ᐅ Effective Energy Strategy for New Construction KfW70 Without Oil or Gas

DerBjoern schrieb:

How did this unusual setup come about? Why don’t you also have the heat pump prepare the domestic hot water, since it’s more efficient?

For the underfloor heating, the ground-source heat pump only needs to heat the water to an estimated 30°C (86°F) (is that about right? I don’t recall the exact flow temperature), whereas for hot water supply—for showering and similar purposes—we like to have 54°C (129°F) stored in a 270-liter (71-gallon) water tank. On one hand, the significant extra effort required by the ground-source heat pump to raise the water temperature that high is inefficient (for your information: the electric backup heaters are turned off on both units, since we don’t want to heat with electricity directly but only operate the devices with it). On the other hand, why should the ground-source heat pump operate outside its efficient working range to generate more heat when 30°C (86°F) is sufficient for the underfloor heating?

Additionally, we only have about 48 square meters (517 square feet) of horizontal ground collectors (8 mats, each 1.0 x 6.0 meters (3.3 x 19.7 feet), installed over an area of 6 x 13 meters (19.7 x 42.6 feet) at a depth of 1.5 meters (5 feet) with appropriate spacing). This means, first, significantly less excavation work and therefore lower costs; second, we remain much more flexible regarding the garden area in terms of overbuilding and planting; and third, deep drilling is not an option for us.

This also allows the ground to regenerate well during the summer months.

The air-to-water heat pump costs about 2400 euros, can be installed flexibly (it doesn’t have to be in the same room as the ground-source heat pump), and as I mentioned earlier, it efficiently uses the waste heat from the heating circuit distributor and the condenser dryer (have you ever been in a room where such a dryer is running? You know how hot it gets!). In our utility room, this means we can safely do the following: first, store food without concerns; second, place the cats’ food bowls without the wet food overheating, spoiling, causing illness, or attracting flies unnecessarily; and third, where else should the "sudden" heat from the dryer, which runs during the day when no one is home, go? Outside? That would be inefficient!

Speaking of efficiency, the air-to-water heat pump consumes 0.2 kW per hour. When we shower in the morning (currently 2 adults, as the children are still small and tend to bathe in the evening), the device runs for about 2 hours; if there is also bathing in the evening, it runs for another good hour, and the dryer runs for about 2 hours…

Our heating technician has offered this package for a long time. We first inspected it in two reference houses because we were initially concerned about the relatively high noise level of the air compressor. Including excavation, installation, and so on, the package was considerably cheaper, though I can check the exact savings for you. Operating costs are also lower compared to systems with just ground-source heat pumps or just air-to-water heat pumps (which he also installs on customer request, as not everyone wants or can have a second unit).

This system has now been running perfectly for several years!

By the way, in summer, the temperature in that room is really cool, making it ideal for storing salads and similar items prepared during the day for a barbecue in the evening, for example.

Cascada schrieb:

By the way: Brine heat pump AND air source heat pump... how does that work? Also, manifold distributors for underfloor heating should be insulated. In a reasonably modern utility room, there is no waste heat left – except from the dryer.
Best regards

To clarify again: The manifold distributor for the heating circuits is located in the utility room, no matter which room is being heated. EVERY pipe in the underfloor heating starts in the utility room, thus indirectly generating heat from the floor, similar to geothermal heat.

Behind the distributor is the guest bathroom, where not all pipes could run through. Since it’s not possible to push the pipes free of tension at a 90-degree angle onto or into the floor within just 10 cm (4 inches) width of the distributor, the pipes run in a relaxed curve out of the distributor, across the utility room floor, and then back out towards the door. I have attached one of the floor plan drafts (red bar indicates the distributor).

P.S.: The freezer and the pump unit for rainwater harvesting also produce some waste heat, although not much. The central vacuum system unit is also installed there, but I don’t think it generates significant heat.

Illo77 schrieb:
For underfloor heating, the ground source heat pump only needs to heat the water to approximately 30 degrees Celsius (about 86°F) (is that correct? I don’t remember the exact flow temperature). For hot water demand like showers, we prefer 54 degrees Celsius (about 129°F) in the 270-liter (about 71 gallons) water tank. On the one hand, the significant extra effort required by the heat pump to raise the water temperature to this higher level is inefficient (just to clarify: the electric backup heater is switched off on both units, because we want to avoid electrical heating and only want to operate the devices electrically). On the other hand, why should the heat pump have to work outside its efficient operating range in a less efficient mode to generate more heat when 30 degrees Celsius (about 86°F) is sufficient for the underfloor heating?

The ground source heat pump should also alternate between heating domestic hot water and heating water. Currently, the air source heat pump is running inefficiently.

Additionally, we only have 48 square meters (about 517 square feet) of surface collectors (8 mats each measuring 1.0 x 6.0 meters on an area of 6 x 13 meters, installed at a depth of 1.50 meters (about 5 feet) with appropriate spacing). This means, first, significantly less earthworks and therefore lower costs; second, much greater flexibility regarding garden space in terms of covering and planting; and third, a deep borehole is not an option for us.

Of course, if there isn’t enough space for collectors, that’s a different matter. Purely from a cost perspective, the money spent on the air source heat pump might have been better invested in ground collectors.

