Recirculating Domestic Hot Water Systems

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CaleffiNorthAmerica,America,Inc.Caleffi NorthInc.th3883W. Milwaukee9850 South54 StreetRdMilwaukee,Wisconsin 53208Franklin, WI 53132T: 414.238.2360414.421.1000 F:T:F:414.421.2878414.238.2366Dear Plumbing and Hydronics Professional,Dear Hydronic Professional,How often do yound turn on faucets, bathtubs or showers, and thenof idronicsCaleffi’ssemi-annualjournalWelcometo the2 editionwaitfor warmwaterto arrive?This–iscommonin manydesignhomesandforhydronic professionals.commercial buildings. It results in wasted water, wasted energy andannoyedoccupants.of idronics was released in January 2007 and distributed to overThe 1st edition80,000 people in North America. It focused on the topic hydraulic separation. Fromthe feedback received, it’s evident we attained our goal of explaining the benefitsA Technical JournalfromCaleffi Hydronic SolutionsCALEFFI NORTH AMERICA, INC3883 W. Milwaukee RdMilwaukee, Wisconsin 53208 USATel: 414-238-2360FAX: 414-238-2366E-mail: idronics@caleffi.comWebsite: www.caleffi.usTo receive future idronics issuesFREE, register online www.caleffi.us Copyright 2017Caleffi North America, Inc.Printed: Milwaukee, Wisconsin USAMostpeople would be surprised to learn that several thousandand proper application of this modern design technique for hydronic systems.gallons of heated water is wasted in a typical household, over a year,If you haven’tyet receiveda copy oftemperatureidronics #1, youdo sosending in thewaitingfor waterat the desiredto canarriveat byfixtures.attached reader response card, or by registering online at www.caleffi.us. Thepublication will be mailed to you free of charge. You can also download theThisissue journalof idronicsshowshowourtoWebavoidcompleteas a PDFfile fromsite.this waste and annoyanceusing recirculating domestic hot water systems. They range fromThis seconddirt buildings,in hydronic systems.Thoughnot a rinandsmallto complexmultitopic to our industry, the use of modern high-efficiency equipment demands abranchsystemsin largerthoroughunderstandingof buildings.the harmful effects of air and dirt, as well as knowledgeon how to eliminate them. Doing so helps ensure the systems you design willoperatemethodsat peak efficiencyand providetrouble-freeservice.Modernand hardwarecanlongprovidethe xrecirculatingDHWWe trust you will find this issue of idronics a useful educational tool and a handysystems.pagesaheaddescribeto size,detailand adjustreferenceThefor yourfuturehydronicsystemhowdesigns.We alsoencourageyou to sendus feedbackon this issueof idronics using the attached reader response card or bythesestate-of-the-artsystems.e-mailing us at idronics@caleffi.com.We hope you enjoy this issue and encourage you to send us anyfeedbackSincerely,about idronics by e-mailing us at idronics@caleffi.com.For prior issues please visit us at www.caleffi.us, and click on theicon. There you can download the PDF files. You can alsoMark OlsonGeneraltoManager,registerreceive hard copies of future issues.Caleffi North America, Inc.Mark OlsonGeneral Manager & CEOINDEX1. INTRODUCTIONSUMMARY2. SINGLE-LOOP RECIRCULATION SYSTEMSAPPENDIX A: PIPING SYMBOL LEGEND3. MULTIPLE-BRANCH RECIRCULATIONAPPENDIX B: HEAD LOSS ESTIMATING METHODSSYSTEMS4. DESIGN OF MULTI-BRANCH RECIRCULATIONSYSTEMS5. ELECTRONICALLY-MANAGED RECIRCULATIONSYSTEMSDisclaimer: Caleffi makes no warranty that the information presented in idronics meets the mechanical, electrical or other code requirements applicable within agiven jurisdiction. The diagrams presented in idronics are conceptual, and do not represent complete schematics for any specific installation. Local codes mayrequire differences in design, or safety devices relative to those shown in idronics. It is the responsibility of those adapting any information presented in idronics toverify that such adaptations meet or exceed local code requirements.10%Cert no. XXX-XXX-XXXX

