Portable Air Conditioner – All you need to know

by Martin Schlobach | Last updated: Mar 7, 2022 | 1 comment

Some of the links on my blog are affiliate links. This means that if you click on the link and buy the item, I will receive a commission at no extra cost to you. My opinion remains unaffected.

Portable air conditioners gain importance as summers get hotter. In this article you will find everything you need to know about portable air conditioners. You will find, for example:

How does a portable air conditioner work?
Modification of portable air conditioner to two-hose technology
Simplified cooling load calculation form
Do I need a portable air conditioner?

Top 5 – Mobile Air Conditioners 2022

Winner

1st Place

Amazon's Choice

5th Place

JUNG AIR CAMRY TK06 mobile Klimaanlage mit Fernbedienung, 3,6 KW, 12000BTU, 60dB, 24h-Timer, Entfeuchtungsfunktion, Klimagerät Mobil mit Abluftschlauch, Energieklasse A, 120m³ Raum Kühlung*

De'Longhi Pinguino PAC EL98 ECO

JUNG AIR TV06

Rating: 8.1 / 10

Rating follows

Review

482,31 EUR

Price not available

Go to shop*

Winner

1st Place

De'Longhi Pinguino PAC EL98 ECO

Rating: 8.1 / 10

Review

482,31 EUR

Go to shop*

Amazon's Choice

5th Place

JUNG AIR TV06

Rating follows

Price not available

Go to shop*

* Affiliate Link - Last updated prices on 2025-01-26 / Picture source: Amazon affiliate program

Table of Contents

1 Portable air conditioners in the field
2 Types of portable air conditioners
3 Which portable air conditioner is the right one?
4 Conclusion

Portable air conditioners in the field

To be precise, a portable air conditioner is not a full air conditioner, it is only a “partial air conditioner with cooling function“. We speak of full air conditioners only if they can ventilate, heat, cool, dehumidify air and humidify air. However, the humidification function is not covered by Portable air conditioners.

In split and two-hose units, moreover, no conditioned fresh air is brought into the room from outside, so that we can speak here of recirculating air cooling units. For reasons of practicability, I will continue to use the terms “portable air conditioners” or “mobile air conditioners” in this article.

Portable air conditioners are used in areas where the retrofitting of permanently installed air conditioners is difficult or no longer possible. But Portable air conditioners have also become interesting for short-term use to cool certain areas.

De'Longhi Pinguino PAC EX100 Silent portable air conditioner

The Carnot cycle

Before we look at the different functional steps of a portable air conditioner, let’s take a step back and look at the idea of the Carnot cycle and the ideal heat engine, because these are important for understanding a refrigeration machine and thus also a portable air conditioner.

In the concept of an ideal heat engine, heat energy is converted into mechanical work without losses, which would correspond to a perpetuum mobile of the second kind. According to the second law of thermodynamics, however, this is impossible. Heat energy can never be completely converted into mechanical work. Mechanical work, however, can be completely converted into heat energy.

The physicist and engineer Sadi Carnot then tried to describe the maximum efficiency of a heat engine with the “ideal gas” in a closed system. This theoretical cycle is called the “Carnot cycle” in his honour.

In the Carnot cycle, the ideal gas absorbs heat energy $Q_1$ at high temperature $T_1$ . Part of the heat energy (exergy part – usable part of the energy) is converted into mechanical work $W$ (for example kinetic energy or electrical energy) and the other part is released as non-usable heat energy $Q_2$ (anergy) at a lower temperature $T_2$ . A heat engine with a high efficiency therefore converts as much of the heat energy as possible into usable energy (mechanical work) and only gives off a small amount of residual heat (see Figure 3 – Figure 1).

The thermal efficiency of the Carnot cycle is described via the quotient of useful energy $W$ and the supplied heat energy $Q_1$ . However, it can also be represented with the help of the two temperatures $T_1$ and $T_2$ . The following applies: the higher the temperature difference and the lower the temperature, the higher the efficiency.

