Heating energy demand KfW 55 / KfW 70 and consumption costs

With a gas heating system, it is definitely still possible to build KfW55. You just need solar thermal energy for hot water and heating, and a controlled residential ventilation system with heat recovery.

And for that, an appropriate construction method above the requirements of the Energy Saving Ordinance. So more than the 0.24 U-value wall.

There are 2 independent values that must be met, see evaluation from my energy consultant in the attachment.

Yes, Ht' must also be undercut. The requirements of the Energy Saving Ordinance are moderate here, and if in doubt, the wall just has to be a bit thicker. The crux, however, is usually the primary energy demand, which results from plant technology and building standard.

Primarily, the Energy Saving Ordinance concerns the building envelope, colloquially speaking, how much heat escapes through windows, exterior walls, floors, ceilings, etc.

This applies to the previously valid Thermal Insulation Ordinances of 1978, 1984, and 1995. The Energy Saving Ordinance, including its updates until 2016, was explicitly defined so that not only the building envelope or only the plant technology is considered, but rather the combination under certain framework conditions must achieve an efficiency standard.

The annual heating energy demand is calculated according to the LEG/PHI method (PHPP) on the actual heated area (energy reference area) (instead of usable building area according to the Energy Saving Ordinance)

Presumably, you get these values when calculating a house according to Energy Saving Ordinance standard using the PHI method. The purpose of the PHI method is indeed to determine the heating load and heating energy demand. Passive houses are heated with LLWP, meaning the supply air is directly heated, and here 10 W/m² energy reference area should not be exceeded because otherwise the supply air flow becomes too hot.

The costs for operating an air-water heat pump and a gas boiler with solar support will not differ significantly in the long term, at least not fundamentally. For both plant technologies, it is more important that they are properly sized and operated. The investment is somewhat higher for the heat pump, maintenance possibly somewhat cheaper, and in operation everything depends on natural gas and electricity prices. No one can tell you today how these will develop in 5-10 years—but it is rather unlikely to get cheaper.

To determine heating costs, you can assume a heating energy demand of 40-50 kWh/m² usable area for KfW55 or Energy Saving Ordinance 2016, thus 60-70 kWh/m² living area + 700-1000 kWh/person for hot water.

You will not recover the additional costs due to the KfW55 standard through energy savings. Subsidies help a bit, but it is better to build 3 m² less; you do not have to pay for that and also do not have to heat it.

Primarily, the Energy Saving Ordinance is about the building envelope, in plain terms how much heat escapes through windows, exterior walls, floors, ceilings, etc.

No matter how much technology the house is stuffed with, if the building envelope falls below the U-value, a controlled residential ventilation system, SWWL, photovoltaic system, storage, etc. will do you very little good. The goal is always to plan the building envelope first. Then you can think about the primary energy indicator!

Where does the superstition come from that you can compensate for a poor U-value with technology? These are two independent values that must be met, see my energy consultant’s assessment in the attachment below.

Thank you very much for the excerpt from the assessment; did the energy consultant also determine and specify the heating energy demand alongside the primary energy indicator? The primary energy value is calculated from the calculated energy demand and the primary energy factor.

The actual value is breathtakingly low; that would result in an energy demand of almost nothing?

Is the house already built, or are there already figures from the heat meter for comparison (after heating the screed, etc.)?

The operating costs for an air-to-water heat pump and a gas boiler with solar support will not differ significantly in the long term, at least not fundamentally. For both system technologies, it is more important that they are properly sized and operated. The investment is somewhat higher for the heat pump, maintenance perhaps somewhat cheaper, and operation depends entirely on natural gas and electricity prices. No one can tell you today how these will look in 5-10 years—but it’s rather unlikely to get cheaper.

That is, as you say, the famous crystal ball about how the costs for gas/electricity will develop. According to the current status, gas would probably be somewhat cheaper both in terms of acquisition (including gas connection, etc.) and in ongoing operation, right? I have not yet obtained an offer for a gas condensing boiler because I had always assumed an air-to-water heat pump, but I am currently doubting that.

To determine heating costs, you can assume for KfW55 or Energy Saving Ordinance 2016 a heating energy demand of 40-50 kWh/m² of usable area, i.e., 60-70 kWh/m² of living space + 700-1000 kWh/person for hot water.

You will not recoup the additional costs of the KfW55 standard through energy savings. The subsidies help a bit, but it is better to build 3 m² less, as you don’t have to pay for or heat that space.

We are building without KfW funds; based on the current plans, we would probably fall into the KfW55 region regarding heating energy demand. I only assumed this breakdown based on the figures from the Wikipedia entry, and we have to comply with the Energy Saving Ordinance 2016 anyway.

A brief and rough analysis of the heat pump database regarding air-to-water heat pumps in 2017 showed (unless I miscalculated) an average of 59.80 kWh/m²a per heating surface for heat pumps that had a heat meter.

However, this includes hot water (in most cases), usually with controlled residential ventilation heat recovery, and many heat pumps only started operation during 2017. So it’s possible that the results also include screed drying or other one-time special effects.

Once 2018 is over, one might be able to extract more reliable figures for heat pumps installed in 2017.

And an appropriate construction method above the requirements of the Energy Saving Ordinance. So more than the 0.24 U-value wall.

The value according to the Energy Saving Ordinance 2016 is a U-value of 0.24, that is correct. But for the exterior wall, you need at least a U-value of 0.20 or better, i.e. if you want to build with solid brick, you need at least a T8 (unfilled). This is because the masonry has the greatest leverage to achieve the U-value.

Thank you very much for the excerpt from the evaluation, did the energy consultant also determine and specify the heating demand in addition to the primary energy value? The primary energy value is calculated from the calculated energy demand and the primary energy factor.

The actual value is breathtakingly low, that would result in an energy demand of almost nothing?

Is the house already built or are there already figures from the heat meter for comparison (after heating up the screed, etc.)?

Is that so? I’ve never dealt with that, since with a basement and solid construction (brick without ETICS) the focus was more on achieving the U-value for KfW55. We only arrive at the average U-value (with those few decimal places) through an individual thermal bridge verification. That’s just how it is when you want a 36.5 cm brick without ETICS.

The technology is: air-to-water heat pump, central controlled residential ventilation with heat recovery, fireplace, photovoltaic system. Although the photovoltaic system is not yet included in the primary energy value since the offer was not yet available.

The house will be built soon.

The total heating load is/should be 5.6 kW