HYDRONIC HEATING CONTRACTOR
We discussed the potential of earth-linked energy as an alternative to conventionally powered snow-melt systems in my January column (pg. 28). This month, we will finish this series by continuing to look at Mother Earth as an energy alternative.
Probably one of the most interesting discoveries, as it pertains to earth-powered snow-melt systems, comes from Japan. The Japanese started by spraying water on the snow to help melt it, which worked reasonably well for their location. They soon realized, however, that water is a precious resource that should not be wasted.
That fact, coupled with subsidence of the ground surrounding their wells, was a good reason to explore other alternatives, They decided to drill some wells, drop plastic tube heat exchangers into the wells, and circulate water between the wells and the targeted snow-melt areas.
At present, 19 operational sites in Japan use this underground thermal energy storage. Most of these UTES systems were installed during the 1990s and serve common public areas such as parking areas, bridges, entrances and exits of tunnels, and occasionally residential parking and sidewalk areas.
An interesting point of these UTES systems is that they operate their circulators year-round, thereby taking advantage of the free solar energy falling on the face of the snow-melt surface, hence charging the earth and raising the temperature of the earth to enhance their ability to melt snow the following winter.
One system in particular, serving a bridge in Hiroshima, has the vertical bore holes heat dissipation pipes and a circulating pump buried in the bridge's concrete decking. Typical entering water temperatures into the snow-melt system are about 43°F. Based on metering/monitoring devices, the system collected 77.8 gigawatts of energy, and delivered 88.08 gigawatts of energy indicating that the heat stored during the summer months was efficiently used during the winter.
You can melt snow with a low-grade energy source.
Another experimental system located at Hokkaido University used the same basic technology of VBH connected to horizontal heat dissipation pipes in a highly conductive cementitious material. The researchers monitored the amount of energy falling on the face of the snow-melt surfaces, the differential in temperature across the exposed surface and the flow rate to determine net solar gain efficiencies. In this particular situation, on an annual basis, they determined the net solar efficiency to be about 36%.
Of particular interest is the fact that the "solar collection" system was active not only during the summer months for obvious reasons, but also showed net gains into the earth storage system even during brief sunny periods in March. Their studies showed that 4 vertical ft. of heat exchanger is needed per square foot of melting surface. This ratio provided an .80 snow-melt factor, meaning that 80% of the time, no appreciable snow accumulated on the melting surface. Of the 20% of the time that snow did accumulate on the surface, it was less than 3/4-in. thick, melted shortly thereafter and never allowed ice to form on the melting surface, an important factor in operating a safe snow-melt system.
Although this type of system may not be in every person's budget and, in most cases, there is probably not adequate well-drilling space to make it work, it shows that you can melt snow within reasonable parameters with a low-grade energy source, and that there are many more potential opportunities that are just waiting for an application.
There's enough waste heat from the sanitary sewer running underneath the street to maintain safe, snow-free pavement at a dangerous intersection with a steep hill. By incorporating 3/4-in. PEX tubing into the walls of the concrete sewer pipes below the street and circulating a solution of antifreeze and water between the tubular heat exchanger and the paved surfaces, it would be possible to maintain a reasonably dry surface for most of the time during normal snowfall periods. This would require a small (comparatively speaking) circulator that could easily be powered with photovoltaic solar cells.
Another excellent potential use would be a lake, pond or river that never freezes during the winter. Again, by incorporating some means of heat exchange (coiled PEX dropped into the bottom of the pond, lake or river) and circulating a light solution of ethyl alcohol and water through this tubing, which would be embedded into the pavement or sidewalk, nearly zero energy snow melting could be performed.
I implore mechanical engineers, designers and contractors to employ some of these unique ideas in their day-today quest. Is it going to cost more initially than a conventional system that uses an off -the-shelf energy resource such as a gas or oil boiler? I think that is a given, but I also know that there is a large contingency out there that doesn't always do things based on pure economic analysis. These are the people who do things a certain way because it's the "right thing" to do for the environment.
If we all do the right thing for the environment, our children, our grandchildren and their great-grandchildren will be able to enjoy the world the same way we and our parents and grandparents have. We are protecting our heritage.
Tune in next month when we start our journey into the microbial workings inside our plumbing and heating systems.
Until then, happy environmentally sound hydronicing!
Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 303/778-7772.