Reckoning thermal yelds
The heating systems through radiant panels must be sized according to the features of the house and to geographical conditions, so as all heating systems. Especially, we must consider external minimum project temperatures, day-degrees and insulation of the house to define radiant power to be installed.
In unfavourable conditions (wall transmittancy over 0,9 W/mq °C), it might be needed to install up to 50 W/m3 per room. The needed power decreases thanks to the insulation of the house, to increasing of minimum project temperature, and to the decreasing of day-degrees. For instance, in passive houses we can go down to 12 W/m3. Definitely in passive houses we can install radiant panels to inhance comfort and the heat sensation on the skin.
The size of the system depends on more factors, such as:
1) use of the house (usual, for holidays)
2) if the system is the only heating system or it has to help a resident system
3) personal habits
Another important thing to consider is that we can quite surely foresee the electric consumption and the cost per year. Indeed, the installed power is in a 1:1 report (COP=1) with thermal power needed to heat a room.
Let’s see 2 practical instances of maximum consumption:
1) We need to heat a room with 20 sm area and 2.7 m height; if we hypothesize the room is slightly insulated (0,8 W/sm °C) and it needs a thermal power 30W/m3, then the needed power is exactly
30 (W/m3) x 20 (sm) x 2.7 (m) = 1620 W
If we consider the system continuosly switched on (it never happens with a chrono thermostat installed), the radiant panel un 5 hours absorbs
1620 (W) x 5 (h) = 8100 Wh = 8,1 kWh
If we hypothesize to pay energy 0,22 €/kWh, we can reckon the cost per day:
8,1 (kWh) x 0,22 (€/kWh) = 1,72 €/day
2) We need to heat the same room ( 20 sm, 2,7 m height) with a sufficient insulation ( approximately 0,5 W/sm °C). In this case the needed power per m3 is 22 W/m3, then the total power will be:
22 (W/m3) x 20 (sm) x 2.7 (m) = 1188 W
If we consider the system continuosly switched on (it never happens with a chrono thermostat installed), the radiant panel un 5 hours absorbs
1188 (W) x 5 (h) = 5940 Wh = 5,94 kWh
If we hypothesize to pay energy 0,22 €/kWh, we can reckon the cost per day:
5,94 (kWh) x 0,22 (€/kWh) = 1,23 €/day
3) If we try to heat the same room ( 20sm, 2.7 m height) in a passive house, with an excellent insulation (approximately 0,12 W/sm °C), the needed power is 5W/m3.
Then the total power will be:
5 (W/m3) x 20 (sm) x 2,7 (m) = 270 W
If we consider the system continuosly switched on (it never happens with a chrono thermostat installed), the radiant panel un 5 hours absorbs
270 (W) x 5 (h) = 1350 Wh = 1,35 kWh
If we hypothesize to pay energy 0,22 €/kWh, we can reckon the cost per day:
1,3 (kWh) x 0,22 (€/kWh) = 0,28 €/day
Important: when we decide to install electric radiant panels with infrared rays emission, it’s advised to lightly oversize the system. Indeed, due to the decreasing of the needed temperature by 1-3°C, we can obtain significant savings on energy consumption.
Obviously, if we can get energy from our photovoltaic system, heating becomes a null cost system.
In facts radiant panels installation allows to heat not the air of the environment, but the skin, the objects, the walls, the floor. With this system, we can feel the heating flow almost immediately.
This means that a radiant panel can be lit where and when it’s needed. This way, the cost of energy consumption becomes minimum, even for those who don’t own a photovoltaic system.
Overall, installing control units to manage electric absorbtions, we can decrease consumption, and it is not needed to change the power available for the builnding (famous 3,3 kW, 6 kW, 10 kW or more, offered by energy suppliers)