Air to water heat pump, split or single unit? What to choose ?

These are often referred to as split-system heat pumps and sometimes as single-system heat pumps. Depending on the country, one or the other type of heat pump is more often installed. In France, for example, 90% of installed heat pumps are split. This article explains the difference between these two types of heat pump.

  • Monobloc: the entire refrigeration circuit is in the outdoor unit.
  • Bibloc: the refrigerant circuit is in two parts, one inside and one outside.

NB: you can request a quotation for a split-system or single-system heat pump from our network of RGE Qualipac-qualified installers, using the form below (valid in France and Belgium).

The Bibloc or Split heat pump

This type of heat pump is the most common in France, but not in Switzerland, except in border regions. Bibloc heat pumps are also known as split heat pumps. The principle is easy to understand. Part of the refrigeration circuit is in the outdoor unit. This is the part that captures heat from the outside air. It consists mainly of the evaporator, compressor and expansion valve.

The outer block is then connected to an inner module, also known as the hydraulic module, via refrigerant lines, to close the refrigerant circuit at the condenser. The condenser is the 4th major component in the refrigeration circuit. It can take the form of a plate heat exchanger, or a coaxial condenser.

It's the heat exchanger that redistributes the calories captured outside, to the house's water circuit, and to the domestic hot water tank if the latter is produced by the heat pump.

The fact that there is a refrigerant link between the two units, indoor + outdoor, means that refrigerant is constantly circulating between the inside and outside of the house:

  • This represents a higher refrigerant charge than for a monobloc model where the circuit is confined to the outdoor unit.
  • This increases the potential risk of refrigerant leaks, which depending on the fluid used, can be harmful to the environment, but will of course put the entire heat pump system at risk until the leak is detected and repaired by a refrigeration engineer.

This kind of split installation requires the full know-how of a refrigeration engineer, to make the indoor-outdoor connection according to the rules of the art, and then to troubleshoot if anything goes wrong. Not every heating engineer has these skills.

A split heat pump does NOT perform better than a single-package heat pump, contrary to what you may read in some places. There's no reason why it should have better power or a better COP. It's all in the arrangement of the components, just a matter of design and choice.

The split system is restrictive because it limits your choice of professionals.

The monobloc heat pump

With this type of heat pump, the outdoor unit contains all the major components of the refrigerant circuit. These include the evaporator, compressor, expansion valve and condenser. The heat is then transferred via a water pipe from the outdoor unit to the house's technical room.

The refrigerant is confined to the outdoor unit. No refrigerant passes between the inside and outside of the house.

Remote pipes buried in the garden will need to be installed, through which water with a little glycol will circulate to prevent freezing in the most extreme winter weather conditions. Unfortunately, this glycol leads to a loss of power, as glycoled water doesn't transmit calories as well as pure water, so there's a loss of efficiency in the process.

No fluid handling certificate is required for a heating engineer installing this type of device, except for commissioning a heat pump containing more than 2kg of fluid.

With a monobloc heat pump :

  • Installation is simpler and less costly
  • There's also the cost of long-distance pipes to transport the water from the inside to the outside. These are not included in the price.
  • There's no need for an interior module in the house, so you save space compared to split models. But unless you're a fan of the Wim Hof method, you'll still need a domestic hot water tank.
  • There's no need to call in a refrigeration engineer for installation or repairs, since they're still a rare commodity and their rates are often higher than those of heating engineers or other sanitary fitters.
  • The power that can be transmitted from the outdoor unit is limited to the flow of water that can pass through the remote pipes. As a result, it will be difficult to increase the system's power, should the need ever arise, since it will never be possible to pass more water through the pipes, which have a fixed cross-section. With a split system, you can play with the parameters of a refrigerant gas to modulate power, or even change the gas, which is simpler.

Advantages and disadvantages of Bibloc vs Monobloc

PAC BiblocGood power transmission of heating, directly by the refrigerant.
Possibility to go up to higher temperatures heating water, like a Daikin Altherma 3H HT.
More flexible in terms of power modulationor power evolution, by retrofitting.
The need for a refrigeration engineer to connect the refrigeration circuit.
Higher fluid load
A little more expensive to install
- Device a little more expensive
Takes up space inside the home
PAC MonoblocNo need for refrigeration skills to connect individual heat pumps if they have less than
2kg of fluid in their circuit
- Device cheaper
Cheaper installation
- Installation less space consuming
Less risk of leakage of gas
- Gas outside, so it's possible to use it in all safety. security gases ecological but flammable, such as propane or R290 and other
Loss of yield due to the glycol in the water that links the interior to the exterior.
- Need to install remote control lines for water transport + circulation pump.

The split-system heat pump makes most sense in the case of a high-temperature heating water requirement, for example if you're renovating old radiators and keeping them in place. But then the COP will be poor...closer to 2 than 4. It is also relevant in the case of a home that will evolve over time and require more power in the future. It will be easier to adapt the split heat pump to the new conditions.

The PAC Monobloc makes sense if the technical room is small, if the house is not likely to change significantly, if you want to save money on installation and equipment, or if you don't want to depend on the specialized skills of refrigeration specialists who are sometimes hard to find. Last but not least, it provides peace of mind by keeping refrigerant gas out of the house, reducing the risk of serious fire caused by flammable gases such as R32 or R290.

The future in Bibloc or Monobloc?

In France today, as mentioned above, the majority of air-to-water heat pumps are based on the split model. And you only have to look at the EDF website, which is obliged to promote renewable energies because of the CEE tax, to realize that they are clearly pushing towards split models.

In Switzerland, the trend is not as pronounced, firstly because manufacturers are not pushing for split but rather monobloc models, and secondly because refrigeration specialists are not as present as in France, if not trained in large enough numbers. Sanitary fitters, however, are very present throughout Switzerland, and install heat pumps that they can control and connect without any specific knowledge, i.e. monobloc models.

The future will be marked by changes in refrigerants: R410A is already disappearing, to be replaced by R32, which has a GWP (Global Warming Potential) 3 times lower (around 700), but is slightly flammable. On the other hand, some manufacturers such as Vaillant and Alpha-Innotec are already looking further ahead and using a gas that is even less damaging to the ozone layer, with a ridiculously low GWP of 3, namely propane or R290. However, this gas is much more flammable. The trend is therefore in the direction of safety, and we can imagine that more and more manufacturers will offer monobloc models and push towards these solutions for safety reasons with R290 gas. Indoor-outdoor connections would then be made with water, rather than with this kind of environmentally-friendly but flammable gas.

Also read to increase your heat pump culture:

Daikin split heat pump reviews

Opinions on a NIBE packaged heat pump

How does a PAC work?

About the author

Juliena mechanical engineering graduate and specialist in climate engineering since 2009, has become a writer specializing in renewable energies, with expertise in heat pumps and photovoltaic solar panels for individual housing.