Heating Systems: Chapter 1
Introduction to Heating in HVAC
In this module, we will give a brief overview of heating systems and their components. We will also explore how heat is generated and distributed in heating systems.
Overview
Heating systems have a simple purpose: to ensure our comfort. Heating systems raise the temperature of cold spaces to keep us warm and cozy! Fireplaces are some of the oldest and most simple heating systems.
The main components of any modern heating system in HVAC are:
Thermostat,
Heat source,
Burner system,
Heat exchanger, and
Heat distribution system
We will now define each of these components!
Thermostats control the temperature of your home. Think of the thermostat as your TV remote. When you want to change channels, you press a button on your remote. When you want to change the temperature of your home, you press a button on your thermostat!
In order to increase the temperature of your home, you also need a source of heat. The heat source, or fuel, can be a substance like natural gas, oil, or firewood. We mix this heat source with oxygen in the burner system.
In the burner system, we apply a spark of heat to this fuel-oxygen mixture, starting combustion. Recall that combustion is the process of burning and requires fuel, air, and heat. Combustion in the burner system creates the heat we use to heat our homes!
Once we have created heat in the burner system, we must transfer this heat to the air or water in our homes. The heat exchanger is the component that makes this possible. Heat exchangers move heat from the burning fuel to the air or water that we want to be heated.
So far, we combusted a heat source in the burner to create heat. Then we transferred this heat to the air using the heat exchanger. And, finally, we need a way to distribute this hot air to our rooms. This is where the distribution system comes in!
In heating systems, the distribution system provides a path for heat to enter each room inside your home. When we distribute air, we use ductwork. When we distribute water, we use pipes. Ductwork and pipes provide a path for heat to enter your room and keep you warm!
Let’s talk about the difference between creating heat and distributing heat. Heat creation is the process of making heat. Heat distribution is the process of moving this heat where we want it.
Think of agriculture — we create food on farms, but then we distribute it to grocery stores so we can access it. The same is true of heat creation and distribution. Heat is created in the burner system, but we use ductwork and pipes to distribute it to our rooms!
Generating Heat
Gas is one of the most common fuels used by heating systems. Gas heating systems rely on combustion to produce the heat that warms our homes. Modern gas heating systems burn fossil fuels like natural gas, propane, and butane.
Oil heating systems also rely on combustion. Burning oil generates heat we can use to heat air or water in our homes.
We can also use electricity to heat our homes. Your oven is an example of an electric heater! We pass electricity through its coils, generating heat. Instead of using this heat to warm our homes, we use it to cook food.
Gas and oil heaters both rely on combustion but use different fuels. Electric heaters create heat with electricity instead of burning fuels. All heaters rely on the natural flow of heat from hot to cold spaces. They create heat, and it flows to a cooler place that we want heated.
Distributing Heat
Recall that heat transfer is the movement of heat from one place to another.
We can transfer heat using three methods:
Conduction,
Convection, and
Radiation.
We primarily rely on convection to distribute heat in our homes. Recall that convection causes hot air to rise and cool air to fall. We make use of this by placing heaters below areas we want heated, so that heat rises into them naturally.
Convection causes hot air created by the heating system to rise into our homes. This hot air transfers its heat to the air in our homes, warming us up. After it transfers its heat, the air cools down and settles. It is then heated again by the heating system and the cycle repeats!
Furnaces and Boilers
Recall that a furnace is a heating unit that uses combustion to heat entire homes or buildings. Furnaces provide warmth by sending hot air, steam, or water to different spaces that we want to be heated. Furnaces are the most popular way to heat homes in the United States!
Furnaces mix fuel with air in the burner system to start combustion. This heats up the heat exchanger, which then transfers heat to the air. Because of convection, this hot air naturally rises through ductwork and into our rooms.
Furnaces that heat water instead of air are called boilers. Instead of exchanging heat with air, the heat exchangers in boilers heat water. You can use this hot water in your home for showers, cooking, and other day-to-day tasks!
Boilers use the same method of heat creation as furnaces. However, instead of ductwork, they rely on pipes for heat distribution. Pipes are sturdier than ductwork, so they are better suited for transferring water, which is heavier than air.
Boilers also rely on pumps. This is because, unlike air, water does not rise naturally through convection. Pumps use electricity to force water up through the boiler and into radiators in our rooms.
This hot water heats the radiator. Cool air in our rooms flows over the warm radiator, absorbing its heat. This heated air keeps us warm and cozy! We place radiators on the floor so that convection naturally distributes their heat throughout our rooms.
We use furnaces to heat air, and boilers to heat water. Both create heat in the same way. They use burners to mix fuel with oxygen, starting combustion and creating heat. They then transfer this heat to air or water using heat exchangers.
