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!
This is, of course, just a rough estimate. A colleague of mine has the same floor area in his house and also uses an air-to-water heat pump. Well, I don’t know his heating load. And of course, the overall system design is always a factor. But a seasonal performance factor (SPF) of 3.5 for an air-to-water heat pump is very optimistic. I would expect an average of about 3. In the Agendagruppe Lahr, the average was around 2.6.
Ground boreholes over 400 meters (1,312 feet)? Did you read that correctly? Normally, they are around 120 meters (394 feet), and even then you need some luck.
We have a similar size, but we don’t have a heat load calculation yet.
Forget geothermal energy... it’s too expensive. Cancel photovoltaic panels; they look good in brochures, but you probably won’t see a return on investment. Maybe the technology will improve in five years, so consider installing empty conduits now.
We’ve also decided on a heat pump. Which type and size, I can’t tell you yet—we’re still waiting to find out. Then you can think about the ventilation system again; today, I wouldn’t build without it anymore.
We have a similar size, but we don’t have a heat load calculation yet.
Forget geothermal energy... it’s too expensive. Cancel photovoltaic panels; they look good in brochures, but you probably won’t see a return on investment. Maybe the technology will improve in five years, so consider installing empty conduits now.
We’ve also decided on a heat pump. Which type and size, I can’t tell you yet—we’re still waiting to find out. Then you can think about the ventilation system again; today, I wouldn’t build without it anymore.
S
Sebastian7916 Jul 2016 20:14You buy green electricity, and suddenly you have no coal energy anymore.
And 300-400 euros heating costs per month? Yeah, right... definitely not with a ground source heat pump. And not with that size either...
I also find the pump selection a bit too large – I would have expected a maximum of 11 kW.
Solar panels do pay off – very conservatively calculated usually after about 10-15 years. And with today's modules, you get some extra time... but you won’t get rich from it.
And 300-400 euros heating costs per month? Yeah, right... definitely not with a ground source heat pump. And not with that size either...
I also find the pump selection a bit too large – I would have expected a maximum of 11 kW.
Solar panels do pay off – very conservatively calculated usually after about 10-15 years. And with today's modules, you get some extra time... but you won’t get rich from it.
BeHaElJa schrieb:
Are you referring to my numbers or tabs... I wanted to question the 400 € heating costs per month.. where does that come from?
My 3.5 and 4.5 included hot water. Of course, higher costs are possible, but I was conservative and generalized.Not yours, I meant, for example, the 300 to 400 euro costs. I heat about 200 sqm (2150 sq ft) with a ground source heat pump (because only part of the basement is heated) and my annual costs are around 400 euros. For double that size (I have KfW70 standard, which is basically the minimum now) and maybe more windows and less favorable geometry, the annual heating costs could be two to three times higher than this rough estimate. I would still check if the heating load can actually be that high; it really sounds excessive. Oversizing the system increases costs regardless of the heat source used.
(By the way, including hot water, my annual performance factor is well over 5, but the winters were mild.)
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