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Is it possible to test a boiler efficiency?

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Comments

  • ChrisJ
    ChrisJ Member Posts: 15,583
    Steamhead said:

    captainco said:

    @Steamhead Therefore it makes no difference if the flue is warm or not. It is the temperature of the outside air and the temperature of the flue gases that determine the draft of a flue. Obviously inside and outside pressure is another factor assuming the inside pressure is greater than the outside pressure. But how often does that occur?
    Neither Code or manufacturers instruction address room pressure whatsoever.

    This is something to watch out for when setting up an oil or power gas burner using a barometric draft regulator. If we do the start-up on a mild day, the chimney won't develop as much draft as on a very cold day. So if after setting the draft, your barometric is opening up most of the way on that mild day when you're tuning the burner, it probably won't be able to handle the excessive draft when the weather gets cold. This will affect the fuel-air mixture and reduce efficiency.

    We solve that problem by installing a barometric one size larger than the chimney connector, and enlarging the opening in the chimney connector to match.

    I've read that a LOT of scorched-air systems cause room pressures to change when they're running, causing excessive infiltration and exfiltration. There were some articles online that discussed this, I'll have to see if I can find the links. Not sure if anyone's ever set up a differential manometer to show ΔP between inside and outside.
    I know one guy that has.
    Including in his bathroom for a bit to check fart fan performance.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Steamhead
    Steamhead Member Posts: 16,796
    ChrisJ said:

    Steamhead said:

    captainco said:

    @Steamhead Therefore it makes no difference if the flue is warm or not. It is the temperature of the outside air and the temperature of the flue gases that determine the draft of a flue. Obviously inside and outside pressure is another factor assuming the inside pressure is greater than the outside pressure. But how often does that occur?
    Neither Code or manufacturers instruction address room pressure whatsoever.

    This is something to watch out for when setting up an oil or power gas burner using a barometric draft regulator. If we do the start-up on a mild day, the chimney won't develop as much draft as on a very cold day. So if after setting the draft, your barometric is opening up most of the way on that mild day when you're tuning the burner, it probably won't be able to handle the excessive draft when the weather gets cold. This will affect the fuel-air mixture and reduce efficiency.

    We solve that problem by installing a barometric one size larger than the chimney connector, and enlarging the opening in the chimney connector to match.

    I've read that a LOT of scorched-air systems cause room pressures to change when they're running, causing excessive infiltration and exfiltration. There were some articles online that discussed this, I'll have to see if I can find the links. Not sure if anyone's ever set up a differential manometer to show ΔP between inside and outside.
    I know one guy that has.
    Including in his bathroom for a bit to check fart fan performance.
    Was it explosion-proof? >:)
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    ChrisJCanucker
  • bob_46
    bob_46 Member Posts: 813
    Comon practice when commissioning make-up air equipment and inflatable buildings.
    bob
  • captainco
    captainco Member Posts: 792
    It is not the flue the has to be heated but the cold air that occupies it. Why is it cold? Because your mechanical room pressure stinks!

    A few years ago I had to help a contractor on a high rise apartment, 15 stories tall. I would say the flue was 150' tall or more. We were they on a 40 degree day and the draft in the flue was over -.10"w.c. without anything operating. There were 2 - 3,750,000 btu boilers and a couple of 2,000,000 btu water heaters. No barometrics on any equipment. For the record, barometrics can only control up to about .08".
    An engineer wanted to install additional combustion air fans but there already was one there. A water heater attached to the flue with a drafthood was melting its controls and wiring weekly.
    Anytime you flue pressure is negative with nothing operating that is a sign your room pressure is greater than outdoors and combustion air is more than adequate.
    Barometrics and Blast gates were added to each piece of equipment. The Blast Gates reduced the draft to where the barometrics could now control. In the summer the water heaters operated in the common flue by themselves and still had excess draft. Plus anything with a drafthood isn't connected to a flue, it is just in the vicinity of it. Therefore the drafthoods were eliminated, which was pretty much mandatory on any job I helped a contractor.
    Never had another failure and the property saved over $35,000 the next year in fuel.
    Does anyone know what "laminar flow" is? Laminar flow means heat always travels to the center of a pipe or duct and cool air stays on the outside. If you want the heat to transfer to the pipes then you make them smaller, make the surfaces uneven or add baffling. In the case of flues, you don't want the flue gases to make contact with the surface of the flue and give off its heat. I want as much heat to remain in the flue gases as possible. Obviously when you put 300 - 500 degrees into a flue pipe the flue has to get warmer.

    I have a 3-story apartment. Each floor has its own water heater and boiler or furnace, all common vented into the same flue. 3 heaters and 3 water heaters. There no way the water heater on the 1st floor, operating by itself, is going to heat the common flue.

    It is a stupid installation in the first place but is allowed by Code in most places today. It violates the 7 times rule and the smallest appliance must exit first rule.
    Not once in 35 years have I ever recommended or had to recommend making a flue smaller to solve a venting problem. Bigger yes. Restrict it because it worked too good, but never smaller. Control combustion air, attach equipment to flues (no drafthoods allowed) and fire the equipment properly.

  • HVACNUT
    HVACNUT Member Posts: 5,803
    edited August 2017
    0
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,215
    I've read this post with considerable interest and I do agree with cap's presentation of true combustion efficiency. One detail that I believe is incorrect in your combustion number of mod cons is the combustion air inlet temp. Conventional equipment usually uses partially heated air, maybe, 60F, while modcons are using outdoor air. This potential error inflates the combustion efficiency on modcons 1 to 2 points. In addition modcons heat with more electrical energy, so real life efficiency is not reflected in ratings, nor are the actual energy usage numbers. However, the statement saying that oversizing equipment up to double has no virtually no effect on efficiency does not match testing by National Bureau of Standards testing of Atmospheric boilers. It is true that running an atmospheric boiler at constant 50% cycling load results in only a minor reduction in efficiency, however, when taking into account the variable load that occurs through a heating season, the seasonal efficiency reduction is significant.....my figures are about 15%. I have found that stack dampers do help with reducing the efficiency loss some and field experience has seen fuel usage reductions of about 10% when replacing 2x sized equipment for those right on with heat loss calcs.... using DOE output number as the basis for heating capacity. Of course there are other factors, such as the system i have in mind using standing radiation and it's percentage of radiant output vs convection maybe improving with the smaller boiler, but that maybe counteracted by a hotter heat exchanger since the smaller boiler was operating at higher water temperature.
    I believe your statement is much more true for forced draft equipment, since standby losses are much lower for this design in general.
    The other error I believe is just using the corrected combustion number and saying that is why Modcons save so much fuel. Your combustion numbers are almost exclusively focused on the "Con" not the Mod of mod cons. Testing and field experience by many here have shown the biggest gains from mod cons appears to be due to the mod of the unit. Stage fired multiple single input boiler installations and input modulation on none condensing equipment not only can provide more efficient steady combustion, but can have a radical impact on how the heating system interacts with the building and occupants. Mod input typically delivers less intense heating most of the season, which in turn should reduce hot air stratification and air infiltration and exfiltration, may increase the radiant component of radiators and decrease convection to deliver better black body temperature comfort to spaces. Properly sizing equipment and adding modulation tends to reduce fuel usage in the steam systems about 15% or more. My experience with hot water mod cons, even in low temp systems( max water temp at design around 140F, about 110F typical winer day) was only about 20% savings. Other factors may be at play, I'm sure, but this seems in line with most experiences when replacing equipment in properly functioning systems with modcom type units. The conclusion many have come to is that the mod part of equipment accounts for about 2/3 the savings, and the con only about 1/3. The biggest savings we have ever seen was using a modulating radiant output burner in a 100 year old Pacific steam boiler( huge combustion chamber surfaces) with about 30% reduction in fuel use over a well tuned LO/HI/Off standard gas power burner. Overall this steam system saw about a 70% reduction in fuel use after all things were repaired and corrected with the addition of the modulating radiant burner.

    To learn more about this professional, click here to visit their ad in Find A Contractor.
    ChrisJMilanDGordyHVACNUT