What is Heat Pump in HVAC System? Definition, Parts, Working, Types, COP

In this article, we will learn what is heat pump in HVAC system, along with definition, parts, working philosophy, different types of heat pumps, types, COP, etc.

Let’s explore!

What is Heat Pump in HVAC System? Definition

Definition of Heat Pump

The heat pump, a mechanical device, transfers the heat energy from one place to another place. These devices are primarily used in houses and buildings for inside or outside heat transformation. It takes heat from the air or ground and uses that heat to warm the inner spaces of buildings and offices. Sometimes these devices are used to cool the places by reversing their actions.

Heat Pump Basics

During the 19th-century, heat pumps were used in salt mines for evaporative cooling.  They were employed for heat production instead of coal and wood fire. With scientific development, they evolved into more effective forms of devices used for heating purposes. Now, these devices have a wide range of applications in both the residential and commercial sectors. These are used for both temperature states, either cooling or heating of a space. It consists of a fluid also known as a refrigerant. It alters the state of fluid by absorbing heat in it. Then it displaces the fluid in the desired location. Fluid reverses the action and releases what it has absorbed in it.

Basic Concept of Heat Pumps

During the whole process, fluid remains in a continuous motion, and It does more than four to five tasks at a time. Firstly, it absorbs heat from the surroundings. Then it displaces towards the heat needed. It releases its stored heat there, and it returns to the first position for another heat exchange. A heat pump is an umbrella term used for a device that transfers thermal energy from the heat source to the heat sink. Air conditioners and refrigerators are familiar terms of heat pump, but it does not apply to cooling only. It applies to ventilating, heating, air conditioning, and cooling. Its working principle is somehow opposite to the refrigerators and air conditioners.

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Explanation of Heat Pump with Example

Have you ever noticed how a hot cup of tea becomes cold after some time? Why does it happen so? It happens due to the natural flow of heat. Heat displaces from a hot place to a cold place; for example, the heat of teacup moves in the colder surrounding.

It is a natural behavior of heat. But the heat pump reverses this natural flow. It absorbs heat from the cold environment and releases it in a hot environment. Heat pumps are mostly installed outside the walls of the home. Such devices work in the place of both heater and cooler.

During the cold days, heat pumps absorb the heat from the outside and transfer this heat to the inside of the rooms. While on hot days, it pulls the heat from inside of the homes and transfers it outside of the house, which gives a cooling effect to residents.

To carry out the work, heat pumps use some external forces. Heat pumps use electricity as a power resource. They work in both climate conditions, so there is no need for a separate installation in respective seasons.

During cold days, an electric heat strip is used for indoor heat purposes. Heat pumps don’t release any harmful gases as they don’t burn any fossil fuels. So, they are more environmentally friendly.

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Important Terms in Heat Pumps

Every product has its wordbook, lexicon, and jargon specific to that particular device and its working. Like all other devices, heat pumps also have a distinctive vocabulary associated with them. We will elaborate on them shortly.


HVAC stands for heating, ventilation, air conditioning, and cooling. These are different tasks that are done by the heat pump.

Split System

The split system is used for two separate air conditioning systems for both indoor and outdoor units. They need no duct to conduct heat transfer. This system is more efficient, calm, and energy conserving.

Outdoor Unit

It is the unit of a system that hangs outside of the space. It consists of various components, including a propeller fan, circuit board, heat exchanger, and compressor. All these components do teamwork for the desired results. The outdoor unit is also known as a condenser or heat exchanger, as it exchanges heat with the indoor unit.

Indoor unit

It is part of a heat pump system placed inside the space in which it is working. It directly connects with the outdoor unit consisting of a fan, remote signal receiver, heat exchanger, and filters. These components work collectively and distribute conditioned air in the surrounding.

Heat Source

This term primarily refers to the place from where heat is taken or absorbed. Heat pumps take air from colder space, so that would be called a heat source.

Heat Sink

It refers to the place where the heat pump releases the absorbed heat. It is the place for which the heat pump is for working.


A duct is a tube that works as a bridge between an indoor and an outdoor unit. It carries the heat from the source and releases it in the sink. Ducts vary in size, shape, and manufacturing materials. Some are made of plastics, while others are of metal, fiberglass, and vinyl.

Duct system

It is the network of ducts throughout the home or offices. Through the duct system, we can efficiently distribute the conditioned air in more than one house room.


It stands for an energy-efficient ratio which is a unit to measure the cooling efficiency.


The coefficient for performance is a unit used to measure the heating efficiency of a heat pump.

Heating and Cooling Capacity

It can be defined as a maximum output figure that a heat pump can produce.

Air Filters

Air filters are made up of plastic and fibers to capture pollutants and dust particles from the air, which escapes the room.

Air to water pump

Heat pumps are also used to warm the water. The air to water pump pulls the heat from the air and pushes it into the water.


