower RH the less frost build up.

i would expect you would require reduced defrost times with lower RH than that of higher RH for better energy efficiency.

from what i remember you can set up the einsteins to reduce the defrost times depending on the RH do the 255 front ends do this?

mad fridgie
05-02-2012, 12:23 AM
Yes humidity levels effect evaporative devices.
Be care of your assumptions, you are basically correct for supermarket applications, but low humidity on some AC systems can make the AC freeze more. The AC has been designed to allow for dehumdification, when this does not occur, the load is reduced, the SST drops and can below freezing.

cold.man
05-02-2012, 11:31 AM
cheers for the input mad fridgie !!!