[Greenbuilding] one more pleasure (or not) of heating with wood

Fri Jan 7 11:42:52 CST 2011

Lynelle, 

Greetings from Missouri, where we are treated to a month of clouds in a typical November.  Solar pre-heat can be one of the most cost-effective solar installations if done right, even here. 

Good solar panels can boil water!  I've seen this happen, it is real.  They can definitely produce higher temperature water than you need under the right conditions. 

There are two ways to get rid of excess heat in the summer, if you don't have the luxury of a hot tub:

1.  Don't make excess heat.  Use a drainback (or is it draindown?  I can never keep these two terms straight) system that leaves the collectors dry when heat is not required. The water drains into a tank when not needed.   This uses a more complex controller, but eliminates need for antifreeze in your collectors, even in Ontario.  This is really a very straightforward solution.  If I built another solar water heater this is what I would do. 

2. Have a heat-dump circuit.  In a glycol (antifreeze) collector, the controls can be really simple - a little pump run by a solar cell.  Size the system so that in the summer it matches your typical usage, and it won't overheat under normal conditions.  But if it does overheat, then you will need a solenoid valve and a little control that dumps domestic hot water on the hot side of your solar tank straight down the drain.  If your system is sized correctly, this will almost never be used, so it is not a big waste. Dumping 10 gallons will cool off your solar storage tank a lot, and the heat was free anyway. I've wasted more than ten gallons trying to wash my dog.  

3. Throw a tarp over the collectors when you are going on vacation, as I did before I installed the heat dump.  There is no good reason to do this except for desperation born of poor planning.  

There are arguments pro and con for each system. 

You always need a tempering valve after a solar water preheater to eliminate any risk of sending scalding water to someone in a shower.  

If you can generate all of your hot water in the summer, and then 30% or 50% in the winter, you probably have a system that has the optimum payback.  

--Lawrence Lile, PE, LEED AP, CEM

> -----Original Message-----
> From: greenbuilding-bounces at lists.bioenergylists.org [mailto:greenbuilding-
> bounces at lists.bioenergylists.org] On Behalf Of Lynelle Hamilton
> Sent: Friday, December 31, 2010 7:38 AM
> To: Environmentally-preferable design, construction, building elements
> Subject: Re: [Greenbuilding] one more pleasure (or not) of heating with wood
> 
> I agree with John. My house had to have a "primary" heat source, even
> with R-42 in the walls, R60 in the ceiling, R-34 in the floor,
> Thermotech windows etc. etc. and a /wonderful /masonry heater. Everyone
> who has looked at the house has said that the heater will actually be
> the primary, but it can't be designated as such. Thus, I have a propane
> fired high efficiency tankless heater to drive the radiant and provide
> hot water, and a /lot /of redundancy.
> 
> I've had really mixed reviews on using solar for pre heat---what do I do
> with the excess heat in the summer, as I have no pool to heat! Winter
> gain here, southeastern Ontario, is not great, given cloud cover.
> 
> Lynelle
> 
> On 30/12/2010 23:52, JOHN SALMEN wrote:
> >
> > If I can make a bad analogy - a woodstove is like a diesel tractor -
> > can be abused and keep on running - whereas a 'heating system' is for
> > a consumer something more like a car that needs to be kept current and
> > have all the bells and whistles - something big with a big logo (has
> > to have a lot of 'tonnage'). Not sure which is better but both have a
> > degree of stubbornness, and chauvinism attached to them.
> >
> > That said - wood is no longer technically a primary heating system in
> > houses based on insurers requirements and costs for insurance so there
> > will always be some other 'primary' form of heating in place.
> >
> > I have a love-hate thing with woodstoves. Based on the love of the
> > form and quality of the heat and our rural life we used it for years.
> > My hatred stems from the basic pollution of a wood stove and how they
> > fail and the consequences of that failure in 'wood burning
> > communities'. I spent the majority of my life in heavily polluted
> > cities and where I live now rurally is quite pristine in terms of air
> > except in the winter where levels can exceed an urban smog index. This
> > is true of a lot of rural communities in the world.
> >
> > This can be improved upon and a masonry stove is the ultimate (and the
> > only option that I have flogged) but that is a major investment and
> > generally is only purchased by people that can afford it as a
> > secondary major heat investment and decoration. The default for people
> > is the basic low cost (approved?) plate steel woodstove which breaks
> > down very quickly - loses efficiency and subsequently doesn't meet any
> > of the emissions standards they are supposed to and then goes on being
> > used for a decade or so. The classic cast iron stoves work well but
> > still need to be maintained on a regular basis to meet emission
> > standards and at a certain point need to be totally overhauled.
> > Historically in my area the classic loggers woodstove was a 50 gallon
> > drum with a door and flue welded on to it. Our community is currently
> > offering $500 rebates to 'anyone' that will turn in an old stove and
> > get something a little cleaner to pull in those 30 yr old stoves.
> >
> > What got to me personally is that regardless of how well I had planned
> > burning we are subject to rapid weather changes - including inversions
> > and wind patterns that could quickly create a negative pressure and
> > bring that smoke back into our house. That was not the environment I
> > had planned for my children despite the romance of the wood fire and
> > the easy access I have for wood. We have switched to a hot water
> > radiant system that is being converted now to solar - still not ideal
> > but I think an improvement in the community and for my household.
> >
> > John
> >
> > _JOHN SALMEN ENVIRONMENTAL DESIGN_
> >
> > /4465 UPHILL RD//,. DUNCAN, B.C. CANADA, V9L 6M7/
> >
> > /PH 250 748 7672 FAX 250 748 7612 CELL 250 246 8541/
> >
> > /terrain at shaw.ca///
> >
> > ------------------------------------------------------------------------
> >
> > *From:*greenbuilding-bounces at lists.bioenergylists.org
> > [mailto:greenbuilding-bounces at lists.bioenergylists.org] *On Behalf Of
> > *Reuben Deumling
> > *Sent:* December 30, 2010 5:44 PM
> > *To:* Greenbuilding
> > *Subject:* [Greenbuilding] one more pleasure of heating with wood
> >
> > We've had lots of fun on this list lately enumerating these pleasures,
> > but one that hasn't been mentioned occurred to me this week.
> > I've been helping several folks upgrade their furnaces lately--natural
> > gas furnaces, heat pumps, etc. Anyway, in the course of these
> > upgrades, I've realized one must trust the experts (of which I am not
> > one) to assess the value of upgrading from, say, one 1970s vintage
> > heatpump to another, new, 'high efficiency" heatpump. Not for me,
> > these kinds of upgrades. Lots of money and the damn thing still runs
> > on fossil fuels. But back to the matter at hand: a wood stove lasts.
> > This may be my favorite characteristic at least of well made European
> > ones (I am not familiar with other styles). There isn't really
> > anything or at least not much of anything to wear out--and they have
> > nice lines that don't go out of fashion. I've now replaced some cast
> > iron baffles and heat shields in several Morso stoves, and recemented
> > some of the seams, but other than that, there's not much to be done.
> > The stove I'm most familiar with my parents bought new in 1981. It has
> > been heating their houses for thirty winters straight. I don't see why
> > it wouldn't do another 30 or even 60.
> > In this field, where we breathlessly follow the newest most efficient
> > wizzle-beep, it is nice every now and then to stop and appreciate the
> > stuff that lasts, that was always good, that we aren't likely to
> > improve on any time soon.
> >
> > Reuben Deumling
> >
> >
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