MISTING SYSTEM

WATER LINES

A misting system uses lines -- pipes, tubes, hoses, cables, channels -- to "deliver" the water from the supply source to the nozzles. In hopes of avoiding confusion we will use the general term "lines". The main considerations for the water lines are size, material of construction, and water pressure rating.

Sizing

A misting system uses narrow water supply lines to take advantage of available water pressure. These supply lines are sized based on the diameter of the line. Most supply line material is measured "nominally", which is an average diameter along the length of the line. The sizing used in misting systems is fairly standard. 3/8" and 1/2"/ 9mm and 15mm diameters are the most commonly used. 3/8"/ 9mm is typically used for all basic systems. 1/2"/ 15mm is used for large industrial projects where much more water flow is needed.

Thicker walled lines have greater durability and higher pressure tolerances as well as greater cost. Wall thickness does not affect line size (diameter). 1/2"/ 15mm L copper (thin-walled) has the same outer diameter as 1/2"/ 15mm K or M (medium- or thick-walled) copper. The same applies to plastic. The diameter stays the same on the outside, but the inside gets smaller as the walls get thicker. As a result, water volume in the line will decrease slightly as wall thickness increases. This may be helpful to be aware of, but will have little effect in a misting system.

FLEXIBLE OR RIGID
Flexible lines can be very easy to work with and install. They need no special tools and allow for virtually any nozzle spacing -- just cut the line wherever you want to place a nozzle. They can also be a perfect choice when setting up a system in hard-to-reach areas, or is situations where the tubes must make several bends and turns. Flexible tubes also allow for flexibility in the overall design of the misting system because nozzle spacing can be decided on the spot, and because sections can easily be removed and re-configured.

Flexible materials may be made of various plastics or nylon and might or might not be reinforced with braiding. With any flexible tube, be careful not to bend it into too tight a curve. It can kink the tube and diminish or completely shut off the water flow. Flexible lines are available in stock lengths as short as 24 inches / 61 centimeters or as long as 500 feet / 152 meters. Some are treated to withstand outdoor exposure by being treated with a UV protective coating. Flexible lines cannot be painted, but are often available in more than one color to blend with the surroundings.

Rigid lines range from plastic, such as PVC to copper to stainless steel. Rigid lines make a neater looking installation and can be painted or powder coated to blend in to the surroundings. Rigid lines also stabilize the nozzles so origin of the spray remains constant. Rigid lines can be compression fitted like flexible lines, or solvent welded for long-lasting leak-free connections. Often a combination of flexible and rigid lines are used -- flexible around obstructions and rigid for a neat appearance where visible.

LINE MATERIALS

The selection of line material is based on water pressure, flexibility needs and durability requirements. All are rated to withstand certain ranges of water pressures. Some of these can only be used with Low pressure, but others can be used with Medium or High pressure. Make sure your choice is rated to work with your misting system's pressure.

Following are some materials that may be used for lines in a misting system.

Plastic / Thermoplastic

Compared to copper lines, plastic is lightweight, easy to work with, doesn't corrode and may be priced about 75% less. Most plastics stretch and contract to accommodate variations in water temperature. Plastic lines, especially flexible lines, are great for a portable misting system because of their light weight. Some plastics can be joined with solvent fittings, other can only use push-in fittings or compression fittings. There are many kinds of plastics used for these lines. Here are the most popular:

PVC (polyvinyl chloride) and PE (polyethylene) lines are ideal for outdoor misting systems. PVC lines are rigid, PE lines are flexible and cannot be solvent welded. Both are low-cost and very easy to install. They will not rust or corrode; and have insulative qualities that prevent condensation from forming on pipes carrying cold water.

CPVC (chlorinated polyvinyl chloride) is another rigid plastic used for water supply lines that handle low water pressure loads. CPVC will last a long time, though is not quite as tough as copper, and can stand up to water with corrosive minerals.

PVC, PE, and CPVC are available in different wall thicknesses called "Schedules". The most commonly used wall thicknesses for a misting system are Schedule 40 (rated at about 300 psi / 20 bar), and Schedule 80 (rated at about 500 psi / 34 bar).

PEX is remarkably durable within a wide range of pressures. Flexible, it can be installed with fewer fittings than rigid plumbing systems. Works well for corrosive water conditions.

