ᐅ Combine an air-to-water heat pump with a wood-burning stove connected to the central heating system
Created on: 29 Mar 2020 14:13
G
GSGaucho
Hello everyone,
We are currently planning a single-family home built with solid construction to KFW55 standard.
Two full stories, partially basement, without basement about 230m² (2,475 sq ft) of living space for 5 people.
The location is southern Germany at 550m (1,804 ft) above sea level. The shell construction planning is fixed, and the shell and gable roof have already been contracted. Construction start is week 22/2020.
I have also already contracted a 23kWp photovoltaic system on the south/west roof of the house and the south/east roof of the garage.
Due to economic reasons, a battery storage system is currently not an option.
The heating load according to calculation is about 5.5 kW at -15°C (5°F) ambient temperature.
Now it’s time to plan the heating system:
Current status is:
Now I have the first offer for a Stiebel Eltron LWZ 8 cs Premium.
Am I correct to assume that under the above parameters the LWZ 5 cs would also be sufficient?
How can I best integrate the Hoxter stove into the heating system?
As a layperson, I currently see two options:
Option 1
An 800-liter (210-gallon) buffer tank only for heating operation, without domestic hot water.
Domestic hot water is generated by the air-to-water heat pump during daylight; the heat pump runs mainly during the day and stores heat in the screed. From 4 p.m. onward, the Hoxter stove is fired.
The heating circuit would then have to switch to the buffer tank when a certain temperature X is reached in the stove circuit or the heat pump buffer.
Option 2
The air-to-water heat pump always charges the buffer tank with a maximum flow temperature of about 40°C (104°F). If this temperature is exceeded by the stove operation, the heat pump switches off. Also, the heat pump would be programmed to operate only during daytime.
I understand that the combination of air-to-water heat pump with a buffer tank is suboptimal. But a stove without hydronic integration also makes no sense, as it would quickly overheat.
My current bidder is almost unreachable for technical evaluation at the moment, fully booked, so I have no real information about integrating the stove yet.
What do you suggest?
Which other air-to-water heat pump manufacturers would you consider for this configuration?
Thank you very much,
GSGaucho
We are currently planning a single-family home built with solid construction to KFW55 standard.
Two full stories, partially basement, without basement about 230m² (2,475 sq ft) of living space for 5 people.
The location is southern Germany at 550m (1,804 ft) above sea level. The shell construction planning is fixed, and the shell and gable roof have already been contracted. Construction start is week 22/2020.
I have also already contracted a 23kWp photovoltaic system on the south/west roof of the house and the south/east roof of the garage.
Due to economic reasons, a battery storage system is currently not an option.
The heating load according to calculation is about 5.5 kW at -15°C (5°F) ambient temperature.
Now it’s time to plan the heating system:
Current status is:
- Underfloor heating in all rooms except for the pantry and storage/technical room in the basement.
- Central ventilation system combined with an air-to-water heat pump. Air-to-water heat pump installed indoors in the basement.
- A hydronic wood-burning stove from Hoxter with firing from a separate room, i.e., no wood/dirt in the living room. I still have 30rm (cords) of beech wood stored free of charge.
- Due to the high capacity of the photovoltaic system and the stove, I see no sense in a trench collector.
- An 800-liter (210-gallon) buffer tank can be placed almost directly under the Hoxter stove in the basement. The distance to the air-to-water heat pump is about 2.5m (8 feet).
Now I have the first offer for a Stiebel Eltron LWZ 8 cs Premium.
Am I correct to assume that under the above parameters the LWZ 5 cs would also be sufficient?
How can I best integrate the Hoxter stove into the heating system?
As a layperson, I currently see two options:
Option 1
An 800-liter (210-gallon) buffer tank only for heating operation, without domestic hot water.
Domestic hot water is generated by the air-to-water heat pump during daylight; the heat pump runs mainly during the day and stores heat in the screed. From 4 p.m. onward, the Hoxter stove is fired.
The heating circuit would then have to switch to the buffer tank when a certain temperature X is reached in the stove circuit or the heat pump buffer.
Option 2
The air-to-water heat pump always charges the buffer tank with a maximum flow temperature of about 40°C (104°F). If this temperature is exceeded by the stove operation, the heat pump switches off. Also, the heat pump would be programmed to operate only during daytime.
I understand that the combination of air-to-water heat pump with a buffer tank is suboptimal. But a stove without hydronic integration also makes no sense, as it would quickly overheat.
My current bidder is almost unreachable for technical evaluation at the moment, fully booked, so I have no real information about integrating the stove yet.
What do you suggest?
Which other air-to-water heat pump manufacturers would you consider for this configuration?
