Several Swedish companies are seeing business opportunities in the growing demand for district cooling systems. One of these, Snowpower, is taking a novel approach by using a simple raw material that’s found in abundance in northern Sweden: snow. The Snowpower system uses a 60,000 cubic meter pile of stored winter snow to cool the Sundsvall Hospital during the warmer months.
Like district heating, which is common throughout Sweden and many other countries, district cooling employs a network of pipes connected to multiple buildings or even an entire neighborhood. But instead of the warm water in a district heating system—often using waste heat or cogeneration from nearby industry—district cooling circulates water at a temperature lower than the ambient air. The source of chilled water is usually a lake or the sea, but that of course requires a waterfront location. District cooling is used in industrial process applications such as computer data centers, mines and power plants, as well as the more familiar air conditioning for personal comfort.
In 1990, about 10 percent of the cars on European roads were equipped with air conditioners, a figure that’s grown to nearly 90 percent today. And it’s not just in our cars that we’ve come to expect air conditioners; some form of comfort cooling is installed in an estimated 40 percent of all offices, hotels, hospitals, airports and shopping malls in Europe, and about 80 percent of similar structures in Japan and the United States. Today’s small-scale systems, where a compressor drives a refrigerant fluid, are not as energy-effective or environment-friendly as they might be (see sidebar).
District cooling offers a range of advantages for users, energy companies and society as a whole, for example:
- Lower emissions of greenhouse gasses
- Faster phase-out of ozone-depleting HCFC gasses as required by the international Montreal Protocol and many national laws
- Elimination of noise pollution from local compressors
- Improved esthetics (local compressors require storage rooms or sheds, and are seldom particularly attractive)
- Improved energy efficiency from larger systems
- Improved reliability with more centralized maintenance requirements
New life for an old technology
People have used snow and ice to keep cool in the summertime for centuries. As late as the early 1900s, businesses throughout Sweden would saw up blocks of ice from frozen lakes during the winter and stack them for storage under thick layers of sawdust. When summer came, horse-drawn wagons would make delivery rounds to local homes and businesses.
And there’s of course no shortage of snow and ice in the north of Europe. During a normal winter, Stockholm’s street clearing crews dump about a million cubic meters of snow in the city’s waterways, while across the Baltic in Russia, St. Petersburg tips as much as 25 million cubic meters into the Neva River. While a boon for motorists and pedestrians, this snow removal brings with it both logistical problems and environmental impacts, and both cities are looking into ways they can use snow for district cooling. Similar studies are underway in Turkey, Canada, Japan and other cities in Russia.
With the spread of electrification, refrigerators and freezers, the old ways of exploiting the winter freeze were largely forgotten. But by the 1970s researchers in Japan and the US were looking into using snow to cool indoor air. But water is a lot easier to cool with snow than air, says Kjell Skogsberg, the CEO for Snowpower who wrote a doctoral thesis on technical solutions for district cooling at the Luleå University of Technology (LTU) in Sweden’s far north.
The installation at Sundsvall Hospital is an important case for the study of district cooling. The basic principles are simple, with the snow bank stored near the hospital and insulated with a layer of wood chips. As the snow melts, the runoff water is filtered and pumped via a heat exchanger to hospital buildings. Then the warmed water is routed back to the snow bank to be chilled again.
The Sundsvall plant uses a combination of natural and artificial snow made by cannons. “The Sundsvall installation shows that the technology works and that we can save money by using snow for cooling,” Skogsberg explains. “The best approach, though, would be to have the snow stored in an underground bunker.”
Technical and environmental advantages
Studies at LTU have looked at the environmental impacts of snow cooling systems compared with traditional approaches. The technology for snow cooling is simple: a lined pit in the ground is filled with winter snow and covered with an insulating layer. Melt water, just above the freezing temperature, is collected at the bottom, filtered and pumped via underground pipes to the customer.
Comparative studies show that the primary impacts from both snow cooling and traditional air conditioning systems occur during operation. Snow cooling is a clear winner, however, for its lower impact on climate, acidification and excess fertilization of waterways. Snow cooling requires more materials and much more ground surface area than compressor-based air conditioning to achieve the same effect, but a facility getting double use as a snow tip reduces this impact significantly. Air conditioning consumes much more energy than district cooling with snow.
Article published in September 2009