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Is it worth buying a heat pump?

Heat pump – is an energy-efficient heating, cooling and water heating device that uses heat from the environment (air, water or soil) and transforms it for use in your home or office. The main advantages of heat pumps:

Energy savings : use up to 75% of energy from renewable sources.
fickle : works for both heating and cooling.
Ecological : minimal carbon dioxide emissions.
Comfort : stable temperature throughout the year.

But all this is beautiful in words, but in reality there are some peculiarities. To make the right choice and decide what is needed for a real object, you need to understand it a little. Sellers and speculators will sell and disappear from life forever, and the user must figure out why this piece of iron did not live up to the intentions and fairy tales of the seller…

Let's try to understand the essence of the problem without complex formulas of thermodynamics, elementary physics and mathematics. In this article we will consider the heat pump type AIR-WATER . So... a little patience! This is very important!

The reality of heat pumps: What you need to know about COP

Almost everyone has heard rave reviews about heat pumps: how "brilliant" they are, how they offer savings, and what " "Impressive COP" they have. Such discussions can be heard especially anywhere, even at bus stops. But let's be honest: everything is marketing . It doesn't always reflect reality. Let's figure out what COP (coefficient of performance) is and why it's not as simple as it seems.

On paper, this sounds great. In laboratories where engineers work under ideal conditions (for example, +7℃ outside and +35℃ in the heating system), a heat pump can display such values. Some models even reach a COP of 7 or higher. But real life is not a laboratory.

COP: What is this, actually?

COP , or coefficient of performance, shows how much heat the heat pump produces compared to the electrical energy it consumes. For example, COP = 5 means that for every 1 kW of electrical energy, 5 kW of heat is obtained.

Why is the real COP different?

1. Perceived temperature

The air temperature indicated in the weather forecast does not always coincide with our feelings. For example:

At +8 ℃ with high humidity and wind, humans will feel cold.
At the same temperature of +8 ℃ V. dry and windless weather can be comfortable.

These conditions directly affect the efficiency of the heat pump. Humidity is particularly important at low temperatures (+5℃ to -5℃). Humid air significantly increases the load on the system, reducing its performance.

2. Test conditions

Standard heat pump tests are performed at:

+7 ℃ extern air
+35 ℃ temperature water V. system heating

In such conditions, the COP looks great, for example 4.65. But in real life:

The temperature can be +2 ℃, humidity — 98% and wind improves heat transfer.
Under such conditions, the COP may drop significantly below the declared values.

Why do I choose +7℃ and +35℃ for testing? Because these are convenient, predictable conditions that give good results in marketing materials. But they do not reflect operation in harsh climate conditions.

Example from practice

Let's assume that a heat pump with a capacity of 10 kW is installed:

One is in northern Germany.
The other is in southern Italy.

What will be the COP of these two systems? The answer is simple: it will vary. In northern Germany, the humidity is higher and the temperature often drops below 0℃. Under these conditions, the actual COP will be lower than in Italy, where the air is drier and the winters are warmer.

How to correctly evaluate a heat pump?

Consider the actual climate. Compare the test conditions with the climatic characteristics of your region.
Pay attention to humidity. Especially if you live in an area with frequent rain or high humidity in winter.
Don't rely solely on COP. Look at the seasonal coefficient of performance (SCOP), which takes into account temperature changes throughout the year. Although this is not entirely true either. One year it will have an excellent COP, and the next year (warmer but more humid) it will be very bad.

Heat pumps are a truly efficient heating solution, but only if you choose wisely. Keep in mind that the stated COP is only part of the story, and actual performance depends on many factors, including climate and operating conditions.

An official report by independent experts on SOR is provided for your review. It will help you understand what SOR is and how to make the right choice.

All the necessary links for double-checking the data are also provided. As can be seen from the table, the situation is not so beautiful for air-to-water systems (especially air-to-water), for SPLIT and MONOBLOCK systems. There is practically no efficiency!

