Wood Boiler - Radiant Floor Heating Questions

Re: Wood Boiler - Radiant Floor Heating Questions

I just installed an Alpha in our off-grid home and I couldn't be happier.

http://bluecloudpowerco.blogspot.com/2012/01/toasty-warm-feet-with-energy-to-spare.html

It is certainly possible to run a system off a single pump and maintain multiple zones. You will need to use zone valves instead of individual circulating pumps. Whether or not it will work for your particular situation will depend on your flow requirements. You need to calculate the volume of water you need to move and the pressure (i.e. head) that the pump will need to push against and double check to make sure it fits within the Alpha's specifications. If not, Grundfos does make higher flow variable speed pumps, as does Wilos. If energy consumption is your main concern, you just need to figure out what your flow requirements are and decide which single pump or combination of pumps will get you the most bang for the watt. In my case, I could have also gone with 3 Ivan Labs El-Sid pumps (one on the boiler and one for each zone). This would have used about the same amount of electricity and would have just barely met my flow requirements. I went with the Alpha because it was significantly cheaper than 3 El-Sids and met my flow requirements with room to spare.

If you do go with zone valves, make sure do your research and find a reliable model. From my understanding, zone valves can be the weak link in the system. For simplicity sake, I ended up eliminating my zones, so I don't have any suggestions.

I don't have an outdoor wood boiler, so I can't speak to speak to its electricity consumption outside of the water pump, but I assume it would be pretty low. It will probably have an electronic damper and possibly a fan. The thermostat itself should be negligible.

Your third question is a tough one because it depends on so many factors. It all about heat transfer rate. Radiant heat is not fast and is not really designed to be. Since floors tend to have a lot of thermal mass, they warm up slowly. The benefit is, they also hold that heat for a long time so they cool down slowly as well. If you want quick heat, install baseboard heaters or use some other method of heat transfer. All of the following factors can greatly affect the heat transfer rate in a radiant system:

• In-concrete versus staple up
• Use of heat transfer plates in staple up
• Water temperature
• Water velocity
• Water vs. Glycol
• Boiler Capacity

...and a whole host of other factors that I'm probably not considering.

That being said, I have relatively poor heat transfer (staple-up PEX without heat transfer plates) and a lot of mass in my floor. If I turn my boiler on, the thermostat doesn't move at all for about 2 hours. After the first 2 hours, the temp goes up about 2-3 degrees per hour.

Cheers,
Bill

Re: Wood Boiler - Radiant Floor Heating Questions

Re the water heater for infloor heat, I know one guy from Germany who set up several cabins for rent here in Nova Scotia, and for wintertime use, he used a 20 gal domestic electric water heater to supply the infloor heat, one for each cabin. Of course the hot water was mixed down to a cooler temp before being sent to the floor coils. The cabins were about 20X20 feet, and the water heaters if I remember right had just one element, rated 1500 watts, which is why I argued with him that it wouldn't supply enough heat. He informed me that it's done that way in Europe and with his experience with it, it would indeed work. I assume it did, but never did have a chance to verify that.
Re maintaining outdoor furnace water temperature, when the water is hot enough, the draft fan, if the unit has one, is shut down, and the draft entry door is closed, to smother down the fire. There are times however, when if there's been a good hot fire, and the circulator etc shuts down, closing the draft etc will not cool the fire in time, and the water will over heat, thus the necessity of a dump zone to get rid of that extra heat for safety reasons.
If your off grid power supply is limited, you should definitely confirm the consumption of any draft fans, zone valves, circulators etc. While their combined consumption may be considered nil for anyone living on grid, it could be shockingly high for someone living off grid. You may need power for things other than just the furnace/heating system.

Re: Wood Boiler - Radiant Floor Heating Questions

Totally agree with you Coot!

Re: Wood Boiler - Radiant Floor Heating Questions

I have built a couple units out if 10 gallon hot water heaters that performed well. I add a small 1/35 hp circulator pump and build a "A" coil out of a couple copper Transmission coolers ( 8 x 12 ) and put them on a manifold in the output duct. I used a 50/50 antifreeze mix as the fluid medium . I left the thermostat and overload breaker in place, but used a relay to override it so it starts heating as soon as the heat pump comes on. I set the thermostat on the water heater at 140 deg's and that's about it. I left it as a open loop so pressure is not a issue and it remains fail safe by removing the pop off valve.

It's amazing how well they work. The antifreeze is 140 deg coming out and the return fluid is 95 deg or so. I have never saw the heater element run a few minutes at the end of a heating cycle. The trade off is the 1,500 element, not energy efficient.

These units were used on Boats and the antifreeze was used so the units would not freeze during shutdown. The 10 gallon size was used because of space constraints. I would think a larger one would give more reserve capacity. They were used in conjunction with small Water to Air Heat pumps once the output air dropped below 95 or so degrees. You can see I was getting a 40 degree rise in air temps from the in/out fluid temperatures.