Is an air-to-water heat pump (PAC) the ideal solution?
First the weather
In cold regions, it may be preferred to a geothermal heat pump solution with sensors buried in the ground or on an aquifer (groundwater table), more adapted to climatic conditions, but also more expensive. We, therefore “forget” the “air-water” solution when we operate in regions with a harsh climate and we consider it with a mild climate, even in coastal areas. The region is not necessarily a criterion, on the other hand, the altitude is taken into account. Above 600 meters, the pump captures the calories in a source at too low a temperature. It will saturate and will no longer work.
It is also better to automatically forget this solution when the dwelling is located in a residential area. “In these places, pay attention to the noise level emitted by the machines. Progress has been made in the field, but most heat pumps remain noisy with an acoustic power of between 60 and 70 decibels, which gives a pressure level of around 38 to 43 decibels at 5 meters. A fairly low sound level (30 to 50 decibels characterizing places of rest or “intellectual work”), but still too high compared to the volume required by a neighbor accustomed to a level ranging from 0 to 30 decibels, the “norm” in very quiet places. We also forget the “backyard” that resonates, also remembering that neighbors can sometimes be more bothered by the sight of the machine.
The known “global” context and the actual characteristics of the dwelling are also to be taken into account. Houses of 100 m2 or less, built after 1988, already have adequate insulation. Most heat pumps currently on the market are therefore overpowered with regard to their needs.
Today, in a BBC – low-consumption building – the very low heating needs no longer justify an air-water heat pump, first of all, advise to insulate the envelope before installing a heat pump.
Which air-to-water heat pump (HP) model to choose?
Everything will depend on the configuration of the premises and the work envisaged, depending on the space: one-piece or two-piece.
First point of size: ensure that the heat pump will have an optimal location. A minimum of 2 m2 is required, but this depends on the area to be heated and the model chosen. The “air-water” heat pump models sold on the market can indeed be monobloc or block. A “one-piece” heat pump includes all its elements inside a “carcass”, it is positioned either inside or outside the dwelling.
A “split” heat pump is a machine in separate elements where the air exchanger, the compressor, and the expansion valve are installed under a “casing” on the outside while the water exchanger is inside. . A refrigeration link (which must be insulated) connects the two units. Advantage? The water is contained in the indoor unit and does not freeze. There is therefore no need for antifreeze, which tends to cause a drop in the COP*. Energy performance coefficient. It is the ratio between the number of kWh consumed and rejected at a given outdoor temperature. A COP of 3.3 means that for 1 kWh consumed, the machine will restore 3.3. The COP of an air-water heat pump will oscillate between 2 and 5 while a geothermal heat pump can reach 7.
Note that if a one-piece heat pump can be installed by a plumber-heating engineer, it must be commissioned by a qualified operator, while a “split” heat pump can only be installed and commissioned by a certified operator (article R543- 78 of the Environmental Code). Given this decree and the typology of professionals, professionals foresee the imminent disappearance of “split units”.
The nature of the issuers
Another criterion for choosing the heat pump model: the nature of the transmitters present or program in the works and particularly their water supply temperature. A heat pump is strongly discouraged coupled with “high temperature” radiators: it will work much less well. And the performance of the heat pump will be lower: more electricity will have to be consumed to raise the temperature of the heating circuit.
The nature of the issuers is of another interest. It will allow knowing if it is relevant to propose a reversible heat pump allowing the “refreshing” or if this functionality is superfluous. Remember that radiators are not capable of emitting cold, unlike floor or ceiling heating. If the customer wants to cool his house via his heat pump, and he does not have underfloor heating, it is possible to install fan coil units. However, using the “cooling” function of the heat pump throughout the hot season risks “annihilating” the energy savings made during the winter.
Knowledge of the supply temperature of the transmitters will then guide you in advising the temperature of the heat pump. Attention, if the market has clearly taken the fold of the “high temperature”, higher than 65°C, it is not necessarily the most relevant solution since, high or low temperature, the electrical back-up or the coupling to the boiler will generally be advised. As the term suggests, a high-temperature heat pump is capable of producing water at 65° C with outside temperatures of -15° C while a standard heat pump will supply water at 45° C with -10° C exteriors. For the user, the difference will be seen above all in terms of price. However, there will be an important consequence on comfort: if a standard heat pump is installed with a water temperature of 45°C instead of a “high temperature” which will give 65°C, sufficient ambient temperature will never be obtained and the backup will be regularly called upon. Hence the importance of thermal diagnosis upstream in order to choose the most appropriate equipment.
Finally, if your customers rely on their heat pump to produce DHW, they will need to be advised of a model with the appropriate technology and power. It takes 500 watts more heat pump power per person for use in DHW production: today there are more financially advantageous solutions. There is also heat pumps only intended to produce domestic hot water, the DHW is then produced and then stored by a thermodynamic water heater.
Labels and certifications
- The Eurovent certification makes it possible to check the acoustic power emitted by the machine, especially refrigeration machines.
- The Qualipac designation implies a quality approach with products certified by a standard (NF PAC) and qualified companies employing people trained in technical training centers.
- The equipment must be labeled NF PAC or EN 1411.2
What gain in boiler backup?
To calculate the energy savings induced by the installation of a heat pump backing up an existing boiler, go to the Promotelec website (“thermal comfort” section). You can access the “Pac Optim” online simulator for free.
The “Inverter” or “Flash Injection” function
More and more heat pump models are called “Inverter” or flash injection (superior model). This means that the pump adapts its heating or cooling power according to the needs of the house. It’s all about the compressor. In the case of “flash” injection, a gas-liquid mixture offers better performance, especially with high-temperature emitters.