A heat pump consists of a fluid that absorbs the heat from the heat source and releases it into the sink. This fluid is called a refrigerant.


It is a systematic distribution of conditioned air in the different zones or areas of the house. It includes the opening and closing of different ducts for the desired zones.

Parts of Heat Pump


It is the leading component of a heat pump. The condition of heat depends upon the quality of the compressor used in it. It compresses the refrigerant and fluid contained in it to meet the cooling or heating desire. It circulates the refrigerant from the heat source to the heat sink.

It vaporizes the fluid from low pressure and temperature to high pressure and temperature. It might be a single-stage compressor only for one purpose, while a double-stage compressor is used for heating and cooling purposes. The selection of a compressor depends upon its heating or cooling capacity, efficiency, and the refrigerant used in it.

Heat Pump Condenser

It is part of the outdoor unit of a heat pump system. Its working depends on climate change. It either gathers heat from the surroundings or releases gathered heat into the surroundings. It consists of a condenser coil that takes compressed fluid vapors from the compressor.

This coil carries these vapors and helps in rapid transfer into inside space. In an air conditioning system, condensers are mainly used to warm the refrigerants.


It is the inner coil of a heat pump system that absorbs the heat in it. A low-temperature heat exchanger containing a low-temperature liquid or refrigerant, which converts low-temperature liquid into low-temperature vapors with low pressure, is a heat pump evaporator.

This conversion of fluid into vapors is done by heat absorption from the heat source.

Expansion Valve

The conversion of high temperature and pressure liquid into lower temperature and lower pressure liquid is done by some throttling devices known as throttles or expansion valves. When the high pressured and high-temperature liquid enters into the throttle device, it alters the pressure and reduces its pressure.


Fans provide continuously desired air from the surroundings to the system, especially in the evaporation process.

How Does Heat Pump Work? Working Principle

Its working principle consists of the expansion and compression of refrigerants through their different components. The working fluid or refrigerant passes through its main parts, including the condenser, compressor, evaporator, and expansion valves.

The operating principle on which a heat pump delivers is the physical property of a fluid. The principle says, “the more the pressure of the liquid, the more it will have a high boiling point.” If the liquid pressure is low, it will require a low temperature to evaporate.

In the first stage, fluid is compressed through a compressor connected to an electric power resource. The refrigerant also absorbs electric energy partially. The temperature and pressure of the fluid are increased. In the second stage, its temperature and pressure are reduced to a significant extent.

Fluid vapors are converted to liquid with low temperature and pressure. Now the fluid flows into the expansion valves. Its pressure is further reduced and sent forward to the separator. It separates vapors from fluid and sends them back to the compressor while fluid flows into an evaporative chamber where it is evaporated.

Types of Heat Pumps

There are various types of heat pumps present in markets. They differ from each other in quality, size, and working.

Air Source Heat Pump

It is the most commonly used heat pump across the globe. It transfers the heat from the outside heat exchanger, also known as the heat source, to the inside heat exchanger, also known as the sink.

At the source, the air is forced with fins, while at the sinking, the air is either directly released in inner space or through heat emitters. Heat emitters are the devices that are employed to spread heat throughout the building.

It consists of a heat exchanger coil that absorbs the heat from open-air through an outdoor setup. It also consists of an indoor hot coil that spreads heat in the ducts. During hot climates, the process reverses, and the heat emitters collect the heat from inside by using inner heat exchangers and then release that heat in the open air through the outer air exchanger.

They are pretty inexpensive and very less cost-effective in installation. They have double benefits and are used in houses and offices for both heating and cooling purposes.

Geothermal Heat Pump

It is also known as a ground source heat pump due to its functionality. These devices take heat from the soil rather than air. These devices take advantage of the constant temperature beneath the earth in every season.

They also take heat from the deepwater due to its constant temperature. They are costly and challenging to install due to their complexity. To achieve desired heat, boreholes or trenches are drawn in soil for vertical or horizontal ducts piping.

These ducts carry out the heat from the deep holes and release it to the desired places. Installation of geothermal heat pumps requires proper installation service. The reversing of such a working operation is quite complex. Still, a system can cool the heat building by collecting heat from the building and releasing it into the earth.

They are more energy-efficient devices used for heating space and water. They are a very eco-friendly and clean system. Although emissions of gases from ducts can increase the greenhouse effect, there is a very rare chance of leakage.

Water Source Heat pump

A water source heat pump works the same as a geothermal heat pump, but it uses water as a heat source instead of soil or air. It takes heat from the water reservoirs and converts that thermal energy for heating of a place. This system consists of a widespread network of pipes and ducts.

Those pipes consist of a fluid that absorbs heat from the water. It needs a huge amount of water to carry out the process. It is pretty expensive and difficult to install due to different types of equipment and installation complexity. It needs proper consultation and site visits before installation.

But water source pumps are more energy-efficient rather than air or soil heat pumps. Because water has a very high heat capacity, it can store a lot of heat compared to soil or air. Another main factor is the constant temperature of the water.

Moreover, seasonal changes cause significantly less effect on water temperature. These devices are used to heat water, swimming pools, and houses.

Hybrid Heat Pump

As the name is mentioned, such heat pumps are connected to more than one heat source. It might be air, soil, or water, depending on the outside situations. When the outside temperature is normal or hot, these devices take heat from the air.

When the outer air temperature is low, especially in winter, they take heat from the ground resources. These devices can store the heat in summer as well.

Solar Heat Pump

Solar heat pumps are connected to the solar panels from where they extract the required heat. Solar panels give low-temperature heat to the heat pumps and conserve energy by meeting the electric needs of heat pumps.

Solar heat pumps are more efficient and less expensive. They are also highly effective during the winter when the outside air temperature is low, but panels can absorb heat even at low temperatures.

Exhaust Heat Pump

In this system, heat is driven out from the exhaust air of buildings. It takes the heat from the ventilation system and reuses it for heating purposes. The construction consists of a heat pump, hot water cylinder, extractor fans, and heating coil.

It extracts warm air from the ventilation ducts while the ventilation system is present mainly in moisture-producing places such as baths, kitchens, and utility rooms. The heat from ventilating ducts is extracted by the refrigerant, which after compression, condensation, and evaporation, releases heat in bedrooms and desired spaces.

COP of Heat Pump

COP stands for coefficient of performance. It can be defined as a ratio of useful heating or cooling produced by the heat pump to the required energy to carry out the work. Its formula is


Here Q is the total amount of heating or cooling done by the heat pump, while W is the total work done by the system to produce that heat. Watt or kilowatts are used to measure the amounts. It briefs us on how much heat is produced by consuming 1 W of energy.

For example, if a 500 W system produces 4.5 COP, we give 500 Watts energy to a system it will produce 4500 KW heat in return. If a system produces 100% heat in the given energy output, its COP will be 1. COP is always less than 1 because no heat pump is efficient enough to give a 100% result. The COP of cooling and heating is not always the same; it differs from each other.

  • COP (heating)= Q(heat)/ W
  • COP (cooling)= Q(cool)/ W

Application of Heat Pump

Heat pumps are used both in residential and commercial sectors to increase or decrease the temperature of their spaces. A heat pump is the best choice for heating or cooling a building or water because of its efficiency. Common buildings, including houses, offices, schools, hospitals, and hotels, have a wide range of applications. In commercial buildings and industries, heat pumps are also used in warehouses to maintain the specific heat required for the stored stuff. These heat pumps are also used in water and space heating.

Advantages of Heat Pump

A heat pump has many benefits. A few pros of getting a heat pump are:

  • They have low running cost: They have a high upfront cost, but if we look at the long-term savings, it saves a lot of energy and hence, bills.
  • It requires less maintenance: The other types of combustion devices require much maintenance, but a heat pump only requires an annual checkup that anyone can do.
  • They are considered much safer than combustion-based heating devices because it does not involve the burning of fuels.
  • It reduces carbon emissions: a heat pump reduces carbon emissions and has 150-300 percent efficiency. If it uses 1 kilowatt of energy (electricity), it gives out 3 kilowatts of energy (heat) back. The European Heat Pump Association declared that heat pumps contribute to an annual reduction of 916 million tons of CO2 emissions in the EU.
  • It can act both as a heater and cooler: it can act as an AC in the summer and as a heater in the winters.
  • It has a long lifespan: on average, a heat pump function for 14-15 years.

Disadvantages of Heat Pump

A heat pump is the best alternative to combustion-based devices, but some cons must be kept in mind while purchasing a heat pump. Those cons are:

  • It has a high upfront cost: its price, combined with installing it, goes too high.
  •  Complexities involved: installing a heat pump requires a little research as it is necessary to know the heat movement and the geology of a place before installing one.
  • Loss of efficiency in winter: some heat pumps fail to function when exposed to low temperatures.
  • Installing a heat pump requires significant work: some penetrations must be made to your house, and your house activities will be disrupted due to the installation process.
  • The danger of contributing to global warming: If a heat pump runs on nonrenewable electricity, then it still contributes towards CO2 emission because nonrenewable electricity is made by burning fossil fuel.

Reference High Rated Course

HVAC Fundamentals and BMS Controls

A Practical Introduction to the BACnet Protocol

HVAC Psychrometry, Air Handling System and Duct Selection

Refrigeration & Air conditioning – Design and calculation

Become an HVAC PRO The Ultimate HVAC Guide


Heat pumps are energy-efficient, inexpensive, and eco-friendly devices used for both cooling and heating purposes. The devices use soil, water, air, solar panels, or hybrid resources for a heat source and have a wide range of applications in both residential and commercial sectors. There is a variety of heat pump which is designed for different climates and places. Before choosing a heat pump, you must know its working principle, efficiency, cost, and installation.

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