Furthermore, this setup allows the ground to regenerate well in summer.

The air-to-water heat pump costs about 2400 Euros (approximately), can be installed flexibly (it doesn’t have to be in the same room as the ground source heat pump), and as I already mentioned, it efficiently utilizes the waste heat from the heating circuit distributor and the condenser dryer (have you ever been in a room with such a dryer running? You know what intense heat that produces). In our utility room, this means we can 1. safely store food, 2. safely place the two cats’ feeding bowls without the wet food overheating and spoiling, which would cause illness or attract unnecessary flies, and 3. where else should the “sudden” heat from the dryer during the day when no one’s home go? Outside? That would be inefficient!

Yes, I know how much heat that generates. I use a condenser dryer myself. But even without a greywater heat pump, the energy isn’t lost since it stays within the building envelope.

And speaking of efficiency, the air-to-water heat pump consumes about 0.2 kW per hour. When we shower in the morning (currently 2 adults, as the children are still young and usually bathe in the evening), the unit runs about 2 hours, and if bathing occurs in the evening, it runs roughly an hour longer. The dryer runs for about 2 hours…

I strongly believe that the ground source heat pump would operate more efficiently due to its generally better possible annual performance factor.

Our heating technician has been selling this package forever,

I believe that, since he also profits from the purchase costs.

And the operating costs are also lower than installations with purely ground source or purely air source heat,

I doubt that operating costs are lower compared to pure ground source systems, but probably compared to pure air source systems, yes.

The whole system has been running very well for several years now!

I’m sure it has.

Overall, this concept can work. If the property simply doesn’t allow for more collector area, it may be a viable solution. However, regarding purchase and operating costs, it’s probably not the ultimate solution. And if your heating installer has been promoting this concept “forever,” then it’s certainly not without some vested interest...

I need to jump in here.

I don’t quite understand how you can reduce the collector area so drastically, unless you are using more energy in the form of electricity or other energy sources (e.g., a fireplace). For a living area of 125m² (1350 sq ft), we have an estimated ratio of collector area to living space of 1:1. You want to get energy from 48m² (520 sq ft) or 78m² (840 sq ft) for about 160m² (1720 sq ft) of living space.

The heat for water and heating is primarily generated by geothermal energy both in your case and ours. Additionally, the heat loss from the condensation dryer is present in both situations. The only advantage on your side is that you use the ineffective heat from the utility room, and the ground source heat pump may operate in slightly more efficient conditions. However, this does not explain the large difference in the collector area ratio.

DerBjoern schrieb:
It’s good that everyone offers a different concept; otherwise, it becomes really impossible to compare. The best approach is to select the most suitable system concept based on the calculated heating load and then request offers for that concept from several providers.

Do you want to understand, or are you just unable to? Three heating companies provided offers, and all three companies proposed exactly the same options: gas with solar, geothermal, geothermal combined with air-to-water heat pump, district heating...

Company 1 submitted their offer through the carpenter; Companies 2 and 3 prepared their offers based exactly on Company 1’s proposal...

And you say these can’t be compared? Then nobody would need to request anything anywhere, and no company would ever prepare any offers...

Musketier schrieb:
I need to jump in here.
I don’t quite understand how you can reduce the collector area so drastically unless you are using additional energy sources, such as electricity or others (e.g., a fireplace). For our 125m² (1,345 sq ft) living space, we estimate a collector area to living space ratio of about 1:1. You want to extract energy from 48m² (516 sq ft) or 78m² (840 sq ft) for around 160m² (1,722 sq ft) of living area.

The heat for domestic hot water and heating is primarily generated by geothermal energy, both in your case and ours. Additionally, the heat loss from the condensing dryer applies to both of us. The only advantage on your side might be that you use the inefficient heat from the utility room and that your geothermal heat pump may operate in somewhat more efficient conditions. However, this doesn’t explain the huge difference in collector area ratios.

All I can tell you is what is installed here with us and others in our region… Vaillant geoTHERM VWS brine-to-water heat pump 61/3 combined with Vaillant compact collectors VWZ KK8 (8 collector mats, each 6 x 1 m (20 x 3 ft))… For domestic hot water, a Vaillant geotherm VWL BM/2 is used.

Excerpt from Vaillant: “Ground-coupled brine-to-water heat pumps obtain around 75% of the produced heating energy from the ground. Compact collectors provide a solution for accessing geothermal heat on small plot sizes and when using low-temperature heating systems. Compact collectors consist of several prefabricated collector mats that are laid horizontally approximately 20 cm (8 inches) below the frost line (around 1.2 to 1.5 m (4 to 5 ft) deep) in the ground. The compact collector is flushed with a brine mixture (water with antifreeze). Due to their hydraulic properties, compact collectors are not suitable for high-temperature applications (e.g., radiator systems or high domestic hot water demand) when compared to geothermal collectors or energy probes.”

Perhaps the term “low-temperature heating system” is the key here...
I’m not familiar with your heating concept—I only know that underfloor heating was always mentioned, probably due to the high insulation standard as a timber frame building built to KFW70 standard with controlled mechanical ventilation and heat recovery. Although we generally like it comfortably warm, we don’t need much heating (the electric backup heating is, by the way, switched off).