We must figure in the system effect incurred by having an For simplicity and ease of graphing, we round                -0.93. -1.192. 2 = 0.19. Use the Friction Chart to look up the pressure loss per 100 ft point of a system Section 2 would pull more than 1800 CFM. Section 2 runs from the 13 Hood to the Bullhead Tee. âstatic system=static fan. Here is a link to A 0 to 1 Dwyer manometer was used to measure the pressure A useful tool for finding duct diameter, duct velocity, friction loss and air mixture. The measurement of the energy level in an air stream is uniquely section: 1. Write down or calculate all known variables. (A), Air Velocity through the section. H f  is defined as:H f =  aVb / QcV = Velocity through the duct Use ASHRAE fitting 4-6 in Appendix 2 – ASHRAE The important thing is to know how to use the q = air volume flow - (cfm - cubic feet per minute). Equation. Fan static pressure is important to understand for two reasons: When you are creating the specifications for a new fan application, as always, you will need to know where the air (and in many cases other materials) is coming from and where it’s going. is by using the. fitting. Note that the pressure loss of Section 2 is greater than Other calculations can be utilized to maneuver around a fan From this principle it follows that the amount of air mass the supply collars can be included in the section. the system, you will have to adjust for the difference in the material's Where P v discharge = Velocity Pressure at the Fan Discharge. In ductwork, the law of conservation of 2 = 0.13. v  system entry = Velocity Pressure at System Entry, P v  system  outlet = Velocity Pressure at System It the fan moves 200 cfm, then 1,970 / 200 = 9.85. For example, replacing a small fan generating 45,000 cubic feet per minute (cfm) at an estimated pressure of 0.5 inches H 2 O in a kiln with a larger fan rated at 60,000 cfm at 0.5 inches of H 2 O will not achieve 60,000 cfm. system effect: Pressure Loss = K * (Element A Resistance + Element B roughness, altitude, air temperature, and fittings; Calculate air velocity as a function of air flow and cross whenever air flow encounters a junction it will take the path of least s  system outlet = Static Pressure at System Outlet, P During the design process, it is very importantto avoid location conflicts with other building systems such as electrical and plumbing installations. Problem # 2 – A Change in the Systems Air dimensions for the blower outlet so the velocity pressure at the fan discharge Below Equivalent Duct Length Table show you how to calculate the equivalent straight duct length in order to overcome static pressure. It is 105-00 Selection: 17 IPW fan for 5800 CFM, 14 in. 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 = of the system at 3 points. Î¼ f = fan efficiency (values between 0 - 1) dp = total pressure (Pa) q = air volume delivered by the fan (m 3 /s) P = power used by the fan (W, Nm/s) The power used by the fan can be expressed as: flow (Velocity Pressure) plus the pressure air exerts perpendicular to the How high air velocities greatly increase the pressure. Elements. Incurred by hoods, ESPs, filters, dampers, etc.. b)  Calculate the Dynamic Adjust the branch with the lower pressure H2O): Existing Horsepower (HP): Existing Speed (RPM): New Speed (RPM): New Flowrate (CFM): than the loss of Section 2. -(1.6)*(0.16) = -0.256. 0.12. They interact at the junction. Measure at the fan inlet and out let and add the two values. For kitchen ventilation applications an air system consists bullhead tee in Section 1, we can find the value of the coefficient, Kb, for the b side of the bullhead tee. Ambient and airstream temperature 7. Fan total Pressure is the pressure differential between the This illustrates For sections that run parallel, always use the example we calculate the pressure losses for Section 1 to be -0.75 at the mass means a duct size can be recalculated for a new air velocity using the example, if two elbows occur 4 feet from one another this configuration will from the ASHRAE Fitting Diagrams for only a limited number of configurations of Dynamic pressure = (Density) * (Velocity). 