Air conditioner power consumption. Selection of air conditioner based on cooling capacity and cooling power

How much does the air conditioner consume? We are concerned about this issue. Because on warm summer days you don’t want to receive electricity bills equal to winter heating bills. To prevent the summer heat from causing a black hole to form in the family budget, you need to know what the power consumption of an air conditioner is. If you don’t know, then at least have an idea of how much energy an air conditioner consumes and what it depends on.

Air conditioner consumption

What does the air conditioner consume:

Refrigerant– this is not interesting to us;
Air– ordinary air from the room is also uninteresting;
Electricity- but this is exactly what we need.

If there is no electrician within a radius of 10 meters, then let’s figure out what the power of the air conditioner is and how it differs from the power consumption.

Air conditioner energy consumption, like any other device, is measured in watts (W), 1 thousand W is one kW. If an air conditioner with a power consumption of 1 kW runs for 1 hour, you will have to pay for 1 kW/hour. The cost of 1 kW can be found in your electricity payment receipt.

Power (cooling power). It so happens that the “power” of an air conditioner is also measured in kW - this is how much heat the air conditioner will remove from the room in an hour. These techies don’t care about humanists at all. So we go into the store and see a 4 kW (4 thousand watt) air conditioner. Yes, that’s 20 rubles per hour (if the price for 1 kW is 5 rubles), and for a day 480 rubles! Stop. Let's figure it out.

Power is always 3-4 times higher than energy consumption, add to this the fact that the colder the air, the less energy the air conditioner consumes. On the sunny side it burns more kW, where greater efforts must be made to cool the air.

In stores they show us its maximum power. This is done for marketing purposes. But the air conditioner does not work at its maximum capacity all the time. The difference between the maximum operating power and the energy consumed is the air conditioner's energy efficiency (EER).

What does all of this mean? A 4000 watt air conditioner can be highly energy efficient. This will make it less expensive than a 2500 watt alternative with low energy efficiency.

EER and COP coefficients

We entered the store and already heard: “Can I help you?” Feel free to ask, which air conditioner has more EER? High energy efficiency allows you to save on electricity. The smaller the room and the temperature, the faster an air conditioner with a high EER will cool it. But don't cool the street!

Air conditioner power- this is the main indicator, and the “4000 watts” code gives us little information. Don't forget about the size of the room. The larger the room, the more powerful the air conditioner is needed. If the room is small, then a weak air conditioner with a low EER is sufficient.

What is COP? Modern air conditioners can act as a heater. The difference between the heating power and the energy consumed is COP.

If in Russian, then this is the efficiency factor. The higher it is, the better. After all, it will take less time to heat the room to a certain temperature. Thanks to this, less electricity will be consumed - you will spend less money on heating, but you do not need to heat the street.

How does all this affect your wallet?

We've covered EER, COP and air conditioning power, but how do you apply it all? Our problems: the room is hot or cold, since utility companies have their own plans for heating. Factors to consider: size and thermal load of the room (sunny side or not, glass area, floor, etc.). The task: to choose an air conditioner that can cool the room as efficiently as possible in the shortest possible time.

If the room is 25 m2 Buy an air conditioner with a cooling efficiency (EER) of 2 kW, then it will cool the room for a long time. If the room is on the sunny side, then the situation will worsen many times over. A situation may arise that the air conditioner threshes all day long at the limit of its capabilities, and the electric meter turns up tens of kW.

To prevent this from happening, a more powerful cooling device is needed. 2.7 kW or 3 kW - if your windows face south and are not in the shade. There is no need to think about heating, because if you choose the right cooling coefficient, then COP will also be sufficient. Manufacturers often make the heating power a little higher.

Can't find an air conditioner yourself? Then contact the specialists. A stingy person pays a lot for electricity - here, as with energy-saving light bulbs: it is better to spend money first, and then recoup the investment.

Or, more precisely, the cooling capacity of the air conditioner. The amount of heat that an air conditioner removes from a room per unit of time. The power of the air conditioner should not be confused with the electrical power consumed. Consumed - spent on transferring a certain amount of heat from the room to the street. The cooling capacity of an air conditioner is on average 3 times higher than the power consumption. There is no violation of the law of conservation of energy here, because the air conditioner does not absorb heat from the room, but transfers it to the street.

This, by the way, explains the funny fact that an air conditioner operating in heat pump mode is a very efficient heater. For 1 kW of electrical power expended, the air conditioner creates a heating power of more than 3 kW. Even more funny is that the heating capacity of an air conditioner with a reversible compressor is higher than its cooling capacity. Heat is simply easier to transfer from one place to another than cold.

To indicate the rated power of an air conditioner, BTU is traditionally used - British thermal unit, equal to 0.293 watts. Air conditioner power ratings are often multiples of 1000 BTU. Additionally, the cooling capacity in BTUs is almost always indicated on the air conditioner label. For example, an air conditioner with a rated cooling capacity of 9000 BTU is labeled with the numbers “9” or “09”. Experts usually call it, respectively, “nine”. We will tell you more about the model ranges of air conditioners and their rated capacities below.

