ᐅ Which heating system? Air source heat pump / gas / geothermal heating
Created on: 26 Mar 2015 19:57
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Nina132
Hello everyone,
we are building a single-family house with 155m2 (1,670 sq ft) and want to try to meet KfW55 standards (at least that is what is stated in the contract). Underfloor heating is mandatory. We are working with an architect who also acts as the general contractor, so the house will be delivered turnkey.
The challenges are as follows:
1. North-facing slope – no opportunity for solar panels
2. Sloped site – the ground floor (GF) will be partially built into the hillside at the back. The bedrooms will be on the GF, while the living area is on the upper floor (UF) with a level exit “onto” the slope. By embedding the GF on one side, we can have a reasonably flat garden at the top.
3. There are currently just two of us, but a child is planned in about five years
4. We want a large bathtub and will therefore need a lot of hot water
5. I like to ventilate frequently and thoroughly
6. The utility room is on the GF along with the bedrooms. Could there be noise issues?
Now about the heating decision.
Originally, especially my partner wanted a ground source heat pump. That is probably the best option in terms of quality and ecology, but it is very expensive.
An air source heat pump is of course an alternative, but I’m concerned about electricity costs in winter because I suspect that, especially the GF, will cool down quickly due to the hillside situation.
Our architect recommends a gas condensing boiler, saying this is standard for 80% of new builds. We actually wanted to move away from gas and oil, but electricity also involves fossil fuels – at least indirectly. Of course, this would probably rule out KfW55 compliance, but I think KfW70 would also be acceptable.
What are your thoughts?
we are building a single-family house with 155m2 (1,670 sq ft) and want to try to meet KfW55 standards (at least that is what is stated in the contract). Underfloor heating is mandatory. We are working with an architect who also acts as the general contractor, so the house will be delivered turnkey.
The challenges are as follows:
1. North-facing slope – no opportunity for solar panels
2. Sloped site – the ground floor (GF) will be partially built into the hillside at the back. The bedrooms will be on the GF, while the living area is on the upper floor (UF) with a level exit “onto” the slope. By embedding the GF on one side, we can have a reasonably flat garden at the top.
3. There are currently just two of us, but a child is planned in about five years
4. We want a large bathtub and will therefore need a lot of hot water
5. I like to ventilate frequently and thoroughly
6. The utility room is on the GF along with the bedrooms. Could there be noise issues?
Now about the heating decision.
Originally, especially my partner wanted a ground source heat pump. That is probably the best option in terms of quality and ecology, but it is very expensive.
An air source heat pump is of course an alternative, but I’m concerned about electricity costs in winter because I suspect that, especially the GF, will cool down quickly due to the hillside situation.
Our architect recommends a gas condensing boiler, saying this is standard for 80% of new builds. We actually wanted to move away from gas and oil, but electricity also involves fossil fuels – at least indirectly. Of course, this would probably rule out KfW55 compliance, but I think KfW70 would also be acceptable.
What are your thoughts?
B
Bauexperte1 Apr 2015 11:34Hello,
The building envelope is not made “only” of bricks; the roof, insulation, façade, and windows are also part of it. When applying the 15% rule, there must always be a mix of various measures. These affect both the primary energy demand (type and amount of energy) and the building envelope (filled brick, better insulation, better windows, etc.). As always, there are exceptions: simply connecting to a district heating network whose heat comes at least 50% from renewable energy or waste heat or combined heat and power (CHP) plants may suffice.
That is why I wrote that it always has to be calculated based on the specific building!
Best regards, Bauexperte
Bieber0815 schrieb:I mean exactly what I wrote: “a 15% reduction in primary energy demand and at the same time at least a 15% better building envelope.” The Renewable Energy Heat Act does not allow either/or in this case, although there are many ways to achieve the goal. By the way, the term primary energy refers to the type and amount of energy taken from the natural sources used.
I don’t understand the second part of the sentence :-(. Also in terms of “in addition”? Isn’t it enough to reduce the primary energy demand to 85%?
Bieber0815 schrieb:You can—alternatively to using renewable energy—improve the energy efficiency of your building by, for example, better insulating the building envelope, using heat recovery ventilation, or other measures the Renewable Energy Heat Act (which requires renewable energy in new buildings) recognizes. Specifically, this means the building must reduce the requirements of the currently applicable Energy Saving Ordinance (EnEV) by at least 15%. Proof is provided by an energy performance certificate according to the Energy Saving Ordinance.
Now I’m confused again. What is a better building envelope? How is “better” assessed if not by the primary energy demand of the house? For example, measures to reduce heat loss (e.g., at the envelope) reduce the primary energy demand to 85%: done, the builder can install a gas condensing boiler without a heat pump, solar thermal system, or photovoltaic panels.
The building envelope is not made “only” of bricks; the roof, insulation, façade, and windows are also part of it. When applying the 15% rule, there must always be a mix of various measures. These affect both the primary energy demand (type and amount of energy) and the building envelope (filled brick, better insulation, better windows, etc.). As always, there are exceptions: simply connecting to a district heating network whose heat comes at least 50% from renewable energy or waste heat or combined heat and power (CHP) plants may suffice.
That is why I wrote that it always has to be calculated based on the specific building!
Best regards, Bauexperte
B
Bieber08151 Apr 2015 11:46Bauexperte schrieb:
I mean exactly what I wrote: "15% reduction in primary energy demand and at the same time at least 15% better building envelope". Thank you, then the "correct" (first part of the sentence) was not entirely right, I had understood it differently until now. I still haven’t understood how the improvement of the envelope is determined (I do understand that the envelope consists of walls, windows, doors, roof, and floor slab or basement walls), but I’ll accept it as it is for now. In any case, I am wiser than before! Many thanks for the patient answers!
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Bauexperte1 Apr 2015 12:12Hello,
as a reminder: the building must exceed the requirements of the applicable energy saving ordinance by at least 15%
Best regards, Bauexperte
as a reminder: the building must exceed the requirements of the applicable energy saving ordinance by at least 15%
Bieber0815 schrieb:Here are 3 examples among many -
I still don’t understand what exactly defines the improvement of the building envelope...
- While it is usually sufficient for the building envelope of a KfW 70 efficiency house to use a Poroton T10 - 36.5 with a U-value of 0.254, using a Poroton T8 - 36.5 with a U-value of 0.21 can already be a first step toward meeting the 15% rule.
- If installing double-glazed windows – along with other measures – is sufficient to achieve the KfW 70 efficiency house standard, then installing triple-glazed windows is another step.
- If 200 mm (8 inches) of insulation in the attic typically achieves KfW 70, increasing to 240 mm (9.5 inches) can be the next step.
- and so on.
Best regards, Bauexperte
B
Bieber08152 Apr 2015 08:26Bauexperte schrieb:
3 examples out of many These are examples of how an improvement can be achieved. That’s clear enough. But how does a professional evaluate the improvement (14%, 15%, or maybe 16%)? One way would be to look at the U-value: before 0.254 W/m²·K (I added the unit here, hopefully correct), after 0.21 W/m²·K, difference 0.044 W/m²·K or 17% less compared to “before.” Of course, this is only the U-value of the brick as given in the example. Maybe one should consider a (weighted?) U-value for the entire building envelope (meaning: the sum of all U* A for all parts of the envelope). Or perhaps simply the resulting primary energy demand?
Sorry if I’m being slow to understand or not expressing my question clearly…
The energy performance certificate lists all building components along with their respective areas and U-values, from which an overall U-value for the house is derived. There are also calculated or standard deductions for thermal bridges (using standard values usually works better), which are then used to calculate the transmission heat loss (Ht). Therefore, constructive improvements are possible. The building must be at least 15% better than the energy-saving regulations specify.
The primary energy demand is a value that accounts for the energy consumption of your heating medium during production and delivery. There are predefined calculation factors for each energy source. The heating demand of the house is then multiplied by the factor. For example: heating demand of 100 × 1.1 (factor for gas) = primary energy of 110. Again, the target is to be at least 15% below the energy-saving regulations.
This is a strongly simplified explanation; in my opinion, it can only be explained precisely with a sample project. As already mentioned, there are numerous possible measures.
The primary energy demand is a value that accounts for the energy consumption of your heating medium during production and delivery. There are predefined calculation factors for each energy source. The heating demand of the house is then multiplied by the factor. For example: heating demand of 100 × 1.1 (factor for gas) = primary energy of 110. Again, the target is to be at least 15% below the energy-saving regulations.
This is a strongly simplified explanation; in my opinion, it can only be explained precisely with a sample project. As already mentioned, there are numerous possible measures.
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