What Is A Heat Pump System? How Does It Work?

What Is A Heat Pump System?

Being as brief as possible, it pumps heat. That's it!

The concept of a 'pump' is incomplete without 'against the spontaneous flow.' There are ion pumps in the body that serve to transport a certain ion against its concentration gradient. You may have seen a water pump pumping water against gravity. So, there is transport from an area of low concentration to a region of high concentration. The same applies to the heat pump. Here, we have a 'heat source' for the 'region of low concentration' and 'heat sink' for the 'region of high concentration.'

Yes. You heard it right. Concentration, whether high or low, is not what matters here. The real difference is between the natural and the energy-driven routes. A flow or transport that would otherwise not happen.

Defining a heat pump has become a lot easier. Any device that drives the heat flow from a heat source to a heat sink is a heat pump. A heat pump is more about the mechanism and the application of the principle mentioned above than the device itself because you'll observe this application in various regions around you.

History

Most people might think this is a recent invention. It's actually a feat of the 19th century. Not so new!

Robert C. Weber, an American inventor, invented the heat pump. He applied the principle to his freezer as a heat source and a gallon of water as a heat sink. These became popular when the fuel prices rose back in the 1970s.

Heat Source

Heat can be extracted from below the ground, from the groundwater, or the air. A perfectly engineered system is required to accomplish this.

There are various kinds of heat pumps. We will talk about all of them in a bit, but the most common one is the air source heat pump.

Air Source

Heat is transferred from outside air to indoors by a refrigerant. It is your air conditioner working in reverse. Many air conditioner units have the option of converting to a heat pump. So is the case with refrigerators.

Ground Source

When the surface temperature is below zero, the ground temperatures are way higher. For instance, on a cold winter day, at a depth of 10 feet, when the air temperature is 30 F, the ground temperature will be 50 F. Experts say that the Earth's temperature remains constant 20 to 30 feet below the ground (somewhere between 60 to 65 C). Pipelines can be put under the ground to bring the heat at the surface. This can be done in two ways:

Closed-loop pipeline: has the same water circulating again and again.

Opened-loop pipeline: extracts water out and channels back in the ground.

The hot water from the ground goes to a heat exchanger, and the heat pump circulates the heat in the room.

Water Source

Those living near lakes or ponds have a greater advantage. The heat can be extracted through the water by a closed-loop pipe system. A closed-loop pipe is put under the water. Water circulation brings hot water to the top. Many use a refrigerant for improved efficiency. This heat pump is very rare due to its cost and complicated process.

How Does It Work?

The process is rather simple, but still, most people find it confusing. It is not complicated if understood with an open mind.

Firstly, I will talk about refrigerators.

The working principle is the same for refrigerators and heat pumps. In a refrigerator, the cool liquid refrigerant passes through the evaporator inside the refrigerator compartment. It takes the heat from the air inside and turns to gas. The gas is then compressed. Its volume decreases, and temperature increases. The gas is then passed through a condenser where a powerful fan blows away all the heat. A condenser is just a black coil at the back. If you stand in front of a running air conditioner, you can hot air coming out. But there is no fan in a refrigerator because the place to be cooled is small. When the gas condenses, its temperature decrease. The liquid is still hot. So, it passes through an expansion valve, which has a small needle-like opening. The pressurized refrigerant is pushed out of this opening, and it expands. The expansion causes the temperature to decrease below zero.

Do not get confused with the condenser coil and evaporator coil. In a heat pump, the condensation occurs inside the room, so we call it a condenser. In an air conditioner, the evaporation occurs inside the room, so we call it an evaporator. They actually form part of the heat pump system serving individual functions.

Heat pumps

Similar to a refrigerator, there are two coils in a heat pump. Both are hollow and are made of copper. The evaporator coil absorbs the heat from the surrounding, causing the refrigerant to heat up and turn into gas. The same fan is used to blow air over the evaporator. The boiling point of the refrigerant is so low that it absorbs heat even from cold air. The gas is then compressed, and that causes its temperature to increase significantly. The hot fluid then passes through the condenser coil inside the room. This is where heat transfer occurs. The gaseous refrigerant condenses, thus turning to liquid. The liquid then goes through an expansion valve, becoming vapour. This increases the surface area of the fluid. It passes through the evaporator and becomes fully gaseous by absorbing ambient heat. The refrigerant must be fully gaseous when it reaches the compressor. This process is repeated until the room's air is at the same temperature as the refrigerant is.

Before You Install

Do consider the following when installing a heat pump in your house or at work for industrial purposes.

1- Type of Heat Pump

Make sure which type of heat pump you need. Some are reversible to cooling. They are more expensive.

When using a reversible heat pump, arrangements must be made to shift to the cooling system. The vent for air conditioners is above the mid-wall.

