Manufacturers of household air conditioners with a reverse cycle in the technical documentation for the product, as a rule, indicate the temperature range in which the air conditioner can be operated. The lower limit of this range rarely drops to temperatures below -5 ° C for the “cold” mode and 0 ° C for the “warm” mode. What happens to the air conditioner if this limitation is neglected? What needs to be done so that the air conditioner can be operated at lower temperatures without the risk of damaging it? These questions are especially relevant in winter conditions and therefore require an answer..
If you follow the manufacturer’s recommendations, the best way to operate the air conditioner in the cold season at negative outside temperatures is to preserve it..
Preservation of the air conditioner for the winter provides for the following measures.
- Condensing refrigerant into the outdoor unit, which includes the following operations:
– connecting the gauge manifold to the service port;
– turning on the air conditioner “cold”;
– closing the liquid valve of the air conditioning compressor-condensing unit;
– closing the gas valve at a suction pressure below atmospheric;
– disconnection of the gauge manifold.
This will avoid loss of refrigerant through leaks in the external freon line.. - Disabling or blocking the compressor start circuits, eliminating erroneous compressor starting.
- Fencing of the compressor-condensing unit of the air conditioner in order to exclude its damage by ice or falling icicles (if necessary).
What if you can’t do without an air conditioner in winter? How to reduce the risk of serious air conditioner breakdown?
Let’s find out what happens inside the air conditioner at low ambient temperatures. It is known that household air conditioners do not produce cold or heat, they only “pump” heat from one thermally insulated volume to another, that is, according to the principle of operation, these are “heat pumps”. For heat transfer, special substances are used – refrigerants. Heat exchange between refrigerant and ambient air takes place via air heat exchangers.
Schematically, it looks like this:
- heat from the air in one thermally insulated volume is absorbed by the refrigerant through the heat exchanger;
- the refrigerant is pumped by a compressor to another heat exchanger;
- the heat accumulated by the refrigerant through the heat exchanger is discharged into the air.
The performance of an air heat exchanger, or the amount of heat that can be given or received by refrigerant through a heat exchanger, depends on the design and temperature of the air passing through it. Therefore, the essence of the main problem limiting the use of a household air conditioner with a reverse cycle in winter is the change in the performance of the heat exchanger of the compressor-condensing unit when the ambient temperature drops. Moreover, when working on “cold”, the heat exchanger turns out to be oversized (too large), and when working on “heat” – undersized (too small).
When the air conditioner operates in the “cold” mode, additional problems also arise:
- reduced performance of the refrigeration machine;
- increasing the duration of the transient operating mode of the refrigerating machine (air conditioner);
- “leakage” of liquid refrigerant into the compressor crankcase;
- the problem of starting compressors at low ambient temperatures;
- drainage water drainage problem.
Let us dwell on the negative consequences of these problems. Namely:
- decrease in the cooling capacity of the air conditioner;
- freezing of the indoor unit of the air conditioner and, as a result, an even greater decrease in performance, the risk of water hammer and damage to the compressor;
- malfunction of the condensate drainage system (condensate flows through the ice-covered heat exchanger past the drainage bath onto the fan and is thrown into the room);
- deterioration of cooling of the compressor electric motor, periodic operation of thermal protection, risk of thermal breakdown of insulation;
- excessive rise in the compressor discharge temperature, risk of damage to the plastic parts of the four-way valve;
- the risk of water hammer when starting the compressor due to boiling up of the refrigerant that has leaked into the compressor;
- freezing of the drain line.
Fortunately, the listed problems that arise when the air conditioner is operating in the “cold” have a solution. This is the use of a winter air conditioner kit.
Fig. 1. Thus, the retarder is installed
Fig. 2. Installed crankcase heater
The winter kit includes.
Fan speed retarder. It solves the problem of reducing the performance of the heat exchanger of the condensing unit by reducing the air flow passing through it. The sensitive element of the moderator is a sensor that monitors the condensing temperature. The executive element is the fan speed regulator for blowing the heat exchanger. The retarder implements the function of maintaining the set condensing temperature. Along the way, the problems of reducing the performance of the air conditioner, freezing of the indoor unit and others associated with the oversize of the heat exchanger of the compressor-condensing unit are solved (Fig. 1).
Compressor crankcase heater. It solves the problems of starting a cold compressor by preventing damage to it (fig. 2). The protection mechanism is as follows: when the compressor stops, the crankcase heater installed on the compressor turns on. Even a small temperature difference between the compressor and the rest of the outdoor unit, created by the crankcase heater, eliminates refrigerant leakage into the crankcase. The oil does not thicken, the refrigerant does not boil up when the compressor is started.
Drainage heater. It removes condensate from the air conditioner if the drain is routed outside. Several types of drainage heaters are currently used. By the method of installation, they can be divided into 2 groups:
1 – drainage heaters installed inside the drainage line;
2 – drain heaters installed outside the drain line.
A variant of the winter air conditioner kit is shown in Fig. 3.
Fig. 3. Kit for “adaptation” of the air conditioner to work in winter:
1 – fan speed retarder;
2 – crankcase heater;
3 – drain heater
What are the problems that arise when an air conditioner operates with a reverse cycle on “heat” at negative temperatures?
Note that there are two sources of heat, which “pumps” the air conditioner into the room..
First, it is the heat that is taken from the outside air. Secondly, it is the heat of the compressor compression and the heat generated by the compressor electric motor. The first component strongly depends on the outside air temperature and, in fact, determines all the negative phenomena occurring in the air conditioner at low outside temperatures. In order for the heat from the outside air to flow in the right direction, the phase transition temperature of the refrigerant (evaporation) must correspond to a certain value, which is a characteristic of the heat exchanger and is called the total differential.
What happens in an air conditioner operating on “heat” at temperatures close to 0 ° C? The phase transition temperature for the normal heat transfer process is set below the ambient temperature by the value of the total difference, which for outdoor units of household air conditioners is 5-15 ° C. That is, even at an ambient air temperature of + 5 ° C, the phase transition (evaporation) temperature, even for a good heat exchanger with a small drop, is negative. This leads to the fact that the heat exchanger begins to become covered with frost, heat exchange with air worsens, the total temperature difference increases, the evaporation temperature drops. Since the performance of the air conditioner is almost proportional to the pressure (temperature) of evaporation, it also drops.
The capacity of the heat exchanger, “overgrown” with frost, is not enough to evaporate the incoming liquid refrigerant, and it begins to flow to the compressor suction.
What are the consequences for the air conditioner this can cause?
- The defrosting system of the outdoor unit, periodically switched on, leads to the formation of ice inside the condensing unit of the air conditioner and, in turn, to blockage or destruction of the fan blades.
- Liquid refrigerant that has not evaporated in the heat exchanger enters the suction line, then into the liquid separator, then into the compressor, causing water hammer.
- Overheating, and then (if liquid refrigerant enters the compressor housing) freezing of the compressor.
The reason for the listed consequences is the too low performance of the heat exchanger of the air conditioning compressor-condensing unit when the outdoor temperature drops.
Unfortunately, there are no effective methods to increase this productivity. The consequences are usually disastrous. Therefore, it is categorically impossible to turn on the air conditioner for “warm” at negative ambient temperatures..
To summarize, we can say:
The best way to operate the air conditioner in winter is conservation. If necessary, you can operate the air conditioner, but only in the “cold” mode and provided it is equipped with a winter set.
Can air conditioners be used effectively in winter to heat a room, or should other heating systems be prioritized?