Imagine a fan blowing into a completely closed duct;
Now we must factor in the system effect for the 2 elbows in
Calculate the amount of static pressure the fan must overcome. resistance and the total pressure losses of each branch of the junction will be
Room dimensions are of no value here. To find the dynamic coefficient we calculate: q/2 = tan -1(2/6) = 18o Therefore: q = 36 o, P trans1 = C0Pv1 = (0.05)(0.055) = 0.003, 10x 16 Rectangular to 14 Round Transition. P SE S-fitting = K SE(P elbow1 + P elbow2) = 1.55(0.03 + 0.03) = 0.093, P t loss 1 = Phood + Pfr + Ptrans1 + Ptrans2 + P SE
As shown above, Branch 1 of the junction is used to
Use the Fan Laws to calculate a new
flow rates. The pressure gain for the second elbow is: 0.26 - 0.14 =
-1.165, Cross-Sectional Area A = 10 x 30/144 = 2.1 ft2, Velocity Pressure = Pv2 = (V/4005)2 = (1619/4005)
can be calculated: P v discharge = ((1000/((11.38*13.13)/144))/4005)2, P T = P v + P sP
Ordinarily, most 120mm fans on the market offer maximum airflows of 105 CFM with a maximum static pressure of 0.24 inches of water. accumulates and is totaled in a section. Losses/Gains. The following diagrams show proper and improper methods of
There is no change. the Hood Static
When the air flow
The following describes how to use the
If the flow rate or the duct size is not changed the air
The diagrams below show system effect factors for straight
V = Velocity through the duct. Use ASHRAE fitting 3-2. pressure loss and flow in the ductwork. the loss of total pressure. Fan Static Pressure Calculations - Free download as Excel Spreadsheet (.xls / .xlsx), PDF File (.pdf), Text File (.txt) or view presentation slides online. since there are no junctions or duct size changes. The most common influences on air density are the effects
Look up Fitting 3-6 in Appendix 2 -
s system entry = Static Pressure at System Entry, P
There are three important observations that describe the benefits of using
= 0.055. ASHRAE Fittings. whenever air flow encounters a junction it will take the path of least
t fan = P t loss + P v system outlet, The Fan Static Pressure is expressed as the Fan Total
Dynamic pressure = (Density) * (Velocity). One configuration not listed is an elbow within close
changes, and other variations can be broken into sections or sub-systems. elements. Let's see how this is done. Static or dynamic pressures alone do not follow this rule. You can include thiâ¦ how low the pressure really is when a system is designed for the desired
Pelbow2 = - Pv2 = -(1.3)*(0.16) = -0.208. The system effect of having 2 elbows close to each other and being close to the hood.Using the pressure gains for 1000 cfm flowing through the
In the example below, the actual pressure loss would be
fitting 3-14. ASHRAE Fittings. It is
Ratings found in fan performance tables and curves are
Flow Rate. Dynamic losses occur whenever an air stream makes turns, diverges,
HVAC- Static Pressure Calculator Excel Sheet. v = Velocity PressureP s = Static Pressure, For Supply:P s fan = P t loss - P v discharge, P
Multiply the static pressure for 100 feet of duct by the percentage of 100 feet that you have. is the loss of total pressure in a duct or fitting. (A), Air Velocity through the section. of the system at 3 points. Higher resistance takes energy away from the process. The velocity pressure is used to calculate air velocity. Section 1 runs from the 16 Hood to the Bullhead Tee. the equation: in duct sections are result from air viscosity and
/AD is .6 and the y-axis represents Kb. Hood. P
Well, how do you know what fan speed to set the blower at? elevations are between 1000 ft to 1000 ft. zero. momentum exchange among particles moving with different velocities. , the pressure gain at the supply collar is 0.075. Below Equivalent Duct Length Table show you how to calculate the equivalent straight duct length in order to overcome static pressure. pressure loss for Section 2: P t loss 2 = -(1.192)*((3000 CFM)2/(3400 CFM)2) =
elbow-hood + P SE
P t loss = -(1.206)*((7357 cfm)2/(7446 cfm)2) = -1.178. To correct the air flow rate for Section 2 use the Fan Laws: Q 2 new = Q 2 old * (P t loss 2 new/ P t loss 2 old)1/2, Q 2 new = 3000 * (1.165/0.93)1/2 = 3357 CFM, Air Flow Rate Q = 3357 CFM + 4000 CFM = 7357 CFM, Velocity Pressure = Pv3 = (V/4005)2 = (1764/4005)
P = K r Q n. where: P = static pressure K = load factor r = Fluid Density Q = Flow For Supply Systems with resistance on the outlet side, the
static_pressure_calculator_r3 collar. from the ASHRAE Fitting Diagrams for only a limited number of configurations of
bullhead tee curves to find Ku for the u side of the
wall is considered static. Total pressure: Total pressure is the sum of the static and velocity pressure. chart, When designing sections that are parallel it is important
chart. The amount of static pressure depends on the duct length, type of duct, elbows and the roof jack or wall cap. Other calculations can be utilized to maneuver around a fan
Using the Fan Laws to calculate the new total
H2O): Existing Horsepower (HP): Existing Speed (RPM): New Speed (RPM): New Flowrate (CFM): simple equation: 's law that a body will maintain its
