Adiabatic air mixing

[stern]

In order to determine the right size of a heater for an evaporative air cooler I have two cases:
1. 100% fresh air
2. Air mix, 70% Return air, 30% Fresh air

For 1 I get X KW´s

For 2 I get Y KW´s


X=Y , X>Y or X<Y and why?

Thanks,

 

[Drazen]

You would need rather comprehensive course on thermodynamics if you want to cope with that.

First, evaporative cooler is constructed to achieve desired thermodynamic process, and second psychrometric calculation of air scenarios is needed, where data you provided means nothing without design conditions of air, outside air, indoor air.

For the outside air you also need humidity design condition for your area, not high temperature design condition as it goes for calculation of interior heat gains.

This is typical situation where could can get nothing but damage using some rules of thumb.

 

[willard3]

Enlist the aid of someone who understands thermodynamics.

 

[317069]

Sorry Stern I didn't understand your question exacetly
you need to size a heater(I guess electric heater) for an evaoprative air cooling unit, what for?
if this unit is uesed to cool(in summer only) a place located in hot humid region you don't need heater
if this unit is used as a cooling tower it is not related to the air flow
if it is used to provide heating and humidification to the air( like air washer) then you need more details as Drazen said

for your question about air mixing(regardless to evaporative unit).
X>Y because the delta T in case 1 is begger than it in case 2.

 

[stern]

Thank you 317069, for your practical response.

Yes it is an electric heater provided for winter, so during this season only the air is used with no water.

I agree with you, with 100% fresh air there has to be more KW required due to higher delta T.