ᐅ Reliability of an energy calculation for KfW 55 – is it too high?
Created on: 20 Jun 2016 18:01
W
WT1987
Hello everyone,
For our new build with 2 full floors and a basement, we have now received a calculation for the entire KfW application. However, it seems to me that the numbers are being calculated quite high or may even be incorrect.
Some data about the house:
Is that the electricity consumption I should expect, or am I misunderstanding something? That seems very high!
Thank you in advance.
For our new build with 2 full floors and a basement, we have now received a calculation for the entire KfW application. However, it seems to me that the numbers are being calculated quite high or may even be incorrect.
Some data about the house:
- Architect’s plan shows living area: ground floor 75m² (807 ft²) & upper floor 70m² (753 ft²) (difference due to open space)
- Clear ceiling height: ground floor 2.7m (8 ft 10 in) & upper floor 2.5m (8 ft 2 in)
- Basement is unheated, air-water heat pump located in the basement
- Attic is not developed
- Air-water heat pump with ventilation system including heat recovery
- The expert assessor calculates a usable floor area of 277m² (2,982 ft²), which seems very high to me! He then uses this to estimate electricity consumption and arrives at a final energy demand of 4,860 kWh/year
Is that the electricity consumption I should expect, or am I misunderstanding something? That seems very high!
Thank you in advance.
toxicmolotow schrieb:
Considering that each room in our house has four exterior walls, I think the value is very good.toxicmolotow schrieb:
Our house has 7 rooms (+2 corridors).toxicmolotow schrieb:
Only two rooms don’t have four exterior walls (bathroom and children’s room), but a corridor and a living room each have five.That sounds to me like 6 floors with a flat roof.
Each room on a different level, except the bathroom and children’s room, and the living room at the very top. 😀
T
toxicmolotof21 Jun 2016 16:55Oh man... the ratio of exterior surface area to volume isn’t particularly extraordinary in this context.
Ideally, a sphere would be best, or to prevent it from rolling away, say, an igloo. Close to that is the building cube (modern term: urban villa).
But for every differently shaped building component, you pay an energy penalty. The only thing probably less ideal is an L-shaped bungalow, because there are no shared floors and ceilings between rooms.
Ideally, a sphere would be best, or to prevent it from rolling away, say, an igloo. Close to that is the building cube (modern term: urban villa).
But for every differently shaped building component, you pay an energy penalty. The only thing probably less ideal is an L-shaped bungalow, because there are no shared floors and ceilings between rooms.
S
Sebastian7921 Jun 2016 17:04Fortunately, individuality and personal taste still count for something 😉
E
elVincent25 Jun 2016 23:51Meeting the KfW55 requirements is more challenging due to transmission heat losses than primary energy demand. For our project, the allowed primary energy demand for KfW55 was 45.79 kWh/m² per year (square meter per year), while we achieved 25.81 kWh/m² per year. This would also have comfortably met the KfW40 standard (< 33.3 kWh/m² per year). The transmission heat loss needed to be below 0.266 W/m²K (watts per square meter kelvin), and we achieved 0.246 W/m²K. However, we were still significantly above the KfW40 target (< 0.209 W/m²K).
We have a transmission heat loss H' T [W/(m²K)] of 0.243. The reference value is 0.256.
Our energy consultant discovered significant errors in the thermal insulation calculation made by the structural engineer hired by the general contractor (GC). Everything had to be recalculated. According to the GC’s structural engineer, the planned construction should have been sufficient for KfW 55 standard. (He used software that is not even approved by KfW.) As a result, the GC had to make considerable improvements to meet KfW 55.
It was a good decision to hire an independent KfW consultant rather than relying on the structural engineer contracted by the GC, who was also supposed to prepare the KfW documentation. (This raises suspicions of fraud.)
The required improvements included:
- Thicker insulation beneath the foundation slab with better thermal conductivity rating (WLG)
- Thicker insulation beneath the screed with better WLG
- Different roller shutters
- Thicker insulation with better WLG on the attic floor ceiling
I am basically doing the same with the TÜV inspector hired by the GC—simply canceled and hired my own site supervisor.
Our energy consultant discovered significant errors in the thermal insulation calculation made by the structural engineer hired by the general contractor (GC). Everything had to be recalculated. According to the GC’s structural engineer, the planned construction should have been sufficient for KfW 55 standard. (He used software that is not even approved by KfW.) As a result, the GC had to make considerable improvements to meet KfW 55.
It was a good decision to hire an independent KfW consultant rather than relying on the structural engineer contracted by the GC, who was also supposed to prepare the KfW documentation. (This raises suspicions of fraud.)
The required improvements included:
- Thicker insulation beneath the foundation slab with better thermal conductivity rating (WLG)
- Thicker insulation beneath the screed with better WLG
- Different roller shutters
- Thicker insulation with better WLG on the attic floor ceiling
I am basically doing the same with the TÜV inspector hired by the GC—simply canceled and hired my own site supervisor.
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