Powerplant for snowmelt

badfish

Hello pros,

I did a snowmelt install recently, large area, a little less than 2800' sq. ft.  3/4" tubing on 9" centers, 16 circuits with centrally located manifold outside. Construction is pavers with insulation underneath(approx R-10?). Heat load calculations call for approx. 350K output. We were originally going with a Buderas C.I.  3-pass.  We are now exploring the option of a wall mount tankless, possibly the Takagi Mobius TM50. What do you think, good or bad ? Any feedback is much appreciated.

Nathan_6

Mod/Con

I would run a mod con boiler to take advantage of the super low return water temp and added efficiency that brings.  Not to mention you could just set the boiler temp to your snow-melts design temp and you wouldn't have to mix the water temp down.  It looked like the water heater you were looking at had a min temp of 100 which could be high for a snow melt depending on your design parameters, not to mention it wasn't all that efficient of a heater.

As I stated personally I would run a dedicated mod/con boiler with a tekmar snow-melt control

Jean-David Beyer

Mod con efficiency

In John Siegenthaler's book on hydronic heating, has a chart on page 48 (Figure 3-10) that shows the steady state efficiency of a boiler as a function of the return water temperature. It shows that you can get quite an efficiency boost if you let your boiler get into condensing mode (if your boiler can tolerate operating in condensing mode). For return water temperatures over about 130F, you get little or no condensing, and it is tough to get over 87% efficiency.



So thinking about various heat emitters, you would normally not get a condensing boiler to run finned tube baseboard heat supplied with 180F hot water, because even with a temperature drop of 20 or more degrees, the return water would be too high to get any benefit. If you have outdoor reset and oversize baseboard, you may be able to get into condensing mode much of the time.



Radiant heat from a slab is a much more favorable use of condensing boilers. One typically uses 120F water in there on the design day and with a 10 degree drop, you could get 93%. As before, with outdoor reset, you could put lower temperature water in most days, and get colder return water.



For snow melting, if you can tolerate getting 60F water out, you could expect an efficiency of a bit over 98%, and if a return temperature of 40F will supply enough heat to melt the snow, the efficiency could go up to 99%.