ᐅ Heat demand calculation according to DIN 12831

Hello everyone,

We are currently building a house and are generally quite satisfied with the construction company. I have already asked a few questions here about the heating system and so on. In the contract, I had it specified that a heat demand calculation according to DIN 12831 should be carried out.

Now, after selecting the fixtures and finishes, I received a calculation according to DIN 4701 (Energy Saving Ordinance 2009).

I still feel on the safe side since everything is documented in writing. What puzzles me now is—shouldn’t the heat demand calculation be done soon? Is the construction company making things difficult for themselves?

We decided beforehand on a geothermal heat pump with brine and heat recovery in a KfW 55 house. Assuming it turns out to be insufficient—what would happen then? (It’s clear that it would either be cold or expensive.) Could it be that we might have to pay a lot more if the heating is undersized? Or am I worrying too much?

Best regards and many thanks,

Hello,

haunt schrieb:
...In the contract, I had it specified that a heat demand calculation according to DIN 12831 must be carried out.

Here, existing deficiencies need to be clarified, whose cause (in the past) unfortunately lay in a certain incompetence of the standards committees regarding the binding SI units.
This has since been corrected following objections from experts.
Heat demand => Energy: unit kWh
Power (heating load according to 12831) => Power: unit kW
This probably concerns the standard heating load (kW). This is regulated EU-wide in conjunction with national annexes and must be prepared bindingly only according to 12831 (in Germany a detailed procedure)!

haunt schrieb:
...Now, after the product selection phase, I received a calculation according to DIN 4701 (Energy Saving Ordinance 2009).

If 12831 was sensibly required, then 12831 must also be included (after all, part of the contract!).
It is not permitted to derive sizing bases for heating systems from the Energy Saving Ordinance! For this, read the fine print in the verification document!

haunt schrieb:
...I consider myself still on the safe side since everything is recorded in writing. What surprises me now is—shouldn’t the heat demand calculation be done soon, and isn’t the construction company making things harder for themselves?

Construction companies build; technical building services (TBS) and efficient system technology are unfamiliar terms for most of them.

haunt schrieb:
...We have already decided on a ground-source heat pump with brine and heat recovery for the KfW 55 house.

This is an economically unfortunate combination. The leap from EH 70 to 55 standards involves substantial investment (mostly the heat transfer coefficient ‘H’T-value). The significant additional effort for the building envelope is usually disproportionate to the benefit, since only a fraction actually becomes effective when combined with a brine heat pump. Cost-intensive factors here also include the source development, unless significant self-performed work applies (e.g., trench collector).

haunt schrieb:
...Assuming this is not sufficient—what would happen then?

The desired room temperatures will not be achieved.

haunt schrieb:
...Or am I worrying too much?

Most people build only once—everything should be right! Hopefully, the general contractor (GC) is capable of delivering a coherent overall concept regarding TBS; otherwise, it will likely become a money pit.

Best regards.

Thank you for the reply. Well, the upgrade to the ground source heat pump was more my idea to do something for the environment and to rely on an alternative heating system. Aware that the initial costs are higher, but the operating costs are then low.

The additional cost for KFW 55 (more like 40) + underfloor heating + heating technology was acceptable! (for me) We didn’t want a passive house.

If 12831 was reasonably requested, then 12831 must also be included (after all, part of the contract!)

Same here – so I understand that the final selection is still pending, since we have redesigned the windows and so on. How does a professional home builder handle this? Do they design the house around the heating system?

Well, we’ll see. It’s still two weeks until the foundation slab.

Deriving the sizing basis for heating systems from the Energy Saving Ordinance is not permissible! Please read the fine print in the certificate for this!

So, the statement in the calculation that heat recovery is sufficient for heating is actually not even legal? Good thing I have legal expenses insurance.

haunt schrieb:
.. Aware that the initial costs are higher, but in return the operating costs are low.

In a ground source heat pump (GSHP) system, with a properly designed source, a relatively high proportion of environmental energy can be utilized. Therefore, from an economic perspective, the requirements for the building envelope are lower. Or, conversely, if you invest heavily in the building envelope, you should avoid the high effort involved in developing the source for a GSHP!

haunt schrieb:
.. How does the professional house builder handle this? Do they design the house around the heating system?

What exactly is a professional house builder? Certainly not a general contractor. Usually, these are construction or business professionals. The complex interaction between the building structure and the technical systems is often missing here. For example, KfW 70 standard houses are sometimes sold with air-to-water heat pumps.

haunt schrieb:
... Well, good thing I have legal expense insurance

A big misconception! Construction-related cases are, and you might wonder why, generally not covered!

I’m curious to see what heating costs I can expect—after all, the loan was 200 euros per month cheaper than planned, or else the stove must be burning through all the electricity bills.

Better for me to push the company now and demand my calculation.

While reviewing my documents, I was surprised at myself...

I had not contractually agreed to receive a heating load calculation.
It states: "Design according to DIN EN 12831" – which is actually even better.

I have now simply asked the construction company for the planning documents, as they should be available on site.