ᐅ Air Source Heat Pump vs. Geothermal System for a New 4,300 sq ft House
Created on: 16 Jul 2016 14:55
M
markus-db
Hello forum members,
I have already read quite a bit in the discussions about ground-source and air-source heat pumps, but most of the projects were in the range of 150–200 m2 (1600–2150 ft2). Since we are planning to build somewhat larger, I am wondering if this changes the considerations, so I created this thread.
Here’s a brief summary of the key data for the building project:
- Project on the outskirts of Berlin
- New single-family house, not KFW 55 standard (because according to the energy consultant, a ventilation system costing over 20,000 € would be required, which we do not want)
- Exterior walls made of aerated concrete 36 cm (14 inches) thick, no additional insulation
- No fireplace planned or desired
- About 300 m2 (3200 ft2) heated living area from ground floor to attic (GF, 1F, attic)
- About 100 m2 (1075 ft2) heated basement area
- Total heated area: 400 m2 (4305 ft2)
- Heating exclusively via underfloor heating (basement to attic, fully planned)
We decided against a gas heating system because although this might currently be economically more favorable than a heat pump (of any type), sustainability is important to us and we are willing to accept higher costs (especially investment costs).
With our energy consultant, we developed two options:
Always included is a photovoltaic system (nominal capacity about 4.5 kWp) with a buffer tank (probably around 7.5 kWh) – the "idea" is to generate electricity for the heat pump ourselves. Of course, this will not cover the full heat pump demand (see below), but even meeting about 50% annually would help. (Excess electricity produced in summer would be sold.)
Option a) Ground-source heat pump: According to the heating load calculation, we need a system with about 18 kW output and boreholes totaling 440 m (1443 ft) depth in this area. This is divided into 5 boreholes of 88 m (288 ft) each.
We have an offer, but unfortunately, no itemized pricing. Without going into too much detail (since the forum is not for assessing my offer), the total cost for the boring works, a Vaillant heat pump with 19.7 kW / COP 4.7 (standard not specified), 300 l buffer tank, 500 l domestic hot water storage, plus all additional costs comes to 42,500 € gross.
Option b) Air-source heat pump: Here, obviously, no drilling is required. The heat pump is a Heliotherm model with 18.5 kW / COP 4.14 (A2/W35) in fully modulating operation, hydraulically decoupled connection, buffer tank and domestic hot water storage similar to option a). Total cost: 25,000 € gross.
(There are additional costs of about 18,000 € for around 400 m2 (4305 ft2) of underfloor heating, and 15,000 € for the photovoltaic system, but these are the same for both options and are therefore excluded.)
Summary of the heating system costs:
- Ground-source heat pump: 42,500 €
- Air-source heat pump: 25,000 €
- Difference: Ground-source heat pump is 17,500 € more expensive upfront
- Air-source heat pump is less efficient than ground-source, especially in winter when it is needed most, so ground-source is cheaper in ongoing energy use
I have the following questions for the experts:
- Do these considerations make sense overall?
- Is it a good idea to partially cover the heat pump’s electricity demand with a self-generated photovoltaic system?
- From your perspective, is the extra investment of 17,500 € for the ground-source heat pump option worthwhile (also considering the heating load of about 18 kW)?
- What other factors should I be paying attention to?
The overall goal is to implement a sensible but as sustainable as possible energy system for the future, without incurring unnecessary costs (unfortunately, I have not won the lottery and funds are limited).
Sorry for the long post, but I wanted to be as precise as possible. If you need more information, please let me know.
Thank you!
I have already read quite a bit in the discussions about ground-source and air-source heat pumps, but most of the projects were in the range of 150–200 m2 (1600–2150 ft2). Since we are planning to build somewhat larger, I am wondering if this changes the considerations, so I created this thread.
Here’s a brief summary of the key data for the building project:
- Project on the outskirts of Berlin
- New single-family house, not KFW 55 standard (because according to the energy consultant, a ventilation system costing over 20,000 € would be required, which we do not want)
- Exterior walls made of aerated concrete 36 cm (14 inches) thick, no additional insulation
- No fireplace planned or desired
- About 300 m2 (3200 ft2) heated living area from ground floor to attic (GF, 1F, attic)
- About 100 m2 (1075 ft2) heated basement area
- Total heated area: 400 m2 (4305 ft2)
- Heating exclusively via underfloor heating (basement to attic, fully planned)
We decided against a gas heating system because although this might currently be economically more favorable than a heat pump (of any type), sustainability is important to us and we are willing to accept higher costs (especially investment costs).
