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Use of Asphalt Paved Surfaces For Solar Heat
vg30e writes "It seems that a company in the Netherlands has found a way to use asphalt paved surfaces as solar heat collectors. Flexible tubes under the surface of the road collect heat from asphalt pavement using water as the working liquid. The heated water is stored underground for later use in defrosting the road, or heating buildings. With all the miles of highway in the continental US, this might be a viable way of collecting massive amounts of thermal energy."
Here's a link to our supplier's page with installation photos for those curious. http://www.invisibleheating.co.uk/photos-of-asc-installation-g.asp
The pipes are filled with anti-freeze rather than water. We use a vegetable based anti-freeze because of it's non toxicity should it leak.
The system is divided into zones, or sections which converge to a manifold. Each zone can be turned off individually, so if someone does damage a section of pipe, it can be turned off without affecting the rest of the system. Anyone who has underfloor heating should have this in place too.
We combine the system with geothermal heating and cooling using boreholes. In the summer excess heat from the building, and from the road is 'dumped' into the boreholes raising the average temperature of the local ground. In the winter we abstract the stored heat which then lowers the temperature back down. The entire system is 'closed loop'. We don't touch the groundwater itself at all, although we do also install open loop geothermal systems.
Inside the building is a heat pump, which (as stated above) works like a fridge, but in reverse. Its basically just a Copeland compressor. It takes in large quantities of water at ground temperature, say 12 degrees C, and compresses that heat into a tank of water (heating it to say 45-50 degrees C) and the water that returns to the ground will exit at something like 6-8 degrees C. Different systems are designed to work with different temperature gradients, so be aware that those are simply example numbers. The larger the difference in temperature, the more efficient the system which is where the road energy comes in. Storing the excess heat in the summer means for example the average ground temp isn't the aforementioned 12 degrees C it's 15 degrees C instead.
A more layman style description can be made using orange squash. Imagine you have a large volume of orange squash. If you find a way to remove some of the orange dilute from the squash you end up with a weaker orange squash, and a volume of orange concentrate. The heat pump works on this idea, except with heat instead of orange squash.
On the whole, systems are surprisingly economical for commercial customers. In the UK installing a geothermal heating system will generally have a payback period of around 5 years when compared to a natural gas boiler. The extra benefit is that you also get almost free cooling with the system whereas with a gas boiler you have to put in extra chiller units. As a final economic litmus test...we are installing a road energy and geothermal system for a small medical centre in the UK ultimately paid for by the NHS, and I'm sure even those outside the UK know the NHS is pretty frugal. ;)