# Ventilation 101...Let's make this a sticky!



## Ou8aCracker2 (Jan 12, 2014)

First and foremost I take no credit for this,thus is simply a copy/paste and all credit is due to Redgreenery over @ ICmag.

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Hey guys,

as you all know if the women don't find you handsome, they better find you handy...

I've got some background experience and have wanted to do a good write up for a while.

I have a collection of source material and will be cutting and pasting from it with a more detailed explanation that is more relevent to our hobby, building cabinets. 

One of the lads in the Lodge says that growing leads to carpentry. I'm sure he's right.

***********************************************************************************************
We are trying to do two things at the same time, sorta like chewing gum and walking. The first thing is to provide
ventilation for the plants living in the grow chamber. The second is to remove the heap of heat generated from our lighting.

This chart gives some recommended ventilation rates for common applications. I recommend 5 Minutes per Air Change and no more than 1-2 MpAC to keep stress down on the plants. High airflow rates cause excessive dehydration which is hard on the plants. 








*********************************************************************************************** 
*COMPARISON OF CABINET DESIGNS* 

*1. Simple Cab - one chamber, no scrubbers or restrictions to airflow.*








CFM = 3.16*Watts/deltaT
where deltaT = 10 *F

Intake Area = 2 x Exhaust Area
Fans - Axial/Computer Fans due to minimal pressure loss

Example: A 400 W HPS in a 3 x 3 x 4 cabinet needs 126 CFM of cooling for a 10*F temp rise above room temperature. 
The 36 cu ft cabinet is ventilated at over 3 Air Changes Per Minute. 

*Pro:* 
Easy to build
Fans - axial 

*Con:*
plants stink up the place
plants are stressed by too much airflow at 3 ACpM.
The plants only need 5 Minutes per Air Changes (MpAC). That's 0.2 Air Changes per Minute (ACpM).

For you hydro guys, this means more rez changes and nute swings because the plants will be drinking alot to keep
up with the dehydration caused by living in a wind tunnel. 

*2. Simple Cab with Scrubber*







CFM = 3.16*(Total Watts)/deltaT 
where deltaT = 10 *F 

Intake Area = 2 x Exhaust Area
Fans - Blower or Inline for high pressure drop across scrubber

Example: A 400 W HPS in a 3 x 3 x 4 cabinet needs 126 CFM of cooling for a 10*F temp rise above room temperature. 
The 36 cuft cabinet is ventilated at over 3 ACpM. The hard part is to match an oversized fan/scrubber combination to get the right airflow.

This design and the simple growbox have cooling requirements that exceed the ventilation requirements of the growchamber by at least 15x. Way too much stress on the plants by living in a wind tunnel.

*Pros:* 
single fan design less equipment to purchase

*Cons:*
Fan operates at 50% or less airflow due to large pressure drop across scrubber
High SP requires a Centrifugal Blower, won't work with Axial fans
Fan/Filter Curves are needed to determine working airflow 
Scrubber is many times larger than Ventilation specs to get light cooling airflow
many restrictions in multi chamber designs require special attention to intakes and intrachamber airflow 
high airflow for to cool lights creates stress on plants
high airflow through scrubber reduces effectiveness
Centrifugal Blower and Inline Fans are very noisy 60-70 db

*3. Simple Cab with CoolTube/Ventilated Hood and Inline Scrubber *







CFM = 3.16*(Total Watts)/deltaT 
where deltaT = 20 to 30 for cooltube

Intake Area = 2 x Exhaust Area
Fans - Blower or Inline for high pressure drop across scrubber

Example: A 400 W HPS in a 3 x 3 x 4 cabinet needs 63 - 42 CFM of cooling for a 20-30*F temp rise in the exhaust temps with a 1-2 *F rise in the growbox. 

The 36 cuft cabinet is ventilated at 2 ACpM. The hard part is to match an oversized fan/scrubber combination to get the right airflow.

The cooltube design is a big improvement over the Simple and Simple cab with Scrubber designs as the overall airflow is considerably less. However 2 ACpM is still 10x over what the plants need and will stress out the plants from excessive airflow.

*Pros: *
single fan design means less equipment to purchase
Cooltube/Ventilated Hood improves cooling significantly by trapping most of the heat in the hood
Less airflow through the grow chamber compared to the above designs but still high. 