Recirculating Domestic Hot Water SystemsFigure 1-11. INTRODUCTIONAll people instinctively desire warm water for washing.Throughout human history that desire has been met inmany ways—from iron pots suspended over fires, tomodern electronically-controlled tankless water heaters.idronics 11 provides an overview of thehistory of domestic water heating.A reliable source of clean and safe domestic hot water(DHW) is now a requirement in most buildings intended forhuman occupancy. The importance of domestic hot waterin providing comfort, convenience and hygiene cannot beoverstated. Delivering it remains one of the most importantresponsibilities of plumbing system designers.There are currently many options for heating domesticwater, using almost any available fuel. Once the wateris heated, the building’s plumbing system must deliverit to fixtures such as showers, tubs, sinks, dishwashers,clothes washers or other processes requiring hot water.The ability of different plumbing systems to deliver hotwater efficiently and safely varies considerably. Forexample, a bathroom sink located 5 feet from a consistentsource of domestic hot water would likely have heatedwater at an acceptable delivery temperature flowing fromits tap within 2 seconds of opening the faucet. The samefixture located 75 feet from the hot water source may notreceive hot water at the same acceptable temperaturefor 30 seconds or more after the faucet is opened. Thisdelay between opening a faucet and having domestic hotwater at an acceptable temperature flow from the fixtureis undesirable from several standpoints:First, it’s annoying to building occupants. People in mostdeveloped countries have become intolerant of waitingfor expected results. They are accustomed to instantlight at the flip of a switch, instant heat from the burnerof a gas stove, and instant operation of an automobilewhen the key is turned or a button is pushed. It’s notsurprising they expect instant hot water to flow from ahot water faucet.Second, the cool water that flows down the drainwhile hot water is making its way from the heat sourceto the faucet is wasted, as is the heat that this wateronce contained. Wasted fresh water (hot and cold) hasbecome a major concern in many areas of North Americawhere long-term drought conditions have worsened atthe same time as population growth, and thus demandfor fresh water, has accelerated.Studies have shown that the average home wastes morethan 3,650 gallons of heated water per year waiting forhot water at the desired temperature to arrive at fixtures.1Assuming this wasted water was originally heated from 50to 120ºF using electricity priced at 0.15/kWhr, the wastedenergy cost is about 94 per year. This is in addition tothe cost of the water itself. Furthermore, some of the heatdissipated from the hot water distribution piping into thebuilding adds to that building’s cooling load, resulting infurther energy costs.1 Klein, Gary. “Hot-Water Distribution Systems Part 1.” Plumbing Systems & Design.Mar/Apr 2004.3

Beyond the costs of wasted water and energy, it’simportant to understand that some domestic hot waterdelivery systems can create conditions that allowpathogens, such as Legionella bacteria, to thrive. Thesepathogens represent a serious health threat. They aremore likely to exist in domestic hot water delivery systemsthat contain piping where heated water could remainstagnant, in some cases for days. They can also developin domestic hot water systems that are continuallyoperated at reduced water temperatures—typically lessthan 140ºF at the heat source. These conditions creategrowth environments favorable to the bacteria. If watercontaining these pathogens is discharged through fixturessuch as showers, the mist created by the shower can beinhaled. This can lead to a serious and even potentiallyfatal disease. Thus, all domestic hot water deliverysystems should be designed to minimize the potential forsuch pathogens to exist.One of the best ways to minimize wasted water andenergy in domestic hot water delivery systems is bycirculating hot water through the system at times whenit would otherwise not be moving because of no demandat the fixtures. Such systems are called “recirculating”domestic hot water systems. They are the principal focusof this issue of idronics.CONCEPT OF A RECIRCULATING DHW SYSTEMFigure 1-2 shows a simple trunk and branch plumbingdistribution system that supplies hot and cold water tothree lavatories and two showers.Domestic hot water is supplied from a tank-type waterheater to the hot water trunk. It flows along the trunk pipingand eventually into a “riser” that leads to the fixture withthe demand. Once that demand stops, hot water flow alsostops in all portions of the system. The water in the trunkand risers cools as heat is dissipated from the piping.If another demand for DHW occurs within a few minutes,and through the same portion of the distribution system,the water temperature in that piping may have onlydecreased a few degrees, especially if the piping was wellFigure 1-2isolation valvesDHW risercold water riserDHW trunkcold water trunkstandard trunk & riser plumbing systemcoldwatersupplystorage water heater4

