I radiators terminals are most common in existing buildings and can be cast iron, aluminum or steel alloys. Their selection in the design phase is carried out according to the values declared by the manufacturers and generally work with:
- Tu = 70 80 ÷ ° C
- Tr = 60 ÷ 70 ° C
The reference design parameter for determining the thermal output of the radiators is Δt (° C), ie the difference between the average temperature of water and ambient air which under design conditions is equal to 20 ° C:
- Dt (° C) Tm = - 20
The yield values are declared for Dt = 50 ° C, or for an average water temperature Tm = 70 ° C and are tabulated or obtainable even for lower values of temperature.
Performing an operation of generator replacement of an existing building, an information on the thermal requirements necessary can be obtained also by the type of radiators, the number of elements and the design temperatures.
The radiators are most common in cast iron and in aluminum, Which can be of help for the consultation of the following tables refer to the most common sizes.
And 'advisable, replacing the old generator with a heat pump, Work lower temperatures in order not to affect the energy savings achievable with the heat pump; reference may be taken to the following values for the flow temperature:
- Tu = 45 55 ÷ ° C.
At a reduced flow temperature corresponds a good energy saving.
The heat output of low-temperature radiators appears to be reduced so to remedy the non-heat input can be increase the number of elementthe radiator or, better, you can initiate actions aimed at reducing the heating requirements such as replacing windows with more efficient windows, insulation of the building envelope, etc. ..
Consider a room heated by a radiator in aluminum with the following dimensions
- height: 68 cm
- depth: 95 cm
- number of elements: 6
The radiator receives water at high temperature by a boiler of conventional type:
- Flow temperature Tu = 70 ° C
- Return temperature Tr = 50 ° C
- Average temperature Tm = 60 ° C
- Temperature Ti = 20 ° C
The average water temperature difference air is t = Tm-Ti = 40 ° C
The consultation of yield data standard is:
- Yield per item: 110 W
- Yield radiator = 6 110 x W = W 660
If the same radiator is fed with water at low temperature produced by a heat pump:
- Flow temperature Tu = 55 ° C
- Return temperature Tr = 45 ° C
- Average temperature Tm = 50 ° C Ti = 20 ° C
The average water temperature difference air is t = Tm-Ti = 30 ° C
The consultation of the table 1.2 (or the same table manufacturer dl) is:
- Yield per item: 74 W
- Yield radiator = 6 74 x W = W 444
We obtained a difference in yield of emitted 216 W. This can be done in several ways:
- 3 add elements to the existing radiator
- intervene isolating the casing to reduce the heating requirements of the environment.
If you want to do the insights on heating with heat pump, You can find valuable information at the following links: