Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Condensate Volume of Mod-Con

jp_2 Member Posts: 1,935
I once asked jim davis about the accuracy of the therms reported, he seems to think that btu's can vary 10% daily, Tim M agreed but to a lesser extent if I remember correctly.

so right off the bat you are looking at at least 5% error in input assumptions. kinda kills your 99.8% efficiency calculation.

and remember if given 100therms, thats 100,000btu's +- what?

you also need to read up on "significant figures" and using them in calculations, this gives you allowable decimal places that can accurately be reported.

does the condensate come solely from the boiler and not the vent?

thinking more, I think measuring condensate really only tells you about dew point here? other variables need to be looked at, would need to know CO2 & CO to tell you combustion eff.

seems more viable to measure inlet and outlet temps as in your other post. then still vol. of gas and combustion eff.

this is still only combustion eff, the whole story is system eff. need to accuarted measure flow! but you know this :)

added: so what is the hourly rate of condensate at 25,ooobtu/H?


  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    After over 3 years, I FINALLY have accurate datalogs for condensate volume. I use a wireless rainfall sensor that reports to a computer interface every 5 minutes.

    When I wrote the program to read the raw data produced by the interface, I had an awful problem with the rainfall sensor. First, I wasn't really sure how it reported and nothing in the manual gave any clue as to actual volume of water--just the millimeters or inches of rain. Unfortunately gallons of water per day equates to hundreds of inches of rain--that I could tell--and I just presemed that I was overwhelming the ability of the thing to report.

    Last weekend I spent hours with the sensor VERY slowly pouring carefully measured amounts of water into it an counting the number of "tips". (The sensor has a see-saw with little cups on both end and tips from side to side as one and then the other fills.)

    After repeated measurements with varying amounts of water (8 oz sometimes, 16 oz others), I calculated 832 tips per gallon of water on average from very consistent values--always plus/minus 1 tip regardless of volume I poured. 832 sounded a bit familiar, but I couldn't think of why...

    Then I finally found a simple accumulating and repeating 3-digit hex counter in the output data that simply reports the number of tips of the bucket. Once it hits "FFF" it simply rolls over to zero and to determine the number of tips in a five-minute period you simply subtract the present value from what it was 5 minutes previously. Transmission errors are noted, but are irrelevant as the counter just keeps counting even if the receiver did not read properly.

    Then I decided to report condensate in pounds as well as gallons. Theoretical condensate equations are in mass, not volume. When I went to make the conversion, I remembered why 832 sounded familiar. At 832 tips per gallon (with "standard" water weighting about 8.33# per gallon) that meant the little bucket holds 1/100th of a pound. I cannot believe this is coincidence--instead it seems utter verification that I had found the proper value.

    I have condensate logs for most of five seasons, but previously I could not interpret them correctly. Now it appears I can.

    This season there have been numerous, extended periods of temps near 32F for 14+ hours in cloudy weather from later afternoon through early morning. From many, many clockings, I know that the boiler is constantly operating at minimum input (25 mbh) during these periods. Condensate production per hour during these periods is extremely stable.

    My next goal is to attempt to predict boiler input (during true modulation at least) based on condensate output and then attempt to calculate actual boiler efficiency. I tried the efficiency thing once and arrived at 98.8% but such seems almost too good to be true.

    Can anyone give me some advice on how to calculate the efficiency? How does the incoming air temperature affect things--especially the theoretical condensate volume? Do such theoretical condensate calculations already include the energy required to heat the incoming air (and the vapor it contains) to the ultimate flue temp? If so, how can I adjust for different incoming air temps?
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Hourly condensate @ 25 mbh @ approx 32F outside temp: 0.21 - 0.24 gallons/hour or 1.9#/hour.

    Since the flue horizontal flue pitches back slightly to the boiler and since I'm nearly positive that the concentric flue is significantly preheating the incoming air I suppose there must be some condensation in the flue itself that drains back to the boiler. I have no idea how much. Always lots of vapor from the terminal plus liquid water constantly dripping from the lowest exhaust port opening.

    Likely coincidence or plain dumb luck, but that 98.8% efficiency (not counting jacket loss) seems to be extremely close--actually a bit shy--to what Viessmann claims is the theoretical efficiency of the Vitodens operating at similar conditions.

  • Abro
    Abro Member Posts: 37

    Mike are you sure that all of your condensing is in the HX and none is in the flue?
This discussion has been closed.