Product Learning Center

What are the HVACR systems?

Heating and cooling are two of the most important concepts of home ownership. In fact, heating and cooling systems are major factors for those looking to purchase homes, and are a critical part of living comfortably in a home.

You may frequently hear the term "HVACR," which is used to describe home heating and cooling systems. The acronym stands for Heating, Ventilation and Air Conditioning, which are the three primary functions of a home system. They control air temperature and humidity, and maintain the quality of the air in the home.

Central Systems

Heating and cooling systems may be classified as central or local. Central heating and cooling is the most standard method, and is defined by a system that produces warmth or cool in one central area and then distributes it throughout the home. There are many types of systems that work as central systems, from traditional split systems to packaged product systems.

Products typically used in central heating and cooling systems include:

Heating

Heating systems keep your home warm and comfortable. If you live in a particularly cold climate, the function of your heating system is a high priority.

Most central heating and cooling systems are classified as forced air systems, because they send air through ductwork for distribution. The ductwork can contain products that filter or clean the air.

Radiant systems create heat and deliver it components such as radiators that radiate the heat into the home. Boilers are a traditional radiant heat source.

Typical heating products include:

Cooling

Whole-home air conditioning systems are central systems that rely on ducts to deliver cooled air throughout the home. An air-conditioning system provides cooling, ventilation, humidity control and even heating (if using a Heat Pump) for a home. Air conditioning units cool refrigerants like Puron® Refrigerant and Freon and deliver them to evaporator coils, which dissipate the refrigerant and blow it into ducts for delivery throughout the home.

Products such as room air conditioners are local cooling options for smaller areas within homes. Instead of delivering cooled refrigerant to a coil and then to ductwork, a room air conditioner contains all the components in a single unit and blows air directly into a room.

Air-conditioned homes often have sealed windows, because open windows would disrupt the attempts of the control system to maintain constant temperature.

Typical air conditioning products include:

An air conditioner is a system used to cool down a space by removing heat from the space and moving it to some outside area.

Product Learning Center
Product Learning Center

The goal is to move cooled air from one area to another. This involves taking indoor air and changing its temperature to what is comfortable and distributing this treated air around a building. Many central air conditioning units are known as "split system", as there is an outdoor condenser and an indoor evaporator that work together to cool the house.

Thermostats

The term "thermostat" commonly refers to any unit that controls the operation of a heating and cooling system. Thermostats are used to turn on heating or cooling systems to bring the home to a set temperature. In addition to basic temperature control, programmable thermostats can be used to manage the timing of the system's functions, which can control overall energy use and costs.

HVAC/R Refrigerant Cycle Basics

This is a basic overview of the refrigeration circuit and how it works. It isn't a COMPLETE description by any means, but it is designed to assist a new technician or HVAC/R apprentice in understanding the fundamentals. Let's address some areas of possible confusion:

01

The word “condenser” can mean two different things. Many in the industry will refer to the outside unit on a split air conditioner, heat pump, or refrigeration unit as a “condenser,” even though it will often contain the condenser, compressor, and other parts. It's better to call the outside component the “condensing unit” or simply the “outside unit” to reduce confusion.

02

Cold and hot are relative terms. Cold and hot are both an experience, a description, a comparison, or an emotion. Cold is a way to describe the absence of heat in the same way that dark describes the absence of light. We will often use the words cold and hot to compare two things, such as by saying, “Today is colder than yesterday,” or to communicate comfort: “It feels hot in here.” These are useful communication tools, but they are comparisons, not measurements.

03

Heat and absolute zero can be measured. We can measure heat in BTUs and light in lumens, but we cannot measure “cold” or “dark.” Absolute cold is the absence of all heat. The point of “true” cold, -460°F (-273.3°C), is known as absolute zero; it is the temperature at which all molecular movement stops. Any temperature above that has a measurable level of heat. While this is a known point at which all molecular movement stops, it has not (and likely cannot) be achieved.

