DS 452 — Energy classes

DS 452 is the Danish standard for thermal insulation of technical installations. It establishes how much heat may escape (or enter) through the insulation on a pipe, a duct, a vessel or a fitting — measured as the U-value for the class's surface heat flow. The standard's full title is Thermal insulation of technical service and supply systems, and it is published by Dansk Standard.

It is easy to confuse DS 452 with other standards, so here is the brief delimitation:

DS 452 explicitly covers all parts of the installation — flat and curved surfaces, ducts, pipe systems, valves, fittings, installation units, units, fans and tanks (quoted from DS 452-3, reproduced in the BAI compendium, p. 6). The key point is that they are operated at a medium temperature between −40 °C and +650 °C — everything from cold-storage rooms to high-temperature steam pipes.

DS 452 has existed since the 1980s, but the edition in force today is the 3rd edition from 2013:

• DS 452, 2nd edition (1999) — had only four insulation classes with permitted U-values of 0.88 / 0.66 / 0.49 / 0.25 W/(m²·K) for flat surfaces. The class was chosen on the basis of "operating parameter I" — a weighted combination of medium temperature, ambient temperature and operating time.
• DS 452-3 (2013) — entered into force on 1 December 2013 with a transitional period until 31 May 2014. As the BAI compendium writes: "from 31 May 2014 all installations must be insulated according to the new standard." The most important change was the expansion to six classes, a clear division between HVAC and industrial systems, a simple indoor/outdoor boundary at 5 °C, integration of the old DS 1102 on space requirements, as well as new rules for pipe supports (whether they are insulated or not).
• Corrigendum DS 452:2013/Ret.1:2018 (dated 2018-10-02) — updates, among other things, table 6.2 (reduced insulation), table 6.4 (the requirements table) and annex tables A.1–A.3. The corrigendum also removes references to DS 1135, which has been withdrawn.
• DS 452-3 new 2020 / subsequent editions — after 2018, Dansk Standard has published consolidated versions with the corrigendum incorporated. The content is technically the same as DS 452:2013 + Ret.1:2018, and the compendium's U-values and requirements table remain the ones in force [UNCERTAIN — the 2020 PDF itself in the source folder is an image scan with no extractable text, so detailed changes from 2018 to 2020 cannot be verified here].

The main line: When a vocational teacher, insulator or consultant says "DS 452", today it means DS 452:2013 with the Ret.1:2018 corrections incorporated. That is the one referred to by both the Isover HVAC Handbook (9th edition, December 2022) and Rockwool.

The classes in DS 452-3 are U-value requirements for flat surfaces (W/(m²·K)). For round pipes, the compendium provides a corresponding equivalent formula per running metre of pipe, in which the outer diameter D_ep (or p_ep, varying notation) is entered.

Why exactly those numbers? The numbers fall towards higher classes — class 6 (0.22 W/(m²·K)) permits five times less heat loss than class 1 (1.17 W/(m²·K)). The reasoning in the compendium: "It has always been the rising oil prices that formed the basis for these calculations, since the payback time on an insulated pipe had to be in proportion to the operating budget. And with the new classes you can make more targeted calculations." (BAI compendium, p. 6).

For the round pipes it can be seen that the U requirement is a linear function of the outer pipe diameter — this is due to the geometry: one m² of outer surface corresponds to an ever shorter length of the pipe, the larger the diameter. As a rule of thumb: use the flat-surface table when you think in square metres, and the pipe formula when you think in running metres.