qwestion about RH and heat rejection

[Yuri B.]

Hello
The higher is the ambient air 's RH the better is heat rejection of the condenser isn't it?

[nike123]

I think that heat rejection of condenser is not affected with RH of air.
http://www.youtube.com/watch?v=IbVmpWvBIB0

[mad fridgie]

Heat rejection of condenser is not affected with RH of air.

Incorrect, (Wrong) the higher the RH , the hgher the density (Wrong). Great SHC and heat transfer properties (Wrong)
As your fan is a fixed volume flow, then your air mass flow would increase.(Wrong)
Of course I presume we are talking about air cooled condensers.
How much of a practical difference, between 0% and 100% it could be a good few %.(Wrong)
Think of it as a bit like alltitude. Right
I AM WRONG
Sorry Nike

[nike123]

Incorrect, the higher the RH , the hgher the density. Great SHC and heat transfer properties
As your fan is a fixed volume flow, then your air mass flow would increase.
Of course I presume we are talking about air cooled condensers.
How much of a practical difference, between 0% and 100% it could be a good few %.
Think of it as a bit like alltitude.

OK, that doesn't seem to coincide with what I concluded by adjusting RH on SIAHUCALC software. Could you check video I posted (in edited 1. post) and comment.

[mad fridgie]

OK, that doesn't seem to coincide with what I concluded by adjusting RH on SIAHUCALC software. Could you check video I posted (in edited 1. post) and comment.

Hi Nike, did check (on coolpack), look at my edit.
We live and learn.
cheers
Mad

[mad fridgie]

Hi Nike, did check (on coolpack), look at my edit.
We live and learn.
cheers
Mad

Mad in your own defence, you have presumed that you had a fixed volume of dry air then you added water vapour, then your density would increase, so would your pressure. Then your original presumbtions would be correct.
The question should now be asked does increase in RH change your locallised air pressure?
Mad Mad Mad (alter egos)

[nike123]

Mad in your own defence, you have presumed that you had a fixed volume of dry air then you added water vapour, then your density would increase, so would your pressure. Then your original presumbtions would be correct.
The question should now be asked does increase in RH change your locallised air pressure?
Mad Mad Mad (alter egos)

Now you talking with someone on same level.

[nike123]

I AM WRONG
Sorry Nike

.............

[Yuri B.]

Thank you
So, making the air, entering the condenser, more humid, wont reduce the load on the latter : heat rejection would worsen, HP would increase.

[mad fridgie]

Thank you
So, making the air, entering the condenser, more humid, wont reduce the load on the latter : heat rejection would worsen, HP would increase.

This is a slightly different question, if you add water to the air stream into the condenser, then the water will vapourize, making the the air cooler. This would certainly help in reducing condensing pressures.

[icecube51]

Yep, thats wy the make small water towers to cool down big volumes of refrig in condensors.
Have two chillers in service contract, both are of the same cooling capacity (265 KW), one has a DX condensor other one is a thirth of the sise but has a watertower to help cooling the small DX condensor. So its thru, if you add water to the air for cooling the condensor, its helps a lot. See wat happens if you have a hot summer day, and the client cals you for help because his systems trips in overheating. Take a firm hose of water and spray it over the condensor wils it is operating. You will see that everything comes back to normal.

Ice

[mad fridgie]

As this was such an interesting question (original), and I am free of Jack (JD), i have calculated a bit further, yes the density does drop, but the SHC does increases. The ratio is in favour of the SHC capacity, thus would very "slightly" beneifit the condenser with increased humidity.

[lana]

Hi there,

Almost all places which have high Rh are placed near the seas or oceans. This means sea level altitude. At this altitude air density is higher than air in higher altitude. When air density is high, air mass flow rate will be higher for the same fan. This increases the condenser performance.
BUT moisture in air does not have latent heat. If you spray liquid water on an air cooled condenser then heat transfer will be so much higher because liquid water has high latent heat.
Moisture in air already lost its latent heat.
When you calculate air cooled condenser and change RH from 10% to 90% you will see that there is negligible difference in performance.
Cheers

[icecube51]

Hi there,
Moisture in air already lost its latent heat.
When you calculate air cooled condenser and change RH from 10% to 90% you will see that there is negligible difference in performance.
Cheers

I cant agry more on the 90% fact, but if you go from 10% to 100%, as i said, spray it whit a hose, than you will see a nice difference.

Ice

[lana]

Spray it with hose means liquid water which has huge amount of latent heat and this will make a huge difference. We are talking about humidity of air which already lost its latent heat and became vapour.

[nike123]

Thank you
So, making the air, entering the condenser, more humid, wont reduce the load on the latter : heat rejection would worsen, HP would increase.

Nope! It will remain same.
Dont confuse humid in the air with water. Humid in air is evaporated water. Therefore, latent heat in humid air is alredy absorbed (by water evaporation) and only sensible heat could be transferred to humid air.

[mikeref]

It's hard to believe you get 40c days Ice?