ᐅ Gas with solar thermal? Or heat pump with photovoltaic? Advice needed
Created on: 5 Feb 2020 08:57
M
Micha8589
Good morning to the forum,
I have been researching heating options for quite some time and have gathered a few opinions, which have only made me more uncertain about my decision. That’s why I thought I’d ask the forum.
My family (2 adults, 1 child) is planning to build the following single-family house at the end of this year or beginning of next year:
Single-family home with pitched roof
Approximately 115 m² (1,237 sq ft)
Solid construction (calcium silicate brick ground and upper floors, brick-clad)
No KFW standard
Building location: southern Mecklenburg
Unfortunately, I can’t provide an energy performance certificate or heating load calculation yet, as the preliminary offer is still being prepared. I am also aware that a general statement can’t really be made since every house and heating behavior is individual.
The construction company advised us to install a modern hybrid heating system consisting of a gas condensing boiler and two solar thermal panels on the roof for domestic hot water, as the initial costs are relatively low (plus installation of the central gas connection), and this technology has proven reliable. The entire house is planned to have underfloor heating. According to the company, they have had very positive experiences with this and consider the technology future-proof. (There is also the idea of a fireplace in the living room.)
On the other hand, I think gas prices will not get any cheaper in the future, and the topic of CO₂ taxes (especially concerning the fireplace) worries me somewhat.
In theory, I would prefer to install a geothermal heat pump combined with a suitable photovoltaic system because this would make me independent of fossil fuels and allow me to heat “off-grid” to a certain extent, depending on efficiency. However, I am hesitant because of the very high initial costs and don’t really know how these compare to operational costs. I also can no longer realistically assess which technology offers the best cost-performance ratio (except for air-source heat pumps).
As you can see, I am completely undecided and hope to get some feedback and expertise from the forum.
Thanks in advance for your replies.
I have been researching heating options for quite some time and have gathered a few opinions, which have only made me more uncertain about my decision. That’s why I thought I’d ask the forum.
My family (2 adults, 1 child) is planning to build the following single-family house at the end of this year or beginning of next year:
Single-family home with pitched roof
Approximately 115 m² (1,237 sq ft)
Solid construction (calcium silicate brick ground and upper floors, brick-clad)
No KFW standard
Building location: southern Mecklenburg
Unfortunately, I can’t provide an energy performance certificate or heating load calculation yet, as the preliminary offer is still being prepared. I am also aware that a general statement can’t really be made since every house and heating behavior is individual.
The construction company advised us to install a modern hybrid heating system consisting of a gas condensing boiler and two solar thermal panels on the roof for domestic hot water, as the initial costs are relatively low (plus installation of the central gas connection), and this technology has proven reliable. The entire house is planned to have underfloor heating. According to the company, they have had very positive experiences with this and consider the technology future-proof. (There is also the idea of a fireplace in the living room.)
On the other hand, I think gas prices will not get any cheaper in the future, and the topic of CO₂ taxes (especially concerning the fireplace) worries me somewhat.
In theory, I would prefer to install a geothermal heat pump combined with a suitable photovoltaic system because this would make me independent of fossil fuels and allow me to heat “off-grid” to a certain extent, depending on efficiency. However, I am hesitant because of the very high initial costs and don’t really know how these compare to operational costs. I also can no longer realistically assess which technology offers the best cost-performance ratio (except for air-source heat pumps).
As you can see, I am completely undecided and hope to get some feedback and expertise from the forum.
Thanks in advance for your replies.
hegi___ schrieb:
Yes, sorry for going off-topic, but with all these "I know how electricity/gas prices will develop in the future" statements, I just can't help myself. Also this "look at me, I have 10 kWp on my roof, I’m so self-sufficient" attitude.T
ttiggerin11 Feb 2020 22:34Mycraft schrieb:
No, the controlled mechanical ventilation system has nothing to do with this; it does not provide the necessary air volume to achieve effective cooling. However, it remains on during cooling operation.