With our energy consultant, we developed two options:
Always included is a photovoltaic system (nominal capacity about 4.5 kWp) with a buffer tank (probably around 7.5 kWh) – the "idea" is to generate electricity for the heat pump ourselves. Of course, this will not cover the full heat pump demand (see below), but even meeting about 50% annually would help. (Excess electricity produced in summer would be sold.)
Option a) Ground-source heat pump: According to the heating load calculation, we need a system with about 18 kW output and boreholes totaling 440 m (1443 ft) depth in this area. This is divided into 5 boreholes of 88 m (288 ft) each.
We have an offer, but unfortunately, no itemized pricing. Without going into too much detail (since the forum is not for assessing my offer), the total cost for the boring works, a Vaillant heat pump with 19.7 kW / COP 4.7 (standard not specified), 300 l buffer tank, 500 l domestic hot water storage, plus all additional costs comes to 42,500 € gross.
Option b) Air-source heat pump: Here, obviously, no drilling is required. The heat pump is a Heliotherm model with 18.5 kW / COP 4.14 (A2/W35) in fully modulating operation, hydraulically decoupled connection, buffer tank and domestic hot water storage similar to option a). Total cost: 25,000 € gross.
(There are additional costs of about 18,000 € for around 400 m2 (4305 ft2) of underfloor heating, and 15,000 € for the photovoltaic system, but these are the same for both options and are therefore excluded.)
Summary of the heating system costs:
- Ground-source heat pump: 42,500 €
- Air-source heat pump: 25,000 €
- Difference: Ground-source heat pump is 17,500 € more expensive upfront
- Air-source heat pump is less efficient than ground-source, especially in winter when it is needed most, so ground-source is cheaper in ongoing energy use
I have the following questions for the experts:
- Do these considerations make sense overall?
- Is it a good idea to partially cover the heat pump’s electricity demand with a self-generated photovoltaic system?
- From your perspective, is the extra investment of 17,500 € for the ground-source heat pump option worthwhile (also considering the heating load of about 18 kW)?
- What other factors should I be paying attention to?
The overall goal is to implement a sensible but as sustainable as possible energy system for the future, without incurring unnecessary costs (unfortunately, I have not won the lottery and funds are limited).
Sorry for the long post, but I wanted to be as precise as possible. If you need more information, please let me know.
Thank you!
Oh yes, just thinking about the figures: maybe it’s worth considering a central mechanical ventilation with heat recovery system. Apart from a significant increase in comfort, it can reduce ventilation heat losses by more than half, which could save a considerable amount of heating energy, at least in the maximum design scenario. I don’t think the operational cost savings are that high, but if you can also avoid an additional borehole, the difference in investment costs becomes less significant.
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ErikErdgas17 Aug 2016 16:47Hello Saruss,
I completely agree that a mechanical ventilation system with heat recovery should be considered both from an economic and comfort perspective. Since the original poster aims for sustainable construction, I believe such a ventilation system is an essential part of that. Retrofitting it later is theoretically possible, but it is very complex and costly in terms of construction and labor—and unnecessary in a new build project. I would also not only look at the mere installation effort but consider that the property is a long-term investment.
Best regards
I completely agree that a mechanical ventilation system with heat recovery should be considered both from an economic and comfort perspective. Since the original poster aims for sustainable construction, I believe such a ventilation system is an essential part of that. Retrofitting it later is theoretically possible, but it is very complex and costly in terms of construction and labor—and unnecessary in a new build project. I would also not only look at the mere installation effort but consider that the property is a long-term investment.
Best regards
M
markus-db24 Jan 2017 18:11Thank you all for your responses. To wrap up this topic usefully: we have decided to go with the geothermal option. A major factor in our decision was the noise level, after we experienced the offered air source heat pump running live. I definitely don’t want something like that in the (front) garden—I’m a bit sensitive to noise.
For now, we have opted out of photovoltaic panels for cost reasons. However, everything is being prepared accordingly (e.g., a separate meter cabinet or space in the basement, supply lines to the roof, etc.) to allow for retrofitting when we have money available to invest again.
Thanks again to everyone for your input!
For now, we have opted out of photovoltaic panels for cost reasons. However, everything is being prepared accordingly (e.g., a separate meter cabinet or space in the basement, supply lines to the roof, etc.) to allow for retrofitting when we have money available to invest again.
Thanks again to everyone for your input!
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