Note: Due to the second law of thermodynamics, the efficiency of a heat engine can never be 100%. The efficiency of a heat engine in the Carnot cycle is therefore always $\eta$ < 1.

$\boxed{\eta=\frac{W}{Q_1}=\frac{T_1 - T_2}{T_1}=1-\frac{T_2}{T_1}}$

In the case of a refrigerating machine and a heat pump, the process is reversed. Thus, a reverse Carnot cycle is carried out. By supplying electrical energy, mechanical work $W$ can be performed via the compressor, the refrigerant can be compressed and heat energy can be brought from a cold ( $T_2$ ) to a high temperature level ( $T_1$ ).

With a heat pump, the thermal energy is supplied to a heating system and the heat is “extracted” from a room with a chiller (see Figure 3 – Figs. 2 and 3). However, the efficiency of heat pumps and chillers is not given as efficiency, but as coefficient of performance and energy efficiency ratio.

The coefficient of performance of an electric heat pump (COP) is the ratio of heat output $\dot Q_1$ (heat supplied to the heating system) to the expended electrical power $P_{el}$ :

$\boxed{\epsilon_W=\frac{\dot Q_1}{P_{el}} =\frac{T_1}{T_1 - T_2}}$

The Energy Efficiency Ratio of an electrically operated chiller (EER) is the ratio of heat output $\dot Q_2$ (heat extracted from the room) to the expended electrical power $P_{el}$ :

$\boxed{\epsilon_K=\frac{\dot Q_2}{P_{el}} =\frac{T_2}{T_1 - T_2}}$

Figure 3: Comparison of cycle processes: Heat engine, heat pump and refrigeration compressor

Reversed Carnot cycle as refrigeration circuit

To understand the individual components and their function of refrigeration machines, I will now explain them step by step using the reversed Carnot cycle. However, since the Carnot cycle is a theoretical cycle, the real cycle of a refrigerating machine looks somewhat different. I will go into this later.

To describe the cycle and the different states of the refrigerant, the temperature-entropy diagram (T-s diagram) and the pressure-volume diagram (p-v diagram) are used.

Note on entropy: You have probably just read the term entropy. The term entropy has the formula symbol S and is not that easy to explain, but it is important for the representation of circular processes.

A definition that most closely approximates entropy in the context of processes is the following: “Entropy is a measure of the irreversibility of processes“. Entropy increases the more irreversible a process is ( $\Delta$ S > 0). Expressed in a formula, this means: the transferred entropy $\Delta$ S is the quotient of transferred heat $\Delta$ Q and temperature T:

$\boxed{\Delta S=\frac{\Delta Q}{T}}$

A Carnot cycle (whether clock or counterclockwise) is a reversible cycle, i.e. a cycle that is theoretically completely reversible. The sum of the transferred heat energy is always dependent only on the initial and final state, but not on the changes of state that take place. The entropy in a reversible cycle is thus constant $\Delta$ S = 0.

In the T-s diagram you will see the different state and entropy changes of the refrigerant. Thus, in a reversible cycle, the entropy transferred is $\Delta$ S > 0 when heat energy is absorbed and $\Delta$ S < 0 when heat energy is released.

I admit that this can be a little confusing at first glance. I therefore recommend the following video by Jeff Phillips, who explains entropy in a very charming and funny way. Watch it!

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Step 1 – Evaporation of the refrigerant

The first step is the evaporation of the refrigerant. At this point, the refrigerant is liquid and has the lowest temperature in the cycle. The evaporator (1) is nothing more than a heat exchanger through which the refrigerant must pass. Since heat is always transferred from a higher temperature level to a lower temperature level, a fan draws in warm room air (5) through the evaporator (1). The warm room air then transfers its heat to the refrigerant inside the evaporator. This cools the room air and blows it into the room (6).