1000 BTU = 293 Watts = 0.293 kW

Principles for calculating air conditioner power

The first and main factor that is important when calculating the power of an air conditioner:

The power of the air conditioner is calculated for an already cooled room, and not for a hot one

This may sound a little strange at first glance, but the explanation is very simple.

There is a hot room, the air conditioner has started to cool it. For now, we consider the temperature outside to be constant (peak heat).
As the indoor air cools heat flow increases inside the room. We will explain further where the heat gain comes from and how it is calculated. It is important that most of the heat inflow is directly proportional to the difference between the external and internal temperatures (tн - tв)
As the room cools, it becomes more and more difficult for the air conditioner to remove excess heat (heat gain constantly increases), and equilibrium gradually comes between the flow of heat into the room and its removal using an air conditioner.
The required power of the air conditioner is thus equal in absolute value to the heat flow into the already cooled room. At the same time, the air conditioner “copes with its direct responsibilities” - it’s hot outside, but inside the room it’s a welcome 18C.
The required cooling capacity of an air conditioner should not be confused with room cooling rate(by how many degrees does a hot room cool down in an hour). These are different things. In any case, we cannot rely on the cooling rate when calculating the power of the air conditioner, because we will not get the correct answer.
You should always select an air conditioner with a power close to optimal. An air conditioner that is too powerful will be forced to constantly turn on and off to maintain a comfortable temperature. And the number of stop/start cycles is critical to the life of the air conditioning compressor (the fewer, the better).
All other things being equal, you need to choose air conditioner with frequency converter (inverter), because instead of turning the compressor on/off, smooth control of its power is used. A compressor connected to the electrical network (and, as you know, has a constant frequency) has only two power levels - on and off. The fact is that speed control is the only acceptable way to change the power of an air conditioning compressor.

So:

Optimal power air conditioner equal in magnitude to the heat flow into an already cooled room on a hot (and sunny) day, with the estimated maximum number of people in the room, with actively used equipment, and frequently opened doors.
Rated power the installed air conditioner should be as close as possible to optimal power
It is better to choose an air conditioner with an inverter , because it operates over a wider power range and with a very low number of compressor stops/starts.

Sequence for calculating the power of the air conditioner:

We calculate the maximum heat flow into the cooled room
The optimal power is equal in magnitude to the heat gain
From the range of air conditioners with discrete nominal powers choose the one whose power is greater than or equal to the optimal power

Approximate calculation of air conditioner power

When approximately calculating the power of the air conditioner, you should be guided by the following basic rules:

For cooling 10 sq.m. area requires 1 kW cooling power
You should never calculate the power of your air conditioner yourself. The calculation of heat inflows must be carried out by a specialist. This service is free from any self-respecting climate control company.

Exactly. Despite the fact that the rated power of the air conditioner is a discrete value (7, 9, 12, 18, 24, etc. thousand BTU), and it would seem that no special accuracy is required. The fact is that the rule “per 10 sq.m - 1 kW” is an average value for an average room. That is, the average temperature in the hospital. But the rooms are all different. And a non-specialist will simply miss a couple of important factors, and will be mistaken, say, twice as much.

The heat flow, and therefore the optimal power of the air conditioner, depends only indirectly on the area of the room. When accurately calculating power, all methods of supplying heat to the room are carefully and in order, for each method its thermal power is calculated, and the resulting values are added up. The approximate calculation rule, therefore, gives good results in such cases as the average room in an apartment and the average office in an office, but in other cases it lies.

Model ranges of air conditioners by power

Various air conditioner manufacturers have a tradition, practically unbroken, of building model lines of household air conditioners from very specific rated power values. These values are multiples of 1000 BTU.

Air conditioner type	Standard Powers	Non-standard capacities
Wall split systems	7, 9, 12, 18, 24	8, 10, 13, 28, 30, 36
Floor mobile	7, 9, 12
Window	5, 7, 9, 12, 18, 24
Cassette	18, 24, 28, 36, 48, 60	28, 34, 43, 50, 54
Floor-ceiling	18, 24, 28, 36, 48, 60	28, 34, 43, 50, 54
Columned	30, 50, 80
Duct	12 ÷ 200 and above

As you can easily notice, each type of air conditioner has its own “ecological niche” in the power range. This is, in general, not accidental. The choice of the range and specific values of rated power is determined by three factors:

In what area of premises are air conditioners of this type usually installed?
How small is required to set the power step (selection accuracy)
It is more profitable for the manufacturer to produce as few items as possible (standardization)

Wall-mounted air conditioners: installed in small and medium-sized rooms, high selection accuracy is desirable, the highest demand. The range of rated powers is 7-24 thousand BTU, but a large number of gradations. Column air conditioners, on the contrary, are installed in large rooms (restaurant, station hall). And here everything looks the other way around: a high degree of standardization and high power.

Accurate calculation of air conditioner power

Calculation of the rated power of the air conditioner = calculation of heat gain

The method for calculating heat gain consists of carefully summing up the thermal power along all paths and methods of heat entering the room:

Heat gain from heat transfer - through walls, floor and ceiling
Heat gain from solar radiation through the roof
Heat gain from solar radiation through walls
Heat gain from ventilation
Heat gain from people's presence
Heat gain from mechanical equipment
Heat gain from heat generating and electronic equipment
Heat gain when opening doors
Heat gain from lighting

Many of the ways of heat entry are directly proportional to the difference between the external and internal temperatures tн - tв. For simplicity, we will designate it as “temperature difference”. For each heat gain component, there is a default temperature difference value, obtained from the difference between the average temperature on a hot day (30.5C) and the comfortable temperature (20C). All coefficients used in calculations are pre-calculated table values.

Calculation of heat gain from heat transfer through walls, floors and ceilings

"surface area" *
"temperature difference"
The thermal conductivity coefficient is high, for example, for concrete (~2), lower for brick, and very low for sandwich panels (~0.25). Therefore, a good specialist, when calculating an air conditioner for you, will always mention the importance of thermal insulation.
Default temperature difference 10.5 = 30.5 - 20

Calculation of heat gain from solar radiation through the roof

"thermal conductivity coefficient of the material" *
"surface area" *
"temperature difference"
Default temperature difference 18.5 = 38.5 - 20 (roof gets hotter)

Calculation of heat gain from solar radiation through walls

The individual terms look like:
"thermal conductivity coefficient of the material" *
"surface area" *
"temperature difference" *
"correction factor"
The surface area of the walls is counted together with the windows. With other calculation methods this is not the case, that is, walls and windows are considered separately. We assume that when exposed to direct sunlight, curtains or blinds are used, simply because direct sunlight through a window is too strong a heat load; no air conditioner can handle it. Even more important is that we do not consider the maximum power of the air conditioner, but the optimal one, so we assume that the windows are closed and curtained on the sunny side.
Correction factor - table value. Depends on the orientation of the wall to the cardinal points (S, SE, SW, E, W, NE, NW) and on the material of the wall surface (concrete, brick, whitewash, white tiles, etc.).

Calculation of heat gain from ventilation

"Amount of air" *
"Temperature difference" * 1.2
1.2 - coefficient taking into account the heat capacity of air
The amount of air is calculated in cubic meters/hour
Default temperature difference - 10.5C

Calculation of heat gain from people's presence

The terms look like:
"Activity type coefficient" *
"Number of People"
Activity type factor:
- Active - 200
- Medium activity - 150
- Low activity - 100

Calculation of heat gain from mechanical equipment

"Total electrical power consumption" *
"Number of devices" * 0.5 * 0.6
0.5 - coefficient of conversion of mechanical energy into thermal energy. That is, on average for mechanical equipment, out of 1 kW of power consumption, 0.5 kW turns into heat
0.6 - simultaneity coefficient. That is, on average, 60% of mechanical equipment is working at any given time. This coefficient should be adjusted taking into account the individual characteristics of equipment operation.

Calculation of heat gain from heat-generating and electronic equipment

Heat gain from heat-generating (heating) and electronic equipment equal to electrical power consumption. That is, all the power consumed by a TV, computer, monitor, printer, copier, etc. turns into heat completely.

Calculation of heat gain from opening doors

"Total door area" *
"Coefficient of room area"
The larger the area of the room, the less heat gain from opening the doors. For approximate calculations, this coefficient can be taken equal to:
- 47 - for rooms up to 50 sq.m.
- 23 - for rooms from 50 to 150 sq.m.
- 12 - for premises from 150 sq.m.

Calculation of heat gain from electric lighting

"Room area" * 4.5
4.5 is a coefficient that takes into account heat loss from light bulbs that create normal lighting.

The first and main technical characteristic that people pay attention to when purchasing any air conditioner is its power. A distinction must be made between power consumption and performance in cooling and heating modes. The second indicator, speaking conventionally, is interpreted as the amount of cold or heat that the climate control device produces in a certain unit of time. This value is usually indicated either in kW or in thousands of Btu/hour. This is how they choose the power of the air conditioner when making a purchase.

Power consumption and cooling capacity

Power consumption is the consumption of electricity per unit of time (also in kW). The energy consumed is spent on removing some heat from the room to the outside. The magnitude of the cooling capacity is usually several times higher than the power consumption precisely because the heat is not absorbed by the device, but is removed to the street.

Through the total ratio of these two quantities, one can judge the energy efficiency (EER) of the air conditioner, that is, its efficiency in terms of energy consumption. Manufacturers distinguish seven energy efficiency classes, among which devices corresponding to class A are considered the most profitable equipment. They spend the least amount of energy on their work. An important indicator in this case will be annual consumption.

But when talking about selecting the power of an air conditioner, experts mean precisely its cooling capacity, the values of which correspond to the total amount of heat from all heat sources in the room.

As already mentioned, this value has two designations: BTU (BTU) and kW. The first is a British thermal unit, corresponding to 0.293 watts. In labeling, different brands indicate this characteristic differently. Typically, rated power values in BTU are multiples of 1000. If the numbers 7 (07), 9 (09), 12, 18 and so on appear in the marking code or technical documentation, then these are the rated power values, where 7 = 7000 BTU, 9=9000 BTU and further down the list. Experts, accordingly, call them “seven”, “nine”, “dvenashka”, “eighteenth”.

Nominal and optimal power of the air conditioner

The rated power refers to the average performance of the air conditioner when operating in cold conditions. But in each individual case it is necessary to calculate the optimal power, which ideally should coincide as much as possible with the first.

Nominal values are selected by manufacturers for each type of cooling device:

Window units usually have the following standard positions: 5, 7, 9, 12, 18, 24;
Wall splits correspond to the following model range: 7, 9, 12, 18, 24. Sometimes some brands produce non-standard models with the following nominal values: 8, 10, 13, 28, 30;
The cassettes go in this order: 18, 24, 28, 36, 48, 60. Non-standard row: 34, 43, 50, 54;
Channel splits begin the power range with model 12 and sometimes end with 200;
Console installations have the following variety: 18, 24, 28, 36, 48, 60. In a non-standard version: 28, 34, 43, 50, 54;
Columns start at 30 and go up to 100 or more.

This list is not accidental. This has already taken into account the selection of an air conditioner and its power based on the area of the room, the height of the ceilings, and the heat flow from household equipment, electric lighting, people, roof and walls, open windows and ventilation.

Power calculation for a household air conditioner

Insufficient optimal power entails the operation of the device in non-stop mode - it will try to reach the required temperature in the room. If there is an excess of optimal power, the air conditioner will operate in constant start/stop mode and produce too strong flows of cooled air, which cannot be distributed normally around the entire perimeter. Both options instantly wear out the compressor.

Ideally, climate control equipment should operate in such a way that there is no unnecessary heat load, since any air conditioner can only compensate for a limited amount of heat.

Having correctly calculated the power of the air conditioner, after reaching the set temperature, the compressor turns off, and then only the room module functions. As soon as the parameters have increased by a couple of degrees, a command about this is sent to the compressor through temperature sensors, and it turns on again.

When purchasing a household split system or monoblock, you can make a simplified power calculation, taking into account only the area of the room.

It is generally accepted that on average 1 kW = 10 m². Therefore, a room with an area of 17 m² requires a cooling capacity of 1.7 kW. Air conditioners are produced with a power of 1.5 kW, but not all manufacturers have such low-power models. And the next value is usually 2 kW. If the side is sunny, the room is equipped with a large number of equipment, and several people are regularly there, then it is better to give preference to larger values - 2 kW or 7 BTU.

Low power air conditioners correspond to the following table of values:

Area, m²	power, kWt	Power, BTU/h
15	1,5	5
20	2	7
25	2,5	9
35	3,5	12
45	4,5	14-15
50	5,0	18
60	6,0	21
70	7,0	24

A typical calculation of power by room area is done according to the generally accepted scheme:

Q1 = S * h * q / 1000

Where Q- power during cold operation (kW), S- area (m²), h- ceiling height (m), q- coefficient equal to 30 – 40 W/m³:

q = 30 for the shadow side;

q = 35 for normal light penetration;

q = 40 for the sunny side.

Q2- the total amount of excess heat from people.

Excess heat from an adult:

0.1 kW - with minimal activity;

0.13 kW - with low or medium activity;

0.2 kW - with increased activity;

Q3- the total amount of heat inflow from household appliances.

Excess heat from household appliances:

0.3 kW - from PC;

0.2 kW - from TV;

For other devices the value is based on 30% of the maximum power consumption.

The climate control power should be in the Qrange from -5% to +15% of the design power Q.

Please note that this is an approximate estimate and may have errors. Even when selecting a low-power air conditioner for an apartment or office, it is advisable to use the services of professionals and calculate everything for sure, since the simplified method for calculating power provides for a minimum amount of equipment, ceiling height and number of people.

Why do you need an online calculator?

Today, many online storefronts offer a service such as a calculator for calculating the power of an air conditioner, which can easily be used to determine the exact value of the cooling capacity, taking into account all the features of the room. This is very convenient - even a simple layman can use it without special knowledge in the field of air conditioning systems. Why might such a skill be needed? So that an unscrupulous seller does not try to mislead a person by trying to sell him a device of inappropriate power that is lying in a warehouse.

At the end of the article, you can watch a video with detailed instructions on how to use the air conditioner power calculator for an ordinary buyer.

It is worth remembering that these types of standard calculations are only suitable for domestic and administrative premises with an area of no more than 70-80 m², without additional technical equipment and large crowding of people on the territory. The types/types of compressor are also important. This is also taken into account when selecting an air conditioning system for an apartment or office.

Thus, with the calculation of air conditioner power by room area, everything is clear - its results are quite conditional, and they are unsuitable for multi-systems or centralized air conditioning systems in industrial buildings.