04

Boiling isn't always hot. When we say it's “boiling outside,” we mean it's hot outside. That is because when we think of boiling, we immediately think of water boiling in a pot at 212°F (100°C) at atmospheric pressure, which is 14.7 PSI (pounds per square inch) (1.01 bar) at sea level. Boiling is actually just a change of state from liquid to vapor, and the temperature that occurs varies greatly based on the substance being boiled and the pressure around the substance. In an air conditioner or a refrigeration system, refrigerant is designed to boil at a low temperature that corresponds to the system's design. On an average air conditioning system running under normal conditions with a 75°(23.88°C) indoor temperature, the evaporator coil will contain boiling refrigerant at around 40°F (4.44°C). In air conditioning and refrigeration, when we refer to “boiling,” “flashing,” or “evaporating of refrigerant,” we are talking about the process of absorbing heat, otherwise known as cooling.

05

Cooling and heating cannot be “created.” We are not in the business of making heat or creating cool; it cannot be done. We simply move heat from one place to another or changing it from one form to another. When we “cool” a room with an air conditioner, we simply absorb heat from the air into an evaporator and then move that heat outside to the condenser, where it is “rejected” or moved to the outdoors.

06

Heat and temperature aren't the same. Imagine a shot glass of water boiling away at 212°F (100°C). Now, imagine an entire lake sitting at 50°F (10°C). Which has a higher (hotter) temperature? That answer is obvious—I just told you the shot glass had 212°F (100°C) water in it, so it is CLEARLY hotter. But, which contains more heat? The answer is the lake. You see, heat is simply energy, and energy—in its basic form—is movement. When we measure heat, we measure molecular movement; we measure the movement of the atoms stuck together to make water, oxygen, or nitrogen. When molecules move FASTER, they have a HIGHER temperature, and when they move SLOWER, they have a LOWER temperature. Temperature is the average speed (velocity) of molecules in a substance, while heat is the total molecular movement in a substance. The lake has more heat because the lake has more water (molecules).

07

Compressing something makes it get hotter (rise in temperature). When you take something and put pressure on it, it will begin to get hotter. As you pack those molecules that make up whatever you are compressing, they get closer together and start moving faster. If you drop the pressure, the molecules will have more space and move slower, causing the temperature to decrease.

08

Changing the state of matter moves heat without changing temperature. When you boil pure water at atmospheric pressure, it will always boil at 212°F (100°C). You can add more heat by turning up the burner, but as long as it is changing state (boiling), it will stay at 212°F (100°C). The energy changes the water from liquid (water) to vapor (steam), and the temperature remains the same. This pressure and temperature combination at which a substance changes state instead of changing temperature is called its “boiling point,” “condensing temperature,” or, more generally, the “saturation” point.

09

Superheat, subcool, boiling, and saturation aren't complicated. If water is boiling at sea level, it will be 212°F (100°C). If water is 211°F (99.44°C) at sea level, we know it is fully liquid, and it is 1°F (-17.22°C) subcooled. If water is 213°F (100.55°C) at sea level, we know it is vapor and superheated. If something is fully liquid, it will be subcooled; if it is fully vapor, it will be superheated, and if it is in the process of change (boiling or condensing), it is at saturation.

Ductless Mini-Split Air Conditioners

Ductless, mini split-system air-conditioners (mini -splits) have numerous potential applications in residential, commercial, and institutional buildings. The most common applications are in multifamily housing or as retrofit add-ons to houses with "non-ducted" heating systems, such as hydronic (hot water heat), radiant panels, and space heaters (wood, kerosene, propane). They can also be a good choice for room additions and small apartments, where extending or installing distribution ductwork for a central air-conditioner is not feasible.

Like central systems, mini-splits have two main components: an outdoor compressor/condenser, and an indoor air-handling unit. A conduit, which houses the power cable, refrigerant tubing, suction tubing, and a condensate drain, links the outdoor and indoor units.

Advantages

The main advantages of mini-splits are their small size and flexibility for zoning and cooling individual rooms. Many models can have as many as four indoor air handling units (for four zones or rooms) connected to one outdoor unit. The number depends on how much cooling is required for the building or each zone. This can be affected by how well the building is insulated and air sealed. Each of the zones will have its own thermostat, so you only need to condition that space when it is occupied, saving energy and money.

