Just out of curiosity, to better understand the slope of the heating curve, what flow temperatures do you typically run at 0°C (32°F) outdoor temperature, given a certain indoor temperature and insulation level, when using a combination of underfloor heating and a heat pump?
Background of the question:
My logic tells me that if I want, for example, 22°C (72°F) room temperature, the flow temperature must be at least 22°C (72°F) or higher, since I learned that there needs to be a temperature difference for heat transfer to occur.
So if my heating system turns on at 12°C (54°F) outdoor temperature, my flow temperature should logically start somewhere around 22°C–25°C (72°F–77°F). Accordingly, at only 5°C (41°F) outside, it should be around 27°C (81°F), and at 0°C (32°F) close to 30°C (86°F).
The system design usually takes the location and outdoor temperature down to about –12°C (10°F). If at 0°C (32°F) flow temperature is already 30°C (86°F) according to my logic, then at –12°C (10°F) the flow temperature should be about 40°C (104°F). But most underfloor heating designs for heat pumps are based on a maximum flow temperature of 35°C (95°F).
Of course, the insulation of the house and the indoor temperatures still play a role. Or is the increase in flow temperature actually so gradual that it only rises by about 0.5–1°C (1–2°F) for outdoor temperature drops in 0–5°C (0–9°F) increments?
Background of the question:
My logic tells me that if I want, for example, 22°C (72°F) room temperature, the flow temperature must be at least 22°C (72°F) or higher, since I learned that there needs to be a temperature difference for heat transfer to occur.
So if my heating system turns on at 12°C (54°F) outdoor temperature, my flow temperature should logically start somewhere around 22°C–25°C (72°F–77°F). Accordingly, at only 5°C (41°F) outside, it should be around 27°C (81°F), and at 0°C (32°F) close to 30°C (86°F).
The system design usually takes the location and outdoor temperature down to about –12°C (10°F). If at 0°C (32°F) flow temperature is already 30°C (86°F) according to my logic, then at –12°C (10°F) the flow temperature should be about 40°C (104°F). But most underfloor heating designs for heat pumps are based on a maximum flow temperature of 35°C (95°F).
Of course, the insulation of the house and the indoor temperatures still play a role. Or is the increase in flow temperature actually so gradual that it only rises by about 0.5–1°C (1–2°F) for outdoor temperature drops in 0–5°C (0–9°F) increments?
A
Alessandro8 Nov 2021 12:06That is why it is important to monitor the temperature difference (delta T) of each individual heating circuit. As I mentioned above, a flow rate of 3 liters per minute (0.8 gallons per minute) for a heating circuit is actually a design mistake.
I have raised the heating curve from 0.2 to 0.24. The bathroom is now at 22.4°C (72.3°F) with a flow rate of 3 liters per minute (0.79 gallons per minute). I have slightly lowered the flow rates in the other rooms, around 0.8 to 0.9 liters per minute (0.21 to 0.24 gallons per minute).
The outdoor temperature averaged 4.7°C (40.5°F) over 24 hours. The consumption was 13 kWh, of which 3 kWh was for domestic hot water. The heat pump cycled twice in the last 24 hours.
The outdoor temperature averaged 4.7°C (40.5°F) over 24 hours. The consumption was 13 kWh, of which 3 kWh was for domestic hot water. The heat pump cycled twice in the last 24 hours.
Yesterday, I measured the supply and return temperatures directly at the heating circuits. I noticed that, except for the guest toilet, the supply and return temperatures have a differential of 2°C (3.6°F). In the guest toilet, the supply and return temperatures are the same, so I have now reduced the flow there.
This means I need to raise the heating curve and reduce the flow to the other rooms even more to ensure the guest toilet gets warm enough. Around 21°C (70°F) in the guest toilet would be good.
The floor temperature is 24°C (75°F) in all rooms and 25°C (77°F) in the bathroom.
This means I need to raise the heating curve and reduce the flow to the other rooms even more to ensure the guest toilet gets warm enough. Around 21°C (70°F) in the guest toilet would be good.
The floor temperature is 24°C (75°F) in all rooms and 25°C (77°F) in the bathroom.
Malz1902 schrieb:
... in the guest bathroom, the supply and return lines are the same, so I have now reduced the flow.
But does that also mean I need to increase the heating curve and throttle the other rooms more to make the guest bathroom warmer? The radiators in the rooms are probably installed in parallel, right?
(so not a single-circuit system with a bypass?)
Yes, throttle the return line.
Otherwise, the radiators closer to the heat source will take heat away from those further downstream.
If the temperature difference across the radiator is too low, then the radiator is undersized.
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