Splitting basement off to a new zone

Discussion in 'HVAC Heating & Cooling' started by LBPatrick, Oct 14, 2010.

  1. LBPatrick

    LBPatrick New Member

    Messages:
    7
    Location:
    New Jersey
    Hello All,
    First time poster, long time reader.
    Sorry if i use the wrong terminology.
    We purchased a house last year it is heated with hot water baseboard and radiators. There are currently 2 zones in the house, one for the second floor (ZONE#1 ) and another for both the basement and first floor (ZONE #2). What i want to do is remove the basement from ZONE#2 and place it in its own zone.

    From what i understand i need to do is:
    Remove the radiators from ZONE#2 along with any tees in the line
    Add a new T off the boiler supply and return lines to the boiler and create a loop for the new zone (ZONE#3)
    Into this new loop install a monoflow elbow on the return side and pipe it to the existing basement loop
    Add a new honeywell zone valve to the furnace and a new thermostat to control that valve.


    Do i have this correct? IS there anything i need to take into account?

    Thanks in advance.
  2. Dana

    Dana In the trades

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    Location:
    01609
    There are lots of things to take into account, not the least of which is that buy microzoning the place you may run into efficiency robbing short-cycling issues, particularly if the boiler is already 2x+ oversized for the whole-house design-day heat load (which would be typical.) The basement zone is likely to be a very small heat load relative to the boiler's output, but if the radiators have sufficient thermal mass you might be OK from a short-cycling point of view, but may have issues with too low a return water temp entering the boiler (unless it's already protected by the near-boiler plumbing configuration.) A fin-tube baseboard-only zone will be very low mass, and more likely to end up with a short-cycle problem when micro-zoned.

    Do a heat load calc on each zone (in the new configuration), and compare each to the boiler's output. You may need to add some buffering to keep the system running efficiently, and to keep the boiler from short-cycling itself into an early grave. Using a buffer tank as the point of hydraulic separation can cure a world of ills when the immediate heat load of the individual zones are less than 15% of the boiler's output. If your radiation temp requirements are north of 125F (likely, almost CERTAIN, with baseboard), using a buffer with an internal heat exchanger to provide the domestic hot water can increase the overall efficiency as well. But any of this is a lot more expensive than another zone-valve and some fittings...

    Got a zip code, annual fuel use, and the boiler's BTU-out numbers?
  3. peter_

    peter_ New Member

    Messages:
    6
    Location:
    NYC, US
    Yes, there are lots of things to take into account. Therefore, it is recommended getting a local experienced contractor. Fixing mistakes is usually more costly than paying an expert to get radiant floor heating project done for the first time.

    Either way, it is much cheaper to install any radiant heating system now than it's used to be 2-3 years ago.

    -------------------------------------------------
    Brazed Plate Heat Exchangers - http://www.brazetek.com/products
  4. LBPatrick

    LBPatrick New Member

    Messages:
    7
    Location:
    New Jersey
    peter_
    Thanks for the answer, let me rephrase my question so it better suits your answer. "I am thinking of doing some work to my house and came to this forum to get some helpful advice, but apparently at least one of you are unable to read a question and provide actual help so perhaps i should get a local experienced contractor"

    Hmmmmm I wonder peter_ do you know any experienced local contractors?
  5. LBPatrick

    LBPatrick New Member

    Messages:
    7
    Location:
    New Jersey
    Dana,

    Thank you for the response. I was working on other stuff over the weekend. I can send the zip code and BTU numbers tonight or tomorrow, not sure on the annual fuel use (it is gas, maybe the last bill will tell me that). I am guessing the BTU is listed on the boiler someplace (it is a peerless?). What i wanted to do in the basement was to remove the two "old style" radiators and replace with baseboard running some of the perimeter of the new basement play room.

    If i do run the new ZONE does this new zone need to have monoflow valves installed also or can i just run all the the baseboard on thsi new zone in series?
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
    New England
    By knowing how much gas you used, you can relate how much actual heat was needed to keep your house the desired temperature. When you match that up with the temperature data (heating degree days), you can get a good idea of how good the insulation is as well.
  7. Dana

    Dana In the trades

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    Whether or not a monoflow tees would make it work isn't a simple answer, and would require doing the math (including the room-by-room heat loss calc) on the entire system to say if that was necessary, or even going to work under any circumstances. But bear in mind that the heat loss characheristics of a basement are VERY different from the above-grade floors, and it's probably impossible to get it all in perfect balance as a single zone.

