B-3 Hydronic Transfer Units Introduction
Because heat always moves from an area of higher temperature to an area of lower temperature, all buildings either gain or lose heat depending on their surrounding environment. Buildings must have their rate of heat transfer estimated before a means of adding or removing that heat can be specified.
The rate of heat transfer depends on two factors. One is the temperature difference between two bodies or areas. The greater the temperature difference (∆T or “Delta T”), the faster the rate of heat transfer or flow.
The second factor is the material through which the heat moves. For instance, heat moves through a well-insulated wall much more slowly than through an uninsulated wall. Copper is generally used in the hydronic heating industry because it is a good conductor of heat. This means that heat moves through copper quite easily and has a high rate of heat transfer. By comparison, plastic is more of an insulator, and less heat is lost through the walls of plastic tubing than through copper.
Heat in buildings can only be transferred by three means: conduction, convection, and radiation. Heat transfer units are designed to operate using these three methods.
Heat transfer units are also referred to as heat emitters. In this section we will look at the different types of heat emitters and some general installation guidelines for each type. Although the installation of site constructed in floor wall and ceiling radiant panels will be covered in Level 3 studies.
Learning Objectives
After completing the chapters in this section, you should be able to:
- Name types of heat transfer units.
- Describe heat transfer units, including the following:
- In-floor heating
- Radiant panels
- Heat exchangers
- Force flow units
- Unit heaters
- Explain considerations for selecting and installing heat transfer units.
Terminology
The following terms will be used throughout this section. A complete list of terms for this section can be found in the Glossary.
- adjustable louvre: A type of window or vent with slats that can be moved or tilted. These slats can be adjusted to control the amount of light, air, and noise that comes through, making them useful for ventilation and privacy. (Section B-3.1)
- air vents: Steam cannot circulate, nor can radiators emit heat until air has been vented from the system. Thermostatic air vents are installed on each radiator and at the end of each steam main. Thermostatic steam traps also act as air vents. (Section B-3.1 and Section B-3.2)
- baseboard wallfin units: Heating devices installed along the baseboards of rooms. They use electricity or hot water to produce heat, which is then radiated into the room. These units are effective for heating spaces efficiently and are often controlled by thermostats to maintain desired temperatures. (Section B-3.1)
- convector: A heating device that warms up a room by circulating air over a heated surface. The warm air rises and spreads through the room, while cooler air is drawn in to be heated. This process creates a continuous flow of warm air, making the room comfortable. (Section B-3.1)
- forced circulating convectors: Heating units that use a fan or pump to circulate air or water through the convector. They are more powerful than gravity systems and can distribute heat more evenly throughout a room. These systems are often used in larger buildings or where rapid heating is required. (Section B–3.1)
- gravity circulating convectors: Heating units that use natural convection to circulate warm air. They are typically placed near windows and walls where cold air enters. As the air near the heater warms, it rises, creating a convection current that circulates throughout the room. (Section B-3.1)
- heat emitters (units): Steam heating systems use convectors, cast-iron radiators, wall fin tubes, and similar heat-emitting units. (Section B-1.4 and Section B-3.1)
- heat exchangers: Devices designed to transfer heat between two fluids or between a fluid and a solid surface. They facilitate the exchange of thermal energy without the fluids coming into direct contact with each other. They work by maximizing surface area contact between the fluids to efficiently transfer heat from a warmer fluid to a cooler one, or vice versa, depending on the application’s requirements. (Section B-3.1)
- hot flue gases: The exhaust gases produced from combustion processes, such as those in furnaces, boilers, or industrial equipment. These gases are typically very hot and contain by-products of combustion, such as carbon dioxide, water vapor, carbon monoxide, and other pollutants. Hot flue gases are often directed through flues or exhaust pipes to safely remove them from the combustion chamber or heating system. They may also be used in heat exchangers to recover some of their thermal energy before being vented to the atmosphere. (Section B-3.1)
- hydronic fan coil: A unit that uses circulating water to heat or cool air by passing it over coils, adjusting the room temperature efficiently. (Section B-3.1)
- hydronic heating: A system that uses water to heat a building. Water is heated in a boiler and then pumped through pipes to radiators or underfloor tubing. As the hot water moves through these pipes, it releases heat into the rooms, keeping them warm. (Section 3.1)
- radiant panels: Heating devices that are installed in ceilings, walls, or floors of buildings. They emit infrared radiation, which directly heats objects and people in the room without heating the air. This method of heating is efficient and provides comfortable warmth evenly throughout the space. (Section B-3.1)
- radiators: Heating devices that use hot water or steam to warm a room. They consist of metal panels, electrical coils, or hot water pipes that emit heat through radiation and convection. Radiators are commonly found under windows or along walls and are controlled by thermostats to maintain desired temperatures. (Section B-3.1)
Steam heating systems use convectors, cast-iron radiators, wall fin tubes, and similar heat-emitting units. (Section B-1.4 and Section B-3.1)
