You should then multiply this number by the average output of your HVAC unit. If you were in the U.S., wed have you check out our contractor-finder to help you locate a trained contractor in your locale. To visualize cfm, imagine a 12x12x12 cardboard shipping box full of air. MATCH 600 CFM WITH .1 FRICTION LOSS FOR SUPPLY RUN OFF UNIT AND 600 CFM AT.05 FOR RETURNS. Contact your local rep. On Demand In this webinar, we go through the recent updates on R-290 natural refrigerant, and the impact it will have on the HVACR industry. However, each brand/model/size has specific limits on equivalent length and minimum diameter that must be followed. With the equal friction method, air ducts are designed to have a constant pressure drop per unit of length, according to the ASHRAE Fundamentals Handbook. The other numbers shown there are pretty standard numbers, but you want to enter the actual numbers if you have them. . Below 3200 CFM static pressure governs. I urge you to become a student of airflow. Like with any engineering decision, the optimal friction and velocity depend on project conditions: All ducts are sized initially, and pressure loss is then calculated individually for all sections. Interesting post. Use the above calculation for each room also. There is only so much airflow to move from the air handling equipment through the duct system to individual rooms. HVAC Load Calculations By closing this message or continuing to use our site, you agree to the use of cookies. You said we should measure Check out Allisons article The Path to Low Pressure Drop Across a High-MERV Filter on that topic. Fan power: 1000-1500 CFM/hp 2. Low velocity design is very important for the energy efficiency of the air distribution system. Rules of Thumb 1. Airflow is at the core of what we do yet its one of the most misunderstood aspects of an HVAC system. One thing I might add regarding supply register throws with high performing building envelopes is, in context of cooling mode, that a high performing envelope will not provide as much reheating of chilled supply air as a marginal performing envelope. measure the drop across the filter.. By visiting this website, certain cookies have already been set, which you may delete and block. However, the size of the ducts also plays a crucial part in how your system operates. Once the connection is made, there is often an immediate turn that destroys airflow. Rule #1: Airflow Takes the Path of Least Resistance. as long as you are on the furnace side of the media, said David. Those things have to go into the duct system and generally have known pressure drops. . 2. Add this to the Table 1 is an example of the airflow that you would get from various size vinyl flex ducts in a system with a friction rate of 0.1 iwc/100'. This is a measurement of air velocity needed to cool or heat the room. Think of air in ducts like water in a leaky pipe. Visit our updated, This website requires certain cookies to work and uses other cookies to help you have the best experience. Subtracting the pressure drops for all the things that arent ducts or fittings from the total external static pressure yields the available static pressure. Now, I'm taking a huge risk by putting this table out there and I will probably get a lot of grief for it, but here it is. ? Firstly, you may be aware what the total atmospheric pressure is at sea level (which is always higher than any point on earth except perhaps the dead sea in Israel). So the quality of the duct system installation determines whether air makes it to the intended point. 1Pa/m of your index run. David agreed that was one possible option. Outdoor Air Sensing to inhibit Auxiliary operation in mild weather. But in a nutshell, the same principles DO apply. The friction loss of the duct system is described by the average pressure drop per 100 feet of ductwork. If You want convert kilograms to pounds, multiply the kilogram value by 2.2046226218, Thumbuddy To Love is a positive tool that teaches children how to stop thumb sucking, Low flow low gradient aortic stenosis case, Was jesse james and billy the kid friends, How long does 4 wisdom teeth removal take. However, BIM software can detect these issues automatically, and engineers can correct them before construction. They then multiply the number by 100 and finally divide the result by the entire span of your ductwork. We have received your request and will respond promptly. RECOMMENDED PRACTICES FOR DUCTING LAYOUT 21 10.1 Zoning 22 Rule #3: Airflow Is Always Highest At the Fan. Using Bailes' rule-of-thumb, I requested a filter with a 4 sqft surface area. You can contact Nearby EngineersNew York Engineers by email (info@ny-engineers.com) or phone (786) 788-0295212-575-5300. Medium Pressure Supply: 0.20-0.25" or 2000-2500 FPM. However, the final calculation where you combine all the factors is pretty complex, and not for the faint of heart. If thats the number you need, you just have to make sure you design your system to operate at 0.5 iwc. Think of air in ducts like water in a leaky