updated Jan. 2023
Are you in the mood to learn more about how different kinds of air conditioners work? You must be since you’re here. Maybe you’re considering purchasing a new model to replace an old system that has long since ceased to be cost-effective, or perhaps you’re contemplating the purchase of your very first AC unit and want to know what your best option is going to be. Regardless, you’ll have to consider several available types of air conditioner and decide which one will suit your needs best. Learning how a heat pump AC unit works can help you determine whether you can make practical use of one in your home, or if you would be better served by a different type of air conditioning system.
Heat pumps are becoming increasingly popular with many American homeowners because they can be extremely efficient and provide significant cost savings over long periods of use. However, there are several circumstances that homeowners in specific areas should consider before they decide to use a heat pump AC unit in their home. Below, we’ll explain each of these factors in detail so that you can make an informed decision for your heating and cooling needs.
How Does a Heat Pump Air Conditioner Work?
For a while now, the status quo for HVAC installation has remained the same: an air conditioner to cool the air in the summer, and a furnace to warm it up in the winter. Most homeowners have one or both of these units installed in their houses, depending on their local climate. However, recent years have seen significant advancements in HVAC technology, including more efficient and environmentally-friendly techniques like geothermic and solar-powered heating. One such advancement is the heat pump air conditioner, a single unit that can switch between heating and cooling your home depending on the season. Modern heat pumps were first invented in the early 20th century, but it was not until the last decade or two that they became popular in US homes.
When the time comes to upgrade or replace your HVAC system, it’s worth looking beyond the standard air conditioners and furnaces to see what other options are available. Heat pumps are a great choice for anyone living in a climate that’s especially warm in the summer and cold in the winter, necessitating an HVAC system that can handle both temperature extremes. As anyone who’s spent significant time there knows, Santa Rosa is in one of those climates, making a heat pump a great option for the Bay Area. That’s why we put together this blog post that goes over how a heat pump works and covers a few of the pros and cons of replacing your current HVAC system with a heat pump.
What is a Heat Pump AC Unit?
When it comes to cooling, heat pumps have much in common with standard air conditioners. They use a series of components to cause state changes in refrigerant that circulates throughout the system, allowing it to absorb heat from inside the building where it is housed and release it to the air outside. However, heat pumps are also able to reverse this process when the building needs to be warmed — causing the refrigerant to absorb heat from the outside air and release it into the home instead. As such, heat pumps do not rely on the methods that standard furnaces use, such as burning gas or heating oil.
Here’s a more detailed breakdown of the refrigeration cycle so that you can better understand the cooling process:
- Refrigerant begins in your system as a cool, low-pressure gas. The compressor in your air conditioner compresses the refrigerant until its pressure rises.
- The refrigerant, now a high-pressure gas, makes its way into the condenser. Here, it condenses into a liquid and absorbs heat from the air in your building (or from the outside when a heat pump is set in reverse).
- The hot, high-pressure liquid refrigerant passes through the expansion valve, where its flow is restricted. The expansion valve allows only a small portion of the liquid to pass through at a time, which forces its pressure to drop.
- The low-pressure liquid refrigerant ends up in the evaporator, where it releases the heat it has collected to the air outside (or in) and reverts into a gas, ready to enter the compressor again and repeat the cycle until the desired temperature in your building has been achieved.
How a Heat Pump Works
For the most part, a heat pump works more or less identically to a standard air conditioner. Both AC units and heat pumps use a refrigerant cycle to transfer heat from one place to another, either cooling or warming up the air in your house. This makes heat pumps a relatively energy-efficient way to heat your home since it only redirects and transfers heat instead of having to generate it by burning fuel or pouring electricity into a heating coil. Without getting too technical, here’s a quick rundown of how the refrigerant cycle works in an air conditioner:
AC units include four main components: the compressor, the evaporator, the condenser, and the blower fan. The compressor holds the main motor of the unit and acts as its “heart,” controlling the flow of refrigerant through the system. It’s also directly connected to the thermostat in your house. When the thermostat detects that the temperature in your home is getting too warm, it sends a signal to the compressor, which switches on and starts the refrigerant flowing.
Refrigerant, also sometimes referred to as “working fluid” for the air conditioner, starts out as a low-pressure gas in the system. When the compressor switches on, it increases the pressure on the refrigerant, compressing it into a high-pressure gas. The compressor also forces the gas through the refrigerant line, passing it into the condenser coil, where it condenses into a liquid. As the refrigerant condenses, it also releases any heat it was holding into the air. A fan blows across the condenser coil while this is happening, pushing the heated air outside as exhaust.
