ᐅ Effective Energy Strategy for New Construction KfW70 Without Oil or Gas
Created on: 18 Oct 2014 18:10
U
Username_wahl
Hello,
we are planning to build within the next 1-2 years, approximately 170-190 sqm (1830-2045 sq ft) for 5 people, meeting the KfW 70 standard. We definitely do not want gas or oil heating.
We are considering an air-to-air heat pump with automated ventilation for the house, including heat recovery and domestic hot water heating using waste heat (as seen from a prefabricated house supplier).
Since heating with electricity can be expensive, we would like to combine this system with a photovoltaic (PV) installation.
What do you think about this? How do the initial investment and running costs compare to a conventional heating system?
As additional options, I am also thinking about solar thermal and a wood stove (with a heat storage unit?), but I am skeptical about whether these can be integrated smoothly. Of course, it should also be economically viable in the medium term.
we are planning to build within the next 1-2 years, approximately 170-190 sqm (1830-2045 sq ft) for 5 people, meeting the KfW 70 standard. We definitely do not want gas or oil heating.
We are considering an air-to-air heat pump with automated ventilation for the house, including heat recovery and domestic hot water heating using waste heat (as seen from a prefabricated house supplier).
Since heating with electricity can be expensive, we would like to combine this system with a photovoltaic (PV) installation.
What do you think about this? How do the initial investment and running costs compare to a conventional heating system?
As additional options, I am also thinking about solar thermal and a wood stove (with a heat storage unit?), but I am skeptical about whether these can be integrated smoothly. Of course, it should also be economically viable in the medium term.
Passivhaus schrieb:
Hello, I would like to be more independent from rising energy costs.ypg schrieb:
You should mention the flow temperature and explain why a gas heating system is a problem for you. That way, it would be easier to address your question. Because, in principle, a gas heating system can be a reasonable option.Sorry, I missed your information.
Doesn’t everyone want to be independent? In the end, it’s a matter of cost: how much can I afford to invest in additional technology to be self-sufficient? But you will always depend on electricity.
You first have to pay off the investment.
We are currently heating with a ductless mini-split heat pump, powered by photovoltaic electricity.
The unit initially consumes about 900 W, then quickly reduces to around 300 W once the target temperature is reached, and eventually switches off by itself. It heats up the room immediately, similar to a fan heater, since the warm air is blown directly into the space. The maximum 900 W is easily supplied by the photovoltaic system during the day, even in winter, except in case of persistent fog.
The heat is retained long enough in a well-insulated house.
Because it is a heat pump system, the unit produces at least 3 kWh of heat from 1 kWh of electricity. At 14 cents per kWh of electricity (photovoltaic electricity!), this equals roughly 4.5 cents per kWh of heat, which is hard to beat in terms of cost.
Furthermore, the system does not require radiators or piping. Installation cost for the complete setup was around 400 euros. The unit (3.7 kW) was purchased with a 20% discount off the retail price for 571 euros.
In summer, it cools the space—hard to find a better way to use self-generated power. It also reduces humidity, helping to prevent mold growth.
However, if you want warm floors, you will need a different solution that also supports underfloor heating. We use both a (pellet) boiler and the mini-split heat pump—as well as a wood-burning stove.
The unit initially consumes about 900 W, then quickly reduces to around 300 W once the target temperature is reached, and eventually switches off by itself. It heats up the room immediately, similar to a fan heater, since the warm air is blown directly into the space. The maximum 900 W is easily supplied by the photovoltaic system during the day, even in winter, except in case of persistent fog.
The heat is retained long enough in a well-insulated house.
Because it is a heat pump system, the unit produces at least 3 kWh of heat from 1 kWh of electricity. At 14 cents per kWh of electricity (photovoltaic electricity!), this equals roughly 4.5 cents per kWh of heat, which is hard to beat in terms of cost.
Furthermore, the system does not require radiators or piping. Installation cost for the complete setup was around 400 euros. The unit (3.7 kW) was purchased with a 20% discount off the retail price for 571 euros.
In summer, it cools the space—hard to find a better way to use self-generated power. It also reduces humidity, helping to prevent mold growth.
However, if you want warm floors, you will need a different solution that also supports underfloor heating. We use both a (pellet) boiler and the mini-split heat pump—as well as a wood-burning stove.