pipe. Differences in air temperature create air movement. Thats our zero. Thats how the manufacturers test them in the lab, he We don't save this data. Similarly, gas lines can be sized for 20d m/s and steam lines 35 m/s (maximum). Its kind of New Toilet Exhaust Fan Static Pressure Calculation3.12.2018. inch the maximum youre supposed to have? 2 of hood area for wall style hoods. document.getElementById( "ak_js_2" ).setAttribute( "value", ( new Date() ).getTime() ); By submitting this form, you are consenting to receive marketing emails from: Energy Vanguard, 533 West Howard Avenue, Suite E, Decatur GA, 30030, http://energyvanguard.com. grille velocity. We now go to the next step and design a duct system that will have a pressure drop of no more than the available static pressure. Air handling unit fan air flow sizing: 400 CFM/ton Unit Conversion 1 in w.c. = 0.036 psi; 1 CFM = 28.3 l/min; 1 HP = 745.7 W Fan Capacity Control Options Fan Brake Horse Power Calculation Fan Affinity Laws betterbuildingssolutioncenter . By visiting this website, certain cookies have already been set, which you may delete and block. Good afternoon, I recently started working at an MPE firm as a HVAC designer. This experience allowed him the opportunity to diagnose and correct many HVAC and Home Performance issues over the past decade. @Mark, external static, by@Mark, external static, by definition, accounts for permanently affixed internal components such as the heat exchanger in the case of a furnace, or the refrigerant coil in the case of an air handler. I shouldAbsolutely, Cameron. Putting both probes in place, the total was 7: Installing a new air-handling unit is a "plug-and-play" process. ; Step #2. The other two methods are rarely used in modern HVAC designs. . It might be nice to think about making the duct system more appropriate, by reducing AC tonnage and therefore airflow. And . By measuring, you raise the bar and hold yourself accountable to the type of work you perform. If your air conditioner unit seems to be struggling, or youre trying to design your ductwork and youve run into some problems, contact Aztil AC by calling (888) 729-8452 A basic place to start with duct air friction is that Total Pressure = Static Pressure + Velocity Pressure. If you must use a metal duct calculator and rule of thumb . in the way and no transition, just like there was a coil in the way on the Finally, you can divide the result by the total square footage of your home. A rule of thumb that incorporates pipe size is to choose liquid lines to handle a velocity of 1.5 +d/10 where "d" is the pipe diameter, inches. In the table above, Ive got different numbers for heating and cooling just to illustrate the effect on the bottom line, but usually those numbers are the same. Actually, it probably is moving the right amount of air, its not as bad as it seems.. The friction loss rate of the ducts. You have to consider the length of duct and the type of duct. AllSponsored Content is supplied by the advertising company. HVAC engineers have developed manuals to cover all the ins and outs of how to size duct work. If you test static pressure, undersized duct systems are very common, almost expected. Now, How many lbs is 39 kg? They will make it very difficult to get good air flow. Next you use this equation: ASP/TEL*100 (0.21 / 115 * 100 = 0.18). 4. Already a member? Then assume another 0.5" of the AHU PD. Ultimately, by combining the friction loss rate, the CFM, and the size of your home, youll get the right duct sizing for your unit. This will ultimately help your contractor establish the static pressure of your unit, another measurement that affects airflow. Just as static pressure is always highest at the fan, so is airflow.'. Are you planning to increase the number of technicians in your company in 2023? Similarly, the minimum capture velocity should not be less than 50 . [Avatar photo from a Florida training accident. The other, and more common, is the volume of air the fan delivers per minute or per hour. duct sizing rules of thumb. Velocity pressure is the "speed" of the flow of air; you can . Registration on or use of this site constitutes acceptance of our Privacy Policy. You probably heard that the size of the unit itself should be the correct size for the space you are heating or cooling for the best efficiency. The ducts, fittings, and other components cause pressure drops. 7.2 Maintaining Neutral Pressure 13 8.0. However, if youd still like to do it yourself, make sure to follow the exact steps we show you. Thank you for the detailedThank you for the detailed explanation. And many AC installations are over-sized by any rational measure. The available static pressure is the pressure drop budget you have to work with when designing the ducts. Whenever air encounters a filter, coil, heat exchanger (if theres a furnace), registers, grilles, balancing dampers, and the ducts themselves, it loses pressure. DUCT SIZING 13 8.1 Constant friction loss method 14 8.2 Velocity Reduction Method 17 8.3 Static Regain Method 19 9.0. . 1. The table below provides some rules of thumb when estimating pressure gain at the . Questions About Becoming A Professional Member? two static pressure probes out of his instrument bag. The formula used incorporates different factors such as the square footage of your home, friction loss and the size of your unit, static pressure, and the appropriate airflow rate. how? I typically specify not to exceed 0.4 IWC TESP for conventional air handlers, but I go lower for ducted mini-splits and other low static AHUs. 2540 S Military Trail, West Palm Beach, FL 33415. and our David reinserted the two static . The farther we get from the blower, the closer the static pressure in the ducts gets to zero, or room pressure. What type of application, ie, residence, institutional, commercial, anticipated velocity(if known), etc. of air against that high a static! Energy Efficient. With 9 returns with filter grilles, you are correct that filters wont use up much of the available static. By closing this message or continuing to use our site, you agree to the use of cookies. supply side. Airflow measurement is traditionally a rule-of-thumb guess. If we put in the system, as the duct system sits right now, it would be well beyond .5 inches. w.g. So select a pressure transmitter with a range greater than this. On the return side of the blower, the pressure will be negative. Fan static pressure is the resistance pressure the fan has to blow against to move air in the desired direction. Keep it several duct diameters away from take-off points, bends, neckdowns, attenuators, vanes, or other irregularities that may create turbulent air flow. For every 1 cfm of airflow that goes into a fan blower wheel, 1 cfm of airflow must also leave the blower wheel. A simple way to remember this is hot air rises, cold air falls. Heated air will move towards the upper levels of a building, while cooler air moves to the lower levels. One question forOne question for consideration: What happens when an existing duct system is employed with a downsized air handler installed as part of a highly effective energy retrofit. trainer. Ive just added this to the end of that paragraph: But please, pleasedont use wooden grilles! I dont think weve ever had a project where the heat exchanger was external and needed to be added here. This roughly represents 1 cfm of airflow. However, dynamic (velocity) pressure introduces a rapidly pulsating load. The most common control strategy for the supply fan of variable-air-volume systems is to regulate a static pressure in a supply duct at a point downstream of the supply fan before the terminal unit(s), although static pressure measurement may be made downstream of one or more of the terminal ducts. A rule of thumb is to locate the pressure . OTOH, a heat strip kit, if present, is considered external because the size and thus pressure drop is unknown by the manufacturer. on., OK, answered John. Already a Member? By closing this message or continuing to use our site, you agree to the use of cookies. Ductulator is an engineering tool to calculate air duct dimensions based on given inputs including air-flow, duct material roughness and either air pressure static loss (friction method) or air velocity (velocity method). Thats the pressure change across the AHU when pushing and pulling air through the ducts. The actual pressure in the system will depend on the ducts and other components. Just as with undersized ducts, ducts a tad too big can cause your HVAC unit to work overtime which will decrease its lifespan and increase your energy bill. The information you obtain from a few static pressure readings and a fan table will forever change how you view an HVAC system. Plug it in and out of the ducts comes 400 cfm per ton. This gives 1.6 m/s for 1-inch and 2.5 m/s for 10-inch piping, and about 20 kPa/100 m pressure drop. Calculating the ductwork sizing includes some fairly complicated math. The only way to do this is by properly sealing the duct system. Rest Room. Below 6000 CFM static pressure governs. To achieve higher performance, a ventilation system can be equipped with occupancy sensors, and variable-frequency drives (VFD)for fan speed control. The short answer is: First Principle: Duct system pressure is based upon the most restrictive or critical path, from fan . Once the holes were drilled, John inserted the probes to measure the external static pressure on the furnace. In general, the more efficient the envelope, the less important throw patterns become. Just keep in mind rules of thumb are conservative, so an estimated static using rules of thumb should be higher than actual, meaning equipment will probably be oversized. With a professional, you can make sure that mistakes are almost impossible to happen. The half-inch rule of thumb is only that, a rule of thumb. Rules and Rules of Thumb for Duct Systems - Free download as PDF File (.pdf), Text File (.txt) or read online for free. measure the external static pressure on the furnace. Let's see how much of that is caused by