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?
Mycraft schrieb:
Has anyone here ever observed the behavior of the systems and the corresponding room temperatures over a longer period? These snapshots don’t tell you anything. The supply temperature constantly fluctuates. That means it can be completely different even in the same house with the same outdoor and indoor temperatures. Loosely quoting Klaus Kinski: “I don’t understand the question.” 😀
The supply temperature is always going up and down.
Mycraft schrieb:
... The supply temperature is constantly fluctuating. That means it can have completely different values in the same house under the same outdoor and indoor temperatures.What kind of control is that?
While the flow rate (and thus the heating output) can vary—depending on the number of rooms currently being heated—under constant outdoor and indoor temperatures, the supply temperature is usually stable, or it is adjusted to the target temperature as long as the current heating output is sufficient.
D
Daniel-Sp23 Dec 2021 13:10If the heat pump is controlled by the return flow, this is not the case. Then the supply temperature depends on several factors. For example, the current heating output/compressor frequency, volume flow, difference between return flow and return flow setpoint, and the heat transfer (HT) of the house. From this, the temperature spread and therefore the supply temperature are determined. This applies to all Novelan, AIT, and I believe also Nibe heat pumps.
For these heat pumps, the control variable return flow setpoint is more suitable for performance comparison.
For these heat pumps, the control variable return flow setpoint is more suitable for performance comparison.
@driver55
The flow temperature naturally fluctuates. For that reason, I don’t really understand the purpose of this entire thread.
No, it isn’t, because it depends on what is happening inside the house at the moment as well as what happened in previous hours. Additionally, neither the inside nor the outside temperature is ever truly constant; they constantly vary. A house is not a laboratory specimen but is usually occupied.
The flow temperature naturally fluctuates. For that reason, I don’t really understand the purpose of this entire thread.
konibar schrieb:
but with constant outside and inside temperatures, the flow temperature is usually constant,
No, it isn’t, because it depends on what is happening inside the house at the moment as well as what happened in previous hours. Additionally, neither the inside nor the outside temperature is ever truly constant; they constantly vary. A house is not a laboratory specimen but is usually occupied.
Mycraft schrieb:
@driver55
Supply temperature always fluctuates. For that reason, I don’t really see the point of the whole thread.
No, it does not {supply temperature}, because it depends on what is currently happening inside the house and also on what happened in the last few hours. In addition, neither the indoor nor the outdoor temperature is ever constant and both constantly vary.I’m not sure if we are talking about the same thing:
Of course, the supply temperature oscillates around the target temperature due to the hysteresis of the heat pump compressor.
But it is generally constant for today as well as tomorrow, depending on the slope and offset of the control in relation to the outdoor and indoor temperature.
Independent of that, the flow rate of the heating water fluctuates and therefore so does the radiator temperature.
(Supply temperature and radiator temperature are NOT the same!)
It may be that the control system "remembers" the type of use of the rooms and temporarily increases output when activated
so that the target temperature is reached faster.
But these are all transient states. On average, in the steady state, the supply temperature will be constant, depending on the outdoor temperature and settings.
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