Your Heat Pump's Three Operation Cycles

Your Heat Pump's Three Operation Cycles
A standard heat pump has three operation cycles that work together to make your heat pump effective. Heat pumps play an essential role in many peoples' homes. Heating cycles warm your home by drawing thermal energy from the air and bringing it into your home in the colder months. A heat pump can cool your home in warmer seasons and climates by pulling heat from the indoor air and releasing it back outside. Understanding the different heat pump operation cycles is crucial to maintaining an efficient, effective pump. This can, by extension, ensure the overall comfort and temperature of your home.

How Does a Heat Pump's Cooling Cycle Work?

The cooling cycle — or the heat pump refrigerant cycle — is the series of processes your heat pump goes through to cool the air and your home. A basic cooling cycle for a heat pump functions in the following way:
  1. Heat pumps contain a liquid refrigerant circulating line that is connected to an expansion device. In the cooling cycle, the refrigerant travels through this expansion device. During this step, the refrigerant changes to a liquid-vapor mix.
  2. In the cooling cycle, the indoor coil functions as an evaporator. When the refrigerant travels through the indoor coil, it extracts heat from the indoor air. After boiling, the refrigerant and air mix becomes a vapor.
  3. The vapor then cycles through the accumulator and the compressor. Once heated, the vapor travels to the outdoor coil, which, in this case, works as the condenser.
  4. The outdoor coil then releases the heat within the vapor to the outdoor air, allowing the refrigerant to cool again.
True to its name, the heat pump refrigeration cycle is how the pump lowers the indoor temperature in your home. It is essential during the summer months or in any climate in which hot temperatures are the norm. Regular maintenance and inspections, especially right before and after the hot summer months, can ensure that its cooling cycle works effectively and efficiently when you need it most.

What Is a Heat Pump's Heating Cycle?

In contrast to the heat pump's cooling/refrigeration cycle, the heat pump's heating cycle can pull cold air from the outside, heat it and release it into your home. This function is especially desirable in cold months and climates. The heating cycle is essentially the reverse of the cooling process:
  1. First, the liquid refrigerant travels, via its circulation line, into the expansion device. During this step, the refrigerant changes from liquid to a kind of liquid-vapor mix.
  2. This liquid-vapor mix then travels to the outdoor coil — in the heat cycle, the outdoor coil functions as the evaporator coil.
  3. Once outside, the refrigerant gathers heat from the outside air until it reaches a boiling point. At this point, the refrigerator transforms into a lower-temperature vapor.
  4. From the outdoor coil, the low-temperature vapor travels to the accumulator and then into the compressor. Once in the compressor, the vapor is compressed. This compression causes the vapor to heat up. This heated vapor then transfers heat into your home's indoor air, which can help warm the home's interior.
  5. Once the heat releases into the home, the refrigerant itself can cool and return to its liquid form.
An effective heat pump with an exceptional heating cycle can be an incredible luxury to have, particularly during the colder seasons of the year. As is true with the cooling cycle, regular heat pump maintenance, especially as the weather and seasons change, is the best way to ensure heating cycle efficiency and performance. A defrost cycle senses condensation and sends hot air to the outdoor coil, which melts frozen condensation.

What Is a Defrost Cycle?

The defrost cycle essentially functions as a fail-safe against heat pump damage during the heating cycle. When the air outside is frigid, it can condense and freeze on the heat pump's outside coil. This significantly impacts the coil's — and the heat pump's — ability to heat effectively. The heat pump must switch over to its air conditioning function to combat the frozen condensation on the outdoor coil. The defrost cycle usually includes the following steps:
  1. The heat pump senses condensation and will automatically switch from the heat cycle to the cooling process.
  2. Once the heat pump switches over to the cooling cycle, it sends hot vaporous air to the outdoor coil.
  3. The hot vapor can then resolve the frozen condensation and will turn off the outdoor fan.
Most heat pump systems also include heat strips that are connected to the system's automatic defrost controls. Once the heat pump switches over to its defrost cycle, the heat strips will activate and release the warmth into the home's interior. Your home will continue to warm up, even though the pump itself is cycling through its defrost process. Due to these complex processes and switches, the defrost cycle requires care and maintenance to function properly each season.

What Is Heat Pump Short Cycling?

How often a heat pump cycles can show its effectiveness. As a natural part of their processes, an efficient, well-maintained heat pump operates through on-off cycles to attain and maintain the home's interior temperature. You may notice that these on-off cycles are getting shorter and shorter as your heat pump works throughout the months and years. This problem is called "short cycling" and indicates an issue within your heat pump and its ability to function efficiently. Several common factors may cause a heat pump to begin short cycling. The most common factor usuallydates back back to the time of the heat pump's original installation. If the heat pump is not sized correctly for the rooms and home, this can significantly affect the pump's ability to self-regulate. Short cycling can also occur due to a refrigerant leak, icing in the coils, clogged air filters, issues with the thermostat and control board, compressor issues and more. If you do notice that your heat pump is short cycling, you should seek professional maintenance and repair services as soon as possible. Quickly addressing the problem can help to avoid more significant heat pump issues, and even system breakdowns, in the future.

How Often Should a Heat Pump Turn On and Off?

Depending on your home and heat pump, the cycle length will vary. Your heat pump cycle should be long enough to heat or cool your home without overworking the system. Usually, a 10 to 20 minute cycle and shutdown is normal, and your pump should run two or three cycles per hour at most. Your heat pump should not run constantly, unless the weather conditions are below freezing for long periods. In this case, your pump will run consistently to maintain the temperature. If your pump is short cycling in pleasant weather, you should call a specialist for repairs. A hat pump technician will be able to locate, diagnose and repair the cause and get your heat pump back to normal quickly. What are the warning signs of short cycling?

