Most of us have the experience that a small room could be cooled down in several minutes, but for a larger space, the temperature decreases slowly even though the air conditioner has been operating for a long time. It doesn't mean the air conditioner has not enough cooling ability; instead, a most important physical concept contributed to the situation—thermal inertia, which is often being omitted.

 

I. What's thermal inertia?

 

Thermal inertia is the insensitivity level of an object or space to the temperature exchanges. Simply, it means the higher the thermal inertia, the slower the temperature exchanges; and the lower the thermal inertia, the faster the temperature exchanges.

 

It is not simple data, which is determined by three factors: mass, specific heat capacity, and the heat exchange conditions.

Inside the buildings and rooms, the thermal inertia performs mainly in walls, ceilings, floors, appliances, and the air itself. All those items will store heat.

 

II. Why does a larger house have a higher thermal inertia?

 

1. More items which store heat in the house

 

The larger house has wider wall areas, larger air volume, more concrete and bricks used in construction, and more space to put appliances and decorations. These are all heat storages. When the outside temperature is high, those heat storages have absorbed much heat already.

 

2. Air conditioning is to remove heat first, not to lower the temperature

 

The core task of air conditioners is not to blow cold air but to remove the heat from indoors to the outdoors steadily.

In large spaces, the air conditioner needs to remove heat from walls, floors, appliances, and the air steadily. The larger the space, the more heat needed to be removed, so it took a longer time.

 

3. The surface temperature determines the body temperature

 

Though the temperature had been cooled down, if the wall is hot, the floor is hot, and the appliance surface is hot, according to reflection heat transfer, the human body will feel its heat as well.

That's why people still don't feel cool even though the temperature already shows 24℃ in the large house. Thermal inertia makes it much slower for people to get "real coolness."

 

 

III. Why it may not necessarily solve the issue by purchasing a larger capacity cooling device?

 

Most people will choose a larger capacity air conditioner to cool a large house, such as a floor standing air conditioner or a cassette air conditioner. But the common questions are unreasonable gas-liquid distribution, cold air cannot reach the areas with heat burden, unreasonable air-return design, and long-term stays of heat in a partial area. As a result, the energy consumption rises, but the comfort has no significant improvement.

 

IV. For cooling in the large spaces, the key is to deal with the thermal inertia

 

1. Start the air conditioner in advance, rather than operating it when it's hot

2. Focus on the airflow coverage, rather than the cooling capacity

3. Zoning control, separately dealing with the thermal inertia

4. Matching the air conditioning systematically rather than focusing on the unit datas

 

In large houses, villas, and commercial spaces, VRF, ducted air conditioners, and joint-combined systems are more suitable in both comfort and energy savings.

 

In the large houses, it's not harder to blow cold air but to remove more heat, which is the thermal inertia that influences it. What determines the comfort is not only how big the air conditioner is, but also whether the whole system is recognized and allowed to operate by following the physical rules.

To those living in extremely cold regions, a common question comes when it is needed to heat by an air conditioner in winter: can the air conditioner outdoor unit operate freely in an extremely cold environment or not? Particularly under the ultra-low temperatures of -30℃ and -40℃, is the air conditioner able to supply reliable heat?

 

1. What are the limits of traditional air conditioners?

 

Traditional non-inverter or inverter air conditioners are available to operate under the ambient temperature of -7℃ to -15℃. When the temperature goes further lower, the situations below will occur:

 

i). Apparent decrease of heating capacity;

ii). Severe frost on the outdoor unit and defrosting affect heating performance.

iii). The compressor is hard to start or does not even start.

 

In case of that, traditional air conditioners can not start freely under the temperature of -30℃ and even -40℃.

 

2. Advanced technology: EVI technology

 

For cold regions, air conditioner manufacturers will develop the air conditioner models with EVI (Enhanced Vapor Injection) technology. By adding additional jet ports for gas in the compressor, the technology allows the refrigerant to keep enough pressure and flow under the extreme cold condition, improving the heating ability under low temperature. Adopted with EVI technology, the air conditioners could provide stable heating under -25℃ to -30℃ environments. Some high-end models are claimed to start freely under -35℃.

 

3. Impossibility under -40℃

 

Under a -40℃ environment, even the high-end air conditioning models are still facing great challenges:

 

i). The starting difficulty: Thickening of the refrigerant oil makes it difficult to lubricate the compressor.

ii). The decreasing heating capacity: Even if the system can start, the heating capacity will be significantly reduced.

iii). The increasing power consumption: Even if the system can start, the heating capacity will be significantly reduced.

 

Common solutions to the -40℃ environments are ultra-low temperature air source heat pumps (customized commercial/engineering machines), rather than ordinary household air conditioners, or electric auxiliary heating and gas heating with air conditioning used in conjunction.

 

4. Options for the cold areas.

 

For regions in the Mongolia plateau, Northern Russia, and Canada, it is recommended to choose low-temperature heat pump air conditioners with EVI technology or directly choose air source heat pump heating units, whose operating limit can be extended to -35℃ or even -40℃, or combine them with backup heating methods such as floor heating and electric heaters to ensure comfort and safety in extreme weather.

 

Traditional air conditioners can't start at -40°C. Even some high-end low-temperature heat pump models claim to be able to operate, but they require extremely demanding technical support and operating environments. For users in extremely cold regions, choosing a professional ultra-low-temperature heat pump product is the only reliable way to heat your home in winter.