*Cons:*
Fan operates at 50% or less airflow due to large pressure drop across scrubber
High SP requires a Centrifugal Blower, won't work with Axial fans
Fan/Filter Curves are needed to determine working airflow 
Scrubber is many times larger than Ventilation specs to get light cooling airflow
many restrictions in multi chamber designs require special attention to intakes and intrachamber airflow 
high airflow for to cool lights creates stress on plants where only 0.2 ACpM is needed
high airflow through scrubber reduces effectiveness
Centrifugal Blower and Inline Fans are very noisy 60-70 db

*4. Two Stage Cooling/Ventilation with cooltube and scrubber*







LIGHTING CFM = 3.16*(Total Watts)/deltaT
where deltaT = 20 to 30 *F

VENTILATION = 1 - 5 MpAC (Minutes per Air Change) or 0.2 to 1 Air Change Per Minute (ACpM)

Intake Area = 2 x Exhaust Area for EACH section

Fans - Axial for Lighting maximum airflow, minimal pressure loss
Small blower, inline or axial for scrubber

Example: A 400 W HPS in a 3 x 3 x 4 cabinet with a ventilated hood needs 63 - 42 CFM of cooling for a 20-30*F temp rise in the exhaust temps with a 1-2 *F rise in the growbox. 5 Minutes between Air Changes requires only 7 CFM through the scrubber.

*Pros:* 
unrestricted airflow through lighting allows fan to operate at maximum rated flow
low air flow rates allow for smallest scrubber
use of less expensive fans as design is more efficient
Lighting exhaust deltaT can be 20-30*F while maintaining low grow chamber temps
Much quieter as axial fans operate at 20-30 db compared to 60-70 for centrifugal fans 

*Cons:* 
more equipment
more intake and exhausts require more light proofing
ventilation design is more complex

*5. Multi Chamber Designs*







LIGHTING CFM = 3.16*(Total Watts)/deltaT
where deltaT = 20 to 30 *F per ventilated hood

Rule of thumb: 20*F temp rise for no more that 4 hoods chained together for a combined rise of 80*F

VENTILATION = 1 - 5 Min/Ch (Minutes per Air Changes)

Intake Area = 2 x Exhaust Area for EACH section

Fans - Axial for Lighting maximum airflow, minimal pressure loss
Small blower, inline or axial for scrubber

Example: Two 3 x 3 x 4 cabinets with a 400 watt HPS with a ventilated hood needs 63 - 42 CFM of cooling for a 20-30*F temp rise in the exhaust temps of each hood for a total of 40* to 60* temp rise with a 1-2 *F rise in the growbox. 5 Minutes between Air Changes requires only 14 CFM through the scrubber.

*Pros:* 
unrestricted airflow through lighting allows fan to operate at maximum rated flow
low air flow rates allow for smallest scrubber
use of less expensive fans as design is more efficient
Lighting exhaust deltaT can be 20-30*F while maintaining low grow chamber temps
Much quieter as axial fans operate at 20-30 db compared to 60-70 for centrifugal fans 

*Cons:* 
more equipment
more intake and exhausts require more light proofing
ventilation design is more complex


*Ventilation Chart*







*RECOMMENDED SPECIFICATIONS FOR GROWBOXES:*

*Simple Cabinet* - airflow to maintain temperature within 10*F of ambient

*Cool Tube or Ventilated Hood* - exhaust air temp 20 - 30 *F. Hoods can be connected together to a common fan at 20 *F rise per hood, no more than 4 hoods for a total rise of 80 *F.

*Grow Chamber Ventilation* - 1 to 5 Minutes per Air Change. This is different for every type of light and setup. The more heat that is removed using a cool tube or ventilated heat means you can drop the grow chamber ventilation down further. The plants don't need very much air exchange and over 1 ACpM will cause unnecessary stress.

You will see a variety of equipment used to ventilate growboxes, tents and rooms. My recommendations are to put your money into a cool tube or a ventilated hood. Cooling a bare bulb with a centrifigal fan and scrubber combo is a big waste of money. 
There's no need to scrub your light cooling air in a well designed system.

I'm going to show this handy chart again that show Air Flow Rates for Common Bulb Sizes. This chart is useful in two ways. For the cabinet builder, find your bulb size and the amibient temp rise you want and get the air flow needed off the chart.

*INTAKE SIZING*

Getting the intakes right is the biggest challenge in setting up a growbox. The intake area needs to be at least equal to the exhaust area and up to 2x to reduce losses.

A = pi * (radius)^2 = (pi *diameter)^2/4

*Areas for common duct and pipe sizes*







Thanks to Freezerboy for the nice picture. This is a common mistake when using a number of small holes to equal one big one. The only solution is to calculate the area for the big hole and divide by the AREA of the smaller holes to get the number of small holes needed.







In this case one 9" hole needs 80 x 1" holes to be equivalent.

I'd like to point out that making one big hole is better than a bunch of little holes as each little hole has it's own Vena Contracta losses which do add up.

