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home build heater possible?

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Posted by efmamj_jasond on October 21, 2004, 3:49 pm
 
Any advise in self building a solar heater?

Is it possible?

Many thanks,

Daniel




Posted by Gary on October 22, 2004, 1:16 am
 
efmamj_jasond wrote:


If you provided a bit more info it would be easier for people to give
you useful advice:
How much space you have, how is the space oriented, do you want to
heat water for showers etc, or do you have in mind space heating, are
you thinking about a big project or a small one, approximately where
are you located...?

Gary

Posted by efmamj_jasond on October 22, 2004, 2:45 pm
 Gary, Anthony,

Many thanks for your answers.

More details:

Location: Chile, (3326'S) Near Santiago
Roof orientation: North
Available space: Plenty!. (12 mts x 5 mt roof)
Target: just shower/dish washing warm water. less than 100 lt/day
Project size: Small

Main advantages: very hot summer during summer, fwe cloudy days
Main disadvantages: some days ice temperatures (below 0oC) before sun shine
during winter.
Roof cannot support a very heavy structure (no more than 50Kg/sq mt) so as
collector might be outside, but warm water recipient should be located
between cieling and roof.
Water pressure, low (less than 0,6 ATM ~ 8 PSI)

Want to use solar heater as an alternative to an existing gas heater during
summer to save money and avoid pollution.

Will appreciate any advise, recomendation, reference, etc.

Questions:

- Can be collector element soldered with normal procedures? (i.e. plumb
soldering)
- Is it possible to use "thermal pump" (dont know how to say in english,
sorry) in a split design? (i.e. collector separated from warm water storage)
- which is the best material for water storage? inox steel tank? cooper
tank?
- best (cost effective) suggested isolation?

saludos,

Daniel.

PS, sorry if my english is a little rusty, long time no practice.





Posted by Gary on October 23, 2004, 1:29 am
 efmamj_jasond wrote:

see below

Here are a couple potential solutions to think about:

BATCH HEATERS:
Batch (also called passive or Integrated Collector/Storage) heaters:
These heaters combine the collector and the tank in one unit.
They are the simplest and least expensive systems, and they make a
pretty manageable Do It Yourself project.  Basically, they consist of
a hot water storage tank enclosed in a glazed box.  Cold water flows
into the tank, is heated by the sun, and then flows to your regular
hot water tank where it is heated more if its not already hot enough.
There are no pumps, controllers, antifreeze, ... its as simple as it gets.

Here is a sample commercial one with full specifications and
installation instructions (so you can get an idea how they work):
http://www.sunearthinc.com/copperheart_system.htm
(there is a lot of water heating info on this site if you look around)

This link as plans for a simple batch heater that could be built for
very little if you can find an old hot water tank to use for the
collector tank:
http://www.solaror.org/Publications/Batch_Plans.htm

For your situation, some of the pros and cons for a batch heater:
Pro:
Simple and cheap
Relatively easy to build
Will probably provide almost all of your hot water in summer
Low maintenance -- not subject to scaling problems,
                antifreeze problems, component failures, ...

Con:
Subject to freezing in cold weather
Weighs a lot
Tends to lose a lot of heat over cold nights

The freezing can be addressed by draining the system in the coldest
months.  For your occasional below freezing mornings, just insulating
the pipes to the collector should be sufficient.  The tank itself does
not freeze easily because there is so much mass.  You can extend the
season of a batch collector by providing an insulated cover that you
put over the glazing at night (maybe hinged like a door).  This
prevents the big heat loss at night through the glazing.

A 50 gallon batch heater will probably weigh over 500 lbs when full.
Because the limitations of your roof, you might want to build in on
the ground, or spread the load over a good sized section of roof.

CLOSED LOOP COLLECTOR/TANK SYSTEMS:
These systems use a roof mounted collector and a separate hot water
storage tank.  A non-toxic antifreeze solution is circulated through
the collector and then through a double wall heat exchanger where it
transfers heat to the hot water storage tank.  This is a much more
complex system.  In addition to the tank and collector, there are
typically one or two pumps, a heat exchanger, a differential
controller, an expansion tank, and a bunch of miscellaneous valves and
air purgers.  As  Do It Yourself project, its a pretty substantial
undertaking (but doable).  Most people who build their own buy the
components, and assemble and plumb them.   You can take this a step
further by also building the collector, but this is a non-trivial task.

The Pro/Con for the closed loop:
Pro:
Not subject to freezing -- will heat water all year
May provide a greater percentage of your hot water
Roof mounted collectors are light weight

Con:
More complex and expensive
More difficult to build
More maintenance

I'd suggest that you take a look at the first few HomePower articles
at this link:
http://www.homepower.com/magazine/downloads_solar_thermal.cfm

These are free downloads, and they cover both closed loop antifreeze
systems and drainback systems.  They should give you a good idea of
what you would be tackling.

If you decide to go this way, here are a couple potential ways to save
some money at the cost of more of your labor :-)

Build the entire collector yourself from copper tubing and copper
sheet (lots of soldering).  I have seen plans for doing this on the
Internet.

Buy the collector absorber panel preassembled, but build the rest of
collector -- several places will sell just the absorber plates e.g.:
www.solarenergy.com
This cuts the collector cost from about $5 per sqft to as low as $0
per sqft (depending on glazing).

Make the heat exchanger by wrapping soft copper tubing around the
outside of the hot water storage tank -- this also eliminates one of
the pumps.  The tubing needs to be thermally bonded to the tank (maybe
someone knows a good way to do this?), and then insulated over.

---
A final note: if your current gas hot water heater is a conventional
gas heater (i.e. a tank with flue passage up the middle), it will have
fairly high standby losses even if the water coming into to it is hot.
You may be able to completely turn it off during the summer, and avoid
these standby losses.


Gary










Posted by efmamj_jasond on October 25, 2004, 8:40 pm
 many thanks for your vere complete ansewr.

my problem is how to buy these kind of devices here in Chile.

anyway, where could I get a very simple block diagram of a "closed loop
collector/tank system" in order to understand the usage of both pumps,
differential control, etc.

on the other hand, my house has solar generated electricity, so devices
working 100% of the day must be 12V, otherwise, the inverter will kill the
batteries soon. mmmmmmmm.....




storage)


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