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'[OT:] Solar water heating economics'
2005\02\09@192214 by Richard.Prosser

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I'm looking into the possibility of getting some solar panel for hot water
heating and I've just got some rough costings that seem to point pretty
clearly toward it & would appreciate comments.
The basics are that I can get a system installed for $NZ4000 and get an
interest free loan over a 3 year term to cover it.

The Figures are :-

Monthly Power Bill (averaged over year) - $250
% spent on water heating 66% Estimated (will have to look into this) = $165
/ month water heating costs
% Replaced by solar panel (according to the shop)  - 66%
= $108.9/month saved.

$4000 over 3 years, interest free = $111 / month.

i.e. After 3 years at my current costs I will get 67% free hot water. If
the price of power increases I will start saving sooner.

Any comments on the figures? - particularly the claim wrt 66% power
reduction in hot water heating using the solar panels.

Incidentally, these are standard panels, no heat pipes or evacuated tubes,
just black panels with a glass cover.

Richard P

2005\02\09@193105 by Bob Axtell

face picon face
I think that is very close to being correct. But do you get much sun
where you live?
I've got plenty of sun here, easy to loan some.

--Bob

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2005\02\09@200621 by Richard.Prosser

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Christchurch NZ, ~42 degrees south.  About 1974 sunlight hours per year on
average.

I'll take you up on that loan in about 6 months - We've got pleanty
ourselves at the moment.

RP



I think that is very close to being correct. But do you get much sun
where you live?
I've got plenty of sun here, easy to loan some.

--Bob

Richard.ProsserspamKILLspamPowerware.com wrote:

>I'm looking into the possibility of getting some solar panel for hot water
>heating and I've just got some rough costings that seem to point pretty
>clearly toward it & would appreciate comments.
>The basics are that I can get a system installed for $NZ4000 and get an
>interest free loan over a 3 year term to cover it.
>
>The Figures are :-
>
>Monthly Power Bill (averaged over year) - $250
>% spent on water heating 66% Estimated (will have to look into this)
= $165
{Quote hidden}

2005\02\09@202832 by Jinx

face picon face
> % Replaced by solar panel (according to the shop)  - 66%

Is that a local opinion - ie does it take into account the sun
angle at that latitude ? Could you / would you include a
tracking mechanism ?

2005\02\09@210932 by Russell McMahon

face
flavicon
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> I'm looking into the possibility of getting some solar panel for hot
> water
> heating and I've just got some rough costings that seem to point
> pretty
> clearly toward it & would appreciate comments.
> The basics are that I can get a system installed for $NZ4000 and get
> an
> interest free loan over a 3 year term to cover it.
>
> The Figures are :-
>
> Monthly Power Bill (averaged over year) - $250
> % spent on water heating 66% Estimated (will have to look into this)
> = $165
> / month water heating costs
> % Replaced by solar panel (according to the shop)  - 66%
> = $108.9/month saved.
>
> $4000 over 3 years, interest free = $111 / month.

I'd be (VERY) doubtful about that claimed rate of return. I've done
some figuring based on Auckland NZ conditions.
Key questions are, what is the panel area for that money and what
efficiency do they claim. You can find mean daily sunlight hours month
by month for various locales on the web.  I have some here but
shouldn't spend too much time on this right now - ask if you can't
don't suitable figures. As a guide from (failing) memory Auckland does
about 8 kwH/day/m^2 in best summer month and about 2.5 kWh/day /m^2 in
worst winter month. Average that at 4 units/day/m^2. So annual input
is 4 x 365 = 1440 units. Pricing power at $NZ0.15/unit (and it's less
here at present) thats about $220 per year if you get 100% use of the
insolation. Which you don't. There is panel loss, distribution loss
and any ancillary mains power costs (which should be low). Say $200
pa/m^2.

