Zero-energy Attefall. How would you have done it?

[InsidersUnited]

So how do you calculate zero energy? With more people, hot water consumption increases, but you also get a bit of additional body heat.

Guessing you produce as much energy as you use?

I have a cabin with a separate electricity meter, in the summer it uses 350-400 kwh/month, now in November, which was a cold month, it used 600 kwh. So it uses only about 200-250 kwh more in a winter month, i.e. for heating. It's heated with an air/air heat pump.

That's why I'm hesitant about whether it's worth insulating so much unless it's done for the sake of wanting to be "zero emitters," which in itself is a nice thought. 👍

 

[Thomas_Blekinge]

I'm wondering a bit about your reasoning. Is it like a challenge to build energy-efficiently, but in a small format? Or a pursuit of heating costs? Or even for good environmental reasons?
However, I think that the climate footprint of a complicated build over its lifespan might be greater than that of a regular building, I haven't done the calculation. All building materials also have to be manufactured and transported.
Burning wood sounds climate-neutral, but there's a misconception. CO2 from wood burning will be released into the atmosphere NOW and contributes to warming, but it is reabsorbed by new trees only over the next 30-60 years, by which time it's too late.

 

[Pligg85]

Forget the absurd and build smart. Well-insulated and airtight. Put the extra effort, thought, and money into the ventilation and the pump instead.

Then, if it's in the size of 25 square meters and down to 30-35 kWh per sqm in heating per year, it doesn't matter. It can be more expensive to strive for a minimum.

 

[Ulltand]

I am thinking a bit about your motivation. Is it as a challenge to build energy-efficiently, but in a small format? Or a quest for heating costs? Or even for good environmental reasons?
I do think, however, that the climate footprint of a complicated build over its lifespan might be greater than a regular building. I haven't done the calculations. All building materials must also be produced and transported.
Burning wood sounds climate-neutral, but there's a flaw in that thinking. The CO2 from wood burning will be released into the atmosphere NOW and contribute to warming, but it will be reabsorbed in new trees only over the next 30-60 years, by which time it's too late.

You have points that it might not be the most effective way to get environmental benefits. I pondered my motivation a bit—partly a challenge but perhaps primarily a desire to be less dependent on purchased energy. After everything that has happened in the energy sector, one can no longer be sure of the supply, and especially not the price.

But then I realize that it doesn't have to be zero energy since I have access to wood if the heat pump can't be run. A slightly off-grid system with solar panels and batteries then becomes more beneficial than 40 cm of insulation...

 

[Rulf.K]

In my opinion, it's silly to use insulation that results in walls 50cm thick. If you still want to maximize living space economically in a small house, I recommend PIR insulation and a very small FTX unit for ventilation. Connecting the studios to the existing heat pump via a culvert can mean remarkably little energy is used.

With some solar panels, the energy declaration can also be improved regarding the electricity you use yourself.

 

[sinuslinus]

This is the cabin I'm considering as the basis for the project. Half-timbering or whatever it's called allows you to quickly erect the frame and build on as you go.

[image]

The house in the picture has the insulation on the outside of the roof. Problem solved. 😉

 

[igelkotten82]

In my opinion, it's foolish to use insulation that results in 50cm thick walls; if you still want to maximize living space in a small house despite it being economically disadvantageous, I recommend PIR insulation and a very small FTX unit for ventilation. If you connect the Attefall house to an existing heat pump via an underground duct, it can consume incredibly little energy.

With a few solar panels, the energy certificate can also be improved regarding the electricity you use yourself.

I completely agree with Rulf.K. For example, you can use industrial sandwich panels with PIR insulation for walls and roof. Either outside the log cabin or inside. 20 centimeter thick panels give a U-value of 0.11. Then minimize the number of windows. Preferably insulate over the frames on the outside to reduce the thermal bridge in the frames and have at least 0.5 in U-value on the glass.
Spontaneously, I would have chosen an instantaneous water heater for hot water if you don't connect it to the house's possible heat pump, as it results in virtually no waste of hot water. Extra beneficial in a cabin that's not always in use.
With solar panels on the roof and wall in the right direction, you can then take the opportunity to shower when the sun shines. Together with an air/air heat pump, the heating should be incredibly low, especially when you are personally in the house and your body heat contributes. The air/air heat pump can then also be used for cooling to increase comfort on hot summer days.