*How to Check Your Cabinet for Proper Ventilation* 

For they guy wanting to know how well his cabinet is working, you can get the EFFECTIVE AIR FLOW rate from this chart. Here's how to do it. Measure the temperature of your exhaust air and subtract the ambient temperature to get the temperature rise number. Use the bulb size line and temperature rise to get the EFFECTIVE AIRFLOW RATE.







For example, a 250 W HPS lamp in a growbox with 90*F exhaust in a 70*F room is operating with 40 CMF of effective airflow.


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## Ou8aCracker2 (Jan 12, 2014)

Here is an excellent fan sizing guide from Grainger Fans who produce the Dayton line which many cab builder use.

http://www.grainger.com/images/vent_fundamental.pdf

I found an ventilation engineering course on the EPA website. There is a wealth of information here but it is very technical.

http://www.epa.gov/air/oaqps/eog/bces/toc/full_toc.htm

This site has some good info too
http://www.mil-embedded.com/articles/id/?3281

Fans are a pressure producing device which are basically air pump. Air flow is created by the fan's pressure. It doesn't take much pressure to move air which has little mass compared to water or hydraulic fluid. Air pressure is measured in Inches of Water which are 1/28 of a pound per square inch. 

Computer Fans (Axial) produce about 0.2 inches of water pressure and are ideal for unrestricted blowing. They can move a lot of air but don't block them up.

Centrifugal Blowers produce more pressure than an axial fan. Typically the ones used by most cab builders produce about 0.5 inches of water pressure and will work with more static pressure such as scrubbers. The shape of the fan blades make a big difference in the pressure produced by the fan.

Industrial blowers will produce much higher pressures but they require multiple horsepower motors to drive them.







Static Air Pressure is measured with a manometer which is just a U shaped tube filled with water. This picture shows the manometer measuring the intake side of the fan which has 1 inch of water pressure. If you stick a ruler next to the tube one side is 1" higher than the other.







Every fan manufacturer can provide you with a fan curve for your fan which is produced by operating the fan with various static pressures and taking flow measurements. All they do is put a variable damper on a duct and move it from fully open to fully closed.








This fan curve is for 1200 CFM fan that will produce 0.6 inches of water pressure.

*When the fan is fully blocked, it creates 0.6 inches of STATIC PRESSURE and 0 CFM AIR FLOW.* 

*When the fan is unrestricted, it creates 0 inches of STATIC PRESSURE and 1200 CFM AIR FLOW.*








Now if you have a fan speed controller and can change the speed of your fan this is what happens at different speeds. The fan operates with the same shape curve but with with an identical shaped curve.


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## Ou8aCracker2 (Jan 12, 2014)

Every ventilation system can be described by a SYSTEM RESISTANCE CURVE where the static pressure and airflow are graphed together.

If you took a big fan and connected it to your growbox and put a duct on the exhaust with a damper so the airflow airflow could be adujsted and measured the static pressure as the air flow is increased, this curve would be made. 

Every "SYSTEM" has a unique resistance curve.

AIR FLOW = K * SQRT(PRESSURE) where K is a unique system constant 








Point A is my cab with an Axial Fan producing 0.2 in of static pressure and 1000 CFM of air flow (not too realistic eh!)

Point B is my cab with an Centrifical Blower producing 1.0 in pressure and 2000 CFM air flow.







Now let's do something to our cabinet to change the system constant K. Let's say our Cab has two intakes and Curve A is normal. If we block up one intake, we have changed our system constant K to a new number and we get Curve B.

My cab with 2 intakes and an axial fan producing 0.2 in static pressure has an air flow of 700 CFM on curve A

My cab with 1 intake and the same axial fan at 0.2 in static pressure has an air flow of 500 CFM on curve B.

Changing the system will produce a new system curve and a new system constant K.


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## Ou8aCracker2 (Jan 12, 2014)

The Operating point is where the Fan Performance Curve crosses the System Resistance Curve.








In this case a 0.6 in 1200 CFM fan is operating with 0.25 in of Static Pressure and producing 1000 CFM. The resistance of the system causes reduced performance.

*STATIC PRESSURE WORKS AGAINST AIR FLOW AND IS CAUSED BY RESISTANCE*







A new operating point is created by changing the speed of the fan without making any changes to the system.
This is the same as upgrading from a low performance fan to a heavy duty industrial type.







Changing the System Resistance moves the operating point along the Fan Performance Curve. In this example I cut a new intake and reduced the System Resistance from Curve A to Curve B that increased air flow from 1000 to 1150 CFM.

A while back I threw out a simple formula for calculating air flow. Here's a better calculation that takes Area into consideration.

CFM = K * SQRT (PRESSURE) * AREA

What's interesting is that doubling the intake area will double the air flow. 

