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?
guckuck2 schrieb:
An oversized heat pump leads to short cycling. However, if the underlying underfloor heating system is reasonably well configured, this should not necessarily cause a “short circuit” that makes the return flow spike, thereby prematurely ending the cycle and then restarting shortly after, once the return flow has dropped again. Yes, exactly.
The consequence of improper settings can be that the hysteresis becomes too small.
This can happen if you try to maintain the supply temperature as precisely as possible.
But this is not necessary! It is perfectly fine for the temperature to fluctuate by a few degrees between the switch-on and switch-off points.
Maybe a few more liters of water could be added to the heating circuit?!?
(Well vented?)
Therefore, I would try to figure out which setting causes the small hysteresis and increase it accordingly.
This morning the outside temperature was 3°C (37°F) and the supply temperature was 26.5°C (80°F) with a 3.5 K delta T. The room temperature everywhere was around 20-21°C (68-70°F).
The energy integral was something around -115 degree-minutes.
According to the controller, the compressor modulation was 33%. I have now recorded the compressor starts and run hours and am curious to see the values this evening and tomorrow morning at the same time after 24 hours have passed.
The energy integral was something around -115 degree-minutes.
According to the controller, the compressor modulation was 33%. I have now recorded the compressor starts and run hours and am curious to see the values this evening and tomorrow morning at the same time after 24 hours have passed.
A
Alessandro22 Nov 2021 08:41Depending on the manufacturer’s specifications, you can calculate how many starts your heat pump should or may have to ensure a lifespan of 20 to 30 years.
Fifteen starts per day are absolutely no problem if the hydraulics are properly designed, the heat pump receives good flow, and it is well lubricated.
You always have to keep in mind that the majority of heat pump owners don’t think about optimization or settings.
And I would argue that of the heat pumps installed, certainly more than 50% are oversized. During transitional seasons, almost every heat pump is oversized anyway...
If compressors had to be replaced every 5 to 10 years, people would start an outcry.
There are also virtually no forum posts where people complain that the compressor failed after 2 to 10 years.
Of course, optimization makes sense especially when it comes to saving money, and some systems are really very poorly adjusted.
Most of the time, however, the problem lies in the screed...
Here and especially in the other forum, optimization is always taken to the extreme. 🙄
Fifteen starts per day are absolutely no problem if the hydraulics are properly designed, the heat pump receives good flow, and it is well lubricated.
You always have to keep in mind that the majority of heat pump owners don’t think about optimization or settings.
And I would argue that of the heat pumps installed, certainly more than 50% are oversized. During transitional seasons, almost every heat pump is oversized anyway...
If compressors had to be replaced every 5 to 10 years, people would start an outcry.
There are also virtually no forum posts where people complain that the compressor failed after 2 to 10 years.
Of course, optimization makes sense especially when it comes to saving money, and some systems are really very poorly adjusted.
Most of the time, however, the problem lies in the screed...
Here and especially in the other forum, optimization is always taken to the extreme. 🙄
lesmue79 schrieb:
This morning the outdoor temperature was 3°C (37°F) and the supply temperature was 26.5°C (80°F) with a temperature spread of 3.5 K. The room temperature everywhere was around 20-21°C (68-70°F).
The energy integral was roughly -115 degree minutes.
According to the controller, the compressor modulation was 33%. I have now noted the compressor starts and operating hours; I’m curious to see the values later this evening or tomorrow morning at the same time after 24 hours have passed. 33% corresponds to how many watts? My compressor currently runs at 32Hz with 788 watts at an outdoor temperature of 2.7°C (37°F).
Flow rate aside, according to the datasheet, the nominal flow rate of my heat pump is 540 l/h (1.4 gpm) at 5K
540 x 1.16 x 5 = 3132 watts
The heating load of the house is 3176 watts at 20°C (68°F) everywhere, without considering the mechanical ventilation with heat recovery.
If I open all circuits fully, the system delivers 700 l/h (1.8 gpm), but I have to throttle it back because some circuits are relatively short, so I end up at around 600 liters (1.6 gallons).
The underfloor heating is somewhat hydraulically flawed when it comes to certain individual rooms.
540 x 1.16 x 5 = 3132 watts
The heating load of the house is 3176 watts at 20°C (68°F) everywhere, without considering the mechanical ventilation with heat recovery.
If I open all circuits fully, the system delivers 700 l/h (1.8 gpm), but I have to throttle it back because some circuits are relatively short, so I end up at around 600 liters (1.6 gallons).
The underfloor heating is somewhat hydraulically flawed when it comes to certain individual rooms.
Dennis89 schrieb:
What is 33% in watts? My compressor is currently running at 32 Hz with 788 watts at an ambient temperature of 2.7°C (37°F).The electrical power consumption at that moment was, I believe, 400 watts.
I think I can also display the frequency somewhere...
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