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-dbM
markus-db16 Jul 2016 14:55Hello 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!
M
markus-db16 Jul 2016 15:31BeHaElJa schrieb:
*Edit* I just noticed you have a heating load calculation... 18 kW?! Wow. We heat 190 sqm (2045 sq ft) with 5.3 kW.Thanks for the information. I will check again with the energy consultant to understand how that figure was determined. We have planned several floor-to-ceiling window areas – that is surely a major factor.
I suspect the missing ventilation, at least accounting for 3-4 kW. Otherwise, it seems fine.
Still, I would consider adding a buffer tank for both setups.
Otherwise, do the calculations... Seasonal performance factor (SPF) of 4.5 for a ground-source (water-to-water) heat pump and 3.5 for an air-to-water heat pump... then you can plot your house parameters accordingly. Assuming 20 kWh per square meter per year, you would break even after 57 years, which is questionable. At 25 kWh, break-even comes in 45 years. Including the BAFA subsidy, at 25 kWh it would be about 35 years. The borehole should last longer... still, with the price difference, a ground-source heat pump seems challenging.
These are all assumptions without considering photovoltaic systems – this is only indicative.
Still, I would consider adding a buffer tank for both setups.
Otherwise, do the calculations... Seasonal performance factor (SPF) of 4.5 for a ground-source (water-to-water) heat pump and 3.5 for an air-to-water heat pump... then you can plot your house parameters accordingly. Assuming 20 kWh per square meter per year, you would break even after 57 years, which is questionable. At 25 kWh, break-even comes in 45 years. Including the BAFA subsidy, at 25 kWh it would be about 35 years. The borehole should last longer... still, with the price difference, a ground-source heat pump seems challenging.
These are all assumptions without considering photovoltaic systems – this is only indicative.
I also find the heating load quite high. We have just under 300m² (3,230 sq ft) and are at 7kW. So I would question whether that’s accurate. Either the wall construction and insulation are poor, or someone just made a rough guess without proper calculation.
Excluding gas, in my opinion, doesn’t quite make sense with the statement "Your money is limited." With that heating load, you’ll likely end up with electricity costs of around €300-400 (about $320-430) per month in the winter using a heat pump. Whether that’s worth it…?!
And regarding sustainability: especially in winter, a heat pump basically becomes a disguised coal heater because you don’t get much from the roof in terms of solar energy. The sustainability promised by the green lobby is therefore quite questionable.
If you go with a heat pump for your house, then geothermal is the way to go. However, the extra cost for drilling is so significant that you might as well get an air-to-water heat pump instead... with the money saved, you could heat for a very long time.
I would consider a fireplace for supplementary heating in winter, add a ventilation system, and then opt for an air-to-water heat pump combined with photovoltaics. Otherwise, I would choose gas, save money, wait 10–15 years, and then invest in the latest generation heat pump. For now, we are skipping the heat pump and photovoltaics, but we are installing the ventilation system and fireplace in combination with gas. After a long year of weighing options and running the numbers, this was the most economical solution. We’ll reassess in 10–15 years.
Excluding gas, in my opinion, doesn’t quite make sense with the statement "Your money is limited." With that heating load, you’ll likely end up with electricity costs of around €300-400 (about $320-430) per month in the winter using a heat pump. Whether that’s worth it…?!
And regarding sustainability: especially in winter, a heat pump basically becomes a disguised coal heater because you don’t get much from the roof in terms of solar energy. The sustainability promised by the green lobby is therefore quite questionable.
If you go with a heat pump for your house, then geothermal is the way to go. However, the extra cost for drilling is so significant that you might as well get an air-to-water heat pump instead... with the money saved, you could heat for a very long time.
I would consider a fireplace for supplementary heating in winter, add a ventilation system, and then opt for an air-to-water heat pump combined with photovoltaics. Otherwise, I would choose gas, save money, wait 10–15 years, and then invest in the latest generation heat pump. For now, we are skipping the heat pump and photovoltaics, but we are installing the ventilation system and fireplace in combination with gas. After a long year of weighing options and running the numbers, this was the most economical solution. We’ll reassess in 10–15 years.
Even with compliance to the energy-saving regulations standard, the heating demand is still quite high, but there could also be a significant domestic hot water requirement, depending on the number of occupants.
In general, the higher the demand, the more worthwhile it becomes to invest in a more expensive heating system that provides heat more cost-effectively. By the way, the difference in the seasonal performance factor between air-source and geothermal systems is significantly larger than the often quoted 3.5 versus 4.5.
The post above mine is unfortunately not objective, as numbers are thrown around without any comparison or indication of their source.
Sent from mobile
In general, the higher the demand, the more worthwhile it becomes to invest in a more expensive heating system that provides heat more cost-effectively. By the way, the difference in the seasonal performance factor between air-source and geothermal systems is significantly larger than the often quoted 3.5 versus 4.5.
The post above mine is unfortunately not objective, as numbers are thrown around without any comparison or indication of their source.
Sent from mobile
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