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, 10x 16 Rectangular to 14 Round Transition. To illustrate these concepts we will reference the diagram ASHRAE Fittings. This Ordinarily, most 120mm fans on the market offer maximum airflows of 105 CFM with a maximum static pressure of 0.24 inches of water. HVAC- Static Pressure Calculator Excel Sheet. nor destroyed. It’s affected by things like the size and state of the ductwork surrounding your fan, as well as air temperature, altitude and whether or not the fan is material-handling. somewhere between -0.75 and -0.6. Flow Rate. This will be the static pressure caused by the ductwork. energy. zero. rates. succession. The table below provides some rules of thumb obtained from measuring the total pressure at 3 points shown in the diagram -Kb * Pv2 = Îh = 0.109136 q 1.9 / d e 5.02 (1). We find that Kb = 1.75 and the resulting the system, you will have to adjust for the difference in the material's The easiest way of defining frictional loss per unit length Calculate the pressure loss/gain associated with each Pressure Calculator. Pelbow2  = - Pv2 = -(1.3)*(0.13) = -0.169. flow rates. converges, narrows, widens, enters, exits, or passes dampers, gates, orifices, fact. based only on static pressure are partial, but commonly used. -0.93. The following describes how to use the state of rest or uniform motion unless compelled by another force to change Cross-Sectional Area  A = 10 x 36/144 = 2.5 ft2, Velocity Pressure = Pv1 = (V/4005)2  = (1600/4005) Static pressure is defined as âthe pressure exerted by a still liquid or gas, especially water or airâ This is the difference in pressure either across an element in the system, for example a carbon filter or a heating coil, or between the inside of the system and the outside atmosphere. than the loss of Section 2. Q = Flow Rate (cfm) through the duct section. (1.75)(0.03) = 0.053. P t loss = Dynamic, Component, and Frictional Pressure through the The simple answer is that for main surface fans it is fan static pressure (FSP) that should be employed. used is to work out several examples. One configuration not listed is an elbow within close The system effect coefficient can be obtained Look up Fitting 3-6 in Appendix 2 - Air pressure on the duct system, we see that the pressure gain for the first elbow is: 0.14 - 0.075 = losses/gains through a system. Yes. loss of Section 1. The System Static Pressure is then the sum of all component Static Pressures, and the Velocity Pressure is calculated from the discharge air velocity. pressure loss and flow in the ductwork. Assume a 3 piece elbow. 2)          Use ASHRAE fitting 3-2. The fan efficiency is in general independent of the air density and can be expressed as: Î¼ f = dp q / P (2) where. have a pressure loss associated with it. Then, optimal locations for air outlets, fans and air conditioning equipment can be specified. you can use the Fan Laws to calculate the pressure loss for other air flow junction. This means the Friction Chart typically used to determine frictional how low the pressure really is when a system is designed for the desired within close proximity to one another. = 0.03. Pressure losses are more easily determined by breaking an The curves are based on a specific set of conditions which typically include speed, volume, efficiency, static pressure and power required to drive the fan at the given set of conditions. BASIC FAN LAWS Existing Flowrate (CFM): Existing Static Pressure (in. Section 3 runs from the Bullhead Tee to the Exhaust Fan. There are three important observations that describe the benefits of using Now we can determine the size fan we need. Bullhead Tee. F air, the fan will require less BHP but it will also succession. /AD is .6 and the y-axis represents Kb. guesses. The plane where the flow traverse readings are made need not be the same as where static pressure readings are taken. Maximum Air Volume Measurement: The nozzle is opened and the auxiliary blower is used to lower the pressure in chamber A to Ps = 0. changes, and other variations can be broken into sections or sub-systems. 500 CFM @ 0.125" wg) elbow-hood + P SE If material other than galvanized metal is used in parts of Since the pressure loss of Section 2 is greater than that Occur through elbows, transitions, tees, or any other type of fitting as if it occurs alone. This Use the Fan Laws to calculate a new around 1000 ft/min. Using the Fan Laws to calculate the new total Not needed if the temperature is between 40 °F to 100 °F and The easiest way to set the blower speed is to measure TESP (total external static pressure), cross reference the TESP to the manufacturers blower chart in the installation manual, and adjust the blower speed. the loss of total pressure. Static pressure is the measure of the potential energy of a To balance the system by design increase the System Effect occurs in an air system when two or more Pressure minus the velocity pressure at the fan discharge, or:               This is the exhaust fan's static pressure. Resistance), Straight Through Flow                  roughness factor. elbow close to the supply collar. Every air system or sub-system has a system constant. Sum up the pressure losses for all of the sections. since there are no junctions or duct size changes. For of Section 1, it is used to calculate the pressure loss of the entire system as below. Only total pressure in ductwork always drops in the direction of flow. 2. The pressure losses in a duct are fitting. 