Manu1986
2015-10-06 12:10:06
- #1
Hello everyone,
as a construction layman, one is dependent on information from the internet and recommendations from professionals. With the latter, I always like to hear a second opinion and hope to find it here.
The following question:
In general, one often reads/hears that a heat pump works particularly (or only?) efficiently in "well-insulated" houses. "Well" is probably a matter of definition again, but I have concrete numbers, facts, and a brand of the heat pump with which, hopefully, one can get to the bottom of the question whether the system offered to us by the builder makes sense:
It is a solid house as a semi-detached house with just under 160 sqm spread over the ground floor, upper floor, and converted attic. There is also a basement, one room of which is used as living space.
A Stiebel Eltron LWZ 303i with integrated ventilation system is to be used as an air-water heat pump, and subsequently, the initial question arises, whether this setup with the mentioned heat pump is sensible and efficient?
Perhaps as an additional complement: With this setup, one would reach KfW 70, which, however, has recently become "standard" and is no longer subsidized. Of course, the provider could also take measures to achieve KfW 55, but he advises against it because the additional costs are not in relation to the savings and the subsidies are also not much (interest-) cheaper. That makes sense to me so far, only, as mentioned, the reports unsettle because one should pay attention to "good insulation" when using heat pumps, and we do not know where "good" begins or ends.
In this context, I would have one more question: Would it perhaps even be sufficient to rely “only” on a 36 cm Poroton brick instead of 24 cm Poroton bricks with 12 cm ETICS?
as a construction layman, one is dependent on information from the internet and recommendations from professionals. With the latter, I always like to hear a second opinion and hope to find it here.
The following question:
In general, one often reads/hears that a heat pump works particularly (or only?) efficiently in "well-insulated" houses. "Well" is probably a matter of definition again, but I have concrete numbers, facts, and a brand of the heat pump with which, hopefully, one can get to the bottom of the question whether the system offered to us by the builder makes sense:
It is a solid house as a semi-detached house with just under 160 sqm spread over the ground floor, upper floor, and converted attic. There is also a basement, one room of which is used as living space.
The construction specification includes, among other things, the following:
Regarding masonry sealing:
To protect against rising damp, we apply a strip seal with an overlap on the basement perimeter and internal masonry on the floor slab. In the soil-contacting area of the basement exterior walls, a highly flexible, two-component bitumen sealing system against ground moisture is additionally applied according to VOB, Part C, DIN 18336, as well as insulation panels1. This sealing system exceeds the crack-bridging required by DIN 18195.
The masonry:
The basement
The basement is constructed with an external wall of high-quality basement bricks with a thickness of 30 cm, on top of which insulation panels are applied as required, and inside is built with perforated bricks according to structural requirements in 17.5 cm or 11.5 cm thickness.
The living floors
The living floors are built externally from perforated bricks with a thickness of 24 cm (in combination with
external thermal insulation composite system*), internally from perforated bricks according to thermal and
structural requirements in 17.5 cm or 11.5 cm thickness.
* The external masonry receives a thermal skin 120 mm thick according to the Energy Saving Ordinance with fabric plastering and a white or light-pastel colored silicate or silicone resin render. U-value = 0.188
Floor slabs
The basement and ground floor ceilings are executed using prefabricated elements as reinforced filigree slabs with cast-in-place concrete or as precast slabs. Ceiling thickness and reinforcement according to structural requirements. A wall barrier sheet is laid between ceiling and masonry. The underside of the ceilings is smooth ready for wallpapering as exposed concrete.
The roof:
The roofs are built as carpentry-style purlin roof trusses in softwood of quality class S10 and cut class A/B according to structural requirements. [...] To protect against drifting snow and for good roof ventilation, a diffusion-open underlay membrane with battens and counter battens is applied over the full area, and the roof covering prepared. The roof overhangs measure approx. 50 cm on the eaves side with tongue-and-groove boards and approx. 25 cm on the gable side with verge boards. The roof is covered with high-quality concrete roof tiles with a 30-year factory guarantee in the colors “Classic red,” “Dark red,” “Tile red,” or “Dark gray,” secured against storms. Ridge, hips, shaped parts, passage stones with ventilation pipe covers, and verge stones are, of course, included in the fixed price.
Windows
The house receives in the basic equipment white, high-quality plastic windows and patio doors with a frame thickness of 82 mm, triple thermal insulation glazing, and concealed tilt or tilt-and-turn fittings from the company Roto or equivalent. The all-round running, welded-in-the-corner rubber lip seals are replaceable. As weather protection, a drip edge made of anodized aluminum is integrated into the horizontally lower sash frame. The steel reinforcement provides the necessary stability; the mushroom head locking system increases security.
[...]
If roof windows are shown or named in the plan documents and the additional construction description, they will be installed as pivot windows between the rafters. They feature top-mounted one-hand operation and permanent ventilation flap, air filter, sash and frame made of naturally clear-coated pine, thermal insulation glazing, exterior cover, and aluminum-coated flashing frame.
In the basement rooms, plastic windows in rough construction dimensions of 75x50 cm with thermal insulation glazing are installed, number according to plan documents. Where necessary, the basement windows are provided with plastic light wells with galvanized cover grates and anti-lift security.
Roller shutters
All rectangular openable windows in the living floors larger than 1 m² receive, as far as technically possible, heat-insulated roller shutter boxes with plastic slats in white or gray colors with ventilation slots and side wall-mounted belt winder operation in the masonry. For window sizes over 4 m², the roller shutter has a gear transmission for easier operation. Lateral shifting of the roller shutter slats is prevented by a special locking mechanism. Roof windows and dormer windows, as well as fixed glazing window elements, do not receive roller shutters.
Dry construction and insulation
The rafter fields of the ceiling surfaces and roof slopes in the attic are highly insulated with 200 mm mineral wool boards, WLG 035, and clad with 1.25 cm thick gypsum plasterboards on counter battens 2.4/4.8 cm. A PE foil as a vapor barrier is stretched over the mineral wool boards over the full area. The joints of the dry plasterboards are finished ready for wallpapering. A trim profile is installed between slope and ceiling to prevent cracking4. You will receive a high-quality and windproof execution, which will be proven by a blower door test. From the corridor in the upper or attic floor, if technically possible, a heat-insulated foldaway staircase approx. 60 x 120 cm leads to the attic room or unconverted attic.
A Stiebel Eltron LWZ 303i with integrated ventilation system is to be used as an air-water heat pump, and subsequently, the initial question arises, whether this setup with the mentioned heat pump is sensible and efficient?
Perhaps as an additional complement: With this setup, one would reach KfW 70, which, however, has recently become "standard" and is no longer subsidized. Of course, the provider could also take measures to achieve KfW 55, but he advises against it because the additional costs are not in relation to the savings and the subsidies are also not much (interest-) cheaper. That makes sense to me so far, only, as mentioned, the reports unsettle because one should pay attention to "good insulation" when using heat pumps, and we do not know where "good" begins or ends.
In this context, I would have one more question: Would it perhaps even be sufficient to rely “only” on a 36 cm Poroton brick instead of 24 cm Poroton bricks with 12 cm ETICS?