 

[Rabbithole]

If it is to be an attefall with a limitation on building area, then absolutely thin walls with high-quality insulation like PIR or vacuum panels. SIP panels can fix both the floor, walls, and roof. Glass with a U-value of 0.5 on the cassette to avoid cold drafts. Just set windows with normal placement and sun shading/awnings.

Air-to-air heat pump for sure, maybe an indol for hot water or a Nilan Compact S that solves everything.

A house in attefall size with good insulation requires almost no heating at all, so hot water is a bigger consumer. A few solar panels on 1/3 of the roof area should be enough.

A good layout is also important!! Minimize the mantel area.

If it's just a cabin, you can build with ecological insulation and make the walls thicker if you want.

 

[Ulltand]

I completely agree with Rulf.K. For example, you can use industrial sandwich panels with PIR insulation for walls and roofs. Either outside the log cabin or inside. 20 centimeter thick panels give a U-value of 0.11. Then minimize the number of windows. Insulate preferably over the frame on the outside to reduce the thermal bridge in the frame and have at least 0.5 in U-value on the glass.
Spontaneously, I would have chosen a flow-through water heater for hot water if you don't connect it to the house's potential heat pump, as it gives zero waste of hot water. Especially good in a cabin that isn't always used.
With solar panels on the roof and wall in the right orientation, you can then take the opportunity to shower when the sun is shining. Together with an air/air heat pump, the heating should be incredibly low, especially when you are present in the house and body heat contributes. The air/air heat pump can also be used to cool for increased comfort on warm summer days.

I've looked a bit at PIR elements but backed out due to the likelihood of it being expensive to integrate with the rest of the construction.

However, you can insulate with the material without the metal casing. Could there be a fire risk aspect then?

 

[Ulltand]

In my opinion, it's foolish to use insulation that results in 50cm thick walls. If you still want to economically disadvantage yourself with a small house to get more living space, I recommend PIR insulation and a very small FTX unit for ventilation. If you connect the attefallshus to an existing heat pump via a culvert, it can use up dangerously little energy.

With a few solar panels, the energy declaration regarding the electricity you use can also be improved.

Unfortunately, there are hardly any FTX units in that size. The energy declaration disregards the user's consumption, so it helps less in that regard. However, hot water production can be accounted for. Solar power only provides something to count on for a few months a year. Unfortunately, you can't credit the surplus in June.

 

[Rabbithole]

Fire protection is not something to worry about. Once you get to the insulation stage, everything is lost anyway. You still have enough protection with the wall covering.

PIR insulation boards are vapor-tight, nothing strange in itself and not difficult to build with.

It is possible to build the thinnest possible frame on the inside, mount PIR boards, and then thin plaster on the outside.

 

[Rabbithole]

Unfortunately, there are hardly any FTX in that size. The energy declaration disregards the user's consumption, so it helps less well in that regard. But hot water production can be included. However, solar power only provides something to count on for a few months each year. The surplus in June unfortunately cannot be credited.

There are plenty of small FTX systems, for Attefall houses maybe 2 pulsating mini FTX are preferable.

 

[Ulltand]

There are lots of small FTX systems, for attefallshus perhaps 2 pulsing mini FTXs are preferable.

I've looked into pulsing and it's appealing from a cost and installation perspective.

Is there conventional FTX with a flow rate of 10 l/s?

 

[Rabbithole]

I've looked into pulsating and it's appealing from a cost and installation perspective.

Is there conventional FTX with a flow of 10 l/s?

https://ventilation.se/sv/products/mitsubishi-lossnay-vl-50-miniventilation#product-information

There are quite a few, just search for Mini FTX and you'll find a lot of reasonable options. The small ones have an efficiency of around 70-80%.

I like to separate ventilation from heating with
Mini FTX
LLVP
LVVP (hot water)

 

[igelkotten82]

I've looked into pulsating, and it is appealing from a cost and installation perspective.

Is there a conventional HRV system with a flow of 10 l/s?

I've looked at Pax Eos HRV in connection with Attefallshus. However, I have no practical experience with it, but on paper, it seems adequately sized. The systems with ceramic core and alternating airflow direction I've heard do not work so well and also require two of them in a bathroom, which makes the cost quite high.