Glycol in Refrigerant Unit

How did you come to the conclusion that the unit you bought cannot remove enough heat to do the job?

1st. the original supplier...Maybe he is looking for a coil sell. Secondly, "Armchair" H-Vac people. Most have said you cannot run glycol through a unit designed for gas and get anything close to the original performance. Some said something about rifle barrel tubing vs. smooth tubing. Me, I am a structural kind of guy, so I am out of my league. But my thought was a BTU is a BTU is a BTU, if we tweek the flow until we get max transfer of BTUs and a warm return temp. we should get something. That is why my first instinct is to install a "flute" header and see what happens.

I'm still a little confused . . .

You didn't say in your original post that the unit you bought was designed for refrigerant gas, rather you said, "We recently purchased a 4 fan, 37,000 BTU Unit Cooler. X-plosion Proof Class 1, Div, 1 Group C&D etc, etc...The unit was to be operated with Propylene Glycol at 30%-35% with a supply side temp of -3 / -4C (-25/-27F)," and in your second post you say, "Most have said that you cannot run glycol through a unit designed for gas . . ."

Starting with the glycol vs gas issue, refrigerant gas compressors will not handle liquids, so if you have a cooling unit designed for gas, the issue with cooling coils is moot.

If your system was designed to pump liquids, and the cooling coil for gas was installed by the manufacturer, then they should replace it with one designed for the glycol liquid you describe.

Thirdly, if your only heat source is a 1.5 HP motor running at full load and has somewhere in vicinity of 85% efficiency, then the heat load is only about 200 watt-hours, or 700 BTU, and it doesn't take much of a coil to remove that much heat, so the one you have should be sufficient, given that the problems with gas and liquid don't get in your way.

Okay...Let's see if I can clarify. Original thread..."After a significant lead time (several months) a unit which utilizes refrigerant arrived"...I meant Gas refrigerant. Second thread..."Most have said that you cannot run glycol through a unit designed for gas"

In the plant, primary cooling is done with ammonia compressors and secondary cooling is achieved with glycol. Ammonia cools glycol through series of heat x-changers. In the room we have a 1 1/2" supply and a 1 1/2" return line which was ran for supplying unit cooler with glycol. A compressor and condenser is not needed in this case. Only the storage room unit cooler which was to have a glycol supply run through the coil and return back with the rest of the hot side glycol throughout the plant. What we have is a unit cooler (Evap Unit) designed to receive compressed gas (Refrigerant)from a compressor. We want to add 1 1/2"-2" headers and connect the coils both on the inlet and outlet sides and simply run glycol through this unit vs. compressed gas (refrigerant) and see if it will achieve a desired affect.

Things are getting a little clearer now.

There's still the issue that (unless you left out something) you don't have much heat input in the room you want to maintain at 13^o C.

I assume that the cooling coil is large enough to actually provide 37,000 BTU cooling, so that's not an issue. What is the pipe diameter, and how many layers of coils are there, and what is the area through which forced air is blown?

The only problem you may have is that the cold side pressure of the glycol is insufficient to allow enough flow to the low side (high temp) return given the pipe diameter and length. I would bet a dollar to a doughnut that if your coils are made of 3/8" tubing or larger, it will provide enough cooling -- maybe very inefficiently, but nonetheless sufficient.

Heat input in room consists of one 1.5hp pump motor and of course the five .5hp fans on the unit itself. (Original thread erroneously said four fans) So no, not much heat gain. Cooling coil is 10 rows (Layers) stacked (running) horizontally of 3/8" tubing making two complete hoz. loops. Up / Back, Up /back , Total surface area of fins is 1,344 sq. in. 96" long by 14" high. Supply side pressure un-reduced is 75 psi through 1 1/2" pipe. We made up 1 1/2" headers with pulled tees to attach to each 3/8" tube both on supply and return side.

I think we are almost there...Thanks for your input

I think you're almost there too. The five fans on the evaporator will only add about 1150 BTU so the total is still only 1850 BTU.

Specific heat of air is 0.24 BTU/lb/deg F, and density of air is 0.077 lb/cu ft. (I would assume that humidity will either not be added or will be low after some time.) Moving 4100 cu ft of air with 5 fans is not much of a load, but without knowing CFM of them, a fair guess is that a 0.5 HP fan will move at least 400 CFM, so worst case is that 5 of them will move 2000 CFM or 1/2 air change per minute or roughly 30 air changes per hour. By my seat-of-the-pants calculation, the outlet temperature only needs to be 1 degree higher.

We are installing as we speak...We will fire it up and see how it goes...We will also hold off on a new coil until and if disaster strikes. This won't be the only inefficient thing in the plant. Its a shame you can accomplish more on a blog like this than you can talking to the OEMs of the world. Appreciate all your input and we will drop you a line and let you know how things go. I owe ya a beer, or whatever your poison may be. Be good, be safe, be yourself...

Thanks again.

Beer's fine . . . !

Good luck, and please let me know how it works.