Calculation of the cooling capacity of multi-zone systems and central air conditioners

When purchasing and installing multi-zone air conditioning systems, in any case, you will have to contact representatives of climate control companies, since it is impossible to do this yourself. What is usually taken into account when calculating the power of central air conditioners or multi-split systems? This:

the maximum value established by the manufacturer at which the device can operate for a long time at maximum load without interruption;
permitted power that consumers are allowed to connect to their communications;
maximum length and lifting height of the pipeline.

From these three points the total power with which VRV or VRF installations can operate is already derived.

First, in a central air conditioning system, the power is always calculated for each individual indoor module according to the principle described above for split systems or monoblocks installed in small rooms. Here, accordingly, there will be greater heat flow from appliances, people, walls, roof and windows. It all depends on the design of the building, its purpose and the equipment it contains.

Afterwards, external installations are selected taking into account the power of all internal units and the absolute maximum outdoor temperature, which is set by the manufacturer in the technical documentation. If the values are exceeded due to the installation characteristics of the external module, then protective screens and barriers are used.

Some premium manufacturers have the ability to exceed the power rating of the outdoor module by approximately 30%. At the same time, the functionality of the entire layout does not suffer from this.

Based on the selected power, the operating current and its maximum operating values are determined with some margin. This is necessary to select the rated value of the circuit breaker. The protection should operate when the permissible values for pressure, current and other parameters are exceeded.

For central air conditioning, it is always wiser to use an online air conditioner power calculation and expert advice, since selecting a unit based on cooling power does not provide precise guarantees regarding the serviced area without taking into account the entire heat load. And only a professional can determine this.

Air conditioning compressor power calculation

If the power was calculated incorrectly, or the device was already too old, and the compressor broke down, you will have to replace it with a new one. The question arises of how to find out the power of the air conditioning compressor so as not to repeat mistakes.

The compressor, the main element of the internal device (design) of the external module, is responsible for all processes associated with the movement of coolant along the refrigeration circuit in air conditioning devices. It is also responsible for cooling capacity, so it fails under abnormal load.

As a rule, the power characteristics of this part are determined at the manufacturer, so it is necessary to build on the data in the manual. There is absolutely no need to calculate the power of the air conditioning compressor to select a new one. The size of the old unit must be taken as a basis. But this is applicable in a situation where there is a breakdown due to the end of the device’s service life.

If the malfunction is associated with incorrect selection of permissible cooling capacity values, then you need to contact a specialist. You should not try to independently calculate the power of the air conditioner compressor, which will depend on many factors:

compressor type;
number and diameter of cylinders;
coolant used.

It is better to calculate the power of the air conditioner online to install a new device, since replacing the compressor is cost-effective only in household systems with cooling characteristics of 10 kW or more and in semi-industrial models.

In recent years, when weather forecasters almost every year announce another historical maximum temperature, air conditioning is a real savior from the summer heat. In order not to languish in the unbearable heat in the summer, you need to take care of purchasing an air conditioner in advance. In order for this useful device to serve you as efficiently as possible, a number of conditions must be met, one of which is the correct calculation of the air conditioner power.

Principle of operation

The name “conditioner” comes from the English “condition” - condition, condition. That is, an air conditioner is a device designed to maintain various indoor air conditions within specified values, creating a controlled microclimate, and not at all for cooling, as is commonly believed. Thus, the first operating air conditioners were designed to combat excessive humidity in printing rooms of printing houses, where high humidity negatively affects print quality.

However, in our time, the name “air conditioner” is firmly attached to a device whose operation is based on processes that accompany a change in the state of aggregation of the refrigerant liquid. Therefore, ionizers or humidifiers are not called air conditioners, even though they are such, in essence. In devices commonly called air conditioners, there is a continuous transfer of heat from the interior of the room to the surrounding space, or, if necessary, vice versa. How does this happen?

How does an air conditioner work?

Heat transfer occurs with the help of a coolant, which at different times used different substances; in the first air conditioners, ammonia served as the coolant. Currently, freon is used as a coolant for air conditioners. To “capture” and release heat, the properties of a phase transition are used, that is, the transition of a substance from one state of aggregation to another.

Everyone had the opportunity to become acquainted with this property of phase transition during summer swimming. Coming out of the water, a person experiences cold, even if the thermometer exceeds the thirty-degree mark. Why? Because water, evaporating from the surface of the body (that is, changing its state of aggregation from liquid to gaseous), actively takes away heat from the surrounding space, including the surface of the body. Motorists know that contact of exposed areas of the body with volatile liquids such as gasoline, thinner or acetone causes a significant feeling of cold, even in summer. If the temperature is close to zero, skin contact with gasoline can cause frostbite.

A method of simple salvation from heat stroke is based on this same property - wet any piece of cloth and apply it to the head. As long as the liquid impregnating the fabric evaporates, nothing threatens the head; it will be cooled (that is, heat is taken away) by the process of phase transition. An air conditioner works in much the same way, with the only exception that evaporating freon into the surrounding space would be too wasteful. Evaporation occurs inside a special tubular circuit, which is called an evaporator. The freon itself remains inside the circuit; only heat escapes into the surrounding space.

