Delta is commonly used to refer to a difference between two points. So in this case, a delta of 110 degrees means whatever your target temperature is, the radiator should be 110 degrees away from that temperature. Trying to reach 70° means a temp of 180 at the radiator when heating, or -40° when cooling. OP was pointing out that -40° obviously isn’t a feasible temperature for a water-based radiator, so they simply aren’t great for cooling.
Energy transfer is proportional to the difference in temperature between the 2 things (delta T), their contact surface area (in this case the length of the radiator and the size of the fins), and time. If you want a room to change temperature quickly and with radiators that don’t take up an entire wall then you need the water temperature to be very different from the room temperature.
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Delta is commonly used to refer to a difference between two points. So in this case, a delta of 110 degrees means whatever your target temperature is, the radiator should be 110 degrees away from that temperature. Trying to reach 70° means a temp of 180 at the radiator when heating, or -40° when cooling. OP was pointing out that -40° obviously isn’t a feasible temperature for a water-based radiator, so they simply aren’t great for cooling.
Temperature difference between the radiator water and room air.
Energy transfer is proportional to the difference in temperature between the 2 things (delta T), their contact surface area (in this case the length of the radiator and the size of the fins), and time. If you want a room to change temperature quickly and with radiators that don’t take up an entire wall then you need the water temperature to be very different from the room temperature.