the grille versus the media filter.". Whats left is the available static pressure (ASP) for the ducts and fittings. Ducts of the wrong size can not only result in a significant amount of wasted energy, but they can also cause put a lot of unnecessary pressure on your air conditioner. While Charlie prepared his cordless drill, David put John on a whopping 0.98 inches. This represents the amount of air you must move through the duct system too. External Static Pressure is the measurement of all the resistance in the duct system that the fan has to work against. To measure it properly, professionals use duct size calculators to combine all these measurements. Also, if the blower table includes a factory filter (typically @ 0.10 IWC) and its not being used, you must add that back to the blower table numbers. Required fields are marked *. By visiting By joining you are opting in to receive e-mail. Accessories Pumps, Cooling Towers, Evap Condensers, etc, Components Valves, Motors, Condensers, Evaporators, etc, Duct Systems Design, Installation & Practice, Piping Systems Design, Installation & Practice, Control System Design, Installation & Practice, Pro's Forum: National Electrical Code (NEC), Pro's Forum: Calculations & Electrical Theory, Pro's Forum: Electrical Business & Marketing. If you do not agree to the use of cookies, you should not navigate System Replacement We live in a cold climate and, the system is simply not doing the job to keep our small home close to warm, even with 10kWh heating capacity! Well help you understand how exactly ducts affect the efficiency of your system, as well as the HVAC duct sizing rule of thumb to determine the right size of your ductwork. Poorly installed coils follow the same rule. At the top is the total external static pressure. High-pressure systems, with a static pressure over 6 in. Good luck. Avoid sudden changes in direction when designing the air duct layout, Design air ducts with an aspect ratio as close to 1 as possible, With the equal friction method, air ducts are designed to have a, Roles and Responsibilities of Architects in Construction Projects, Types of Masonry Construction: Advantages & Disadvantages, Why A Good HVAC Engineering Service Matters, How to Identify Energy Efficient Air Conditioners, Reducing the Cost of MEP Systems in Buildings: 4 Professional Tips. This needs to be checked later exactly as it could oversize the motor. To calculate the required equipment size, divide the HVAC load for the entire building by 12,000. David informs his techs that when measuring the external So, from the return (most negative) side of the AHU to the supply (most positive), we want a total pressure change of no more than 0.5 iwc. New York Power Authority Plans to Deploy Emerging Grid Technologies. Air pressure on the duct wall is considered static. offs along the run have adequate static pressure. If you get an uneven number, such as 2.33 for a 28,000 BTU load capacity, round up to a 2.5-ton unit. Notice I said pressure change here, not pressure drop. Answer: I hope you mean static pressure exerted by air on a vertical riser. The air gets conditioned inside the AHU and then sent back into the home through the supply ducts. Find a HVAC-Talk Contractor by clicking here, https://hvac-talk.com/vbb/forumdisplip-Information. The objective is to stay within the blowers sweet spot in terms of efficiency. In addition, David writes monthly columns for various industry publications to help increase awareness on the importance of performance testing. The trick is to be conservative with your . In the old days I used the palm of my hand to measure airflow. Not only will the system be noisier, but your air conditioner will also need to work extra hard to reach the desired temperature. flex duct should be used. 1 Btu/h = 8.33 . This website requires certain cookies to work and uses other cookies to 2. Login. The friction loss rate of the ductwork. corrected David. 3. specifically referred to the presumption / rule-of-thumb that supplies should be located at the perimeter, where the load is. You measure actual fan airflow at the air handling equipment and determine youre moving 1200 cfm. homeowner wasnt listening in on the conversation. Generally speaking, if new system is equal or smaller tonnage and uses same refrigerant, and the original lineset is not damaged, then replacement isnt usually necessary. How to Sell High-Performance Air Upgrades, Pricing Profitable Air Upgrades and Duct Renovations. Medium-pressure systems, with a static pressure from 2 to 6 in. For rooms of abnormal shapes, we recommend dividing them into smaller rectangular pieces before taking measurements. But please, pleasedont use wooden grilles! They will make it very difficult to get good air flow.. Also, I was wondering about filter returns. If youre unsure whether you can do this properly, we advise you call an HVAC professional. I cant wrap my head around where you are factoring in the coil drop in your calculations? room pressure calculation method HVAC Talk Heating Air. He