The performance of a heat pump in cooling mode is characterized by either the Energy Efficiency Ratio (EER) or the Seasonal Energy Efficiency Ratio (SEER), both of which are measured in BTU/(hr W) (note that 1 BTU/(hr W) = 0.293 W/W), with higher values indicating better performance.
COP change depending on outlet temperature
Pump type and source	Typical use	35 °C	45 °C	55 °C	65 °C	75 °C	85 °C
Pump type and source	Typical use	(e.g. underfloor heating screed)	(e.g. underfloor heating screed)	(e.g. heated wooden floor)	(e.g. radiator or hot water supply)	(e.g. radiator and hot water supply)	(e.g. radiator and hot water supply)
Pompă de căldură cu sursă de aer (ASHP) de înaltă eficiență, temperatura aerului -20 °C[56]		2.2	2	–	–	–	–
ASHP în două etape, temperatura aerului -20 °C[57]	Low source temperature	2.4	2.2	1.9	–	–	–
ASHP de înaltă eficiență, aer la 0°C[56]	Low outlet temperature	3.8	2.8	2.2	2	–	–
Prototip de pompă de căldură transcritică cu CO2 (R744) cu răcitor de gaz cu trei căi, sursă la 0 °C[58]	High outlet temperature	3.3	–	–	4.2	–	3
Pompă de căldură geotermală (GHP), apă la 0 °C[56]		5	3.7	2.9	2.4	–	–
Măcinare GSHP la 10°C[56]	Low outlet temperature	7.2	5	3.7	2.9	2.4	–
Theoretical limit of the Carnot cycle, source -20 °C		5.6	4.9	4.4	4	3.7	3.4
Theoretical limit of the Carnot cycle, source 0 °C		8.8	7.1	6	5.2	4.6	4.2
Limita teoretică a ciclului Lorenzen (pompă de CO2), retur lichid 25 °C, sursă 0 °C[58]		10.1	8.8	7.9	7.1	6,5	6.1
Theoretical limit of the Carnot cycle, source 10 °C		12.3	9.1	7.3	6.1	5.4	4.8

CONCLUSION: Don't believe in miracles! A heat pump is a good product that really does its job, but it is not a panacea for everything. Don't be fooled by advertising and marketing scams!

What types of heat pumps are there?

“Heat pump” is a subjective concept, which does not have a specific terminology, technology or product. Everything that surrounds us can be called a heat pump. For example, the Universe, a kettle heating water in the kitchen, our body, the weather, an air conditioner. Therefore, if you were offered an air conditioner and told that it is a “heat pump”, in fact, the seller did not lie. Another thing is whether this “heat pump” will meet our expectations!

MONOBLOCK

The product in the configuration MONOBLOCK It is mainly intended for heating (or cooling, if it has a reversing function) swimming pools, spaces for which the heating system is not vital. Or for regions with moderate temperatures where temperatures do not drop to zero. To understand how a heat pump works, it is very important to know how it is built, especially how it works COMPRESSOR of a heat pump and its characteristics heat exchangers .

MONOBLOCK is a design in which all the components of the heat pump are combined in a single module located outdoors. This means that the compressor, heat exchangers (condenser and evaporator), refrigerant and coolant (e.g. antifreeze) are under the direct influence of the environment, including rain, frost and wind. This design requires increased attention to protecting the system from adverse conditions and additional measures to maintain its functionality during the cold season.

To ensure the correct and long-lasting operation of the heat pump, it is essential that the oil in the system circulates efficiently, ensuring constant lubrication and cooling of the compressor. However, as the ambient temperature drops, the viscosity of the oil increases, which can lead to operating difficulties and even compressor blockage.

In systems where the compressor is exposed to the environment, it is necessary to use an electric heater for the compressor oil bath. This device prevents the thickening of the oil and ensures its normal circulation. However, the presence of an electric heater is associated with additional energy costs and may cause delays in starting the heat pump, especially at the time when its operation is most needed for heating.

Heat exchangers at Monobloc.

Since MONOBLOCs are not designed to operate in low temperature regions, the requirements for the heat exchanger are minimal, as the original purpose of the MONOBLOC is to heat water in swimming pools, where heat exchangers do not necessarily need to operate at low ambient temperatures.

Essentially, the concept of a LARGE HEAT EXCHANGER does not exist, because the best heat exchanger is a HUGE heat exchanger. Which, in fact, is not applicable in MONOBLOC type systems. In order for the system to operate efficiently at any ambient temperature, the heat exchanger must be very large. By this external criterion, you can understand whether the seller is lying or not when he says "I promise operation down to -25 °C ”.

If air-freon heat exchanger (evaporator) is reduced, the system will work, but not at low temperatures, since there is such a concept as SUPERHEATING, which cannot be ensured at low temperatures if the heat exchanger is small. For the system to work at -25 °C » the heat exchanger must be huge (sometimes several times larger than for an air conditioner).

Freon-water heat exchanger (condenser) is essential for system efficiency. For example, you can install a freon-water heat exchanger with a surface area three or more times smaller and it will work (which u(Some people do.) The secret lies in the coolant flow rate and the required temperature delta (to keep the condensation level) within normal limits.

Therefore, with a decrease in the surface area of the heat exchanger, it is necessary to increase the flow rate (flow rate) of the coolant through it. This leads to an increase in the power of the circulation pump and, consequently, to an increase in costs.

We can say that such a pump does not consume much. This is not true! The operating time of the circulation pump is much longer than that of the compressor itself. And reality! All this "good stuff" is outside. Let's imagine the ambient temperature is -10°C. The system starts working.

