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Simple Low Cost Radiant Floor Heat System
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By connecting directly into the hot and cold water lines of an existing hot & cold water system and using a back flow preventer, you can by simply adding a 1/25 hp pump, an in line thermostat, some shut off valves, along with some 3/4" fittings, have a simple radiant heat systems thermal source. The pump used is the UPS15-42SF which has a thermostat control as well as 3 speeds. New cost for the pump new is around $211.05. I used a salvaged pump which cost $25. The cost for the water heater was $138.00.
The number of pipes seems large because the mechanical room also serves as the hook up for the washing machine as well as the access port to the bath tub plumbing.
An off switch was placed in on the thermostat line in order to prevent the heating system from competing with the hot water requirements when a person is taking a bath. This prevents the need for a seperate hot water heater. A timer was also added to pump motor line to make sure that the floor radiant system didn't interfere with other normal hot water uses.
By using an energy audit (http://w.geocities.com/goldenmeandomes/24energy.htm) it can be determined that I will require approximately 100,000 BTUs/day of energy to heat the structure. Being as the concrete floor acts as a heat sink with a release rate over 12 hours, I can schedule the 30,000 BTU/hr hot water tank to run a total of approximately 3 hours to achieve the BTU's required. Because the energy discharge rate may not match the tank recharge capabilities, the total run time will have to be worked out empirically. Initially, I can schedule 2 hours running from 4 to 6 a.m. and 1 hour running from 4 to 5 p.m. At a electrical rate of $0.07/kwh, using 30 kwH/100,000 BTU''s, and a hot water tank rate of 30,000 BTU's/hour for 3 hours/day, gives me a cost of approximately $2.00/day, or $60/month. If natural gas can be used instead of electric, at a price of approximately $.65/100,000 BTU's, you can reduce the heating cost to around $20/month.
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The X Plex tubing is attached to rebar which is placed over impermeable plastic and 1 1/2" insect resistant EPS insulation. Fiber reinforced concrete was placed over the tubing.
This system was used to heat a 24' dome.
Recommendations:
1. I would use at least 3 zones instead of 2 in the future. One for the bathroom and utility room, one for the downstairs bedroom, and one for the kitchen-dining-living room combination. In this project I left the living room and upstairs to be totally heated by the backup woodstove.
2. I would recommend spacing the tubing more evenly to get a more even heating of the slab.
Note:
The initial heating of the slab will require a considerable energy input and therefore no timer should be used initially. The 5 C.Y. of concrete must be raised from 50* F to at least 70* F, which entails around 400,000 BTU's of energy. That would require around 13 hours of a 30,000 BTU hot water heater.
This system can easily be converted to all hot water solar collector, or even to wind generated electric system.
For detailed information on how to lay tubing go to URL: http://www.radiantdesigninstitute.com
Resources:
Pump charactericstics: http://www.johnstonesupply.com/
Tubing characteristics: http://vanguardpipe.com/pdfs/Vanex%20Techdata.pdf
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posted 2/26/03 rlc
revised 3/13/03 rlc
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