ᐅ Air-source heat pump combined with a hydronic (water-based) fireplace
Created on: 30 May 2018 13:50
A
Almo85
Hello everyone,
We are currently in the middle of building and I need to decide on a heating system soon.
My question is: Is it worthwhile for me to have a hydronic (water-based) fireplace combined with an air-source heat pump and a mechanical ventilation system with heat recovery?
Key data for the single-family house:
- Single-family house with 175 m² (1880 sq ft) of living space
- Annual primary energy demand: 24.50 kWh/m²a
- Energy demand of the building: 13.6 kWh/m²a
- Transmission heat loss: 0.29 W/m²K
- Heated building volume: 705 m³ (24,899 cu ft)
- Thermal energy demand of the building: 9,277 kWh (at 100%)
- Building heating load according to simplified method: 6.5 kW (calculated for me)
- Roth Thermoaura heat pump with 7 kW output
- Helios mechanical ventilation with heat recovery
- Preparation for a hydronic fireplace and accordingly a buffer tank with 850 liters (224 gallons)
My thought is that the air-source heat pump becomes inefficient on cold winter days and consumes a lot of power through the electric backup heater. In this case, the fireplace could cover the peak load and support the heating system. On the other hand, the heating system would need to constantly heat not a 300-liter but an 850-liter buffer tank.
What are your opinions and experiences on this? How cost-effective is this setup overall? I assume I can get firewood relatively cheaply through a friend.
Best regards,
Almo
We are currently in the middle of building and I need to decide on a heating system soon.
My question is: Is it worthwhile for me to have a hydronic (water-based) fireplace combined with an air-source heat pump and a mechanical ventilation system with heat recovery?
Key data for the single-family house:
- Single-family house with 175 m² (1880 sq ft) of living space
- Annual primary energy demand: 24.50 kWh/m²a
- Energy demand of the building: 13.6 kWh/m²a
- Transmission heat loss: 0.29 W/m²K
- Heated building volume: 705 m³ (24,899 cu ft)
- Thermal energy demand of the building: 9,277 kWh (at 100%)
- Building heating load according to simplified method: 6.5 kW (calculated for me)
- Roth Thermoaura heat pump with 7 kW output
- Helios mechanical ventilation with heat recovery
- Preparation for a hydronic fireplace and accordingly a buffer tank with 850 liters (224 gallons)
My thought is that the air-source heat pump becomes inefficient on cold winter days and consumes a lot of power through the electric backup heater. In this case, the fireplace could cover the peak load and support the heating system. On the other hand, the heating system would need to constantly heat not a 300-liter but an 850-liter buffer tank.
What are your opinions and experiences on this? How cost-effective is this setup overall? I assume I can get firewood relatively cheaply through a friend.
Best regards,
Almo
I am not aware of any funding options for something like this and consider it highly uneconomical.
You are spending thousands of euros on piping, controls, and hydraulics to run the heat pump continuously at a loss (with a huge hot water storage tank) because you are afraid the electric heating element might turn on at some point.
As already mentioned, these only activate nowadays at -10°C (14°F) or lower.
It would be better to invest an extra 1,000 to 2,000 euros in a good heat pump. Or even choose a ground-source heat pump right away, if that is possible.
You are spending thousands of euros on piping, controls, and hydraulics to run the heat pump continuously at a loss (with a huge hot water storage tank) because you are afraid the electric heating element might turn on at some point.
As already mentioned, these only activate nowadays at -10°C (14°F) or lower.
It would be better to invest an extra 1,000 to 2,000 euros in a good heat pump. Or even choose a ground-source heat pump right away, if that is possible.
Alex85 schrieb:
...
You spend thousands of euros on piping, controls, and hydraulics to operate the heat pump continuously at a loss (huge hot water storage tank)... Everyone says something different. I just spoke with a heating engineer who said that, especially with a heat pump, the support of a water-bearing fireplace makes a big difference.
The water storage tank is separate... I can’t recall the exact term right now. So, only one half is buffered with the heated water.
It’s really hard for me to decide, especially because opinions on this vary so much.
Almo85 schrieb:
That would be ideal, yes, but I think it will turn on fairly often. Do you have an idea of how much it was for you when the heating element kicked in? I also see the downside that the extra water in the storage tank needs to be heated more because of the larger volume. It was an incredible 300 kWh in total, but you have to consider that the heat pump was in emergency operation for 5 days in well below freezing temperatures due to an installation error. Without this mistake, it would probably have been not even 50 kWh, more likely significantly less.
