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Scott Davis

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Reply with quote  #1 

Solar hot air, solar hot water and solar electric are all options. Which is best?

All three options are great projects, I've built all three and they each have their advantages. One of the goals of the SimplySolar e-mail group is to keep solutions as simple as possible, so air and water based systems get the most focus here. They are very safe, much less expensive and offer a much quicker payback.

Air and water based panels of the same size each capture about the same amount of heat. These are the main points to consider in choosing:

Factors to consider for Air:

Air Pros:

- Very easy to build

- Freeze protection is unnecessary

- Least expensive with quickest payback

- No need for thermal storage as heat is used immediately

- Almost instant heat when the sun is shining

Air Cons:

- Panels usually are situated nearer the house, though good success has been obtained with outdoor buried ductwork

- Thermal storage is more difficult

- Larger ductwork required

- Larger holes in house

- Difficult to use for solar domestic hot water

 

Factors to consider for Water (hydronic):

Water Pros:

- Lots of flexibility in panel placement

- Build as big as you like

- Easy to bring small pipes into house

- Easily transport heat where you want

- Ability to store heat in an easy to construct thermal storage tank (which can be used simultaneously for domestic hot water and space heating)

- Still have heat on cloudy days (as long as there aren't too many in a row)

- Heat can be distributed in a more controlled and comfortable manner by installing an under floor radiant heat system

- Easier to insulate pipe

- By using the panels for both space heating and hot water, they are useful year round

Water Cons:

- Slightly more difficult to build than air, but not much more.

- Freeze protection is required - accomplished by either installing a drain back system so that the water is in a warm environment when the sun isn't shining or adding antifreeze and leaving the water continually in the loop.

- If you want to store heat (optional), you'll need a thermal storage tank. They are easy and inexpensive to build, but they will require some space in your basement, crawl space, garage or outdoors.

- For space heating, you'll need to install a distribution system such as under floor radiant heat or baseboard heat (but that can be done easily and inexpensively).

In summary, for an inexpensive infusion of quick heat as long as the sun is shining, air is a great option. For a more controlled distribution of heat with storage and the ability to heat your solar domestic hot water, a water system is the way to go. They both have their place and I'm happily using both here.


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Take care, Scott MD

SGT1

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Reply with quote  #2 
Wonderful general simple and hi-tech info for all, I have reson to believe!

Screen air solar (SolarTec 1980) are still running today as
Space heating

Electronic and Paper Media Air "Cleaning"

Water heating (hybrids of simplicity)


The HW was not as dificult since common fancoils are in distributors' stock all over the country and designed for HW radiating - but work fine for heat reclaim from a closedair solar and insulated tubing ducting.

When it fits the Air Solar combo space heating and HW make-up  only requires a vinegar flush each year inside at the fancoil ALfinCUtube Heat Exchanger (HX), and maybe a drop of oil on the blower if not sealed.

The 3-layer-screened (common 500 deg baked door screen off a roll)  collectors produced a little over 3000 btuh in Dayton OH normal to the sun on winter days, on 8 x 4 ft area collectors.
2) 3x10's special, cooked a 11700 sq ft Miami OH "pantek" styro and board home (house required 6kw in worst peak day of any coldest winter since 1980)

Plumbed for watching thermal siphon issues and ducted for resisting winter-off cycle cooling by cold air dropping down the ducting to a fancoil that would be at a floor level - were both important. A peanut 33w circulator was fine for upto 2 (?3) collectors.
An hour of heating at over 40,000 btuh was easy in one 119 gal HW tank for a big blast in homes under 2500 sq ft.  6 Collectors was almost too big in 3500 sq ft ranch and cooked HW in an 80 gal tank way faster than a couple could use all summer for most the need.

The first systems had almost hand made 3-way duct diverter, and a simple zone motor damper 24v.
Other simple devices were ? ALCO induction relay that we wired the pigtail hot down hot back at plugg (if you touched-closed the prongs, the fan came on) -into the cube relay that (like relay in a box with a transformer) but used the coil as the transformer, as one piece unit. Two 24v wires out of the relay were closed by snap discs, controls, etc. Some just used axial fans of refg motors that ran over 25 years (dusty a bit- but 4"pleated filters worked well).etc.

The same with another advantage of Air solar is as Air-Rotation. It drew ceiling air from a warmest spot (not at first thought by some 'efficient') and distributed it to the day-time occupied ceiling registers which were re-fin-positioned to throw air straight to the floor , yielding "floor radiant heating" for one. Another advantage is the differential between the floor and ceiling room air temps went to near only 1-deg.
Today the solar Air easily (if fits) uses hvac low flow variable IQ blowers on newer furnaces and heatpumps on 'idle' to get circulation, as those motors 'seek' to meet CFM set ups.
xactdude

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Posts: 44
Reply with quote  #3 
sgt1,
the information you posted here is something I am very interested in looking at, (talking about the fan coil hw system).  do you have any links to more information on putting a system like this together?
thx
mj
ChrisJ

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Posts: 95
Reply with quote  #4 
Not sure but maybe this is what your thinking of.

http://www.altheatsupply.com/shop-by-needs/outdoor-wood-furnace-parts/water-to-air-exchangers/240-000-btu-water-to-air-heat-exchanger.html

Chris

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