You have to change the pressure produced by a fan by 4 times to double the air flow.

If you want to improve your cabinet, adding intakes, increasing duct size and adding more surface area to scrubbers is the way to increase air flow.


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## Ou8aCracker2 (Jan 12, 2014)

So what actually makes the Air move?

All a fan does is makes a difference in pressure between the intake and exhaust. Let's call this the Total Pressure.

Resistance to the air flow is called Static Pressure and what's left over is called Velocity Pressure. 

It's the Velocity Pressure that pushes the air. The Static Pressure is best described as pressure losses in the system.

TOTAL PRESSURE = STATIC PRESSURE + VELOCITY PRESSURE

or another way to look at it is

VELOCITY PRESSURE = TOTAL PRESSURE - STATIC PRESSURE

Static pressure is your enemy in a good ventilation system. If you find your cabinet door hard to open, then you have high static pressure. If you open your cab door and the air flow from the exhaust increases, then you need more intake area.


The fan curve is useful for converting static pressure readings into actual airflow.

Let's say I have a nice fan that is rated at 0.5" WC. Measuring the static pressure at the exhaust I find 0.05" WC and the static pressure at the inlet is 0.25" WC which would give me a Total Static Pressure of 0.3 and an air flow of 950 CFM.

The velocity pressure would be 0.5 - 0.05 - 0.25 = 0.2" 




 

*Duct Air Flow Calculations*

Here's the full formula for calculating the air velocity in a duct knowing the Velocity Pressure

velocity = 4005 * SQRT( velocity pressure) * SQRT (0.075/air density) where 0.075 is the density of air at 68*F

Let's ignore air density for now.

v = 4005 * SQRT (Vp)

To calculate the air flow in a duct, multiply velocity (ft/min) by the area of the duct (ft*ft) 

v * A = 4005 * SQRT(Vp) * A 

with velocity in ft/min and area in square feet

Flow = 4005 * SQRT(Vp)*A CFM (cubic feet per minute)







********************************************************************************************* 
*Static Pressure Losses*







Now let's say I have this growbox with two chambers and some inlet and outlet ducts connected to a 0.5" 1200 CFM Fan

The Total Static Pressure at the fan is 0.3" which will give me a flow of 950 CFM using the fan curve.
The Vp is 0.5-0.3=0.2

The Total Static Pressure loss for the system is 0.3" which is 0.1 for the inlet air ducting, 0.1 between chamber B and A and 0.1 between A and the outlet of the fan.








Now let's try to improve the airflow between chamber A and B by adding a second vent.

Wow, the static pressure in chambers A and B are the same so there is no more loss and it also dropped the static pressure at the fan inlet to 0.2". Going off the fan curve the airflow increased from 950 to 1050 CFM with the velocity pressure increasing from 0.2 to 0.3.







Let's add a second intake. This reduces the Sp down to 0.05" in each intake duct and drops the Sp down to 0.1" at the Fan.

The overall airflow is improved to 1125 CFM which is almost the full rating of the fan at 1200 CFM.

In this example by removing an internal restriction and opening up the intakes, the airflow was improved from 950 to 1125 CFM.


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## Ou8aCracker2 (Jan 12, 2014)

This is the handiest chart that I've ever seen. It's based on a cooling formula that I've come across in a few places during my research.

CFM = 3.16 * Watts Dissipated / delta T in *F








If I had a dollar for everytime someone asked how many CFM's do I need for my Cabinet....

Here's a handy chart to for ventilation for each type of light bulb. For a simple cabinet use the 10*F curve.

For ventilated hoods and cooltubes, you can size your airflow to the exhaust temps. I'd recommend 20 to 30 *F. The hood traps most of the heat inside. The heat inside the hood stabilizes and is the same as the exhaust temp. With a cooled hood only the radiant heat from the light is transferred to the grow box.

Large rooms that connect several hoods in series to a common fan, 20*F per hood, and no more than 80*F total for the exaust temp rise. 














>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Cooling lights and providing ventilation for your plants are two different things. 

I believe more than One air exchange per minute is excessive and causes undue stress on the plants.

The one pass ventilation and scrubber designs that expose the plants to all the light cooling airflow cause unnecessary stress on the plants as well as requiring oversized fans and scrubbers.

It is better to cool the lights separately using ventilated hoods or cooltubes with unrestricted fans. This drops the requirements down for area ventilation significantly. I sure like putting in small fans and scrubbers which saves $$$ in equipment and operating costs.

One other point of interest, the suggested airflows are in the 5-10 Minutes per Airchange for most uses involving people and habited spaces. High air change rates in the 1 to 5 Air Changes per Minute are found in applications where a lot of fumes need to be ventilated like a paintbooth. Many growboxes are constructed this way leaving the plants exposed to unnecessary stress.

