Evaporative Cooler - Efficiency
Evaporative Cooler - Efficiency
(OP)
Hello there, first thread!
My friends and I just finished building an evaporative cooler using some cellulose panels and a walmart vent. We are pumping water at ambient temperature and we need to calculate the efficiency. I know that its a ratio between the temperatures, but since we are using water vapor I believe that the relative humidity has to be included somewhere.
I'm really stumped and I'm afraid of thermodynamics, but hopefully with this project we will get a better hang of it. Any assistance will be appreciated!!!
Thanks,
Paul.
My friends and I just finished building an evaporative cooler using some cellulose panels and a walmart vent. We are pumping water at ambient temperature and we need to calculate the efficiency. I know that its a ratio between the temperatures, but since we are using water vapor I believe that the relative humidity has to be included somewhere.
I'm really stumped and I'm afraid of thermodynamics, but hopefully with this project we will get a better hang of it. Any assistance will be appreciated!!!
Thanks,
Paul.





RE: Evaporative Cooler - Efficiency
1. You need to measure the pump current and calc W (A).
2. Measure the inlet air dry and wet bulb temps.
3. Measure the outlet air dry and wet bulb temps.
4. Use a psychrometric chart from ASHRAE to determine enthalpy at each of the inlet and outlet.
5. Measure inflow air velocity. Calculate mass airflow.
6. Multiply the mass flow by the difference in enthalpies to get cooling effect, W.
7. Divide to get efficiency.
RE: Evaporative Cooler - Efficiency
Since its a direct evaporative cooling system, open system, wont the performance be dynamic due to the changes in humidity?
RE: Evaporative Cooler - Efficiency
RE: Evaporative Cooler - Efficiency
Work out your sensible cooling gained at the cost of humidifying the air
Entering/leaving wet bulb should be about the same, the fan heat will raise it a bit.
Evaporative cooling follows the constant wet bulb of the entering air.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Evaporative Cooler - Efficiency
RE: Evaporative Cooler - Efficiency
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Evaporative Cooler - Efficiency
As the evaporator coolers are used in the dry arid areas to cool and add moisture to the air. As the air passes through the cooler, the dry air give sensible heat to the moisture and result in the evaporation of the water and this moisture contents is then added to the air. Thus accounting for the energy balance in the two fluids.
RE: Evaporative Cooler - Efficiency
RE: Evaporative Cooler - Efficiency
Termcool: Thanks for the explanation!
JStephen: Yes you are right, its performance, not really efficiency. And yes, the cooling effect is more a feeling than something else.
Ok, so I think I'll proceed with Cinimace steps and perform the calculations. Hopefully I can find the air flow specifications of my vent, cause otherwise its going to be quite a chore... thus, its winter here (not the best season to finish this project), so the cooling feeling will almost go unnoticed. :S
RE: Evaporative Cooler - Efficiency
I know its Q*density, but... how can I have Q out of a store ventilator? :S
RE: Evaporative Cooler - Efficiency
Charts are set up with a pound of dry air and so much moisture for every pound of dry air.
You can then determine how much moisture 'accompanies' each pound of dry air before and after the humidification/evaporative cooling
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Evaporative Cooler - Efficiency
For example, 90F is DB, 70F is WB before entering the cooler and 75F is DB after the cooler then Eff. = (90-75)*100/(90-70) = 75%. You should note that, like JStephen suggested, the efficiency here is figurative.
RE: Evaporative Cooler - Efficiency
RE: Evaporative Cooler - Efficiency
Es = (DBD/WBD)*100% = (T1-T2)/(T2-T3)*100%
where:
DBD = Dry Bulb Depression (T1-T2)
WBD = Wet Bulb Depression (T1-T3)
T1 = Dry Air (inlet) INTO cooler, F-deg
T2 = Dry Air (outlet) FROM cooler, F-deg
T3 = Wet Bulb Temperature(officially), but the temp of the return sump water (draining from pads) can be substituted as a "close enough" approximation.
...common 2"-thick aspen-excelsior pad coolers achieve 85%-90% with new, clean pads; efficiency is highest at LOW airflow rates.
...newer Celdek/Munters, etc. celulose (sp) pads can achieve 90%-95%, but only at higher airflow rates.
Tucson, AZ.