Furnaces and boilers have different heat distribution systems. In furnaces, convection causes hot air to rise directly into our homes through ductwork. Boilers use pipes and pumps to force heated water up into radiators, which heat our rooms using convection.
Gas and oil heaters combust fuels to create heat, while electric heaters rely on electricity. Furnaces and boilers both use burners to create heat. However, they distribute this heat differently — furnaces use ductwork, while boilers use pipes and pumps.
Types of Heat Sources
In this module, we will describe the properties, advantages, and disadvantages of different types of heat sources.
Introduction
Throughout history, humans have relied on different sources of heat. To start, we burned whatever was available — typically wood in early human history. However, now we know that different fuels have various advantages and disadvantages.
One consideration when choosing a fuel is the ease of combustion — some fuels burn easier than others. Certain fuels, such as butane, combust instantly in air. This makes it easy to burn them and create heat. However, this also makes it more difficult to control when they do combust.
Control of combustion is another important factor. Some materials, like wood, are easy to control. However, gases like butane and methane are difficult to control once they start burning. The “Gates of Hell” in Turkmenistan is a crater where methane has been burning non-stop for 40 years!
Uncontrolled combustion can be very dangerous, as fire has the ability to destroy homes and take lives. Therefore, fuels that are easier to control once they combust are safer.
We must also consider the amount of heat a fuel produces when burned. For example, if we burn the same amount of natural gas and firewood, the natural gas would produce more heat. This means that natural gas is a more efficient and cost-effective fuel.
Burning fuels can also produce smoke and harmful gases that have a negative environmental impact. For example, coal is a good source of heat, but it causes air pollution when burned. Reduced air quality harms people and the planet.
Recall that some common types of heaters are gas, oil, and electric. Gas and oil heaters both rely on combustion but use different fuels. Electric heaters pass electricity through metal coils to create heat.
Gas Heating
Recall that gas heating systems rely on combustion to produce the heat that warms our homes. Modern gas heating systems burn fossil fuels like natural gas, propane, and butane.
With the creation of more and more gas pipelines throughout the U.S., the availability and popularity of gas heating systems have increased. More than half of the residential houses and commercial buildings in the U.S. rely on gas heating systems!
Gas heaters can produce very high temperatures. This means they can be used even in the coldest regions of the U.S.!
Gas heaters produce a lot of heat, so they require a lot of power. Because of this, they often run into electrical issues. For example, the system will receive power, but still not run.
Gas heaters often face problems with combustion as well. This is because there must be the perfect amount of gas in the burners. If there is too little gas, the flame will not produce enough heat. If there is too much gas, the flame will get too large and become a safety hazard.
Gas heating systems have several advantages. Gas produces more heat and can heat homes faster than other fuels. Natural gas is much cheaper than electricity. Gas heaters also produce less smoke than oil heaters.
Gas heating systems also have several disadvantages. For example, they need a pipeline connection to supply gas and a chimney to remove smoke. They can even leak carbon monoxide, a potentially fatal gas. They can also leak gas, which could cause a fire.
Oil Heating
Oil heaters, like gas heaters, rely on combustion, but they burn oil instead of gas.
Oil heaters were very popular in the 1900s but have mostly been replaced by gas heaters. This is because gas in the U.S. is cheap and widely available. Gas can also be moved to our homes quickly and easily through pipelines. On the other hand, the oil in your home must be refilled manually, just like the oil in your car.
Recall that burning oil can produce soot, a black powdery substance. Soot can buildup on the components inside the system, causing them to fail or work less efficiently. This forces us to consume more fuel to produce the same amount of heat. We can solve this problem by occasionally cleaning the system.
Oil heaters have several advantages. Unlike gas heaters, they do not create dangerous carbon monoxide. Also unlike gas heaters, oil heaters do not require pipelines. This is because we store oil in refillable cans.
The storage of oil in cans could also be regarded as a disadvantage, as we must refill these cans ourselves. Also, like gas heaters, oil heaters can leak and cause fires. The BP oil spill is a very large-scale example of the dangers of oil leaks.
Electric Heating
Electric heaters have metallic coils. We pass electricity through these coils, heating them up. Cool air from your home then passes over these coils, absorbing their heat. This hot air warms your home! Ovens are examples of electric heaters, but they cook food instead of heating homes.
Electric heaters are smaller than oil or gas heaters. This is because they do not combust fuels, so they do not get as hot as oil or gas heaters. They require less space around them and can be smaller.
When oil and gas heaters burn fuels, some heat is lost in the form of smoke. Because electric heaters do not burn fuels, they do not waste any heat. This means they are more efficient than gas or oil heaters.
