Hello everyone,
As a construction novice, you really have to rely on information from the internet and recommendations from professionals. With the latter, I always like to get a second opinion and hope to find one here.
Here is my question:
Generally, you often hear that a heat pump works especially (or only?) efficiently in "well-insulated" houses. What “well” means is of course open to interpretation, but I have specific numbers, facts, and a particular heat pump model that should hopefully help clarify whether the system offered to us by the builder makes sense:
It is a solid construction semi-detached house with just under 160 sqm (1,722 sq ft) spread over the ground floor, upper floor, and an extended attic. Additionally, there is a basement, with one room used as living space.
An air-to-water heat pump, specifically the Stiebel Eltron LWZ 303i with an integrated ventilation system, is planned. This raises the initial question: is this setup with the specified heat pump sensible and efficient?
As an additional note: This setup would achieve KfW 70 standard, which has recently become the norm and is no longer subsidized. Of course, the builder could also take measures to reach KfW 55 level, but he advises against it because the extra costs are not proportional to the savings and the subsidies are not significantly (interest) more favorable. That makes sense to me so far, but as mentioned, the reports suggesting that heat pumps require “good insulation” make us uncertain, and we don’t really know where “good” insulation starts or ends.
In this context, I have another question: Would it perhaps even be sufficient to use 36 cm (14 inches) Poroton bricks instead of 24 cm (9.5 inches) bricks with 12 cm (5 inches) external insulation?
As a construction novice, you really have to rely on information from the internet and recommendations from professionals. With the latter, I always like to get a second opinion and hope to find one here.
Here is my question:
Generally, you often hear that a heat pump works especially (or only?) efficiently in "well-insulated" houses. What “well” means is of course open to interpretation, but I have specific numbers, facts, and a particular heat pump model that should hopefully help clarify whether the system offered to us by the builder makes sense:
It is a solid construction semi-detached house with just under 160 sqm (1,722 sq ft) spread over the ground floor, upper floor, and an extended attic. Additionally, there is a basement, with one room used as living space.
The construction specifications include the following:
Regarding masonry waterproofing:
To protect against rising moisture, we apply a strip waterproofing layer with overlap on the basement perimeter masonry and interior masonry on the floor slab. In the soil-contact areas of the basement exterior walls, a highly flexible, two-component bitumen waterproofing system is applied against ground moisture according to VOB, Part C, DIN 18336, as well as insulating panels1. This waterproofing system exceeds the crack-bridging requirements according to DIN 18195.
The masonry:
The basement
The basement floor is built with an exterior wall of high-quality basement bricks 30 cm (12 inches) thick, followed by insulating panels as needed, and internally with perforated bricks according to structural requirements, either 17.5 cm (7 inches) or 11.5 cm (4.5 inches) thick.
The residential floors
The residential floors have exterior walls made of perforated bricks with a thickness of 24 cm (9.5 inches) (in combination with an external thermal insulation composite system*), and interior walls made of perforated bricks according to thermal and structural requirements, 17.5 cm (7 inches) or 11.5 cm (4.5 inches) thick.
* The exterior masonry receives a 120 mm (4.7 inches) thermal insulation layer in accordance with the energy saving regulations, with a fabric-reinforced skim coat and a white or light pastel-tinted silicate or silicone resin render. U-value = 0.188
Floor slabs
The basement and ground floor ceilings are constructed using prefabricated elements as reinforced filigree slabs with in-situ concrete or as precast concrete slabs. Thickness and reinforcement are according to structural requirements. A wall barrier membrane is installed between the slab and masonry. The undersides of the ceilings are smooth exposed concrete and ready for wallpapering.
The roof:
The roofs are built as carpenter-constructed purlin roofs made from softwood graded S10 and cut class A/B according to structural requirements. [...]
To protect against wind-driven snow and ensure good roof ventilation, a vapor permeable underlay membrane with battens and counter battens is fully applied, and the roof covering is prepared. The eaves have overhangs of about 50 cm (20 inches) with tongue-and-groove boards, and the gable sides about 25 cm (10 inches) with verge boards. The roof is covered with high-quality concrete roof tiles with a 30-year factory warranty in colors “classic red,” “dark red,” “brick red,” or “dark gray,” all wind-secured. Ridge tiles, hips, shaped components, roof penetrations with vent pipe caps, and verge stones are included in the fixed price.
Windows
The basic equipment includes white, high-quality uPVC windows and patio doors with a frame thickness of 82 mm (3.2 inches), featuring triple-glazed energy-efficient glass and concealed tilt-and-turn or tilt/turn hardware by Roto or equivalent. The continuous, welded corner rubber lip seals are replaceable. For weather protection, a drip cap made of anodized aluminum is integrated into the horizontal bottom frame. Steel reinforcement provides necessary stability, and mushroom-head locking pins enhance security.
[...]
If roof windows are indicated or mentioned in the planning documents and additional building specifications, they are installed as pivot windows between rafters. They feature top-operated single-handle operation, permanent ventilation flap, air filter, sashes and casings made of lightly varnished natural pine, energy-efficient glazing, and aluminum-coated plastic outer flashings and mounting frames. In basement rooms, uPVC windows with rough opening dimensions of 75 x 50 cm (30 x 20 inches) and energy-efficient glazing are installed according to plans. Where necessary, basement windows receive plastic light shafts with galvanized steel grilles and anti-lift security.
