The application of variable frequency drives vfd has proven to save energy for pumps and fans with variable flow requirements. Why can we consider as acceptable the affinity fan laws to evaluate the centrifugal compressor behaviour. You want to double the airflow by modifying the fan to accommodate a 20 hp, 1800 rpm motor. Engineers use a shorthand for estimating the effect of speed rpm on power. N fan speed q flow cfm p pressure static inches of water hp horsepower. Note that there are two sets of affinity laws affinity laws for a specific centrifugal pump to approximate head, capacity. Law 3 means that as rpm is reduced, power consumption brake horsepower is reduced by the cube. For example, lets say that a direct drive fan moves 15,000 cfm at 2. P 1 p 2 n 1 n 2 3 or d 1 d 2 3 where p is equal to power, n is equal to shaft speed, and d is equal to impeller diameter. Usually, pump performance curves are based on standard electric motor speeds in rpm. The new york blower company is committed to supporting and supplying necessary equipment to meet the critical demands of the supply chains essential to aid america in this time of need. First if the impeller diameter is held constant and the speed of the fan is changed.
Fan affinity offers affordable strategy, design, and marketing automation services to support the growth goals of todays sports organizations, schools and nonprofits. The affinity laws are derived from a dimensionless analysis of three important parameters. The affinity laws of centrifugal pumps or fans indicates the influence on volume capacity, head pressure andor power consumption of a pump or fan due to. Q1q2 n1n2 where q is the volumetric air flow and n is the shaft speed. Louvers to supply makeup air determining cfm after the model is known, the cfm must be determined. Represented in figure 3 are the three affinity laws. Our calculations prove the affinity laws and provide numerical estimates of the air delivery, thrust and drag on a rotating fan. Affinity fan and pump laws what is the effect of a changing speed. First if the impeller diameter is held constant and the speed of the fan is changed, then flow rate varies directly with the speed. These laws are mathematical expressions that define changes in pump brake horsepower bhp, head and capacity when a change is made to pump speed, impeller diameter, or both. Hvac equipment and systems fan affinity laws for the.
The exact relationship between speed, diameter, and efficiency depends on the particulars of the individual fan or pump design. Ali the air delivery rate is proportional to its rotation speed and. Fan laws and system curves new york blower company. Leave a comment if you would like to discuss the affinity laws or variable frequency drives. Fan laws the fan laws are derived from a dimensional analysis, using the pitheorem as a formal procedure. Affinity fan laws for centrifugal compressor posted in student. After examination of a few axial fan curves, i have come to the conclusion that this is either grossy inaccurate or the fan curves are wrong. Pump efficiency is considered as a constant and variation in speed and impeller diameter is analyzed for the variation in above said parameters. The affinity laws are frequently cited for energy savings calculations in vsd applications with pumps and fans, and they are just as frequently misused in an attempt to simplify those calculations. The affinity laws or fan laws, as they are sometimes referred to play an important. The affinity laws for pumps fans are used in hydraulics andor hvac to express the relationship between variables involved in pump or fan performance and power. Hvac equipment and systems fan affinity laws for the mechanical. The pump speed, head, and flow relationships are expressed by the affinity laws.
As far as i know, this just could be applied when the compressibility factor is. Worked fan law examples fan laws the empiricalmeans very basic. Affinity fan laws for centrifugal compressor student. If the diameter does not change the fans must be geometrically similar. If the speed should remain a constant, the affinity laws state. Affinity laws when investigating flow phenomena, cost factors often favour the use of models which are geometrically similar to the original, fullsized equipment see similarity conditions. This page provides information and resources regarding the affinity laws that are used to project new performance points and curves for a pump or fan given a known performance point or curve.
Often times a fan s speed or impeller diameter will be changed. The performance of a fan is standardly expressed in terms of three affinity laws stated as under. For this type of testing it is necessary that models are not only geometrically similar, but are also subjected to similar physical conditions. Typical independent variable q usually gpm liquids or cfm gases. These rules are critical for heating and cooling installers, who must select products. Axial propeller tube axial vane axial mixed flow low pressure high pressure extended pressure centrifugal airfoil backward inclined radial forward curved axial fans an axial fan discharges air parallel to.
Q 1 rpm 1 q 2 rpm 2 basically this equation says that if fan rpm increases by 10% then the flowrate q would increase by 10%. They are also used for scaleup purposes when performance parameters exceed that of existing pumps refer to figure 2. Consult local code requirements or the table below for suggested air changes for proper ventilation. Basic pump parameters and the affinity laws instructor. The fan laws are a group of useful equations for determining the effects of a change in the speed, the diameter of the fan and the density of air in the system. The affinity laws were developed using the law of similitudes which provide 3 basic relationships. This method is referred to as the affinity laws or fan and pump laws. The affinity laws for centrifugal pumps and fans are used to express the influence on volume capacity, head pressure andor power consumption due to. The process of arriving at the affinity laws assumes that the two operating points that are being compared are at the same efficiency.
