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Quick calculation of the required cooling capacity for living and office spaces

Important information on the cooling of entire flats:

In most cases, individual rooms are no larger than 50 m². And the calculated cooling capacity of e.g. 65 m² cannot simply be used for a flat sized 65 m² consisting of several rooms.

The air conditioning system can in fact manage a cooling capacity for the entire flat's room volume, but only provided a thorough air circulation.

In simplified terms, the cold air produced by the air conditioning system is much heavier than the warmer room air. Therefore, the cold air is only to be found wherever the fan can transport it to.

And this kind of homogenous air distribution in several rooms cannot be achieved by an air conditioner. Depending on the position (air flow direction) a certain degree of cooling will take place in the adjoining room, but there will be hardly any noticeable cooling in rooms further away.

Hence, it is important that the air conditioning system is provided with a powerful radial fan with an adjustable flow direction. In contrast to axial fans, radial fans have the advantage that the heavy cold air can be transported much further with momentum.

For this reason, the models of the PAC series are equipped with an extremely powerful radial fan. The infinitely variable air guide can be directed diagonally upwards and the cold air will be widely distributed even into adjoining rooms.

Quick calculation of the required cooling capacity for living and office spaces

How much power is required to cool a room? The rule of thumb: Every cubic metre of room volume requires a cooling capacity of 30 watts.

According to this rule of thumb, the required cooling capacity can quickly and easily be determined, as can be seen from the following example calculation with a room's floor space of 35 m² and a ceiling height of 2.5 m:

35 m² x 2.5 m ceiling height =
87.5 m³ cubature x 30 watts =
2,625 watts

This is only a rough calculation formula for typical living and office spaces. The required cooling capacity further depends on the room's "thermal load": insolation, insulation, the number of persons and heat sources also play a role in the selection of an air conditioner.

Exception attic flats:

In attic rooms it is more difficult to determine the precise cooling capacity, since the user often doesn't know about the exact roof insulation. Which is why we recommend adding ten per cent to the determined cooling capacity for good measure, especially in old buildings. Experience has shown that one can take a power of 50 to 60 watts per cubic metre room air as a basis. In case of very poorly insulated roofs and many skylights, still more.

Practical knowledge of cooling techniques: functional principles and technological differences at a glance

Monobloc or split unit, one-hose or two-hose technology, evaporation cooler or refrigeration system? If you are looking for the ideal device to provide refreshingly cold air in rooms with high temperatures, you may easily lose track of things in view of the manifold options and techniques.

First of all: there is no such thing as one and only one optimal technique. As diverse as the parameters such as room size, cooling method, degree of comfort, installation work and, of course, budget may be, as particular can the individual perfect solution be.


It is for this very reason that Trotec has numerous high-quality devices working on different cooling techniques available for you. This way you will always find the device suitable for your personal requirements and benefit from the best value-for-money ratio offered by a leading brand supplier!

Mobile air conditioning systems – convenient refrigeration systems

Some basics about cooling technology for a better understanding: Unlike air coolers, all air conditioners of our PAC series cool the room air with the help of a powerful compression refrigeration system. A refrigerant is led through two heat exchangers – a condenser and an evaporator. By means of a compressor and an expansion valve, the refrigerant is exposed to changing pressures within this closed circuit, which results in the gas heating up during compression and cooling down during decompression. The heat is discharged to the outside at the condenser, and the cold is blown into the room at the evaporator.

Dehumidification at the same time

Since the air can cool down to below its dew point at the evaporator, humidity contained in the air condenses simultaneously. This means that the air is not only cooled but also dehumidified, which promotes personal well-being and creates a more pleasant room climate, since stuffy humid air is generally perceived as unpleasant.

Depending on the construction, these refrigeration systems are available from Trotec as split or monobloc air conditioners, the latter with either one-hose or two-hose technology.



Functional principle compression refrigeration system

In split devices such as the PAC 4600 the condenser (external unit) and the evaporator (internal unit) are constructively separated.

The external unit positioned on a balcony, terrace or outdoors is connected to the air conditioner via a connection line without requiring an exhaust air hose.

Split devices do require slightly more installation work for connecting the external and internal unit, but they work agreeably efficiently and in pressure-tolerant recirculation mode. Moreover, they are pleasantly quiet as the more noisy compressor is integrated in the external unit.

Functional principle split air conditioner

Monobloc air conditioners with one-hose technology

This is the most common type of construction of Trotec's PAC air conditioners. The entire technology is integrated space-savingly into the housing and the process-related hot air is discharged to the outside by means of a central exhaust air hose through a window or door gap – that's why it is referred to as one-hose technology.

The permanent discharge of warm air creates a slight underpressure, which evens out by trailing warm air from outside and adjacent rooms. The positive effect is that this way the room is continuously supplied with fresh air. This also means, though, that approx. 20 % of the energy can be lost.

Monobloc devices with one-hose technology score in particular with their advantageous combination of powerful cooling and extremely easy handling. They can be conveniently and flexibly put into operation in different rooms.

Monobloc with one-hose technology

Monobloc air conditioners with two-hose technology

As with one-hose devices, the process-related hot air is discharged to the outside through an exhaust air hose, but additionally, the device is supplied with the same amount of fresh air via a second hose.

In contrast to one-hose devices, this allows for pressure-tolerant recirculation operation without trailing warm air from outside, which makes these devices more efficient but also requires slightly more installation work.

Monobloc with two-hose technology

Adiabatic cooling with mobile air coolers

Diagram adiabatic cooling

Air coolers like the PAE 25 from Trotec are direct air coolers and, unlike PAC air conditioners, do not have an integrated cooling unit but cool the room air using the natural principle of water evaporation, which is also referred to as adiabatic cooling. Everyone knows this cooling effect, for example from sweat evaporation or cooler air in the vicinity of water falls, rivers and lakes.

The physical principle in short: In order to evaporate, the water requires energy. This energy is extracted from the ambient air in the form of heat, which makes the air cooler. It is important to note that the energy stored in our room air can be divided into sensible (or perceptible) heat and latent (i.e. hidden) heat.

The interesting thing is that only the sensible heat is temperature-relevant and can be measured with a thermometer. Since this sensible heat is consumed during evaporation and then stored as latent energy in the water vapour contained in the air, the adiabatic cooling method is an entirely natural and moreover cost-effective cooling method requiring no external energy for the cooling process. In practice, however, it is more suitable for smaller rooms, as the effective radius of adiabatic cooling units cannot be increased as easily as in case of high-performance compression refrigeration systems.

Unlike industrially used passive coolers, almost all air coolers available for private use are based on the principle of direct cooling – which means that they directly feed moisture into the incoming air. Therefore no additional process air discharge is required, which on the one hand makes the devices extremely easy to handle since they only have to be set up and switched on, but on the other hand also increases the room humidity level.

Air coolers operate the most efficiently in rooms containing rather dry air and they can only reduce the temperature until reaching the air saturation limit, for example from 25 °C/50 % RH to a theoretical value of maximally 18 °C/98 % RH. In the case of air coolers for private use, the efficiency level is in practice lower and depends on various factors such as the fan performance and the surface of the evaporation filter. As can be read from the theoretical example values, the use of direct coolers simultaneously causes the humidity level in the room to rise perceptibly for process-related reasons, which is not always desirable. An increasing humidity level also reduces the devices' cooling capacity.

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