What Are the Warning Signs of Short Cycling?

Short cycling is not always obvious, especially if you are a first-time homeowner. It can be constructive to maintain some day-to-day awareness of how your heat pump is functioning. This awareness can allow you to address problems quickly as they arise. The following warning signs are some of the most common indications that your heat pump may be short cycling:
  • The heat pump is making strange or loud noises. When your heat pump is short cycling, you may notice significantly more noises than usual. These noises may be more intense and louder than the noises made by your heat pump's regular, properly functioning cycles.
  • You notice uneven temperature distribution in your home. If you notice an unusual distribution of hot or cold air in the different parts of your home, this is one of the most obvious signs that your heat pump may be short cycling. Uneven temperature distribution can exist as literal hot spots in your home or cold patches and areas of the house that feel drafty.
  • Your energy bill randomly increases. Keep a close eye on your energy bills throughout the year. Normally, your energy consumption will shift slightly during the year, which will naturally result in slight increases and decreases in your energy bill. If you notice a drastic increase in your energy bill, this is usually a clear sign that something is wrong, and heat pump short cycling is a common culprit. If you suspect short cycling, contact an HVAC professional as soon as possible to avoid any additional bill increases due to a malfunctioning heat pump unit.

How Do You Prevent Heat Pump Short Cycling?

There are many reasons that your heat pump may begin to short cycle. A short-cycling heat pump can cause you both stress and physical discomfort — you want your HVAC system to be in tip-top shape all year long to keep you and your loved ones comfortable. In most cases, you can prevent heat pump short cycling through regular maintenance, system upgrades and timely repairs as they arise. Many homeowners have their HVAC systems, including heat pumps, checked out by professional HVAC technicians several times a year — usually when the seasons change. This commitment to consistent maintenance can help you to identify any potential problems, such as refrigerant leaks, a malfunctioning control board or thermostat, run-down unit components and more. Regular check-ups from an HVAC technician will often save you a considerable amount of money in the long run. Just like regular car maintenance and oil changes, your HVAC system — including your heat pump — will run better and longer when it receives consistent care and frequent inspections. It can also be helpful to upgrade your system throughout the years to avoid inefficiency problems in the future. Troubleshooting a short cycling heat pump.

How Do You Troubleshoot A Short Cycling Heat Pump?

Depending on your level of home improvement know-how and DIY capabilities, there are some methods that you can try to troubleshoot your heat pump yourself. For example, if you can identify a leak in your unit, that is likely the cause of the pump's short cycling. If you feel confident in your repair skills, you may be able to fix the leak yourself. Likewise, if you can pinpoint the problem with the air filters, you may be able to clean and change the filters yourself. There are a couple of factors you many homeowners can locate if you know what to look for. Some telltale signs include:
  • Thermostat malfunctioning or calibrated incorrectly.
  • Leaking refrigerant.
  • Damaged control board.
  • Restricted airflow.
  • Improper sizing.
In nearly all cases, HVAC maintenance and repair requires a specialized set of skills and a considerable amount of knowledge about the design and function of the heat pump in question. As such, it's unlikely that an amateur homeowner will be able to diagnose and then fix issues with a short cycling heat pump accurately and securely. Contact an experienced HVAC technician as soon as you notice any potential problems with your heat pump, including short cycling. Professional know-how will nearly always be the best and most effective investment of both your time and money.

Find the Perfect Heat Pump at Ingrams Water and Air

We at Ingrams Water and Air Equipment offer a comprehensive line of innovative and dynamic HVAC products. You can rely on our expertise and experience for any HVAC solutions. We have many heat pumps to fit a variety of needs that you may have, whether you need a new central unit, or you want to add heating or cooling to a new space with a ductless mini-split. Let us help you find the system that you've always deserved!
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One of my three heat pumps' demand defrost control was damaged over the summer by a slug. For whatever reason, the board is fully exposed under the service access panel, so bugs can easily access it. The repair tech installed a new control board as specified by Rheem. Worked fine in a/c season, but was defrosting way too often in heating mode. The board, a new version issued by Rheem, had faulty defrost logic, and had to be replaced again with an older version of the board. Even with the correct board, the heat pump still randomly defrosts when there is no frost at all on the outdoor coil. The defrost cycle is short, but it's wasteful and causes needless wear and tear on the heat pump. Heap pump defrost technology on American heat pumps is primitive -- even with so-called demand defrost controls. My Mr. Cool mini-split almost never defrosts unless the coil is iced. It may do a needless defrost once a year or so, but it's far better than the two Rheem split systems. And, of course, the indoor fan and compressor modulate, but the outdoor fan runs at a constant, full speed (for some reason). The two Rheems are three years old so too young to replace. I wish Mr. Cool universal units were available then and I probably would have selected them.
Dennis Senko
Great article, but I think that your statement about the "vapor" being released to the outside air (#4 in "Cooling" section), and being released into the home, (#5 "Heating" section) is a bit misleading. It makes it sound as though the actual refrigerant vapor is being released, which is of course, not the case. Perhaps the word "heat", replacing "vapor" would make more sense. Other than that, it is a good explanation of how a heat pump functions and what a homeowner should know about their heat pump.
Rebekah Muller
Thank you for this catch!
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