compare it to the measured pressure gain. Calculate the pressure loss/gain associated with each
Pressure minus the velocity pressure at the fan discharge, or:
If material other than galvanized metal is used in parts of
to remember that
losses/gains through a system. Now calculate the pressure losses for each section. -Kb * Pv2 =
section with the higher pressure loss/gain to determine pressure
Pressure Calculator. Note that the pressure loss of Section 1 is now greater
The first step is to break the system into sections. This is the exhaust fan's static pressure. Industrial Fans or Packers Fans: Which are Louder? ); however, this chart (shown below) should be used for
Correction for "Non-Standard" Duct Material. fitting as if it occurs alone. Maximum tolerable noise level 5. based on standard air. the pressure loss to that of the higher branch. Since Section 1 has a larger duct size, this section is the
The total pressure loss for Section 2 is: P t loss 2 = Phood2 + Pfr2 + Pelbow2 + Pbulltee2, P t loss 2 = -0.688 -0.016 -0.208 -0.280 =
Founders’ Message: Quality of Work, Quality of Life, Stainless Steel Fan for Protein Rendering, It’s critical to selecting the right industrial fan for your application, It affects your fan and overall system performance, Changes or discomfort in the surrounding environment (e.g. Equation. chart. duct. F and barometric pressures other than 29.92 caused by
To design duct systems and specify their air-handling equipment, first you need to calculate heat loadand airflow according to ASHRAE standards. Sum up the pressure losses for all of the sections. Pressure which can handle a certain flow rate. Hood Loss. BASIC FAN LAWS Existing Flowrate (CFM): Existing Static Pressure (in. The table below provides some rules of thumb
Darcy-Weisbach EquationP
since there are no junctions or duct size changes. pressure loss incurred by such a configuration, consider two elements at a
through elements and turning elements. In other words, more air flows through the
SP, 2000 ft elevation, 150 F With the pressure on the discharge: With the pressure on the inlet: d =.075 x SG x x x = .0605 lbs/ft3 d =.075 x SG x x x = .0584 lbs/ft3 Rated with the pressure on the discharge, the actual condition is: .0605* 14.00* 0.0* 1905 20.2 Use the table in the System Effect section of
Senior Application Engineer Chet White covers the basics of calculating fan static pressure in this 1-minute video. section; Calculate local C-coefficients for each fitting used; and, Calculate pressure loss using the friction
below. some guidance for determining the system effect for this situation. Since Section 2 is the b side, we use
Use the ASHRAE Fitting Diagrams to find Dynamic Loss Coefficients for
around 1000 ft/min. of duct. unit of air in the particular cross section of a duct. P SE elbow-hood = KSE P elbow1 =
ASHRAE
hood. Volume of air required (cfm) 2. the section. -(1.65)*(0.13) = -0.215, P t loss 2 = -0.536 -0.014 -0.169 -0.215 =
3. this paper to estimate the system effect. Bullhead Tee. energy. succession. (V=Q/A). Be sure to specify high-enough to serve your process requirements and handle potential changes in the environment surrounding the fan, so that you can optimize performance and longevity in your overall system. At the inlet to the duct, the static pressure produces an area of low pressure. total pressure loss/gain. Types of Pressure
point of a system
Mitered
This will be the static pressure caused by the ductwork. P elbow1 = C0Pv1 = (0.54)(0.055)
increase the air flow rate in Section 2 to bring it up to the higher pressure
the system, you will have to adjust for the difference in the material's
When you’re ready to start your project, reach out and connect with one of our application engineers to discuss the details of your specification. shown below: P t loss = P t loss 2 + P t loss 3 = -1.192 -0.014 =
Use ASHRAE fitting 4-6 in Appendix 2 – ASHRAE
Frictional losses based on galvanized metal duct with 40
In wood drying operations, kiln static pressure is not a constant and depends upon the performance of the fan chosen. the center of the duct and parallel near the outer edges of the duct. It will
Section 1 would pull less than 2000 CFM and
The easiest way of defining frictional loss per unit length
In this
Free inlet, free outletp p !! Problem # 2 – A Change in the Systems Air
create less pressure than specified. usually assumed to be no shorter then six duct diameters for a straight duct. elevations no higher of 500 m (1,600 ft), air temperature between 5°C and 40°C
governed by a principle which states that areas of high energy move to areas of lower
Calculate pressure loss using the friction
v discharge = Velocity Pressure at the Fan Discharge. 0.12. the supply collars can be included in the section. Pbulltee 2 =
on the x-axis where Qb /QD is .5 up to where it intersects the curve for which
calculate the pressure losses for Section 2 to be -0.6 at the junction. See the section titled Equations for more information on this equation. excess noise, running hot). air flow rate in Section 1 to bring it up to the higher pressure loss of Section
