I don't get why you are chilling the light exhaust if you are just dumping it outside anyways. Just wondering.
Instead of typing it, I'll cut & paste from:
http://www.hydroinnovations.com/product3.htm
The Ice Box is a safe and effective way to water-cool the air leaving your reflectors without adding a/c or more fans. It uses a water to air heat exchanger to water cool the hot air your reflectors produce. Water-cooling is much more effective and efficient than air-cooling, here's some science to prove it: Water has a thermal conductivity of 0.6 W/ (m*K) which is much higher than the thermal conductivity of air which is only 0.03 W/(m*K). Water also has a much higher specific heat capacity than air. What that means is water can absorb and remove from your garden 4 times the heat nearly 20 times faster than air! We aren't just talking about air cooling your reflectors, this goes for your air conditioning system too. Once heat is released in to your room the ability to efficiently remove that heat is lost. Air is only cooled with electricity whereas water can be cooled in dozens of ways with little or no energy. Further only 30% of the energy used in air conditioning is converted into usable cooling power, the rest is wasted. It doesn't take a rocket scientist to figure out that water-cooling will reduce your electric bill ... making your grow room a much happier place for you and your plants. In addition to cooling the heat from all those miniature suns we have in our grow rooms, if the water running through the Ice Box is cold enough, it can actually add supplemental air conditioning to your room, making them great for every operation from hut to warehouse.
Here's how it works:
The Ice Box design consists of a copper heat exchanger with a molded plastic housing. One side of the housing is designed to slip over a duct flange and the other side is designed to attach to your existing air ducting to run to an inline fan. Air from your room is pulled through your reflector just as it is now, and then over the Ice Box heat exchanger before exiting right back into the room. Cold water is circulated through the Ice Box, which is what draws the heat from the air before it exits back into your room. And a little bonus for all of us, with this device there is no need for air to enter or leave the growing environment, improving CO2 efficiency and reducing the introduction of pests, fungi, etc. Increased CO2 efficiency means lower costs for CO2 production and, for those of us burning gas to create CO2, even more control over heat production since we're not having an open flame in our rooms for quite as many hours a day. To adequately cool the air flow from a 1000 watt bulb, the circulated water only needs to be 10 degrees cooler than the ambient temperature in your room. So if you want to maintain a room temperature of 75 degrees, your water temperature only needs to be 65 degrees for the air temperature entering the reflector to be the same as the air temperature exiting the reflector. If you want to add supplemental air conditioning to your room, bring the water temperature down by more than 10 degrees and when it exits your reflector it will be cooler than the room itself. To cool the water you would need 1/4 hp minimum per 1000 watt reflector-yes, chillers use energy but not as much energy as a/c! Remember how much more efficient water cooling is over air. If additional cooling is needed for harsh environments the Ice Box itself can also be easily daisy chained for cooling power that is doubled, tripled, quadrupled. You get the picture.