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.

HRV on modcon exhaust to preheat intake air?

markp1
markp1 Member Posts: 56
Wondered if anyone has done this, or has thoughts on it...

If the intake air is preheated, the overall efficiency is increased. Instead of letting the heat go out the flue, why not put an HRV on the flue exhaust to preheat the incoming fresh air from the outside?

Comments

  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    edited October 2014
    The contaminants and low pH would destroy the aluminum core in the HRV in very short order. Bad idea for many reasons.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    No way. God forbid there was a breach of exhaust.
  • markp1
    markp1 Member Posts: 56
    So maybe not then with an HRV, but isn't the principle the same as the industrial air preheaters? Or am I chasing a white unicorn? :)
  • Don_197
    Don_197 Member Posts: 184
    How long is your vent? If there was room...(and it didn't take you over your TEL (total equivalent length) Limit (remember the flex would be more restrictive than cpvc).......THEORETICALLY you could have a section of STAINLESS STEEL flex venting on both the the intake and exhaust......you could wind them around each other in a spiral, and then build a box around that section. Would it be worth it? NOT IN A MILLION YEARS LOL!! The cost and labor to do this would take forever to recoup on the few percentage points of efficiency you would gain. A similiar idea would be to cut off the intake pipe at the outside wall, then cut it off at the boiler, and let the room air "preheat" your intake air. I don't recommend this either unless your boiler is actually listed for "single pipe" installation. Read carefully, I am not telling you to seal off the intake out the outside wall......."cut it" and leave it open.
  • Jamie Hall
    Jamie Hall Member Posts: 22,891
    Then there is a very legitimate question: your burner is set up for the outside air density which it is getting now, If you preheat that air, the density changes, which would upset your burner calibrations. So... would you actually gain or lose? Remember that industrial setups with air preheaters are adjusted for that condition.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Ironman
    Ironman Member Posts: 7,339
    markp1 said:

    Wondered if anyone has done this, or has thoughts on it...

    If the intake air is preheated, the overall efficiency is increased. Instead of letting the heat go out the flue, why not put an HRV on the flue exhaust to preheat the incoming fresh air from the outside?

    Seriously?

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I do not know about heating systems. In internal combustion engines, admittedly a different thing, great effort is made to avoid raising the temperature of the incoming air. The hotter the air, the lower the efficiency of the engine.
  • icesailor
    icesailor Member Posts: 7,265

    I do not know about heating systems. In internal combustion engines, admittedly a different thing, great effort is made to avoid raising the temperature of the incoming air. The hotter the air, the lower the efficiency of the engine.

    The reason for Intercoolers on turbocharged engines. The higher air temperatures of compressed air have less air than the uncompressed air. The reason to compress it is to increase the air/O2 volume in the combustion air.

    Then, there's the contradictory issue of Exhaust Gas Temperature (EGT). Why is exhaust gas in an internal combustion engine more efficient when it is at a certain ideal (hot) temperature and the exhaust temperature in boilers are more efficient when they are cold and making condensate? The higher exhaust temperatures mean a more complete fuel burn. There's condensate in high altitude engines. Look at it forming clouds in the form of vapor trails.
  • Gordy
    Gordy Member Posts: 9,546
    edited October 2014
    Low exhaust temp in a boiler indicates the most Btus used possible thus higher efficiency.

    Higher exhaust gas temp in an internal combustion engine is to be more efficient in the aspect of the environment.

    Whether the intake air on a boiler is getting ambient inside air, or ambient winter time outside air can not be a huge effect on efficiency. I mean really your talking about a range of 55* all the way down to -25* and more so would it not be much harder to tune the mixture if that is even an issue. Verses a steady state ambient indoor temp. Plus we all know indoor air is more humid which is less dense than cold dry outdoor air (less O2), and winter time air is usually very dry so more O2 no.


    How much either way effects efficiency is pretty small.

    Now when your talking internal combustion engine that can be huge.