ᐅ Air-to-water heat pump combined with solar thermal and a wood-burning stove: costs, benefits, and practicality
Created on: 1 Feb 2015 15:57
M
M.Mustermann
Hello everyone,
Here are a few key points upfront:
We plan to build a single-family house with 121sqm (1300 sq ft) of living space this summer. Ground floor and upper floor, for 2 adults and 2 children.
The roof will face south.
We will use Ytong (30cm (12 inches)) blocks, with triple-glazed windows. Underfloor heating will be installed.
We live in Hesse, Rhine-Main area.
A air-to-water heat pump will be installed since we do not have gas and do not want to have any tanks for gas, oil, or pellets either inside the house or buried in the garden.
We would also like a fireplace for coziness and because we have almost free access to firewood. Solar thermal is also being considered; the question is whether it is worthwhile and if it should be used just for hot water or also for heating.
The following offer has already been presented to us:
A Nibe air-to-water heat pump split system with building heat load up to 7 kW, a buffer storage tank of 270l (71 gallons) with an additional 100l (26 gallons) buffer tank including Pedotherm underfloor heating.
For solar, 4sqm (43 sq ft) – 2 collectors and a 230l (61 gallons) buffer tank would be added.
The extra cost for solar is about 4000,- €.
For connecting a hydronic fireplace, including piping, pump, return lifting, and drainage protection, nearly 3000,- € is charged.
I am calculating about 3500,- € for a fireplace with an external chimney.
So, including the air-to-water heat pump, it would be over 10,000,- € for the fireplace and solar combined.
Regarding the questions:
The buffer storage tank seems very small for this project—is that accurate?
What makes sense for the heating system, considering it should pay off as much as possible? Because of the fireplace desire, it might not be possible, but well, the fireplace is a luxury and would be accepted even if it is not cost-effective.
I am concerned about only having an air-to-water heat pump in the cold season, due to electricity costs, and 7 kW building heat load seems low (though I have no expertise). A friend has an air-to-air heat pump and currently the electricity costs are extremely high.
What makes sense? What else should I include in the calculation, what might I have overlooked or should consider?
What do you think about Nibe?
Regards,
Max
Here are a few key points upfront:
We plan to build a single-family house with 121sqm (1300 sq ft) of living space this summer. Ground floor and upper floor, for 2 adults and 2 children.
The roof will face south.
We will use Ytong (30cm (12 inches)) blocks, with triple-glazed windows. Underfloor heating will be installed.
We live in Hesse, Rhine-Main area.
A air-to-water heat pump will be installed since we do not have gas and do not want to have any tanks for gas, oil, or pellets either inside the house or buried in the garden.
We would also like a fireplace for coziness and because we have almost free access to firewood. Solar thermal is also being considered; the question is whether it is worthwhile and if it should be used just for hot water or also for heating.
The following offer has already been presented to us:
A Nibe air-to-water heat pump split system with building heat load up to 7 kW, a buffer storage tank of 270l (71 gallons) with an additional 100l (26 gallons) buffer tank including Pedotherm underfloor heating.
For solar, 4sqm (43 sq ft) – 2 collectors and a 230l (61 gallons) buffer tank would be added.
The extra cost for solar is about 4000,- €.
For connecting a hydronic fireplace, including piping, pump, return lifting, and drainage protection, nearly 3000,- € is charged.
I am calculating about 3500,- € for a fireplace with an external chimney.
So, including the air-to-water heat pump, it would be over 10,000,- € for the fireplace and solar combined.
Regarding the questions:
The buffer storage tank seems very small for this project—is that accurate?
What makes sense for the heating system, considering it should pay off as much as possible? Because of the fireplace desire, it might not be possible, but well, the fireplace is a luxury and would be accepted even if it is not cost-effective.
I am concerned about only having an air-to-water heat pump in the cold season, due to electricity costs, and 7 kW building heat load seems low (though I have no expertise). A friend has an air-to-air heat pump and currently the electricity costs are extremely high.
What makes sense? What else should I include in the calculation, what might I have overlooked or should consider?
What do you think about Nibe?
