Heat pump efficiency

Heat pump and climate

Choosing a heat pumps is an extremely complex decision in the modern world. The demand has appeared – the supply has also appeared. And this is where the problems begin. Both on the part of the buyer, who does not understand exactly what a heat pump and forms their opinion from unauthorized sources, as well as from the seller, who often does not know what he is selling or, worse, unjustifiably "embellishes" the capabilities of the equipment. Let's take a concrete example.

All the vendors, advertising agencies and distributors promote the so-called "advantages" of heat pump in the form of value COPThis is a scam. COPThe (heat pump efficiency) is an abstract concept. All heat pumps of the same type and technology have identical heat pump efficiency, regardless of brand. But the actual heat pump efficiency depends significantly on environmental conditionsLet's analyze:

A. Heat pump brand X – 10 kW, air-to-water, monobloc.

Announced COP: 4.5. Installed in southern Romania, at outside temperature of +2 °C and relative humidity moderate.

B. The same heat pump brand X.

Installed in northern Romania, at outside temperature of -2 °C and moisture moderate.

The results will be completely different. If someone thinks that temperature is the decisive factor, they are wrong. Few people know that air humidity is an equally important parameter, as is atmospheric pressure. For example, at +8 °C and moderate humidity we can feel thermal comfort, but at the same outside temperature and high humidity, discomfort becomes evident.

Buildings, animals, and equipment also react to these climatic factors. The mistaken idea that temperature alone determines “weather” – propagated by the press and weather forecasters – leads to errors in the design of heating and air conditioning systems.

For the correct functioning of a heat pumps, and high heat pump efficiency. it is important to consider the following:

• Air temperature – official value published by meteorological centers. It is measured 1.5–2 meters above the ground, in the shade, in a shielded enclosure.

• Felt temperature ("Feels like") – takes into account wind speed (wind chill), relative humidity (heat index) and solar radiation.

• Atmospheric pressure.

• Air humidity.

Types of humidity: what matters?

1. Relative humidity (%)

The percentage of water vapor saturation at a given temperature.
The colder the air, the less water it contains, but relative humidity can reach 100%.

Example:
At -10 °C, air may contain a little water, but if it is saturated, relative humidity it is 100%.
In winter, in the morning, at -5…0 °C, relative humidity it is often 100% – especially in foggy or frosty conditions.

2. Absolute humidity (g/m³)

The actual amount of water vapor in 1 m³ of air.
Maximum in summer, on hot and humid days.

Example:
At +30 °C – up to 30 g/m³
At 0 °C – maximum 5 g/m³
At -10 °C – below 2 g/m³

Conclusion:

• Relative humidity it is maximum in winter, around 0 °C.

• Absolute humidity it is maximum in summer, at +30 °C and above, in tropical climates.

The impact of humidity on heat pumps

Both types of moisture are essential:

• Relative humidity determines ice formation and defrost frequency.

• Absolute humidity affects the heat capacity and latent energy of evaporation.

Therefore, the heating or cooling process in one region is completely different from another. We cannot compare the selection of equipment between Nordic countries, Japan and regions like Moldova or Ukraine.

Comparative example:

In Krasnoiarsk, at -20 °C and dry air, the pump can operate more stably than in Kishinev at -2 °C with relative humidity high. In this case the efficiency of the heat pump will be higher in Krasnoiarsk.

Sometimes it is even easier and cheaper to heat a building in Krasnoyarsk than in Chisinau. Why? In the morning, in winter, at -5…0 °C, relative humidity often reaches 100%. Then, through the crystallization of water vapor, the air becomes "dry".

The process of defrost can start even at +5 °C or more. In this case, air-to-water heat pump consumes energy to "protect itself", not to heat the building, the efficiency of the heat pump decreases significantly.

The COP (heat pump efficiency) becomes irrelevant if we consider:

• compressor crankcase preheating;

• preheating the system;

• cyclic operation;

• defrosting with energy taken from the building.

Result: huge costs for maintaining thermodynamic losses, to the detriment of useful energy.

The climate of the region: how are we doing?

In Romania, Moldova, Ukraine and southern Russia, winters have been milder in recent years. Temperatures:

Romania (plains, south and center):

• December: -1 °C…+3 °C

• January: -4 °C…+1 °C

• February: -3 °C…+3 °C

Bucharest: January -1…-2 °C

Ukraine (center and south):

• December: -2 °C…-5 °C

• January: -3 °C…-7 °C

• February: -2 °C…-5 °C

Kiev: January -5 °C
Odessa: January -2 °C

Moldova:

• December: 0…-2 °C

• January: -2…-4 °C

• February: -1…-3 °C

Kishinev: January -2…-3 °C

These data clearly show that the misunderstanding the climate of the region can lead to design failures, especially in the case of monoblock, which are not adapted to local conditions. For more details about types of heat pumps, check out this article:

Types of heat pumps

Conclusion

The correct misunderstanding of the climate of the region can lead to:

• Wrong choice of type heat pump

• Low or no yield

• High energy consumption

• High maintenance costs

The most vulnerable are monoblocks that do not have heat pump efficiency as a good benchmark for an efficient air conditioning system (heating and cooling), especially those without EVI (vapor injection). Therefore, the system must be chosen according to outside temperature, relative humidity, pressure and the architecture of the building.

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