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Kemphas
17-04-2012, 12:27 PM
Hello,

This is my first time to the forums here, hopefully you guys can help me out.

I have a Stainless Steel Nema 4X enclosure that is 84"H 24"D 48"W. I was trying to size a Thermo Electric Heat Exchanger from a supplier. I have ~ 500 Watts in my enclosure, with direct sunlight, external temperatures of 105F and Delta P required of Degrees (Max internal Temp 90F).

The supplier stated with R12 Insulation and there 2500 BTU Exchanger i can achieve 16Degrees Delta; however, there 2500 BTU exchanger is not C1Div2 rated so i have to use there 1500 BTU Heat Exchanger.

Now im no genius but if i have 2 heat exchangers, i would have a cooling capacity of 3000 BTU? But when they performed there magic calculation that they wont tell you how they get they said with the two 1500 BTU Heat Exchangers i would only get 10 degrees Cooling.....


Does this sound right to you, because i use to work for a company that supported Telecom and while i wasnt an engineer or involved in sizing air conditioners i dont be worked with some of the people on occasion and dont recall an stipulation or anything about having more heat exchangers lower the cooling capacity.


I know its harder and harder to increase Delta P and thers a point you wont get above ~ 25 degrees Delta P but if i have 2 x 1500 BTU heat exchangers should they not at least make up the cooling capacity and capability supplying at least the same minimum amount of Delta P as a 2500 BTU Unit?

These Heat Exchangers are new for us using, we normally use Vortec Coolers and don't experience problems. But i tell you chasing this tail has made me wake up at 3 AM this-morning and here i am typing on this forum. The attempt of this has become futile, mundane, and down right aggravating. Hopefully someone here can shine some light in a fashion i can understand why i don't get at-least the same cooling capacity out of a 17% increase in BTU Cooling Ratings.

- Thanks.

aramis
17-04-2012, 02:48 PM
Welcome to RE forums!

Though your phrasing and use of temperature delta Ps gave me a headache, they are absolutely right if the heat exchangers are installed in series, they will not perform the same because one is subject to much lower temperature differential.

However if they are installed in parallel you would be right, the capacities would add up IF AND ONLY IF both HE get the flow the capacity was calculated with.

Kemphas
17-04-2012, 03:35 PM
Yeah sorry I remember the term delta p from when I was doing ac maintinance in Telecom being the difference in condenser and evaporator. I have really bad memory for names and have kind of a scatter brain.

This is a heat exhanger by eic solutions model 145 I believe. I don't know exactly hoe they could be installed in series as there is no refrigerant. They ate both mounted to the side of the controller have the same outside air and both have the same temperature inside air. The have a fan that pulls air from the sides and pushes out the front. I'll post a link when I get to the offfice.

Kemphas
17-04-2012, 04:34 PM
http://www.eicsolutions.com/1500btu-thermoelectric-air-conditioner.php

aramis
17-04-2012, 10:12 PM
Series means that (all) the air going through one will also go through the second one.

In this case they will operate with different temperature differentials.

If you see their performance chart it depends heavily on the temperature difference with the ambient. If the same air will be circulated through the second one it will perform much worse.

Installed in parallel it means that both will get the same air conditions at their intake, provided both have the same amount of air.

Anticipating your next question, yes they could vary their air intake depending on how they are installed!

Brian_UK
17-04-2012, 11:07 PM
I think that you may be suffering from a terminology problem.

The makers state that you will only get a 10 drop across the 1500 unit and they are correct. The unit is rated for that duty.

The fact that you have two of them does not make the unit provide a different rate of cooling, all you have now are two units that are each rated at 10.