Can the air conditioner be used for heating in cold weather and how to prepare it for this?

It will be cold soon, and you have not yet decided how to heat your home? Using an air conditioner for these purposes is very economical and tempting, but you don't want to risk its performance, right? We will help you figure out whether it is possible to use the air conditioner for heating in cold weather, why and in what cases it can be dangerous for the equipment.

We will also tell you what to do so that the air conditioner can be used longer, at lower temperatures. Let us see how appropriate and effective such an application is. For complete clarity, we will show all the important points in the photos and diagrams, and at the end of the article you will find informative videos on the topic.

Why does the split system heat up?

To understand what can go wrong when the air conditioner is turned on in frost, first you need to figure out what happens during normal operation of the system for heating.

Unlike portable heaters of any type, the split system does not produce heat from the consumed energy, but only transports it from the street to the house or vice versa, depending on the mode. Does it sound unrealistic to take heat outside when the temperature is below zero? This is only at first glance.

The main components of any split system are a compressor, a radiator with a fan in each unit and a pipeline with freon connecting them. The refrigerant is the main magician in this kit: it is thanks to its physical properties that it becomes possible to get warm in the cold and cool in the heat.

Freon path in air conditioners used in winter for heating at low temperatures looks like this:

• The cooled liquid refrigerant is supplied from the radiator of the indoor unit.
• Getting into the outdoor unit, it heats up and evaporates, because the boiling point of the refrigerant is -40 or -51⁰C, and it's warmer outside even in winter. After passing through the street radiator, the freon temperature rises, that is, it receives thermal energy.
• The resulting energy is low-potential, and therefore cannot be immediately transferred to the air in the room. The compressor compresses the gaseous refrigerant and its temperature rises to 70 - 90⁰WITH. In this state, freon is supplied to the indoor unit.
• Passing through the radiator of the indoor unit, blown by a fan, the refrigerant gives off heat to the room air, while it cools down and condenses into liquid. The circle is closed, everything is repeated from the beginning.

Thanks to this principle of operation, the split-system is also referred to the group of heat pumps, because they transport and pump heat from the street to the room in the same way, or vice versa.

For operation, electricity is needed by the pump itself - the compressor, as well as two fans. Together they consume 3 to 7 times less energy than the system produces, which means heating an air conditioner is 3 - 7 times more economical than an electric and gas convector, an infrared stove or other heater.

Why is frost dangerous for an air conditioner?

The principle of operation of the air conditioner is quite simple, but changing conditions at any of the stages can lead to serious damage.

First, starting a cold compressor is dangerous. The oil in it thickens at low temperatures, and therefore the unit operates with increased load.

In addition, without lubrication from the friction of metal parts, chips are formed, which clog and disable the system. Therefore, even a new compressor installed to replace a broken one can quickly fail even with correct operation.

Secondly, the freon in the external radiator may not have time to evaporate. The heat exchange activity depends on the temperature difference. Therefore, with a small plus on the street freon, warming up from -40⁰C, will absorb a lot of heat energy.

If the street is -30⁰C, then the refrigerant may not have time to warm up even to the boiling point. The result is the ingress of liquid freon into the compressor and its inevitable breakdown due to water hammer.

The third danger is freezing of condensate and icing..

The ice shell on the outdoor unit impedes heat transfer and can interfere with the fan, which increases the load on all parts of the system. Automatic defrosting is designed to solve this problem, but water flowing from a heated radiator often immediately freezes in the sump. When a certain thickness of the ice layer is reached, the fan blades freeze into it, and the air conditioner loses its performance.

Condensation in the drain pipe can also freeze at the point of exit - if the air conditioner is running for cooling. This may be necessary in winter in server rooms or in the above-mentioned defrosting mode. Such an ice plug prevents further drainage of condensate, and it begins to ooze along the wall, provokes the development of mold in the indoor unit, and can disable it.

Even cooling operation in winter can lead to problems. In this case, the air conditioner takes too much cold from the street, and the condensation on the indoor unit turns into frost and ice. Naturally, this is also detrimental to the equipment. In addition, the problem of the cold start of the compressor remains relevant.

What kind of air conditioners can you warm up with?

When buying a split system, you should look for the word "reversible" in the description: it indicates the ability of the device to change the direction of the freon flow and work for heating.

After the described problems, you may get the impression that the heating function in air conditioners is useless and dangerous for the device, but this is not so. Split system although it will not save in severe frosts, it will help to create a comfortable microclimate in the off-season, when the central heating is turned off, and it is colder outside, or in a temperate climate.