    "Old style" radiators tend to put out much more even heat than fin-tube baseboard, have more thermal mass (good, for avoiding short-cycling), and still put out a low temp (good for efficiency, should you move on to a condensing boiler some day.) It's cheap, can be made to do the job at 140F & up, but I personally would NEVER rip out functional high-mass antiques to replace them with baseboard if leaving them was an option. (Replacing them with thin steel panel radiators or cast-iron baseboard, if it fit the space better, maybe.) Radiators will usually provide more even heat, higher comfort, and the higher mass will reduce the risk of short-cycling.
  8. LBPatrick

    LBPatrick New Member

    Messages:
    7
    Location:
    New Jersey
    Dana,

    On the furnace there are to BTU numbers , 145,000 and 117,000. The old style radiators are just too large for how she wants the kids play room (and my pool table) laid out so i am stuck with going with the slant fins No clue on the fuel use for the boiler.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    The bigger one is input, the smaller one is output... 117/145~80% efficiency (max, and you almost never get max). The rest goes up the flue, or other standby losses.
  10. Dana

    Dana In the trades

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    Location:
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    Unless this house is in Antarctica or your basement is 10,000 square feet the basement zone is going to short-cycle if using low-mass radataion like SlantFin type fin-tube baseboard. 117KBTU/hr could easily be 3x the total heat load of your entire house, and very likely more than 10x the design-day heat load of an insulated basement. You'd be slightly better off going with ca$t iron convecting baseboard, but there's no way it would have sufficient thermal mass.

    Basements have very different heat loss characterisics than first-floors, making it very diffucult (or impossible) to balance well. From a comfort point of view it's better to set it up to run as it's own zone. Not knowing the full configuration of the rest of the radiation & their respective loads it's difficult to guess just how short & frequent your burn cycles are. Measure them- if they're under 5 minutes/burn for temp-maintenance burns (as opposed to recovery from overnight setbacks or bumping up the thermostat) you'd gain some efficiency using a Beckett Heat Manager or Intellicon HW+ type economizer control, which should extend the burns somewhat while reducing the overall duty cycle. The smaller your zones, the more benefit you'll get out of it.

    Another approach to dealing with micro-zones (micro, in terms of the boiler output) is to add mass- a tank of water either in series with the zone plumbing, or set up as the hydraulic separator in a primary/secondary for entire system, from which all zones draw their heat:

    [​IMG]

    In this configuration the mass of the buffer participates in all calls for heat. There are various approaches to controlling it, but with the boiler slaved to the buffer as it's only zone controlled by an aquatstat on the tank, the hysteresis of the aquastat and volume of the water sets a minimum burn time for the boiler. (This is probably a bit more money, design, and more plumbing than you were going for though, eh?)

    If you take the buffering hydraulic separator approach, there are buffers out there with internal heat exchangers for heating potable water, sometimes refered to as "reverse indirect" hot water heaters, which could add the domesting hot water heating load to the boiler, further improving it's as-used AFUE (and would have higher efficiency than a standalone hot water heater during the heating season, dropping to about the same efficiency as a standalone tank during the summer.) It'll be a bit over a grand for a ~23-28gallon reverse indirect, but A: It'll never need replacing and B: With 117KBTU of heat going in it it'll deliver as much first-hour gallons as a 180KBTU tankless (at about the same efficiency as a tankless for 6-8 months out of the year. There are often subsidies availble for a reverse-indirect that wouldn't be available for a simple buffer tank, and in your situation it should be plumbed as the hydraulic separator as above. With a gas-fired boiler the tank temp should be set to ~140F, to avoid sub-130F return-water, which creates destructive condensing conditions in the boiler/flue. If there is enough radiation in all of the zones/room to deliver design-day heat at 140F, you could just leave it there, otherwise you might have to bump it up 5/10/15F for mid-winter operation. Most fin-tube can deliver heat at 140F, but you'd need ~50% more running length to deliver the same amount of heat that it would deliver with 160-170F water.

    Setting up your basement zone with enough baseboard that it COULD be run at 140F on design day makes it more efficient, even without a buffer or buffering hydraulic separator, and should you ever replace the boiler with a condensing version you could do better than 90% efficiency, ALL of the time, whereas if you set it up to need 160F or 180F water the best you could do is mid-80s.

    As-is where-is, your ~80% combustion efficient boiler is probably 2-3x oversized for your peak heat loads (5-10x oversized for the typical or average mid-winter load), short-cycling, and delivering ~65-70% net efficiency. With a economizer control you can probably hit the low mid-70s with it, and with well designed buffering system & controls or slightly higher. (Cood bee rong, offen am- need more info on your fuel use, zip code, & heating degree-day data to know for sure.)

    Done a heat-loss calc yet?
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