Evaporative cooling in greenhouse

[rwsmith99]

I work at a research facility which uses several greenhouse facilities. There are two greenhouses side by side with nearly identical volumes. One ("A&quot is a gabled design and the other ("B&quot a semi-quonset (curved roof) design. Both are 30ft. in width and 100ft. in length with similar peak heights.

Greenhouse "B" has two 40" belt drive exhaust fans, each run by 3/4hp 220v single phase motors. "A" has four belt driven 48" fans, two run by 1/2hp 110v motors and two run by 3/4hp 110v motors. The air movement in "B" is such that cooling is approx. 10 deg. F below outside ambient temperature under 80+ deg. F days. Under identical conditions, "A" is only able to stay at ambient temperature or perhaps a degree below. Both have identical evaporative cooling pad systems. All the motors in "A" are 1725 RPM running 3" pulleys with A-size belt grooves. (I think the fan drive pullies on the "A" fans are approx. 20". The fan pullies on the 40" fans in "B" are considerably smaller than 20".)

Where should we spend money to increase the cooling capabilities of "A"?

Thanks, RWS

 

[quark]

RWS!

It's better first to check the wet bulb temperatures in the two green houses. I am new to green house terminology, that is why I cannot visualize the construction. If in Green House A the DBT is very nearer to WBT or the difference is equal to the 'design approach' of the evaporative cooler, then that will be the lowest temperature.

If so, as your outside atmosphere (ambience rather) is same for both the green houses, air in green house A may not be circulated in a proper way. Check it out.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[LouBall]

Hi RWS,
There are many factors and variables to consider in this situation.
Since these buildings are greenhouses, I would assume they have some form of transparent covering. Is the area of this covering the same on both buildings? There may be a considerable difference in the heat-gain from the sun between these buildings.
You described the fans as "exhaust fans". Are they truely exhaust fans which are used to pull air out of a structure, or are they evaporative coolers? If they are evaporative coolers pushing air into the building, are there adequate and equal openings to let the air out?
Regards,
LouBall

 

[rwsmith99]

Quark and Louball, thanks for the posts. The issue has been resolved by changing all 4 fan motors in &quot;A&quot; to 3/4 hp motors, allowing a change in drive pullies from 3&quot; to 3 1/2&quot; (per fan mfr. recommendations.) The resulting increase in fan RPM boosted each fan's performance from <13k CFM to >17.5k CFM, giving us effectively an &quot;additional&quot; fan. &quot;A&quot; now stays about 2 deg. F warmer than &quot;B&quot; instead of >10 deg. F warmer, a much easier management situation. Again, thanks for your assistance!
--RWS

 

[quark]

rwsmith!

Cheers! By the way can you provide some details regarding green house construction?

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.