The lower temperature limit at which the split system can be turned on for heating depends on the model - it is indicated in the instructions.

There are certain patterns in the distribution of these temperatures:

1. Air conditioners with a linear type of control can usually only be turned on up to -5⁰C, because the compressor constantly turns off and has time to cool down before restarting.
2. Inverter models usually work up to -15⁰C, but some specialized devices are effective up to -20 and even -30⁰WITH.
3. It is sometimes possible to expand the operating temperature range declared by the manufacturer by installing a winter kit - we will talk about this in more detail later.
4. Monoblock air conditioners with heating function do not depend on the outside temperature, but they do not differ in efficiency either. In winter they work like conventional convector, with an efficiency slightly less than 1.
5. Systems with R22 refrigerant are less efficient and resistant to low temperatures than those filled with R410A or R32 freon.

It is worth noting that even those models that operate smoothly at low temperatures significantly reduce the efficiency and economy of heating when it gets colder outside.

Given the limitations of operating temperatures and variability in performance, air conditioning cannot be the main heating appliance for housing in northern regions.

Differences in the device of frost-resistant air conditioners

Why can one air conditioner be turned on at 30-degree frost, while others are undesirable to start already at -5⁰WITH? The answer is simple: features of the structure and configuration. The cost of a split system is not always directly proportional to its capabilities, and therefore it is useful to know what effective design solutions exist.

To understand whether it is possible to turn on a specific air conditioner for heating in winter, or if it is dangerous for the device, pay attention to such details.

Firstly, a low temperature kit must be installed from the factory to prevent cold starts of the compressor and freezing of condensate.

As we already mentioned, inverter models are preferable in winter, since their compressor does not stop when the set temperature in the room is reached, but only slows down. This means that it will not cool down every time and start with overload, besides, it is more profitable in terms of energy consumption.

The heat exchanger of the outdoor unit can be enlarged so that the freon inside has time to completely evaporate and absorb maximum heat from the air before it enters the compressor.

There are also double-circuit heat exchangers, in which the performance is regulated by connecting an additional freon circulation circuit. The outdoor unit and heat exchanger can include additional casings and heat accumulators to use the energy that is generated by the operating equipment.

An oversized compressor compresses the gas more strongly, heating it to higher temperatures. In industrial models, there are also scroll compressors that are not afraid of the ingress of liquid freon.

The refrigerant itself can have different properties. Cheap and common R-22 evaporates at -40⁰C, while being able to absorb heat 233 kJ / kg. In comparison, the newest R-32 evaporates at -51.7⁰C, and can hold heat up to 390 kJ / kg.

This means that under the same conditions, the second will heat up faster and more efficiently in the heat exchanger, and air conditioner or split system will work with less energy and higher efficiency.

The type of refrigerant also affects the type of oil that lubricates the compressor. R-22 works with mineral oil that maintains a permissible viscosity down to -5⁰C, and R410A and R32 - with synthetic, resistant to -7⁰WITH. It would seem that the difference is small, but in combination with other factors, it is significant.

The more of the listed upgrades there is in the air conditioner, the lower the temperature it can operate. However, for many inverter models you don't even need to know the maximum permissible temperature: the electronic control simply will not start the system if it is too cold outside.

Winter air conditioner kit

Recently, more and more often you can find proposals for equipping an air conditioner with a winter kit. The sellers of this equipment assure that its installation will make the air conditioner an efficient heater for the whole winter, even in frosty weather. Is this so - we will figure it out.

Components of a set for winter work

A low-temperature kit usually includes 3 components: a sump heater, a compressor crankcase and a fan speed controller. Sometimes there is also a temperature sensor and a control board - separate for each component or common to all.

Sump heating is necessary so that the condensate flowing down from the radiator does not freeze when defrosting mode is turned on.

The crankcase heater is a wire or plate that surrounds the compressor where oil collects.

It is advisable to turn on the compressor heating before starting the air conditioner so that the oil has time to warm up. In practice, however, heating often occurs either only during operation or only during downtime. Only the second option will provide safety for the compressor, but it is less profitable due to increased energy consumption.

Adjusting the fan speed determines the activity of heat exchange between freon and the outside environment: the stronger the air flow, the more heat is transferred. When working for heating, this is not critical, because the maximum heat transfer is needed, and the high fan speed is set from the factory.

