Fog Chiller

The first time that you use a glycol fogger, you will notice that the fog billows out of the nozzle, out and up - giving a "pea soup" effect. A frequently-asked question is "Can I make the fog hug the ground, like in movie graveyards and swamps?"

The way that glycol fog rises up is quite natural. It is hot vapor, fresh from the heat exchanger. It is hotter than the surrounding air, so tends to rise.

In order for the fog to stay close to the ground, it must be colder than the surrounding air. You need to build a fog chiller. Everybody agrees on this.

But nobody agrees on the best way to build a fog chiller. Everybody has their own theory on how to make the best chiller.

We have collected some information on fog chillers...

Particularly notable chillers
Other chiller links
Design tips
How not to build a fog chiller
Wolfstone fog chiller - Mk II

Particularly notable chillers

We have a small gallery of notable chillers. Some are innovative, and some are simply excellent implementations of classic designs.

It is difficult to present a complete historical picture, because some ideas just keep popping up again and again. Just because a design is reminiscent of another does not mean that any design feature was copied. It is frequently the case that several great minds are independently struck by the same wonderful thought.

Except when explicitly stated, pictures and drawings are taken from the indicated sources, and are included by permission.

Early History On Halloween-L

During the summer of 1995, fog was frequently discussed on Halloween-L, including chilling glycol fog. Some of the key ideas discussed in this important time frame:

making a fog chiller out of a "beer cooler"
use of a long cool-down pipe between fogger and cooler
air induction
adding salt to the ice
fog reservoirs
fog expansion areas
fog distribution systems
fan-forced fog distribution
use of quick-dissipating fog juice for low-lying fog

Here are some of the more interesting historical bits...

Scott Axworthy (3 Jun 1995):

Even if you buy a fogger you still have to get the fog where you want it. A fog distribution system can really help if you want to maximize your fogger's capabilities. The best fog distribution systems consist of a fog reservoir, a blower, and flexible tubing to deliver the fog where you want it. The blower is typically enclosed within a reservoir box and blows directly into the tubing. The fog machine is aimed at a opening in the reservoir box. The blower produces suction in the box and the fog is drawn in. The fog is then distributed out the tubing. The extra air pulled in helps increase the volume of fog produced as well. I used my dry-ice fogger as my reservoir as it already had a blower mounted on it and tubing attachments. I directed tubes outside, and into my shop and garage. I used dryer vent ducting for my tubes but you can also use ADS flexible drainage pipe. I then fed the pipe into carved pumpkins. These pumpkins had a large hole cut in the back for the tubing and used lights instead of candle. The fog shooting out of the eyes and mouth looked great.

The earliest reference that I have found about chilling glycol fog was in a post on Halloween-L by list founder Don Bertino (16 Jun 1995):

I have heard there is a "chiller box" that you can use to *cool* the fog the comes out of a fog machine. Do these things use nitogen (sp?) or CO2? You could use that. That would make the fog *hang* around longer.

This message from Denny Dahm, documents what might be the first home-made fog chiller:

Date: Mon, 25 Sep 1995 05:24:03 -0700
From: milwiron (D.D.)
Subject: More Heavy Fog

My Fellow Fog People,
After letting one of the dogs out at 2:30 this morning (thanks Hoover) and laying there not able to fall asleep again. I started to run the past week through my head, important stuff first and then the really important stuff like Dave's experiments with liquid nitrogen and Nathan's heavy fog suggestions. Since I have a couple of glycol based fog generators, one homemade, one commercial, I wondered how to make cool, heavy fog cheaply. My first thought was to use a small, portable, room dehumidifier (I have one I haven't used in years) and just blow fog across the cooling coils only.
Then using regular ice came to mind. Why not use a cheap beer cooler filled with a couple bags of ice (drink the beer first) and blow the glycol based fog through that. Possibly the ice could be in a tray above the path of the fog if needed. A quick dissipating fog might be best since the fog will rise as it warms. Of course any of this assumes little or no air movement.
As a quick test I cut the bottom off a 2 liter plastic Coke bottle and drill some holes in the bottom part I just cut off, filled the bottle with ice, telescoped the bottom back onto the ice filled bottle and pump some fog into the neck end.
It works amazingly well!
While all my fog will be outdoors this year (praying for little wind), I thought others would like to know about this. Thanks Nathan and Dave for stimulating my brain cells.

Denny Dahm (25 Sep 1995):

1. A one or two foot hose leading from the fogger to the ice container would allow the fog to cool before it hits the ice (saving ice). The fog does cool rather rapidly after it leaves the nozzle and expands.
2. A beer cooler will allow longer contact time between the fog and ice.
3. Adding rock salt to the ice would bring the temp. down further.

