Big Temperature Drop

[THEDUDSTER]

Maybe some of you guru's out here can direct me in a massive temperature drop... We have a room that cannot have a return air supply as it creates explosive gasses while the product is being made. We are in the composites business, where fiberglass resins are being used at all times and the room must maintain 75-80 degrees to keep the resins from reacting prematurely. We use R22 air conditioning system and the return air side pulls ambient air that runs over 100 degrees in the summer months. I was directed to find different system that works to cool this room. The room is approximately 450 sq ft.
We are located in Houston, TX where the humidity is high
In my refrigeration days, we used ammonia because of how low you could get the suction temperature. I am not sure if there is such an air conditioner out there..... Your input is needed!!

[chilliwilly]

You will need to design a system that wiil appear too big for you cubic footage at the first glance. As you will need to take into consideration the air make up for the process you using, that requires a constant air change.

It would be similar to a restaurant kitchen that has a extraction canopy, and open to the dining area. If its really going to be expensive to do that, then how about considering a ground source heat pump/heat dump. Or does the temperature get hotter 6'6" underground where you are?

[Brian_UK]

How does recirculating the air in the room create an explosive atmosphere? I'm intrigued.

[chilliwilly]

It probably increases the PPM to create a volotile atmosphere if the air make up hasn't got a constant change.

[THEDUDSTER]

Thanks guys..... and yes, the Motors that provide the re-circulation, if there were to be a Motor short, blow out, any kind of spark might, not would, ignite the fumes and blow up about 2 square blocks. Same conditions that you might find in a chemical plant. Once the air inside the duct work ignites, the flames would probably travel down the supply duct and ignite the actual room that we are drawing the air from. The chain reaction could be very dangerous.
Now back to my problem....... I saw a guy today that uses one air conditioner to circulate in his room, and one that blows directly from the short side of the room at the intake of the 1st air conditioner. Thus getting twice the temperature drop on the second AC unit. I thought, "this is a good idea!" May even work in my situation. To use a second unit that re-circulates the main flow from the outside air and would use this same principal. Any thoughts on this?

[Rob White]

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Could you use heat exchangers that remove the heat from
the expelled air and transfer it to the input air. Then cool the input
air to required temp.

Modern heat exchangers are over 80% efficient.

Regards

Rob

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[ICE/RUNNER]

From what you have said your main concern is the potential for inginition of fumes from your process. Have you thought about using Ex/Exd equipment to reduce the potential for ignition. The company I work for design and build AC systems for use on oil rigs and where ever there is a potential risk we use Ex/Exd rated motors both on the evaporator and the condenser. A common one we do is a pressurization fan feeding fresh air to a DX coil with fire dampers fitted both up stream and down stream of the pressurization fan, these close automatically in the event of a fire or fault situation with the motor.

[MikeHolm]

How about ceiling radiant cooling. No motors, just a condensate drain needed.