Googles - here's a worldwide table.
Only has WN NZ but should be a good guide.

       http://energy.caeds.eng.uml.edu/solbase.html


To get a 3 year payback that $4000 panel would need to be
$4000/$200pa/3 years = 6.7 m^2. Is it? If it was a 1.2 x 2.4m panels =
2.88 m^2 with perhaps a 2.5 m^2 effective area that would give a
payback of $4000/$200/2.5 = 8 years. And I'd be pleasantly surprised
if that worked out. And that's in Auckland. In Winter the weekly
savings are about $2 and in summer about $8.

I have some ideas for LOW cost air solar heating which may allow home
heating at reasonable cost and payback time. You may wish to discuss
some time.

Above figures assume the $4000 is an all up figure and that it
requires zero maintenance.

Working his savings backwards -
$111/month = $3.50/day = 23 units =~ 6 m^2 of panels.
How large are they?
Less than 6 m^2 I suspect.



       Russell McMahon


2005\02\09@214349 by Richard.Prosser

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This was what I was told as being applicable for Christchurch as installed
- without tracking (which would be complicated).
I guess that verification of  this figure is basically the question I am
asking. Is it "reasonable"  allowing somewhat the large number of variables
involved.
(Size of panel, hot water usage etc.) I am hoping someone in a similar
climate already has this information.

RP





> % Replaced by solar panel (according to the shop)  - 66%

Is that a local opinion - ie does it take into account the sun
angle at that latitude ? Could you / would you include a
tracking mechanism ?




2005\02\09@215405 by Richard.Prosser

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face

Just looking at the handouts.
The panel size on the costing sheet is named differently from the ones on
the
glossy handout but they are :-
2 sqr m
3.1 sqr m
4.409 sqr m.

I suspect the cost sheet is for the middle one & I'll need the larger
variety (at least).

RP

Russell McMahon
....
Working his savings backwards -
$111/month = $3.50/day = 23 units =~ 6 m^2 of panels.
How large are they?
Less than 6 m^2 I suspect.



2005\02\09@221519 by Russell McMahon

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> asking. Is it "reasonable"  allowing somewhat the large number of
> variables
> involved.

There's only ONE key variable we don't know.
viz: What is the panel area they are offering for $4000. All the rest
can be figured well enough from that.


       RM

2005\02\09@235746 by Russell McMahon

face
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> The panel size on the costing sheet is named differently from the
> ones on
> the
> glossy handout but they are :-
> 2 sqr m
> 3.1 sqr m
> 4.409 sqr m.
>
> I suspect the cost sheet is for the middle one & I'll need the
> larger
> variety (at least).

   3.1 x 3 kWh/m^2 * $0.15 x 365 = $600 pa saved.

Average of 3 kWh/m^2/day seems more likely for Christchurch.
Also panel area will be less than full size.
also panel efficiency < 100%.
Possibly far less for a non leading-edge design.


       RM

2005\02\10@141829 by Howard Winter

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Russell,

On Thu, 10 Feb 2005 15:04:32 +1300, Russell McMahon
wrote:

> Googles - here's a worldwide table.
> Only has WN NZ but should be a good guide.
>
>         http://energy.caeds.eng.uml.edu/solbase.html

It also, unless mt eyesight really is going, has no
mention of any of the UK!

Cheers,


Howard Winter
St.Albans, England


2005\02\10@143316 by Bob J

picon face
The thing you have to weigh into your payback formula is
maintenance...how much will it cost you if one of the major components
goes out.  That is what financially will typically kill alternative
heating/cooling projects.  I looked at gettting a geothermal
heating/cooling system for our new home.  Everything looks great on
paper and there are real possibilities of getting a  good return on
your investment ONLY if the equipment works that long.  I spoke to a
few people that had geothermal systems that ended up switching back
when it was going to cost them $4000 to dig the yard up to put a new
loop in because there was a leak somewhere.  That was on top of, in
one owner's case I talked to, the repair expenses associated with
pumps going bad, evaporator coils going bad due to corrosion, etc.
Long-term the total cost of the geothermal system cost more to operate
and maintain than a high-efficiency gas furnace with conventional
air-conditioning.  And being down with no heat for a long period of
time in the winter for repairs obviously isn't a good thing.

