Hempcrete For Museum Storage RH Control

Validating the techno-economic viability of hemp lime construction for passive and low energy moisture control in museum storage

Abstract

Museums require storage for cultural heritage collections that provide stable environments, ensuring that risks of deterioration from environmental conditions are reduced as far as possible. Incorrect levels of relative humidity (RH) can lead to physical, chemical and biological degradation, devaluing historic collections and damaging institutional reputations. Analysing the historical development of RH guidelines for the storage of museum collections through a review of literature on the risks and effects of incorrect RH, past and current recommendations for RH levels and fluctuations, and past and current practices to control RH clarifies the current approach to provide suitable and sustainable storage for cultural collections. Standard practice has been to regulate RH by relying on large-scale heating, ventilation and air conditioning systems which has had significant impact on institutional carbon footprint, energy use and operating expenditure but which has not always achieved the required stability. Contemporary research on biobased construction materials has highlighted the potential for their transient hygrothermal behaviour to buffer internal environment, providing good indoor air quality and energy savings. A key knowledge gap is the lack of assessment to identify the extent to which such hygrothermal behaviour can moderate RH levels and fluctuations under dynamic museum storage conditions. This thesis explores the hygrothermal performance of hemp lime concrete (HLC), in augmenting the regulation of RH within a museum storage building in a temperate climate. The key objectives of the investigation were to assess the moisture management capacities of HLC through a literature review of relevant studies and in situ monitoring of a museum store utilising HLC as part of a low energy RH control system and to put the findings of the assessment into the context of conventional museum RH control practices by comparing performance and operational costs with other low energy museum stores. The assessments were carried out using a case study, the Science Museum’s Hempcrete Museum Store (HMS). By evaluating the performance of the case study over several years, from 2012 to 2020, through transient, first and second steady states of building use, the moisture management capacity of HLC as used in the building’s wall construction has been shown to augment the moderation of RH to meet the museum requirements by reducing reliance on energy consuming mechanical systems.

The comparison with the effectiveness achieved in controlling RH in other low energy storage buildings during the same period demonstrated that the hygroscopic properties of HLC decreased the need for mechanical control, cutting operational expenditure by a minimum of 30% while still maintaining levels in the museum’s specified range of 40% RH to 60% RH. Buffering capacity of the HLC has been shown to reduce the effects of mechanical system function and malfunction and to sustain specified conditions through passive means. One of the most important findings during the in situ monitoring has been the effect of the thermodiffusion phenomenon across the porous HLC walls, which results in internal RH rising during periods of higher external temperatures, confirming the feasibility of using dehumidification rather than heating and ventilation as active controls to achieve specified conditions.”

By Marta Leskard
University of Bath

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