Heat Pump Types and the Dream Team with Solar Systems
Introduction: The Right Heat Pump for Every Application
Every building is unique and requires a sophisticated heating system. Heat pumps do not come in just one version – there are numerous types for every application.
The three most common heat pump types:
- Air-water heat pump
- Ground-source heat pump (brine-water)
- Air-air heat pump
The designation always reveals:
- First word: Heat source (where does the heat come from?)
- Second word: Heat carrier (what distributes the heat?)
Air-Water Heat Pump
The most popular variant in Germany. It extracts heat from the outdoor air and transfers it to the heating water.
Operating Principle
Outdoor air (heat source)
│
▼ Fan draws in air
│
Evaporator (heat absorption)
│
▼ Refrigerant circuit
│
Condenser (heat release)
│
▼
Heating water → Underfloor heating / RadiatorsStructure
- Outdoor unit: Evaporator with fan
- Indoor unit: Compressor, condenser, control
- Split design: Outdoor and indoor units separate (common)
- Monoblock: Everything in one unit (more compact)
Advantages
The air-water heat pump impresses particularly with its simple installation:
| Advantage | Explanation |
|---|---|
| Low installation cost | No drilling or groundwork |
| Usable everywhere | No special plot requirements |
| Quick installation | Installed in a few days |
| Retrofit possible | Suitable for existing buildings |
Disadvantages
Using outdoor air also brings some disadvantages:
| Disadvantage | Explanation |
|---|---|
| Efficiency in cold | Less efficient at low temperatures |
| Noise | Outdoor unit can be audible |
| Appearance | Outdoor unit visible |
| Varying output | Dependent on outdoor temperature |
When Sensible?
- Standard solution for most detached houses
- When no groundwork is possible
- With limited budget for installation
- For retrofits in existing buildings
Ground-Source Heat Pump (Brine-Water)
This heat pump uses the constant temperature of the ground as a heat source. Also known as geothermal heat pump.
What is "Brine"?
Brine = Water + antifreeze
This mixture circulates through pipes in the ground and transports heat to the heat pump.
Two Variants
Ground Collectors (Horizontal)
- Pipes laid flat under the ground (1–1.5 m deep)
- Large area required
- Rule of thumb: 1 m² collector area = ~25 W output
The required collector area depends on the desired heating output:
| Heating Output | Required Area |
|---|---|
| 5 kW | ~200 m² |
| 8 kW | ~320 m² |
| 10 kW | ~400 m² |
Ground Probes (Vertical)
- Deep boreholes (40–150 m)
- Less space required
- More constant temperature at depth
- Rule of thumb: 1 metre depth = 40–80 W output
The required borehole depth varies depending on ground conditions and desired output:
| Heating Output | Borehole Depth |
|---|---|
| 5 kW | 60–125 m |
| 8 kW | 100–200 m |
| 10 kW | 125–250 m |
Advantages
Using constant ground heat offers decisive advantages:
| Advantage | Explanation |
|---|---|
| High efficiency | Constant ground temperature (~10°C) |
| Constant year-round | Independent of outdoor temperature |
| Very quiet | No outdoor unit with fan |
| Long lifespan | Ground collectors last decades |
| Highest SPF | Often above 4.5 |
Disadvantages
The high efficiency comes at the cost of some limitations:
| Disadvantage | Explanation |
|---|---|
| High installation costs | Groundwork or drilling expensive |
| Permit required | Often necessary for drilling |
| Space requirement | Collectors need large area |
| Not possible everywhere | Ground conditions important |
When Sensible?
- New build with large plot (collectors)
- Suitable ground for drilling
- Long-term investment planned
- Maximum efficiency desired
Air-Air Heat Pump
The air-air heat pump transfers heat directly via air – without heating water.
Known as: Air Conditioning!
The air conditioners in hotels or warmer countries are air-air heat pumps. They can:
- Heat (heat from outside to inside)
- Cool (heat from inside to outside)
Two Main Variants
Split System
- Outdoor unit: Evaporator/condenser
- Indoor unit: Heat release directly to the room
- Connected by refrigerant lines
Air Heating with Heat Recovery
- Uses exhaust air as heat source
- Fresh air is heated with the waste heat
- Often used in passive houses
Advantages
The air-air heat pump offers advantages particularly in well-insulated buildings:
| Advantage | Explanation |
|---|---|
| Cooling possible | Air conditioning in summer |
| Quick response | Heat directly in the air |
| Low installation cost | No heating system needed |
| Individual room control | Each room individually |
Disadvantages
As a pure air heating system, this has limitations:
| Disadvantage | Explanation |
|---|---|
| No hot water | Additional solution needed |
| Draughts possible | Warm air is blown in |
| Dust and allergens | Filtering important |
| Less efficient | Than air-water for heating |
When Sensible?