It's another matter if the air conditioner works for cooling at temperatures below +14 - +18⁰allowed by the manufacturer. Then the freon can give off too much heat, and the indoor unit will begin to freeze: it will be covered with frost and ice, the condensate will freeze. To prevent this from happening, the fan is slowed down.

Is it advisable to install a winter kit

After installing the low-temperature kit, the owner may have a question: can the air conditioner now heat the room at low temperatures outside? The answer is yes, it is possible, it is now safe for the air conditioner. An exception is unqualified installation or homemade equipment.

Is it effective? Heating by an air conditioner is appreciated for its efficiency: its efficiency can reach 3 - 5 or even 7, depending on the model. This is achieved by the fact that the split system is the only heater that does not produce heat. Compressors and fans require far less energy to operate than the system can move into the home.

The declared efficiency, or, as the manufacturers write, COP, is relevant when working on heating at +7⁰ outside. With a cold snap, the temperature difference between air and freon decreases, which means that heat exchange deteriorates and the efficiency of the air conditioner decreases.

At temperatures below -15⁰With the efficiency of the air conditioner, it decreases to about 1%, that is, for every kilowatt of electricity consumed, you can get only 1 kW of heat. Such indicators are also possessed by ordinary convectors or infrared heaters, which are cheaper and do not depend on the temperature outside.

Of course, these calculations are approximate, the result strongly depends on the model of the air conditioner, the low-temperature set and even the connection diagram of the second one. But the fact is that the lower the temperature outside, the less efficient and economical the heating by the split system.

Considering that the cost of a good winter kit for turning on the heating by the air conditioner with the installation can be 40 - 150% of the cost of the air conditioner, and it will help to work effectively only up to -15⁰From, the expediency of the purchase is highly controversial.

Another thing is if you need to cool the room in winter. For example, for a room with equipment. Then the lower limit of permissible temperatures drops from +16 declared by the manufacturer to severe frosts, and the efficiency of the air conditioner will not decrease.

Installation and connection of the winter kit

As we already mentioned, a professional installation of a low temperature kit is not a cheap pleasure. Not every owner of a split system is ready to pay 5,000 rubles or more for the opportunity to turn on air conditioner for heating at a temperature 10 - 15 degrees lower than stated. If you are not ready for such expenses, you may be interested in installing the winter kit yourself.

Recall that in order to operate in winter, the air conditioner needs heating of the pallet, the compressor crankcase and the RDK unit - a condensation pressure regulator that controls the fan speed. You can buy a ready-made kit and install it yourself.

Then you are freed from the complexities of choosing and searching for components, and also save money for installation, but you will certainly lose the guarantee for the split system. Naturally, self-installation is an additional hassle.

The most economical option is to buy 2 segments heating cable, better self-regulating, and connect them yourself. Fan speed control during heating operation can be neglected, why - we told above.

To heat the pallet, a heating cable length of about 3m is required. They lay it around the radiator both from the outside and from the inside, as well as along the entire pallet with a snake. You can connect it as a factory heating, to the main phase, supplying the outdoor unit - then the cable will always warm up while the air conditioner is plugged into the outlet, even when it is idle.

Alternative options are to bring a separate cable with a plug to the outlet and turn it on manually, connect it to the network through a thermal relay on the street or through a timer.

To warm up the oil in the compressor, wrap a piece of heating cable around it at the bottom. Electrical connection is carried out together with pallet heating.

If you have purchased a RDK, you need to find a free space for it in the control compartment, above compressor, and fix it with self-tapping screws. The electrical connection is different for different models and is always described in detail in the instructions. For correct operation, the sensor included in the kit is attached to the middle loop of the radiator, smeared with thermal paste, and wrapped with heat-insulating material.

Conclusions and useful video on the topic

Some practical points are difficult to fully imagine from the text description, so we suggest you see and evaluate everything with your own eyes.

How to install the winter kit can be seen in this video:

What can happen to the air conditioner when operating without a winter kit is shown here:

The experience of heating a house only with air conditioners is described in detail here:

Summing up, let's say that most air conditioners are designed to heat the room only in the off-season, before turning on the main heating. Even those models that are capable of operating at -30⁰They are unlikely to be able to provide enough heat in such a frost. However, if in your area the temperature rarely drops below -15⁰C, then heating with a split system is a very profitable and successful solution.

Do you already have a split system installed? Do you use it in cold weather? Did you need to install a low temperature kit? Share your experience, additions and amendments to the article in the comments.