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pump-to-air-to-water heat-The outside air is an energy source unlimited and always available: its use by means of a heat pump, in addition to being free, requires no no authorization process.

It appears as a source with a variable temperature: in fact, daily temperature variations occur and, in the long term, seasonal variations.

When designing a system in heat pump it is important to take account of these changes, drawing on the normalized temperature values ​​for each geographic location: annual maximum and minimum temperature, average monthly temperatures.

La UNI 5364 associated to the main places a minimum outdoor temperature project: in areas not mentioned in the standard climatic parameters can be calculated according to altitude and exposure with respect to a reference city, according to the UNI 10349.

By virtue of temperature rises outside, the DPR 412 / 93 divided the whole country into six climate zones each of which corresponds to a different duration of the exercise period of the heating system.


This division is carried out by means of the number of "Degree Day": Parameter corresponding to the sum, extended to all the days of the heating season of sun daily positive differences, between the ambient temperature, fixed conventionally to 20 ° C and the average outdoor temperature daily.

This parameter gives immediate information on the climate zone in fact much the higher its value, the more the climate of the location object is rigid.
In the following table, you specify the parameters for each climate zone:

Duration season
heating days
number of hours max
A <600 105 6
B 601-900 121 8
C 901-1400 137 10
D 1401-2100 166 12
E 2101-3000 183 14
F > 3000 200 No restriction

Climate zones as per DPR 412 / 93

Along with the minimum temperature of the project, including the seasonal average temperature is a value to be taken into account in the design phase: this can be easily obtained from the normalized data of the locality.

The relationship between the number of degree-days and the number of days of the heating season corresponds to the difference between the internal temperature of project ti = 20 ° C and the average temperature seasonal:

Δtm = (Degrees Day / Time season heating days) * ° C

By difference with the internal temperature of the project, it dates back to the average temperature of the winter season:

tm (° C) = ti - Δtm

For the sizing of the heat pump can be energetically convenient to refer to a temperature between the average temperature and the seasonal minimum external project, rather than directly to the latter.


Degree Day GG 2468 = g ° C
Climate zone: E
Outdoor temperature: Te =-5 ° C
Duration of the heating season D = 183 days
Internal temperature of the project: ti = 20 ° C
Δtm = DD (° Cg) / D (g) = 2.468 / 183 13.5 ° C =
tm (° C) = ti - Δtm 20 = - = 13.5 6.5 ° C

For the location in question is the minimum temperature Te = project-5 ° C and the average temperature
Seasonal tm (° C) = 6.5 ° C. The sizing of a heat pump in operation monovalent must be carried out at the minimum temperature of the project, while in case of operation bivalent, The dimensioning must be carried out to a temperature between the minimum design and the seasonal average.

If you want to do the insights on heating with heat pump, You can find valuable information at the following links:

Rossato Group Srl
Via del Murillo, km 3.500, 04013 Sermoneta LT - Italy
Share capital € 200.000,00 fully paid up - no. REA LT-107494
VAT-CF IT01745300598

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