BY MARK EATHERTON
HYDRONIC HEATING AUTHORITY
WE BEGAN DISCUSSING the potential of waste heat recovery as an alternative to conventional heat sources for powering commercial snow-melt systems in my October column (pg. 42).
In one particular case that I mentioned last month, a transportation system in a major city used waste heat from the condensate from the city's district steam system to power the snow-melt system. The managers of the operations decided it made longterm sense to invest in the application because the transportation system is a government tax-subsidized operation.
This is a classic example of a potential application that has been proven all over the world, but it's underutilized as a potential energy source for snow-melting operations. Whole towns in Europe snow melt the streets and sidewalks for free using the waste heat recovered from the local electrical generating plant. This type of thinking can raise the base operating efficiencies of a typical steam turbine electrical plant from a paltry mid-40% operation to a booming 80% efficient operation.
How many turf-conditioned athletic fields using conventional gas-or oil-fired equipment are a stone's throw from a power plant? How many indoor sporting arenas with hockey rink refrigeration systems have humongous snow-melt boilers sitting right next to the condensing units for the ice-rink system?
Members of the energy engineering community must think outside the box and use their imagination to make the connections between the points of use and the points of available waste heat. Will it require more money than a conventional system? I think that is a given. You don't get something for nothing without some kind of investment. Think of it as an investment in our future and our future generation's future.
Think also of the possibilities. Placing a flat-plate or plate-and-frame heat exchanger in the heat rejection stream of even the smallest cooling system and directing that heat to a snow-melt system not only can reduce the energy needed to melt snow, but it may also increase the efficiency of the heat rejection system. Improved heat rejection can increase the efficiency of the cooling system, thereby further reducing the environmental impact.
Think about the tons of refrigeration equipment at the local grocery store. Think about the reduction in slip-and fall-related lawsuits caused by icy conditions in the parking lots and the increased efficiency of the cooling systems as a whole. It could equate to a lower total food bill. But I digress. Back to the subject at hand.
We were recently chosen to be the hydronic heating contractor on a driveway ramp-replacement program for a major underground parking structure located in the heart of downtown Denver. This ramp never had a snow-melt system installed on it originally. You could tell from all the bumper scars and skid marks on the walls of the ramp.
Our biggest challenge was that no natural gas is available for a conventional modulating condensing boiler. We had direct resistance electric, at about $2.50 per therm, or we had district steam available at $ 1.50 per therm, which meant we also had hot condensate available for FREE. The medium-rise apartment/commercial complex of buildings that occupied the space above the underground parking facility was completely heated with steam. All the condensate was metered and discharged in the same mechanical room as our physical plant's location.
The consulting mechanical engineer seized this opportunity and designed a system of a flat-plate heat exchanger, controls and piping that would capture this free energy and harvest it for use as a snow-melt heat source.
The installation is backed up by steam from the district steam system, but I doubt that there will ever be many occasions that the backup plan has to be put in place just because of the nature of the systems. Their loads are parallel.
During the winter months when snow-melt demand will be highest, the building's space heating needs will also be the highest. A large stream of free waste heat will be available to be recovered and diverted to the entrance and exit ramps.
Our first winter of operation is coming up this year, and the building's management/owner team and the mechanical engineers are closely monitoring the project.
The control of the system is such that the first stage of heat production is derived from the building's waste heat condensate recovery. If that proves inadequate for the given operating conditions, a second stage is brought online with a one-third steam capacity. If the demand continues to increase, a two-third's steam capacity is brought on line, and the one-third capacity dropped out. If this still proves to be inadequate (nuclear winter), then all stages can be brought online to satisfy the need for heat.
I personally doubt the system will ever see more than first and second stage of operation, but you know the members of the engineering community and their need to make sure their telephone does not ring because they undersized the physical plant.
Tune in next month as we continue our journey looking for alternative energy sources for snow-melt systems. Until then, happy steampowered 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.