ᐅ Heat pump is not compatible with a hydronic (water-heated) fireplace.
Created on: 20 Oct 2023 18:54
J
Jessica388
Hello everyone,
I hope someone here can help us because our heating engineer doesn’t seem to be able to…
Key data
New build 2022 with 250 m² (2,691 ft²)
Heat pump Viessmann Vitocal 200-A
Multifunction storage tank MFS1000S
Water-heated stove with heating capacity on the water side of 8 kW
Photovoltaic system
Electric heating element
I am attaching the schematic of the storage tank layout.
The stove was initially connected under “old” and now it has been modified.
Everything works fine as long as the underfloor heating is off.
When the underfloor heating is on, our hot water temperature doesn’t exceed about 55°C (131°F).
When the underfloor heating is off, the temperature ranges between 65–75°C (149–167°F), either via the electric heating element during sunshine or by stoking the stove.
Now, however, this energy seems to be wasted. It can’t be that the underfloor heating requires 70°C (158°F) supply temperature to achieve a flow temperature of 35°C (95°F), right? The return water is only slightly cooler. So the water should only need to be heated by a maximum of 5°C (9°F).
We assume either a) something is still connected incorrectly, or b) the cold water from the underfloor heating causes such circulation that the hot water cools down within minutes.
What can be done about this?
Has anyone experienced similar problems?
Normally, we should almost run without electric power, but currently the heat pump switches on almost every hour to heat hot water…
I hope someone here can help us because our heating engineer doesn’t seem to be able to…
Key data
New build 2022 with 250 m² (2,691 ft²)
Heat pump Viessmann Vitocal 200-A
Multifunction storage tank MFS1000S
Water-heated stove with heating capacity on the water side of 8 kW
Photovoltaic system
Electric heating element
I am attaching the schematic of the storage tank layout.
The stove was initially connected under “old” and now it has been modified.
Everything works fine as long as the underfloor heating is off.
When the underfloor heating is on, our hot water temperature doesn’t exceed about 55°C (131°F).
When the underfloor heating is off, the temperature ranges between 65–75°C (149–167°F), either via the electric heating element during sunshine or by stoking the stove.
Now, however, this energy seems to be wasted. It can’t be that the underfloor heating requires 70°C (158°F) supply temperature to achieve a flow temperature of 35°C (95°F), right? The return water is only slightly cooler. So the water should only need to be heated by a maximum of 5°C (9°F).
We assume either a) something is still connected incorrectly, or b) the cold water from the underfloor heating causes such circulation that the hot water cools down within minutes.
What can be done about this?
Has anyone experienced similar problems?
Normally, we should almost run without electric power, but currently the heat pump switches on almost every hour to heat hot water…
J
Jessica38821 Oct 2023 10:28RotorMotor schrieb:
That’s just the household electricity consumption.
Or where do you see anything about the heat pump’s consumption?
The heat pump keeps having peaks, which is also called short cycling.
It simply can’t release the heat because 90% of the rooms have their thermostatic valves set almost closed.
Turn the heating curve down to 0.4 and open the room thermostats, then we’ll check again in a month. ;-) Just these changes and that should reduce the electricity consumption? I’m happy to try it!
Do I need to change anything else?
Then these peaks should disappear immediately tonight, right?
Jessica388 schrieb:
And our heating engineer explained to us that even if the domestic hot water is set to 65 degrees, the heat pump can still turn on to produce warm water for the underfloor heating. Because the measurement is taken elsewhere. Sorry, but none of this makes sense to me.
That’s why I’m asking here for help Have you set the domestic hot water temperature to 65°C (149°F)? That also consumes a lot of electricity. It’s enough to occasionally heat it that high, but otherwise, you can set it somewhere between 45-50°C (113-122°F), depending on what is enough for showering and so on.
I think the confusion comes from the fact that you have two separate circuits. You’re not drinking the water that runs through your underfloor heating.
So your domestic hot water is a different system. However, I don’t know what kind of tank you have or how it works. We have a buffer tank that is solely for the underfloor heating. So the water in our buffer tank is not used for domestic hot water. But that might be different in your case.
That means, even if your domestic hot water is at the correct temperature, the heat pump can switch on to raise the supply temperature for the underfloor heating (as Rotormotor said). Since your underfloor heating supply temperature is around 27°C (81°F), I rather suspect the domestic hot water. What is the setpoint temperature for that? Every degree less on the domestic hot water setpoint saves you real money.
Here is an excerpt from our table showing the daily consumption of our heat pump. The 19.5 is an outlier — that was the day when the plasterers taped up our outdoor unit. =D
That is still quite high for the current outside temperature, but we only recently moved in and the house is still damp.
R
RotorMotor21 Oct 2023 10:48Ah, one more thing: Is a domestic hot water circulation system installed and active?
KoalasAreCute21 Oct 2023 10:50kati1337 schrieb:
Here is a section from our table showing the daily consumption of our heat pump. The 19.5 is an outlier, as that was the day when the plasterers had taped off the outdoor unit. =D
This is generally still quite high for the current outdoor temperature, but we have just moved in and the house is still damp.
I just want to quickly add that the dates are missing and the daily difference values cover the last 3 weeks. I occasionally take meter readings and update this table accordingly.
Jessica388 schrieb:
You seem to know your way around this? Yes, somewhat—it’s not rocket science. But you do need to understand the relationships involved. For a layperson, though, it can often be quite difficult. For example, many people don’t realize that living in a house with underfloor heating is quite different from one with conventional radiators. And when you add a heat pump as the heat source and a fireplace on top of that...
Jessica388 schrieb:
Can we „book“ you? We’re from 96472 Rödental… No, unfortunately not.
I’m just doing the cleaning here… 🙂 🙂 🙂
But first, try the settings that Rotormotor suggested. Then we’ll see what to do next.
J
Jessica38821 Oct 2023 10:55kati1337 schrieb:
Have you set your domestic hot water to 65°C (149°F)? That uses a lot of electricity. It’s usually enough to heat it up to that temperature occasionally, and otherwise set it somewhere between 45-50°C (113-122°F), or whatever temperature is sufficient for showering and similar uses.
I think the confusion comes from the fact that you have two separate circuits. You’re not drinking the water that’s circulating through your underfloor heating.
Your domestic hot water is a separate system. However, I don’t know what type of storage tank you have or how it works. We have a buffer tank exclusively for the underfloor heating system. So the water in our buffer tank is not used for domestic hot water. That might be different in your case.
That means even if your domestic hot water is set to the correct temperature, the heat pump might still activate to raise the supply temperature for the underfloor heating (as Rotormotor mentioned). Since your underfloor heating supply temperature is around 27°C (81°F), I suspect the domestic hot water setting. What is your target temperature there? Reducing the domestic hot water setpoint by each degree saves real money.
Here is an excerpt from our chart showing the heat pump’s daily energy consumption. The 19.5 kWh is an outlier; this day included when the plasterers sealed off the outdoor unit for us. =D
Overall, this is still quite high for the current outdoor temperature, but we just recently moved in and the house is still damp.
No, it is set to 54°C (129°F). The high consumption on sunny days comes from the electric heating element, and on overcast days from the stove.
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