insulated. The temperature at which it emerges from thefixture may be suitable within 3 or 4 seconds of openingthe faucet. This scenario is probably acceptable to theperson using the fixture.However, if there is no demand for DHW through thepiping for longer periods of time, perhaps an hour, orovernight, the water will have cooled substantially. Whena DHW demand occurs, it will take substantially longer—perhaps 30 seconds or more depending on pipe sizes,length of flow path, and air temperature surrounding thepiping—before DHW at the desired temperature flowsfrom the fixture. This can annoy the person waiting forthe anticipated comfort of the hot water at a desirabletemperature. It also wastes most of the water betweenthe heat source and fixture.Figure 1-3 shows how the standard system of Figure 1-2can be modified to include recirculation.The system now includes a small recirculation circulatorand a pipe that brings hot water not drawn off at a fixtureback to the heat source. The hot water piping now formsa complete circuit with the heat source, as compared tothe “one-way” path for hot water in the traditional trunkand branch system of Figure 1-2. Each fixture is suppliedby a short “riser” pipe from the hot water trunk. This risershould be as short as possible to minimize the watervolume not contained within the recirculating circuit.The end of the hot water supply piping connects to areduced-size return pipe, which leads back through thecirculator to the heat source. A check valve is installedin this return pipe to ensure that cold water cannot flowbackward towards the hot water risers.The size of the return pipe is smaller than the hot watersupply pipe. This is possible because the return pipe isnot responsible for carrying hot water to any fixture. Itonly has to carry sufficient flow to compensate for theFigure 1-3check valveDHW trunkcold water trunkrecirculationcirculatorcoldwatersupplyDHW return piperecirculating trunk & riser plumbing systemstorage water heater5

Figure 1-42. SINGLE-LOOP RECIRCULATION SYSTEMSThe fundamental objectives of adding a recirculatingfunction to a domestic hot water delivery system are:1. To ensure delivery of heated domestic water at allfixtures within 1-3 seconds of opening a faucet, orotherwise creating a demand.2. To significantly reduce water waste associated withclearing hot water piping of cooler water after a period ofno demand.The basic recirculation system shown in Figure 1-3could achieve these objectives. However, the plumbingdesigner also needs to ensure that:heat loss of the hot water supply piping—a quantity thatcan be calculated based on information given in a latersections.The recirculation circulator must be compatible with freshwater. Any wetted components within that circulator mustbe made of bronze, stainless steel or a suitable engineeredpolymer. These components must also conform to theno-lead requirement that applies to all domestic waterplumbing components within the United States.In some systems, the recirculation circulator operatescontinuously (24/7). In other systems, it runs based on a timerwith specific user-set on-times and off-times; the off-timestypically are overnight hours, or times when the building haslittle, if any, need for DHW throughout its plumbing system.The circulator might even operate automatically based on“learned” DHW usage patterns that have been sampledover several days. In any case, the objective is to ensurethat hot water is immediately available at the fixturesbased on some criteria that are acceptable to the buildingoccupants, and if possible, reduce electrical use by turningthe circulator off at other times.The system shown in Figure 1-3 is very simplified. Itdoes not include the components necessary to ensurethat domestic hot water at potentially high temperaturesdoesn’t reach the fixtures, nor does it ensure that stabletemperatures are maintained within the recirculationcircuit. The components and details necessary for thesefunctions are discussed in section 2, as well as in latersections of this issue of idronics.63. The water temperature delivered from any fixture issafe under all conditions.4. The domestic hot water delivery system does notcreate conditions favorable to growth of pathogens suchas Legionella bacteria.This section combines all four requirements into systemsthat are suitable for homes or small commercial buildingswhere a single-loop recirculating system is feasible. Latersections expand these concepts into more elaboratesystems suitable for larger commercial or institutionalbuildings.BURN PROTECTIONOne of the greatest hazards associated with heatedwater is the risk of moderate to severe burns when skin isexposed to excessively heated water at sinks, showers,bathtubs or other fixtures.The ability of hot water to burn human skin depends onits temperature and exposure time. The higher the watertemperature, the shorter the time required to producea burn of a given severity. Figure 2-1 shows how burnseverity of adult skin is affected by water temperatureand exposure time.In a shower, adult skin can be exposed to water at110ºF indefinitely without risk of burns. However, attemperatures above 110ºF the risk of burns increasesrapidly. Water at 120ºF will create a first-degree burn toadult skin in approximately 8 minutes. Water at 130ºFwill cause first-degree burns to adult skin in about