Because they rely on large amounts of electricity, electric heaters often encounter electrical issues. The protective component, called the fuse, can blow out if the system receives too much electricity. If the fuse blows out, the system will stop working.
Overload switches are an element that is designed to turn the system off it receives too much electricity. However, sometimes these switches can fail to do their job. This image shows an overload switch that failed and caught fire from the excess electricity entering the system.
Electric heaters have many advantages. They are more compact than gas or oil heaters. They do not burn fuels, so they do not need chimneys to remove smoke. They are also much more efficient than gas or oil heaters.
Electric heaters have one main disadvantage: price. They consume a lot of electricity, and this can lead to a costly electricity bill.
Gas and oil heaters both rely on combustion but use different fuels. Electric heaters use electricity to create heat instead of burning fuels. Each type of heating has various issues, properties, advantages, and disadvantages.
Question #1: We mix the __________ with oxygen in the burner system.
Heat source
Thermostat
Heat exchanger
None of the above
Scroll down for the answer...
Answer: Heat source
We mix the heat source with oxygen in the burner system.
Question #2: In the burner system, combustion occurs and ________ the heat we use to warm our homes.
Distributes
Extinguishes
Creates
Removes
Scroll down for the answer...
Answer: Creates
An HVAC installer should be physically strong, able to read blueprints, and have great time management.
Question #3: The ____________ transfers heat created by the burner to the air, then the distribution system carries this hot air to our rooms.
Fuel
Thermostat
Heat exchanger
Ductwork
Scroll down for the answer...
Answer: Heat exchanger
Fuel mixes with air in the burner, creating heat. The heat exchanger transfers this heat to the air. The distribution system carries this hot air to our rooms.
Question #4: Heat distribution is the process of making heat, and heat creation moves this hot air where want it.
True
False
Scroll down for the answer...
Answer: False
Heat creation is the process of making heat. Heat distribution is the process of moving this heat where we want it. The question statement is false.
Question #5: While gas and oil heaters combust fuels to create heat, electric heaters rely on electricity.
True
False
Scroll down for the answer...
Answer: True
Oil and gas heating systems burn fuels to create heat, while electric heaters use electricity. This statement is true.
Question #6: We make use of convection by placing heating systems above the areas we want heated.
True
False
Scroll down for the answer...
Answer: False
Convection causes hot air to rise and cool air to fall. We make use of this by placing heaters below areas we want heated, so that heat rises into them naturally.
Question #7: Furnaces transfer heat through the air using ductwork, while boilers transfer heat through water using pipes and pumps.
True
False
Scroll down for the answer...
Answer: True
We use furnaces to heat our air and boilers to heat our water. Furnaces and boilers also have different heat distribution systems — furnaces use ductwork, while boilers use pipes and pumps.
Question #8: Which of the following is NOT a factor for choosing a fuel?
Ease of combustion
Weight of the fuel
Control of combustion
Amount of heat produced
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Answer: Weight of the fuel
We mix the heat source with oxygen in the burner system.
Question #9: Gas heating systems often face problems with combustion or __________ issues.
Mechanical
Electrical
Environmental
Financial
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Answer: Electrical
Gas heaters produce a lot of heat, so they require a lot of power. Because of this, they often run into electrical issues.
Question #10: Gas heating systems are cheaper than electric heaters but produce more smoke than oil or gas heaters.
True
False
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Answer: False
Gas heating systems are cheaper than electric heaters, and they produce less smoke than oil or gas heaters. The first part of the question statement is true, but the second part is false.
Question #11: Gas heating systems require a pipeline connection to supply gas and a chimney to remove smoke.
True
False
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Answer: True
This statement is true.
Question #12: Some of the main issues in oil heaters are caused by the buildup of _____ on the systems components.
Oil
Gas
Smoke
Soot
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Answer: Soot
Burning oil can produce soot. If this soot builds up on components, it can cause them to work less efficiently or even fail.
Question #13: The fact that we store oil in refillable cans can be both an advantage and a disadvantage.
True
False
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Answer: True
This statement is true. This can be an advantage if we are heating a home that does not have access to a gas pipeline. However, it can also be a disadvantage because we must refill the oil ourselves.
Question #14: Electric heaters are more _________ than oil or gas heaters.
Dangerous
Compact
Wasteful
None of the above
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Answer: Compact
Electric heaters take up less space than oil or gas heaters, so they are more compact. This is because they do not combust fuels, so they are not hot on the outside and pose less of a safety hazard.
Question #15: What is the main disadvantage of electric heating systems?
Size
Fuel consumption
Price
All of the above
Scroll down for the answer...
Answer: Price
Electric heaters have one main disadvantage: price. They consume a lot of electricity, and this can lead to a costly electricity bill.