Scott Axworthy (25 Sep 1995)

On a releated topic, a fog machine is not all you need for a good fog setup. You also need a fog distribution system. A fog distribution system gets your fog to the areas that need fogging. Professional distribution systems consist of a distribution box, a squirrel cage fan, and distribution hoses. The distribution box is typically about the size of a large ice cooler. (Hmmmm!) The fan is installed *inside* the box. The output of the fan is to a 4" round flange that exits outside the box. The fan draws air from inside the box. Four inch flexible dryer tubing or ADS drain pipe then hooks to the flange and is directed to the area that you want the fog. On the other side of the box you need another 4"ish round hole. The output of your fog machine is directed into this hole. The fan creates a negative pressure in the box and sucks in fog and air. It is then delivered to the areas that you need it. The hoses can be Y'd so that the fog can go to different areas.
Not only is it convenient, but it seems to expand the volume of fog by introducing extra air. Now back to the ice cooler box. This is an excellent point to introduce dry ice to cool down the fog and air. The fog coming out the tubes will then drop down and be a ground hugging type of fog instead of a smokey mist.
I whipped out a distribution system in about 5 minutes. I went up into the attic and got out my dry ice fog machine (that I built from a 30 gallon drum). This already had a squirrel-cage fan on top and hose distribution. I fire my F300 directly into the input of the squirrel cage fan and instant distribution system. I haven't tried cooling mine yet but I know that this is the method used by the professional systems.

Nathan Kahn (2 Oct 1995):

Ideally, the drier hose should be as far from the fogger output nozzle as possible, but not so far that the fog doesn't go into the hose. This will help to dry the fog, and you will not have as much residue in your hose as you would have if the hose was directly up against the fogger output nozzle.

Wow! Halloween fogging can sure make a lot of progress in a few months!

Death Lord - Ice Vac

Death Lord is the only guy I know of who has spent literally years building and testing chiller designs.

[photo] This is "Ice Vac", an early design. It consists of a small shop vacuum cleaner full of ice cubes.

Fog goes in the normal dirt entry. Chilled fog is pulled from the bottom of the tank. A dimmer switch slows the motor and keeps it from chopping up the fog too much.

[Death Lord does not keep online information about earlier designs like this, because he considers them to be inferior. He was kind enough to send me this picture for the archives.]

Death Lord - 1997

This picture from 5/14/97 shows another early Death Lord design.

[Death Lord does not keep online information about earlier designs like this, because he considers them to be inferior. He was kind enough to send me this picture for the archives.]

Death Lord - Fog On The Rocks 2000

Through the year 2000, Death Lord was still using a design similar to that of 1997, but with some upgrades and a new name - "Fog On The Rocks".

[photo]

[photo] This picture of the inlet shows that the original design has been modified with the addition of a "muffin" fan, where the metal piping attaches to the ice chest.

[These pictures are from a year 2000 archive of Death Lord's web site.]

Death Lord - Fog On The Rocks 2001

In 2001, Death Lord started a new series of "Fog On The Rocks" fog chiller designs.

A platform holds the ice up, and the fog is injected beneath it. This is reminiscent of Denny Dahm's ice tray suggestion of 1995. Other features are an expansion chamber and controlled back-pressure. The back-pressure was controlled by having numerous small fog outlets.

[photo]

[photo] This is the ice platform - a prominent feature in all future Death Lord designs.

[photo] Fog On The Rocks 2001, ready to go!

[These pictures are from a year 2001 archive of Death Lord's web site.]

Death Lord - Fog On The Rocks 2002

The 2002 version of "Fog On The Rocks" features three outputs made from threaded plastic plumbing fittings, so that the chiller could also serve as a fog distribution system, reminiscent of the Wolfstone 1998 fog chiller. If you don't need all the outputs, you screw in a plug.

[photo] This photo shows two of the outlets plugged.

[photo] This is a later 2002 design, featuring only two outlets. Notice that the inlet is now at a right angle to the outlets, so the fog can't shoot straight through the chiller and out.

[These pictures are from a year 2002 archive of Death Lord's web site.]

Death Lord - Fog On The Rocks 2004

The 2004 version of Fog On The Rocks continues to use a platform to hold up the ice, with an expansion chamber underneath the ice, into which the fog is injected.

The change is that fog output is via a single, larger outlet.

Death Lord - Fog On The Rocks 2005

Death Lord's 2005 design is similar to Fog On The Rocks 2004, but adds a venturi to the input, reminiscent of the Wolfstone 1998 fog chiller.

[photo]

Death Lord considers this latest version of Fog On The Rocks to be best design and no longer supports earlier designs. For construction details, go to http://deathlord.net .

gotfog.com

gotfog.com's chiller (http://gotfog.com/fog_machine_chiller.html

) is a simple, basic cooler design, with a wire mesh tube running through the ice chest from input to output, along the long axis of the ice chest. Ice is packed around the tube.

The tube gives the fog an uninterrupted flow, while maintaining contact between fog and ice.

Using the measurements from gotfog, we can compute the surface area of the fog/cold interface:

19-1/2" long 3" wire tube = 184 square inches

[photo] The full gotfog setup puts the fog machine on top, with a pair of 90-degree bends that are hauntingly similar to Death Lord's 1997 design.

Scott's

Scott's Death Lord-inspired chiller (http://www.geocities.com/Area51/Nebula/6037/chiller.htm

) is just an ice chest with input and output connectors along the long axis. Think of it as Death Lord's 1997 design without the internal tube.

[photo]

Lacking the tube to protect the flow of fog, you have to be careful about how the ice is loaded in. Scott tells how he does it.

Ron Tye

Ron Tye uses a simple approach that I'll call "up and over" (http://www16.addr.com/~rmtye

). Large-diameter pipes with holes drilled in them are used to pump fog into the cooler and collect it for output, with a baffle in between. The photo is stamped 8/16/2001, but Ron first described his home-made chiller in May 1999. This may be the same design.

[This is a slightly edited version of one of Ron's pictures.]

The baffle in the middle serves two purposes: (a) it holds the ice up against the pipes, allowing you to pile up a lot of ice; (b) it makes the fog travel up and over the baffle, increasing fog/ice contact.

The baffle can be made of just about anything capable of holding up to moisture and the weight of the ice. Ron used whatever plastic he had on hand; roughly 3/32" thick.

Note: You can make a variation on this chiller by running the input and output pipes along the long axis of the cooler. This works even better, by providing a larger fog/ice contact area, but requires either a larger cooler or smaller pipes.

Tressler - Blow-By Fog Chiller

Tressler's chiller uses a technique he calls "blow-by", which uses a Y to combine fast-moving air and fog, with results rather like an aspirator (http://members.aol.com/tressler3d/Halloween/page0011.html

). Instead of chilling the fog, he chills ambient air and mixes that with the fog. He first described the design in October 2000.

[Tressler never responded to my request to use his diagram, so I drew a better one.]

Tradeoffs:

The fog doesn't get as cold: the temperature drop is proportional to the temperature difference. Ice and hot fog have a large temperature difference, and thus greater temperature drop. Ice and ambient air have a smaller temperature difference, so less cooling.
The air from the blower is moving rapidly, and there is a lot of it. When it hits the fog at the Y, it might slam the fog against the walls of the pipe, making some of it recondense.
The fog never touches the blowers, which would otherwise smack the dropletts around and recondense them, making the blower blades slimy in the process.

Chuck Rice - Liquid-Filled Coils

Chuck Rice designed and built a chiller into a piece of stovepipe, containing coils of copper tubing (http://www.wildrice.com/Halloween/Construction/FogChiller

). Ice water is pumped through the coils.

[This is a slightly edited version of one of Chuck's pictures.]

Using the measurements from Chuck, we can compute the surface area of the fog/cold interface:

25 feet of 1/4" tubing = 235 square inches
50 feet of 3/8" tubing = 705 square inches
940 square inches total

Terror Syndicate

Terror Syndicate's second book describes a chiller built into a custom-built insulated wooden chest approximately 10x12x36" (http://terrorsyndicate.com

). A bundle of 12 copper pipes go through the chest, and the fog flows through the copper pipes. Ice is packed around the pipes. You can think of this as Chuck's chiller in reverse.

Using the measurements from Terror Syndicate, we can compute the surface area of the fog/cold interface:

12 times 30" of 1/2" tubing = 678 square inches

Devious Concoctions #1

Brent at Devious Concoctions describes a chiller intended for dry ice use. Loops of copper tubing are used to conduct the heat from the top of the box, where the fog is flowing, down into the dry ice (http://www.deviousconcoctions.iwarp.com/fogchiller.html

This is different from other designs that use tubing, because nothing flows through the tubing. It simply serves as a heat conduit - a cheap way to get lots of metal.

[photo] This is the longer of two chillers built on the same principle. It is shown loaded with dry ice.

[photo] This is a shorter one, not yet loaded.

For more information, please see Brent's old web site http://www.deviousconcoctions.com/fogchillers.htm .

Devious Concoctions #2

Brent has more chiller information at his new web site http://www.deviousconcoctions.com

. It includes a new design with fog rising through an ice platform. The ice platform is reminiscent of Death Lord's Fog On The Rocks 2001, but Death Lord's platform forms a ceiling for the hot fog to rise against, and Brent's platform is a cold passage that the fog must pass through.

