Types of heat pumps

Comparative technical and economic characteristics of three types of air-to-water heat pumps

Below is a detailed technical and economic analysis of three types of air-to-water heat pumps: monobloc, system SPLIT and FULL SPLITThe correct choice of heat pump type has a great importance on the efficiency of the system in general (COP, consumption etc.) For each variant the following are analyzed separately:

• Advantages and disadvantages of construction;

• Particularities of the fixed and variable speed compressor (inverter);

• The influence of vapor injection (EVI) technology;

• Heat losses and recommendations regarding thermal insulation.

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🔹 1. Monoblock (external installation, all hydraulics are outside)

⚙️ Construction:

All components — compressor, circulation pump, hydraulic circuit (water or antifreeze), control electronics — are located in a single outdoor block. Heat is transferred directly from the outdoor unit to the heating system.

✅ Advantages:

• Simple installation, especially in small buildings without a technical room.

• Compact design and minimal connections.

• No refrigerant lines required — the hydraulic circuit is directly connected.

❌ Disadvantages:

• Antifreeze is required on the outside, otherwise there is a risk of freezing.

• If it is not desired to introduce antifreeze into the heating system, an intermediate heat exchanger or a coil tank is required.

• The compressor and all electronics are in the cold — critical at temperatures below –10 °C.

• Requires electric crankcase and pan heaters — these consume energy even in standby.

• Heat loss: parasitic heat generated by the compressor and other components is lost to the atmosphere.

🔸 Parasitic heat:

• Fixed compressor: ≈ 15–18% of the energy consumed is dissipated as heat.

• Inverter compressor: between 12 and 15%.
  → This energy is completely lost in the case of the monoblock.

⚙️ Inverter / fixed speed:

• Fixed compressor: cheaper, but:

  • operation through frequent starts/stops;

  • shorter lifespan;

  • requires buffer tank.

• Inverter:

  • soft start, high COP at partial loads;

  • higher cost and complexity (possible defects);

  • includes: frequency converter, EMI filters, sensors.

💡 Conclusion:

These types of heat pumps are a suitable solution for simple applications, summer swimming pools, economical systems, in areas with mild winters. Frost protection is essential. Low efficiency in the cold season. It is important which types of heat pumps are chosen specifically for one object or another if the choice is a Monobloc PDC.

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🔸 2. SPLIT system (external unit + refrigerant circuit + internal heat exchanger)

⚙️ Construction:

• The compressor, fans and condenser are located outside.

• The plate heat exchanger (condenser) is installed inside the building.

• A refrigeration line (up to 10–20 m) is installed between the two.

✅ Advantages:

• All hydraulics are inside — there is no risk of freezing and no need for antifreeze.

• Superior energy efficiency than monoblock, thanks to internal heat exchange.

• There is no need for buffer tanks or intermediate coils.

❌ Disadvantages:

• Insulation of the refrigeration circuit is critical: the freon after the compressor reaches 70–90 °C — losses and overheating of the walls can occur.

• More complex route assembly: strict requirements regarding length, inclination and welding.

• As with the monoblock — crankcase and drainage heating is required.

• Risk of freon leaks, need for refilling.

⚙️ Inverter / fixed speed:

• Same advantages and disadvantages as the monoblock.

• The length of the path influences the correct operation of the inverter (resonances, pressure variations).

• More difficult diagnosis.

💡 Conclusion:

Types of SPLIT heat pumps are ideal for homes with a technical room and the possibility of installing a refrigeration circuit. They require careful installation and appropriate thermal insulation.

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🔹 3. FULL SPLIT (all components inside, only the air-freon evaporator outside)

⚙️ Construction:

All the main components — the compressor, valves, electronics, heat exchanger — are located inside. Only the evaporator with fans remains outside. The freon is transported to the outside via the refrigerant line.

✅ Advantages:

• Components are protected from the cold — the compressor, electronics and valves operate at optimal temperature.

• The parasitic heat generated (compressor, inverter, etc.) remains inside and contributes to heating.

🔸 Parasitic heat:

• Inverter: ≈ 12–15% remains inside.

• Fixed compressor: up to 20–27% (depending on configuration).

• No crankcase heating is required — ambient heat is sufficient.

• No need for antifreeze.

• Minimal risk of breakdowns in winter — the crankcase does not require preheating or in minimal quantities.

❌ Disadvantages:

• More complex control system, especially for long routes.

• It must be sized correctly for temperature differences (risk of loss of efficiency).

• Higher cost.

⚙️ Inverter / fixed speed:

• The inverter is very efficient: the outdoor unit operates optimally, low starting current.

• Fewer cycles — increased durability.

💡 Conclusion:

Types of heat pumps FULL SPLIT They are the most efficient air-to-water technology and can be recommended for energy-efficient buildings, where stability, economy and avoidance of frost risks are important. It is the best option if the indoor unit can be installed in a heated space.

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🔸 Optional: vapor injection (EVI)

EVI Compressor:

• Provides two-stage compression — increased efficiency at low temperatures (–15…–25 °C).

• Useful in cold regions.

• More expensive and more complex (injection, additional exchanger, valves).

• Increases COP by 10–30% in heating mode in frost.

❌ Disadvantages:

• Requires specialized maintenance.

• More difficult diagnosis.

• Useless in mild climates.

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📊 Conclusions and recommendations

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📊 Technical and economic analysis – 10 kW heat pump

Purpose of the report: evaluating the performance of a 10 kW heat pump under different outdoor conditions and flow temperatures.

Parameters analyzed:

• COP (coefficient of performance);

• Electrical power consumed;

• Thermal losses (auxiliary consumption, losses, etc.).

Methodologies: The COP varies depending on the outdoor temperature and the flow temperature. The thermal load is constant: 10 kW.

Analyzed outdoor temperatures: +5, 0, –15, –25 °C
Temperature of the tower: +35, +45, +55 °C

Systems analyzed:

• Geothermal heat pump (stable COP)

• Standard air-water

• Air-water inverter

• Air-water with EVI (vapor injection)

Results:

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📌 Explanation of the graphs:

1. COP (Coefficient of Performance)
   FULL SPLIT has the highest constant COP due to the placement of components inside.
   SPLIT has average efficiency.
   Monoblock — the weakest, due to losses and outdoor location.

2. Energy consumption (kW)
   The lower the COP, the higher the consumption.
   At –25 °C and flow +55 °C:

   • Monobloc: ~5.9 kW for 10 kW thermal

   • FULL SPLIT: ~4 kW

3. Parasitic heat losses (kW)

   • Monoblock: up to 1 kW

   • SPLIT: ~0.6–0.8 kW

   • FULL SPLIT: only 0.1–0.2 kW

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Conclusions:

• Geothermal pumps (Types of ground-to-water, water-to-water heat pumps) offer the best COP constant, regardless of the outside temperature.

• The COP drops drastically for air-to-water systems (Monobloc heat pump types) at low temperatures.

• Inverter and EVI compressors increase efficiency at negative temperatures.

• The tour below or equal to +35 °C is significantly more efficient than +55 °C.

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📎 Annex:

Detailed calculation tables, graphs and Excel file are provided separately.

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