Regards,
Max
M.Mustermann schrieb:
only up to 50 € saved on heating costs, what do you mean, per month or per year? I’d rather ask to be sure. Our air-to-water heat pump costs 720 € per year (3600 kWh * 0.2 €). About 285 € of that (4 kWh * 356 days * 0.2 €) is for the ventilation system. That leaves 435 € electricity costs for the remaining 12 months. Let’s assume you need twice as much energy in winter as in summer — 12 months plus 5 winter months equals 17 months total — so price per summer month: 435 € / 17 = 26 €; price per winter month = 52 €.
How much of the 52 € you save by heating less is still open, since you probably won’t heat 24/7. If we estimate 30%, you save 0.3 * 52 € * 5 months = 78 € per year.
These are many assumptions and approximations. I just want to show you that it might be unnecessary. Better to just have a small, nice visible fireplace for the look and leave it at that.
@ Wastl
What kind of ventilation system do you have? Our mechanical ventilation with heat recovery doesn’t run 365 days a year and currently uses a maximum of 20 watts per hour. That’s not 500 watts per day. Even on the highest setting, our Zehnder unit definitely doesn’t consume 4000 watts in 24 hours. Something doesn’t add up...
How large is your house/heating load? Climate zone?
@ M.Mustermann
If you live in a "warm" region and the building envelope is well insulated, then just use the air-to-water heat pump and that’s it. Solar will never pay off. The water-bearing stove isn’t worth it either for the low heating load of 121m² (1300ft²). Also, the efficiency of the air-to-water heat pump suffers because a buffer tank has to be installed. Only an air-to-water heat pump that goes directly to the underfloor heating — without a buffer tank and without individual room control. Based on experiences of friends and family, we also left out a small stove. The room gets warm too quickly, plus the work, dirt, wood storage, chimney sweep, and costs for the chimney... especially with mechanical ventilation with heat recovery. So: just take the air-to-water heat pump and everything will work out.
What kind of ventilation system do you have? Our mechanical ventilation with heat recovery doesn’t run 365 days a year and currently uses a maximum of 20 watts per hour. That’s not 500 watts per day. Even on the highest setting, our Zehnder unit definitely doesn’t consume 4000 watts in 24 hours. Something doesn’t add up...
How large is your house/heating load? Climate zone?
@ M.Mustermann
If you live in a "warm" region and the building envelope is well insulated, then just use the air-to-water heat pump and that’s it. Solar will never pay off. The water-bearing stove isn’t worth it either for the low heating load of 121m² (1300ft²). Also, the efficiency of the air-to-water heat pump suffers because a buffer tank has to be installed. Only an air-to-water heat pump that goes directly to the underfloor heating — without a buffer tank and without individual room control. Based on experiences of friends and family, we also left out a small stove. The room gets warm too quickly, plus the work, dirt, wood storage, chimney sweep, and costs for the chimney... especially with mechanical ventilation with heat recovery. So: just take the air-to-water heat pump and everything will work out.
Cascada schrieb:
@ Wastl
What kind of ventilation system do you have? Our controlled residential ventilation does not run 365 days a year and currently uses a maximum of 20 watts per hour. That is not 500 watts per day. Even at the highest setting, our Zehnder consumes far less than 4000 watts in 24 hours. Something doesn’t add up...
How large is your house/heating load? Climate region? The 4 kW is an estimate. We have an all-in-one solution: the LWZ 403 SOL. In other words, an air-to-water heat pump with integrated mechanical ventilation with heat recovery—I cannot read how much energy is used for heating, hot water, and ventilation separately. The 4 kW per day figure comes from an LWZ forum, where a technician from Stiebel posted it as a guideline. We have about 140 square meters (1507 square feet) of living space north of Munich, south-facing with many hours of sunshine and a few frost days.
M.Mustermann3 Feb 2015 20:52We don’t have gas in our town, otherwise it would have been an option, but it’s not.
I didn’t expect so little benefit from a water-based (hydronic) fireplace.
I’m a bit puzzled right now; the non-water-based fireplace has the disadvantage of distributing heat poorly, since the living room is only 35 sqm (376 sq ft) and has just one door.
Advantage: at least €3000 saved compared to the water-based fireplace.
Disadvantage: the living room could get too warm quickly, with poor heat distribution.
We had also considered the idea of a central ventilation system (a decentralized one is absolutely not an option), but according to my research, prices start at €7000, and I’m afraid the budget is too small. I also don’t fully understand it yet, since there are ventilation systems that require maintenance with professional duct cleaning, and others that don’t.
I need to think about this first.
Thanks in advance for the help so far!