H
Hausbauer130 May 2018 22:05For subsidies, search for BAFA and "Förderübersicht Biomasse". Good luck.
Almo85 schrieb:
Hello everyone,
we are currently in the middle of construction and I need to decide on a heating system soon.
My question is: Is it worthwhile for me to have a water-bearing fireplace combined with an air-source heat pump and mechanical ventilation with heat recovery?
Best regards
AlmoShort answer: No.
Long answer: No, because you have a building heat demand of 6.5 kW under worst-case conditions. Internal gains (such as people, cooking, showering, etc.) were almost certainly not taken into account. Your stove will easily provide 5 kW on the air side. If it burns for 5 hours to fully charge the storage tank, you will have indoor temperatures well above comfortable levels.
If you don’t mind carrying firewood around in your underwear, then it might be a good idea.
What you should also not forget: Your parents live in a very drafty house, while you are in a quite airtight KfW-standard house.
And finally: The two-flue chimney (required due to mechanical ventilation with heat recovery) costs about 5,000 € (euros). The pressure monitor is around 2,500 €. Then add another 5,000 to 7,500 € for the stove and control system... plus chimney sweeping every year.
Thank you for your replies!!
Thank you for your opinion.
Pro and con opinions are gradually balancing out! Some people are absolutely sure about it... it definitely makes a difference with an air-source heat pump, while others are completely convinced of the opposite.
Regarding costs: We will definitely have a chimney. The only question is whether to have a stove insert with or without water heating.
I am excluding the two-flue chimney from the cost calculation because it is already installed due to the controlled ventilation system.
The pressure monitor is said to cost about 600-700 € (around 700-800 USD), which I also need because of the controlled ventilation.
My heating engineer will prepare everything needed up to the chimney for 400 € (about 430 USD). In addition, there are costs for an 850-liter (225-gallon) storage tank instead of a 300-liter (80-gallon) one. The 850-liter tank is divided so that the hot water is only buffered in one part of the tank.
The stove insert will cost me more, and the control system integration will be handled by the heating engineer, but the electrician and chimney sweep must also be involved.
In summary, I have extra costs of about 3,000-4,000 € (3,200-4,300 USD) for the water-heated chimney compared to the chimney without water heating. I find it hard to decide whether this 3,000-4,000 € investment will pay off in the near future since some are completely convinced, and others are not.
It shouldn’t get too warm, as the underfloor heating is regulated with the water-side heat from the chimney and the air-source heat pump, and excess heat does not flow into the underfloor heating (this is my assumption).
I hope I have been able to explain my decision difficulty quite well.
Best regards,
Alex
fragg schrieb:
And finally: The two-flue chimney (due to controlled ventilation system) costs about €5000. The pressure monitor around €2500. Then another €5000-7500 for the stove and the control system... Plus chimney sweep every year.
Thank you for your opinion.
Pro and con opinions are gradually balancing out! Some people are absolutely sure about it... it definitely makes a difference with an air-source heat pump, while others are completely convinced of the opposite.
Regarding costs: We will definitely have a chimney. The only question is whether to have a stove insert with or without water heating.
I am excluding the two-flue chimney from the cost calculation because it is already installed due to the controlled ventilation system.
The pressure monitor is said to cost about 600-700 € (around 700-800 USD), which I also need because of the controlled ventilation.
My heating engineer will prepare everything needed up to the chimney for 400 € (about 430 USD). In addition, there are costs for an 850-liter (225-gallon) storage tank instead of a 300-liter (80-gallon) one. The 850-liter tank is divided so that the hot water is only buffered in one part of the tank.
The stove insert will cost me more, and the control system integration will be handled by the heating engineer, but the electrician and chimney sweep must also be involved.
In summary, I have extra costs of about 3,000-4,000 € (3,200-4,300 USD) for the water-heated chimney compared to the chimney without water heating. I find it hard to decide whether this 3,000-4,000 € investment will pay off in the near future since some are completely convinced, and others are not.
It shouldn’t get too warm, as the underfloor heating is regulated with the water-side heat from the chimney and the air-source heat pump, and excess heat does not flow into the underfloor heating (this is my assumption).
I hope I have been able to explain my decision difficulty quite well.
Best regards,
Alex
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