Otherwise, yes, heating is done with gas via the underfloor heating system, and cooling is provided by the air-to-air heat pump. In my case, this is the most cost-effective solution. Although cooling is optional, I still recommend it to everyone (in addition to the shading concept) since summers are getting warmer, but of course, everyone has to decide for themselves. I don’t really understand this either.
So, if I understand correctly, the cooling from the air-to-air heat pump is not used through the underfloor heating since it wouldn’t be very effective, but also not through the controlled mechanical ventilation system.
Implementing that would mean a very high initial cost because you are essentially purchasing two systems instead of one.
Schlenk-Bär schrieb:
So in summer, you then draw warm air from outside into the house, right? Yes, but even here the function of the mechanical ventilation with heat recovery is hardly significant. Because what a mechanical ventilation system achieves in this area is minimal. It is not designed for cooling or heating, but it is very efficient for air exchange. Simple as that.
During the day in summer, the mechanical ventilation usually runs at minimum ventilation, which is about 70 cubic meters per hour (about 41 cubic feet per minute) in our case. In contrast, the air-to-air heat pump circulates about 700 cubic meters per hour (about 412 cubic feet per minute) on its lowest setting. So that is ten times the volume.
About one cubic meter (35 cubic feet) of warm air enters the house per minute, but around ten cubic meters (353 cubic feet) are circulated and tempered.
The mechanical ventilation is really the least of the problems in summer.
Schlenk-Bär schrieb:
If mechanical ventilation and air-to-air heat pump are separate systems, do you have separate air supply and exhaust vents in each room? No, we have an open-plan design: practically the entire ground floor is open, and all the doors upstairs are kept open at all times.
ttiggerin schrieb:
So the cooling from the air-to-air heat pump is not used via the underfloor heating, if I understood correctly, because that does not bring much benefit, and also not through the mechanical ventilation. Yes, because both provide little benefit since they are not designed for that purpose and cooling is only a side effect.
Cooling needs to happen in the upper parts of the rooms because that is where heat accumulates. Cooling the floor does little to no good (which is why chilled ceilings are efficient and useful), and the mechanical ventilation system is simply too weak at its highest setting to circulate the required air volume.
ttiggerin schrieb:
Implementing this would mean a very high initial cost since you’re basically buying two systems instead of one. The heating concept needs to be tailored individually for each house. What works for you might not work the same way for your neighbor. There is a suitable solution for every requirement.
However, gas boilers (to come back to the original question) are still the number one heating source for single-family homes and will most likely stay that way for a while. This is because the technology is well established and with comparable operating costs to a heat pump, you can heat the house but need only about half the investment. You could also factor in the interest rates for a more detailed comparison.
It is also interesting to often read that everyone knows the function, costs, and problems of air conditioning and immediately dismisses it with the phrase: “No thanks, way too expensive and unreliable.” Yet, with heat pumps for heating, people either consider it carefully or have one installed without much thought.
Over the years here on the forum and beyond, I have still noticed that active cooling as a retrofit option is becoming increasingly popular because alternative measures (like shading, etc.) are not sufficient and tightly sealed, well-insulated houses simply become too warm during summer.
T
T_im_Norden12 Feb 2020 12:27I am still unclear about how you bring cooling into the house with this concept.
Normally, an air-to-air heat pump has a system for distributing the warm air or, in your case, the cool air.
Normally, an air-to-air heat pump has a system for distributing the warm air or, in your case, the cool air.
This is the usual approach, with evaporators inside the house and an outdoor unit. Completely separate from the heating and ventilation systems. A combined unit would only be unnecessarily expensive and bulky.
This way, each device has its own function. They coordinate with each other, ensuring a consistent and desired temperature and air quality all year round, at more or less reasonable operating and investment costs.
This way, each device has its own function. They coordinate with each other, ensuring a consistent and desired temperature and air quality all year round, at more or less reasonable operating and investment costs.
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