Flat collectors or gas condensing boilers

Hello everyone,

I have been a silent reader of this forum for some time now and would now like to ask for your advice or help.

We are planning to build a house this fall.
Currently, we are in the preliminary decision phase regarding which heating system we will use.
The shortlist is:

1. Heat pump with ground collectors + solar thermal + water-based fireplace + ventilation system with heat recovery
2. Gas condensing boiler + solar thermal + water-based fireplace + ventilation system with heat recovery

We want to achieve KFW 55.

Here are some data about the house.

Heated living area 250m²
3 full floors (1 of them basement)
U-value ceiling: 0.13W/m²K
U-value exterior walls: 0.19W/m²K
U-value floor slab: 0.16W/m²K
U-value windows: 0.9W/m²K

Is anything missing?
What do you think of the plan and which of the two options would you recommend and why?
In the case of the heat pump, is it more sensible to use photovoltaics instead of solar thermal to power the pump?

It would be great if some of you could comment on the project.
Many thanks in advance for your efforts and have a nice evening.

Best regards
ha_celine

KFW 55 is of course easier to achieve with a heat pump. Water-based fireplace? How often do you really use it? I fear that the effort and the benefit are in no way proportional. Solar thermal? My heat pump consumes on average 1.5 kWh per day (about 30 cents) for hot water preparation for two (wasteful) people. When the sun is shining, I don’t need heating. Thanks to large window areas, not even in winter. So solar thermal would never pay off. But the question is whether you look at it from the financial or the ecological side. Photovoltaics for the heat pump is pointless. If you have enough electricity from the photovoltaic system, the heat pump doesn’t run. If the heat pump has to work properly, the photovoltaic system doesn’t produce electricity. The overlap is pretty small. If there were a usable and affordable storage option, I would retrofit photovoltaics immediately. But that will probably take a while. I would rather invest the money for the water-based fireplace and solar in the windows. 0.9 is relatively high. Sometimes the simplest solution is the best.

throw away the water fireplace.. use a normal stove.. for that either plan the floor plan quite open so that the heat spreads in the house and/or (and this is better) add a controlled residential ventilation with heat recovery. 0.9 windows? Which company still installs such old parts? Personally, I absolutely do not believe in the solar parts, no one has ever really convincingly shown me what you actually save there. Photovoltaics is (today) a matter of belief/taste... We have one... but also invested quite a bit in technology/house control... Whether it pays off? I will see in a few years.. You can easily reach KfW55 with insulated slab (about 3000-5000 euros) and the brine-water heat pump, as long as you have a decent house builder with "real" windows^^ We took additional window areas, plus brine-water heat pump and insulated slab... and we are 0.8% past KfW40..

Hello waldorf and milambar,

Thank you for your quick responses. What both of you seem to imply is that the water-based fireplace is rubbish – in my case. I actually only came to this conclusion because we wanted a fireplace in the living room and dining room for coziness. Since we heat there now and then anyway, I wanted to use the energy right away. However, I’m not fixated on the water-based fireplace – as I said, a normal one is fine for me too.

A few more details that might provide a bit more insight:
The gas connection is already on the property, but it is a long property and we would have to lay about 40m of gas pipe on our property from the connection to the house.
About 1500m² are available – so this should be more than sufficient for flat-plate collectors.

With the Kfw thing, it’s more about insulation, meaning how good our final energy consumption actually is. If we can realize funding, that would of course also be good.

The windows with 0.9 are what the energy consultant used as a calculation value for us. g-value 0.5 and 32% frame portion.

It would be nice if a few more people could share their opinions, but many thanks again to the first two responses.

Best regards
ha_celine

Yes, I'm not telling you anything new, but water-bearing fireplaces are crap... so you either keep heating them all the time or you don't... because the necessary additional equipment (control, piping, etc.) required costs many times what you can generate with occasional heating...

Otherwise, if you have enough space, why not a [Flächenkollektor]? It actually brings something with proper dimensioning and decent execution...

Just a quick info..
we have ~153m² of living space.. and needed ~180m² of surface collectors.
So you have more than enough space to easily supply several houses..
I can warmly recommend company AEN (headquarters in Rostock) for your question..
The guys know exactly what they are doing.. and their documentation is amazing!
(Quote from the environmental office: "Can you please pick up the folders here, we don’t need that much data)

We are building in central Lower Saxony.. So the guys from AEN also operate "outside" the area.

On the topic of gas..
have it calculated by the basic supplier what it would cost..
connection fee, ground work, piping...

and remember that in some building regulations nothing stationary (house, garage) is allowed to be built over the pipeline.

For us, the whole connection stuff would have been just as expensive as the brine-water heat pump+collectors+earthworks...

And yes, the costs for a warm water fireplace are absolutely disproportionate to the benefit.... The magic word here is: open floor plan and/or controlled residential ventilation+HRV

cheers