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Are 2 zones more/less efficient?

raemac Member Posts: 14
I have 2 floors with two mains and electric commercial zone valves set up with a thermostat for each one. My first floor thermostat call for steam and the boiler runs for about 1/2 hour and then shuts off. Then the second floor usually does the same thing. Wouldn't it be more efficient and use less fuel to have them both on 1 stat and fill up the whole system with steam?


  • Efficiency

    Why not wire it up so both zones heat at the same time, and this will confirm or deny everyone's ideas about this. I for one believe this system to be wasteful of fuel, and probably yields little comfort as a zoned setup.--NBC
  • Eastman
    Eastman Member Posts: 927
    edited February 2014
    somewhat related

    Let's say the system has twice the edr needed after envelope improvements. Perhaps a zoning strategy could allow one to install a boiler that was sized for half the edr? For example, suppose one implemented a cycle based system set a 1 cph. Zone 1 (with half the edr) leads the call for heat and is allowed up to 30 minutes of runtime, at which point the load is immediately handed off to Zone 2. The sequential calls eliminate extra cycles, and the boiler output matches the edr of the zone.

  • Fred
    Fred Member Posts: 8,541
    I suspect?

    I suspect what you are suggesting would work but I suspect it does nothing for efficiency. I would think it is far more efficient to heat the entire house during the first half hour cycle than to heat each half for a half hour each. Given the thermostat is on one level or the other, the boiler cycle will be as required to satisfy the stat and the added bonus is the heating of the other area, at least to some degree. If that isn't adequate, then it may make sense to run the second zone just for the incremental temp. In essence, one zone would be the whole house and the second zone, if needed would be to increase the temp by a couple incremental degrees. I doubt that would even be necessary, but it is an option???
  • Eastman
    Eastman Member Posts: 927
    I think I follow you

    I think I follow you,

    It sounds like you are describing the typical zone sync that systems such as tekmar and honeywell provide for hydronic systems. All demands start together, but end at different times.

    That's certainly better than random independent heat calls, but one is still stuck with twice the boiler, twice the near boiler piping capacity, and twice the cycles that the building really requires. That seems much worse than a smaller boiler cycling half as often.
  • Fred
    Fred Member Posts: 8,541
    Maybe I misunderstand?

    It would seem to me that a smaller boiler, serving two separate zones would run twice as often. Not sure I understand why you think it might run half as many cycles. Also, I assumed this is an existing installation and the current boiler and piping is sized for the entire structure. If that's the case, it just doesn't make sense to me that you would create two separate zones that, in theory makes the current boiler way over-sized for either zone, wastes fuel by the shear fact it is now over-sized and runs more cycles that necessary to heat the entire building. Of course if you have specific needs to have different temp zones (for some health or other reasons) then I understand doing what needs to be done to satisfy that requirement. Otherwise, I don't think changing out the boiler and/or piping will ever pay for itself. Maybe it's an option when the boiler dies but I think I'd have many more options, down the road, to have a boiler sized for the entire building than one that's sized for only half the building. But that's just my "comfort zone" (no Pun Intended.