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
The point about the heat is not really referring to the underfloor heating, but rather to the fact that the fireplace itself produces so much heat that you can easily get more than 25°C (77°F) in the living room, and then you have to open the windows wide to prevent the room from overheating.
Is affordable wood supply even guaranteed? It didn’t sound 100% certain, and if that supply stops, the calculations would change again.
Is affordable wood supply even guaranteed? It didn’t sound 100% certain, and if that supply stops, the calculations would change again.
ares83 schrieb:
The point about the heat is not really about the underfloor heating, but rather that the fireplace itself generates so much heat that you can easily reach over 25°C (77°F) in the living room and then have to open the windows to prevent the room from overheating.
Is a reliable and affordable supply of wood secured? It didn’t sound like it was 100% certain, and if that changes, the calculations will need to be adjusted.There are plenty of forests around us and several suppliers.. and yes, at the moment I can get wood quite cheaply. The fireplace is supposed to be used more often in the evenings anyway, and I hope that the heat won’t build up in the living room thanks to the mechanical ventilation with heat recovery, but will circulate quite well.
M
Mastermind14 Jun 2018 21:43A water-heated wood stove in a new building with a heating load of 6.5 kW at design temperatures of around -10/-12/-14 degrees Celsius (14/10/7°F) is absolutely crazy.
Sorry if that sounds harsh, but that’s the reality.
Chimney costs? Annual fees?
Pressure monitors?
Water heating stove?
Hydraulics?
On one hand, the costs are a total no-go!
On the other hand, there’s a clear interface problem between the trades involved (heating engineers vs. wood stove installers) – nobody is to blame.
I’ve seen this firsthand with people I know.
Heat pump systems are completely different from a wood stove.
A heat pump should be able to heat the underfloor heating directly without a buffer tank. A wood stove, however, needs to heat into a buffer tank and then be mixed down to a flow temperature that is suitable for underfloor heating.
P.S. Save your money and invest it in a ground-source heat pump, for example, with ground collectors or trench collectors. Take advantage of the government grant of 4000–4500 euros (USD equivalent) – done.
The costs you save on the stove and chimney will pay for themselves easily. At the same time, you’ll have significantly lower annual energy expenses.
P.S. I have a stove without water heating in a new building myself.
Looking back, I would save that money and invest in a more efficient heating system.
Sorry if that sounds harsh, but that’s the reality.
Chimney costs? Annual fees?
Pressure monitors?
Water heating stove?
Hydraulics?
On one hand, the costs are a total no-go!
On the other hand, there’s a clear interface problem between the trades involved (heating engineers vs. wood stove installers) – nobody is to blame.
I’ve seen this firsthand with people I know.
Heat pump systems are completely different from a wood stove.
A heat pump should be able to heat the underfloor heating directly without a buffer tank. A wood stove, however, needs to heat into a buffer tank and then be mixed down to a flow temperature that is suitable for underfloor heating.
P.S. Save your money and invest it in a ground-source heat pump, for example, with ground collectors or trench collectors. Take advantage of the government grant of 4000–4500 euros (USD equivalent) – done.
The costs you save on the stove and chimney will pay for themselves easily. At the same time, you’ll have significantly lower annual energy expenses.
P.S. I have a stove without water heating in a new building myself.
Looking back, I would save that money and invest in a more efficient heating system.
M
Mastermind14 Jun 2018 22:05Just for comparison, according to your data, your house requires about 10,000 kWh of heat energy for heating.
Depending on the number of occupants, you can add a flat 1,000 kWh for hot water.
So, a total of 11,000 kWh of heat to produce.
If you achieve a seasonal performance factor (SPF) of 3.5 with the air-source heat pump you mentioned,
11,000 ÷ 3.5 = approximately 3,100 kWh of electricity consumption.
At €0.25 per kWh, that costs you €775.
For comparison, a ground-source heat pump with an SPF of 5:
11,000 ÷ 5 = 2,200 kWh of electricity consumption.
At €0.25 per kWh, that costs you €550.
You save almost €225 annually.
With rising electricity prices, the savings potential increases.
If the electricity price doubles in 10 years, it makes a difference whether you pay €1,550 for the air-source heat pump or €1,100 for the ground-source heat pump.
In addition, subsidies are significantly higher. Also, a ground-source heat pump does not necessarily require drilling...
As I said, there are collectors (flat/ground collectors available to purchase, DIY options, or trench collectors for around €1,000–2,000).
Depending on the number of occupants, you can add a flat 1,000 kWh for hot water.
So, a total of 11,000 kWh of heat to produce.
If you achieve a seasonal performance factor (SPF) of 3.5 with the air-source heat pump you mentioned,
11,000 ÷ 3.5 = approximately 3,100 kWh of electricity consumption.
At €0.25 per kWh, that costs you €775.
For comparison, a ground-source heat pump with an SPF of 5:
11,000 ÷ 5 = 2,200 kWh of electricity consumption.
At €0.25 per kWh, that costs you €550.
You save almost €225 annually.
With rising electricity prices, the savings potential increases.
If the electricity price doubles in 10 years, it makes a difference whether you pay €1,550 for the air-source heat pump or €1,100 for the ground-source heat pump.
In addition, subsidies are significantly higher. Also, a ground-source heat pump does not necessarily require drilling...
As I said, there are collectors (flat/ground collectors available to purchase, DIY options, or trench collectors for around €1,000–2,000).
Mastermind1 schrieb:
...
Additionally, the subsidies are significantly higher. And a ground-source heat pump doesn’t necessarily require drilling.
As mentioned, there are collectors (flat/ground collectors available for purchase, or DIY options, or trench collectors for around 1000-2000€)Sounds good. That’s just how it is. We have had a chimney shaft installed, and we will have a fireplace anyway because we like the atmosphere it creates. It would just be great to integrate it into the heating system as efficiently as possible.
I will discuss with my heating engineer the possibility of omitting the water circuit for the fireplace, keeping the buffer tank small (300 liters (79 gallons)), and designing the whole system with a ground-source heat pump and trench collector instead of an air-source heat pump.
I assume it will take several years until I receive this subsidy, right? Or maybe I won’t get it at all in the end.
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