***********************************************************************************************

*Air Conditioner Sizing*

*BTU/hr = (3.413 * Watts) + (1.25 * Room Area * Delta T)*

*1 TON = 12000 BTU/hr*

*For example, a 144 sq ft room with two 600 W lights within 20* F of ambient would require*
*a 7700 Btu/hr or a 0.64 Ton unit.*


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## Ou8aCracker2 (Jan 12, 2014)

At an intake to a duct, Static pressure inside the duct is converted to Velocity pressure which makes the air move. 

Air Flow (cfm) = K sqrt(SP) * Duct Area







Now all the air around your intake is sitting still and it has to be pulled into the intake and accelerated up to the velocity of the air travelling in the duct.







All the air being pulled into the inlet causes an effect called the vena contracta. Some of the air around the inlet isn't moving at all while some of the air is compressed and expands as the velocity pressure is converted to static pressure. The duct static pressure and entry losses are related to the size of the vena contracta.







The shape of the intake is very important in reducing the hood entry losses.







Sp = (1 + Fd)Vp

Vp= Sp/(1 +Fd)

Assuming a Fd of 0.96, Vp = Sp/1.96 = 0.5 *Sp

so the Velocity pressure is only 1/2 the Static pressure with the so effectively we are losing 1/2 our air flow at the entrance to the duct.

The way to combat Static Pressure losses at the intakes is to reduce the Velocity of the air at the intake by increasing the area of the intakes.

*INTAKE SIZING*

Getting the intakes right is the biggest challenge in setting up a growbox. The intake area needs to be at least equal to the exhaust area and up to 2x to reduce losses.

A = pi * (radius)^2 = (pi *diameter)^2/4

*Areas for common duct and pipe sizes*







Thanks to Freezerboy for the nice picture. This is a common mistake when using a number of small holes to equal one big one. The only solution is to calculate the area for the big hole and divide by the area of the smaller holes to get the number of small holes needed.







In this case one 9" hole needs 80 x 1" holes to be equivalent.

I'd like to point out that making one big hole is better than a bunch of little holes as each little hole has it's own Vena Contracta losses which do add up.

*Darkroom Vents*

I see lot's of guys using darkroom vents which are an excellent way to light trap the intake. From my observations, it appears that they are an obstruction to the airflow and seem to cut the air flow down by 1/2.


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## Ou8aCracker2 (Jan 12, 2014)

Here's a good comparison between the different fan types based on Noise, Air Volume and Static Pressure.















Let's make some noise about noise. Our ears are some pretty special instruments that can pick up very faint sounds to all the way to a rock concert at over 100 db.

Noise level is computed using the formula 10Log(Sound Pressure Level). What's important to know is that every 3db difference in sound is double the noise. Every 10db difference is 10 times the noise.

A 100 db rock concert is 10000000000 times louder than a whisper.

Another measurement to know about is SONNES

1 Sonne = 40 db and 4 Sonnes = 60 db where each sonne is 5 db starting at 40 db.

Bathroom fans are measured in Sonnes to make it easy for the average shopper to compare noise levels. A high quality bathroom fan runs 1 sonne and most of the cheaper ones are 3 sonnes or about 55 db.

Computer fans operate a 20-30db and are 300x quieter than a bathroom fans at 55 db and 10,000x quieter than a centrifical fan at 60-70 db.

*AIR VELOCITY*

While we are talking about noise, a big source of noise in ventilation comes from the rushing sound of the air itself.

Air Flow is the velocity of the air in ft/min * the Area of the duct flow in square feet.

Cubic Feet per Minute = (ft * ft * ft) / min

I just helped out a friend that has a 440 cfm fan hooked up to a 4" duct and he can't stand the noise of it. My suggestion is to increase the duct size or connect the duct to a large cardboard box to drop the air speed down while maintaining the air flow rate.







This is the basic technology behind a muffler or silencer. Increase the area of the ducting to drop the airspeed. Add a grill or grid to even out the flow of air to reduce turbulence and the noise will be significantly reduced.


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## Ou8aCracker2 (Jan 12, 2014)

*MATCHING FANS AND FILTERS*


Matching a fan and a filter can be pretty tricky. You'll see lot's of lively discussions on this topic on this website. Most people rely on a salesman at a growshop or buy a matched fan and filter combo from a reputable manufacturer. Let me tell you that the curves can be easily created and you can verify easily if a fan and filter combination will be suitable for your grow setup.

Each Fan Manufacturer will provide a Flow vs Pressure curve. You'll need to get this to create the Fan Curve.

