A Swedish hospital stores winter snow under wood chips and pumps its meltwater through the building in summer; in its first year it supplied 93% of cooling demand

According to Science Direct, the hospital’s annual cooling demand is about 1,000 MWh.

A hospital in central Sweden found an unusual way to meet its summer cooling needs by storing snow from winter and using it months later. The Sundsvall Regional Hospital uses a large snow storage system designed to preserve winter cold until the warmer months.The Sundsvall hospital has a floor area of 190,000 square metres. According to Science Direct, the hospital’s annual cooling demand is about 1,000 MWh, with a maximum cooling power requirement of 1,500 kW. The local authorities were looking for a cooling solution that fitted environmental targets and national regulations.The findings of the project were published in a 2001 research paper by Kjell Skogsberg and Bo Nordell in Cold Regions Science and Technology.

A large snow storage area

The snow storage facility was built in 1999. It covered an area measuring 140 metres by 60 metres and had a total capacity of 60,000 cubic metres, equal to about 40,000 tonnes of snow.At the beginning of the project, only about half of the total storage capacity was expected to be used. The storage area was built as a shallow pit with a watertight asphalt base.The system was designed to slow down the natural melting of the snow. A layer of wood chips was placed over the stored snow to act as thermal insulation. According to the report, this reduced natural melting to about 20% to 30% of the total snow volume.The researchers also studied how much insulation was needed to keep the snow available through the summer. Their simulations focused on a 30,000-cubic-metre snow storage facility.

How snow can store cooling

Snow and ice melt at 0°C, and melting requires a significant amount of heat. Heat from the surroundings is absorbed as the snow melts. This means that the stored snow can act as a source of cooling when its meltwater is circulated through a cooling system.The researchers looked at the amount of heat needed to warm ice, melt it and then warm the resulting water. This involved the heat capacity of ice, the heat of fusion of water and the heat capacity of water.The hospital system used meltwater rather than directly circulating the snow. Water from the snow storage was pumped to the hospital. After the water helped cool the hospital, the warmer water was sent back to the snow storage area. This created a cycle in which the stored snow supplied the cooling while gradually melting.

A storage area of 140×60 m with a capacity for 60,000 m3 (40,000 tons) of snow was constructed in 1999.

Importance of insulation

Without insulation, the stored snow would not have lasted through the summer. The researchers calculated that an uninsulated 30,000-cubic-metre snow pile would have disappeared by June 17. That would have been well before the end of the hospital’s cooling season.They then compared the results when sawdust was used as insulation. With a 0.10-metre layer of sawdust, about 12,169 cubic metres of snow remained in the simulation. With a 0.20-metre layer, about 19,040 cubic metres remained. The thicker layer performed better because it reduced heat transfer from the surrounding environment into the snow.With 0.20 metres of sawdust, the maximum natural meltwater rate was calculated at 77.4 cubic metres per day. This occurred towards the end of June.The study concluded that with thermal insulation, the stored snow could cover the hospital’s cooling demand from May to August.

How cooling was done earlier

The researchers also noted that people had used ice for cooling long before modern refrigeration. In ancient Greece, ice was collected from lakes and rivers and stored in buildings insulated with materials such as sawdust. Similar methods were used in Europe and North America until cooling machines became common in the early 20th century.Japan had also developed several forms of snow and ice cooling. Traditional Himuros and Yukimuros used stone or wooden buildings to store ice or snow alongside food such as vegetables and fruit. Another Japanese method, known as the All Air System, cools air through direct contact with snow.

Other snow storage ideas

The researchers also looked at seasonal snow storage studies in other places. In Ottawa, Canada, researchers examined whether snow removed from streets and public areas could be transported to a large snow deposit and stored for later cooling.One proposed deposit had a volume of 90,000 cubic metres and was covered with a reflective and insulating layer. The study found that circulating meltwater was the most effective way to extract cold.Another possibility was storing snow in underground rock caverns. Such systems could be built in urban areas and could reduce the distance over which snow would need to be transported.The study also noted a problem with snow collected from cities. Urban snow can contain high levels of pollutants, meaning the meltwater may need to be controlled and treated.