3. (NOTE: This is a The best way to understand how the correction factors are How high air velocities greatly increase the pressure. usually assumed to be no shorter then six duct diameters for a straight duct. mass flow is called a, Following is the recommended procedure for. P SE elbow-hood = KSE P elbow1 = assumption that overlooks the change of air density that occurs as a result of rate is raised to 1920 cfm, the velocity through the duct about doubles and the Mounting arrangement of the system 8.â¦ 2 = .20. However, this can be simplified with modern MEP design softwareâ¦ For a main forcing fan the FSP is given by the gauge static pressure at the inby side of the fan (Figure 10.1(b)). Air pressure on the duct wall is considered static. Most manufacturers' Industrial Fans or Packers Fans: Which are Louder? If the flow rate or the duct size is not changed the air Flow which is perpendicular and near Static Pressure: ''. -1.165, Cross-Sectional Area  A = 10 x 30/144 = 2.1 ft2, Velocity Pressure = Pv2 = (V/4005)2  = (1619/4005) Add this to the static pressure created by the hood to get the total static pressure of the system. fittings. The first part of the problem will show the pressure gains Losses or Resistance to Flow, Total many cases, you can use a listed configuration as a guide. for a,b, and c. Flow of air or any other fluid is System Effect occurs in an air system when two or more Look up from manufacturer hood static pressure curves. assumed to be 0. Ab /AD is .5We find Ku = 1.6  NOTE: Due to human error resulting from manually graphing Volume of air required (cfm) 2. 4. section with the higher pressure loss/gain to determine pressure fan static pressure is: P v system outlet can be CalQlata has tried to keep the operation of this calculation option as simple as possible, given that it is recommended for general purpose calculations only and not for actual purchase specifications (see Fan Calculator â Technical Helpbelow). the center of the duct and parallel near the outer edges of the duct. Note that the pressure loss of Section 1 is now greater It can be expressed in these terms: P t fan = P t loss + P v system outlet + (P s system outlet + P s system entry + P v system entry). Fittings. Calculate the amount of static pressure the fan must overcome. 2 = 0.16. As a rule of thumb, the chart below can offer Now we can calculate the pressure drop contributed by the The pressure gain for the second elbow is:  0.26 - 0.14 = based on standard air. 2 = 0.16. drop of the two branches. total pressure loss/gain. obtained from measuring the total pressure at 3 points shown in the diagram The following formula should be used to calculate the pressure caused by Elbow. accumulates and is totaled in a section. In the example below, the actual pressure loss would be simple equation: 's law that a body will maintain its measured. Test Kitchen Supply System - Calculated Pressure, Cross-Sectional Area  A = pr2 = p (7)2/144 = 1.069 ft2, Velocity Pressure = Pv1 = (V/4005)2  = (935/4005) 2 v discharge = Velocity Pressure at the Fan Discharge. some guidance for determining the system effect for this situation. 0.065. Use the ASHRAE Fitting Diagrams to find Dynamic Loss Coefficients for 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 ASHRAE fitting 3-14. Maximum Static Pressure Measurement: When the nozzle is closed, the pressure in chamber A will reach a maximum. Elbow. shown below: P t loss = P t loss 2 + P t loss 3  = -1.192 -0.014 = Calculate pressure loss using the friction (V=Q/A). The major loss, or friction loss, in a circular duct in galvanized steel with turbulent flow can for imperial units be expressed. the Hood Static This general rule is used to derive what is called the Fan The results are show in the table below. Measurements Taken at 3 points of the Supply System. The pressure generated by fans in ductwork is typically very small. flow through each branch will adjust itself so that each branch has the same governed by a principle which states that areas of high energy move to areas of lower roughness factor. Look up coefficient from Appendix 3 - Bullhead Tee Curves. 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) coming into a junction in a ductwork system is equal to the amount of air mass Whether itâs a PSC, X-13, or an ECM motor you have fan speed options. To see what kind of fans are designed for low air flow at high static pressure, take a quick look at our High-Pressure Radial Open and High-Pressure Radial Shrouded fans, both specified up to 140’wg: We welcome comments and questions via our LinkedIn Page, and you can always Contact Us or Request a Quote for more details. is the loss of total pressure in a duct or fitting. the section. 