As simple as trying to find a motor to spin a fan sounds, the engineer that has to do this needs to know and use the affinity laws for air and hydraulic flow. Dig in to make sure you avoid overestimating or underperforming. Fan types fans are described in three types and several subtypes. They apply to all types of centrifugal and axial flow pumps. Pump performance curves and similarity laws pump performance results are typically obtained from an experimental test of the given pump and are presented graphically for each performance parameter. The centrifugal pump affinity laws, sometimes known as the laws of similarity, describe how changes in rpm affect the gpm, head, and hp in the united states, electricity is at 60 cycles per second hertz. Process engineers lock onto this law as a means to control the flow of process. In my studies of fans i have come across a few sources that have told me that the fan affinity law for centrifugal fans will work for axial fans to a decent approximation. The following three 1tterms are used for the simplified fan law approach. The affinity laws express the mathematical relationship between the several variables involved in pump performance. Fan laws, the use and limits in predicting centrifugal compressor off design performance 93 is operated on a light gas and then operated on a heavy gas, the curve will be steeper for the light gas. The affinity laws for pumpsfans are used in hydraulics, hydronics andor hvac to express the. Note that the affinity laws for pumps are not identical with fans fan affinity laws. Pump curve speed calculator this centrifugal pump curve calculator is meant to quickly calculate the different operating conditions when a centrifugal pump is sped up or slowed down.
Affinity laws can be used to calculate volume capacity, head or power consumption when speed and wheel diameters are changed. This means that 10 percent impeller reduction is 10 percent flow reduction. The affinity laws the affect 0 200 400 600 800 1200 0. If the fan is a centrifugal fan, then the change in performance of the fan can be. A common mistake is to use a fan that is too small or too large for the application, so that it cannot be run at its most efficient point. The affinity laws are a set of rules to describe the interconnected relationships between speed, flow, power, and pressure seen with fans, turbines, and similar devices. The cause for this is the higher volume ratio of the heavy gas.
Affinity laws and other considerations fan application. Q volumetric flow rate cfm n wheel velocity speed rpm d fan blade size. Another set of the affinity laws deal with changes to the diameter of the impeller. Understanding the basic fan laws geoff edwards, the technical product engineer at axair fans uk limited, explains the three basic fan laws when applied to warehouse ventilation studies. Centrifugal fans 7 note that when the flow and pressure laws are combined, the result is a formula that matches the system curve formula p k x cfm2. Centrifugal pump affinity laws are set of mathematical equations correlating the flow rate, head, brake horse power, speed and impeller diameter of the pump. Often times a fans speed or impeller diameter will be changed. The affinity laws are useful as they allow prediction of the head discharge characteristic of a pump or fan from a known characteristic measured at a different speed or impeller diameter. Affinity laws changes in diameter changes in speed d diameter, in or mm q flow, gpm or m3h h head, ft or m p power, hp or kw q flow, gpm or m3h h head, ft or m p power, hp or kw n speed, rpm bernoullis equation v z g gravitational constant l energy losses p s suction pressure p d discharge pressure v s suction. The affinity laws or fan laws, as they are sometimes referred to play an important role in determining centrifugal pump performance when operating conditions change.
The affinity laws of centrifugal pumps or fans can be used to express the influence on volume capacity, head pressure or power consumption of a pump or fan due to 1. Dear mates, two question in regards to affinity laws, dimensionless numbers and behaviour prediction in centrifugal compressors. A hard sphere collision model is used, and subsequently a correction to account for the flow behaviour of air is incorporated. The affinity laws variable frequency drives theory the affinity laws can determine the system performance for centrifugal devices, including theoretical load requirements and potential energy savings.
The correct formula for using the affinity laws when there is a. Fan laws and fan performance fluid flow engineering fluidflow. Introduction a fan is a device that utilizes the mechanical energy of a rotating impeller to produce both movement of the air and an increase in its total pressure. The flow gpm varies proportionally with the change in impeller diameter. The fan laws help us estimate how a fan will operate in a system at. There is a little more to it than this with air density changes but these basic fan laws can keep a field engineer or technician out of trouble. If the fan rpm increased by say 25% then the flowrate would increase by 25%. Using affinity laws, we can accurately calculate the pressure, flow and required. If the fan is a centrifugal fan, then the change in performance of the fan can be predicted quickly through the affinity laws. Pump curve speed calculator affinity law calculator. Variable airflow applications can also cause noise problems. To find out what equations you should be using, read the problem to determine what is changing. In this work we use kinetic theory to attack this problem.
When a fan operates in an unchanging system, the fan laws tell us that the airflow varies proportionally to fan rpm, static. In general, the affinity laws project the new operating points by moving up and down a system curve. Centrifugal pump affinity laws calculation chemical. The energy savings are achievable through affinity laws. Fan laws are used to determine the effect of changes in the conditions of a fans operation. Fan affinity laws affinity laws can be used to calculate volume capacity, head or power consumption when speed and wheel diameters are changed modulate centrifugal pump capacity adapting pump capacity to variable process demand npsh net positive suction head an introduction to pumps net positive suction head npsh. If that is the case then the affinity laws can be used to predict the. The following equations can be used to solve problems dealing with fan laws. Our approach is designed to help organizations generate revenue faster, improve sponsor retention, and condition supporters to. Affinity laws are a set of equations or laws governing the operation.