Next, the now-liquid refrigerant flows through the line into the evaporator coil. In the evaporator, the reverse happens: the liquid refrigerant evaporates, transforming back into a gas. This process causes the refrigerant to absorb heat instead of releasing it, which makes the evaporator coil extremely cold. A blower fan pulls air from inside your house and blows it across the evaporator, allowing the refrigerant to absorb the heat and cool down the air before it’s returned to the ducts. The refrigerant gas then passes back to the compressor, which starts the whole process over again.
So if that’s how an air conditioner works, then what changes if you turn it into a heat pump? It’s actually just one simple addition – heat pumps have a switch that allows the compressor to reverse the flow of refrigerant. That means the condenser coil becomes the evaporator coil and vice versa. Instead of drawing heat out of your home and transferring it outside as exhaust, a heat pump with the flow reversed will draw heat from the air outside and transfer it into your house, warming it. Then, once winter ends and the weather gets warm, you can switch the flow back and run the AC again.
Because air conditioners and heat pumps need to pull air from inside the house as well as outside, they’re typically broken up into two different units. One unit placed inside the house holds the evaporator coil and the blower fan, while another unit placed outside holds the compressor and the condenser coil. This separation allows the unit to keep reusing and filtering the same air from inside the house without letting outdoor contaminants into the air supply.
This process might sound complicated, but it’s been more or less unchanged since air conditioners were first invented over a century ago. The heat transfer cycle is still the most effective and efficient way to cool down a house and it proves to be equally efficient at heating when the flow has been reversed.
Heat Pump Pros and Cons
Because heat pumps must be able to reverse the cooling process that standard air conditioners perform, they tend to have considerably higher upfront prices. As such, some homeowners find the costs associated with purchasing a heat pump prohibitive. Heat pump owners in regions that have balanced climates are likely to offset these costs eventually with the savings from their winter utility bills, since reversing the cooling process uses fewer resources than burning gas or oil in a furnace.
Here’s the catch: in regions with unusually cold winters, heat pumps often cannot draw enough heat from the outside air to warm the interior of a building effectively. For this reason, many heat pumps are augmented with miniature heating coils to supplement heat production during cold snaps. However, these coils are meant to be used sparingly — not relied upon for an entire winter. Using them for a whole winter can cause the system to drain much more power than a standard furnace, making it more expensive to operate and negating the usual cost savings. Heat pump coils can also be difficult to clean unassisted.
Pros of Installing a Heat Pump
Heat pumps are becoming increasingly popular in the United States for several different reasons. Here are a few advantages to installing a heat pump in your home instead of a furnace or other standard heating unit:
Heat Pumps are Energy Efficient
As we alluded to above, heat pumps are significantly more efficient than furnaces, baseboard heaters, and other heating units. In fact, the US Department of Energy estimates that switching from an electric furnace or baseboard heater to a heat pump can actually cut your electricity usage by up to 50%, which is a pretty significant difference. The increased efficiency of a heat pump can be attributed to the refrigerant cycle, which transfers heat instead of generating it inside the unit. During the winter, a heat pump pulls heat from the air outside your house and transfers it directly into your indoor air. That means no heating coils and no fuel consumption.
There are also some alternatives to the standard air-supply heat pumps most people install in their homes. In recent years, geothermic heat pumps have become increasingly popular as well. These systems have refrigerant lines that run deep below the surface of the earth instead of outside, drawing heat from the earth itself. During the summer, geothermic heat pumps use the earth to absorb heat from inside your house as well. These units are fairly expensive to install, but they’re extremely efficient.
Heat Pumps Improve Air Quality
Because they’re constantly cycling the same air through the system, air conditioners and heat pumps actually improve the air quality in your house just by running. All heat pumps have air filters that trap dust and other contaminants as the air flows through the system, so they’re gradually filtering out any junk that gets in your air. It’s worth noting, however, that these filters need to be cleaned or replaced fairly frequently, so make sure you stick to that schedule or the system will run into some problems.
Heat pumps and air conditioners also naturally dehumidify your house as they cool the air, which makes the temperature feel much lower. As the air cools, the molecules suspended in it slow down, which allows water molecules to stick together and condense into droplets, pulling them from the air itself. On the flip side, heat pumps also don’t dry out the air the way most furnaces and heating units do, which means your home will be more comfortable in the winter as well. Anyone prone to nosebleeds knows how uncomfortable dry air can be in the winter, but with a heat pump, you likely won’t even need a humidifier.
