show them how they can selectsmaller flow rates (GPM) by sim-ply increasing the system’s allow-able temperature drop. Tradition-ally in this industry we designaround a magical number of 20°Ftemperature drop. By simply in-creasing this temperature drop to40°F, you will have successfullycut your required flow rate inhalf. It’s all right there on scale#1!

Scale #2 is used to select theproper size pipe to handle yourGPM flow rate. The scale liststwo types of pipe: type L copperand schedule 40 iron pipe. Fromscale #1, you established the re-quired flow rate; now, lookingdown to scale #2, you can selectthe right size pipe to support yourflow rate. No more guessing!

The scale lists pipes sizes from3/8"–12" and gives the frictionloss in feet of head per 100' aswell as in mil inches.

Boiler Facts

By George Carey

Oilheating/December 200924

The systemsyzer

Have you ever wondered if thepipe you are using in that hydronicheating system is the right size?What I mean is, is it the rightsize for a specific flow rate? Everwondered how you calculate theGPM for that heat loss? The an-swers to these questions are veryimportant because they will helpdetermine the proper circulator forthe heating system.

To find these answers, you haveseveral options; you can use somemath formulas that were estab-lished years ago, you can look upthe various charts relating to flowrate in gallons per minute andpressure drop based upon pipe sizesor you can use Bell & Gossett’sSystem Syzer.

The System Syzer was developedby an engineer from Bell &Gossett named Gil Carlson. Per-haps you have heard his name be-fore. He was considered the “Fa-ther of Modern Hydronics” be-cause his name has been associ-ated with things hydronic. He pro-moted the concept of “pumpingaway” and the “point of no pres-sure change”. He developed the cir-cuit setter, a helpful device for bal-ancing hot water systems, and headvocated trimming impellers tofine tune that commercial pumpfor its particular application. Don’twaste energy and horsepower!

He also helped develop and pro-mote the pumping concept knownas Primary/Secondary pumping.Needless to say, he was deeply in-volved in hydronics. This is whyhe developed the System Syzer.He was constantly looking forcharts and books for informationto perform his calculations. Tomake it easier on himself, he de-veloped this little calculator wheel.

It contained all the informationhe would need to design ortroubleshoot a hot water heat-ing system.

The original wheel wasmade of cardboard and was17½” in diameter. Therewere actually two of them;one is located at B&G andthe other one is now in theindustry, given each yearas an award known as theCarlson-Holohan IndustryAward of Excellence. Youmight see it bouncing aroundthe aisles at the various tradeshows during the course of theyear. Check it out if you have achance—it’s very impressive tosee.

Nowadays, the wheel is made ofplastic, measures 8" in diameterand comes with five scales.

The first scale describes the re-lationship that exists betweenflow rate in GPM, Btu load andtemperature difference. If youknow two out of the three piecesof information, the wheel can giveyou the third piece of informationinstantly. For instance, if youknow the Btu load and the de-sired temperature drop, by look-ing at the small window on Scale#1, the necessary flow rate inGPM is selected with a small ar-row pointing at it. Scale #1 isvery useful because it helps youestablish GPM (the required flowrate) easily. Conversely, if you areout in the field on a problem job,by knowing the system’s flow rateand the temperature drop of thewater, you can establish the ac-tual Btu load the system is seeingat that time.

Another example that I use allthe time with heating people is to

Oilheating/December 2009 25

Scale #2 can also be very helpfulwhen you are out in some boilerroom trying to select a new pump.If all of the tags from the boilerand original pump are missing,you can use the existing main hotwater pipe as a guide. Based uponits size, you can look on Scale #2and determine the MAXIMUMflow that particular pipe canhandle. It at least gives you a ba-sis from which to build yourtheory.

Scale #3 confirms the proper pipeselection from scale #2 by checkingthe velocity of the water. It mightseem subtle, but there is a differ-ence between friction loss in headenergy versus the velocity in feetper second of the water movingthrough a given pipe size. Scale #3makes sure that the pipe you se-lect will not be noisy due to thewater moving too fast! The lastthing a homeowner wants to hearwhen the thermostat calls for heatis a whistling noise as the waterscreams through the baseboardpiping. So whenever I select a cer-tain size pipe to handle the GPM, Ialways glance down at Scale #3just to make sure it falls withinindustry standards.

