Which radiators to combine with the heat pump?

12/11/2021 – One thermal system is composed of the following physical elements:
– the generator;
– the distribution system (pipes, pumps, manifolds);
– the emission system, i.e. the terminals such as radiators, convectors, radiant surfaces;
– the regulation system.

Whether it is a new construction or a renovation, the choice of the generator is falling more and more on heat pumps. The most suitable emission systems for a heat pump are low temperature systems such as i radiant floor or ceiling panels e i ventilconvettori.

But if you don’t want to give up the ‘classic solution with radiators‘, is the combination of heat pump and radiators possible?

Yes, but only if there is a pre-analysis based on the possibility and convenience of the intervention, that there is the correct sizing of the distribution lines and the size of the radiators and that a professional heat pump is chosen.

First, by opting for a solution HP + radiators, the heat pump must necessarily be of the type air – water. The heat pump extracts heat from an external source, in this case the air, to heat the water that will reach the radiators.

You could also opt for a heat pump water-water, but being a solution that uses the energy of the water present in the subsoil, it requires an extraction and absorption well and therefore more spaces such as those of suburban residential areas.

Modular wall-mounted aluminum radiator OBLIQUE © K8 Radiators

But which radiators are best associated with an air-water heat pump?

I radiators on the market there are many, but it is possible to distinguish them according to the material in:
cast iron radiators;
steel radiators;
aluminum radiators.

For correct operation with the heat pump le features that the exchanging body should have are:
exchange surface as large as possible;
low water supply temperature.

I aluminum radiators they allow to work at lower temperatures than the others, 45/48 ° C, and have a large exchange surface made of lamellae or tubes. This allows to exchange almost all of the heat contained in the supply water.

Also, if well sized they have one higher output power which allows to adequately heat the room where they are installed without requiring excessive supplies of hot water.

Regarding this last point, to determine the correct sizing, that is the thermal yield of the radiator, the basic principle to start from is always that of work according to the ambient temperature.

The reference design parameter for determining the heat output of radiators is the ∆t (° C), i.e. the difference between the average temperature of the water (Tm) and the ambient air (Ti) which in design conditions is equal to 20 ° C:

∆t (° C) = Tm – Ti


In the technical data sheets the yield values ​​are declared for ∆t = 50 ° C and refer to an average water temperature Tm = 70 ° C (typical high temperature of the condensing boiler).

If the Tm is lowered to 50 ° C, low temperature typical of the HP, we would have: ∆t = 50 ° C – 20 ° C = 30 ° C.

Which radiators to combine with the heat pump? Horizontal aluminum radiator ROADS STF ©Cordivari Design


How can ∆t = 50 ° C be kept unchanged?

By increasing the yield of the radiator by adding a sufficient number of elements to the existing aluminum radiator or by insulating the casing to reduce the heat requirement.

In the first case, the aluminum radiators will be larger than if they were combined with a boiler. But, also in this case the production, through innovative design solutions that see the use of extruded aluminum, has created planar solutions of great aesthetic impact in which there is the right balance between greater extension and final yield.

Other fundamental indications to follow are:
– if the heat pump is in an external technical compartment and therefore the piping is external for a section, it must avoid heat dispersion properly insulating the pipes.
– the diameter of the piping must be suitable for the chosen HP model, i.e. it must be checked that the volumetric water flow of heating has no load losses.


Source: Le ultime news dal mondo dell'edilizia by www.edilportale.com.

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