Basics of Heating and Cooling Systems

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Home Improvement

Regular maintenance can significantly increase the lifespan of a central air conditioner.
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Most people don’t think about their heating and cooling systems until they stop working. We rely on our heating systems to keep us warm during the winter and air conditioning to keep us cool during the summer.

If your house is too cold or hot, calling for professional service is the usual reaction. However, you can save a lot of money on service costs and maintain the efficiency of your heating and cooling systems by doing some quick fixes and maintenance yourself. Before that, it’s essential to understand the basics of how these systems function.

Working of Heating and Cooling Systems

All climate-control devices or systems have three fundamental parts: a source of warm or cool air, a way of spreading the air to the rooms that need heating or cooling, and a control system (e.g., thermostat) to manage the entire system. In a house, the sources of warm air, such as a furnace, and cool air, such as an AC, use the same distribution and control systems. Cool air probably flows through the same ducts that heat does, and the same thermostat regulates both. If any of these three basic components of a heating or cooling system malfunction, it can cause problems.

Heating and air conditioning work on the principle that heat moves from a warm object to a cooler one, similar to how water flows from a higher to a lower level. Furnaces and heaters put heat into the air to make your home warmer, and air conditioners remove heat to make it cooler.

All heating and cooling systems burn fuel, and air conditioners use electricity. Most home heating systems use gas or fuel oil, while others use electricity. An electrically powered climate control unit called a heat pump heats and cools the air. In summer, it extracts heat from the air inside your home, while in winter, it pulls heat from the air outside and uses it to warm the air indoors.

When the furnace is turned on, it uses fuel (gas, oil, or electricity) to produce heat that is then channeled to the living areas of your home through ducts, pipes, or wires. The heat is blown out of registers, radiators, or heating panels. Older systems use the heat they produce to heat water, which, in turn, heats the air in your home. These systems use a boiler to store and heat the water supply, which is then circulated as hot water through pipes embedded in the wall, floor, or ceiling.

When an AC is turned on, it uses electricity to cool a gas in a coil to its liquid state. Warm air in your home is cooled by contact with the cooling coil, and this cooled air is channeled to the rooms through ducts and out registers or directly from the unit itself in the case of room ACs.

In the next section, we’ll discuss the different distribution systems used for heating and cooling homes.

Heating and Cooling Distribution Systems


©2006 Publications International, Ltd. Forced-air heating systems use a fan to move warm air.

After the air is heated or cooled at the source, it must be distributed to different rooms in your home. This can be achieved through various systems like forced-air, gravity, or radiant systems.

Forced-Air Systems

A forced-air system uses an electrically powered fan, known as a blower, to distribute the heat produced by the furnace or the coolness produced by a central air conditioner through a network of metal ducts to the rooms in your home. As the warm air from the furnace flows into the rooms, colder air in the rooms flows down through another set of ducts, called the cold air return system, to the furnace to be warmed. This system can be adjusted, allowing you to increase or decrease the amount of air flowing through your home. Central air conditioning systems use the same forced-air system, including the blower, to distribute cool air to the rooms and return warmer air to be cooled.

The issues with forced-air systems usually involve blower malfunctions. The blower may also be noisy, and it adds the cost of electrical power to the cost of furnace fuel. But because it employs a blower, a forced-air system is an effective way to channel airborne heat or cool air throughout a house.

Gravity Systems

The principle of gravity systems is based on the fact that hot air rises and cold air sinks. Therefore, gravity systems cannot distribute cool air from an air conditioner. In a gravity system, the furnace is located near or below the floor. The warmed air rises and travels through ducts to registers in the floor throughout the house. If the furnace is located on the main floor of the house, the heat registers are usually positioned high on the walls because the registers must always be higher than the furnace. The warmed air rises toward the ceiling. As the air cools, it sinks, enters the return air ducts, and flows back to the furnace to be reheated.


©2006 Publications International, Ltd. Gravity systems rely on warm air rising naturally.

Another basic distribution system for heating is the radiant system. The heat source is usually hot water, which is heated by the furnace and circulated through pipes embedded in the wall, floor, or ceiling.

Radiant Systems

Radiant systems work by warming the walls, floors, or ceilings of rooms or, more commonly, by warming radiators in the rooms. These objects then warm the air in the room. Some systems use electric heating panels to generate heat, which is radiated into rooms. Like gravity wall heaters, these panels are usually installed in warm climates or where electricity is relatively inexpensive. Radiant systems cannot distribute cool air from an air conditioner.

Radiators and convectors, the most common means of radiant heat distribution in older homes, are used with hot water heating systems. These systems may depend on gravity or on a circulator pump to circulate heated water from the boiler to the radiators or convectors. A system that uses a pump, or circulator, is called a hydronic system.

Radiant heating systems work by heating walls, floors, or ceilings, which then warm the surrounding air. Nowadays, radiant heating systems are commonly integrated into houses built on a concrete slab foundation. A network of hot water pipes is installed beneath the surface of the concrete slab. When the pipes warm the concrete, it also heats the air that comes in contact with the floor surface. The slab doesn’t have to be very hot, as it will eventually warm the air throughout the entire house.

