Go back to article: A sustainable storage solution for the Science Museum Group
Initial issues with moisture levels were detected by the more sensitive Hanwell® sensors. Both external BMS T and RH sensors were faulty as was the control software running the AHU fans, resulting in warm moist daytime air being drawn into the store rooms instead of cool dry air at night. There was unanticipated moisture from both the drying concrete floor mass, affecting mainly the ground floor store, and the hemp-lime panels. By July 2012, less than three months before the first objects were to be relocated to the store, RH levels were close to 80 per cent on the ground floor, 70 per cent on the first floor and 65 per cent on the top floor – measurements which fell outside the museums’ own acceptable range.
Ground floor after completion
HMS ground floor environmental data first year of operation. Shows the forced removal of moisture by M&E system until May 2013 when system was turned off
These teething problems required the museum to employ unexpected active mechanisms to reduce the RH levels at least in the short term. Portable dehumidifiers and air conditioners were deployed along with a slight elevation of the ambient temperature. After sensors were replaced, software updated and heaters rewired, operation of the AHU system assisted in reducing the RH to between 40–50 per cent on all floors (Jankovic, 2013). Fluctuations in RH were also considerably reduced through the replacement of faulty dampers, which had caused an imbalance in the airflow from the ductwork. However, both fan and heater operations continued to cause fluctuations between 5–10 per cent/24 hours. RH levels also rose when the dehumidifier condensate tanks went unemptied; this was resolved by connecting the equipment to the hangar’s drainage channel to achieve continuous draining.
With the seasonal rise of temperature, the heaters were turned off in May 2013 which resulted in a slow rise of RH to 60 per cent in the ground floor store room. In order to decrease RH fluctuations, it was decided to allow the building to drift passively through the spring and summer seasons so the entire air handling system was switched off. The store remained in passive mode until March 2014, when the RH levels, which had drifted slowly upwards at a rate of around one per cent per month, rose above seventy per cent on the ground floor. This was considered to be too high and an attempt was made to reinstate the HVAC system with minimal success as handover and training to run the system had never occurred.
HMS ground floor environmental data second year of operation. Spikes in RH and T from January–March are a result of a heating system programme glitch. The single spike in June 2014 occurred when the heating system was turned on briefly to reduce the RH level
Initially, from August 2014, the RH was again reduced using portable dehumidifiers and air conditioners. The original designer was contracted to reinstate the air handling and heating system and he also provided training to the site’s Estates team. Full running of the system was reinstated five months later although mild and damp external conditions meant that initially four hours of daily heating was primarily used to reduce the RH levels. This resulted in daily rapid fluctuations of 10–15 per cent. Fluctuations were reduced once drier external air could be utilised along with heating. Levels were stabilised over three months on the ground floor to 60 per cent and 55–60 per cent on the other two floors. In April 2015, RH regulation was returned to the passive mode and fluctuations were virtually eliminated. Again the RH rose very slowly until, by July 2015, it was around 68 per cent on the ground floor. Because the external air was rarely drier outside the hangar than that within the store due to the wet summer, a single dehumidifier with humidistat set to sixty per cent, connected to the hangar’s drainage, was installed in the ground floor store room. This resulted in stabilisation of RH to just above sixty per cent with virtually no fluctuation whatsoever. RH levels on the other two floors have also dropped slightly, indicating moisture movement through the interconnected porosity of the low-density hemp-lime walls.
HMS ground floor environmental data third year of operation. M&E system operation was reinstated to reduce the rise on RH through November–April. Although the system was supposed to have been turned off in April to allow passive operation, one heater remained functional, resulting in continuous small fluctuations in T and RH
Ground floor environmental data March–June 2015. With the heater turned off, the building returned to full passive mode, with an anticipated slow rise in RH
Component DOI: http://dx.doi.org/10.15180/150405/012