Is it possible to use air conditioning for heating in cold weather and how to prepare it for this job?

Alexey Dedyulin
Checked by a specialist: Alexey Dedyulin
Author: Kristina Veklich
Last update: January 2020

It will be cold soon, but you have not decided yet how to warm your home? To use an air conditioner for this purpose is very economical and tempting, but you do not want to risk its performance, right? We will help you figure out whether it is possible to use air conditioning for heating in cold weather, why and in what cases it can be dangerous for equipment.

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

Why does the split system warm?

To understand what can go wrong when you turn on the air conditioner in cold weather, 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 block, 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 receive heat in the cold and cool in the heat.

Air conditioning operation for heating
When working on heating, the indoor and outdoor units of the air conditioner change roles. As a rule, the flow of freon is redirected through a four-way valve

The way of freon in air conditioners used in winter for heating at low temperatures looks like this:

  • Cooled liquid refrigerant is supplied from the radiator of the indoor unit.
  • Once in the outdoor unit, it heats up and evaporates, because the boiling point of the refrigerant is -40 or -510C, and the street is even warmer in winter. After passing through a street radiator, the temperature of freon rises, that is, it receives thermal energy.
  • The energy received is low-potential, and therefore can not be immediately transferred to the air in the room. The compressor compresses the gaseous refrigerant, and its temperature rises to 70 - 900C. In this condition, freon is supplied to the indoor unit.
  • Passing through the radiator of the indoor unit, blown by the fan, the refrigerant transfers heat to the room air, and it cools and condenses into a liquid. The circle is closed, everything repeats from the beginning.

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

Air conditioning defrost
When Freon evaporates, condensate settles on the tubes - moisture from the air, which instantly freezes. To prevent such growths of ice from melting and not interfere with operation, most air conditioners periodically switch to defrost mode for 5-15 minutes

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

What is the danger of frost for an air conditioner?

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

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

Moreover, without lubrication from friction of metal parts, chips are formed, which clogs and destroys the system. Therefore, even a new compressor installed instead of a broken one can quickly fail even with proper operation.

Secondly, the freon in the external radiator may not have time to evaporate. Heat transfer activity depends on the temperature difference. Therefore, with a slight plus on the street, freon, warming up from -400C, absorb a lot of thermal energy.

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

The third hazard is condensation freezing and icing..

Freezing of the external block
Remember, when working on heating, the split system units change roles, so condensate forms on the radiator that is on the street

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

Condensation in the drain pipe may also freeze at the exit point to the street - if the air conditioner is cooling. This winter is necessary in the server or in the above defrost mode. Such an ice plug prevents further condensate drainage, and it begins to trickle along the wall, provokes the development of mold in the indoor unit, and can damage it.

Even winter cooling work 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 equipment. In addition, the problem of compressor cold start remains relevant.

What air conditioners can be warmed up?

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

Turn on air conditioning for heating
The heating function is in most modern systems, only the temperature at which it is allowed to use differs. It is indicated by the symbol of the sun or the word Heat

After the described problems, it may seem that the heating function in the 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 gets colder on the street, or in a temperate climate.

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

There are certain patterns in the distribution of these temperatures:

  1. Linear control air conditioners can usually only be turned on up to -50C, because the compressor constantly turns off and has time to cool 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 range of operating temperatures declared by the manufacturer by installing a winter kit - more on this later.
  4. Monoblock air conditioners with heating function do not depend on outdoor temperature, but they do not differ in efficiency either. In winter, they work like conventional convector, with an efficiency of slightly less than 1.
  5. Systems with R22 refrigerant are less effective 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.

Air conditioner refill
You can’t just replace the R22 freon in the air conditioner with a more efficient and modern one - its working pressure is half that and the system parts are not designed for more

Given the limitations of operating temperature and inconsistent performance, air conditioning cannot be the main heating device for housing in the northern regions.

Differences in the design of frost-resistant air conditioners

Why can one air conditioner be turned on at a 30-degree frost, while others are undesirable to start already at -50WITH? The answer is simple: structural features 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 in the winter for heating, or whether it is dangerous for the device, pay attention to such details.

Firstly, the low-temperature kit must be built-in already from the factory to prevent the compressor from starting cold and condensate freezing.

As we have 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 and start up every time with overload, moreover, it is more profitable in terms of energy consumption.

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

Air conditioner outdoor unit heat exchanger
The large area of ​​the heat exchanger allows the split system to work efficiently even with a small difference between the boiling points of the refrigerant and air in the street

There are also double-circuit heat exchangers in which the performance is regulated by connecting an additional freon circulation circuit. The external unit and the heat exchanger may include additional housings and heat stores, to use the energy that the operating equipment emits.

A high-power compressor compresses the gas more strongly, heating it to higher temperatures.In industrial models there are also scroll compressors that are not afraid of liquid freon.

The refrigerant itself can have different properties. The cheap and common R-22 evaporates at -400C, while capable of absorbing heat 233 kJ / kg. For comparison, the newest R-32 evaporates at -51.70C, and heat is capable of retaining 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 conditioning or split system will work with less energy and higher efficiency.