One of my neighbors had an older (early 1980's) solar hot water
heating system and he removed it last year...too problemmatic and too
expensive to fix, and lukewarm water on top of that.

If you really want to see a payback on reducing your home energy
costs, spend some money insulating your house.  Our new home has a
R-60-insulated ceiling and all exterior wall panels are SIPS panels
see http://www.sips.org.  Our old home, which is less than half the size,
cost more to heat than the new one.  I don't know how many cans of
stuffit expanding foam I went thru, quite a few tho.  I got a little
obsessed with it :)

I'd advise talking to people that have had such a system as you are
looking at, and see how happy they are with it.  Don't bother talking
to people who have only had the system for three years, you want to
talk to the ones that have had it for 7-10 years.  Typically you will
hear something quite different than the sales pitch.

Regards,
Bob  


On Thu, 10 Feb 2005 13:22:40 +1300, .....Richard.ProsserKILLspamspam.....powerware.com
<EraseMERichard.Prosserspam_OUTspamTakeThisOuTpowerware.com> wrote:
{Quote hidden}

> -

2005\02\10@150852 by Richard.Prosser

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According to NIWA Christchurch & Wellington are about the same - approx
13-14MJ/m2 per day (averaged over a year).
(from the code of practice
<http://www.solarindustries.org.nz/documents/041224%20master%20SWH%20COP.pdf>)

This only works out to ~156 watts/m2 though so its not adding  up. I need
to figure out what I'm doing wrong.

(On a second look 156watts averaged  is 3.744kWh/day so not too far from
your figure of 3kW/hr/m2. On this basis savings would be
3.744 x 0.15 x 365 x 3.1 = $635/year at 100% conversion - still a long way
off what was indicated to me.)
The larger panel would save $840 a year which is getting closer but still
less than advertised.

As you note, I don't think the efficiency of the simple panel will get
anywhere near 100%.
The evacuated glass tube types do get up to 80-90% IIRC but convection
losses in the flat panel
types limit their efficiency particularly if the ambient temperature is
low.
I guess "efficientcy" is really a misleading term. Losses will depend on
the
maximum temperature difference reached, while efficiency can be measured at
a very low temperature rise
where heat losses to the outside are at a minimum. The code of practice
(above)
only requires that a "measurable" temperature difference be used when
evaluating onsite.

I'd like to get a price on the evacuated glass types but suspect that they
may be exorbitant.
I did have a thought about making my own using old flourecent tubes and
home-made heat pipes but
figured I may have problem getting a good enough vacumn and maintaining it.
May not go down too well
with "the boss" either unless  it's well hidden from view. Hail damage
could be a problem also.

I'd still like to have a play with the idea however when I get the time !!

Richard




{Quote hidden}

   3.1 x 3 kWh/m^2 * $0.15 x 365 = $600 pa saved.

Average of 3 kWh/m^2/day seems more likely for Christchurch.
Also panel area will be less than full size.
also panel efficiency < 100%.
Possibly far less for a non leading-edge design.




2005\02\10@153155 by Bob Axtell

face picon face
A lot of folks tinker with solar and wind energy here in AZ.

I seems that passive solar heating is not as much fun as concentrated
forms. Its similar to the standard  way, except that a large reflective
metal
parabola reflects onto a black steel pipe. It concentrates heat very well,
even generating some heat at night with a full moons! The advantage of
it is that a
sensor can sense when it is NOT putting out heat, so can cut off the unit
and let regular heating sources generate it instead.

Seems like these things are about  3 meters long, and 1.5m wide, about
1m high.
Another advantage- the pipe are partially protected from the wind.
During the summer, the
unit generates water at 90C or more.

--Bob



Richard.Prosserspamspam_OUTPowerware.com wrote:

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2005\02\10@153321 by Richard.Prosser

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face

Thanks Bob,
This is the type of information I am trying to find out. The problem is
that due to cheap power in NZ (at least in the past) there are not too many
7 year old systems around.
Our house is only 16 years or so old and is reasonably well insulated
(walls & ceiling - although only single glazed) and we use a heat pump for
heating so energy costs are not too bad  in this regard. But hot water is a
different story. Hence I'm looking at the options.
As an indicator, during cold weather with the heater running close to full
time, the power bill is only about 30% more than during warm weather when
no heating (or cooling) is required. The hot water usage is prettymuch the
same for both cases, although I guess the input water temperature varies by
a few degrees as well.