Thank you very much,
GSGaucho
GSGaucho schrieb:
I’m not promoting a system that only makes sense in isolated cases, but rather one that I see as the most efficient solution. My actual additional costs are definitely lower than what a trench collector system would have cost me if I installed it myself, especially considering the questionable results on purely gravelly soil.
Following your logic, 99.9% of homeowners shouldn’t have a wood stove in their living rooms because it should only be used for economic reasons? Should we then also let 99.9% of firewood in the forest rot unused, releasing CO2 unnecessarily? Or should affected forest owners and the government all switch to wood chips with district heating? Or heat entirely with wood, even at an older age?
But the main thing is that a deep geothermal drilling costing $18,000 (approximately) that receives substantial public subsidies can be praised highly. No one mentioned deep geothermal drilling here.
Please provide a detailed cost analysis. That’s the best way to assess economic feasibility.
N
nordanney16 Mar 2021 20:14GSGaucho schrieb:
I’m not promoting a system that only occasionally makes sense, but one that represents the most efficient solution for me. So basically a customized solution that is generally poor for the plot but makes sense in very specific cases.
GSGaucho schrieb:
By your argument, 99.9% of homeowners shouldn’t have a wood stove in the living room since it should only be used for economic reasons? I didn’t say that. Every normal person has to buy their own firewood, so it’s an economic decision whether to use a hydronic wood stove when heating with a heat pump is effectively cheaper. The fireplace is there occasionally for a cozy atmosphere. It’s not running every evening throughout winter. That’s the difference compared to you.
GSGaucho schrieb:
So should 99.9% of firewood just be left to rot in the forest to release unused CO2? Or should the forest owners and the government now switch entirely to wood chips with district heating? Or fully heat with wood, even at an old age? How about selling the wood and installing a proper heating system? That will probably be the more worthwhile investment in the long run.
GSGaucho schrieb:
But the main thing is to praise a deep geothermal borehole for 18k, which then is heavily subsidized by the public. For the price you mentioned alone, I can get four complete heating systems as air-to-water heat pumps. Just have to add installation, or, like many others, do it myself.
For a heated area of 270m2 (2,900 sq ft), a ground source heat pump with deep drilling would have been the alternative for ME, and then without a wood stove.
Wood heating is completely ruled out. I’m getting old, after all.
The full cost calculation is simple for me at the moment:
880 for the buffer tank with the highest insulation level
300 for return temperature lift with a pump
1,200 additional costs for the boiler
200 circulation pump for the heat pump to the buffer tank
120 for two expansion vessels
approximately 600 for pipes, fittings, pressure relief valves, etc.
That adds up to about 3,500 in total. Whether this pays off in 10 years or never really doesn’t interest me. That’s not even half a percent of the total construction costs including the land.
Anyone having the entire system installed by the heating engineer or not knowing anything about hydraulics, soldering, or the resistance of a PT1000 sensor should probably stay away from this. That may be true.
Wood heating is completely ruled out. I’m getting old, after all.
The full cost calculation is simple for me at the moment:
880 for the buffer tank with the highest insulation level
300 for return temperature lift with a pump
1,200 additional costs for the boiler
200 circulation pump for the heat pump to the buffer tank
120 for two expansion vessels
approximately 600 for pipes, fittings, pressure relief valves, etc.
That adds up to about 3,500 in total. Whether this pays off in 10 years or never really doesn’t interest me. That’s not even half a percent of the total construction costs including the land.
Anyone having the entire system installed by the heating engineer or not knowing anything about hydraulics, soldering, or the resistance of a PT1000 sensor should probably stay away from this. That may be true.
In the forest, the wood is not mine until I take it out. But even if it were mine, why would I harvest wood to sell it? I don’t have a tractor or a winch.
The 18,000 comes from my immediate neighbor. Whether that is a lot or a little, I don’t know. The problem with him was that he missed out on the subsidy, or perhaps his architect or general contractor did, I don’t know.
The 18,000 comes from my immediate neighbor. Whether that is a lot or a little, I don’t know. The problem with him was that he missed out on the subsidy, or perhaps his architect or general contractor did, I don’t know.
T
T_im_Norden17 Mar 2021 09:10GSGaucho schrieb:
Where does it say anything about 2 buffers, 3 pumps, and a mixing valve??
Actually, there are two pumps, one buffer tank, and no mixing valve. The heat pump operates directly in the heating circuit. Is that clear?In the hydraulic diagram you posted.If you don’t have a mixing valve, what temperatures are you using for the underfloor heating?
N
nordanney17 Mar 2021 09:36GSGaucho schrieb:
In the forest, the wood isn’t mine until I take it out of there.So you’re stealing wood from someone else’s forest, or how should I understand that?Similar topics