The refrigerant in the evaporator, on the other hand, begins to absorb the heat of the room. Since the refrigerant has a very low boiling point, it begins to boil, evaporates and changes its state of aggregation from liquid to gaseous.

Figure 4: reversed carnot cycle Step 1: Evaporation

In the T-s and p-v diagrams the distance D to A is described. In the T-s diagram you can see that during the energy absorption from the room air the temperature of the refrigerant remains constant. In the case of a change of state, the temperature does not change until the phase transformation (here from liquid to gas) is complete. The entropy transferred is positive because heat is absorbed.

In the p-V diagram, you can see how the pressure decreases somewhat and the volume of the refrigerant increases significantly, because gases require more volume than liquids. The process in step 1 is called isothermal expansion.

Figure 5: T-s and p-v diagram in the reversed carnot cycle - step 1 - evaporation — Figure 5: T-s and p-v diagram in the reversed carnot cycle – step 1 – evaporation

Isothermal expansion
⇨ Room air gives off heat to the refrigerant in the evaporator and is cooled.
⇨ Refrigerant absorbs heat from the room air in the evaporator and evaporates.
⇨ p-v diagram: Volume increases, pressure decreases slightly.
⇨ T-s diagram: temperature constant, entropy difference $\Delta$ S > 0

Step 2 – Compression of the refrigerant

In the second step, the gaseous refrigerant is sucked into the compressor (2) with the aid of electrical energy, where it is strongly compressed. This increases the pressure and the refrigerant is brought to a much higher temperature level.

Figure 6: reversed carnot cycle Step 2: Compression

In the T-s and p-v diagrams the distance A to B is described. In the T-s diagram, we can see that the temperature of the refrigerant increases during compression and no entropy is transferred. In the p-v diagram, the pressure increases and the volume of the refrigerant decreases slightly. This process is called isentropic (or adiabatic) compression.

Figure 7: T-s and p-v diagram in the reversed carnot cycle - Step 2 - Compression — Figure 7: T-s and p-v diagram in the reversed carnot cycle – Step 2 – Compression

Isentropic compression
⇨ Refrigerant is compressed in the compressor using electrical energy, which increases the temperature and pressure.
⇨ p-v diagram: Volume decreases slightly, pressure increases.
⇨ T-s diagram: temperature increases, no entropy transfer

Step 3 – Condensation of the refrigerant

In the third step, the high-temperature gaseous refrigerant enters the condenser (3), which is also a heat exchanger. Warm outside air (7) is drawn in via the condenser, which has a much lower temperature than the heated refrigerant even at high outside temperatures. This allows the refrigerant in the condenser to release heat energy to the outside air. Heat therefore flows again from a higher temperature level to a lower temperature level.

By releasing thermal energy to the outside air, the refrigerant changes its state of aggregation again and condenses. The very warm exhaust air (8) (approx. 50 – 60 °C) is discharged to the environment via a fan.

Figure 8: reversed carnot cycle step 3: condensation

In the T-s and p-v diagrams the distance B to C is described. In the T-s diagram we can see that the temperature of the refrigerant remains constant during condensation and the entropy transferred is negative (Can only be done in a reversible cycle!), since the refrigerant returns to its initial aggregate state. In the p-V diagram, the pressure increases slightly and the volume decreases, since liquids require less volume than gases. This process operation is called isothermal compression.

Figure 9: T-s and p-v diagram in the reversed carnot cycle - step 2 - condensation — Figure 9: T-s and p-v diagram in the reversed carnot cycle – step 2 – condensation

Isothermal compression
⇨ Refrigerant in the condenser gives off heat to the incoming outdoor air and condenses.
⇨ Heated exhaust air is discharged to the environment.
⇨ p-v diagram: Volume decreases, pressure increases slightly,
⇨ T-s diagram: temperature constant, entropy difference $\Delta$ S < 0

Step 4 – Expansion of the refrigerant

In the fourth step, the liquid refrigerant, which is still at high pressure and temperature, passes through the expansion valve (4). This expands the refrigerant and returns it to its initial pressure and temperature. The cycle can now start again from the beginning.