Richard



The thing you have to weigh into your payback formula is
maintenance...how much will it cost you if one of the major components
goes out.  That is what financially will typically kill alternative
heating/cooling projects.  I looked at gettting a geothermal
heating/cooling system for our new home.  Everything looks great on
paper and there are real possibilities of getting a  good return on
your investment ONLY if the equipment works that long.  I spoke to a
few people that had geothermal systems that ended up switching back
when it was going to cost them $4000 to dig the yard up to put a new
loop in because there was a leak somewhere.  That was on top of, in
one owner's case I talked to, the repair expenses associated with
pumps going bad, evaporator coils going bad due to corrosion, etc.
Long-term the total cost of the geothermal system cost more to operate
and maintain than a high-efficiency gas furnace with conventional
air-conditioning.  And being down with no heat for a long period of
time in the winter for repairs obviously isn't a good thing.

One of my neighbors had an older (early 1980's) solar hot water
heating system and he removed it last year...too problemmatic and too
expensive to fix, and lukewarm water on top of that.

If you really want to see a payback on reducing your home energy
costs, spend some money insulating your house.  Our new home has a
R-60-insulated ceiling and all exterior wall panels are SIPS panels
see http://www.sips.org.  Our old home, which is less than half the size,
cost more to heat than the new one.  I don't know how many cans of
stuffit expanding foam I went thru, quite a few tho.  I got a little
obsessed with it :)

I'd advise talking to people that have had such a system as you are
looking at, and see how happy they are with it.  Don't bother talking
to people who have only had the system for three years, you want to
talk to the ones that have had it for 7-10 years.  Typically you will
hear something quite different than the sales pitch.

Regards,
Bob





2005\02\10@162138 by Jinx

face picon face
> >         http://energy.caeds.eng.uml.edu/solbase.html
>
> It also, unless mt eyesight really is going, has no
> mention of any of the UK!

"Sitting in an english garden waiting for the sun,
If the sun don't come you get a tan from standing in the english rain"


2005\02\10@184906 by James Newtons Massmind

face picon face
We have done the following so far, all prices include installation except as
noted:

- solar water heater $1000 (some effect, we might have saved $10/month)

- tile floor in kitchen $800, self installed (some effect, the kitchen floor
stays cool year round)

- insulation $200, self installed (some effect, minor if any)

- double pane windows $8,000 (considerable difference in sound and
temperature isolation. Cooling/heating bill dropped about $20/month.)

- hardwood floor $8,000 (total waste. Looks nice, but no return on
investment other than a happy wife)

- wood stove $4,000 (WOW! Heating bill eliminated! About $100/mo savings for
the 4 or so months that heating is needed at night. Maybe $40/month overall)

The PV system ($11,000 gasp) will be installed at the end of this month. It
will have a 471 KW capacity averaged over summer and winter months. It MAY
save about $100 to $150 per month in electric use.

If you add all that up, we have increased our debt (home equity loan) by
$32,200 in return for a monthly savings of about $200. This is a payback of
161 months or 14 years. All the items mentioned have a service life better
than that with the exception of the wood stove, which will need to be
rebuilt ($500) every 5 to 10 years or so, but at a payback of 100 months or
8 years, it's well worth it.

If I had it to do over again, I would do:
- the wood stove, since it doesn't matter if you are insulated, you just
load it up and bake! And I would install it. Same stove would be $2800, we
got ripped on the shipping and install.
- the PV system (probably)
- double pane windows (perhaps)

And I would skip the insulation (total waste) and solar water (mostly a
waste). I would do tile rather than hardwood through the entire house and I
would lay it myself. A nice slate in the living room and ceramic glazed with
some pattern in the bedrooms. The white glazed tile in the kitchen shows ANY
dirt, but that just means we keep it clean. I think a house with tile floors
would make good use of the cold night air and stay cool in the day with the
double pane windows closed up tight.