2- Choice of Wetted Material

Copper is considered the best due to its reliability. It is a good conductor does it is an optimum choice for ground or water source heat pumps. But copper should not be used when connecting the outdoor unit to the indoor unit. Instead, some insulating materials are available on the market.

3- Optimum Efficiency

Now that you understand its principle of working, let's make it easier for the heat pump. Reducing the temperature difference between the heat sink and the heat source can increase your heat pump efficiency. To ensure this, install the heat pump in a warmer environment. If you live in a cold area, we highly recommend you go for an EVI low temp DC inverter heat pump which is able to work efficiently and stably at low temperature.

4- Noise

Some heat pump systems can be noisy, or they can get loud after some time. So it would help if you do not place them near the windows. It can be dangerous to put them on the floor due to the supply lines. The roof would be an ideal place, but the piping cost would rise.

Post statement: Weigh your priorities. Going for a warmer environment may cost you the risk of getting a shock or disturbing noise.

Components of Heat Pump

Heat pumps do not burn fuel or work by solely turning electricity to heat. That is why heat loss is reduced, and electricity is conserved. Below are some main components of a heat pump that are put together to minimize energy loss and maximize the process's efficiency.

Condenser

The name explains the purpose of this component. In a split unit, the condenser is the coil present inside the room. Pressurized hot gas passes through this coil, giving its heat out. The refrigerant condenses and goes outside in the evaporator.

Evaporator

It does precisely the opposite of the condenser. It is placed in the outdoor unit of the split heat pump. But in an air conditioner, this component is called the condenser because now condensation is occurring in this part. It has a fan in front of it to increase airflow over it. This helps better extraction of heat from the air. The fluid turns to a gaseous form. The gaseous refrigerant is then compressed and turned into hot pressurized gas.

Reverse valve

It reverses the direction of the flow of the refrigerant. It is electrically operated and used to turn the heat pump into an air conditioner or vice versa. The structure is a bit complicated. So, for better understanding, watch an animation.

Compressor

The compressor is the heart of the system. It has an electric motor which runs a small piston. The piston pulls the gaseous refrigerant from the evaporator and pushes it into the condenser. As the volume of refrigerant increases in the coil, it gets compressed, and the temperature rises. Then the hot refrigerant is passed through the condenser.

Refrigerant

Refrigerant is the heat carrier in this system. Without this substance, heat cannot circulate. It has to have the physical properties ideal for the heat pump. There are many, but most importantly, it must have a low boiling point. It can absorb heat from very low temperatures if it has a low boiling point.

Air Circulator

Although it serves the purpose of a fan, it doesn't look like one. Its shape moves the air ensuring maximum contact with the evaporator, thus increasing efficiency. It helps develop a convectional current in heating and cooling systems. As heat pump outlets are installed near the floor, air circulators spin and take the ceiling's cold air.

If it's an air conditioner, the air moves from the ceiling to the floor as hotter air is near the ceiling. A DC motor is used to spin this fan so that its spinning direction can be reversed.

Different Types of Heat Pumps

As I mentioned earlier, there are various kinds of heat pumps, so here are some.

The three most common heat pumps are:

1- Air Source Heat Pumps

These being the most common are the best. The upfront cost is high, but it can save you a lot yearly. Heat is extracted from the air outside to heat the air inside. Air source heat pumps can be used as water heaters, unlike other heat pumps. They can become air conditioners in summer. They are electrically operated.

2-Water Source Heat Pumps

It is somewhat similar to the ground source system, except the loop is not under the ground. But this requires a pond, lake, or a deep-water body for proper operation. The installation costs are less as compared to the ground source. There is no digging involved. Water source heat pump is the least common among these three.

If you have a water body near you, it does mean you should go for it. The efficiency of this system depends on the location, area, and climate of the place. You might even require a cooling tower to transfer heat in and out of the building. So do consult an expert before making any decision.

3-Ground Source Heat Pumps

A closed-loop of a rust-free pipe is placed way below the ground. The temperature at this level is higher than the surface. The water circulates in this loop. The water heats up below the ground. Water then passes through a heat pump. This system is used in space heating or cooling. The ground temperature remains constant and works efficiently. This system is cost-effective for spacious buildings.

What About the Uncommon Ones

1- Hybrid Systems

It is necessary to have a backup source of heating if the climate is extreme. Most heat pumps don't work efficiently at very low temperatures. These include air heat pumps. The solution is to have a combo.

Combo one: Ground and air source heat pump

Air heat pumps use for moderate winter and switching to the ground system when the temperature drops significantly.

Combo two: Heat pump and gas boiler

These are more common combos. Many people already have boilers, so they use boilers as a backup when they turn to heat pumps.

2-Solar Heat Pump Systems

Solar panels are planted on the roof to run the heat pumps. This can lead to having zero running cost. These are more beneficial if used with air source heat pumps as they are electrically operated.