Figure 10: reversed carnot cycle Step 4: Expansion

In the T-s and p-v diagrams the distance C to D is described. In the T-s diagram we can see that the temperature of the refrigerant decreases after passing the expansion valve and no entropy is transferred. In the p-V diagram, the pressure decreases and the volume increases a little. This process is called isentropic (or adiabatic) expansion.

Figure 11: T-s and p-v diagram in the reversed carnot cycle - Step 2 - Expansion — Figure 11: T-s and p-v diagram in the reversed carnot cycle – Step 2 – Expansion

Isentropic expansion
⇨ Refrigerant passes the expansion valve and the temperature and pressure decrease.
⇨ p-v diagram: volume increases slightly, pressure decreases,
⇨ T-s diagram: temperature decreases, no entropy transfer.

The real cycle of a refrigerating machine

For the theoretical explanation of a refrigeration compressor, the reversed Carnot cycle is excellently suited. However, the real cycle of a refrigeration compressor looks somewhat different, since the thermodynamic processes are very complex. For simplification, the real refrigeration cycle is shown in a log p, h diagram. In a log p, h diagram, the various state variables of the refrigerant can be represented graphically as a function of pressure and heat. I would like to refer you to an excellent article by gunt on the basic knowledge of the refrigeration cycle process, in which the log p, h diagram is explained in detail. In the following figure you can see a log p, h diagram for the refrigerant R134a.

R 134a phdia a3 rp | Building Services Tutor — Figure 12: “Log-p-h-Diagramm R 134a mit beschrifteten Isolinien” by Reiner Mayers. Licence: CC BY-SA 4.0

Types of portable air conditioners

Portable air conditioner without exhaust hose (fan with water cooling)

No products found.The marketing gurus of these days are back in their prime, with “portable air conditioners without an exhaust hose” being touted as inexpensive and energy-efficient ways to cool a room. I have only included these types of units in this article because they are being touted as “portable air conditioners” in many stores.

Important: Portable air conditioners without an exhaust hose are not air conditioners with a closed refrigeration cycle, but fans with water cooling. Here, the form of evaporative cooling is utilized. A cooling capacity as by a monobloc or split air conditioner will never be achieved with these devices. If you want to save your money here, you can also build such a device yourself. There are many video tutorials on the Internet. Here is one from American Tech:

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Similar to what is shown in the video by American Tech, the following products are also fans with water cooling:

Preview	Product	Price
	Manwe Mobile Klimageräte Mini Luftkühler Klimaanlage Persönliche Air Cooler USB...		Go to shop*

* Affiliate Link - Last updated prices on 2025-01-26 / Picture source: Amazon affiliate program

Portable monobloc air conditioner with exhaust hose

Portable air conditioner with single hose technology

No products found.Portable air conditioners with single-hose technology are almost predominantly offered today. The air conditioner draws in room air (5), cools it down and distributes the cooled air into the room via a fan (6). The resulting waste heat (8) is conducted to the outside through a window or door via an exhaust air hose (9).

In order for the condensation process to take place in the condenser (3), air is drawn in from the room at the condenser (7). This creates a negative pressure in the room, since the air that is blown out of the room must also flow back in. This is usually done through a door or window from a neighboring room (11).

Figure 13: Functional sketch: Portable monobloc air conditioner with single hose technology

Below you will find examples of portable monoblock air conditioners with single hose technology:

Preview	Product	Price
	Argo ORION PLUS Portable air conditioner, 230 V, Wei*		Go to shop*

* Affiliate Link - Last updated prices on 2025-01-26 / Picture source: Amazon affiliate program

Portable air conditioner with two-hose technology

Portable air conditioners with two-hose technology are hard to find today, although they run more efficiently. For its function, the air conditioner also draws in room air (5), cools it down and also distributes the cooled air into the room via a fan (6). The resulting waste heat (8) is conducted outside through a window or door via an exhaust air hose (10).

