16 Heat emitters/Terminal units—Modern hydronic systems can have many types of radiation to provide heat throughout a structure, including baseboard, convectors, radiators, hydro air coils, radiant, etc. Heat emitters receive heat from the hot water circulating through the piping and deliver heat to the areas where they are installed. Types of Heat Emitters (aka terminal units) Typical hot water heating systems deliver heat by convection. They circulate water through heat emitters, warming the air around them. As the air is heated, it expands, becomes less dense and rises. As the warm air rises, the colder air it displaces falls, creating heat convection currents. These convective currents don’t require a mechanical means to move the air. Baseboard Heating Finned-tube baseboard and cast-iron baseboards use convection to circulate heat. Cooler air at the floor level enters the bottom of the baseboard and because of the heated material in the baseboards, heat is transferred to the air which then moves up the wall. Baseboard location is usually along outside walls to help these convective currents and to remove the feeling of a cold wall or window. Finned- tube baseboard features copper tubing with aluminum fins attached. Manufacturers have different types, sizes and numbers of fins per inch. With these variables, the manufacturer rates the Btu output per linear foot based upon a given supply water temperature. Typical finnedtube baseboard is ¾" copper tubing with ½" and 1" available. One inch is typically 12 National Oilheat Research Alliance for commercial applications and has a higher heat output, ½" and ¾" are similar in output, but overall length of the loop is shorter with ½". Finned-tube baseboard heats up rapidly and dissipates its heat quickly. Surface temperatures of the units are not an issue as they are protected with covers. This system works well when there is enough clearance to create convective currents. Cool air enters the bottom and the heated air comes out the top front grates. Furniture placement in front and proper space under the cabinet are critical for the finned-tube baseboard to work properly. See below, Figure 13 for Ratings Charts. Cast iron baseboard heats up slowly and cools off slowly. Surface temperatures are high and there are no protective enclosures. Cast iron baseboard also provides radiant heating because the large mass of iron stays hot even after the circulator shuts off, and slowly releases energy into the space. Convectors Convectors are similar to fin tube baseboard, but tend to be higher, thicker, and not as long. They heat up quickly and cool off quickly. Surface temperatures are not an issue as they are protected with covers. Like finned-tube baseboard, they need enough room in front to create convective currents. Radiators Cast iron radiators deliver heat in a way that is similar to cast iron baseboard; they heat up slowly and cool off slowly, but surface temperatures are high and there are no protective enclosures. They are relatively large and have higher water content than baseboard heating. Figure 13 Hot Water Ratings: BTU/HR. per linear ft. with 65°F entering air Element Water Flow Pressure drop+ 110° F 120°F 130°F 140°F 150°F 160°F 170°F 180°F 190°F 200°F 210°F 215°F 220°F NO. 30-75 baseboard with 3/4'' E-75 element 1GPM 47 160* 210* 260* 320* 360 450 510 580 640 710 770 810 840 4 GPM 525 160* 220* 270* 340* 400 480 540 610 680 750 810 860 890
NORA Advanced Hydronics
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