Figure 2-1setting of the control device and themeasured water temperature leaving thewater heater can easily be 10ºF or more.This variation could make the differencebetween an acceptable and safe watertemperature at the point-of-use, versusa water temperature that could lead to aserious burn.Beyond the accuracy and repeatabilityof the temperature control device onthe water heater is the relative ease ofadjusting this device. A person whois frustrated with hot water deliverytemperatures that are too cool for theircomfort may overcorrect by turningthe temperature control device up wellbeyond point of safe delivery temperature.10 seconds. Water at 160ºF will cause a first-degreeburn to adult skin in less than 1 second! Children canexperience similar burns in half or less of the timerequired to burn an adult. Elderly people are also moresusceptible to burns due to reduced nerve sensitivelyand slower reaction times.The consequences of serious and possibly irreversibleburns caused by overheated domestic water shouldnever be taken lightly. Beyond the potentially lifealtering medical issues faced by the victim is the legalliability associated with designing, installing or adjustingthe domestic water heating system that caused theburn. It is therefore a highly recommended and oftenlegally mandated practice to equip domestic hot watersystems with devices that reliably protect against suchconditions.Unless otherwise required by local code or regulation,domestic hot water should never be delivered fromfixtures intended to supply water directly to human skinat temperatures above 120ºF. In most cases, water at atemperature of 110ºF is acceptable for showers, bathtubsand lavatories.It’s also possible that a hot water systemthat has to deliver hot water at temperaturesas high as 195ºF for sanitation purposesalso supplies hot water to a lavatory forhandwashing. Without proper anti-scaldmixing provisions, it’s inevitable that such a situation willeventually cause serious burns.Another possibility is that the hot water system thatnormally supplies water at perhaps 120ºF, has beenspecifically designed to boost the water temperaturein the system to 160ºF or higher at certain times to killpathogens such as Legionella bacteria. During this typeof “thermal disinfection” cycle, it’s imperative to protectall hot water fixtures in the system from dangerously highdelivery temperature.All these possibilities demonstrate that it’s not a goodidea, or even legal, to rely on the temperature controldevice at the water heater to consistently deliver safehot water temperatures at the points where hot water isdrawn from the system (e.g., the “points of use”).Most devices designed to heat domestic water aresupplied with thermostatic controls that should limitwater temperature. The accuracy of these control devicesvaries considerably. Variations between the temperature7

POINT-OF-USE TEMPERATURE PROTECTIONOne commonly used method of providing “point-of-use”temperature protection is a thermostatic mixing valveconforming to the ASSE (American Society of SanitaryEngineering) 1070 standard. Figure 2-2 shows an exampleof such a valve installed beneath a lavatory.temperature. This regulation is created by the movementof a non-electric thermostatic element within the valve, asshown in Figure 2-4.Figure 2-4HOTCOLDFigure 2-2MIXEDFigure 2-3Figure 2-3 shows anASSE1070-listedthermostatic mixing valvethat is equipped withMPT connections.Thermostaticmixingvalves listed to theASSE 1070 standard aredesigned to be installedclose to the fixturefrom which hot waterwill be drawn. As such, they are called “point-of-use”mixing valves. Caleffi ASSE 1070 mixing valves can beconfigured with tail pieces to match PEX, MPT threads orsoldered connections.These valves continuously adjust the proportions ofentering hot and cold water so that the mixed waterstream leaving the valve remains at a set (and safe)8The thermostatic element contains a special wax thatexpands and contracts with temperature changes. Thiselement is fully immersed in the mixed-flow stream leavingthe valve, and thus it continually reacts to changing inlettemperatures and flow rates. The thermostatic elementadjusts the open area of the ports that allow hot waterand cold water to enter the valve. As the open area ofthe hot water inlet port decreases, the open area of thecold water inlet passage increases, and vice versa. If thetemperature or pressure at either inlet port changes, thevalve quickly and automatically compensates to maintainthe set outlet temperature.Thermostatic mixing valves listed under the ASSE 1070standard are also pressure compensated. If cold waterflow to the valve is interrupted, the valve must immediatelyreduce the flow of hot water leaving the valve to asmall percentage of normal flow. This action requires aminimum temperature difference of 18ºF (10ºC) betweenthe hot water inlet and mixed water outlet. Valves listedto the ASSE 1070 standard must also have internal checkvalves in both inlet ports.Figure 2-5 shows how the basic recirculation system ofFigure 1-3 can be modified to include an ASSE 1070-listedthermostatic mixing valve at each fixture.