Heat Pumps are Cheaper to Run
As we mentioned above, heat pumps use significantly less electricity than other electric-powered heating units like furnaces and baseboard heaters. You can actually measure this by looking at a statistic called the coefficient of performance, or COP. Put simply, COP is the ratio of how much heating or cooling a unit provides compared to the energy it uses. Most electric furnaces, for example, have a COP of about 1, which means every kilowatt of electricity it uses represents about 1 kilowatt’s worth of heat. Heat pumps, on the other hand, tend to have COPs of 3 or more, which means every 1 kW of electricity creates 3 kW of heat.
However, that comparison only applies to electric furnaces, which aren’t exactly known for being the most efficient options. What happens when you compare a heat pump to a gas furnace? The answer will depend pretty heavily on where you live since electricity and natural gas prices are highly regionalized. That being said, in many places, Santa Rosa included, a heat pump will come out less expensive than even a natural gas furnace, which is a testament to the superior efficiency of these units.
Heat Pumps are Safer than Gas Furnaces
Heat pumps running on electricity are also safer than gas-powered furnaces. Just to be clear, that’s not to say that furnaces are dangerous – today’s furnaces feature plenty of safety features designed to make sure nothing dangerous escapes the unit into your house. Still, all fuel-burning furnaces share a potential for a gas leak, which can be extremely dangerous. One byproduct of the fuel-burning process is carbon monoxide, one of the most deadly gasses in the world. What makes carbon monoxide so dangerous is that it replaces oxygen in the air and in your lungs without tipping off your body’s risk sensors. That means you won’t even realize you’re not breathing oxygen until you start to suffer the symptoms of oxygen deprivation, including confusion and dizziness. If a gas leak occurs at night, you and your family could breathe in the carbon monoxide and suffocate before you even wake up.
These events are extremely unlikely, but having a fuel-burning furnace in the home can be a source of anxiety for some people. Electric heating units like heat pumps don’t burn any fuel, which means there’s no carbon monoxide being created during the heating process – or anything else dangerous, for that matter. The closest thing to a hazard present in a heat pump is the refrigerant itself, but that’s only dangerous if you drink it or allow the gas to fill a very cramped space. Heat pumps also don’t have any flammable substances inside, which means combustion is impossible unless the electrical wires spark a small fire.
Heat Pumps are Environmentally Friendly
Most furnaces are powered by natural gas, which is plentiful in North America. However, despite being present in large quantities, natural gas isn’t an unlimited or renewable resource, which means it will eventually run out. This makes gas furnaces somewhat less environmentally friendly than some of their competitors, including heat pumps. While it’s relatively clean-burning, especially compared to oils like petroleum, it does release nitrogen oxides and other contaminants into the atmosphere, contributing to smog and climate change. Natural gas is also difficult to extract from the ground since it forms deep in the earth’s core, far below oil. The most common process of extracting natural gas is called fracking, and it frequently causes methane and other pollutants to escape into the environment, even contaminating groundwater.
Of course, heat pumps aren’t completely friendly to the environment. They operate using electricity, and while electricity usage doesn’t create any toxic side effects, many methods of electricity generation do. Coal and natural gas are often burnt to create electricity, which means heat pumps are indirectly contributing to damaging the environment. However, as cleaner power generation methods like wind and nuclear plants are developed, electric units like heat pumps will become more and more environmentally friendly while fuel-burning furnaces will likely be left in the past.
Cons of Installing a Heat Pump
While there are plenty of advantages to installing a heat pump in your home, they’re not always the best option for everyone. Here are a few drawbacks to a heat pump that you can avoid with other units:
Heat Pumps are Expensive
While heat pumps can save you plenty of money on your monthly heating bills, they do come with a fairly steep initial cost. There are a ton of different types of heat pumps, but installing a standard central air pump will cost an average of $10,000 or so. That’s a significant investment, and many people don’t have that much cash available to them when their old furnace or heater starts to break down. Installing a new electric furnace can cost as little as $2,000, depending on the size of your home, so it can sometimes be difficult to justify paying five times as much for a heat pump. However, you should keep in mind that a heat pump isn’t just a replacement for a furnace, but for an air conditioner as well. When you consider that a new air conditioner and a new gas furnace can each cost $5,000 easily, suddenly the cost of a heat pump doesn’t seem so outrageous.