I believe it is more like: a maximum of 3 kWh heat from one kWh of electricity at this price level! Especially in winter with cold outside air, I expect a significantly lower efficiency. Also, warming the building envelope with warm air is difficult due to the low heat capacity, particularly when distributing heat across multiple rooms. The comfortable temperature with air heating is usually higher compared to heating the building envelope. So as a standalone system, it is generally quite impractical.
Air is a very sluggish energy carrier, or perhaps the slowest, if I’m not mistaken...
We decided on a ground source heat pump with horizontal collectors for heating, and an air-to-water heat pump for hot water supply. The air-to-water heat pump is installed in the utility room, where it uses all the heat from that space (the manifold for the underfloor heating is located in that room, so every heated room starts there, which releases quite a bit of heat; in addition, there are electrical appliances like a condenser dryer that also emit a lot of heat).
For a while, (or maybe they still do?) electric utilities liked to promote air source heat pumps, since they consume a lot of electricity, which benefits those companies.
I would rather install a solar thermal system on the roof; it doesn’t just use direct sunlight like a photovoltaic system but also extracts heat from the air and rain... however, it is more expensive to install (photovoltaic prices have dropped a lot recently).
What about a pellet stove?
I’m not a fan of gas either, but that mostly has to do with my role as a firefighter and my personal experiences with gas.
We decided on a ground source heat pump with horizontal collectors for heating, and an air-to-water heat pump for hot water supply. The air-to-water heat pump is installed in the utility room, where it uses all the heat from that space (the manifold for the underfloor heating is located in that room, so every heated room starts there, which releases quite a bit of heat; in addition, there are electrical appliances like a condenser dryer that also emit a lot of heat).
For a while, (or maybe they still do?) electric utilities liked to promote air source heat pumps, since they consume a lot of electricity, which benefits those companies.
I would rather install a solar thermal system on the roof; it doesn’t just use direct sunlight like a photovoltaic system but also extracts heat from the air and rain... however, it is more expensive to install (photovoltaic prices have dropped a lot recently).
What about a pellet stove?
I’m not a fan of gas either, but that mostly has to do with my role as a firefighter and my personal experiences with gas.
D
DerBjoern4 Nov 2014 08:23Illo77 schrieb:
Air is a very, very inert energy carrier or the most inert one if I’m not mistaken... Actually, air adjusts its temperature very quickly. However, air can only transport small amounts of energy. That’s probably what you mean.We decided on a ground source heat pump with horizontal collectors for heating, and an air-to-water heat pump for domestic hot water. The latter is installed in the utility room, where it utilizes all the heat available in that space (the underfloor heating manifold is located in that room, so every heated room starts there, which releases a lot of heat. Additionally, there are electrical appliances like a condensing dryer that also emit considerable heat).What led to this unusual setup? Why don’t you produce the domestic hot water with the more efficient ground source heat pump as well?
In which region will the house be located? Air-to-air heat pumps should only be used in high-performance KFW55 houses or passive houses with minimal heating demand.
KFW70 seems quite suitable for a ground-source heat pump. We live in a rather cold region in Germany, have a KFW70 house with just over 200 square meters (including the basement) heated—underfloor heating throughout. The energy consumption is reasonable—unlike some air heat pumps here in the new development.
However, unlike gas heating, you need to have a good understanding of heat pumps to optimize the system—and especially work with an experienced heating installer (no buffer tank, no individual room control, etc.).
There are plenty of pros and cons discussions about controlled mechanical ventilation to form an opinion.
We have one installed.
By the way: ground-source heat pump AND air heat pump... how does that work? Also, heating circuit distributors should be insulated. In a reasonably modern utility room, there is no waste heat anymore—except from the clothes dryer.
Best regards
KFW70 seems quite suitable for a ground-source heat pump. We live in a rather cold region in Germany, have a KFW70 house with just over 200 square meters (including the basement) heated—underfloor heating throughout. The energy consumption is reasonable—unlike some air heat pumps here in the new development.
However, unlike gas heating, you need to have a good understanding of heat pumps to optimize the system—and especially work with an experienced heating installer (no buffer tank, no individual room control, etc.).
There are plenty of pros and cons discussions about controlled mechanical ventilation to form an opinion.
We have one installed.
By the way: ground-source heat pump AND air heat pump... how does that work? Also, heating circuit distributors should be insulated. In a reasonably modern utility room, there is no waste heat anymore—except from the clothes dryer.
Best regards
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