Figure 2-5shower valve #2(internal ASSE 1016 protection)shower valve #1(ASSE 1070 protection)ASSE 1070 listedthermostatic mixing valve(typical each fixture)check valveDHW trunkcold water trunkrecirculationcirculatorDHW return pipecoldwatersupplystorage water heaterShower valve #2 in Figure 2-5 is assumed to containan internal thermostatic and pressure-compensatedassembly that provides protection based on the ASSE1016 standard, and thus no external mixing valve isneeded. Many shower valves now have this capability.However, older shower valves may not have anytemperature or pressure compensation. Shower valve #1in Figure 2-5 is assumed to be such a valve. As such, anexternal ASSE 1070 thermostatic mixing valve has beeninstalled.The benefits of having an ASSE 1070 thermostatic mixingvalve at each fixture include:1. The maximum supply water temperature can beindependently adjusted at each fixture. This is especiallyuseful in systems that supply hot water for washing orsterilization at temperatures well above 120ºF, but alsosupply hot water to lavatories, sinks or showers whereskin contact occurs.2. The water heater, hot water trunk and recirculationreturn piping can operate continuously, or based on otherspecific conditions, at temperatures high enough to killpathogens such as Legionella bacteria.POINT-OF-DISTRIBUTIONTEMPERATURE PROTECTIONWhen all fixtures served by thesystem require the same maximumhot water temperature, and theheat source will be operated athigher temperature to eliminatepathogens, a single “point-ofdistribution” thermostatic mixingvalve with an ASSE 1017 listing canbe used, as shown in Figure 2-6.In any recirculating hot waterdistribution system, there willbe times when the circulator isoperating but no hot water isbeing drawn at the fixtures. Underthis condition, heat continuallydissipates from the piping formingthe recirculation loop. If the loop isrelatively short and well insulated,the rate of heat loss should bevery small. If the loop is long anduninsulated, the rate of heat losscould be substantially higher.To maintain the recirculating hotwater at the desired deliverytemperature, the heat lost from the loop must be replaced.This requires some water flow between the loop and thehot water source.In systems with point-of-distribution mixing valves thatdo not fully close their ports, the rate of heat transferbetween the heat source and recirculation loop can bestabilized by installing and adjusting two valves. In Figure2-6, these valves are identified as the “bridge valve” and“return valve”.When there is no demand for hot water at the fixtures, theflow of return water in the recirculating loop will equal therate of hot water flow from the tank to the inlet port of themixing valve. This flow rate should be adjusted so that therate of heat transfer from the tank to the recirculating loopexactly balances the rate of heat loss from the recirculatingloop. This allows the water temperature leaving thetemperature-activated mixing valve to remain stable.The bridge valve, and possibly the return valve, must beadjusted when there is no domestic water draw on therecirculating loop (e.g., all fixtures are off).9

Figure 2-6ASSE 1017thermostaticmixing valvesupply pipe(insulated)return valvereturn echeckvalverecirculationcirculatorThe bridge valve andreturn valve should bothbe globe-style valves foraccurate flow regulation.storage water heaterBegin with the bridge valve fully closed and the returnvalve fully open. Turn on the recirculating circulator andlet it run for several minutes. Under this condition, thesupply water temperature leaving the point-of-distributionmixing valve will likely be lower than the setting of thevalve (since there is no flow returning to the water heater).Slowly open the bridge valve and monitor the temperatureleaving the point-of-distribution mixing valve. It will beginrising as some water returns to the water heater and anequal flow of hot water moves from the water heater tothe hot port of the mixing valve. When the temperatureleaving the mixing valve remains stable and is at or veryclose to the temperature set on the point-of-distributionmixing valve, the bridge valve is correctly set.The return valve can remain fully open unless a situationoccurs where the bridge valve is fully open, but thetemperature leaving the mixing valve is still too low. Ifthis occurs, partially close the return valve to add flowresistance. This forces more flow through the bridge valve.Repeat the previously described procedure of slowlyopening the bridge valve until the water temperatureleaving the mixing valve is stable.In Figure 2-6 the hot water supply and return (recirculation)piping are shown with insulation. This significantly reduces10Figure 2-7cold waterrecirculationcirculatorCaleffi Tankmixer