The air conditioner works as follows:

The compressor compresses freon to 15-20 atmospheres and releases it into the condenser.
At the outlet of the compressor, due to a sharp drop in pressure, freon immediately turns into hot steam.
In the condenser, freon transitions from a gaseous state to a liquid state (condensation), accompanied by the release of a large amount of heat. It is at this stage that heat transfer occurs, so the condenser must be in contact with the outside air.
Liquid freon enters the evaporator, where a further decrease in pressure leads to the transition of the refrigerant from a liquid to a gaseous state (evaporation), which is accompanied by active heat absorption. The evaporator must be in contact with the air of the refrigerated room.
The coolant gas from the evaporator enters the compressor and the cycle begins again.

If you need the air conditioner to work for heating, then the four-way valve redirects the air flow so that warm air enters the room, and heat is taken from outside. Of course, this requires that the outside air itself be warm enough to heat the refrigerant. When the air temperature outside approaches zero, that is, exactly then. When heating becomes truly necessary, it becomes impossible to use air conditioning for these purposes. Therefore, air conditioners are never used as the main heating device; the maximum is to keep warm during the short “off-season” period.

What types of air conditioners are there?

This is, in a nutshell, the general design of an air conditioner. In practice, the air conditioner is “overgrown” with sensors, electronic control and remote control systems, fans for pumping air and filters for cleaning it, pipelines for circulating freon and removing excess condensate, etc. Whether the air conditioner belongs to one type or another depends on the design and location of these parts. Air conditioners of two different types may be completely different from each other (for example, an industrial air conditioner cannot be confused with what we are used to seeing in everyday life), but the basis is always the circulation of the coolant, which in the process of this circulation changes its state of aggregation.

Air conditioning is considered to be a sign of the new times, but in fact, air conditioners have been with us for quite a long time. Many people remember how the windows of Soviet offices and workshops were “decorated” with characteristic drawers. These were monoblock window air conditioners. The evaporator and condenser in such a device are assembled in a single unit. Such air conditioners had a number of disadvantages, including high noise, reduced illumination due to shading of a large area of the window opening, etc. For these reasons, window air conditioners have been used to a limited extent in everyday life.

A real revolution in the production of air conditioners was made by the appearance of so-called split systems. The first air conditioner in the form of a split system was released by the Japanese company Toshiba in 1961. The company's designers figured out to divide the air conditioner into two parts connected by pipelines - internal and external, removing the most noisy and bulky structural elements from the latter. The internal part, in turn, became possible to place in any convenient place in the room.

So, you have decided to install an air conditioner in your apartment or office. Since an air conditioner is a rather expensive device, the choice of a specific model should be taken with all possible seriousness. One of the most important selection parameters is the power of the air conditioner.

How to calculate the power of a household air conditioner

Why is calculating the power of an air conditioner so important? Because an air conditioner with a power that does not correspond to the tasks assigned to it simply will not be able to perform its functions normally. Of course, you can arrange “sea trials” for the selected air conditioner, but it is customary to prepare a sleigh in the summer, and buy an air conditioner in winter or spring. By the time the real heat begins, to combat which the air conditioner was purchased, all possible deadlines for returning the goods may have long expired.

Before starting the calculations, it is necessary to explain what kind of power we are talking about, since “air conditioner power” is too general and vague a concept. As mentioned above, the air conditioner cannot be used for heating at subzero outside temperatures, so we use the air conditioner most often for cooling, so we need to calculate the required cooling power.

Cooling power is measured in kilowatts (kW) and shows how much heat energy the air conditioner can remove from the room. The concept of “cooling power” must be distinguished from power consumption. Power consumption is the amount of electricity that a device needs to operate. This value is always less than the cooling power, since it is not spent for the direct “production” of heat, but only for its removal. The ratio of cooling power to power consumption is called energy efficiency (EER). For household air conditioners, the energy efficiency value is in the range of 2-4.

For the initial “shooting”, you can use a simplified calculation method, which will help you roughly determine the price category (or the total number of air conditioners, if we are talking about large rooms). As a first approximation, the required air conditioner power is 1 kW per 10 square meters of room area with a ceiling height of 2.5-3 m.

Why are we talking about area and not volume, since the air conditioner cools the air that fills the entire volume of the room? Everything is true, but in everyday life it is customary to operate with the area of the room, and not the volume. Surely you can easily remember the area of your apartment and tell its volume right away? Hardly. In addition, the ceiling height of an apartment or office is, as a rule, standard and therefore equal to 2.5-3 m. For a rough determination of power, such accuracy is quite sufficient and the ceiling height can be considered a constant.

If the room:

located on the sunny side;
has panoramic windows;
“populated” with a large number of office equipment;
filled with people.

then for each of these factors an additional 20 percent of the required power is added.

It makes sense to make a more accurate calculation of air conditioner power for non-standard rooms or large areas, where even a small error can result in the purchase of an unnecessary expensive device. In this case, it is not the power of the air conditioner that is calculated, but the so-called heat gain power of the room. This is a value showing how much heat the indoor air receives. The power of the air conditioner is then selected from a standard range of values so that the air conditioner can remove the heat entering the room. That is, the cooling power should be no less (but not much more) than the heat input power of the room.

