Climate Control of the Arnamagnæan Archive

The small archive of the Arnamagnæan Institute is almost passively air conditioned by being placed between a corridor in a permanently warm Copenhagen university building and the outer wall of the building. It is well insulated towards the warmed building and thinly insulated towards the outside, so that its temperature is approximately one third of the way between the building interior temperature and the running average outside temperature. The annual average temperature in the archive is above the annual average outside so that the annual average relative humidity (RH) is automatically lower than that outside: it is about 50%. The day to day RH remains steady over the entire year because of humidity buffering by the walls and by the hygroscopic content of the archive. Fine control of the RH is provided by pumping in outside air when it is, by chance, of the right water vapour content to push the archive RH towards its target 50% RH. The energy consumption by the pump is negligible but there is heat from the usually warmer building interior passing through the archive to the outside, so it does use energy. The RH has remained within the envelope of 48% to 58% over a period of 7 years. The temperature has varied within the range 14°C to 24°C with a gentle annual cycle.