heat loss, which decreases the required recirculationflow rate. Designers should check with local plumbingcodes to verify any minimum insulation requirements fordomestic hot water piping.In systems where the point-of-distribution valve can fullyclose its ports, the bridge valve and return valve canbe eliminated. Figure 2-7 shows an example of such asystem using Caleffi’s TankMixer assembly, which meetsASSE 1017 protection standards and can fully close itshot port when necessary, thus eliminating the need for abridge valve or a return valve.The Caleffi TankMixer assembly provides all reprotection, as well as recirculation. It is available withthreaded, sweat and press fit connections. The latter, asshown in Figure 2-7, allows the complete assembly to beinstalled without any soldered joints.Designers should also note that use of a singlethermostatically actuated point-of-distribution ASSE1017 mixing valve that is set no higher than 120ºF does notprotect the hot water distribution system from Legionella.Such protection requires higher water temperatures,which are discussed next.LEGIONELLA PROTECTIONOne biological impurity that can be present in domestichot water systems is Legionella bacteria. There arecurrently over 40 known types of these bacteria, whichare naturally present in rivers, lakes, wells or stagnantpools of water. These bacteria are also found in municipalwater mains and can, to some extent, survive municipalwater treatment processes.Legionella bacteria can multiply in water at temperaturesbetween 68 and 122ºF. Below 68ºF, the bacteria arepresent, but remain dormant. Tempered water between77 and 113ºF provides an optimum growth environmentfor Legionella bacteria. Growth is also aided by thepresence of biofilms, mineral scale, sediment or othermicroorganisms within plumbing systems. Dead-legplumbing systems that harbor stagnant water alsoprovide an enhanced growth environment and should beavoided.Figure 2-8 shows the relationship between the status ofLegionella bacteria and the temperature of the water inwhich they exist. Legionella bacteria can be rapidly killedby maintaining heated domestic water at 140ºF or higher.Figure 2-8160Kills bacteria instantly140Kills 90% of bacteria in 2 minutes120Kills 90% of bacteria in 2 hours10080Optimum temperaturefor growth of bacteria60Surviving bacteria inactive32Domestic hot water systems that maintain the heat sourceand distribution piping, including the return piping in arecirculating system at temperatures of 130ºF or higher,provide excellent protection against Legionella bacteria.Some systems maintain these high water temperaturescontinuously. Other systems operate with a timedsterilization cycle in which the water temperature iselevated to 160ºF or higher and circulated throughthe entire recirculation system for a specific time. Thissterilization cycle is typically activated at a time ofreduced water usage, such as during nighttime hours ina residential system.In the absence of specific codes or standards thatrequire otherwise, the following water temperatures andassociated cycle durations have been commonly used foronce-per-day sterilization of domestic hot water deliverysystems:158ºF (70ºC) for 10 minutes149ºF (65ºC) for 15 minutes140ºF (60ºC) for 30 minutesThese temperatures and durations would be required atthe hot water fixture farthest away from the hot watersource.During the sterilization cycle, it is essential to protectfixtures against scalding hot water. Use of ASSE 1070point-of-use mixing valves, as shown in Figure 2-5, canprovide this protection.11

Figure 2-9ASSE 1070 mixingvalves at each fixturesupply temperature sensorelectronically controlledmotorized mixing valvecontroller &data loggerrecirculationcirculatorreturn pipe (insulated)cold watersupplyreturntemperaturesensorstorage water heatersome systems, the temperature drop isquite small, perhaps only 1 or 2ºF due toshort piping lengths and insulation aroundthe piping. In systems with long runs ofuninsulated piping carrying relativelyhigh temperature water, the temperaturedrop can be substantial. This can leadto water temperatures at the farthestfixture that are either too low from acomfort standpoint or too low based onprotection against Legionella growth.Thus, the piping path between the heatsource and the farthest fixture requiringhot water becomes the focus.The objective of a single-loop recirculationsystem is to establish a flow rate than canmaintain a specific minimum supply watertemperature at the fixture farthest from theheat source.Meeting this objective requires a meansto evaluate piping heat loss. That lossdepends on the type of piping material(s)used, the pipe size and length, thewater temperature inside the piping, thepresence or absence of pipe insulation,and the air temperature surrounding thepiping.If a sterilization cycle is required, it is not possible to use athermostatic point-of-distribution mixing valve, as shownin Figure 2-6. However, electronically-controlled mixingvalves, in combination with proper controls, can allow forsterilization cycles in a recirculating system and providereduced hot water temperatures at other times. Reducingthe water temperature circulating through the systemduring non-sterilization periods reduces piping heat loss,and thus reduces fuel use.Figure 2-10a can be used to esti

3883 W. Milwaukee Rd Milwaukee, Wisconsin 53208 USA Tel: 414-238-2360 FAX: 414-238-2366 . tubs, sinks, dishwashers, . hot water at the desired temperature to arrive at fixtures. 1

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