Geothermal heat pump capable of 1500 btu/sec
Hello,
I was having a conversation with a fellow grain producer and the topic of alternate heat sources for grain dryers came up in light of a propane shortage experienced throughout the Midwest recently.
I suggested that a geo thermal heat pump placed under a sillage pit, which naturally generates heat through fermentation, could provide the necessary heat to operate the grain dryer. I believe the minimum heat requirement for a grain dryer is 1500 btu/sec. What would building such a system entail, and thank you for any responses to my off normally topic question.
Other crazy ideas involve recycling wasted heat from warm air that exits grain bin during drying process. Grain drying appears to be a necessary evil for the foreseeable future, and the status quo of simply burning fossil fuels to achieve heat generation days seem to be numbered.
Patrick Hume
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Replies
Patrick,
Why are the crops not drying down in the field? Are you going for extra yield when an earlier maturity variety might field dry and not require supplemental drying.
I am not suggesting you go back to ear corn and corn cribs but it seems there is much more grain drying than in the past.
That’s 5.4 million BTU per hour, so 5.4M BTUH.
Most heating systems are measured in BTU per HOUR, not per second, so you need that bigger per hour number for proper comparison.
I’ve never seen such a large geothermal system outside of specialized systems used for power generation. Those specialized systems are either located in special spots to take advantage of unusual geologic conditions (like in Iceland), or use VERY deep injection wells to get water to flash to steam. These wells are typically in the mile+ depth range, but exact depth depends on what is going on underneath the surface in your area.
Outside of the fancy specialized geothermal systems, I’m not sure what would really work in your situation. 5.4M BTUH works out to almost 1.6 megawatts of electricity (direct energy conversion, no heat pump CoP numbers), which rules out solar on any reasonable scale for a small private project.
You could potentially burn alchohol, like ethanol, if you have a nearby producer. You may be able to use something akin to landfill gas too, which is just methane produced by decomposition of organic matter. The trick is that you need a LOT of that methane, so you need a LOT of stuff decomposing to meet your needs.
I think your best bet to replace propane would be to try burning some kind of waste material that may be cheaply available in large quantities in your area. Wood chips, wood pulp, other types of plant matter waste. You can get good size wood pellet burners, for example. A lot of what you choose is going to be determined by what you have available in your area unless you want to stick with conventional fuels.
Note that a specialized geothermal system to handle the heating needs of a grain dryer would be a REALLY interesting project and I’d love to see someone try it. If you were to seriously consider going this route, I’d try doing it as a consortium with a large, centralized facility to try to spread out the construction costs and lower any one organizations risk. During the off-season you could use the thermal energy to generate electricity as an IPP (independent power producer), selling back into the grid. You’d have enough energy available to make this worthwhile, and the revenue from selling your off-season output could be used to help offset the costs of building the facility.
Bill
Large amounts of heat for moderate periods (a month per year?) without using fossil fuels is interesting. Electricity via a (edit:future clean) grid is the obvious solution, with or without a heat pump. Maybe someday trucked in liquid hydrogen.
Heat recovery as an optimization on a current system makes sense to me.
Electricity from the grid will most likely be primarily sourced from coal and natural gas in the Midwest. Using grid electricity for heat will likely result in MORE fossil fuel consumption than burning the same fuel directly for heat in this region. If you could find a big enough heat pump to handle the required heating load that would be different, but I’m not aware of any big enough.
5.4 M BTUH is a commercial size boiler. It’s equivalent to 5,400 cubic feet of natural gas consumed PER HOUR of operation. Thats pretty close to the US average of just over 5,000 cubic feet PER MONTH to heat a typical home.
Bill
Agreed, current solutions (there may not be any that are economically viable) and future ones are separate issues. My comments were about the latter.