The power of heat influx is calculated using the formula:

Q – heat input power (kW/1000)
S – room area (m2)
h – room ceiling height (m)
q – room illumination coefficient (kW/m3). For a room with normal illumination, this coefficient is 0.035.

Having calculated the power of the air conditioner, to the resulting value we add 0.1 kW for each person in the room, 0.3 for each piece of equipment (computer, TV, etc.). A household refrigerator will give us 0.5 kW, and a powerful refrigerated display case (if we are calculating air conditioning for retail premises) - at least 1.5-2 kW.

The power of the air conditioner in kW must be no less than the obtained value Q. However, the power of foreign-made air conditioners is often indicated not in kW, but with the number 7, 9, 12, 18 or 24. Household models most often have 7 or 9, and they are called that - "seven" or "nine". What do these numbers mean?

This is the power in thousands of BTUph (or BTU/h) - British Thermal Unit per hour (British Thermal Unit per hour). This power designation is found on air conditioners manufactured in countries that use imperial (feet) units, or manufactured for sale in these countries. A thousand BTUp is approximately equal to 0.3 kW.

Example of power calculation

So, we need to calculate the air conditioner for a room with an area of 30 m2, a ceiling height of 5 m (we specifically take a non-standard room for which the “accelerated” calculation method is not suitable), in which there are always five people and three computers. The lighting is normal. We count:

Q= 30*5*0.035+5*0.1+3*0.3=6.65 kW

To effectively cool this room, you will need an air conditioner (or several) with a total cooling capacity of 6.65 kW.

If necessary, convert kilowatts to BTUph:

As you can see, everything is extremely simple. By correctly calculating the required power, you can make the use of an air conditioner truly effective.

Typical calculation of air conditioner power

A typical calculation allows you to find the power of the air conditioner for a relatively small room: a separate room in an apartment or cottage, an office with an area of up to 50 - 70 square meters. m and other premises located in permanent buildings.
Cooling power Q (in kilowatts) is calculated using the following method:
Q = Q1 + Q2 + Q3, where

Q1 - heat inflows from the window, walls, floor and ceiling.

Q2 is the sum of heat inflows from people.

Q3 is the sum of heat inflows from household appliances.

Example of a typical air conditioner power calculation

Let's calculate the power of the air conditioner for a living room with an area of 26 square meters. m with a ceiling height of 2.75 m in which one person lives, and also has a computer, TV and a small refrigerator with a maximum power consumption of 165 W. The room is located on the sunny side. The computer and TV do not work at the same time, since they are used by one person or take into account both parameters.

First, we determine the heat inflows from the window, walls, floor and ceiling. Let's choose the coefficient q equal to 40, since the room is located on the sunny side:
Q1 = S * h * q / 1000 = 26 sq. m * 2.75 m * 40 / 1000 = 2.86 kW.

Heat inflows from one person in a calm state will be 0.1 kW.
Next, let’s find heat inflows from household appliances. Since the computer and TV often do not work at the same time, only one of these devices needs to be taken into account in the calculations, namely the one that generates more heat. This is a computer whose heat output is 0.3 kW. The refrigerator emits about 30% of the maximum power consumption as heat, that is, 0.165 kW * 30% / 100% ~ 0.05 kW.
Q3 = 0.3 kW + 0.05 kW = 0.35 kW

Now we can determine the estimated power of the air conditioner:
Recommended power range Qrange (-5% to +15% of design power Q):
3.14 kW< Qrange < 3,80 кВт

Now all that remains is to choose a model with suitable power for cooling the room. Most manufacturers produce split systems with capacities close to the standard range: 2.0 kW; 2.6 kW; 3.5 kW; 5.3 kW; 7.0 kW. From this range we choose a model with a power of 3.5 kW.

It is interesting that models from this series are often called “7” (seven), “9” (nine), “12”, “18” “24” and even the marking of air conditioners is carried out using these numbers, which reflect the power of the air conditioner in a way other than the usual kilowatts, and in BTU/hour.
(BTU - British Thermal Unit. 1000 BTU/hour = 293 W).

cooling power 2.5 kW.

Power calculation using additional parameters

The typical calculation of air conditioner power described above in most cases gives fairly accurate results, but it will be useful for you to know about some additional parameters that are sometimes not taken into account, but significantly affect the required air conditioner power.

Taking into account the flow of fresh air from a slightly open window
Taking into account the influx of fresh air when calculating the power of the air conditioner

The method by which we calculated the power of the air conditioner assumes that the air conditioner operates with the windows closed and no fresh air enters the room.
In the instructions for the air conditioner It is also usually stated that it must be operated with the windows closed, otherwise the outside air entering the room will create an additional heat load. Following the instructions, the user has to periodically turn off the air conditioner, ventilate the room and turn it on again. This creates certain inconveniences, so buyers often wonder if it is possible to make the air conditioner work and the air to be fresh.