I would also spend money to try out some of these ideas:
http://www.massmind.org/other/spac
http://www.massmind.org/other/cooltower
http://www.massmind.org/other/windmills

If you want to save money, I would do a wood stove and look into an
attachment to allow it to heat water. I'm amazed at how much firewood is
available free for the cutting and moving.

Now, if I could just rig up a generator to it...

---
James.



> {Original Message removed}

2005\02\10@210320 by Jinx

face picon face
> - wood stove $4,000 (WOW! Heating bill eliminated! About
> $100/mo savings for the 4 or so months that heating is needed
> at night. Maybe $40/month overall)

Richard lives in an area particularly susceptible to winter inversions
which causes a lot of smoke to hang around, causing pollution and
health concerns. New environmental laws have been introduced to
make wood burner installations more efficient and cleaner. No open
fireplaces in Christchurch from next year for example, and older stoves
must be replaced as of last year. If you use wood/coal/gas it's sensible
to insulate and have a wet-back for hot water

Me ? Woolly hat and jumper ! Hardly ever cold during winter and seldom
put a heater on. A lot of "complaining" about the cold is unnecessary, and
it's pretty easy to get warm

2005\02\10@211331 by Russell McMahon

face
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Consider solar air heating into a rock or water reservoir.
Make it yourself. As a (very) background task i'm looking at doing
this here. Cost per energy should be able to be far far lower than for
solar water heating or Photovoltaic. I have some low cost low-lifetime
panel ideas which SHOULD give a better ROI than more permanent
materials - and if it doesn't work as well as hoped the capital cost
is far lower and you can walk away from it easier/sooner/happier.

Air has far lower mass than water so roof loading is not as great an
issue. Roof area available to me is large enough to allow much much
larger panels than are usually used for water-solar, due to cost. Rock
or water thermal storage allows days at a time low/no sun days.


> If you add all that up, we have increased our debt (home equity
> loan) by
> $32,200 in return for a monthly savings of about $200. This is a
> payback of
> 161 months or 14 years.

Adding in the hardwood floor isn't really correct as it wasn't (I
assume) an energy saving issue. Wife happiness is crucial but is
included in other budget entries. So it's about $24,000 for $2400
savings pa or about 10 years payback at linear payback. That's far
longer in real terms due to dsicounted cash flow. Depends on interest
rate you use. In $ terms it's probably only marginally worthwhile ;-(/

Now, air solar ... :-)


       RM

2005\02\11@000834 by Vern Jones

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face
Hello Richard,
I have waited until now to respond to this. I have long term experience with
living in a Solar house. My Hotwater heating system is what is known as a
bread box (2-40 Gallon tanks in an insulated box with about 2 sq m surface
area with a glass top. I initially had an on demand backup heater (AC
Powered) this was a nice idea, but cost more in maintenance than it saved. I
replaced it with a conventional 40 gallon hot water heater, and changed the
computers code to bring it on only when needed (it's been there 21 years)
The solar hot water heater has been there 25 years. Since every thing except
the blowers and shutters are passive every thing has worked well for 25
years. I had to replace a blower motor about 10 years ago ($50 USD) The
original Solar hot water heater was $1800 with a tax rebate of $900 at the
time.

Wood heat is used as the backup source of heat (only needed when there is
cloud cover for more than 2 days in the winter).

Summer cooling is provided with Cool Tubes (large plastic pipes buried under
ground) air is pulled through these by a blower.

Powered louvers are used for controlling air flow for heating or cooling.
Under the house is an insulated rock storage area with an area if 118 cubic
meters. Cooling and/or heating air is circulated through this storage area.

Controlling this system was a Z80 with Analog temperature inputs and Relay
outputs for the fans, blowers and louvers.

This all worked fine until a couple of months ago, ZEEK, my old trusty Z80
died this winter, so things haven't been working too well. I am in the
process of building a new computer control system to take over the duties of
house sitting. (25 years of service with a Z80 working 24x7) The e-proms
were only supposed to be good for 10 years.

