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Zone system (fire away) (9 Posts)
Zone system (fire away)Dear Steam Folks --
This is a good opportunity for me to review some heating theory.
I am listening to suggestions.
It is time to replace a Peerless, running 555 sq ft.
I am considering Smith Series 8-4H(467 sq ft) or a Burnham MST 513.
I am in Western Maine.
Below is an explanation given to a friend who thought the MST 513 was too small with 123,000BTU
Residential steam has its own language and calculations. The calculations go backwards and forwards. Going forwards with the Burnham furnace, 1.35 gallons/hour of oil makes 189,000 BTU. 86% of that does not go up the chimney, leaving an available heating capacity of 164,000 BTU. Still going forward, 75% of the available heat gets to the radiators with 25% lost in the piping, giving the 123,000 BTU (513 sq. ft. EDR steam) delivered to the radiators.
Now going backwards, EDR is the Equivalance of Direct Radiation measured in square feet with 215 degree steam in a 70 degree room. One square foot of EDR is 240 BTU. All radiator segments have an EDR rating. The above 75% available heat is the 1.33 Pick-up Allowance when calculating heating demand from need, being radiators. The furnace is rated with this differential built in (513 EDR net rating).
There are three zones in my building, the front, rear and upstairs. The literature does not recommend zone systems with a condensate pump (gets the water back in the boiler when the valve is closed). There are obvious inherrent inefficiencies in a zone steam system. But that is the system which got me to the ball, so I am going to dance with it.
The EDR for each zone (Housing Units):
Front - 143 sq ft
Rear - 195
Upstr - 235
Total - 573 sq ft EDR
With all three units demanding heat, this furnace cannot deliver enough steam to heat the building. Steam will be condensing and returning to the boiler before the radiators are filled. Furnaces are sized to meet the worst case situations, coldest day of the year, will it match demand? The answer is no, not if all three units are calling for heat. But reality is not quite so clear, guessing this is one reason the literature does not get into steam zones.
The furnace does a lot of sequential running. First one zone calls for heat, then another, with the upstairs demanding the most and having the most exposure for heat loss. Whenever any unit calls for heat, the furnace will provide 513 EDR. Somewhat regularly there is demand from two units at once and rarely all three. Below are the three combinations of two unit demand possibilities.
F,R - 338 sq ft
F,U - 377
R,U - 430
With these combinations, the furnace can keep up. The conditions for relative efficiency are that two units demand heat at a time and in the worst case situation (below zero temperatures), the furnace can keep up by alternating between combinations of two units. Living in the part which demands the most heat, and knowing where my bread gets buttered, I have no problem monitoring the comfort of my customers in while in the depths of the winter.
It would be nice to find a variable oil fired burner which fits this boiler (I do not think this is possible), or come up with some controls which will sequentially direct the steam in demanded or expected zones. The simplist may be whenever the front or rear unit demands heat, both zones open up with the 3rd and largest zone staying independent. My preference in controls would be whenever any unit calls for heat, the next coolest one also gets heat.
Those are my thoughts, any suggestions are appreciated.
Doesn't it get cold in Maine?Knowledge is a great thing.
Experience is much better.
Your talking about major changes to a heating system and although you have a good idea of what you want to do some things are not so cut and dry. The standard pick up factor of 1.33 may not be enough if piping has no insulation. If your total heat loss has been calculated why would you want to go through under sizing the boiler and when it gets 5 below zero have the house go cold?
Heating design is for the total comfort of the people who live there. It is not guess work.
Please hire a heating engineer and tell him what you would like to do. He can guide you according to your budget. And when the temperature drops you'll be able to sleep at night. Good Luck
overly complicated systemis this 1-pipe or 2-pipe?
the complication of a small, zoned system is not only in the difficulty of handling condensate return, but also venting. you really would need to over-vent the mains on each of the 3 legs, so that if only 1 zone is calling, that leg can handle all of the pipes in between, plus the boiler steam chest.
has this system always been configured this way, or was it done in an attempt to balance a badly vented system?
this system which got you to the ball is really a pumpkin in disguise, and should be returned to its original operation, without zones, running at a few ounces, and with a gravity return.
there are probably some modulating burners available which could give you the variable output [controlled by pressure]. why not post some pictures of the boiler piping so we can see if anything else is "non-standard" in this system.
why not order some of the steam books from the shop here, and see what would be proper for this system.--nbc
Duff and Nicholas,
Thank you for your suggestions.
I am replacing the boiler in an existing system. The building has been updated with windows, doors and lots of insulation. Whichever boiler goes in will follow specs with a new header. I have lived in this building 12 years.
To my knowledge, the system was designed with zones. The building was poorly maintained and master trapped after the fact, exactly as Dan describes. I re-packed valves, replaced radiator vents, re-trapped the system, isolating the zones with traps, then discovered Dan's books, replacing and adding main vents, and changing to a vaporstat. Valve motors were wearing out, replaced, and added relays so the boiler could set back when there was no demand. Electronic thermostats were installed and the relays were also used to power the closing action on the zone valves.
It is a one pipe system. One pipe systems have an elegance and simplicity which my zones and condensate pump definitely complicate. But the zones work, when heat is needed it arrives. The valves could be removed and the system run as a single zone with a new furnace sized appropriately. Having sorted out and upgraded all the zones, I am trying to use what is available. Downsizing a little (reflecting heat loss improvements) may well be foolish, which is why I am asking if there are options for taking advantage of a zone system.
ProperlySize the boiler and use TRV's.
More work to do...I would find out what the actual heat loss is per zone, especially the two smallest. If they are about 50% of the radiation capacity, you could just use an alternating timer on the two small zones, each would get 1/2 hour to run, while the other is held off. Some relays that can delay opening of a new zone when the other two are running could also work.
I understand there are two stage oil burners available, you just have to look for themThe Steam Whisperer (Formerly Boilerpro)
Chicago's Steam Heating Expert
Noisy Radiators are a Cry for Help
Simplifying overly complicated systemWhen steam systems are properly installed, the aim of the Deadmen has been to allow all radiators (sized perfectly for the room heat-loss) on a given floor to receive steam simultaneously. This is done with ample main venting. Sometime in high-rise buildings, to have the steam travel up first to the top floor. Whatever the size of the building, the aim is still simultaneous steam arrival.
When the system venting becomes unbalanced in later years through lack of proper maintainence, it is like a car with brakes dragging on a couple of wheels, slowing it down. The zoning here is like putting a bigger engine in the car instead of fixing the brakes.
With timers and sequencers on this system, you will have such added complexity of controls, that it will be difficult to diagnose any future problems.
With a gravity return system, with good main venting (back-pressure 2 ounces), it will be easier to manage. Any slight imbalance of temperature can be adjusted with trv's.-NBC
Zone SystemHaving a better understanding of the heat loss makes sense (kind of fundamental). A two stage again adds complications and also makes sense. They seem to be rarely used, possibly with reason, but not necessarily so.
One other thoughtYou should be able to reduce the amount of capacity for the pick up factor since it is very unlikely that all three zones would call at the same time, so the load will be much lighter during piping warm up.The Steam Whisperer (Formerly Boilerpro)
Chicago's Steam Heating Expert
Noisy Radiators are a Cry for Help