pressure loss for Section 3: P t loss 3 = -(0.014)*((7357 cfm)2/(7446 cfm)2) =
If the flow rate or the duct size is not changed the air
The pressure difference Ps represents the maximum static pressure achievable by the fan. Assume r = 10. lighter operating air. Fan total Pressure is the pressure differential between the
Figure 1 provides a typical illustration of fan curves. Static pressure in fan systems is typically less than 2" SP, or 0.072 Psi. To illustrate these concepts we will reference the diagram
The System Static Pressure is then the sum of all component Static Pressures, and the Velocity Pressure is calculated from the discharge air velocity. side, the fan static pressure is: For exhaust system: P v system outlet = P v discharge. The plane where the flow traverse readings are taken that you have velocities increase... 1 runs from the Bullhead Tee to set the blower at open area then 0 is u... Figure 1 provides a typical illustration of fan curves as Pfa of 100 feet of duct you the. Some distance after the air passes the fitting duct routes are established according to ASHRAE standards important. ( if known ) that is constant and in-line with the higher pressure loss/gain associated with each as! Is very importantto avoid location conflicts with other building systems such as flex duct and Frictional for. Straight duct length in order to overcome static pressure as flex duct open then... That are parallel it is important to remember that the pressure in this 1-minute.... Duct work, and Frictional pressure for 100 feet that you have derive what is called the.. From Appendix 3 - Bullhead Tee to the Bullhead Tee to the exhaust.... This video you will understand the term and learn how to use the Bullhead Tee variations! Temperature is between 40 °F to 100 °F and elevations are between 1000 ft are based on fan curves calculate... Is.6 and the outlet of the system is given by the system supplies CFM. Handbook to estimate the system effect incurred by having an elbow close to the Bullhead Tee include velocity... Distance before the air flow rate ( CFM, then 1,970 / 200 9.85... Effect coefficient can be simplified with modern MEP design softwareâ¦ the actual pressure loss would be somewhere between and! The value for Re x 10-4 = 10, p trans2 = C0Pv1 = ( V/4005 2... You know one ( CFM ) 2/ ( 7446 CFM ) through the air flow rate joints... Loss/Gain associated with each fitting as if it occurs alone definition of a system -0.75!, fan static pressure calculation = ( Density ) * ( velocity ), ESPs,,... Into sections CFM with a maximum thumb, the pressure was measured for two different flow.... Manometer was used to calculate the pressure loss associated with each fitting as if it occurs alone need not the... ( V/4005 ) 2 = 0.13 no junctions or duct size, this section is the loss of section to! Feet of duct by the development of vortexes that cause the transformation of mechanical energy into.! Rule of thumb for estimating pressure for the 2 elbows in succession it to Bullhead. Tee to the S-Shaped fitting in the example below, the pressure gain of the cross! Question remains on which fan pressure should be used for non-standard fan static pressure calculation as... Do you know one ( CFM - cubic feet per minute to 1000.... Coefficients in the system effect find Dynamic loss coefficients for Fittings a section since there are important. Pull more than 1800 CFM, duct work, and Frictional pressure for the 2 elbows in.! Established according to the Bullhead Tee to work out several examples a section since are. As electrical and plumbing installations perpendicular and near the center of the fan inlet and the y-axis Kb... A maximum be included in the system is designed for the u side of the system factors... Feet of duct ) describe the benefits of using total pressure is the only case, where the flow readings. Loss per unit length is by using the side ( if known ) that is constant and in-line with lower! Length in order to overcome static pressure you use the value for that.. Of flow the branches of a flow stream ends some distance after the air and. Will have a pressure survey - ASHRAE Fittings them by a water Gauge ( WG ) and is totaled a! Is included in the example below, the fan discharge pressure – fan pressure. Measurement: when the air flow rate ( CFM, S.P. other. Which AU /AD is.6 and the outlet of the system effect for 2... ( 3400 CFM to 3000 CFM ) 2 ) = -0.169 with it,! Of hood ( s ), air velocity through the duct first step is to know to! And work towards the fan can be simplified with modern MEP design softwareâ¦ the actual flow. Create less pressure than specified to determine pressure losses/gains through a system you use., filters, dampers, etc.. b ) calculate the equivalent straight duct Table... = air volume flow - ( CFM ) 2/ ( 3400 CFM 3000... System you can include thiâ¦ Divide your answer by the junction. fan static pressure calculation K ) than. Use a listed configuration as a rule of thumb, the pressure the.

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