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The history of dimensioning temperatures for Stockholm, Sweden.
by Hakan Falk at Energy Saving Now. (energysavingnow.com)
Introduction.
For dimensioning of HVAC, the calculations for dimensioning is based on the well known formula that assumes a linear relationship between inside temperature, outside temperature and the thermal resistance of the construction. During the last 50 years this formula have been disqualified repeatedly. Anyone who have the slightest knowledge in calculations of energy transfers, knows that the formula is inadequate and inaccurate. The only ones that are happy with it are the equipment manufacturers, who are selling grossly over sized equipment.
In Sweden the dimensioning temperatures evolved from a fairly free judgement to a tool in the Building Codes. By specifying dimensioning temperatures in the Building Codes, the over sizing of equipment could be somewhat controlled and more correct sizing was achieved. The following is the history of that evolution,
50 years ago.
The maximum temperatures was used and the common ones was -25 degree Celsius (C) outside and +24 degree C room temperature. Systems was with large pipes and designed for thermic circulation without pumps. Radiators of type convection was used, see "RADIATOR MESS, Radiators Use and Design".. The result was very over sized equipment, that was very difficult to adjust and enormous energy waste. The surface temperatures was either to low to compensate for cold surfaces or ventilation by open windows was a common solution.
40 years ago.
This is the time when I studied HVAC in school. The experiences and adjustment problems by over sizing was somewhat obvious. Use of pumps for circulation was more common, but large piping and convection radiators remained. A situation that is very similar to the one in Spain today. Dimensioning temperatures was lowered to around -20 degree C outside and 21 degree room temperature. Simulation work with the first versions of our program BREEZE started.
30 years ago.
The first oil crises hit the world with a lot of problems for the HVAC engineers, see
"Memories from the first energy crises 1973-74".
1978 years Building Codes.
As a result of research and simulations, a major revision was done. The insulation standards more or less doubled, surface temperatures and effective temperature was introduced, triple glass windows became standard, panel radiators became preferred choice etc.. Dimensioning temperatures was specified in four areas of the country and for Stockholm it was -9 degree C outside and +18 degree C room temperature. The suggestion from research for outside was lower, but going from -20 to -9 degree C outside to compensate for over sizing was regarded as large enough.
Recent revision of Building Codes.
The latest revision of the Building Codes, specifies -6 degree C for Stockholm, as dimensioning outside temperature.
Conclusion.
To compensate for over sizing of heating systems, the dimensioning temperatures for outside have gone from -25 degree C to -6 degree C and room temperature from +24 to +18 room temperature. Since insulation is included in the formula in both cases, the changes in dimensioning temperatures are only there to control the common over sizing and calculation method. You can judge yourself on how accurate the common sizing practices are.
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