First, the electrical resistance of the compressor is turned on. It is necessary to bring this temperature from +12 to +20 10°C. Then the compressor starts working. First, the compressor itself must warm up, then the refrigerant is heated. Only after that – the heat carrier circulating through the heat exchanger is heated.

How much money is needed for this, no seller will say. And… at this wonderful moment, unpleasant news came: defrosting, which will “take” most of the heat “pumped” in the previous process. And so on in a cycle. Beautiful?

Above the 46th parallel, it is not recommended to use MONOBLOC type devices for heating rooms for which heating is vital! SPLIT: What is it and how to choose the right option? The heating equipment market often presents devices that are actually converted air conditioners.

Yes, an air conditioner is also a heat pump, but with different functionalities and purposes. However, the technologies ideal for air conditioners are not always optimal for heat pumps in the climatic conditions of our region.

Heat pump or air conditioner?

Any air conditioner can be "converted" into a heat pump. For example:

You buy an air conditioner for 600 euros (you only need the external unit).
Instead of the internal unit (evaporator), a freon-water plate heat exchanger is installed.
The fan is replaced by a circulation pump.

After such modifications, this device can be sold for 3,000 euros – and believe me, there will be many buyers. Will it work? Yes, but only when it is warm outside. So, when choosing a heat pump, make sure that you do not buy a system with low resources, for example, 48,000 BTU, which is more suitable for air conditioning than for heating.

What is the difference between an air conditioner and a heat pump?

1. Design and heat exchanger

A heat pump has a much larger heat exchanger than an air conditioner of the same capacity.
If the device is declared as operating at temperatures down to -25℃, this heat exchanger will be even higher.

If the device does not indicate low temperature parameters, then it is most likely an adapted air conditioner and not a full-fledged heat pump.

2. Energy efficiency

Air conditioners and some modified units can "cope" with heating, but at temperatures below zero degrees their efficiency drops sharply.
Some energy is spent on maintaining the system in cold conditions, especially if the compressor is located outside.

When is SPLIT a good choice?

SPLIT systems, specially designed for heating, are applicable in our regions. But they will be effective only under one condition: The heat pump is not the only source of heat in the house. The main problems of SPLIT systems in cold climates:

The compressor and heat exchanger, located outdoors, operate in difficult conditions.
It is often necessary to expend energy on "self-service" of the system, especially in cold weather.

Summary

If you choose a heat pump, carefully check its parameters and purpose.

For main heating systems, select devices with a large heat exchanger surface area and the ability to operate at low temperatures (down to -25℃).
If the heat pump is an auxiliary heat source, SPLIT may be a good option.

Don’t let marketing fool you. Buying a “customized air conditioner” can lead to a big expense, without the expected result. Choosing a temperature of -25℃ does not mean that “there are no such temperatures in our region”. There will be! Definitely! And also – the indicator of the possibility of operating the device at low temperatures is a direct indicator of its efficiency.

FULL SPLIT heat pump

The FULL SPLIT heat pump consists of two modules:

An internal module containing all components, including a compressor, a freon-water plate heat exchanger (condenser), electronics, etc.
An external module, which consists of an air-freon heat exchanger (evaporator) and a fan (fans).
Since the system is not limited by form factor dimensions, this allows the heat exchangers to be placed over a larger area and the use of steam injection technology without restrictions.
The parasitic (excess) thermal energy generated by the freon pipeline, compressor (and this is about 12-20% of the total generation capacity), remains inside the room, transforming this energy from parasitic into useful. The heating temperature of the compressor itself is often in the range of +70ºС … +85ºС, sometimes up to 100ºС and more (depending on the refrigerant used).
Ease of operation and maintenance of the system, regardless of the weather.

What does -25°C mean for a heat pump?

Example: How temperature affects heat pump performance

Option 1: Standard conditions (+7°C / +35°C)

Heat pump capacity: 12.91 kW of thermal energy.
Home consumption: 60 W/m² at a temperature of +7°C and comfortable humidity.
Stable operation: The heating capacity of the pump covers the needs of the house.
BEER is 4.49

Option 2: At ambient temperature (0°C)

High humidity: This is typical for our region at these temperatures.
Home consumption: It starts to exceed 60 W/m².
Performance loss: The heat pump loses efficiency (11.93 kW) and energy is wasted on system maintenance (COP = 3.86).

Option 3: At ambient temperature (-12°C)

Home consumption: It far exceeds 60 W/m².
Performance loss: The heat pump loses even more efficiency (8.89 kW) and energy is wasted on system maintenance (COP = 3.02).

