ᐅ KfW 40 standard, ground-source heat pump worthwhile or better air-to-water?

Dear forum members,

I have been considering the idea of building a house for several weeks now. The building will be around 160 sqm (1,722 sq ft) and will be located in Duisburg, a city not known for heavy snowfall or freezing temperatures. I already have a plot of land and am in discussions with two general contractors (GC). One GC follows the philosophy of monolithic construction using a ground-source heat pump, while the other initially planned an external thermal insulation composite system (ETICS / external wall insulation) combined with an air-to-water heat pump. I have now also asked the latter to provide a quote based on monolithic construction. Both GCs achieve an energy efficiency class of A+ with their building methods. Currently, I favor the second GC due to almost identical build quality and significantly lower costs; however, I would have to cover the drilling cost myself if I want a ground-source heat pump there.

This raises the question for me whether a ground-source heat pump is really worth it. The drilling costs amount to 12,000–13,000 euros. Fundamentally, I wonder if I will ever recoup that money by installing such a heat pump. Unfortunately, I lack practical experience regarding the energy consumption of both types of heat pumps. My current assumption is that winters will remain mild and electricity costs will continue to decrease.

I look forward to your experiences.

Best regards

P.S. GC1 plans to use the Vaillant flexoCOMPACT exclusive model 58/4 up to 5.28 kW ground-source heat pump, and GC2 proposes the Bosch CS5800iAW as the air-to-water heat pump, if that is of interest.

itizniti schrieb:

Basically, I’m wondering if I would ever recoup the money spent on installing a brine-to-water heat pump.

No, you won’t. Although a brine heat pump is more efficient, if you are only about 10% “better,” we’re talking about annual heating cost savings of around 50€ per year (about 55 USD).

That said, brine heat pumps do have advantages. Possibly active cooling in summer, and the aesthetic benefit of not needing an outdoor unit.

P.S. Keep in mind that in Duisburg, you need to consider water protection regulations, which can also cost you some extra money. I live west of you.

P.S.2 Also keep in mind that you might bring craftsmanship issues into your house if you force a general contractor to build a monolithic structure, which they (and their subcontractors) may not really be familiar with.

nordanney schrieb:

No, you won’t get that. The ground-source heat pump is more efficient, but if you’re only 10% “better,” we’re talking about heating cost savings of around €50 per year (about $55).

Thank you very much for your quick response! I assume you also have an air-to-water heat pump yourself, right? Unfortunately, there is a lot of conflicting information online about energy consumption.

nordanney schrieb:

That aside, the ground-source heat pump also has advantages. Potentially active cooling in summer. Plus the appearance, since no outdoor unit is needed.

The Bosch outdoor unit isn’t all that unattractive ;-) and it seems the air-to-water heat pump also offers cooling.

nordanney schrieb:

P.S. Keep in mind that in Duisburg, you have to pay attention to water protection regulations, which can also incur some additional costs. I live west of you.

Fortunately, I’ve already spoken with the authorities here, so there shouldn’t be any issues. But thanks for the tip 🙂

nordanney schrieb:

P.S.2 Also remember that if you force a general contractor to do a monolithic construction method, which they (and their subcontractors) may actually have little experience with, you might be bringing construction defects into your home.

That’s a very good point! I was already planning to discuss the general contractor’s experience with monolithic construction methods anyway. Your remark definitely strengthens my decision to hire a building inspector (TÜV, DEKRA, etc.) to oversee the construction.

Best regards

itizniti schrieb:

Many thanks for your quick reply! I assume you also have an air-to-water heat pump yourself, right? Unfortunately, there's a lot of information online about the energy consumption.

When we built a few years ago, ground-source heat pumps were also available. Now we have a renovated house with an air-to-water heat pump. So I’m familiar with both.

Take a look at the funding opportunities for ground-source heat pumps. I’m not fully up to date, but in the past, the varying subsidies have significantly narrowed the cost gap. The efficiency of a ground-source heat pump is independent of the weather. The annual performance factor remains consistent. I doubt you would only save 50€ (~$55) from it. If you build a 150 m² (1,615 sq ft) house to KfW55 standards, your calculated energy demand is 55 x 150 = 8,250 kWh per year. The ground-source heat pump has an annual performance factor of 4, while the air-to-water heat pump averages around 2.8 (assuming the maximum stated figure is not reached throughout the year). This results in consumption of 8,250 / 4 = 2,062.5 kWh for the ground-source pump and 8,250 / 2.8 = 2,946.43 kWh for the air-to-water pump, a difference of roughly 900 kWh. At €0.30 per kWh (~$0.33), that’s a saving of about €270 (~$295) annually.

What also speaks in favor of the ground-source heat pump, in my view, is the cooling capacity and the noticeably quieter operation. My preference – without having examined the actual costs (expenses minus subsidies) in detail – would be the ground-source heat pump.

wiltshire schrieb:

If you build a 150 m² (1,615 sq ft) house with a KfW55 standard, you have a calculated energy demand of 55 x 150 = 8,250 kWh per year. The ground source heat pump achieves an annual performance factor of 4, and the air-to-water heat pump an average of 2.8 (assuming the maximum value is not reached over the year). This results in an energy consumption of 8,250 / 4 = 2,062.5 kWh for the ground source heat pump and 8,250 / 2.8 = 2,946.429 kWh for the air-to-water heat pump, which is a difference of around 900 kWh. At 30 cents per kWh, that amounts to €270 per year.

However, this calculation is not just conservative, it is extremely pessimistic.
A new build of 150 m² (1,615 sq ft) with a well-planned air-to-water heat pump (here in the Rhine/Ruhr region) should consume around 2,500 kWh of electricity per year, including hot water (I used 1,500 kWh last year for a 120 m² (1,292 sq ft) house as a neighbor of the original poster). The consumption will not be more than 300–500 kWh above that annually (based on my own experience and a properly planned heating system).
With a planned KfW40 standard, as mentioned, the difference will be even smaller.