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!
B
Bauexperte19 Jul 2016 12:34Sebastian79 schrieb:
- even without it, surprisingly warm water arrives very quickly...Good to read that again There is so much discussion about saving potential through elaborate weekend settings; but no one mentions that a circulation line (unnecessary, in my opinion) can erase much of those savings.
Regards, Bauexperte
B
Bieber081519 Jul 2016 12:53Bauexperte schrieb:
Recirculation line Is it really unnecessary in standard single-family homes? I only know our house (without recirculation), but I thought that the more common case is without recirculation. Is it different elsewhere?
S
Sebastian7919 Jul 2016 13:10Well, it always depends on the layout – our main bathroom and the basement bathroom are fairly directly connected, while the kitchen and the kids' bathroom are not. You definitely notice it there, but in my opinion, it’s not a big issue.
In terms of costs, it wasn’t significant, but the frustration afterwards over something missing is much worse. That’s why I definitely wanted to have a circulation system.
The pump hardly consumes any electricity, but the heat loss is noticeable – so I will take another look at how to optimize the settings.
At least within my circle of friends and family, almost all houses have a circulation system – my parents don’t have one, and there you really have to wait a long time for hot water.
In terms of costs, it wasn’t significant, but the frustration afterwards over something missing is much worse. That’s why I definitely wanted to have a circulation system.
The pump hardly consumes any electricity, but the heat loss is noticeable – so I will take another look at how to optimize the settings.
At least within my circle of friends and family, almost all houses have a circulation system – my parents don’t have one, and there you really have to wait a long time for hot water.
B
Bauexperte19 Jul 2016 13:17Bieber0815 schrieb:
It’s not really necessary in typical single-family homes, is it? Correct, because the pipe runs are consistently kept short.Bieber0815 schrieb:
I only know our house (without a circulation system), but I thought not having circulation was the more common case. Is it different elsewhere?There is still a persistent rumor these days that water runs for "several" minutes before warm water comes out of the tap. This is comparable to the assumption held by many home builders that drywall partitions provide worse sound insulation than 11.5mm (0.45 inch) interior walls made of solid building materials.Regards, Bauexperte
M
markus-db3 Aug 2016 03:55First of all, thank you very much for the many replies and the discussion. (Unfortunately, I have not been receiving notification emails from the forum and did not expect such a large response, so I only just saw it now).
To answer a few questions:
- I have now received the heating load calculation, but I am somewhat skeptical. It is a simplified calculation according to "DIN EN 12831 Supplement 2 2012-05," which results in 0.06 kW/sqm (0.06 kW/sqft) and a total heating load of 18.28 kW (62,355 BTU/h) (which, based on my probably too simple calculations, should correspond to a calculation for 18.28/0.06 = 304 sqm (3,272 sqft)?). I cannot fully understand it yet, but I will have to take a closer look tomorrow and consult with the energy consultant, as it is a bit late today.
- Regarding the "sustainability question": Yes, it is a large house planned for two families (actually not “families” directly, as it is one family but currently two generations, and with upcoming children, then three). Even for that, it is still quite big, that’s true. However, that does not mean that all other sustainability considerations should be disregarded.
- About the question on "drilling over 400 meters": I meant the total drilling length in meters – for example, 5 drillings of 80 meters (262 feet) each are planned.
- I also learned in a conversation with the heating technology company why the cost difference between an air-source heat pump and geothermal heating is so high: It is because the total drilling length must actually be that high, as in Berlin the standard value for the extraction power from the ground in the area where we are building is 35 W per meter of drilling. This is a guideline set by the state and must not be (strongly) exceeded. In Brandenburg, for example, this does not apply, and one can plan for a higher extraction power, so there, for example, instead of 5 drillings, only 3 would be needed, which would of course reduce costs.
- However, if the heating system were to be oversized, it might be possible even in Berlin to manage with one drilling less, which should reduce the absolute cost difference accordingly.
That’s all for now. Thanks again for your responses!
To answer a few questions:
- I have now received the heating load calculation, but I am somewhat skeptical. It is a simplified calculation according to "DIN EN 12831 Supplement 2 2012-05," which results in 0.06 kW/sqm (0.06 kW/sqft) and a total heating load of 18.28 kW (62,355 BTU/h) (which, based on my probably too simple calculations, should correspond to a calculation for 18.28/0.06 = 304 sqm (3,272 sqft)?). I cannot fully understand it yet, but I will have to take a closer look tomorrow and consult with the energy consultant, as it is a bit late today.
- Regarding the "sustainability question": Yes, it is a large house planned for two families (actually not “families” directly, as it is one family but currently two generations, and with upcoming children, then three). Even for that, it is still quite big, that’s true. However, that does not mean that all other sustainability considerations should be disregarded.
- About the question on "drilling over 400 meters": I meant the total drilling length in meters – for example, 5 drillings of 80 meters (262 feet) each are planned.
- I also learned in a conversation with the heating technology company why the cost difference between an air-source heat pump and geothermal heating is so high: It is because the total drilling length must actually be that high, as in Berlin the standard value for the extraction power from the ground in the area where we are building is 35 W per meter of drilling. This is a guideline set by the state and must not be (strongly) exceeded. In Brandenburg, for example, this does not apply, and one can plan for a higher extraction power, so there, for example, instead of 5 drillings, only 3 would be needed, which would of course reduce costs.
- However, if the heating system were to be oversized, it might be possible even in Berlin to manage with one drilling less, which should reduce the absolute cost difference accordingly.
That’s all for now. Thanks again for your responses!
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