Condensate Volume of Mod-Con

Mike T., Swampeast MO

25 cubic feet per hour of natural gas was steadily consumed during a 16 hour period.

Continuous, steady fire with flue temp average of 93° (±2°F) during the period. Mainly nighttime, cloudy with temp nearly steady and average of 32°F and RH 80% during the period.

400 cu.ft. = 11.33 cu. meter

Theoretical condensate volume of 11.33 cu.meter @ 1.53 kg/cu meter:

11.33 * 1.53 = 17.33 kg (38.2#, 4.6 gal) theoretical condensate

Condensate produced: 12.86 kg (28.35#; 3.4 gal)

á = 0.74 (á = theoretical / actual condensate)

Unrecovered condensate volume:

38.2# - 28.35# = 9.85#



Does this mean?

93°F flue - 32°F outside air temp = 61°F difference

61 * 9.85# = 600.85 <I>maximum unrecovered condensate BTUs<B> during a 16-hour period</B></I>

With the only boiler losses remaining...

Absolute temp rise of combustion air

plus

The jacket????

Here are some additional measurements made during nearly identical conditions (both quite steady):

Incoming air temp: <B>69°F</B> (test fitting of Viessmann concentric flue) triple verified--opening slide coupling caused temp to drop as expected assuming the 5' horizontal flue was significantly heating the incoming air. 55°F ambient air temp in basement near boiler.

Flue temp @ outlet (outdoors): 89°F

Combustion Air Loss @ 10% excess air

400 * 11 = 4400 cubic feet of combustion air

raised from 69°F to 93°F = 24°F delta-t

@ 0.018 btu per cuft/°F heat capacity of dry air

4,400 cu.ft. @ .08 cu.ft./pound = 352# combustion air

latent heat at about 50% RH = about 7 btu/pound ??? (Brad White??) (outdoor air 32°F; 80% RH; combustion air @ boiler 69°F; temp at outlet 89°F) [value changed from 10 btu/pound]

352 * 7 = 2,464 btu <I>latent flue gas heat loss</I>

4400 * 24 * 0.018 = 1,900 btu <I>flue temperature loss</I>

400,000 btu consumed

- 2,464 btu latent flue temp loss ????

- 1,900 btu flue temp loss

<U>- 601</U> btu condensate loss

= 395,035 btu utilized = 98.8% boiler efficiency????