To answer this question, we need to figure out why the air conditioner can work effectively together with fresh air ventilation, but cannot with an open window. The fact is that the ventilation system has a very specific performance and supplies a given volume of air to the room, so when calculating the power of the air conditioner, it is imperative to take this thermal load into account. With an open window, the situation is different, because the volume of air entering the room through it is not standardized in any way, and the additional heat load is unknown.

You can try to solve this problem by setting the window to winter ventilation mode (opening the window slightly) and closing the door in the room. Then there will be no drafts in the room, but a small amount of fresh air will constantly flow inside. Let us immediately make a reservation that operating the air conditioner with the window slightly open is not provided for in the operating instructions for the air conditioner, so we cannot guarantee normal operation of the air conditioner in this mode. However, in many cases, such a technical solution will allow maintaining comfortable conditions in the room without periodic ventilation.

If you plan to use the air conditioner in this mode, you must consider the following:

The power of Q1 should be increased by 20 - 25% to compensate for the heat load from the supply air. This value was obtained based on a single additional air exchange at an outside air temperature/humidity of 33°C/50% and an indoor air temperature of 22°C.
Electricity consumption will increase by 10 – 15%. Note that this is one of the main reasons for prohibiting the operation of air conditioners with open windows in offices, hotels and other public premises.
In some cases, the heat gain may be too great (for example, in very hot weather) and the air conditioner will not be able to maintain the set temperature. In this case, the window will have to be closed.

Guaranteed 18 – 20°C

Many buyers are concerned about the question: is air conditioning hazardous to health? The Answers to Frequently Asked Questions provide a few simple rules that you can follow to protect yourself from the risk of catching a cold. One of these rules is that the temperature difference between the air outside and inside the room should not be too large. So, if it is 35 - 40°C outside, then it is advisable to maintain the temperature in the room at least 25 - 27°C. But such recommendations are not suitable for everyone, because for some people a comfortable temperature does not exceed 20°C. The problem is that the typical calculation of air conditioner power is made in accordance with Building Codes and Rules, and SNiP 2.04.05-91 states that for Moscow the estimated air temperature in the warm season is 28.5 ° C. Accordingly, maintaining the minimum possible temperature in the room at 18°C is guaranteed only when the outside air temperature does not exceed 28.5°C.

Since the typical calculation is made with a small margin, in practice the air conditioner will be able to effectively cool the room at an outside air temperature of up to 30 - 33 ° C, however, when the temperature increases to 35 - 40 ° C, its power will no longer be enough. Therefore, those who “like it cooler” can be advised to increase the power of Q1 by 20 - 30% (the calculator uses an average value of 25%).

Top floor
Attic air conditioning

If the apartment is located on the top floor and there is no attic or technical floor above, then the heat from the heated roof will be transferred to the room. A roof located horizontally, and even dark in color, receives several times more heat than light walls (for example, compare the temperature of the asphalt and the wall outside the room on a sunny day). As a result, heat inflows from the ceiling will be higher than taken into account in the typical calculation, and the power Q1 will need to be increased by 10 - 20% (the exact value depends on the actual heating of the ceiling; the calculator uses an average value of 15%).

Large glazing area

How much does a large glass area affect heat gain? The easiest way to understand this without complex calculations is to turn to an analogy and consider heating a room in winter. This analogy is appropriate because the thermal insulation of a building does not depend on whether it is warmer inside or outside, and heat gain or loss is determined only by temperature differences. In winter, the temperature difference between outside and inside air can exceed 40°C for a long time (from -20°C to +20°C). In summer, the difference is two times less (from +40°C to +20°C). Despite the fact that heat loss in winter is twice as large as heat gain in summer, the same formula is used to calculate the power of heaters as for calculating an air conditioner - 1 kW per 10 sq.m.

This is explained precisely by the influence of solar radiation penetrating into the room through the window. In winter, the sun helps to heat the room (you've probably noticed that on a frosty sunny day the apartment is noticeably warmer than on cloudy weather). And in the summer, the air conditioner has to spend up to 50% of its power to compensate for heat gain from the Sun.

In a typical calculation, it is assumed that the room has one window of standard size (with a glazing area of 1.5 - 2.0 sq.m). Depending on insolation (the degree of illumination by sunlight), the power of the air conditioner changes by 15% up or down from the average value.
If the glazing area is larger than the standard value, then the power of the air conditioner must be increased. Since the typical calculation already takes into account the standard glazing area (2.0 sq.m), then to compensate for additional heat gain for each square meter of glazing area over 2.0 sq.m, you need to add 200 - 300 W for strong insolation, 100 - 200 W for average illumination and 50 - 100 W for a shaded room.

If the sun comes into the room during the day, there must be light curtains or blinds on the window - they can reduce heat gain from solar radiation.

What else should you pay attention to?

If taking into account additional parameters has led to an increase in power, then we recommend choosing an inverter air conditioner, which has variable cooling capacity and will therefore operate effectively over a wide range of heat loads. A conventional (non-inverter) air conditioner with increased power, due to the specifics of its operation, can create uncomfortable conditions, especially in a small room.