3- Exhaust Heat Pumps

These are common for industries. Hot exhaust gases can be turned into heat pumps before being released into the atmosphere.

Pros and Cons of Heat Pumps

Pros

Heat pumps are the best when it comes to:

Efficiency

The biggest advantage you get is immensely increased efficiency. If properly installed, air sourced heat pumps can reach an efficiency of 300%-500%. Ground sourced heat pumps can achieve an efficiency of 400%.

On the other hand, if we use a coiled heater for water heating, most of it is wasted. Even if we use coiled heaters for space heating, they can only be 100% efficient.

Although air sourced heat pumps use electricity to heat air/water, they don't use as much electricity as those coiled heaters do.

Water sourced heat pumps carry similar efficiency as ground source heat pumps do, but they might not be so reliable and require shallow water sources such as lakes, rivers, etc.

Low Running Costs

Running costs are way lower than combustion-based systems. Even if some heat pump systems can cost you over $10000, you can save as much as $1700 per year, based on a research study by the University of Melbourne.

For the ground source heat pump, every unit of electricity consumed produces four units of heat.

Air and ground source heat pumps can even run on solar panels.

Reliability

Heat pumps have considerably longer lives. A heat pump normally has an estimated life of 15 years. If the installation is done professionally, heat pumps can last for even more.

Reversible in Summers

Air source heat pumps can be reversed in summers to work as an air conditioner if they are equipped with a reversing valve. That's a two in one advantage.

Ground source heat pumps are reversible too. Temperatures below the ground can remain low for a very long time. So is the case with water sourced heat pumps. Both can provide space cooling too.

Low Maintenance Costs

The maintenance is almost nonexistent except for the electric ones. But if a fault comes up, it can be a costly process. Leakage in the ground pipes can lead to decreased efficiency.

Anti-humidifiers

Heat pumps do not dehumidify the air in winter, but traditional gas heaters do. You won't be needing a humidifier in winter.

Heat pumps do the opposite in summer. They take the moisture out of the rooms as condensation occurs on the evaporator.

Government Grants

Many governments are grants for installing heat pump systems. The purpose is to foster the use of environment-friendly heating systems.

The government of Ireland announced a grant of $4200 in April of 2018. Only air to water heat pumps was eligible for the assistance.

The government of the UK launched the RHI scheme, providing grants paid over seven years. It is still available to avail. Again, it is only for air to water heat pumps.

Cons

Cons that heat pumps come with:

Expensive to Buy and Install

Heat pumps are expensive to install. Installation costs you more than actually buying the heat pump.

Air sourced home heat pump can cost you between $2000 and $8000, including installation. But for ground source heat pump then the costs can be somewhere between $12000 and $45000.

Furthermore, if not properly handled, the installation might destroy your gardens or leave holes in the walls. As many people are now converting to heat pumps, they face this destruction.

Difficult to Install

Installing heat pumps is a complicated task. Technical knowledge is required to reach maximum efficiency. Many substandard companies claim to have expertise in installing heat pumps. But due to a lack of knowledge, full efficiency is never reached.

A minor leak in the pipeline might result in damaging your walls or low water pressure. So, don't go for a cheaper way as this is a one-time process.

Inefficient in Extreme Weathers

Heats pumps are not recommended for those living in extreme weather. Very low temperatures mean less heat available to the heat pump. So, it will continue to struggle, and your electric bill will continue to rise. A backup heating system is thus important. This makes the process very expensive.

Which Heat Pump Is Better for You?

To help you decide with your favorite and the most suitable heat pump, here are some suggestions based on different climates:

Freezing Weather All Year Long

Air to water or air heat pumps are not suitable for this climate. The refrigerant won't be able to scrap heat out of the cold air. A ground source heat pump is ideal for space heating. But for hot water, you'll need to have a fuel-burning boiler. Typically, combos are required for this type of climate. So, don't panic.

Solar panels can power a ground source heat pump.

Hot Summers and Cold Winters

Air to water or air heat pump is the perfect match for this climate. As it is electrically operated, it can heat up to whichever temperature you like. You don't need air conditioners for summer time as it is reversible.

You can power it with solar panels to get zero running costs.

Spacious Buildings

For space, heating ground source or water source is an excellent and reliable option. They provide heating all year long as the ground temperatures remain constant. For water heating, an air-to-water heat pump is recommended. This combo is ubiquitous. And of course, you can power both heat pumps by solar panels, thus zero running costs.

If the temperature falls way below zero, boilers are recommended.

Industrial Use

In factories where high temperatures are required, ground and water source heat pumps are not an option. For these purposes, air sourced heat pumps are beneficial. There are heat pumps designed especially for industrial use. They can reach temperatures required for melting materials. Gas burners for coiled heaters are way costlier to run in applications like these.