In order for the condensation process to take place in the condenser (3), outside air (7) is drawn in (9) at the condenser via a second hose, the outside air hose. This means that there is no negative pressure in the room, as the air that is blown out of the room is drawn in from the outside air.

With the two-hose technology, there is thus a system separation between the air above the evaporator and the air above the condenser. In the technical sense, a two-hose unit is a circulating air cooling unit. This means that no fresh outside air flows in.

Figure 1: Functional sketch - Portable monoblock air conditioner with two-hose technology — Figure 14: Functional sketch: Portable monobloc air conditioner with two-hose technology

Below you will find examples of portable monobloc air conditioners with two-hose technology:

Preview	Product	Price
	TROTEC Lokale Klimaanlage PAC 3550 Pro mit 3,5 kW (12.000 Btu), EEK A zugfreie Kühlung des Raumes...		Go to shop*

* Affiliate Link - Last updated prices on 2025-01-26 / Picture source: Amazon affiliate program

Comparison: single-hose technology or two-hose technology

Which is better? A portable air conditioner with single-hose technology or a portable air conditioner with two-hose technology?

The question of whether a single-hose air conditioner or a two-hose air conditioner is better is discussed in many forums and comments. Unfortunately, a lot of misinformation is spread. For this reason, I would like to explain briefly why a portable air conditioner with two hoses is better and more efficient than a single-hose air conditioner.

As I described in the section on the reversed carnot cycle, in a two-hose air conditioning system the outside air is used directly for the condensation process via the condenser and the heated exhaust air is transported directly outside. There is therefore a system separation between the air above the evaporator and the air above the condenser. The principle is therefore similar to that of a split air conditioner, where the outdoor unit with condenser is installed outside the building.

The single-hose air conditioner, on the other hand, uses the room air for the condensation process in the condenser and thus creates a negative pressure in the room. This means that this air must flow in from somewhere. The air cooled by the portable air conditioner therefore mixes with the warm air flowing in, so that the air drawn in via the evaporator of the air conditioner is warmer than with a two-hose air conditioner.

In the report “Effectiveness of mobile air conditioners”(article only in german) by the Federal Institute for Occupational Safety and Health Germany (baua), measurements showed that with a single-hose unit, the cooling air drawn in from the room for the condenser is as high as the air that has to flow in through the windows and doors. This means that on warm days almost the entire cooling capacity is needed to cool the air flowing in. The baua has therefore named the single-hose unit “ventilation unit with low cooling function”. A portable air conditioner with two-hose technology therefore runs more efficiently!

My advice: Make sure you convert your single-hose air conditioner into a two-hose air conditioner. It’s easy and you don’t need many components. Below you will find a small instruction:

Modification of portable air conditioner to two-hose technology

You don’t need much to convert your portable air conditioner with single-hose technology to a two-hose air conditioner:

an old cardboard box
a scissor
parcel tape
a connector for the ventilation pipe
a ventilation pipe with connecting clips

Product	Price
Westcott E-30283 00 Easy Grip Softgrip Schere, rostfreie Klingen, blau-schwarzer Kunststoff-Griff,...	2,99 EUR 2,45 EUR	Go to shop*
tesapack Ultra Strong - PVC-Klebebänder für festes Verpacken und sicheres Bündeln - Braun - 66 m...	9,01 EUR	Go to shop*
ABS Lüftungsrohrverbinder, Rundrohr Ø 150, Abgangsrohr Awenta 150 mm, PVC ...*	9,49 EUR	Go to shop*
Intelmann Alu Flexrohr 150mm, Länge 3m + 2 Edelstahl Schlauchschellen*	16,06 EUR	Go to shop*

* Affiliate Link - Last updated prices on 2025-01-26 / Picture source: Amazon affiliate program

Step 1: In the first step, hold the box against the air supply grille for the condenser. This is usually located at the back in the lower part of the air conditioner. There you look at how you need to cut the box to cover the area completely.

