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?
O
Oetzberger25 Oct 2021 07:24guckuck2 schrieb:
In the end, nothing had to be throttled, the flow rate everywhere remained at maximum.Then you were lucky with the design of your underfloor heating system. Or you have a good heating engineer or planner.KingJulien schrieb:
@guckuck2 Lucky you. Did you have a good plumber?There are certainly worse cases. The calculations were done room by room. The key to success is definitely the pipe length/density; the temperature level can then be chosen individually.
The balance only works because we agreed on a uniform temperature. Some people prefer to sleep at 19°C (66°F) and have 24°C (75°F) in the bathroom. This needs to be taken into account in the pipe lengths/density and/or by increasing the supply temperature and then throttling room by room.
guckuck2 schrieb:
There are reportedly people who prefer to sleep at 19°C (66°F) and have 24°C (75°F) in the bathroom. This needs to be taken into account with pipe lengths/density and/or by increasing the supply temperature and then throttling room by room. That’s why the desired room temperatures are defined in advance, so nothing needs to be throttled later.
H
Hausbau 5525 Oct 2021 11:34Hello Lesmue, according to your table, a flow rate of 14.3 liters per minute = 858 liters per hour was calculated. Are you still below the maximum possible flow rate of the heat pump with this value? After your throttling, you are below 500 liters per hour. That is a really significant reduction in flow rate. Can you comment on that? Or are my numbers not correctly represented?
It was close to 0 degrees Celsius (32°F) early on here. What heating load/heating output was achieved at that time? How far did your heat pump (Vaillant Arotherm Split 3.5 kW) reduce its output?
It was close to 0 degrees Celsius (32°F) early on here. What heating load/heating output was achieved at that time? How far did your heat pump (Vaillant Arotherm Split 3.5 kW) reduce its output?
The problem is that it is a standard general contractor / prefab house provider design. The heating load is calculated at 3.2 kW at -12°C (10°F), but there is an inherent error because the controlled mechanical ventilation was not included in the heating load calculation.
Transmission losses are 2424 watts, plus 752 watts of ventilation losses, totaling 3176 watts. Assuming a heat recovery efficiency of 70% in the controlled mechanical ventilation, the ventilation loss reduces to 225 watts, which means the total heating load would be only 2649 watts.
The underfloor heating is of course designed for the full 3176 watts, although this includes rooms calculated at 20°C (68°F) that are actually intended to reach only about 18-19°C (64-66°F) (bathroom, guest room, bedroom, hallway).
The utility room can be completely excluded because it is already too warm due to external heat sources (inverter, heating circuit distributor, etc.) despite the underfloor heating being switched off.
Accordingly, the actual volume flow is lower than the calculated value.
The fact that the floor heating design is primarily for foot comfort is shown by the bathroom circuit; how exactly are you supposed to set 0.3 liters per minute on a Tacosetter valve? The calculated flow velocity in this circuit is actually 0.0 m/s.
In the guest room, at 0.8 L/min, it is 0.1 m/s. The system is designed for a maximum supply temperature of 30°C (86°F).
That is why many Tacosetters appear as if they have zero flow according to the calculation. I already have almost no adjustable flow for the 20°C (68°F) setting, and in reality, since I want only 18-19°C (64-66°F), even less.
I have already mentioned that I fully closed the circuits once and then reopened them until a minimal resistance was noticeable. However, this is barely visible because the Tacosetters only reliably display flows from about 0.5 L/min.
Transmission losses are 2424 watts, plus 752 watts of ventilation losses, totaling 3176 watts. Assuming a heat recovery efficiency of 70% in the controlled mechanical ventilation, the ventilation loss reduces to 225 watts, which means the total heating load would be only 2649 watts.
The underfloor heating is of course designed for the full 3176 watts, although this includes rooms calculated at 20°C (68°F) that are actually intended to reach only about 18-19°C (64-66°F) (bathroom, guest room, bedroom, hallway).
The utility room can be completely excluded because it is already too warm due to external heat sources (inverter, heating circuit distributor, etc.) despite the underfloor heating being switched off.
Accordingly, the actual volume flow is lower than the calculated value.
The fact that the floor heating design is primarily for foot comfort is shown by the bathroom circuit; how exactly are you supposed to set 0.3 liters per minute on a Tacosetter valve? The calculated flow velocity in this circuit is actually 0.0 m/s.
In the guest room, at 0.8 L/min, it is 0.1 m/s. The system is designed for a maximum supply temperature of 30°C (86°F).
That is why many Tacosetters appear as if they have zero flow according to the calculation. I already have almost no adjustable flow for the 20°C (68°F) setting, and in reality, since I want only 18-19°C (64-66°F), even less.
I have already mentioned that I fully closed the circuits once and then reopened them until a minimal resistance was noticeable. However, this is barely visible because the Tacosetters only reliably display flows from about 0.5 L/min.
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