[photo] The box is 36" long by 12" square.

Ghosts Of Halloween - Trash Can Chiller

Adam, from Ghosts Of Halloween, built a high-volume chiller out of a 3/4th size trash can containing a coil made of 18 feet of aluminum dryer hose.

A nice feature of this design is that fog blasting out of the machine does not slam straight into a cooler wall. Instead, it swirls around, through the coils.

[photo]

Adam's web site is http://ghostsofhalloween.com/. They built the chiller for Halloween 2001.

Design tips

We learned a lot from our first experiments in fog chilling. Here is a list of design tips, both from our own experience, from chiller discussions on e-mailing lists, and a few we have seen in operation.

The name of the game is "surface area", where the fog meets the cold. The greater the surface area of this interface, the better the chiller will perform.
- Bigger is better. The bigger the chiller, the larger the area of the interface, and the cooler the fog winds up. Note that the payoff only comes from stretching the chiller in the direction of fog flow. If you also make the chiller taller and don't route fog through that area, you are wasting cubic.
- The longer the path through the chiller, the better - it increases contact area between ice and fog. You can increase the path while keeping the same chiller size by zig-zagging the path through the chiller.
- Calculation of surface area where fog and cold touch can be used as a rough yardstick to estimate performance of chillers. The larger the surface area, the better.
- It might be a good idea to play tricks to increase the surface area of the fog/cold interface - such as adding fins like those on a heat sink.
The less obstruction to the flow of fog, the better. Every time the fog hits something, a bit of fog recondenses into fog juice.
If using an ice chest or drink cooler in the design, use a plastic one that has insulation inside the walls. Cheap coolers made out of bare styrofoam are structurally weak, and the chemicals in the fog attack the foam.
It helps if the fog has a moist environment. Physical contact between the fog and water-ice is a simple way to get that. Some haunters water the grass before dispensing fog.
Some have reported that a mix of 50/50 dry ice and water ice works best. The dry ice provides incredible cold and the water ice provides cheap surface area and moisture.
It's OK to add a fan if your fog is sluggish or has to travel far. But it's not a good idea to run the fog through the fan. Instead, use the fan to provide additional air to boost the fog along.
The colder the weather, the harder the chiller must work in order to make the fog lie low. Fog chillers should be tested under conditions closely approximating battle conditions.
The 4-inch rule!

Let's devote a lot of attention to what I have come to call "the 4-inch rule", because it's important and not obvious...

The stuff shooting out of the fogger nozzle is a vapor - nearly invisible because it is composed of individual molecules flash-evaporated from the fog fluid. As the vapor shoots out the pin hole in the nozzle, it expands, which causes it to undergo adiabatic cooling and condenses into tiny droplets. It is at this point that the fog becomes visible.

The fog must have an expansion area after the nozzle. The technical notes at www.rosco-ca.com state:

Rosco offers a 4" diameter ducting hose (6" for the Model 4500) to duct the fog. A Hose Adaptor is also available to attach the hose to the front of the fog machine. In addition to aiding in the attachment of the hose, the Hose Adaptor leaves a necessary air space at the face of the machine so the fog can mix with fresh air. Never use a hose smaller than 4" or attach any hose directly to the face of the machine. In both cases, most of the fog will recondense and turn back to fluid.
For most applications the minimum diameter duct used should be 4 inches. When fog is constricted, it tends to recondense into fluid reducing the output and creating an unwanted residue. Likewise, recondensation can occur if the ductwork is placed directly over the front of the fog machine. The aerosol is created when the "flashed" vapor mixes with fresh air. If flexible hose is used, an openwork frame should be used to keep an air space in front of the machine (see below). If rigid ductwork is used, simply keep the front of the machine 3-4 inches from the duct. If the fog needs to travel long distances in ductwork, a squirrel cage fan can be added. The fog should not come into contact with the fan blades. The air should be added through a "Y" connection.

This a Rosco Hose Adapter. Note the open cage construction - it gives the hose an offset, providing the fog with expansion room and ambient air.

You don't shove the hose all the way over the adapter. It just goes over the outer ring, leaving a large air gap.

How not to build a fog chiller

We're coming clean with the story of our first fog chiller.

Wolfstone fog chiller - Mk II

We haven't completed our Mk II chiller yet. Please be patient, we have a lot of mistakes to make.

Thank you for visiting. Your comments are welcome.
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Fog Chiller

Particularly notable chillers

Other chiller links

Design tips

How not to build a fog chiller

Wolfstone fog chiller - Mk II