Then use the ventilation pipe to draw a suitable hole on the back of the box where the connector for the ventilation pipe will later be inserted. Now cut out everything. You can now insert the connecting pipe into the hole and fix it with parcel tape. Afterwards, I taped and reinforced all the corners and edges as well as weak points with the parcel tape.

I had to extend the red dotted line with cardboard afterwards, because the distance from the box to the air conditioner was too small. In my case it looked like this.

Modification of portable air conditioner to two-hose technology - Cut and extend cardboard box

Modification of portable air conditioner to two-hose technology - Cut cardboard to size

Modification portable air conditioner - Fasten connector for ventilation pipe - 01

Modification portable air conditioner - Fasten connector for ventilation pipe - 02

Modification portable air conditioner - Fasten connector for ventilation pipe - 03

Modification portable air conditioner - Fasten connector for ventilation pipe - 04

Step 2: The box can then be attached to the portable air conditioner. Here, make sure that the entire intake grille for the condenser is under the box. The actual conversion from a single-hose air conditioner to a two-hose air conditioner is now complete. Next, connect the flex hoses to the portable air conditioner.

Modification portable air conditioner - Finished two-hose air conditioner - 01

Modification portable air conditioner - Finished two-hose air conditioner - 02

Step 3: Attaching the flex hoses was not quite as easy as I thought at first. However, with a bit of tinkering and patience it worked well. After everything is in place, you can hang the flex tubes out of your window or door.

Modification portable air conditioner - Attach hoses to portable air conditioner 01

Modification portable air conditioner - Attach hoses to portable air conditioner 02

Modification portable air conditioner - Attach hoses to portable air conditioner 03

Modification portable air conditioner - Attach hoses to portable air conditioner 04

Window sealing for portable air conditioner

Modification portable air conditioner - Ready-made two-hose air conditioner with hoses

Modification portable air conditioner - Ready-made two-hose air conditioner - Hoses out of the window

Modification portable air conditioner - Ready-made two-hose air conditioner - Hoses out of the window 02

Note: A window seal for Portable air conditioners to attach to doors, windows or skylights is almost never included and must be purchased separately. I chose the HOOMEE window seal* because it is also suitable for roof windows.

Window sealing is mandatory, as it greatly reduces the backflow of warm outside air into the air-conditioned interior and diverts the warm air from the air-conditioning unit to the outside via the exhaust air hose.

Preview	Product	Price
	HOOMEE Fensterabdichtung für Mobile Klimageräte, Wäschetrockner, Ablufttrockner, Hot Air Stop zum...	21,99 EUR	Go to shop*
	REDTRON Fensterabdichtung für Mobile Klimageräte, Klimaanlagen, Wäschetrockner und Ablufttrockner...	12,99 EUR	Go to shop*

* Affiliate Link - Last updated prices on 2025-01-26 / Picture source: Amazon affiliate program

Portable split air conditioner

In a portable split air conditioner, all components are not located in one unit as in a monobloc air conditioner, but there is an indoor unit and an outdoor unit. The evaporator (1) is located in the indoor unit and the condenser (2) in the outdoor unit. This allows a split air conditioner to run more efficiently, as the waste heat produced is always outside the rooms to be cooled. All that is needed is a wall opening through which the cooling lines (9) can be routed.

In the indoor unit of the unit, the room air is drawn in (5), cooled down via the evaporator (1) and distributed as cooled air into the room (6) via a fan (10). In the compressor (2) the refrigerant is compressed and transported to the outdoor unit via the refrigerant pipe (9).

At the outdoor unit, outdoor air (7) is drawn in via the condenser (3), where the refrigerant gives off its heat to the outdoor air and condenses. The very warm exhaust air (8) is then blown away via a fan (10). The condensed refrigerant is transported back to the indoor unit via the refrigerant pipe. There the refrigerant passes the expansion valve (4), expands and the cycle starts again.