I didn’t expect so little benefit from a water-based (hydronic) fireplace.
I’m a bit puzzled right now; the non-water-based fireplace has the disadvantage of distributing heat poorly, since the living room is only 35 sqm (376 sq ft) and has just one door.
Advantage: at least €3000 saved compared to the water-based fireplace.
Disadvantage: the living room could get too warm quickly, with poor heat distribution.
We had also considered the idea of a central ventilation system (a decentralized one is absolutely not an option), but according to my research, prices start at €7000, and I’m afraid the budget is too small. I also don’t fully understand it yet, since there are ventilation systems that require maintenance with professional duct cleaning, and others that don’t.
I need to think about this first.
Thanks in advance for the help so far!
@ Wastl
So, you have an air heating system and not underfloor heating – is that correct? Just for comparison: we heat (including a partially heated basement) about 200sqm (2150 sq ft) in a cold region with four people. The consumption for heating and hot water in 2014 was under 2000 kWh. And the electricity consumption of the mechanical ventilation system with heat recovery is less than €40 per year.
From this perspective, an actual consumption of 3600 kWh for 2014 is quite significant for a 140sqm (1505 sq ft) new build in a milder climate...
@ M.Musterman
If the heat load calculation is available (with or without mechanical ventilation with heat recovery), then for a new build in your warm region, an air-to-water heat pump alone is definitely sufficient and suitable – the heat load for the 121sqm (1302 sq ft) is certainly not high in a new build. As already explained (and based on practical experience in my circle of acquaintances), I would completely avoid a second heat source (even a small decorative wood stove) and potentially invest the money saved into a mechanical ventilation system with heat recovery. If you “offset” the stove and chimney costs, the additional expense is significantly lower.
In a mechanical ventilation system with heat recovery, there is a filter inside the unit that first cleans the outside air – including pollen, for example. We also have a second filter before the air intake shaft. There are filters behind the exhaust vents inside the house that trap dust leaving the rooms. The only requirement is that the filters need to be vacuumed or replaced at certain intervals. That’s all...
So, you have an air heating system and not underfloor heating – is that correct? Just for comparison: we heat (including a partially heated basement) about 200sqm (2150 sq ft) in a cold region with four people. The consumption for heating and hot water in 2014 was under 2000 kWh. And the electricity consumption of the mechanical ventilation system with heat recovery is less than €40 per year.
From this perspective, an actual consumption of 3600 kWh for 2014 is quite significant for a 140sqm (1505 sq ft) new build in a milder climate...
@ M.Musterman
If the heat load calculation is available (with or without mechanical ventilation with heat recovery), then for a new build in your warm region, an air-to-water heat pump alone is definitely sufficient and suitable – the heat load for the 121sqm (1302 sq ft) is certainly not high in a new build. As already explained (and based on practical experience in my circle of acquaintances), I would completely avoid a second heat source (even a small decorative wood stove) and potentially invest the money saved into a mechanical ventilation system with heat recovery. If you “offset” the stove and chimney costs, the additional expense is significantly lower.
In a mechanical ventilation system with heat recovery, there is a filter inside the unit that first cleans the outside air – including pollen, for example. We also have a second filter before the air intake shaft. There are filters behind the exhaust vents inside the house that trap dust leaving the rooms. The only requirement is that the filters need to be vacuumed or replaced at certain intervals. That’s all...
Cascada schrieb:
@ Wastl
So, you have an air heating system and not underfloor heating – is that correct? Just for comparison: we heat about 200 sqm (2,150 sq ft), including a partially heated basement, in a cold region, with four people living here. The energy consumption for heating and hot water in 2014 was under 2,000 kWh. The electricity consumption of the controlled ventilation system is less than €40 per year.
Seen this way, 3,600 kWh actual consumption in 2014 is quite a lot for a 140 sqm (1,500 sq ft) new build in a milder climate... No. We have underfloor heating throughout the entire house (the basement is unheated, as it is a utility basement). In addition, there is a central ventilation system integrated into the same unit as the regular heating system. Heat recovery is also built into the same unit. However, the systems themselves operate independently from each other.
If your heating and hot water consumption is only 2,000 kWh, you’re really doing well. There are four of us, and we like it warm (24–25 degrees Celsius (75–77°F) in the living room). Our central ventilation system does not have a separate meter – the entire unit is connected to a dedicated meter.
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