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Zoning 1-pipe

Therm_lag Member Posts: 30
Zoning is discussed in several other threads, though I'd like to clarify issues particular  to  energy saving for 1-pipe steam.  Is it possible to zone sections of loop piping (e.g., upfeed) and fill separate zones sequentially?  The objective would be to  size new or substantially derate existing boiler to building design load and NOT  to EDR.   Any  method to avoid the demands (and potential waste) of excess EDR would be particularly useful in buildings where insulation, window upgrade, and air seal reduce load substantially below that at time radiators / boiler were sized.  In addition to enabling boiler size to better match building load, zoning might improve response to  solar, occupancy/activity, and wind loads.

Response will be of value, and will be acknowledged, in  “Steam Heating: Past, Present, & Future”  presentation at the ACI 10 conference, April 2010


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    an interesting proposition

    i would guess that this could be workable, with zones in the building areas of greatest heat loss, and of simple heat maintenance. it might allow also for smaller diameter steam mains, which translates to less metal [in each zone] to heat up at the beginning of the cycle. the response to plunging outside temperatures would have to be much slower than is now the case. would the occupants understand the necessity [give them green sweaters]? 

    even better in the search for greater economy/efficiency would be the use of a fully modulating burner in the boiler, going from 25% to 100% of EDR. i wish we could only have more confidence in the only steam pressure-regulating controls available to us on the market!

    an alternative to the modulating burner would be the use of multiple boilers, of maybe each 25% of EDR which could be staged as the building first heats up, and then goes on to temperature maintenance. this would still need valving for control of multiple water levels, but could be quick in response to temperature changes.

    the real economy in steam heating may be the use of the residual heat final flue gas temperatures to produce some domestic hot water--nbc
  • Of interest.....

    Take a look at my article in the resources section "Taking Another Look at Steam Boiler Sizing Methods".   I have another on two pipe sizing methods that is in the works.
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert

    Noisy Radiators are a Cry for Help
  • Therm_lag
    Therm_lag Member Posts: 30
    Zoning 1-pipe example ?

    Nicholas - Thanks for this!  

    Owners of buildings where 1-pipe

    steam will be maintained need a way to ONLY satisfy building heat loss, and

    advantage themselves by installing a boiler that size if possible.  Seems one way possible would be to have portions of distribution system w/ EDR no greater than total building loss, size boiler to total building loss, and alternate steam delivery to portions of deistribution system based on actual loss occurring.  The objective:  fully fill radiators during sequential fillings OR partially fill radiators, sufficient to meet loss.   With either fill strategy one must carefully balance the portions of distribution system.  I'd like to know of one building where this

    was shown possible.

    BoilerPro - Thanks for this, though I did not locate "Taking Another Look" resource.  Have more specific directions to this?
  • Therm_lag
    Therm_lag Member Posts: 30
    edited May 2011
    1-pipe zoning detail


    Best design practice for single pipe steam systems called for  radiators with output sized to the heat loss of each room during the coldest weather (heating design temperature, -4°F  in Chicago,  IL).  A boiler (typically one central unit) was selected with capacity to fill the steam distribution system completely.  Balanced  distribution would then fill all radiators simultaneously.  The output

    capacity of the boiler had to be at least equal to the total “equivalent direct radiation” (EDR) of the radiators.  If radiator capacity equaled heat loss, and boiler capacity equaled radiator EDR, then the boiler would operate continually only during design conditions.  Various controls were employed to limit boiler operation at other temperatures through the heating season.  Most steam systems currently have a cycle or temperature control that responds in some way to indoor temperature.  The comfort control prevents overheating by cycling the boiler on and off.  Cycling reduces efficiency as the burner must produce steam before heat is delivered, and the boiler dissipates heat to the chimney after each burner cycle. 

    Now fast forward to an old steam heated building that has new insulation, new windows, and less air leakage.  Heat loss could be half of that  assumed when the need for radiation was calculated.  This means the radiations, and the boiler, are twice as large as necessary.  The boiler is matched to radiation capacity, though the amount of heat  required to maintain comfort is now much less. 

    Now assume the distribution system can be divided in two, with half the total EDR in each of two zones (see graphic of zoned steam system).  Many buildings already have two distinct steam supply piping “loops.”  Work to re-pipe steam distribution to serve  separate zones may only require limited work in the basement.  

    With the boiler only required to heat half of the radiation capacity at a time, satisfying the design heat loss of either of two equal zones will only require a boiler sized to serve the EDR present in either of the zones, not both.  Control will be needed to assure that pipes and radiators are completely filled in each zone.  This can be   accomplished with zone valves on two pipes coming from the  boiler connected to each of two zones.  When the original boiler  might operate half the time at design temperature, a new boiler will operate continuously, supplying heat to each zone alternately at these conditions.  A boiler with output capacity matched to building

    load will have longer on cycles and fewer off cycles.  Operation  through the heating season will be more efficient than a boiler with output capacity matching total radiation in the building..  On average a boiler properly sized to load will have half as many off cycles and the total time the boiler wastes heat while off will be half. 

    Possible Advantages

    In some buildings, zones may be arranged to avoid energy waste due to overheating.  Consider the common situation of zone discomfort due to external load.  Say steam is required to maintain temperature at the north area of a building as solar heat enters windows of south apartments.  Only admitting steam to the north zone, when the south zone thermostat registers within the comfort temperature, will prevent waste of unneeded steam and avoid  overheating the south apartments.

    When boiler replacement is planned or required due to irreparable breakdown, matching the new boiler to load rather than to total  EDR may reduce the size and cost of a new boiler.

    Where the existing boiler can be derated, longer burner cycles and lower flue gas temperatures can be expected.  Derating is a  method to increase the efficiency of the existing boiler.  Zoning  steam distribution and matching boiler output may offer improved efficiency of existing equipment or a newly installed boiler.

    Improved boiler durability can be expected to result from fewer on/off cycles. In general, the proposed down sized or derated boiler will have less abrupt and less extensive change in temperature.

    Providing steam throughout the distribution system quickly will   improve comfort.  Comfort is served by placing steam at each radiator in proportion to the heat loss occurring from the room(s) served by the radiator.  In most cases steam balancing must   compensate for a large volume of air to be pushed out of the piping and radiators, and a large thermal mass of the pipes and radiators to be brought to temperature.  Having the boiler serve only a portion of the distribution system volume and mass as it fills the

    system may improve comfort and reduce the cost to achieve   balanced comfort by eliminating the need for some customary balancing work.

    Low-pressure single pipe steam systems for heating buildings  operate at temperatures slightly above boiling temperature.  

    Raising water to boiling eliminates cost for mechanical distribution of heat (no pump or fan)  – typically 5 to 10% of the cost of a hot water or air system.   A disadvantage of distributing steam is the loss of sensible heat of combustion gases, and latent heat of water vapor in these gases, to the chimney.  While large systems are now available that recover heat from combustion gases, heat recovery is usually a separate flue device added to smaller boilers.  Heat recovery is seldom installed,  partly due to cost of equipment, though perhaps mostly due to lack of awareness of its potential and lack of training for installers.  Heat recovered from flue gas may be used to pre-heat domestic water.  Depending on heat available and DHW heating required, flue gas heat recovery may displace

    half or more of water heating cost, or perhaps 10% of total gas heating expense.  To the extent that heat recovery retrofit cost effectiveness is related to higher percentage of time that vent heat loss occurs, and to size of vent (size of recovery device), the cost  to install flue gas heat recovery may be reduced by matching boiler output to present building heat loss rather than to EDR installed perhaps 100 years in the past. 
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