Radiant systems, especially those that rely on gravity, are susceptible to a number of issues. Mineral deposits can clog the pipes used to distribute the heated water, or the pipes may be arranged at the wrong angle. The boiler that heats the water at the heat source can also malfunction. Hot water systems are rarely installed in new homes.

In the following section, you will learn how the thermostat and other controls maintain the indoor climate created by your heating and cooling systems.

Controls for Heating and Cooling Systems

The thermostat is the basic control that regulates the temperature of your home. It is a heat-sensitive switch that responds to changes in the temperature of the air where it is placed. The furnace or air conditioner is turned on or off as needed to maintain the temperature at a set level, known as the set point. The key component of the thermostat is a bimetallic element that expands or contracts as the temperature increases or decreases in a house.

Older thermostats have two exposed contacts. As the temperature drops, a bimetallic strip bends, making first one electrical contact and then another. The system is fully activated when the second contact closes, turning on the heating system and the anticipator on the thermostat. The anticipator heats the bimetallic element, causing it to bend and break the second electrical contact. The first contact is not yet broken, however, and the heater keeps running until the temperature rises above the setting on the thermostat.

More modern thermostats have coiled bimetallic strip elements, and the contacts are sealed behind glass to protect them from dirt. As the temperature drops, the bimetallic elements start to uncoil. The force exerted by the uncoiling of the elements separates a stationary steel bar from a magnet at the end of the coil. The magnet comes down close to the glass-enclosed contact, pulls up on the contact arm inside the tube, and causes the contacts to close, completing the electrical circuit and turning on the heater and the anticipator. As the air in the room heats up, the coil starts to rewind and breaks the hold of the magnet on the contact arm. The arm drops, breaks the circuit, and turns off the system. At this point, the magnet moves back up to the stationary bar, keeping the contacts open and the heater turned off until the room cools down again.

The latest heat and air-conditioning controls use solid-state electronics for controlling the air temperature. They are typically more accurate and more responsive than older systems. However, repair to solid-state controls usually means replacement.

Understanding how the heating and cooling systems work in your home will help you prevent problems before they become too serious.

©Publications International, Ltd.

FAQ

1. What is a heating and cooling system?

A heating and cooling system is a system that regulates the temperature of a building. It includes devices like air conditioners, furnaces, heat pumps, and thermostats that work together to maintain a comfortable indoor temperature.

2. How does a heating and cooling system work?

Heating and cooling systems work by transferring heat between the indoor and outdoor environments. In heating mode, the system extracts heat from the outdoor air or ground and transfers it inside. In cooling mode, the system removes heat from inside and transfers it outside.

3. What are the different types of heating and cooling systems?

The most common types of heating and cooling systems are central air conditioners, furnaces, heat pumps, and ductless mini-split systems. Each type has its own advantages and disadvantages, and the choice depends on factors like the climate, budget, and size of the building.

4. What is a central air conditioner?

A central air conditioner is a system that cools the entire building by circulating cool air through ducts. It includes an outdoor unit that contains a compressor, a condenser coil, and a fan, and an indoor unit that contains an evaporator coil and a blower. The system is controlled by a thermostat.

5. What is a furnace?

A furnace is a heating system that uses fuel like gas, oil, or electricity to generate heat. It includes a burner that ignites the fuel, a heat exchanger that transfers the heat to the air, and a blower that circulates the heated air through ducts. The system is controlled by a thermostat.

6. What is a heat pump?

A heat pump is a system that can both heat and cool a building. It works by transferring heat between the indoor and outdoor environments using refrigerant. In heating mode, it extracts heat from the outdoor air or ground and transfers it inside. In cooling mode, it removes heat from inside and transfers it outside.

7. What is a ductless mini-split system?

A ductless mini-split system is a heating and cooling system that doesn’t use ducts. It includes an outdoor unit that contains a compressor and a condenser coil, and one or more indoor units that contain an evaporator coil and a blower. The indoor units are connected to the outdoor unit by refrigerant lines.

8. What is a thermostat?

A thermostat is a device that controls the temperature of a building. It senses the indoor temperature and sends a signal to the heating or cooling system to turn on or off. Some thermostats can also be programmed to maintain different temperatures at different times of the day.

9. How can I improve the efficiency of my heating and cooling system?

You can improve the efficiency of your heating and cooling system by properly maintaining it, sealing air leaks, adding insulation, and upgrading to a more efficient system. Regular maintenance, like changing air filters and cleaning coils, can improve the system’s performance and reduce energy consumption.

10. What is the lifespan of a heating and cooling system?

The lifespan of a heating and cooling system depends on factors like the type of system, the quality of installation, and the level of maintenance. On average, a central air conditioner or furnace can last 15-20 years, while a heat pump or ductless mini-split system can last 20-25 years.

11. How can I choose the right heating and cooling system for my building?

You can choose the right heating and cooling system for your building by considering factors like the climate, the size and layout of the building, the level of insulation, and your budget. Consulting with a professional HVAC contractor can help you make an informed decision.

12. How much does a heating and cooling system cost?

The cost of a heating and cooling system depends on factors like the type of system, the size of the building, and the level of installation complexity. On average, a central air conditioner or furnace can cost $3,000-$7,000, while a heat pump or ductless mini-split system can cost $5,000-$10,000.

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