Geothermic heat pumps are more expensive still, ranging from $10,000 up to $30,000 to install. This is because they require pipes installed deep under the surface of the earth, which can be quite a challenge. For now, geothermic heating remains largely the domain of the wealthy class, although look for that to change in the next several decades.
Heat Pumps are Less Effective in Extreme Cold
Because heat pumps work by drawing heat from the air outside and transferring it inside, they tend to struggle when the temperatures outside get very low. No heat outside means there’s nothing to draw inside, so homeowners in especially cold areas might find their heat pump insufficient for the winter cold snaps. You should be fine in Santa Rosa and the surrounding area, but anyone living in Chicago or Minnesota might want to rethink purchasing a heat pump and opt for something else.
Some homeowners in cold climates just install backup furnaces or other heating appliances to use when the weather gets too cold for the heat pump alone. This allows them to take advantage of the convenience and low operating cost of a heat pump most of the year while making sure they stay nice and warm when the weather gets truly chilly.
Heat Pumps Require More Maintenance
Heat pumps and air conditioners are a little more complex than standard gas or electric furnaces, which means all those moving parts require more maintenance to keep the system running smoothly. Upkeep is extremely important for any HVAC appliance, but especially so for heat pumps, since any small problem can reduce the efficacy of the system and lead to larger problems further down the road. While an old furnace can keep chugging for years without even so much as a tune-up, that’s not the case for heat pumps, and you’d be doing yourself a disservice by leaving it to its own devices.
We recommend a yearly maintenance visit from a licensed HVAC technician once a year for both air conditioners and heat pumps. That might seem like overkill, but a single tune-up once a year can end up saving you a lot of money by allowing you to avoid expensive repairs later on. Heat pumps can also easily lose efficiency if something is wrong inside the unit, so avoiding maintenance can actually lead to a sudden spike in your power bill the next month. One tune-up per year is a small price to pay to avoid headaches down the line.
Heat Pumps Take Up More Space
While furnaces can be pretty large, they’re contained into a single unit which makes them easier to find space for in your home. Heat pumps require two units, one inside and one outside, which can be a bit of a pain when you’re first installing one. The two units have to share a wall so the refrigerant lines can connect them together, which is another inconvenience. However, the units themselves aren’t especially huge, so it’s not usually too much of an issue finding space for them both.
Alternatively, many people are choosing to install ductless mini-split systems instead of the standard split system heat pumps. These units are much smaller and blow air directly into the room instead of through the ducts, making them even more energy efficient than a regular heat pump. However, you’ll need to buy a different indoor unit for each room in your house, which makes mini-splits an even more expensive installation than a regular heat pump.
Heat Pumps Don’t Work Without Electricity
This is kind of a no-brainer, but heat pumps and air conditioners require electricity to run, which means you won’t be getting any air when the power is out. This isn’t usually a big deal for an air conditioner, but it can be a problem if you lose power in the winter and find yourself without any heat. The best way to avoid this problem is to either install a backup furnace you can use when the power goes out or just buy a backup generator to run the heat. It can be dangerous to lose heat during the winter, so we’d highly recommend some kind of backup system if you live somewhere with cold winters.
Should You Buy a Heat Pump AC Unit?
In most of California, a heat pump makes sense if you can afford one. Winters throughout the state tend to be mild, and there is usually enough heat in the air that it can successfully be pulled into the home when necessary. For Americans living close to the Canadian border, a heat pump might not be the best choice. It could be a smarter move to simply rely on a conventional HVAC and take steps to make it as energy efficient as possible.
No matter what kind of heating and cooling equipment you use in your home (or commercial facility), make sure you hire a licensed professional contractor to check it over at least once each year and perform service as needed. Doing so will ensure that you enjoy reliable heating and cooling for many years to come.
Call Valley Comfort Heating & Air Today
If you’re interested in learning more about heat pumps or you’re ready to do a little shopping for one yourself, you’ll need to get in touch with an experienced and trustworthy HVAC contractor to help you out. If you’re in Marin, Sonoma, or Napa Counties, feel free to give Valley Comfort Heating & Air a call today and we’ll be happy to assist you with anything you might need. You can visit our location in Santa Rosa, get in touch with us through our website, or just give us a call at (707) 329-4120.