*CANFAN Fan Specifications*













The other curve that you need is the Filter Performance Curve.

The filter performace curve follows the formula

CFM = K * SQRT(Pressure)

The Manufacturer will give you a CFM rating at a certain air pressure in the units inches of water. That's all you need to determine the K constant value for that filter.

K = CFM / SQRT(Pressure)
*
CANFAN Filter Performance Constants*






CANFAN was nice to give us a few operating points for thier fan and filter combo's. That's all we need to get the K value for that filter.

Here's the CANFAN Filter Performance Curves







Now that we have our Fan Curve and our Filter Curves, let's put them on the same graph so we can see the operating points where the two curves cross.










Here's the operating points from where the fan curve crosses the filter curve.


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## Ou8aCracker2 (Jan 12, 2014)

One of the key features of a good growbox design is fitting a carbon scrubber to the ventilation system.

Let's take a look at CANFAN's stuff. They publish decent spec's with their equipment.

I'd like to fit a 6" CANFAN which is rated at 269 CFM with 1.5" WC pressure. This is a workhorse of a fan. http://www.canfilters.com/fan_metal_home.html

Now let's get a nice CANFAN 50 that's rated at 420CFM @ 0.75"WC.
http://www.canfilters.com/canfilters_50.html

Hey this sounds pretty good, I think I can get 270 CFM out of this combo, maybe? Well let's take a look.







The operating point for the 6" CANFAN/50 combo is around 200CFM. Canfan says 210 CFM so that's close with about a 25% loss due to the scrubber. So what gives, the filter is supposed to give 420CFM @ 0.75" and we have a 1.5" Fan, how did we end up running at 50% of the scrubber and 75% of the fan? This is where the fan curve is needed to see how both these components make a system where the actual airflow is the operating point where the two curves cross.

Let's hook this puppy and see what happens. Holy cow this thing is loud. No wonder, look at the noise spec. 6 Sonnes, that's like 70 dB. Look up 70db, its a vaccuum cleaner loud or the same as radio or TV music. And that's the noise of the fan, the fan spec's don't include the air rushing though the ducts either.

Am I happy. Let's see I just spent at least $300 on this stuff, my cabinet is 90* and I can here this thing on the street.

So what are my options. Add a speed controller, box runs hotter. Get a quieter fan, if it's less that 1.5"WC, the box runs hotter. Downsize the lights? Leave the door open?

Every growbox you see fitted with a scrubber/fan combination is using this brute force approach to the ventilation. This is caveman engineering by Fred and Barney. 

An alternative is to run unrestricted quiet fans to cool the lights. A high airflow, low noise computer fan will run with 15-25 db which is whisper quiet compared to this hoover. Add a second small fan pushing through a small scrubber and you're set. Cool, quiet and smell free.


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## Ou8aCracker2 (Jan 12, 2014)

One of the challenges in building a good ventilation system is to get the right amount of airflow. If you're stuck and you need to add or replace a fan, many times it doesn't quite work out.

One of the reasons is that the Air Flow is proportional to the square of the Pressure. Adding a second fan will not double the flow but will increase it by square root of 2, (1.41), or by about 40 percent. To double the Air Flow requires four times the Pressure.

There are two ways to add a second fan and they have completely different effects on the system.

The first way is to add a second fan inline with the first. The fan curve is the single fan curve with the pressure doubled at the same flow rate value.












The second way is to add a parallel fan. This doesn't boost the pressure at all but doubles the air flow at the original fan curve pressure value.







If you like these fans check out the S&P Catalog. The fans have adapters that make it easy to stack and parallel them.

http://www.hvacquick.com/catalog_files/solerpalau_TD_Extended_Catalog.pdf?PHPSESSID=cfh2booc2hmfvl79qmr7oqqii5








System A is very restricted. We can see that the air flow improves quite a bit with series compared to parallel.

System B and C are less restricted and the improvements in air flow are similar between series and paralllel.

System D is an unrestricted system with the parallel fans providing a significant improvement over the series fans.

***********************************************************************************************

I did a little experiment a while ago with 4 computer fans. I connected them in series and boy did they ever make a good amount of pressure and they were pretty quiet too. Each computer fan can produce 0.2" static pressure. Four in series will produce the same pressure as a Dayton blower at 0.75". The noise of a computer fan is around 20 db with the noise doubling every 6 db so four fans would make about 38 db of noise which is way quieter than some of the noisy blowers that start at 65-70db.


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## vostok (Jan 12, 2014)

So you copied all this from ICMAG to paste here, then you want it to be a sticky here? ...why don't you be a bit more original than that ...credit to ICMAG


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## Ou8aCracker2 (Jan 12, 2014)

Yes I did,and it needs to be a sticky here...that is unless you like seeing 1,000,001 ventilation help threads when all someone had to do was their homework.


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## Ou8aCracker2 (Jan 15, 2014)

Bump for good material and something that should be a sticki here.


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## Ou8aCracker2 (Jan 18, 2014)

Bump,hoping this helps someone.


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## SnapsProvolone (Jan 18, 2014)

Some good stuff over at skunkpharm too.


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## a mongo frog (Jan 18, 2014)

applaud the effort on the thread, how ever that much info just seems to confusing for a grow room procedure that is pretty basic and a no brainer. ventalation is basic protocol.


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## SnapsProvolone (Jan 18, 2014)

a mongo frog said:


> applaud the effort on the thread, how ever that much info just seems to confusing for a grow room procedure that is pretty basic and a no brainer. ventalation is basic protocol.


Some larger grows get pretty complicated. A little good information can go a long way.

Links to original source would be kind.


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## a mongo frog (Jan 18, 2014)

SnapsProvolone said:


> Some larger grows get pretty complicated. A little good information can go a long way.
> 
> Links to original source would be kind.


whats a larger grow considered to u?


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## SnapsProvolone (Jan 19, 2014)

a mongo frog said:


> whats a larger grow considered to u?


Anything with 30kW or 10 tons and up for sure. Some of the larger MMC's out here go way beyond that. As an electrician I have worked for several OPCL's where myself and their HVAC contractor both spent some time together with staff figuring out their cooling / dehumidification / electrical needs so I could do my load calcs prior to pulling permits for service changes.

Think rocket science. Small scale toy rockets = simple. Bigger the rocket the more complicated it gets. Not everyone is growing under one or two lights in a tent and may find learning more about this subject helps them tune their system.


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## dadio161 (Jan 19, 2014)

Ou8aCracker2 said:


> Yes I did,and it needs to be a sticky here...that is unless you like seeing 1,000,001 ventilation help threads when all someone had to do was their homework.


No need to be a sticky just because you said so. I vote NO


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## BadAndy (Jan 19, 2014)

yea.....begging for your own thread to be stickied is a little desperate


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## Ou8aCracker2 (Feb 6, 2014)

Bump because I see the same questions being asked over and over and over...just sticky it already mods!


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## Ou8aCracker2 (Mar 7, 2014)

Bump for the same reasons as above.

Is this place even modded anyway?!


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## sunni (Mar 7, 2014)

Ou8aCracker2 said:


> Bump for the same reasons as above.
> 
> Is this place even modded anyway?!


mods delete spam


just curious how you expect us to magically know you want your thread stickied without ever PM'ing a global mod or admin lol


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## Ou8aCracker2 (Mar 7, 2014)

You can lol all you want but you know the main post of this thread has extremely valuable information for noobies and vets alike.If you like seeing the forums clogged with endless "cfm" and "ventilation" help posts then so be it,but it really clogs up the forums.


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## sunni (Mar 7, 2014)

Ou8aCracker2 said:


> You can lol all you want but you know the main post of this thread has extremely valuable information for noobies and vets alike.If you like seeing the forums clogged with endless "cfm" and "ventilation" help posts then so be it,but it really clogs up the forums.


people dont read stickies .

youll still have a cluttered board of vent help posts.

ive had a FAQ sticky in support for years.
go look at the support board

92% of all threads started have every answer in my thread


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## Ou8aCracker2 (Mar 7, 2014)

That's not true.

I started growing over 15 years ago...later I joined OG and read just about every sticky and FAQ that had to do with a question I had before making a thread about said questions and I would only make a thread about said questions if I didn't find what I was looking for or I didn't understand something or everything in the sticky/FAQ's.

Once IG went down I joined ICmag and did the same thing!

It not only saved the forums from one more poster clogging up the forums but helped advance my knowledge and skill level over the years.


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## sunni (Mar 7, 2014)

Ou8aCracker2 said:


> That's not true.
> 
> I started growing over 15 years ago...later I joined OG and read just about every sticky and FAQ that had to do with a question I had before making a thread about said questions and I would only make a thread about said questions if I didn't find what I was looking for or I didn't understand something or everything in the sticky/FAQ's.
> 
> ...


not everyone is you
most people sign up and make a thread they dont read stickies infact id say 8/10 do that
i am by no means saying your thread isnt suitable im saying if your primary focus is to stop the clutter in this subform youll be sorely disappointed


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## GroErr (Mar 7, 2014)

Too much information, not original, asking for a sticky, vote = no. Are you here to get stickies or help fellow growers???