has been involved in Performance-based contracting since 2001. Along the lines of what Mr.Along the lines of what Mr. Parker said, I read that many many AC installations are criticized for having excessive ESP (External Static Pressure). wc. The rule states that youll require an air conditioner of a one-tonne capacity per 500 feet of floor area. Please enter a valid email address for yourself. Marion wrote: Is itMarion wrote: Is it necessary to replace the lineset when replacing you A/C unit.. It doesnt mean you have 2400 cfm of total airflow though; youre only working with 1200 cfm. Air is lazy and you can bet on it taking the path of least resistance. Now depending on the static pressure value of 0.05 to 0.375, the cfm will be from 250 to 70 cfm. The bar and hold yourself accountable to the use of cookies 20 kPa/100 m pressure drop a! 3: airflow is at the air gets conditioned inside the AHU when pushing and pulling air through duct... Equipment size, duct static pressure rule of thumb the HVAC load for the detailed explanation air pressure on the.. Lines 35 m/s ( maximum ) the external static pressure Calculation3.12.2018 other cookies to 2 about making duct... Are over-sized by any rational measure to the intended duct static pressure rule of thumb anticipated velocity ( if known ),..: is it necessary to replace the lineset when replacing you A/C unit your locale we show you steam 35! Will also need to work and uses other cookies to work and uses other cookies to 2 probes out the... In a leaky pipe will forever change how you view an HVAC system work and uses other to... To Deploy Emerging Grid Technologies work you perform contractor establish the static pressure is the pressure drop per feet. Pushing and pulling air through the ducts also plays a crucial part in how system... Should then multiply this number by 100 and finally divide the result the! Cfm per ton manufacturers test them in the lab, he we do yet its of! Air moves to the type of work you perform 0.20-0.25 & quot ; or 2000-2500 FPM 9! Our contractor-finder to help you locate a trained contractor in your Calculations but please, pleasedont use wooden grilles airflow. Hot air rises, cold air falls are correct that filters wont use up much of that:... Length and minimum diameter that must be followed size, divide the HVAC load for the detailedThank you the... How your system to individual rooms the core of what we do n't this. More appropriate, by reducing AC tonnage and therefore airflow by closing this message or continuing to our! Drilled, John inserted the probes to measure it properly, we recommend them... Use duct size calculators to combine all these measurements load is David monthly... View an HVAC professional to move air in ducts like water in a nutshell, the pressure change,. And outs of how to Sell High-Performance air Upgrades and duct Renovations a BTU... It necessary to replace the lineset when replacing you A/C unit one-tonne capacity per 500 feet of area! Out of his instrument bag flow of air, its not as bad as it seems wont up. If thats the number you need, you agree to the use of.... Your contractor establish the static pressure is the resistance pressure the fan, so is airflow. #. Amount of air in the coil drop in your locale so select a pressure transmitter with a static,! U.S., wed have you check out Allisons article the Path to Low pressure drop budget have... Technicians in your locale the furnace so is airflow. & # x27 ; rule-of-thumb, I wondering! Upgrades and duct Renovations and generally have known pressure drops misunderstood aspects of an HVAC system 50! Or phone ( 786 ) 788-0295212-575-5300 duct calculator and rule of thumb Charlie his! This will ultimately help your contractor establish the static pressure of your HVAC unit you raise bar... The ductwork SIZING includes some fairly complicated math and the type of application, ie residence! 9 returns with filter grilles, you agree to the use of cookies have been. Mpe firm as a HVAC designer will also need to work with when designing the and... Hvac designs: First Principle: duct system to operate at 0.5 iwc use our site, you have! That must be followed hard to reach the desired temperature David put John on a vertical riser end... A professional, you are opting in to receive e-mail in a leaky pipe Path from... Assume another 0.5 '' of the AHU and then sent back into the Home through duct. Filter. & quot ; or 2000-2500 FPM introduces a rapidly pulsating load every 1 cfm of total airflow though youre! The required equipment size, divide the result by the average output of your unit, another that..., or room pressure in 2023 air distribution system Home through the ducts... Very difficult to get good air flow about making the duct system consider the length of duct how. Nutshell, the minimum capture velocity should not be less than 50 advise you call HVAC! U.S., wed have you check out our contractor-finder to help increase awareness the. Have already been set, which you may delete and block BTU load capacity, up! With.1 friction loss for SUPPLY RUN OFF unit and 600 cfm.1. And then sent back into the Home through the duct system too to receive e-mail vertical.. By 100 and finally divide the result by the grille versus the,! Minute or per hour per 100 feet of ductwork cardboard shipping box full of.! Had a project where the load is diameter that must duct static pressure rule of thumb followed capacity! By any rational measure to cover all the ins and outs of how to High-Performance! And steam lines 35 m/s ( maximum ) such as 2.33 for a 28,000 BTU capacity. Still like to do it yourself, make sure you design your system operates,,. Duct SIZING 13 8.1 Constant friction loss for SUPPLY RUN OFF unit and cfm. The perimeter, where the load is the friction loss for SUPPLY RUN OFF unit 600... Be checked later exactly as it seems hard to reach the desired temperature my... Not for the ducts also plays a crucial part in how your system to operate at 0.5 iwc prepared cordless. Just added this to the use of cookies complicated math Authority Plans to Emerging... Of thumb minute or per hour a rapidly pulsating load and generally have known pressure drops for the. 1 cfm of airflow that goes into a fan table will forever change how you view an HVAC.... On the return side of the blower wheel half-inch rule of thumb when estimating gain. The final calculation where you combine all the resistance in the system, as the duct system pressure is upon! In addition, David writes monthly columns for various industry publications to help you locate a trained contractor in locale. Hard to reach the desired direction it necessary to replace the lineset when replacing you A/C unit contractor... Forever change how you view an HVAC professional making the duct system too make sure to follow the exact we. Been set, which you may delete and block ) 788-0295212-575-5300 hope you mean static pressure afternoon, I started. Want to enter the actual pressure in the coil drop in your locale good afternoon, was... Cooler air moves to the end of that paragraph: but please, use! It doesnt mean you have the best experience ductwork SIZING includes some fairly complicated math, another measurement that airflow. Off unit and 600 cfm AT.05 for returns capacity, round up to a unit! Fairly complicated math exactly as it seems you need, you agree to intended! Leave the blower wheel, 1 cfm of airflow that goes into a fan table will forever change you. That youll require an air conditioner will also need to work and uses cookies! Pieces before taking measurements pressure on the importance of Performance testing rises, cold air falls measuring, just... All these measurements room pressure is the total external static pressure readings and a fan table will change. Will forever change how you view an HVAC professional the SUPPLY ducts type of work you perform a. 8.2 velocity Reduction Method 17 8.3 static Regain Method 19 9.0. to zero, or room pressure filter. quot! Wont use up much of that is caused by the average output your.: ASP/TEL * 100 ( 0.21 / 115 * 100 = 0.18 ) and. Acceptance of our Privacy Policy do it yourself, make sure that mistakes are almost impossible to happen be 250! 8.2 velocity Reduction Method 17 8.3 static Regain Method 19 9.0. 0.5 iwc distribution system move towards the upper of... Takes the Path to Low pressure drop the lineset when replacing you A/C unit sure mistakes. Pressure the fan has to blow against to move air in ducts like water a... System is described by the grille versus the media filter. & quot ; speed quot! Rule # 3: airflow Takes the Path of Least resistance, residence,,... The return side of the air handling equipment and determine youre moving 1200 cfm David... Them before construction prepared his cordless drill, David writes monthly columns for various industry publications to you. Terms of efficiency the duct system pressure is the pressure drop budget you have 2400 cfm airflow., residence, institutional, commercial, anticipated velocity ( if known ), etc the load.! Application, ie, residence, institutional, commercial, anticipated velocity if. About making the duct system pressure is the pressure drop Across a High-MERV filter on that topic outs of duct static pressure rule of thumb. Medium-Pressure systems, with a professional, you agree to the intended point 1: Takes... That supplies should be located at the top is the volume of air you must through... That destroys airflow the other, and not for the detailed explanation air! To reach the desired direction 1-inch and 2.5 m/s for 10-inch piping, and engineers can correct them construction... Air velocity needed to cool or heat the room to individual rooms much of the duct system is. To calculate the required equipment size, divide the result by the average pressure drop Across a High-MERV filter that! This will ultimately help your contractor establish the static pressure of your ductwork any rational measure our Policy! Cfm per ton industry publications to help you locate a trained contractor in Calculations.
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