Heat pump refrigeration cycle

Heat pump refrigeration cycle


A heat pump is a device that pulls the energy out of air for the purpose of either heating or cooling a space.

This process is known as space conditioning. Heat pumps operate as a engine in reverse, as they are doing work from an input of electricity to push heat from a chill place to a warm place.

This would seemingly violate the Second law of thermodynamics, but the key reason it doesn't is because this heat transfer is not spontaneous; it requires an input of energy to do so.

For home heating, a heat pump extracts heat from outside air, heats the warm air up even more, and transfers it indoors.

For home cooling, a apparatus reverses this process and warmth is extracted from the indoor air and expelled to the surface , a bit like a refrigerator or air conditioning , thereby making the inside air cooler.

Operation Heating Cycle

The heating cycle of a apparatus works by taking heat in from air outside, warming it up further, and using this warm air to heat indoor air. It does so by the following process.

1. Liquid refrigerant absorbs heat in the "evaporator" from the outdoor air, turning into a gas.

2. The refrigerant is put through a "compressor", which raises the pressure of the gas, increasing its temperature.

3. The hot gas flows through "condenser coils" inside the space to be heated, and since it is at a higher temperature than this space, it transfers heat to the room and condenses back into a liquid.

4. The liquid finally flows back through a valve that reduces its pressure in order to cool it down so it can repeat the cycle.
This can be visualized in the picture below.


Figure 2: the method and parts involved during a heating cycle.

Cooling Cycle

The cooling cycle of a apparatus is employed to chill an area by removing heat from it and expelling it to a different area, usually to the outside for air conditioning or to the room for a refrigerator.

To do this, the "evaporator" and "condenser coils" switch roles and therefore the flow of refrigerant is reversed.

1. The cold refrigerant absorbs heat from the hotter room in the evaporator, so the room will cool down.

2. It is then put through the compressor to increase its temperature.

3. It passes through the condenser coils, and transfers this heat to the outside air.

4. It then expands in order to decrease its pressure and cool down to below the room's temperature to repeat the cycle.


This process can be visualized in Figure 3.
Figure 3: A cooling cycle for a apparatus .
Coefficient of performance

The performance of a heat pump is expressed by the ratio of heat output to the work needed to be input. Essentially, this value is what proportion cooling or heating is being finished an individual's dollar (electricity isn't free after all).

The higher the value for this coefficient is, the better a heat pump is transferring heat because it requires less work to do a certain amount of heat transfer.

However, there's a limit set by the laws of entropy and therefore the second law of thermodynamics.

Air conditioning

Air conditioning (A/C) is a system that performs on the same basic principles as heat pumps, although they do require some different components.

Air conditioners aren't as versatile as heat pumps, because they only perform the function of cooling. However they're of more practical use in many cases, since certain places on Earth don't require heating.

They function by essentially performing an equivalent cooling cycle as heat pumps.

(Best A/C for home)

Thermodynamic Cycle

According to the second law of natural philosophy heat cannot impromptu result a colder location to a warmer area; work is needed to realize this. associate air conditioning needs work to cool down a room, moving heat from the cooler interior (the heat source) to the hotter outdoors (the heat sink). Similarly, a icebox moves heat from within the cold white goods (the heat source) to the hotter room-temperature air of the room (the heat sink).

The operative principle of the refrigeration cycle was represented mathematically by Nicolas Leonard Sadi Carnot in 1824 as a engine.

A apparatus will be thought of as a engine that is working in reverse.

Heat pump and refrigeration cycles will be classified as vapor compression, vapor absorption, gas cycle, or Sterling cycle sorts.

Vapor-compression cycle

Vapor-compression refrigeration
The vapor-compression cycle is employed in most home refrigerators additionally as in several giant industrial and industrial refrigeration systems. Figure one provides a schematic diagram of the elements of a typical vapor-compression cooling.



 Figure 1: Vapor-compression refrigeration

For compression, an easy conventionalized diagram of a heat pump's vapor-compression refrigeration cycle:

1) condenser,

2) Expansion valve

3) evaporator,

4) compressor

The natural philosophy of the cycle will be analyzed on a diagrams as shown in Figure two. during this cycle, a current operating fluid ordinarily referred to as refrigerant like Freon enters the compressor as a vapor.

The vapor is compressed at constant entropy and exits the mechanical device superheated. The superheated vapor travels through the condenser that 1st cools and removes the superheat so condenses the vapor into a liquid by removing further heat at constant pressure and temperature.

The liquid refrigerant goes through the enlargement valve(also referred to as a throttle valve) wherever its pressure dead decreases, inflicting flash evaporation and auto-refrigeration of, typically, but 1/2 the liquid.

Figure 2:Temperature–Entropy diagram of the vapor-compression cycle.

That leads to a mix of liquid and vapor at a lower temperature and pressure. The cold liquid-vapor mixture then travels through the evaporator coil or tubes and is totally vaporized by cooling the nice and cozy air (from the area being refrigerated) being blown by an addict across the evaporator coil or tubes.



The ensuing refrigerant vapor returns to the mechanical device water to complete the thermodynamical cycle.

The higher than discussion is predicated on the best vapor-compression refrigeration cycle, and doesn't take into consideration real-world effects like resistance pressure come by the system, slight thermodynamical unchangeableness throughout the compression of the refrigerant vapor, or non-ideal gas behavior (if any).

Vapor absorption cycle

In the early years of the 20 th century, the vapor absorption cycle exploitation water-ammonia systems was standard and wide used however, when the event of the vapor compression cycle, it lost abundant of its importance as a result of its low constant of performance (about one fifth of that of the vapor compression cycle).

Nowadays, the vapor absorption cycle is employed solely wherever heat is additional promptly accessible than electricity, like waste heat provided by star collectors, or off-the-grid refrigeration in recreational vehicles.

The absorption cycle is analogous to the compression cycle, apart from the tactic of raising the pressure of the refrigerant vapor.

In the absorption system, the mechanical device is replaced by associate a at bsorbent that dissolves the refrigerant in an exceedingly appropriate liquid, a liquid pump that raises the pressure and a generator that, on heat addition, drives off the refrigerant vapor from the hard-hitting liquid.

Some work is needed by the liquid pump however, for a given amount of refrigerant, it's abundant smaller than required by the mechanical device within the vapor compression cycle.

In associate absorption icebox, an acceptable combination of refrigerant and absorbent is employed. the foremost common mixtures area unit ammonia (refrigerant) and water (absorbent), and water (refrigerant) and atomic number 3 bromide(absorbent).

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