[Greenbuilding] Eli's Proposed Heating Improvements
schoolhouse at live.ca
Mon Dec 26 19:38:47 PST 2011
On Sat. 24 Dec. Eli outlined both his current wood heating practices and
additionally his concepts for improving the heating efficiency of his dwelling:
Considering the air speed and volume, carbon soot, and potentially embers,
isn't using a Shop Vac on the pit of a recently used chimney pushing the line
a tad too far? Hopefully the list readership recognizes just how dangerous
this can be.
I tend to agree with Rob T 's suggestions regarding heating improvements
(I'm another moose-burgher, but from a not quite so chilly part of Eastern Ontario).
Regarding exterior wood fired boilers, it's my understanding that the fires tend
to run cool due to the water jacket and are thus prone to inefficiency and creosote
I would look closely at the losses occurring in the long lines out to the boiler,
as I suspect they would become quite significant. To prevent freeze-up, units
around here tend to require expensive propylene glycol and thus great quantities
for the interior tank or suffer the losses of an extra heat exchanger. I would think
using cheaper ethyl glycol is risking fatal poisoning or poisoning of your
aquifer. The glycol needs to be pumped, thus an additional electrical cost and
eventual failure site, and really needs a fail-safe power source, yet another cost
and source of failures.
The thermal losses from a large thermal tank need to be accurately determined
(my solar DHWT losses surprised me) and hopefully directed to interior winter
heating needs. Even if non-pressurized, the forces on tall tanks must be managed
structurally and may well shorten the lifespan of common inexpensive materials.
Is your 'significant other' prepared to deal with 10 tons of water throughout the
house? Mine drew the line at 120 gal. :)
When planning our renovation we examined various forms of hydronic heating in
detail - fully expecting that it would be optimal. Such was not the case. However,
from my investigation of interior radiator options, yes, the output is rather linear
wrt inlet temperature in the normal 160 to 190F range, but does tend to significantly
decrease below 140F. At low temperatures, it's difficult to beat antique vertical
tube cast iron radiators. At very low temperatures (80-100F) I've been told to de-rate
cast iron tubes linearly, then divide by a factor of 2 or 3! The heat will be delightful,
but the cost of so many radiators will kill you! In my case, I even examined runs
through old cast iron radiators prior to PEX in a poured slab lift – to try to improve
the match with condensing boilers – it wasn't cost-effective either.
I really agree that the initial target is to reduce the heat load dramatically - preferably
in a well planned/phased manner concentrating on benefit-cost payback. (With great
effort, we were able to get down to a net heat load of about 21,000 Btu/hr at -5.8F for
a forty-plus year old 3130 sq ft dwelling). We really liked Amory Lovins idea of
selecting design and materials such that they provide multiple beneficial uses – thus
providing a much greater benefit for the cost involved.
Once the heat load is minimized, I would suggest examining renewables, such as
taking advantage of passive/active solar to the extent feasible and selecting a reliable
and cost-effective means of heat storage, perhaps solid mass. In calculating an
appropriate amount of thermal mass, I would suggest trying to keep the typical daily
'deltaT' within bounds acceptable to prospective purchasers of your dwelling. A
slightly larger swing might be acceptable for high solar days as at least it is seen as
'putting up with the inconvenience of free energy'. With solar, recoveries and internal
gains, purchased heat can be reduced to 20% of the total annual heat load (perhaps
less depending upon the situation and climate).
However, beware, solar can be a very 'leveraged' investment. Around here, it typically
resembles a stock market equity investment in that “while the pricing of markets on
average tends to be a reasonable reflection of value, markets can and do act irrationally
far longer than one can remain solvent!”. In other words, unless one is very lucky with
having a very stable and predictable local climate, weeks and months can go by with
essentially no solar productivity, so one still must provide alternative heat sources –
hopefully with a measure of redundancy for security. - My 2 cents :)
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