- Passive houses with controlled ventilation
- Supplementary heating for individual rooms
- When cooling is also desired
- For very well-insulated buildings
Comparison of Heat Pump Types
The three heat pump types differ in several important characteristics:
| Criterion | Air-Water | Ground-Source | Air-Air |
|---|---|---|---|
| Typical SPF | 3.0–4.0 | 4.0–5.0 | 2.5–3.5 |
| Installation costs | Medium | High | Low |
| Operating costs | Medium | Low | Medium |
| Space requirement | Low | High | Low |
| Hot water | Yes | Yes | No |
| Cooling possible | (With addition) | (With addition) | Yes |
| Noise level | Medium | Very quiet | Medium |
| Permit | Rarely | Often | Rarely |
The Dream Team: Heat Pump + Solar System
What is better than one sustainable technology? Two combined sustainable technologies!
The combination of heat pump and solar system can heat your own house completely CO2-neutral.
Why Do They Fit Together So Well?
The two technologies complement each other ideally, as this overview shows:
| Component | Provides | Requires |
|---|---|---|
| Solar system | Electricity | Sun |
| Heat pump | Heat | Electricity |
The solar system produces electricity during the day – exactly when the heat pump is working!
How the Combination Works
Solar modules
│
▼ Solar electricity
│
Inverter ──────┬──► Heat pump
│
├──► Household
│
└──► Battery storage (optional)Advantages of the Combination
The combination of both systems brings numerous advantages:
| Advantage | Explanation |
|---|---|
| CO2-neutral heating | With own solar power |
| Lower operating costs | Own electricity costs less |
| Independence | Less grid consumption |
| Eligible for subsidies | Government grants |
| Symbiotic | Systems complement each other optimally |
Disadvantages of the Combination
The combination is not without challenges:
| Disadvantage | Explanation |
|---|---|
| High investment | Two systems to purchase |
| Winter problem | Less solar power when heating most needed |
| Complexity | More components to manage |
Solving the Winter Problem
In winter, heating demand is high but solar production is low. Solutions:
- Larger PV system – still enough yield even in winter
- Battery storage – store energy temporarily
- Optimised charging behaviour – charge battery during day, heat in evening
- Grid electricity as backup – remaining demand from grid (possibly green electricity)
Sizing for the Combination
Rule of thumb for PV system with heat pump:
Normal PV size + 2–3 kWp extra for the heat pump
Depending on heat pump output, the PV system should be sized correspondingly larger:
| Heat Pump Output | Additional PV |
|---|---|
| 5 kW | +2 kWp |
| 8 kW | +3 kWp |
| 12 kW | +4–5 kWp |
Example Configuration
A typical detached house could be equipped as follows:
| Component | Sizing |
|---|---|
| Floor area | 150 m² |
| Heat pump | 10 kW (air-water) |
| PV system | 10 kWp (incl. heat pump demand) |
| Battery storage | 10 kWh |
| Expected self-sufficiency | 60–70% |
Conclusion
| In Brief: The choice of heat pump type depends on many factors: The decision for a heat pump type depends on various factors: | Factor | Best Type |
|---|---|---|
| Limited space | Air-water | |
| Maximum efficiency | Ground-source | |
| Also cooling | Air-air | |
| Existing building | Air-water | |
| New build + garden | Ground-source |
The combination with a solar system is the dream team for sustainable heating. With own solar power, the heat pump becomes a CO2-free heating system.
The Complete Article Series "Heat Pumps"
- The Anti-Refrigerator: How Does a Heat Pump Work? – Fundamentals
- The Components: Heat Exchanger, Compressor and Expansion Valve – Components
- Heat Pump Key Figures and Sizing – COP, SPF and more
- Operating Modes: Monovalent, Bivalent and Hybrid – Operating modes
- Heat Pump Types and the Dream Team with Solar Systems – You are here
Related Article Series
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- Lithium vs. Lead: Which Battery for Solar Systems?
- The All-Rounder: Hybrid Inverters
- AC or DC? System Topologies for Solar Systems
How Does a Solar System Work?
- From Photon to Volt: How Does a Solar Cell Work?
- Structure of a PV System: From Module to Grid Feed-In
- Key Figures for Solar Systems: The Glossary
Battery Storage and Powerstations:
- Battery Technologies Compared: Lithium, Lead and Solid-State
- Powerstations: The All-in-One Solution for Solar Systems
- Market Analysis 2025: Battery Storage and Powerstations