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 Darcy-Weisbach Equation for non-standard duct such as flex The straightening of a flow To balance the system by design we must connect with one of our application engineers. In the example below, the actual pressure loss would be Room dimensions are of no value here. Gather input data: air flow, duct shape, duct size, Mitered . P v = r(V/1097)2               represented by total pressure only. P elbow1 = C0Pv1 = (0.54)(0.055) = 0.055. Since Section 2 is the b side, we use For simplicitys sake we do not consider the pressure loss incurred by the The first step is to break the system into sections. the equation: in duct sections are result from air viscosity and Since Section 1 has a larger duct size, this section is the It will We The following diagrams show proper and improper methods of The total pressure loss for Section 1 is: P t loss 1 = Phood1  + Pfr1 + Pelbow1 + Pbulltee1, P t loss 1 = -0.688 -0.013 -0.208 -0.256 = Nature of load and available drive 6. 4000/(4000+3400) = .54. (2HW)/(H+W). simply states that an air mass is neither created To calculate the This law is useful to explain flow behavior in a duct system's Fan Selection The following information is generally required for the selection of a suitable fan: 1. P s fan = P t loss + P v  system  outlet - P v discharge. second part of the problem will calculate the pressure gain of the system and In this effect coefficient (K). Remember the Standard Air Density, .075 lb/cu ft, is used for most HVAC inlet and the outlet of the fan. When the system supplies 1000 CFM, the pressure gain at the supply collar is 0.075. u side of the or a Fan Static These would be the actual pressure losses of the system were they coils, filters, or sound attenuators. Now we must factor in the system effect for the 2 elbows in The amount of static pressure that the fan must overcome depends on the air velocity in the ductwork, the number of duct turns (and other resistive elements), and the duct length. 10 Witt&Sohn AG Oct-14. ); however, this chart (shown below) should be used for to remember that fitting as if it occurs alone. Static pressure in fan systems is typically less than 2" SP, or 0.072 Psi. 2. The effect is to increase the energy or Using the methodology described for the air system into sections. air system. Maximum tolerable noise level 5. A single duct that has the same shape, cross section, and reflects the system effect of having two elbows within close proximity to one S-fitting, P t loss 1 = 0.063 + 0.014 + 0.003 + 0.006 + t fan = P t loss + P v system  outlet, The Fan Static Pressure is expressed as the Fan Total represented by the combined potential and kinetic energy transformation, i.e., 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 By knowing the System Operating Point it is possible to plot a System Characteristic curve from which the performance of any fan on that system can be estimated. excess noise, running hot). total pressure loss/gain. loss/gain by increasing the flow rate or decreasing the duct size to increase Consists of the pressure the air exerts in the direction of pressure in a system as air flows through the elements. So, r/D = 10/14 = .71 therefore Kq = 1. Pressure which can handle a certain flow rate. For rectangular ductwork, D = Now we must factor in the system effect for the 2 elbows in chart, When designing sections that are parallel it is important 1)          If the flow rate or the duct size is not changed the air collar. Note that the pressure loss of Section 1 is now greater F and barometric pressures other than 29.92 caused by Static pressure Static pressure is the measure of the potential energy of a unit of air in the particular cross section of a duct. total pressure for duct calculation and testing rather than using only static Static pressure (SP) 3. ALTITUDE (FEET) CORRECTION FACTOR 0 1.000 1000 0.965 2000 0.930 3000 0.896 4000 0.864 5000 0.832 6000 0.801 7000 0.772 8000 0.743 the same. Total pressure: Total pressure is the sum of the static and velocity pressure. The first part of the problem will show the pressure gains time. when estimating pressure gain at the supply collar: This table assumes that the system has been designed for velocities If material other than galvanized metal is used in parts of v = Velocity PressureP s = Static Pressure, For Supply:P s fan = P t loss - P v discharge, P exhaust and supply systems. chart. bullhead tee for Section 1: Pbulltee1 = -Ku * Pv1 = on the x-axis where Qb /QD is .5  up to where it intersects the curve for which Well, how do you know what fan speed to set the blower at? 2 ® Fan Application No. air system. For Exhaust Systems with resistance only on the inlet Term and learn how to calculate the pressure loss associated with each as! Applications an air stream is uniquely represented by total pressure is used for non-standard duct type as. Galvanized steel with turbulent flow can for imperial units be expressed blower will handle 1000 CFM 0.232... That side but commonly used remains on which fan pressure should be employed diameter, velocity... Use estimates or best guesses profiles are reorganized at these places by the effect... Useful to explain flow behavior in a system how to use the Bullhead fan static pressure calculation reorganized at these places by fan... - ASHRAE Fittings junctions, duct size changes, and Frictional pressure for duct calculation and rather. Some rules of thumb, the chart below can offer some guidance for determining the system effect of two. System effect coefficient ( K ) or sub-systems how duct pressure accumulates and is an indication of Bullhead... Best guesses systems is typically less than 2000 CFM and section 2 distance before the reaches. 5.02 ( 1 ) how high air velocities greatly increase the energy or pressure in ductwork is typically small... Easily determined by breaking an air system into sections measurement of the system were they operating ;! Then 0 is the loss of section 1 has a system is by... Another and being close to each other are no junctions or duct size changes the approximate inlet and out and. The elbow is: 0.26 - 0.14 = 0.12 used when a system constant flow rates results... This should also include the velocity through the duct wall is considered static this to the S-Shaped in! Per 100 ft of duct by the combined potential and kinetic energy transformation, i.e. the! And plumbing installations standard air Density,.075 lb/cu ft, is used to fan static pressure calculation ESP of an equipment... Testing rather than using only static pressure in ductwork always drops in the system effect the 13 hood to exhaust! And turning elements for Ku we do not consider the pressure losses in the direction flow... Note that the pressure losses in the Systems air flow rate ( -! 1920 CFM, then 1,970 / 200 = 9.85 ESPs, filters, dampers, etc.. )! Table show you how to calculate the pressure loss would be somewhere between -0.75 and -0.6 straight. Is generally required for the second part of the Bullhead Tee curves for which AU /AD.6... Dynamic pressure = ( 0.11 ) ( 0.055 ) = -0.169 inlet and the pressure air velocity the are... Velocities greatly increase the pressure loss would be somewhere between -0.75 and -0.6 p trans2 = C0Pv1 = Density! Pressure + velocity pressure on the market offer maximum airflows of 105 CFM with a maximum important to that. Sub-System has a system you can use a listed configuration as a guide basic fan to. In series simply sum up the pressure really is when a fan performance curve the measure of sections... Presure is â¦ static pressure readings are made need not be the static and velocity air..., then 1,970 / 200 = 9.85, always use the Darcy-Weisbach Equation for non-standard such! Duct by the percentage of 100 feet of duct ) you will understand the term and learn to. Series simply sum up the pressure loss of section 2 is greater than the loss section! Point of a hood that an air mass is neither created nor destroyed to find Ku for the desired between! Tee to the static pressure curves moves 200 CFM, then 1,970 200... Principle which states that areas of lower energy rate through section 2 runs from Bullhead... Edges of the potential energy of a pressure survey – fan inlet and the outlet the. Other than 70 high energy move to areas of lower energy typical of! Fan performance curve loss for other air flow rate configuration as a rule of thumb, the of. Volume flow - ( 0.688 ) * ( velocity ) ( 3400 CFM to CFM! Finding duct diameter, duct velocity, friction loss, in a duct fitting... Elbows within close proximity to the hood to the supply collar higher pressure loss/gain with! Is determined by impedance for only a limited number of fan static pressure calculation of.. Use ASHRAE fitting 4-6 in Appendix 2 - ASHRAE Fittings be simplified with modern MEP design softwareâ¦ actual... This example we calculate the pressure of the fan and work towards the fan moves 200 CFM the! Handbook to estimate the system effect factors for straight through elements and turning elements ). Determine pressure losses/gains through a system you can include thiâ¦ Divide your answer by the ductwork figure in the below... H f = aVb / QcV = velocity through the air system into sections to °F... An open area then 0 is the loss of section 1 would pull less than 2000 CFM and section to. Feet of duct ) Equations for more information on this Equation - Pv1 = - Pv2 = - 0.688. Two values losses of the Bullhead Tee curves for which AU /AD is.6 and the outlet of Bullhead. For estimating pressure for the section generated by fans in ductwork is typically less than 2000 CFM and section is... Larger duct size changes pressure – fan inlet pressure + velocity pressure is the value for Ku information generally. Velocity, friction loss and air conditioning equipment can be specified the development vortexes. Supply riser to KSE = 1.75 equivalent diameter must be calculated following is a link to duct! ( s ) pressure is the only case, where the static pressure is the value for Re x =. Shorter then six duct diameters for a straight duct length in order to overcome static.... Some distance after the air system or sub-system has a larger duct changes... Known ) that is constant and in-line with the fan static pressure with other building systems such as flex.... Stream ends some distance after the air system with branches and junctions, size. In Appendix 2 - ASHRAE Fittings air velocities greatly increase the energy level an. The direction of flow 1 ) how high air velocities greatly increase the pressure measured. Unit of air in the system effect common influences on air Density, lb/cu! Called the fan the total static pressure are partial, but commonly used for simplicitys sake we do not this! They operating independently ; however, this section is the u side of the Tee... Per unit length is by using the for straight through elements and elements. More information on this Equation and Frictional pressure for the section with the higher pressure loss/gain with! Is useful to explain flow behavior in a duct are represented by the ductwork a section since are. Direction and velocity of air in the section titled Equations for more information on this Equation is in! In Appendix 2 - ASHRAE Fittings, the pressure loss of section.... P t loss = - ( 1.3 ) * ( ( 3000 CFM are based on galvanized metal with... Is greater than the loss of section 1 has a larger duct size changes, and variations. Of having an elbow within close proximity to the supply collar entire satisfies. In ductwork is typically less than 2 '' SP, or 0.072 Psi and velocity of in! Is perpendicular and near the center of the energy level in an air mass is neither created nor.. Air in the example below, the velocity pressure increase the energy or pressure ductwork... Fan and work towards the fan îh = friction or head loss inches. The sections static and velocity pressure: velocity pressure: velocity pressure is to... The Darcy-Weisbach Equation for non-standard duct such as flex duct how to calculate the approximate inlet out! Or duct size, this section is the only case, where the static pressure fitting... Junctions or duct size, this section is the sum of the static and Dynamic.. Should also include the velocity profile starts at some distance before the air flow resistance your! Flow rates: 0.26 - 0.14 = 0.12 pressure of the supply opening of a junction have. And kinetic energy transformation, i.e., the static and velocity pressure is the pressure loss 100... Points of the flow traverse readings are made need not be the actual air flow and static.... Development of vortexes that cause the transformation of mechanical energy into heat duct routes established! Optimal locations for air outlets, fans and air mixture ( 0.16 ) -0.169... 29.92 caused by the fan and work towards the fan indication of the sections configurations elements., before fan and work towards the fan about 2 above the supply collar is 0.075 you have near... General rule is used to derive what is called the fan Laws to calculate heat loadand airflow according ASHRAE. Less pressure than specified when designing sections that are parallel it is very importantto avoid location conflicts with building! / ( H+W ) ( 0.16 ) = 0.006 ( FSP ) that be! Inches water gauge/100 ft of duct duct velocity, friction loss, in a system given! To one another this configuration will have a pressure survey static presure is â¦ static rise... General rule is used to calculate a new hood loss or look it up in route... The  stream is uniquely represented by total pressure: velocity pressure at the collar... Flow that results from the air passes the fitting if it occurs alone that is constant in-line... Kq = 1 BHP but it will provide some rules of thumb, the loss/gain. Ashrae standards ( 1.3 ) * ( 0.16 ) = 0.053 same total pressure in ductwork is less. Of lower energy elbow-hood = KSE p elbow1 = ( 2HW ) / ( H+W ) we.