Dear forum members,
As part of our search for the right builder, we are concerned, among other things, about choosing the "right" or most suitable energy concept for our KfW55 / KfW40 house.
Our top choices are a ground source heat pump and an exhaust air heat pump. We generally lean towards a ground source heat pump due to the well-known advantages frequently mentioned online. Since houses are increasingly well insulated and almost "airtight," we are also considering installing a central ventilation system with heat recovery.
Now the second option comes into play: the exhaust air heat pump. I have already read quite a bit about this online, but it has not necessarily convinced me. To put it simply:
- I am concerned that the system is so sensitive that when windows are opened (e.g., for a short airing), the system will need to draw significantly more energy from the electric heater.
- The same applies on cold days, which could lead to unpleasant drafts caused by cold air flowing in.
- I have also read that a cycle can occur if the system has to provide energy to heat the hot water tank by taking heat from the ambient air. Fresh air must then automatically flow in, which again needs to be heated to the desired room temperature. I’m not an energy expert, but there seems to be a catch here.
- What about summer and opening the patio doors? How does the system behave in that case?
As I said, I am just a layperson and find the topic of exhaust air heat pumps challenging. Do you have any experience with them? Which system (ground source vs. exhaust air heat pump) would you recommend from your perspective?
Thank you—we appreciate any advice.
Good luck
Olgus
As part of our search for the right builder, we are concerned, among other things, about choosing the "right" or most suitable energy concept for our KfW55 / KfW40 house.
Our top choices are a ground source heat pump and an exhaust air heat pump. We generally lean towards a ground source heat pump due to the well-known advantages frequently mentioned online. Since houses are increasingly well insulated and almost "airtight," we are also considering installing a central ventilation system with heat recovery.
Now the second option comes into play: the exhaust air heat pump. I have already read quite a bit about this online, but it has not necessarily convinced me. To put it simply:
- I am concerned that the system is so sensitive that when windows are opened (e.g., for a short airing), the system will need to draw significantly more energy from the electric heater.
- The same applies on cold days, which could lead to unpleasant drafts caused by cold air flowing in.
- I have also read that a cycle can occur if the system has to provide energy to heat the hot water tank by taking heat from the ambient air. Fresh air must then automatically flow in, which again needs to be heated to the desired room temperature. I’m not an energy expert, but there seems to be a catch here.
- What about summer and opening the patio doors? How does the system behave in that case?
As I said, I am just a layperson and find the topic of exhaust air heat pumps challenging. Do you have any experience with them? Which system (ground source vs. exhaust air heat pump) would you recommend from your perspective?
Thank you—we appreciate any advice.
Good luck
Olgus
B
Bauexperte2 Nov 2016 00:24Olgus2016 schrieb:
Why wouldn’t a ground source heat pump be considered for a single-family home... am I missing something important?Because the costs and benefits are not in an attractive balance. Choosing a ground source heat pump for a single-family home is usually driven by ecological reasons rather than economic ones.As you correctly pointed out, the performance of ground source heat pumps and air source heat pumps is not significantly different—subsidies from BAFA are available for both types of heat generators, but drilling risks are eliminated with air source heat pumps.
Best regards, Bauexperte
Bauexperte schrieb:
Because the cost and benefit are not in an attractive ratio. Choosing a ground-source heat pump for a single-family home is not usually for economic reasons, but for ecological ones.
As you correctly pointed out, the output of ground-source and air-to-water heat pumps does not differ significantly – government subsidies are available for both types of heat generators, but the drilling risk is avoided with the air-to-water heat pump.
Regards, BauexperteHowever, this cannot be completely accepted as is – even if it is factually correct due to what is probably an unintended mistake. The capacity of all heat generators does not differ, since you always buy a unit with the appropriate capacity for your building project. The efficiency and operating costs, however, vary significantly.
Especially when comparing air-to-water heat pumps versus ground-source heat pumps, the region and building project matter a lot.
The longer and colder the winter, the (significantly) worse the performance of an air-to-water heat pump compared to a ground-source heat pump. On the other hand, air-to-water heat pumps have an advantage in warmer regions due to their lower initial costs. A similar situation applies to exhaust air heat pumps, which are much more sensitive to cold regions or excessive heating demand.
In building projects, the general rule is that a ground-source heat pump becomes increasingly worthwhile the higher the heating load is – because operating costs are usually considerably lower than with an air-to-water heat pump, making the higher initial investment worthwhile.
Even though direct comparisons are not always possible (due to usage patterns, etc.), our neighbors with (split) air-to-water heat pumps have had three times the electricity consumption in recent years for houses of similar size (not counting my basement) compared to my ground-source heat pump. And these were not exceptionally cold winters.