Kitec is a multipurpose pressure pipe that combines the advantages of both metal and plastic. Made of an aluminum tube laminated to interior and exterior layers of plastic, Kitec provides a composite line material for a wide range of uses, often beyond the scope of metal or plastic alone. Kitec is non-corroding, and stands up well to a variety of water compositions and extreme outdoor conditions.

Nylon

"Virgin" nylon is newly manufactured, which is much stronger that recycled nylon. Often UV protected, virgin nylon will withstand the most demanding outdoor conditions. Often used to route high pressure water from pump to copper or stainless steel mist lines, this flexible line can be directly clamped down or fished through conduit in the structure, in the ground or under concrete. Like other flexible lines, nylon can be fitted with simple push-in fittings or compression fittings. Nylon is typically rated up to 1000 psi / 70 bar, and is available in cut lengths, or in rolls from 100 to 1000 feet / 30 to 300 meters.

Copper

Both rigid and flexible copper lines are available. Rigid copper makes a neater installation for your misting system, but is much more difficult to install than flexible copper. it cannot be bent and must use elbow fittings to go around corners or obstacles. Flexible copper line is good for running around obstacles without connections or cuts. It can be joined by several methods, and is the only type of copper line suitable for flare connections. Pre-fabricated copper line is designed for quality and versatility and is a good choice when rigid lines and on-the-job customization are required.

Copper is available in stock lengths of 10 or 20 feet / 3 or 6 meters, and is also available in custom lengths. Copper is highly resistant to corrosion, but is becoming very costly. Copper line is available with three wall thicknesses: Type M is thin-walled, Type L is medium-walled and Type K is thick-walled. In most cases, Type L is used for misting systems and is rated about 1000 psi / 70 bar.

Copper should not be used if the water has a PH of 6.5 or less. The majority of public utilities supply water at a PH between 7.2 and 8.0 but private well water systems often have a PH below 6.5. When this it the case, installing a treatment system to make the water less acidic is a good idea.

Stainless Steel

Stainless steel lines are rated to 3000 PSI and are the ultimate for quality and durability. These lines can be powder coated and painted to match the surroundings.

FITTINGS, CONNECTORS

A fitting isn't necessarily a physical piece of plumbing, but is a general term to describe any of a number of ways that sections of line are "fitted" or joined together. Fittings link together individual sections of the line, link the line to the water supply or pump, and link the line to the nozzles. Typical methods of fitting used for misting systems are:

Compression fitting is the kind that "screws" on with spiraling "threads" which are shaped at the ends of most water lines. Compression fittings commonly have an outer compression "nut" or connector, and a "ferrule" or disk (also called an "olive" in the UK) that fits between the nut and the line. When the nut is tightened, it clamps down on the ferrule, forcing it to conform to the shape of the line and eliminating all space in the joint.

Over-tightening is the most common cause of leaks in compression fittings. If the fitting is overtightened, the ferrule will deform and cause leaks. As a general rule, a compression fitting should be hand tightened.

Compression fittings are easy to use and require no special tools or skills to put together, yet still provide water-tight seals that can withstand the pressures of a misting system. Compression fittings are especially useful when occasional disassembly or partial removal is needed, such as in temporary installation, since these joints can be disassembled and remade without affecting the integrity of the joint. Compression fittings are a good choice in confined spaces where soldering would be difficult or dangerous. But they are not as durable as soldered fittings, and should not be used where the fitting will be subjected to repeated flexing or bending.

Make sure compression fittings for all connections are properly rated. Secure all these fittings with Teflon tape. Check that all fittings are properly tightened.

Some compression fittings use "push-to-connect" or "slip-to-lock" hardware, which combine the compression nut and ferrule into one piece. They are simply pushed onto the line to form the connection. These are quicker and easier than standard compression fittings, but may be less secure.

Solvent fitting is typically used for plastic / thermoplastic lines. It uses a solvent matched to work with the specific type of plastic used for the line. The solvent is applied to the outside of the line end and the inside of the connector, and the two pieces are joined together while the solvent has temporarily dissolved the plastic of both pieces. When the plastic has re-hardened, the two pieces will have been permanently "melted" into a single water-tight unit. These fittings can be more water-tight and durable than compression fittings. Some plastics cannot be solvent welded and must be compression welded.

Crimped or pressed connections use special copper fittings which are permanently attached to rigid copper lines with a powered crimper. The special fittings, manufactured with sealant already inside, slide over the tubing to be connected. Thousands of pounds-force per square inch of pressure are used to deform the fitting and compress the sealant against the inner copper tubing, creating a water tight seal. The advantages of this method are that it should last as long as the lines, themselves, it takes less time to complete than other methods, it is cleaner in both appearance and the materials used to make the connection, and no open flame is used during the connection process. The disadvantages are that the fittings used are harder to find and cost more than sweat type fittings.

Sweat fitting is a means of joining copper tubing using "solder" (a fusible metal alloy) like a metal "glue". A sweat fitting is a smooth disk that easily slips onto the end of a section of the water supply line. The joint is then heated using a torch and solder is melted into the connection. When the solder cools, it forms a very strong bond which can last for years. With experience, sweat connections are quick to create, and when many connections must be made at once, sweat fittings can be quicker to join than compression or flare.

Flare fitting spreads the end of a line section be outward into a bell shape using a flare tool. Then a special "nut" compresses this bell-shaped end onto the next section of line. Flare connections are very durable and can remain water-tight for many years. But they are labor intensive and can be used with only a few misting line materials.

WATER USE

How much water any system will use if often critical information for what kind and size of system you will use. There are 3 things you need to know to estimate water use for any misting system:

1. The water pressure of the system
2. The kind of nozzles your system will use, and
3. How many nozzles the system will use

THE QUALITY OF THE MIST

The size of the water droplets that make up the mist helps determine how much cooling effect you'll be able to feel. As each little droplet evaporates, it cools the air immediately around it. Bigger droplets take (mili-seconds) longer to evaporate than smaller droplets. If they land on you before they've completely evaporated, you're wet. If you're in fairly dry air this can feel great as the water evaporates off of your skin. On the other hand, it can be uncomfortable in extremely humid weather, or if you just don't want to be wet. Also any water that doesn't evaporate must land on something. You'll need to make sure it doesn't puddle and that what it lands on is water-safe.

Smaller droplets evaporate mid-air. This is sometimes called "flash evaporation" because it happens "quick as a flash" and gives a stronger cooling effect. Also, smaller droplet can spread or "drift" more than larger droplets, cooling a larger area.

The lower pressure misting systems that yield larger water droplets also yield fewer water droplets. Fewer, larger water droplets around you cool the air unevenly. You can sometimes feel little spots of cool air surrounded by the unaffected hot air. It can feel like standing by a waterfall. The higher pressure misting systems that yield smaller droplets also yield more water droplets. The air is cooled more evenly and feels more like a fog. You are less likely to feel the warm air and more likely to simply feel the cooled air with these. Same amount of water, different number of droplets. Different cooling effects.

If the diameter of spray droplets is reduced by one-half, the number of droplets produced with a given volume is increased by eight times.
Doubling the droplet diameter will reduce the number produced by eight times.

Here is a sampling of water droplet sizes based on common nozzle sizes using 1000 psi / 70 bar. Water droplet sizes are measured in "microns" (1 micron is .001mm). To give you a size reference, 100 microns is about the diameter of a human hair. The largest of these droplets is just under half that.

.020" / .5 mm - the droplets range from 9.5 microns to 49.9 microns

.016" / .4 mm - the droplets range from 3.8 microns to 47.9 microns

.012" / .3 mm - the droplets range from 1.6 microns to 39.1 microns

.008" / .2 mm - the droplets range from 1.4 microns to 37.9 microns

.006" / .15 mm - the droplets range from 1.2 microns to 36.4 microns

Cooled air is heavier than the warm air. So the droplets evaporate above and around you and the cooled air drifts down onto you.

NOZZLES

The size of the nozzle orifice (opening) balances with your misting system's water pressure and flow rate (amount of water) to create a cooling mist. Every nozzle will spray less water at lower pressures than at high pressures. In fact, certain nozzles will not even work at lower water pressures. As the water pressure at the nozzle increases, the flow rate through the nozzle increases. The higher the water pressure, the smaller the nozzle opening you'll need. It may help to decide on the water pressure you want your system to use before selecting the nozzle.

FLOW RATE

Nozzle manufacturers publish flow rates for their nozzles in gallons or liters per minute (GPM or LPM) or per hour (GPH or LPH) as it relates to different water pressures. Most spray nozzles are listed in a chart that shows their flow rate at one or more water pressure. An example chart is shown below. Note that some charts, like this one, are for general information -- these flow rates should not be assumed for any particular nozzle. Ask your nozzle supplier for charts on specific nozzles.

SIZE	PSI:	40	60	80	100	125	150	200	300	500	1000
	BAR:	2.7	4.0	5.4	6.8	8.5	10	14	20	34	70
.020"/.5mm	GPH	1.50	1.80	2.10	2.40	2.70	2.90	3.40	4.10	5.30	7.40
	LPH	5.68	6.81	7.95	9.08	10.22	11.00	12.87	15.52	20.06	28.01
.016"/.16mm	GPH	1.00	1.20	1.40	1.60	1.70	1.90	2.20	2.70	3.50	4.90
	LPH	3.79	4.54	5.30	6.07	6.44	7.19	8.33	10.22	13.25	18.55
.012"/.3mm	GPH	.750	.890	1.10	1.20	1.40	1.50	1.70	2.10	2.70	3.78
	LPH	2.84	3.37	4.16	4.54	5.30	5.68	6.44	7.95	10.22	14.31
.008"/.2mm	GPH								1.05	1.35	1.89
	LPH								3.97	5.11	7.15
.006"/.15mm	GPH									0.58	0.80
	LPH									2.20	3.03

Differences in flow rate between nozzles sizes at lower pressures are smaller at lower pressures and bigger at higher pressures. Using the smallest nozzles your system's pressure can handle will minimize water use and costs while increasing the cooling effect. Notice that the smallest nozzles won't work with lower water pressures.

General Rule of Thumb:
Nozzle flow for 500 psi / 34 bar equals 75% of the rated flow of 1000 psi / 70 bar; nozzle flow for 250 psi / 17 bar equals 50% of the rated flow of 1000 psi / 70 bar.

The larger nozzles will work well with Low and Medium pressure misting systems. The smaller nozzles should only be used with High pressure systems. If you select too large a nozzle for your water pressure, the pump won't be able to send enough water through it to create a fine mist. If you select too small a nozzle, the over-supply of water through the nozzle may "over-pressure" the pump and damage it. It's not a matter of "more is better" but of balance.

.020" / .5 mm - for systems using very high water volume with less need for complete evaporation. Excellent for Low pressure misting systems

.016" / .4 mm - for systems where airflow and clearance allow for complete evaporation and where higher water volume is used. Good for Low and Medium pressure misting systems

.012" / .3 mm - most common and can be used for most systems. It can be used in both open and enclosed areas with complete evaporation. It provides similar results to the .008" nozzle but with more water (more "oomph"). Excellent for Medium pressure misting systems.

.008" / .2 mm - ideal for systems using less water volume with small droplet size, minimal moisture, and complete evaporation. Excellent for High pressure misting systems; won't work below 250 PSI / 17 bar.

.006" / .15 mm - ideal for systems using very low water volume with small droplet size, minimal moisture and complete evaporation. Only for High pressure misting systems. Won't work below 500 PSI / 34 bar.

A few nozzle options to consider:

Drain Valves will automatically drain the system each time it is turned off. This helps prevent nozzles plugging up due to calcium buildup, meaning much less nozzle cleaning needed. This is especially helpful for large systems or hard to reach nozzles.

Anti Drip Adapters will close each time the system is turned off to prevent dripping from the nozzles. Nozzle-dripping may not be a problem if the water drips onto concrete or dirt. It could be a problem if it drips onto wood or machinery or guests.

Adjustable Angle Some nozzles can rotate or swivel to direct the spray in varying directions.

Materials Some nozzles are made with more durable materials than others. If yours will be a high pressure system that gets a lot of use, you'll probably want to consider higher quality nozzles. For example, stainless steel nozzles and nozzles with tungsten carbide orifices are more resistant to wear.

