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
Wastl schrieb:
No. We have underfloor heating throughout the entire house (the basement is unheated, as it is used for storage). Additionally, there is a central ventilation system installed in the same unit as the regular heating system. The heat recovery is also integrated into this same unit. However, the systems themselves are separate from each other.
If your heating with hot water only uses 2000 kWh, then you are doing really well. There are four of us, and we like it warm (24-25°C (75-77°F) in the living room). Our central ventilation system doesn’t have its own meter – the whole unit is connected to a separate meter.OK – for us, it’s “only” between 21 and 23°C (70-73°F).
But you are definitely overestimating the energy consumption for the ventilation. You should find out how many watts the fan motors use.
In your heating system, is the air heated separately, or does it just pass normally through the heat exchanger?
D
Doc.Schnaggls12 Feb 2015 16:54A completely different question:
Why don't you install a few photovoltaic panels on the roof instead of heating domestic hot water this way (which I don't find suitable in this combination anyway) and generate your own electricity for the air-to-water heat pump (over the course of the year)?
That is very likely the better solution.
@Wastl: That’s nice, we also have the LWZ 403 SOL, but from the subsidiary "Tecalor" installed in the basement...
Why don't you install a few photovoltaic panels on the roof instead of heating domestic hot water this way (which I don't find suitable in this combination anyway) and generate your own electricity for the air-to-water heat pump (over the course of the year)?
That is very likely the better solution.
@Wastl: That’s nice, we also have the LWZ 403 SOL, but from the subsidiary "Tecalor" installed in the basement...
Doc.Schnaggls schrieb:
A completely different question:
Why don’t you install a few photovoltaic panels on the roof instead of using the domestic hot water heating (which I don’t find suitable in this combination anyway) and generate your own electricity for the air-to-water heat pump over the course of the year?
That is, in all likelihood, the better solution.
@Wastl: That’s nice, we also have the LWZ 403 SOL, but from the subsidiary company "Tecalor" installed in the basement...In winter, when I need electricity for the heat pump, there is none coming from the roof. And in summer for domestic hot water? Just three quarters of an hour per day or max. 2 kWh...? We pay a monthly prepayment of 110€ for the heat pump and household electricity together. Considering the low possible self-consumption without storage and the low feed-in tariff, photovoltaic is not worthwhile—especially if the system is financed. Solar power—yeah, you’re right, let’s not even talk about that...
D
Doc.Schnaggls13 Feb 2015 11:29Cascada schrieb:
. With the low possible self-consumption without storage and the low feed-in tariff, photovoltaics aren’t really worthwhile—especially if the system is financed. And solar, well, let’s not even get started on that...Hmm, I wouldn’t fully agree with that. My brother has been living in his house for two years and has an air-to-water heat pump plus photovoltaics installed on the roof. Over the year, he actually earns more money from the utility company than he spends on electricity purchases and loan repayments.
Granted, his feed-in tariff is higher than ours, but even with our tariff, there would still be some surplus.
We plan to add a battery storage system to the utility room as soon as they become more affordable (and thus significantly more cost-effective than today)—by then, this combination will definitely make sense.
Best regards,
Dirk
Although I often agree with @Doc.Schnaggls, in this case I have to agree with @Cascada based on my own experience. Especially when I look at what we have produced and fed into the grid over the past few months, it only pays off to a limited extent.
We have a 5.5 kWp system on the house with an almost perfect south-facing orientation. After self-consumption, in December we only fed about 35 kWh into the grid. Not because self-consumption was very high, but because production was so low. In January, it was a "generous" 90 kWh.
In contrast, our heat pump had an average daily consumption of 24 kWh. That is over 700 kWh for 30 days. Although I did not record the data for December.
Theoretically, @Doc.Schnaggls is right. Why not use the photovoltaic electricity anyway?
Reason:
As an operator of a heat pump, you can obtain reduced-rate heat pump electricity for this purpose. This costs about 0.20 Euro per kWh. However, if you run the heat pump (partly) on photovoltaic power, you lose the entitlement to the reduced heat pump electricity rate. Then the heat pump must be operated with regular electricity at about 0.25 Euro/kWh.
Then the calculation no longer works, especially in winter:
700 kWh × 0.25 = 175 Euro vs. 700 kWh × 0.20 Euro = 140 Euro Difference = 35 Euro
Potential maximum savings via photovoltaic in January: 90 kWh × 0.25 = 22.50 Euro
This results in a loss of 12.50 Euro for January.
The taxation of self-consumed electricity mentioned in the other thread (photovoltaic system) is not yet included here.
I cannot assess the summer months yet. However, I suspect we will not use large amounts of electricity for hot water preparation.
We had originally planned to run the heat pump on photovoltaic power to optimize self-consumption. After several recommendations from electricians and solar experts—especially regarding electricity supply for the heat pump—we decided against it.
We have a 5.5 kWp system on the house with an almost perfect south-facing orientation. After self-consumption, in December we only fed about 35 kWh into the grid. Not because self-consumption was very high, but because production was so low. In January, it was a "generous" 90 kWh.
In contrast, our heat pump had an average daily consumption of 24 kWh. That is over 700 kWh for 30 days. Although I did not record the data for December.
Theoretically, @Doc.Schnaggls is right. Why not use the photovoltaic electricity anyway?
Reason:
As an operator of a heat pump, you can obtain reduced-rate heat pump electricity for this purpose. This costs about 0.20 Euro per kWh. However, if you run the heat pump (partly) on photovoltaic power, you lose the entitlement to the reduced heat pump electricity rate. Then the heat pump must be operated with regular electricity at about 0.25 Euro/kWh.
Then the calculation no longer works, especially in winter:
700 kWh × 0.25 = 175 Euro vs. 700 kWh × 0.20 Euro = 140 Euro Difference = 35 Euro
Potential maximum savings via photovoltaic in January: 90 kWh × 0.25 = 22.50 Euro
This results in a loss of 12.50 Euro for January.
The taxation of self-consumed electricity mentioned in the other thread (photovoltaic system) is not yet included here.
I cannot assess the summer months yet. However, I suspect we will not use large amounts of electricity for hot water preparation.
We had originally planned to run the heat pump on photovoltaic power to optimize self-consumption. After several recommendations from electricians and solar experts—especially regarding electricity supply for the heat pump—we decided against it.
Doc.Schnaggls schrieb:
Hmm, I wouldn’t fully agree with that. My brother has been living in his house for two years now and has an air-to-water heat pump plus solar panels on the roof. Over the course of the year, he actually receives more money from the utility company than he spends on electricity purchases and loan repayments.
Granted, he still benefits from a higher feed-in tariff than we do, but even with our tariff, there would still be a surplus.
We are planning to install a battery storage unit in the utility room as soon as they become more affordable (and therefore significantly more economical than they are today) – by then, the combination will definitely make sense.
Best regards,
DirkAccording to my research (last updated in 2014), legislation has nearly halved solar power subsidies over the past two years. Anyone installing a system with a capacity of up to 10 kW in March 2014 received only 13.41 cents per kWh (kilowatt-hour) of solar power fed into the grid. Systems installed in early 2012 still earned 24.43 cents per kWh. At the same time, system prices are now only slowly decreasing.
Solar power is only profitable if you have an extremely sunny location, manage to obtain the system very cheaply, and have a high self-consumption rate (which is practically impossible without battery storage).
Even back in 2012 (when I moved in), when I was considering this, the return on investment (including financing, reserves, and insurance) was in the low single digits. On a purely economic basis over a 20-year horizon, if I were financing with equity, I would rather invest in blue-chip stocks.
Similar topics