Hereford Archive and Repository. The documents are kept in the concrete building behind the one at the front. photo: Nick Grant.

The UK’s first document archive to be built to Passivhaus standard has saved the owners about £60,000 (AU$103,000) a year in bills, a post-occupancy study has revealed.

The savings are massive cut to energy bills, considering typical document repositories can have heating bills of between £80,000-£100,000 (AU$138,726-$173,407) a year.

The client, Herefordshire Council, also enjoyed a 4.5 per cent saving on build costs.

These recent readings inside the document archive show the level and consistency of relative humidity and temperature over 18 days. Credit: Nick Grant.

The document repository is located behind an office building and thermally separated from it using a fully filled cavity wall without any thermal bridges. It lies on a load bearing concrete block with Precast plank floors. Larson trusses support a cedar single rain screen with 300mm of cellulose insulation. There is 300mm of mineral wool in the party wall.

The designers based their strategy upon the work of architect Tim Padfield and colleagues in Denmark and a British Standard (PD5454 2012) for the storage of archival documents, which allows for a slight and delayed seasonal drifting temperature and relative humidity (RH) so that there is no need for airconditioning.

Use of modelling with PHPP (Passivhaus Planning Package) indicated that the required standard could be achieved with minimal heating and no cooling or heat recovery.

A further, small photograph store, which had lower temperature requirements, was insulated from the adjacent general store room and uses active cooling and adsorption dehumidification.

Archives never use wet heating systems because of the risk of leaks damaging the materials.

Because the standards require power to these rooms to be shut off when they are unoccupied in order to reduce the risk of fire, the heating system is air-based using a circulating fan coil heater connected to a mains gas boiler supplying a low load of under 5kW.

[Insert Interior.jpg. Caption: The interior of the document archive. Credit: Nick Grant.]

Part of the secret of its success compared to conventional buildings is, first, that the building structure and the archive material itself acts as a thermal buffer and, second, because it does not need ventilation because there are very few visitors.

Ventilation is supplied in normal Passivhaus buildings both to moderate the heat gains and humidity from people and to provide an acceptable internal atmosphere for them.

Cutting off almost completely any air infiltration has the benefit of also cutting off variations in humidity from incoming air. An airtightness of 0.35 air changes an hour at 50 Pascals was achieved.

The store is essentially a concrete box. The photograph

The interior of the document archive. Credit: Nick Grant.

store room has a vapour control layer on the walls, floor and ceiling under a continuous layer of internal insulation with a U-value of 0.19W/m2.K to isolate it from the other storerooms. The photo-store is close conditioned to 12°C and 30 per cent RH while the adjacent general storage rooms are allowed to vary between 13-20°C.

The form factor for the entire building is 1.5. Compared to the cost of building to a BREEAM standard, it was found to be five per cent cheaper.

The building was delivered having been dehumidified, although the core of the concrete will take a long time to completely lose all of its moisture.

Some post-occupancy monitoring and evaluation removed some teething problems connected to a back row through the heating pipes even when no heat was required to stop furthermore a dehumidifier had been installed backwards!

Once these problems had been attended to and the documents installed and the building open to the public, the temperature and the relative humidity have remained almost constant.

The designers say that they now strongly recommend a very simple control system combined with a simple low power heating system for any similar venture in a similar climate.

“The performance has exceeded our expectations and the repositories have remained well within the required range of temperature and our age,” the designers said.

“This is in spite of intense activity during the move and the number of teething problems with the building services and BMS.”

The most recent monitored results for the photograph store, five years after construction, posted on Twitter last week, show that, over a period of 18 days, the temperature only varied by 0.2°C and the relative humidity by 0.8 per cent.

Andy Jarvis of consulting engineers E3 commentedd: “The new guidance and passive house have come together and led to a new way of doing this. It’s definitely the way to do it in the future.”

David Thorpe is the author of a number of books on energy efficiency, sustainable building and renewable energy. See his website here.

One reply on “Post-occupancy study shows Passivhaus saves a fortune”

  1. Brilliant. And what the article doesn’t mention, is that the (Passivhaus) public spaces and offices on the front are also performing exceptionally well.

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