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Perfect humidity control for museum

John Barker, managing director of Humidity Solutions explains what to do with a museum and gallery where the humidity swings over a wide range - even when the temperature control is spot on

Managing director of Humidity Solutions John Barker

The solution for St Albans Museum and Gallery was to add a humidifier and dehumidifier with a dedicated controller, so that - with a dead band - the system worked as a single unit to provide a stable humidity without affecting the temperature.

St Albans Museum and Gallery opened in June 2018 and aims to be a leading centre for arts and culture at the heart of one of Britain’s most historic cities. Set over three floors, the newly created state-of-the-art gallery spaces showcase over 2,000 years of priceless heritage and display contemporary artworks – sharing local, national and world treasures with all.

The existing system within the museum claimed to control the humidity by assuming that the moisture content of the outside air was always lower than the required humidity in the space. Therefore, when the humidity in the space increased fresh air was brought in.

However, with a set point of 18°C and 50%rh, the outside air commonly has a moisture content higher than this and hence control was not possible, in fact in the summer months it just exacerbated the issue. In the winter, the desired humidity was simply not achieved. Control can only be achieved with a dehumidifier for the summer months and a humidifier primarily for the low moisture content cold winter period.

Introduced into the temperature ducted system, the Vapac LE09D steam humidifier (pictured above)provides the addition of moisture primarily for the winter months. The Vapac electrode boiler is ideally suited to providing good control and reliable output for the critical area. Modulation of output ensures that the optimum duty is added to provide close control of the conditions. 

The Cotes C30 desiccant dehumidifier (pictured opposite) provides the moisture removal from the fresh air coming into the system. Summer months, and when the gallery has a lot of visitors, are the key times when the dehumidifier will be operating. This dehumidifier is fitted with fan speed regulation so that it can be incorporated within the existing supply ductwork. Taking a percentage of the air through the desiccant wheel it delivers the conditioned air back into the airflow regulating the moisture level. The desiccant process does add some heat into the system – this either reduces the load on the heating coil or is trimmed back by the cooling circuit.

These two individual pieces of equipment work as one via the Neptronic HR020 controller and sensor. The controller provides dedicated controls as the existing control system does not have the facility for humidity. A dead band is set between the humidifier and the dehumidifier to ensure that they never fight against each other and achieve close control of humidity in the gallery. High level humidistats and pressure differential switches were installed to provide a safety back up just in case the temperature system went into fault or the air supply was turned off.

Installation and commissioning was provided by Humidity Solutions’ dedicated engineers who specialise in the installation of such systems, providing a complete service from design to hand over for the client. In this instance the work was carried out during the COVID-19 outbreak so the museum was in fact closed, but the original plan was for out of hours installation to ensure that there was no disruption to the museum or its patrons.

This solution ensured that all the plant and equipment was hidden in the plant room and that the conditioned air was delivered by existing ductwork and grills. In other museum applications Humidity Solutions has installed the equipment in cupboards, behind screens, in redundant fireplaces and under floorboards to ensure that required conditions are achieved effectively but discretely. 

The result at St Albans Museum and Gallery is a fully controllable, stable environment year round, protecting the precious artwork and treasures whilst also maintaining a comfortable and healthy environment for staff and visitors alike.


20 January 2021


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