Roller shutters
All rectangular operable windows in the residential floors larger than 1 m² (11 sq ft) will receive, where technically possible, insulated roller shutter boxes with white or gray plastic slats with ventilation slots and side-mounted strap reel operation in the masonry. For window sizes over 4 m² (43 sq ft), the roller shutter gear is equipped with a transmission for easier operation. Lateral shifting of the slats is prevented by a special locking mechanism. Roof windows, dormers, and fixed glazing window units do not receive roller shutters.
Drywall and insulation
The rafter fields of ceiling surfaces and sloping ceilings in the attic are insulated with 200 mm (8 inches) mineral wool boards with a thermal conductivity of 0.035 W/(m·K). They are clad with 1.25 cm (0.5 inch) thick gypsum plasterboards fixed on counter battens measuring 2.4/4.8 cm (1/1.9 inches).
A polyethylene sheet acting as a vapor barrier is fully stretched over the mineral wool boards. The joints of the drywall panels are finished smooth and ready for wallpapering. Between the slope and the ceiling, a trim profile is installed to prevent cracking4. This results in a high-quality, airtight finish verified by a blower door test. Where technically possible, a thermally insulated pull-down ladder approximately 60 x 120 cm (24 x 47 inches) leads from the upper or attic floor hallway into the attic or unfinished roof space.
An air-to-water heat pump, specifically the Stiebel Eltron LWZ 303i with an integrated ventilation system, is planned. This raises the initial question: is this setup with the specified heat pump sensible and efficient?
As an additional note: This setup would achieve KfW 70 standard, which has recently become the norm and is no longer subsidized. Of course, the builder could also take measures to reach KfW 55 level, but he advises against it because the extra costs are not proportional to the savings and the subsidies are not significantly (interest) more favorable. That makes sense to me so far, but as mentioned, the reports suggesting that heat pumps require “good insulation” make us uncertain, and we don’t really know where “good” insulation starts or ends.
In this context, I have another question: Would it perhaps even be sufficient to use 36 cm (14 inches) Poroton bricks instead of 24 cm (9.5 inches) bricks with 12 cm (5 inches) external insulation?
Interestingly, with a heat pump, the better the system is designed, the more you save the worse the insulation is (compared to other heat sources). However, for low overall costs, it is always better to have a high level of insulation, as this naturally reduces energy consumption. I am quite confident that an air-to-water heat pump works well in a KfW 70 house (I know many who have one), but I would advise against an air-to-air heat pump. The heating load will probably be in the range of about 5-7 kW at around -14°C (7°F), roughly estimated depending on the details. There are already units available that provide enough output without an electric heater even when it is cold. I don’t know the exact location, but I can imagine it working.
B
Bauexperte6 Oct 2015 16:39Hello,
KfW 70 has only been a standard since January 1, 2016, with funding available until March 31, 2016. For this, form 153 is sufficient; it must be received by KfW before the end of March 2016.
In combination with a Stiebel LWZ 303i or Tecalor Integrale (also Stiebel and essentially the same), moving to KfW 55 is only a moderate step. This requires a different masonry unit—such as the T8—insulation beneath the slab foundation, and an independent expert supervision. This might be interesting if the new KfW funding conditions are to be used.
From an economic perspective, it still does not make sense, as the KfW 70 energy standard is currently subsidized. The difference between 55 and 70 means you might save about €100.00/120.00 per year, depending on shower usage.
It is a different situation when KfW 70 becomes the standard under the Energy Saving Ordinance for houses. The step from the Energy Saving Ordinance standard to 55 is moderate, but the savings in energy costs compared to the standard remain unchanged ;-)
Best regards, Bauexperte
Bauexperte
KfW 70 has only been a standard since January 1, 2016, with funding available until March 31, 2016. For this, form 153 is sufficient; it must be received by KfW before the end of March 2016.
In combination with a Stiebel LWZ 303i or Tecalor Integrale (also Stiebel and essentially the same), moving to KfW 55 is only a moderate step. This requires a different masonry unit—such as the T8—insulation beneath the slab foundation, and an independent expert supervision. This might be interesting if the new KfW funding conditions are to be used.
From an economic perspective, it still does not make sense, as the KfW 70 energy standard is currently subsidized. The difference between 55 and 70 means you might save about €100.00/120.00 per year, depending on shower usage.
It is a different situation when KfW 70 becomes the standard under the Energy Saving Ordinance for houses. The step from the Energy Saving Ordinance standard to 55 is moderate, but the savings in energy costs compared to the standard remain unchanged ;-)
Best regards, Bauexperte
Bauexperte
So, the 303 model is discontinued and basically being sold off as surplus. When you run the numbers through a calculator, you realize that the unit is too small. For a building with a typical energy-saving standard, the heating load for this size comes to roughly 7 kW. However, the pump only delivers 4.2 kW. You can probably guess where the rest comes from…
Conclusion: The heating system isn’t practical. You would need the larger pump, the 504, which can handle it. However, the price difference is obviously significant.
Conclusion: The heating system isn’t practical. You would need the larger pump, the 504, which can handle it. However, the price difference is obviously significant.
Similar topics