2Classification of Hydronic heat sources Conventional gas and oil fired boilersCondensing gas fired boilersElectric resistance boilersElectric thermal storage equipmentHydronic heat pumpsRenewable energy heat sources
3Heat sourcesOf these, conventional gas and oil boilers are currently being used in the vast majority of residential and light commercial hydronic systems in the USA.
4Gas and Oil fired designs Most boilers that operate on natural gas or fuel oil can be classified according to their physical construction and heat exchanger material.
5Cast Iron Sectional Boilers The cast-iron sectional boiler is currently the most common type of boiler used in residential and light commercial buildings in North America.
7Cast Iron Sectional Boilers Since the water flows completely around the heat source, these types of boilers are called Wet Base boilers.The wet base boiler is the common configuration for oil fired boilers.
9Cast Iron Sectional Boilers In this type of boiler, water is heated in cast iron chambers called sections.The sections are bolted together to form a boiler block.The hot gases generated in the combustion chamber near the bottom of the boiler rise up through the cavities between the sections and transfers the heat to the water within.
10Cast Iron Sectional Boilers The greater number of sections, the greater the heat output of the boiler.Most cast iron sectional boilers for residential and light commercial applications are sold as packaged boilers.
11Cast Iron Sectional Boilers This implies that components such as the circulator, burner and controls are selected and mounted on the boiler by the manufacturer.The components supplied by the manufacturer assume the boiler will be used in a typical residential system.In some cases one or more of these components may not be best for a specific application.
13Cast Iron Sectional Boilers The amount of metal in cast iron section boilers makes them relatively heavy.Even small cast iron boilers can weigh as much as 300 to 400 pounds.Such boilers typically contain 10 – 15 gallons of water.
14Cast Iron Sectional Boilers The combination of metal and water weight gives cast iron boilers the ability to absorb a significant amount of thermal energy.Such boilers are said to have a high thermal mass.These boilers are known as high mass boilers
15Cast Iron Sectional Boilers A well insulated boiler housing, or jacket as it is commonly called, reduces standby heat loss from the boiler.
16Cleaning Cast Iron Sectional Boilers Some manufactures design the cast iron boilers for vertical passage of the flue gasses.To clean these types of boilers, the sheet metal top panel, flue connection and flue gas collector assembly must be removed before a cleaning brush can be maneuvered between the sections.
17Cast Iron Sectional Boilers Another type of cast iron boiler design uses horizontal passages between the sections with a hinged door to access both the combustion chamber and the flue gas passages.
18Steel Fire Tube Boilers Steel has been used in the construction of boilers for decades.In a steel Fire Tube boiler, water surrounds a group of steel tubes through which the hot combustion gasses pass.
19Steel Fire Tube Boilers Spiral shaped baffles known as turbulators are inserted into the fire tubes to increase heat transfer by inducing turbulence and slowing the passage of the exhaust.The fire tubes are welded to steel bulkheads at each end to form the overall heat exchanger assembly.
20Steel Fire Tube Boilers Although steel fire tube boilers generally have less mass (metal weight) than cast iron boilers of similar capacity, they often hold more water.A typical steel fire tube boiler contains between gallons of water.
22Copper Water Tube Boilers Some boilers use water filled copper tubes as their heat exchanger.These also come in vertical and horizontal tube arrangements.Copper tubes are usually manufactured with fins that greatly increase the are exposed to the flue gasses for improved heat transfer.
24Combined boiler /domestic hot water tank assemblies A large percentage of residential hydronic systems supply both space heating and domestic hot water.Although several methods have been used to provide domestic hot water from a space heating boiler, it is generally accepted that the most efficient approach uses a storage tank that is indirectly heated by the boiler.
25Space heating boiler with an indirect fired water heater
29Dry Base BoilersAnother common configuration is called the Dry Base Boiler.These boilers suspend the water filled heat exchanger above the combustion chamber
30Dry Base BoilersGas fired cast iron boilers and oil fired vertical tube boilers are typically designed as dry base boilers.
31Cast Iron BoilersAll the boilers listed above (except the combo unit) are classified as conventional boilers.Conventional boilers usually operate with a maximum 85 percent efficiency.Conventional boilers are designed to operate with a hot enough exhaust temperature so that the byproduct of combustion, water vapor, will not condense back into a liquid.
32Cast Iron BoilersIf the exhaust temperature were to be lowered and the water vapor were to reach its dew point, other byproducts of combustion would be entrained in this fluid and would create a very caustic environment for the cast iron or steel the unit is made out of.
33CondensateA good analogy to flue gas condensation in a boiler is seen in the exhaust from a car on a cool day.When the car is first started, the temperature of the exhaust pipe and muffler is low enough to cause some of the water vapor produced in the engine to condense by the time it reaches the tailpipe.
34CondensateWater can often be seen dripping from the tailpipe when the car is first started.After the tail pipe warms above the dew point temperature, the water vapor no longer condenses, and the dripping stops.
35Condensing BoilersAfter the energy crisis of the 1970s, higher fuel costs motivated boiler manufacturers to research methods for improving boiler efficiency.Analysis by engineers and scientist found that significant amount of heat can be recaptured from the exhaust stream if the water vapor it contains can be condensed within the boiler.
36Condensing BoilersCondensing boilers are designed with large heat exchanger surfaces to extract more heat from the exhaust gasses compared to conventional boilers.The heat exchangers are made out of stainless steel or some kind of protected metal.
39Condensing boilerCurrently available boilers use high grade stainless steel or proprietary electroplated coatings to effectively eliminate corrosion.Condensing boilers are more expensive than conventional boilers of equal capacity.
40Condensing boilerCondensing boilers that are designed and installed properly, will achieve much more efficiency than conventional boilers.When designed and installed properly these types of boilers can attain 95+ percent efficiency.