The considered operating modes are given for an air-to-water heat pump, FULL SPLIT (all important components inside the room) using the example of operating graphs taken in real conditions, an inverter version with steam injection function (EVI ON). Now imagine the operating modes of a SPLIT heat pump without injection and

(without even thinking) in a situation with the use of a MONOBLOCK heat pump. The temperature of -25°C in the context of the operation of the heat pump is often used as a marketing ploy. In practice, it is far from always possible to guarantee that the device will work efficiently in such conditions. It is especially important to take this parameter into account if the heat pump is the only source of heat in your home.

Technical characteristics of operation at low temperatures

To ensure reliable operation of the system at temperatures of -15°C and below, it is necessary to take into account a number of factors:

1. Increased heat exchanger surface area The lower the temperature at which the system is declared to operate, the larger the heat exchanger must be. This compensates for the decrease in heat exchange efficiency.
2. Evaporative Vapor Injection (EVI) This technology allows the system to operate efficiently at low temperatures, reducing the compressor load and improving performance.
3. Additional energy costs At low temperatures, the system consumes more energy for its own maintenance (e.g., heating the compressor), which increases operating costs.

For homes where the heat pump is the only source of heat, FULL SPLIT systems will be the most reliable choice. They minimize heat loss and ensure stable operation even in difficult climatic conditions.

Component placement It is optimal to have all system components, including the compressor and plate heat exchanger, located indoors. This reduces heat loss and increases operating efficiency.
Device type
- All-in-one PCs they are not suitable for use in extremely low temperatures because all their components are located outdoors.
- SPLIT systems with the EVI function can operate at temperatures down to -15°C and even -25°C, but their performance decreases as the temperature drops.
- FULL SPLIT systems They cope best with low temperatures. All the main components are placed in the heat, which allows the heat emitted by the device to be used to heat the house.

Conclusion

If you choose a heat pump for regions with low winter temperatures, consider:

The system can operate at -15°C or -25°C.
The availability of technologies such as EVI.
Placement of system components in the room.

What is vapor injection technology (EVI)?

Enhanced Vapor Injection (EVI) is a method of increasing the temperature/saturation pressure difference between the evaporator and condenser, achieved by using an economizer and an additional expansion valve. This allows an increase in the temperature of the hot outlet fluid in heating mode (air or water).

How EVI works:

Decrease in saturation temperature in the evaporator (outdoor unit in heating mode) allows the unit to extract more heat from the surrounding air in cold climate conditions.
Refrigerant overheating before injection into the compressor, the pressure and temperature at the compressor outlet increase, which contributes to the increase in the temperature of the liquid leaving the condenser.

ALTAL heat pumps with EVI technology

He would be GENERAL AWHP EVI is equipped with DC inverter compressors or fixed speed compressors with technology HOME technology HOME and inverter compressors allow heat pumps to operate efficiently at low ambient temperatures, providing reliable heating, cooling and hot water supply. Diagram and graph showing the principle of the influence of steam injection on the operation of an air-to-water heat pump system.

How Enhanced Vapor Injection (EVI) technology works

In the diagram shown, the liquid in the condenser 8 (A on the graph) is divided into two parts:

Minor part of the liquid (i) :
- Passes through the additional expansion valve 4 .
- with 6 plates (economizer) (HX), which operate on the countercurrent principle (superheating B on the economizer).
Main fluid flow (m) :
- This is cooled in the economizer 6 (point A on the graph) due to evaporation and overheating of the mass flow injected into the economizer.
- saver 6 works as a subcooler for the main mass flow ( m² ) and as an evaporator for the injected mass.

Superheated steam is then injected into the intermediate steam injection port HOME of the scroll compressor.

Efficiency of EVI technology

Additional cooling :
- Increases evaporator performance 3 by reducing the temperature of the liquid from TLI to TLO, which reduces its enthalpy.
- The heating capacity increases due to the additional condensate mass flow EVI (i).
Improved cycle efficiency :
- The vapor injection compressor cycle is more efficient than a traditional single-stage compressor delivering the same power.
- Additional power is achieved with lower energy consumption because the injected mass is compressed from an intermediate pressure rather than from a low intake pressure.

Advantages of EVI heat pumps

The additional subcooling effect in the EVI configuration allows the heat pump to extract heat from the outside air at lower temperatures. Only this technology can ensure uninterrupted operation of the heating system during the cold period.

Operating temperature range:
- Heat pump with DC inverter compressor or with fixed speed compressor without EVI operates in the range from -10°C .. 20°C to +45°C (outdoor air temperature).
- Heat pumps with DC inverter compressor or fixed speed compressor and EVI technology operate in an extended range: from -25°C to +45°C for refrigerants R32, R410 and from -30°C to +45°C for R290, R513, R1234ze.
- The steam injection function is activated programmatically at outdoor temperatures of +7°C or lower.

Thus, technology HOME makes heat pumps more efficient in harsh climates, providing stable heating at low ambient temperatures.