In the technical sense, a portable air conditioner is a circulating air cooling unit, because no fresh outside air flows into the building.

Figure 16: Functional sketch: Portable split air conditioner

Today, portable split air conditioners are mainly used in industry or on construction sites, as they are very cost-intensive to purchase. They are mainly used when small areas need to be cooled for a short period of time until a permanently installed solution is ready for operation.

Examples of portable split air conditioners:

Product	Price
REMKO RKL 495 DC - lokales Raumklimagerät - Split-Ausführung, für ca. 120m³, Kühlleistung 4,3...	2.198,75 EUR	Go to shop*
TROTEC Klimaanlage Klimagerät PT 4500 S inkl. Wärmetauscher*		Go to shop*
Krone Ulisse 13 DCI Eco Mobiles Inverter Split-Raumklimagerät 4 kW*	2.033,67 EUR	Go to shop*

* Affiliate Link - Last updated prices on 2025-01-26 / Picture source: Amazon affiliate program

Which portable air conditioner is the right one?

How efficient are portable air conditioners?

Now that we know how the cycle of a refrigeration system works and what types of portable air conditioners there are, we can also ask ourselves the legitimate question of whether a portable air conditioner works efficiently and how much electrical energy a portable air conditioner requires.

The efficiency of a refrigeration compressor is described by the energy efficiency ratio (EER) $\epsilon$ “Epsilon”. The energy efficiency ratio depends on the temperature difference of the refrigerant at the evaporator $T_1$ and at the condenser $T_2$ . The following applies: the smaller the temperature difference, the more efficiently the refrigeration compressor works. Furthermore, the energy efficiency ratio describes the ratio of the thermal power extracted from the room to be cooled $\dot Q_2$ and the electrical power absorbed $P_{el}$ at the compressor.

DeLonghi Pinguino PAC EX100 Silent Energy Label

Calculate energy efficiency of a refrigeration compressor

In a formula, the whole thing looks like this:

$\boxed{\epsilon=\frac{\dot Q_2}{P_{el}} =\frac{T_2}{T_1 - T_2}}$

Example calculation of EER over given data

The easiest way to calculate the EER is to have the data of the unit at hand. For our first example, let’s take a closer look at the De’Longhi Pinguino PAC EX100 SILENT portable air conditioner (review). All the important energy data and the EER are given for the unit on the energy label. But what happens if one of the specifications is missing? Quite simple, we calculate it 🙂

Given:

EER $\epsilon$ : 3,6
$\dot Q_2$ (heat output extracted from the room): 2,5 kW
$P_{el}$ (max electrical power consumption): 700 W

$\boxed{\epsilon=\frac{\dot Q_2}{P_{el}}}$

Searched:

It is assumed that one of the given values is missing. Calculate EER, $\dot Q_2$ and $P_{el}$ respectively.

Solution:

Searched: EER $\epsilon$	Searched: $\dot Q_2$	Searched: $P_{el}$
EER = $\dot Q_2$ / $P_{el}$ EER = 2,5 kW / 0,7 kW EER = 3,57	$\dot Q_2$ = EER * $P_{el}$ $\dot Q_2$ = 3,57 * 0,7 kW $\dot Q_2$ = 2,5 kW	$P_{el}$ = $\dot Q_2$ / $\epsilon_{KM}$ $P_{el}$ = 2,5 kW / 3,57 $P_{el}$ = 0,7 kW

Note: This example is an excellent way to see what the energy efficiency ratio expresses. If the EER of a refrigeration compressor is EER = 3.6, means for the use of 1 kWh of electrical energy, 3.6 kWh of thermal energy are drawn from the room to be cooled. The higher the EER, the more efficient the system.

