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?
You definitely need to take action. Before optimizing heating costs, you first need to get the cycling under control.
Falling temperatures have nothing to do with it. The hysteresis is far too low and/or the system is compromised by, for example, a buffer tank or bypass valve.
Do you know what caused the high electricity consumption from around 4:45 AM?
@RotorMotor
From the network, a "specialist" forum. And yes, assuming the compressor as an "irreplaceable" part or total loss if it fails, such a system has that kind of service life.
Falling temperatures have nothing to do with it. The hysteresis is far too low and/or the system is compromised by, for example, a buffer tank or bypass valve.
Do you know what caused the high electricity consumption from around 4:45 AM?
@RotorMotor
From the network, a "specialist" forum. And yes, assuming the compressor as an "irreplaceable" part or total loss if it fails, such a system has that kind of service life.
R
RotorMotor21 Nov 2021 08:33OWLer schrieb:
Today I will probably have between 25 and 30 starts at 9-14°C (48-57°F) ambient temperature. It was somewhat clear beforehand that the heat pump is oversized.
OWLer schrieb:
Let's see if I increase the energy integral further. What value are you currently at?
guckuck2 schrieb:
@RotorMotor
From the internet, from a "specialist" forum. And yes, assuming the compressor is an "irreplaceable" part or represents total failure if it breaks down, such a system has that kind of expected service life. So it's more of an arbitrary estimate than a verified value from testing series.
Are there any results yet for the current series using the refrigerant currently in use?
Such a compressor seems to cost around 1000€.
Very frustrating, but not irreplaceable.
I still agree with you that it’s better to first reduce cycling and only then look at efficiency again.
RotorMotor schrieb:
It was somewhat obvious beforehand that the heat pump is oversized.
What value are you working with?
So it’s more of an arbitrary estimate rather than a verified value from test series. Are there even any results yet for the current model with the refrigerant currently in use? Such a compressor seems to cost around 1000€ (approximately 1100 USD). Very frustrating but not irreplaceable.
I still agree with you that it’s better to first reduce cycling and only then look again at efficiency. An oversized heat pump leads to short cycling. However, if the underfloor heating system behind it is reasonably well balanced, it shouldn’t automatically cause a “short circuit” effect that would suddenly spike the return temperature, prematurely ending the cycle, and then shortly after, after the return temperature drops, start the cycle again. In my opinion, this effect is often overestimated, or it’s more likely that the heat pump is simply trying to push against something and cannot dispose of the heat properly. These are usually poorly executed installations, for example with buffer tanks or overflow valves. In the simplest case, the thermostatic radiator valves (TRVs) are closed, so no heat is drawn off.
The “arbitrary estimate” argument is just talk. These are transferred empirical values, by the way, not exclusive to heat pumps. But go ahead and present your studies, good luck.
Then you might understand why your cost estimate is “a little” off ;-)
A broken compressor is a total loss. Why, someone else can explain that to you.
R
RotorMotor21 Nov 2021 10:53guckuck2 schrieb:
Blah blah arbitrary estimate. These are transferred empirical values, which, by the way, do not only apply to heat pumps. But go ahead and present your studies, good luck.
Then maybe you’ll understand why your cost estimate is “a bit” off ;-)
A broken compressor is a total loss. Why, someone else can explain to you. Why be so unprofessional?
I believe it is important and correct to critically question not only manufacturers but also any statements posted in forums.
Besides, "experiences from a forum" contradict your statement "in theory."
You can easily find posts saying "100,000 and even after 120,000 hours no problems."
But maybe these systems simply haven’t been in use long enough yet to be sure that even 200,000 hours wouldn’t be a problem?
Or there are laboratory tests from manufacturers/testing institutes.
One manufacturer, for example, states a total operating time of 40,000 hours as the expected service life.
Another manufacturer of compressors specifies a design for 150,000 starts.
So, 20 starts during the transition period would not be a problem.
When it gets really cold, the heat pump will release its energy and run longer.
However, I did not find any concrete information regarding Vaillant and the refrigerant.
I get annoyed when users expect information to be handed to them in forums, even though they could easily find it themselves (which you have now managed), and then complain that it’s not of high enough quality. Then either do it yourself or hire someone. This is a user forum.
Malz1902 schrieb:
Which ones do you need or would prefer?
I think with a heating curve of 0.16, only 3 cycles occur within 24 hours, so it seems well adjusted. Changing from 0.16 to 0.1 only altered the indoor temperature by 0.1 degrees. You came from a heating curve of 0.3... and now even 0.1 is sufficient.
A curve of 0.3 with a room setpoint of 20 degrees will likely produce similar supply temperatures at outside temperatures between 5 and 10 degrees Celsius (41 and 50°F) as 0.1/22. It gets more interesting when temperatures drop below 0 degrees Celsius (32°F).
You also keep adjusting the flow rates constantly.
In my 130m² (1400 ft²) KfW60 semi-detached house (with an unheated basement below), I’ve been running 0.15/22 for years. Without solar gains, the room temperatures are usually around 22.5 degrees.
17 heating circuits: Bathroom 2.5 liters per minute (l/min), the rest between 1 and 1.8 l/min. Bedroom 0.5 l/min. Volume flow sensor 63/2. Heat load calculation 5.9 kW.
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