Scale #4 is like a calculator. Thisscale will tell you what the TotalPressure Drop is for a particularloop, zone or even the total system.For example: from Scale #2, youselected a certain size pipe and thescale listed out the unit pressuredrop per 100' of piping. When us-ing Scale #4, you plug in this unitpressure drop per 100' against thetotal length of piping and read thetotal pressure drop in the smallwindow. For example, if I selecteda pipe that offered 4' of pressurefor every 100' of pipe and the total

run of piping was 500', the result-ing answer would be 20' of pres-sure drop. This is helpful informa-tion needed when selecting a circu-lator.

Scale #5 is by the most usefuland yet can be the most confusingscale. It is based upon the fact thatthe head in a hydronic system willvary approximately as the squareof the change in flow rate. Scale #5is set up to perform three func-tions: calculate unknown pressuredrops; establish system curves;and select control valves basedupon their Cv ratings.

When circulators are sold, some-times they are selected by what isknown as the “inventorymethod”…meaning it’s the onlyone available! When this happens,the circulator may be a little toobig or a little too small. By usingScale #5, you can build a systemcurve right on the pump curvechart. By doing so, you can deter-mine exactly where this “inven-tory” circulator will operate. Obvi-ously, if the circulator is a little toobig, it will be pumping more GPMthan required, which might not bea big deal as long as the increasedflow rate does not exceed the pipe’smaximum velocity! If the circula-tor is a little too small, it will bepumping fewer GPM than re-quired, which isn’t necessarily bad,as long as the increased tempera-ture drop does not reduce the out-put of the radiation. In my Hy-dronic System Design seminars,we go over these examples in greatdetail. The guys are amazed whenthey finally “see” what’s going oninside those hydronic systems.

Scale #5 can be used to select con-trol valves based upon their Cv rat-ings. Every valve manufacturer

tests their valves to establish a Cvrating. Cv is a valve coefficientthat states the necessary amountof flow (in gallons per minute) thatmust flow through the valve’s seatopening to cause a 1 pound pres-sure drop across the valve. For ex-ample, a residential ¾" zone valvehas a Cv rating of 3.5. This meanswhen a flow rate of 3.5 GPM ofwater passes through the valve,the valve will cause a 1 poundpressure drop. It will “eat up” 1pound of energy head. Another wayof expressing 1 pound of pressuredrop is 2.31' of head loss. So if thezone valve has a Cv rating of 3.5and you pump 3.5 GPM throughthe valve, the valve itself will cre-ate 2.3' of head loss. This informa-tion is important when sizing a cir-culator, because in addition to cal-culating the pipe and radiationhead losses, you have to accountfor the control valve’s pressuredrop.

Also, by knowing a valve or anycomponent’s flow/head rating, youcan calculate the actual flow in thesystem by the simple use of pres-sure gauges. By reading the pres-sure before and after a device, con-verting this pressure differentialreading into feet of head and apply-ing this head loss to the pumpcurve, you can determine the ac-tual flow rate in the system.

Bell & Gossett’s System Syzer isa very useful tool for anyone in-volved the hydronic heating busi-ness. As Dan Holohan once said,“the System Syzer is the AmericanExpress Card of hydronicheating…don’t leave home withoutit!” If you have any questions orcomments call me at FIA at 1-800-423-7187 or email me atgcarey@fiainc.com

Getting the System Syzer…

You can obtain the System Syzerdisc from Bell & Gossett’s website,www.bellgossett.com. Click on thetab “Selection Software” on theirhome page and scroll down toSystem Syzer, “Order plasticwheel.” If you click on “SystemSyzer”, you can download anelectronic version for your laptop(Windows version—see photo) orone that will run on other platforms.You can also download an instruc-tion manual.—Ed.