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
With the set target values in the heat pump.
The circulation pump from the buffer tank to the plate heat exchanger of the heat pump is controlled with a PWM signal, meaning this pump operates modulatingly.
Outdoor temperature at 0°C (32°F), e.g. return temperature at 27°C (81°F), supply temperature at 32°C (90°F), the pump operates at the lower limit.
Outdoor temperature at -12°C (10°F) (I live in the south), e.g. return temperature at 24°C (75°F), supply temperature at 36°C (97°F), the pump operates in the medium or higher regulation range.
The circulation pump from the buffer tank to the plate heat exchanger of the heat pump is controlled with a PWM signal, meaning this pump operates modulatingly.
Outdoor temperature at 0°C (32°F), e.g. return temperature at 27°C (81°F), supply temperature at 32°C (90°F), the pump operates at the lower limit.
Outdoor temperature at -12°C (10°F) (I live in the south), e.g. return temperature at 24°C (75°F), supply temperature at 36°C (97°F), the pump operates in the medium or higher regulation range.
nordanney schrieb:
So you’re basically stealing wood from someone else’s forest, or how should I understand that? This is getting funny!
I’m currently working on a large project and was able to get about 50 cubic meters (1,765 cubic feet) of top-quality beech wood from a state forest for free.
Here’s how it is in our area: the government is constantly promoting CO2 reduction, but instead of giving away such wood, it prefers to let it rot in the forest and release CO2. There were arguments that we were able to extract the wood from the forest “cost-neutral” using our own equipment. Aside from that, I usually have plenty of leftover wood from construction, or I know a few people who have their own forests and can’t keep up with it. And if I ever buy wood piles for 250 euros per year, it won’t make me any poorer.
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nordanney17 Mar 2021 10:38GSGaucho schrieb:
now this is getting funny!No! You claim that wood costs you nothing, yet you don’t own a forest. Well, actually it’s getting more amusing because your situation is extremely unusual. But you still have to store and dry 50 cubic meters (about 1765 cubic feet). However, it will probably last for the next 10 years.
nordanney schrieb:
No! You claim that wood costs you nothing, but you don’t have your own forest.
Well, actually it’s getting more amusing, since your situation is extremely special. You then have to store and dry 50 cubic meters of wood. But I guess that will be enough for the next 10 years. Well, looking at my environment, I am anything but special.
But anyway, the original question in this thread was how to technically connect the two systems so that they work well together. I never asked anyone else about cost-effectiveness. Everyone has to answer that for their own very specific situation.
However, I no longer discuss the general opinion online that a hydronic stove is the biggest economic nonsense and technically a nightmare. It’s like talking to people for whom KfW40+ standards are the ultimate benchmark, and who think that combining a 10kWp photovoltaic system with a 10kWh battery is a perfect solution.
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nordanney17 Mar 2021 12:48GSGaucho schrieb:
But I no longer debate the general opinion online that a water-heated stove is the biggest economic nonsense and technically a nightmare anyway. You don’t need to, since it doesn’t matter to you how well or poorly the system performs, as you burn through massive amounts of wood anyway. Costs nothing, right? Who cares about theoretical heating costs, technology, or efficiency 😉
nordanney schrieb:
You don’t need to, since it doesn’t matter at all to you how well or poorly the system performs, as you burn through everything with massive wood consumption. Costs nothing, right? Who cares about theoretical heating costs, technology, or efficiency? 😉Exactly, I burn my 5 cubic meters (about 176 cubic feet) per year and am satisfied with that. And the inefficiency of my system—heat pump + photovoltaic + wood—is most clearly reflected in my electricity bill...Similar topics