Example calculation Determine EER via temperatures

If we now want to calculate the energy efficiency ratio based on the temperatures, we can determine the theoretical maximum energy efficiency ratio of the refrigeration compressor at the time of the temperature measurement. What is much better, however, is that we can visualise possible losses in the real refrigeration process of a mobile refrigeration compressor.

For this we take the real measured room temperature of T2 = 26.2 °C, which is drawn in via the evaporator. The measured exhaust air via the exhaust air hose is at T2 = 50.4 °C at the outlet. Here I would say that the real temperature directly at the evaporator is much higher and we can add at least 10 Kelvin. T2 would therefore be approx. 60.4 °C. I measured the temperatures with an Testo 605-H1* Thermo-Hygrometer .

Figure 17: Temperature measurement at the evaporator and exhaust air pipe

Given:

EER $\epsilon$ : 3,57
T1 = 60,4 °C = 333,55 K (273,15 + 60,4)
T2 = 26,2 °C = 299,35 K (273,15 + 26,2)

$\boxed{\epsilon=\frac{T_2}{T_1 - T_2}}$

Searched:

What is the theoretical maximum energy efficiency ratio of the portable air conditioner?
What is the degree of utilisation of the electrical energy used?

Solution:

With our formula, we can determine the energy efficiency ratio quite easily. The temperatures are given in Kelvin.

$\epsilon=\frac{T_2}{T_1 - T_2}=\frac{299,35 K}{34,2 K}=8,75$

The determined energy efficiency ratio in this cycle is thus 8.75, which, however, differs greatly from De’Longhi’s stated energy efficiency ratio (3.6, calculated 3.57). With an energy efficiency ratio of 8.75, we would only need 0.28 kW instead of the required 0.7 kW of electrical power.

However, since our portable air conditioner is not an ideal refrigeration compressor, there are again losses that we have to take into account. To calculate the degree of utilisation of the electrical energy, we therefore take the previously determined energy efficiency ratios and put them into relation.

$\eta=\frac{EER_{real}}{EER_{max}}=\frac{3,57}{8,75}=0,4285$

The utilisation rate is thus just 42.85 %!

Based on this calculation, we can see that there are losses during heat transfer and the process operations as well as the conversion of electrical energy into mechanical work at the compressor, which do not benefit the cycle. Thus, only about 30 – 45 % of the electrical energy used can be utilised. These “losses” must be included in the consideration of the EER.

Are portable air conditioners energy efficient? If a unit has an A++ energy label with an EER of 3.6, it is quite efficient compared to other portable air conditioners of the same size (around an EER of 2.5). However, compared to split and full air conditioners, Portable air conditioners perform poorly. Due to the mobility and the low installation effort, major compromises are made here at the expense of energy efficiency. In my opinion, portable air conditioners are therefore not among the most energy-efficient devices.

Simplified cooling load calculation for your room

The cooling capacity of the air conditioner is the decisive factor for the purchase of a portable air conditioner and should at least correspond to the heat load in your room. This heat load is also called the cooling load.

You can use the following form to roughly calculate the cooling load for your room. The basis for this is the simplified cooling load calculation according to the HEA method. I have transferred this Dimplex data sheet into a form – this is a beta version. I do not guarantee the accuracy of the results, even though I have created the form to the best of my knowledge.

Note: The calculation of the cooling load is regulated in Germany by VDI 2078 and is a very complex calculation procedure. The cooling load is the sum of all heat loads generated in the room, e.g. by solar radiation, electrical devices and living beings, which must be dissipated from the room in order to maintain a desired air temperature. This heat load must be dissipated by the portable air conditioner.

The values given from the HEA method are determined in accordance with VDI 2078 “Cooling load rules”. A room air temperature of 27 °C with an outside air temperature of 32 °C and continuous operation of the cooling unit is taken as a basis.

Call: I’m asking for your help here, so that the form can be expanded or improved if necessary. If you notice any errors or inconsistencies, please leave a comment and I will adjust the form.