Ductless mini-split systems are also often easier to install than other types of air conditioning systems. For example, the hook-up between the outdoor and indoor units generally requires only a three-inch (~8 centimeter [cm]) hole through a wall for the conduit. Also, most manufacturers of this type of system can provide a variety of lengths of connecting conduits. So, if necessary, you can locate the outdoor unit as far away as 50 feet (~15 meters [m]) from the indoor evaporator. This makes it possible to cool rooms on the front side of a building house with the compressor in a more advantageous or inconspicuous place on the outside of the building.

Since mini-splits have no ducts, they avoid the energy losses associated with ductwork of central forced air systems. Duct losses can account for more than 30% of energy consumption for air conditioning, especially if the ducts are in an unconditioned space such as an attic.

Compared with other add-on systems, mini-splits offer more flexibility in interior design options. The indoor air handlers can be suspended from a ceiling, mounted flush into a drop ceiling, or hung on a wall. Floor-standing models are also available. Most indoor units have profiles of about seven inches (~18 cm) deep and usually come with sleek, high-tech-looking jackets. Many also offer a remote control to make it easier to turn the system on and off when it's positioned high on a wall or suspended from a ceiling.

Disadvantages

The primary disadvantage of mini-splits is their cost. Such systems cost about $1,500 to $2,000 per ton (12,000 Btu per hour) of cooling capacity. This is about 30% more than central systems (not including ductwork) and may cost twice as much as window units of similar capacity.

The installer must also correctly size each indoor unit and judge the best location for its installation. Oversized or incorrectly located air-handlers often result in short-cycling, which wastes energy and does not provide proper temperature or humidity control. Too large a system is also more expensive to buy and operate.

Some people may not like the appearance of the indoor part of the system. While less obtrusive than a window room air conditioner, they seldom have the built-in look of a central system. There must also be a place to drain condensate water near the outdoor unit.

Maintaining Your Air Conditioner

The most important maintenance task that will ensure the efficiency of your air conditioner is to routinely replace or clean its filters. Clogged, dirty filters reduce the amount of airflow and significantly reduce a system's efficiency. In addition, when airflow is obstructed, air can bypass the filter and deposit dirt directly into the evaporator coil and impair the coil's heat-absorbing capacity. Replacing a dirty, clogged filter with a clean one can lower your air conditioner's energy consumption by 5% to 15%.

For central air conditioners, filters are generally located somewhere along the return duct's length. Common filter locations are in walls, ceilings, or in the air conditioner itself. Room air conditioners have a filter mounted in the grill that faces into the room.

Some types of filters are reusable; others must be replaced. They are available in a variety of types and efficiencies. Clean or replace your air conditioning system's filter or filters every month or two during the cooling season. Filters may need more frequent attention if the air conditioner is in constant use, is subjected to dusty conditions, or you have fur-bearing pets in the house.

Air Conditioner Coils

The air conditioner's evaporator coil and condenser coil collect dirt over their months and years of service. A clean filter prevents the evaporator coil from soiling quickly. In time, however, the evaporator coil will still collect dirt. This dirt reduces airflow and insulates the coil, reducing its ability to absorb heat. To avoid this problem, check your evaporator coil every year and clean it as necessary.

Outdoor condenser coils can also become very dirty if the outdoor environment is dusty or if there is foliage nearby. You can easily see the condenser coil and notice if dirt is collecting on its fins.

You should minimize dirt and debris near the condenser unit. Your dryer vents, falling leaves, and lawn mower are all potential sources of dirt and debris. Cleaning the area around the coil, removing any debris, and trimming foliage back at least 2 feet (0.6 meters) allow for adequate airflow around the condenser.

Coil Fins

The aluminum fins on evaporator and condenser coils are easily bent and can block airflow through the coil. Air conditioning wholesalers sell a tool called a "fin comb" that will comb these fins back into nearly original condition.