The type of oil that lubricates the compressor also depends on the type of refrigerant. R-22 works with mineral oil that retains an acceptable viscosity of -50C, and R410A and R32 - with synthetic, resistant to -70C. It would seem that the difference is small, but in combination with other factors, it is significant.

Mitsubisi zubadan
Mitsubishi Zubadan - the most famous series of heat pumps operating in winter at temperatures up to -250C. They cost 3 to 5 times more expensive than split systems that can heat only with minor frosts

The more of the listed upgrades there are in the air conditioner, the lower the temperature it is able to work. However, for many inverter models you don’t even have to know the maximum permissible temperature: 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 claim that its installation will make the air conditioner an effective heater for the whole winter, even in cold weather. Is it so - we will understand.

Kit components for winter work

As a rule, the low-temperature kit includes 3 components: heating the pallet, compressor housing and fan speed controller. Sometimes there is also a temperature sensor and a control board - separate for each component or common to all.

Heating the pan is necessary so that condensate draining from the radiator does not freeze when the defrost mode is activated.

The crankcase heater is a wire or plate encircling the compressor where oil accumulates.

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, heating often occurs either only during operation or only during downtime. Safety for the compressor will provide only the second option, but it is less profitable due to increased energy consumption.

Crankcase heater
Thanks to the crankcase heating, it is possible to avoid a cold start and compressor operation with grease thickened in the cold, which means an increased load at startup, wear of moving parts

Adjusting the fan rotation speed determines the heat transfer activity between freon and the external environment: the stronger the air flow, the more heat is transferred. When working for heating, this is not critical, because the heat transfer is required to the maximum, and a high fan speed is set from the factory.

Another thing is if the air conditioner works to cool at temperatures below +14 - +180allowed by the manufacturer. Then freon can give off too much heat, and the indoor unit will start 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 ask a question: is it now possible to heat the room with air conditioning at low outdoor temperatures? The answer is yes, it can, for an air conditioner it is now safe. The exception is unskilled installation or self-made equipment.

Air condition icicles
If the air conditioner drips from the roof and therefore huge icicles form, the winter kit will not save - you need a protective visor

Is it effective? Heated air conditioning is valued 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. To operate the compressor and fans, much less energy is needed than the system can move to the house.

The declared efficiency, or, as manufacturers write, COP, is relevant when working on heating at +70 outdoors. With cooling, the temperature difference between air and freon decreases, which means that heat transfer worsens and the efficiency of the air conditioner decreases.

At temperatures below -150With the efficiency of the air conditioner is reduced to about 1%, that is, for every kilowatt of electricity consumed, you can get only 1 kW of heat. Conventional convectors or infrared heaters also have such indicators, which are cheaper and do not depend on outdoor temperature.

Of course, these calculations are approximate, the result strongly depends on the model of the air conditioner, low-temperature kit, and even the second connection scheme. But the fact is that the lower the temperature in the street, the less efficient and economical is the heating of the split system.

Given that the cost of a good winter kit for air conditioning heating with the installation it can make up 40 - 150% of the cost of the air conditioner, and it will help to work effectively only up to -150C, the appropriateness of the purchase is highly controversial.

The indoor unit is cold
When the air conditioner is used for cooling in winter without a low-temperature kit, frost and ice crust form on the indoor unit

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

Installation and connection of the winter kit

As we already mentioned, the professional installation of a low-temperature kit is not cheap. Not every owner of a split system is ready to pay 5000 rubles or more for the opportunity to include heating air conditioner at a temperature of 10 - 15 degrees lower than stated. If you are not ready for such expenses, you may be interested in the self-installation of a winter kit.

Recall that for operation in winter, the air conditioner needs to heat the pan, the compressor crankcase and the RDK unit - the condensation pressure regulator that controls the fan speed. You can buy a ready-made kit and install it yourself.

Then you get rid of the difficulties of choosing and searching for components, as well as save money for installation, but you will surely 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 than self-regulating, and connect them yourself. The control of the fan speed when working on heating can be neglected, why - we talked about above.

Winter air conditioner kit
When choosing a low-temperature kit, pay attention to the power conditioners for which it is designed. There are 2 types of kits, up to 12 BTU and for more powerful systems

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

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

To warm the oil in the compressor, grip it with a piece of heating cable at the bottom. Connection to the electrician is carried out together with the heating of the pallet.

If an RDK is acquired, it is necessary for him to find a free place in the control compartment, above compressor, and fix it with self-tapping screws.Electrical connection is different for different models and is always described in detail in the instructions. For correct operation, the sensor that comes with the kit is attached to the middle radiator loop, having missed thermal grease, and wrapped with thermal insulation material.

Conclusions and useful video on the topic

It’s hard to fully imagine some practical points from the textual description, so we suggest seeing and evaluating everything with your own eyes.

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

What can happen with the air conditioner when working without a winter kit is shown here:

The experience of heating a home with only air conditioning is described in detail here:

To summarize, we say that most air conditioners are designed to heat the room only in the off-season, until the main heating is turned on. Even those models that are capable of working at -300C 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 the cold? Did you need to install a low temperature kit? Share your experiences, additions and corrections to the article in the comments.

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