Nozzle Tees are the fittings that connect your nozzle to the line. You will need one of these for every nozzle. Select tees based on the size and material of your lines and your system's water pressure.

Some companies will give quantity discounts on nozzle tees and nozzles.

SPRAY PATTERN / NOZZLE SPACING

Nozzles are designed to create a spray that angles out anywhere from 40° - 100°, depending on your system's water pressure. The wider the angle, the more area the spray will cover and the fewer nozzles will be needed. 18, 24 or 30 inch nozzle spacing is standard, but some suppliers will customize spacing to your needs. Nozzle spacing in plastic, nylon, and copper lines can be easily customized during installation, too.

How far in the air the spray "drifts" or spreads is determined by their height off the ground, the system's water pressure and the size of the nozzle, plus the temperature of the water and the outside air.

For maximum cooling effect, it makes sense that you would want a fairly dense curtain of mist. But there is a point at which the system simply cannot make you any cooler, no matter how closely the nozzles are spaced. The final determination of how closely to space the nozzles in your system will be based on, well, your system.

Your system's water pressure, your choice of nozzles, your climate, even your system's configuration and the shape of the structure it is mounted to, all combine to make a system that is uniquely yours. Your misting system supplier's experience is invaluable in determining how far apart to space the nozzles. If installing it yourself, use one of the standard spacings and adjust it based on how many nozzles your system can handle. Spacing adjustments can be made after installation, if necessary. These adjustments will be easier to make in some line materials than others. Go back up to the section on flexible or rigid water lines or line materials if you'd like a review of this.

The number of nozzles any misting system can handle will vary depending on the pump, the type of nozzles used, corresponding flow rate, the number and types of fittings. Too many nozzles can cause a noticeable drop in performance. Most kits will tell you how many nozzles they can handle. Fewer nozzles mean less water used but more nozzles can mean more cooling. Remember, a misting system is a matter of balance.

INSTALLATION

LINES

Misting system supply lines are attached to the support structure by hangers that hold it snugly to the framing while allowing a little "give" (back-and-forth movement). This "give" allows for a certain amount of expansion and contraction of the lines that is normal with a misting system. Allowing for this will help prevent damage to the lines, and possibly to the support structure.

How far apart you position the hangers will depend largely on the kind of lines you use. The more flexible the lines, the more closely you'll need to position the hangers. It is recommended that mounts for nylon lines be spaced 32" or less. And the thinner a rigid line's diameter, the more closely you'll need to space the mounts, perhaps 5 feet apart or less. Also, be sure not to bind rigid lines at the ends. Leave about 1/4' for every 10' of line. This will allow them the same kind of "give" as flexible lines. The better secured the whole line is mounted, the more stable the system will be. Loose lines can cause damage to the system and affect where the mist will be directed.

Lines can be hung by perforated metal strapping called "plumber's tape". Using pre-punched, nailed-on steel straps can prevent accidental damage to the lines during installation. Rubberized mounts or straps in another way to minimize any damage and allow for some flexibility in the lines.

The misting lines need to run 8 to 10 feet above the ground on the bottom outside edge of the fascia, header or beam of the structure's perimeter. It is important to mount the line along the bottom edge of the structure, to prevent mist from spraying onto the top of it, defeating the cooling effect.

Complex systems, commercial and industrial grade systems may well require professional installation. If your manufacturer is outside of your area, they may be able to connect you to licensed and bonded installers in your area. If you have any doubts about installation, contact the manufacturer, since their system may have elements that work in a way unique to their system.

PUMPS

Check your available power before you select the pump for your misting system. Have the unit installed by a qualified electrician. Make sure it is set up with proper GFCI protection. Install your pump near a water and electrical hook-up in a covered area. Choose a spot that is relatively easy to access for maintenance. The best kinds of places are in a equipment shed or garage where it will get ventilation but still be protected from the elements. Install the pump on a level surface, preferably out of the hot sun, out of the rain or any puddles, and away from dust and debris. You'll also want it a bit of a distance away from area you'll be cooling since most pumps can be noisy. Many pumps can be placed up to 400 ft away from the mist line without significant pressure loss.

In places where it is not possible or not economical
to cool the whole structure or area, set up smaller cool areas.

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