B
Bauexperte2 Nov 2016 22:50Saruss schrieb:
In construction projects, a ground source heat pump generally becomes more cost-effective the higher the heating demand – because operating costs are usually significantly lower than those of an air-to-water heat pump, making the higher initial investment worthwhile. Agreed.
Saruss schrieb:
Even though it is not always possible to make a direct comparison (usage patterns, etc.), ... That’s why I tend to avoid that kind of discussion 😀
Regards, Bauexperte
We are still undecided between a ground-source heat pump (also called a geothermal heat pump) and an air-source heat pump. Of course, this depends on the cost, but the ground-source heat pump also offers other advantages beyond just ecological factors.
The heat pump unit itself seems to be similarly priced for both ground-source and air-source systems, with a slight advantage for the ground-source option. Since there is no outdoor unit, there can be cost benefits. However, the drilling required for ground-source systems is expensive. This varies greatly depending on the region, required heating load, and therefore drilling depth.
In an initial consultation with the energy advisor, it was suggested that a single borehole of 100–110 meters (330–360 feet) would suffice, as our heating load won’t be very high. Accordingly, the system can be sized smaller. The estimated cost was around 6,000–7,000 euros (6,000–7,000 USD), which would not be incurred with an air-source heat pump.
On the other hand, the ground-source heat pump offers higher efficiency, meaning annual operating costs are lower (although recovering the initial 6,000–7,000 euro investment would take a long time). Additionally, the ground-source system is supported by a government subsidy (4,500 euros / 4,500 USD), and ideally, the borehole will last for one or more lifetimes. This means that when a new heat generator is needed in 20–30 years, replacing the heat pump in a ground-source system will likely be cheaper.
The ground-source heat pump also supports passive cooling, which the air-source unit only somewhat provides. It has the added benefit of regenerating the heat source.
Because the ground-source system does not require an outdoor unit, there is no need to see or hear such a unit—something that often divides opinions.
For those who implement a ground-source heat pump with a trench collector, which usually involves doing some of the work themselves, drilling can be avoided. The cost is around 2,500 euros (2,500 USD), yet they still receive the 4,000-euro (4,000 USD) subsidy—resulting in a net gain compared to an air-source heat pump.
Last but not least, on paper, the ground-source heat pump is clearly 20–30% more efficient than an air-source heat pump, which positively affects energy demand calculations and helps when meeting energy efficiency standards such as KfW (Germany’s development bank), often leading to additional subsidies.
Therefore, in my opinion, the ground-source heat pump is always worth considering. It is clear that the initial investment is higher than for an air-source heat pump, but the ground-source system offers more, both functionally and non-functionally. Ideally, the investment will break even in the long run.
The heat pump unit itself seems to be similarly priced for both ground-source and air-source systems, with a slight advantage for the ground-source option. Since there is no outdoor unit, there can be cost benefits. However, the drilling required for ground-source systems is expensive. This varies greatly depending on the region, required heating load, and therefore drilling depth.
In an initial consultation with the energy advisor, it was suggested that a single borehole of 100–110 meters (330–360 feet) would suffice, as our heating load won’t be very high. Accordingly, the system can be sized smaller. The estimated cost was around 6,000–7,000 euros (6,000–7,000 USD), which would not be incurred with an air-source heat pump.
On the other hand, the ground-source heat pump offers higher efficiency, meaning annual operating costs are lower (although recovering the initial 6,000–7,000 euro investment would take a long time). Additionally, the ground-source system is supported by a government subsidy (4,500 euros / 4,500 USD), and ideally, the borehole will last for one or more lifetimes. This means that when a new heat generator is needed in 20–30 years, replacing the heat pump in a ground-source system will likely be cheaper.
The ground-source heat pump also supports passive cooling, which the air-source unit only somewhat provides. It has the added benefit of regenerating the heat source.
Because the ground-source system does not require an outdoor unit, there is no need to see or hear such a unit—something that often divides opinions.
For those who implement a ground-source heat pump with a trench collector, which usually involves doing some of the work themselves, drilling can be avoided. The cost is around 2,500 euros (2,500 USD), yet they still receive the 4,000-euro (4,000 USD) subsidy—resulting in a net gain compared to an air-source heat pump.
Last but not least, on paper, the ground-source heat pump is clearly 20–30% more efficient than an air-source heat pump, which positively affects energy demand calculations and helps when meeting energy efficiency standards such as KfW (Germany’s development bank), often leading to additional subsidies.
Therefore, in my opinion, the ground-source heat pump is always worth considering. It is clear that the initial investment is higher than for an air-source heat pump, but the ground-source system offers more, both functionally and non-functionally. Ideally, the investment will break even in the long run.