[Greenbuilding] vent waste heat recovery--in reverse?

[barbara deane-gillett]

   you might alos look into the heat loss caused by internal roof drains in
   large buildings.
       ______________________________________________________________

     From:  Chris Green <pojeros at telus.net>
     To:  Greenbuilding at listserv.repp.org
     Subject:  Re: [Greenbuilding] vent waste heat recovery--in reverse?
     Date:  Sun, 08 Jul 2007 12:35:01 -0700
     >Alan Abrams wrote:
     > >    still perserverating about improving energy efficency in my home--a
     250
     > >    unit, 18 story condominium...
     > >    with maybe 18 soil stack vents, times +/- 160' per stack...or more
     than one
     > >    half mile of at least 4" id pipe...thermosiphoning air from the
     sewer,
     > >    through tempered space, and out through the roof.  Assuming winter
     time
     > >    ground temps (for a relatively shallow sewer) at 45-50d F, is there
     enough
     > >    flow, and great enough delta, to try and recover this heat?  if so,
     how
     > >    would one do it?  perhaps the outflowing air could assist a heat
     pump, which
     > >    could in turn pre-warm water bound for the water heater.
     > >
     > >    crazy?
     > >
     >
     >Crazy? No, but if I understand your idea as trying to use the municipal
     >sewer system as a kind of annualized geo-solar heat source, it's
     >certainly a novel idea.
     >
     >What's the current average airflow through the vent stacks? (current
     >airflow...sorry 'bout the accidental pun there)
     >Can you increase the volume of the airflow by ending the stacks on the
     >roof with black metal pipes and focusing solar heat on them to increase
     >the air flow, sort of like using a solar chimney set up?
     >http://en.wikipedia.org/wiki/Solar_chimney
     >How much can you depressurize the pipes before you start sucking water
     >out of the toilets? ( this sometimes happens when it gets especially
     >windy where I live. )
     >
     >On the other end, in the sewer system, where will the make-up air be
     >drawn from, and will this drop the ambient temperatures in the sewer
     >pipes to a point where stuff could start freezing up in the depth of
     >winter?
     >
     >For that matter, is there anything in the system which could temporarily
     >block the flow at some point? That might lead to bigger problems than
     >the benefit is worth.
     >
     >My gut instinct is that it would be worth the effort to model this on a
     >computer just to see if, and how, it works. On the surface of it, I
     >think the odds are it could work.
     >Don't have a clue if it's cost-effective, though, since you can only
     >pull about 10 degrees max from 45 degree air. Any more than that and I
     >think you'd face the risk of frost build-up in the chimney stack...
     >
     >If it  works as a heating recovery system, it should also be capable of
     >working as a cooling system as well.
     >
     >As I said, a novel idea.
     >
     >Cheers,
     >
     >Chris Green.
     >
     >
     >
     >
     >
     >
     >
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