Plug and Play Radiant Heating
Wednesday, October 7, 2009 at 1:44PM The concept that I looked into regaring the smartFarm was to use geothermal heat as well as solar water heater to heat a greenhouse. The Planting Table design shown would involve heating the soil bed on multiple tables through a connected piping system. The use of threaded couplings and manual valves at each table would allow for flexibility with regards to the number of tables used. The radiant floor system shown on the right of this drawing shows how the greenhouse could be split into two zones for times when only half or less of the floor space is being used.
The results from simple calculations for the heating load from the glass surface of the entire building having an effective U value of 0.756 and 2,620 ft^2 of glass surface are Q = U A delta T -> where delta T was assumed to be 50 deg indoor - 20 deg outside resulted in 59,420 Btu/hr needed. Having two radiant floor loops 16 in on center splitting up the building with 104 deg F water would provide 17,000 Btu/hr or ~ 30% of the heating load.
The result for heating the 4 in soil bed up 20 deg F was determined to be 192 Btu/hr per table (Q = k*(area[ft^2] / depth [in])* delta T). So the assumed 5 tables x 3 rows would equate to 2,880 Btu/hr to maintain the tables at a 20 deg warmer temperature than the surrounding air. The ASHRAE Applications book recommended that the soil not exceed 77 deg F temperature.
These rough calculations would mean that a large volume of 150 deg water would need to be stored from the day time solar collection. Assuming 8 hours of overnight heating, 2 gpm per loop, the table heating system would require 720 gallons and the radiant floor would require 1040 gallons. These numbers are very raw, but they show that additional heat sources would be needed for the greenhouse on a cold night. A potential additional source would be an insulated bed of gravel underneath the greenhouse that would allow for solar heated water to be ran through allowing heat to be stored under the floor for a good portion of the cold nights.
Reader Comments (5)
I really like how this has been modulated. These panels could be designed off site and "plug" into a framing system for the floor, being the walking surface and heating and structure of the module itself all at once. The framing could provide the "link" of water to the module. These modules could be everywhere, not only in the greenhouse, but all places that may need heat. If it is efficient enough, perhaps the complete floor doesn't need to be these panels, but spotted around the building to save economically. This is really awesome.
The idea of plug and play is interesting. I still dont gather the full concept of the actual "plug & play" portion. Would there be a possibility to move these? And then are the solar heating tank and geothermal tanks permanent? Could the tables or mats that actually route the radiant tubing be of such a material that rolls up to increase portability??? Also the hoop houses themselves could be enclosed with a material that could have a greater R-Value while still allowing the necessary light to penetrate.
The plug and play comes from having the tables able to connect/disconnect from the heating system. The heating water eqipment is stationary the piping network is able to serve the space needed. Hoophouses are not greenhouses and would be challenging to add radiant floors to ( non permanent floors).
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