Overall when comparing utility bills, this system has saved about $60 to $80
per month for the last 25 years. The only real failure was the On Demand hot
water backup heater. I had 3 major falures requiring complete replacement of
the unit, and 1 partial replacement. The unit was $400 USD in 1980. A
conventional heater was about $100 and $40 for a contactor to control it and
some added code for ZEEK.

If I had it to do over, I would make very few changes. The major key to the
success of this is low tech devices controlled with a fairly simple high
tech device. Heat/Cool storage and lots of insulation.

Vern
{Original Message removed}

2005\02\11@063031 by Mike Hawkshaw

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face
An old friend of mine has done solar water heating in the UK.

His web page is here:
http://www.anotherurl.com/therm/

He has used a pic and DS1820s to do monitoring and control the pump etc.
Some useful info here.

Cheers.....Mike.

2005\02\11@103954 by Howard Winter

face
flavicon
picon face
Russell,

On Fri, 11 Feb 2005 15:13:24 +1300, Russell McMahon
wrote:

> Consider solar air heating into a rock or water
reservoir.

The Centre for Alternative Technology, near Machynllyth
in Wales, did an experiment using an underground water
tank for heat storage - I don't know if the write-up is
still on their site (http://www.cat.org.uk) but I d
remember it wasn't as successful as they'd hoped, and
they discontinued it after a year or two.  I seem to
remember the biggest problem was insulation - they had
*a lot*, but it wasn't enough.  They used a drip-roof to
collect the heat, I think - how would you transfer the
heat from hot air to the water?  That seems to me rather
trickier than the other way round.

Cheers,



Howard Winter
St.Albans, England


2005\02\11@121633 by Josh Koffman

face picon face
Ok, first disclaimer, I have no idea what I'm talking about. Now that
I've said that, could you do some sort of aparatus that bubbles the
hot air through the water? I don't know how efficient this would
be...I'd imagine smaller air bubbles would transfer heat better, but
that's just a guess.

Now shoot down my crackpot idea (but you have tell me why it won't work) :)

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

On Fri, 11 Feb 2005 15:39:51 +0000 (GMT), Howard Winter
<KILLspamHDRWKILLspamspamh2org.demon.co.uk> wrote:
{Quote hidden}

2005\02\11@150720 by James Newtons Massmind

face picon face
I agree air solar is very interested... I should put up a page on it: Have
any content to share?

---
James.



> {Original Message removed}

2005\02\11@170355 by Russell McMahon

face
flavicon
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> ... how would you transfer the
> heat from hot air to the water?  That seems to me rather
> trickier than the other way round.

If using rock it's "easy" - blow air through suitable sized rocks in
rock bed.

Water - I don't know in detail what others do, but I suspect that PET
bottles are about right in several respects. I've tried using them for
solar storage on a trivially small scale and haven't done any maths on
it yet.  Stack PET bottles filled with suitably dyed water in
insulated containers. They stack nicely, are adequately strong and I
believe will last 10+ years. Maybe much longer but I'm not aware of
lifetime tests on these. When using for direct absorption of
insolation dye water therein such that sun is just discerned through
bottle when held to sun.


       RM

2005\02\11@170402 by Russell McMahon

face
flavicon
face
> Ok, first disclaimer, I have no idea what I'm talking about. Now
> that
> I've said that, could you do some sort of aparatus that bubbles the
> hot air through the water? I don't know how efficient this would
> be...I'd imagine smaller air bubbles would transfer heat better, but
> that's just a guess.
>
> Now shoot down my crackpot idea (but you have tell me why it won't
> work) :)

It would work.

But water would be evaporated far faster than you'd like and the
energy required to pump air through water adds to energy losses.


       RM


2005\02\12@072227 by Jake Anderson

flavicon
face
just so long as you pump this nicley filtered air into your home.
(and get rid of the crud that will get filtered out on a regular basis ;->)

> {Original Message removed}

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