Anyone who would actually read all the info posted, could actually understand it and make use of it would have already found it themselves. Anyone posting asking for basic venting/air-flow questions wouldn't take the time to read this or wouldn't understand it. In between there are a lot of questions or people sometimes post specific questions to get second opinions or validate they're thinking/design. That's why there are so many threads (with repeating subjects/content) on this site, the latter is the most common, people want validation/second opinions, and many like to think they're problem is unique...


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## Ou8aCracker2 (Mar 7, 2014)

Well then by all means groeer go ahead and help them.You'll probably just tell someone using a 400w light in x space needs a 4" inline centrifugal without taking ambient temperature into thought.

The main post is easy enough to understand by anyone with just half a brain should they actually do their homework.

Do things half assed or follow a half assed answer and you get half assed results.

By wanting this thread stickied and it being a sticky,I would be helping others.Anyone that has a question after reading the main post and doing their homework is more than welcome to make a post.

Just tired of seeing all the "how much ventilation do I need" threads when it is all answered in the main post of this thread.


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## sunni (Mar 7, 2014)

Ou8aCracker2 said:


> Well then by all means groeer go ahead and help them.You'll probably just tell someone using a 400w light in x space needs a 4" inline centrifugal without taking ambient temperature into thought.
> 
> The main post is easy enough to understand by anyone with just half a brain should they actually do their homework.
> 
> ...


youre missing the point
Youre still going to see all those threads people barely read stickies they want an answer quick and fast thats all


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## Ou8aCracker2 (Mar 7, 2014)

And those that don't do their homework are doomed from the get go...PERIOD!


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## Maxed Out (Mar 7, 2014)

I found your info quite interesting even though I didn't understand all of it. Now if you explain it in layman terms, remember not everyone succeeds in germination of seeds, I feel that it would benefit more people. That is when it gets attention. Thanks for taking the time to track down the info


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## Ou8aCracker2 (Mar 9, 2014)

Bumpity bump bump


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## SnapsProvolone (Mar 9, 2014)

Most people that you bitch about aren't into reasearch and thought. They want someone to just tell them, "For your setup this is the solution". Of course little or no information is provided and best advice is usually ignored as too costly or complex.

Lots of lazy people, get over it.


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## louislong (Mar 19, 2014)

Hey guys, I am little confused.

In the sample "A 400 W HPS in a 3 x 3 x 4 cabinet needs 126 CFM of cooling for a 10*F temp rise above room temperature.
The 36 cu ft cabinet is ventilated at over 3 Air Changes Per Minute. ", how do you know 400W HPS courses 10F temperature rise? I am just curious how to determine the temperature rises


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## joe macclennan (Mar 19, 2014)

you've got a lot of really good info there cracker. But I agree with both sunni and snaps. Most don't read stickies. 

SO your time would be better spent just answering some of the questions asked on the board.


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## joe macclennan (Mar 19, 2014)

louislong said:


> Hey guys, I am little confused.
> 
> In the sample "A 400 W HPS in a 3 x 3 x 4 cabinet needs 126 CFM of cooling for a 10*F temp rise above room temperature.
> The 36 cu ft cabinet is ventilated at over 3 Air Changes Per Minute. ", how do you know 400W HPS courses 10F temperature rise? I am just curious how to determine the temperature rises


you can convert watts to btu's pretty easy. It's almost 3.5 btu's per watt. 

so that would be @ around 1360 btus/hr for 400 watts.


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## SnapsProvolone (Mar 20, 2014)

Joe is correct. 3.41 btu/watt/hr. Note a 400 watt bulb fed by a ballast will draw more that 400 watts since ballasts waste a bit of energy as heat. Moving hot ballasts out of your grow room helps remove some heat.


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## louislong (Mar 20, 2014)

joe macclennan said:


> you can convert watts to btu's pretty easy. It's almost 3.5 btu's per watt.
> 
> so that would be @ around 1360 btus/hr for 400 watts.


Thanks, now I have some idea about it.


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## Ou8aCracker2 (Mar 20, 2014)

Another method that's worked for me is 3.14cfm x Watts/Tdiff

Example...

Ambient air is 68°F and wattage is 400w and I want a 10°F tdiff (temerature difference,lights on)...

3.14cfm x 400 = 1256cfm

1256cfm / 10°F = 125.6cfm.(after all pressure losses.


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## rocho (Dec 2, 2018)

Hello,
Maybe it has already been explained right there but I am not very skilled with your language and even less skilled with the theory concerned the air physic.

If I reduce the speed of a small 187m3 / h extractor by a dimmer could I know how many W i may give to get ish 80m3 / h?

I only know that 50% of power DOES NOT correspond to 50% of airflow because I asked that to the Vents customer care(model code is TT100)

thanks in advance to those who will help me


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