Condensate Drains

Occasionally pass a stiff wire through the unit's drain channels. Clogged drain channels prevent a unit from reducing humidity, and the resulting excess moisture may discolor walls or carpet.

Window Seals for Room Air Conditioners

At the start of each cooling season, inspect the seal between the air conditioner and the window frame to ensure it makes contact with the unit's metal case. Moisture can damage this seal, allowing cool air to escape from your house.

Preparing for Winter

In the winter, either cover your room air conditioner or remove and store it. Covering the outdoor unit of a central air conditioner will protect the unit from winter weather and debris.

Hiring a Professional

When your air conditioner needs more than regular maintenance, such as when it does not reduce the indoor temperature to a comfortable level, hire a professional service technician. A well-trained technician will find and fix problems in your air conditioning system.

Central Air Conditioning

Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors, or ceilings covered by grills) carry cooled air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home; then it flows back to the central air conditioner through return ducts and registers. To learn how central air conditioners compare to other cooling systems, check out our Energy Saver 101 Infographic: Home Cooling.

Air conditioners dehumidify the air to improve comfort. However, in extremely humid climates, when outdoor temperatures are moderate, or in cases where the air conditioner is oversized, the air may not reach a low enough humidity to achieve a comfortable level. In those instances, homeowners may reduce the thermostat setting or use a dehumidifier. But in both cases this will increase energy use, both for the dehumidifier itself and because the air conditioner will require more energy to cool the house.

If you have a central air system in your home, set the fan to the "auto" mode. In other words, don't use the system's central fan to provide air circulation -- use circulating fans in individual rooms.

Types of Central Air Conditioners

A central air conditioner is either a split-system unit or a packaged unit. In a split-system central air conditioner, an outdoor cabinet contains the outdoor heat exchanger, fan, and compressor, and an indoor cabinet contains the indoor heat exchanger and blower. In many split-system air conditioners, the indoor cabinet may contain the a furnace or the indoor heat exchanger of a heat pump. If your home already has a furnace but no air conditioner, a split-system may be the most economical central air conditioner to install.

In a packaged central air conditioner, the heat exchangers, compressor, fan, and blower are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. This type of air conditioner also is used in small commercial buildings. The supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace.

Installation and Location of Air Conditioners

If your air conditioner is installed correctly, or if major installation problems are found and fixed, it should perform efficiently for years with only minor routine maintenance. However, many air conditioners are not installed correctly. As an unfortunate result, modern energy-efficient air conditioners can perform almost as poorly as older inefficient models.

Typical air conditioning products include:

Choosing or Upgrading Your Central Air Conditioner

Central air conditioners are more efficient than room air conditioners. In addition, they are out of the way, quiet, and convenient to operate. To save energy and money, you should try to buy an energy-efficient air conditioner and reduce your central air conditioner's energy use. In an average size home, air conditioning consumes more than 2,000 kilowatt-hours of electricity per year, causing power plants to emit about 3,500 pounds of carbon dioxide and 31 pounds of sulfur dioxide.

If you are considering adding central air conditioning to your home, the deciding factor may be the need for ductwork.

The most efficient air conditioners use 30% to 50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20% to 40% of your cooling energy costs by replacing it with a newer, more efficient model.

Proper sizing and installation are key elements in determining air conditioner efficiency. Too large a unit will not adequately remove humidity. Too small a unit will not be able to attain a comfortable temperature on the hottest days. Improper unit location, lack of insulation, and improper duct installation can greatly diminish efficiency.

When buying an air conditioner, look for a model with a high efficiency. Central air conditioners are rated according to their seasonal energy efficiency ratio (SEER). SEER indicates the relative amount of energy needed to provide a specific cooling output. Many newer systems have SEER ratings as high as 26.

The standards do not require you to change your existing central air conditioning units, and replacement parts and services should still be available for your home's systems. The "lifespan" of a central air conditioner is about 15 to 20 years. Manufacturers typically continue to support existing equipment by making replacement parts available and honoring maintenance contracts after the new standard goes into effect.

Typical air conditioning products include: