8 1 0 2 y l u j 23 JOURNAL OF DESIGN INNOVATION FOR HYDRONIC PROFESSIONALS 8 1 0 2 y l u j 23 Caleffi North America, Inc. Caleffi North America, Inc. 38839850 SouthW. Milwaukee 54th Street Rd JOURNAL OF DESIGN INNOVATION FOR HYDRONIC PROFESSIONALS Milwaukee,Franklin, WI 53132Wisconsin 53208 T:T: 414.238.2360414.421.1000 F: F: 414.421.2878 414.238.2366 Dear Plumbing and Hydronic Professional, Dear Hydronic Professional, Is an underperforming heat emitter the result of insufficient flow nd rate,Welcome low fluid to the temperature, 2 edition of idronics undersizing, – Caleffi’s improper semi-annual placement, design journal for hydronic professionals. trapped air, or sludge deposits? It could be any or all of these. The 1st edition of idronics was released in January 2007 and distributed to over 80,000 people in North America. It focused on the topic hydraulic separation. From Anthe understanding feedback received, of it’show evi dentheat we moves attained and our goalwhat of factorsexplaining enhance the benefits (orand inhibit) proper that application movement of this modernis vitally design important technique to for those hydronic who systems. A Technical Journal design, troubleshoot, or maintain hydronic systems. Conduction, If you haven’t yet received a copy of idronics #1, you can do so by sending in the from convection,attached reader and response radiation card, all or play by registering rolls, as online do material at www.caleffi.us selections. The Caleffi Hydronic Solutions andpublication the placement will be mailed of those to you materialsfree of charge. within You can a system.The also download ability the to completeestimate journal heat as transfer a PDF file rates from ourusing Web basic site. formulas is also importantThis second when edition designing addresses systems.air and dirt in hydronic systems. Though not a new CALEFFI NORTH AMERICA, INC topic to our industry, the use of modern high-efficiency equipment demands a 3883 W. Milwaukee Rd thorough understanding of the harmful effects of air and dirt, as well as knowledge This issue of idronics discusses the fundamentals of heat transfer Milwaukee, Wisconsin 53208 USA on how to eliminate them. Doing so helps ensure the systems you design will asoperate they apply at peak to efficiency hydronic and heatingprovide long and trouble-free cooling systems.service. Tel: 414-238-2360 It describes how the rate of heat movement in these systems We trust you will find this issue of idronics a useful educational tool and a handy FAX: 414-238-2366 is referenceinfluenced for yourby flow future rate hydronic and systemtemperature designs. Wedifferences. also encourage It also you to send describesus feedback practical on this issue details of idronics that enhance using the attached heat transfer reader response in a wide card or by E-mail: [email protected] varietye-mailing of systemus at [email protected] applications. Website: www.caleffi.us To receive future idronics issues WeSincerely, hope you enjoy this issue of idronics and encourage you to FREE, register online www.caleffi.us send us any feedback by e-mailing us at [email protected]. © Copyright 2018 ForMark prior Olson issues please visit us at www.caleffi.us, and click on the General Manager, Caleffi North America, Inc. Caleffi Northicon. America, There youInc. can download the PDF files. You can also Printed: Milwaukee, Wisconsin USA register to receive hard copies of future issues. Mark Olson General Manager & CEO INDEX 1. INTRODUCTION 2. HEAT TRANSFER FUNDAMENTALS 3. HOW FLOW AND TEMPERATURE CHANGE INFLUENCE HEAT EXCHANGE 4. OPERATING TEMPERATURE OF HYDRONIC HEATING SYSTEMS 5. HEAT EXCHANGER FUNDAMENTALS APPENDIX A: PIPING SYMBOL LEGEND APPENDIX B: THERMAL MODELS FOR FINNED-TUBE BASEBOARD APPENDIX C: THERMAL MODEL FOR A RADIANT PANEL CIRCUIT Disclaimer: Caleffi makes no warranty that the information presented in idronics meets the mechanical, electrical or other code requirements applicable within a 10% given jurisdiction. The diagrams presented in idronics are conceptual, and do not represent complete schematics for any specific installation. Local codes may require differences in design, or safety devices relative to those shown in idronics. It is the responsibility of those adapting any information presented in idronics to Cert no. XXX-XXX-XXXX verify that such adaptations meet or exceed local code requirements. Heat Transfer in Hydronic Systems 1. INTRODUCTION: 2. HEAT TRANSFER FUNDAMENTALS All hydronic heating and cooling systems move thermal Two fundamental concepts apply to all situations involving energy (e.g., heat) from one location to another. In heat transfer: heating applications, this movement takes place across many components, starting at a heat source and exiting 1. Heat always moves from a material at some temperature the hydronic system at the heat emitter(s). Between these to another material at a lower temperature. “end points” of the system, several intermediate heat transfer processes must occur. Examples include heat 2. The rate of heat transfer depends on the temperature moving from combustion gases to water flowing through difference between the two materials. The greater this a boiler, heat passing from one fluid to a different fluid difference, the higher the rate of heat transfer. through a heat exchanger, and heat passing from water inside a copper tube to aluminum fins attached to the To gain a better detailed understanding of how a hydronic outer surface of that tube and finally into room air. system works, heat transfer needs to be classified. A well-established scientific principal is that all heat It’s important for those who design or troubleshoot transfer processes occur through one or more of the hydronic systems to understand the physical processes following modes: by which heat moves. That knowledge can help them quickly identify factors that may constrict heat • Conduction movement. Examples of such constrictions include scale • Convection formation on a boiler’s heat exchanger, heat emitters • Thermal radiation with insufficient surface area, or a thick rug placed over a heated floor slab. CONDUCTION: Conduction heat transfer takes place within solid This issue of idronics discusses the fundamentals of heat materials. It’s the result of atomic vibrations within those transfer as they apply to hydronic heating and cooling materials. The atoms in all materials having temperatures systems. It also shows how the rate of heat movement above absolute zero (-458ºF) vibrate to some extent. The in hydronic systems is influenced by flow rate and higher the material’s temperature, the more vigorous the temperature change of water or water-based fluids. atomic vibrations. Another concept called thermal equilibrium, which When heat is added to a solid material, the atomic applies to all hydronic heating and cooling systems, vibrations become more energetic. These vibrations will be described. The relationship between heat emitter spread out across trillions of atoms that are bonded surface area and required water temperature for a given together, moving towards material at a lower temperature. rate of heat transfer is also be examined. The property that determines how well a material transfers Heat transfer can be a complex subject from a theoretical heat by conduction is called its thermal conductivity. The standpoint. Mathematical models that predict the higher a material’s thermal conductivity value, the faster heat transfer performance of various heat emitters heat can pass through it, with all other conditions being have been developed, and some are presented in the equal. The thermal conductivity of a material is usually appendices. However, the primary objective of this issue determined by testing. The thermal conductivity of many is not to dive deeply into the mathematical theory of heat materials is listed in references such as the ASHRAE transfer. Rather, it’s to provide a solid understanding of Handbook of Fundamentals. fundamentals, along with many practical applications of those fundamentals. Such an understanding can help root Heat moving from the inner surface of a pipe to its outer out potential performance problems at the design stage, surface is an example of conduction heat transfer. Heat long before they reveal themselves as costly mistakes passing from tubing embedded in a concrete slab to within installed systems. It can also help technicians the surface of that slab is another example. The warmth quickly identify performance problems caused by heat felt on hands wrapped around a cup of hot coffee is the transfer “bottlenecks,” rather than faulty equipment. result of heat conduction through the cup. 3 Where: Figure 2-1 Q = rate of heat transfer through the material (Btu/hr) k = thermal conductivity of the material (Btu/°F•hr•ft) ∆x = thickness of the material in the direction of heat flow (ft) ∆T = temperature difference across the material (°F) A = area heat flows across (ft2) Although the value of thermal conductivity for a given material is usually treated as a constant, it does vary slightly based on factors such as the material’s temperature, age and moisture content. The thermal conductivity of certain foam insulations increases slightly as the foam ages. This happens because the gas used to inflate the cells in the DRAFT (4-16-18) foam is slowly replaced with air. The thermal conductivity of freshly sawn wood decreases as its moisture content decreases. Similarly,The mathematical the thermal term conductivity (k/∆x) in formula of dry