Solar Water Heating

I've read a lot of books on the topic. "Solar Water Heating" by Bob Ramlow is far and away the best one I've come across http://www.arthaonline.com/bookpage.html

Silver, can you give specifics on why you liked it so well?

Some Amazon reviewers didn't think it was detailed enough in construction or purchasing info, while others just loved it.  So how was it helpful to you?

I liked a few things. I read a library copy so this is from memory.
First it was obvious to me that Bob wrote with the authority of many years as an installer of solar systems.
Bob provided what I thought was a good set of data for which systems work well in various conditions. He definitely favors the low temp collectors.
He provided plans for just hot water, a few types of heating scenarios, and how to do both.
I think he didn't provide construction information because he provided some excellent reasons to purchase over building your own collectors. As I remember he did give a few collector brand names.

Let say you are building solar water heater. You need solar collector, pipes and water tank. Is it making any sense to dig water tank in the ground?

I'm thinking of situation when you don't have good sun for days, but you want hot water. Making water tank big enough, making it of concrete instead of steel would greatly improve it thermal inertia. Then insulating it because it has to be insulated anyway, and putting it 1-2 foot below the ground surface would be measurable benefit? Solar collector could be just above it, maybe used for rain harvest (but that's not the point)

I made some drawing for the ones who don't like to read if there is no pictures, like me

Oh, dark blue is water to heat, gray is concrete tank, white is polystyrene, brown is earth, red is hot pipe, black is solar collector. And the rest is blue sky. 

I have wondered basically the same thing, seems like a workable concept.

Question:  If the red tube is operating solely on convection, the hot is going to want to stay at the top of the loop, isn't it? 

Here are some other ideas:

1) Create a larger insulated umbrella to encapsulate heat in the earth around the tank along the lines of the Annualized Thermal Inertia concept, (the ATI in WOFATI). 

2)Add extra loops through the tank using:
  a) hot compost pile
  b) rocket mass heater
The more elements support a certain function, the more resilient the system

3) If the system is really efficient, you could also add a loop under the floor for radiant heat. 

wouldn't it be easier to put a standard insulated tank inside your home (or whatever the point of use)? 

Our plan is to have the heat collector be under our south facing windows at ground level and plumbed to connect with the main tank inside the house.  The base of the tank will be above the highest point of the collector so thermosiphoning should bring the hottest water inside.

This seems like the most simple approach to me.

K.B. wrote:
wouldn't it be easier to put a standard insulated tank inside your home (or whatever the point of use)? 

Our plan is to have the heat collector be under our south facing windows at ground level and plumbed to connect with the main tank inside the house.  The base of the tank will be above the highest point of the collector so thermosiphoning should bring the hottest water inside.

This seems like the most simple approach to me.

Yes, having the collectors below the house makes sense, assuming it gets enough sun there.  But unless you are working with some kind of closed loop, the normal water pressure is going to move hot water through the collector into your tank and out your faucet when you turn on the tap, more so than convection.  I think? 

Drug Mile's idea is to have a very large tank (to store several days of hot water) plus thermal mass that would take up a lot of interior space if you tried to put it inside. 

yukkuri_kame wrote:
Drug Mile's idea is to have a very large tank (to store several days of hot water) plus thermal mass that would take up a lot of interior space if you tried to put it inside. 

And I don't want huge water mass above my head. I don't want it in the middle of the house. The only place where I would put it and go to sleep without a worry if it will leak is in the basement. And I just might put it there, dig a hole below bathroom. It is much easier to build huge tank inside hole in the ground, I think, then to make it super strong and put it in the middle of the house.

I'm trying to figure out what is better for hot water storage, to be surrounded with warm air of the house, or with little less warm earth. Who knows?

Ok, let's say this tank is in the basement. Could solar collectors be on the roof? Will the hot water go down? I believe it will. Collectors are almost vertical. There is water inside them. It is getting hot. It must go up, pushing all water to rotate "clockwise". Once the hot water is in the pipe behind the collector, it can only get colder. Why wouldn't it go down?

Is this the same?

yukkuri_kame wrote:
Yes, having the collectors below the house makes sense, assuming it gets enough sun there.  But unless you are working with some kind of closed loop, the normal water pressure is going to move hot water through the collector into your tank and out your faucet when you turn on the tap, more so than convection.  I think? 

Drug Mile's idea is to have a very large tank (to store several days of hot water) plus thermal mass that would take up a lot of interior space if you tried to put it inside. 

Ah - yes, if you are looking to have a bigger than ~50 gallons, I can see how it would be space prohibitive inside the house.

But, I think the trade off is water temp vs volume, in some ways.  A collector can heat a large volume a little or a smaller volume a lot...

With regard to the convection issue, my thought is to go with the convection loop back to the tank as a separate loop than the outlet off the tank to the faucet.  We will have gas for cooking, so I think having an on-demand gas water heater makes sense coming off the solar collector tank.

Collector up, storage down.

http://www.google.es/images?q=thermosiphon%20solar%20collector&oe=utf-8&rls=org.mozilla:en-US:unofficial&client=firefox-a&um=1&ie=UTF-8&source=og&sa=N&hl=es&tab=wi&biw=1152&bih=676

Is it ever winter where this will be? Freezing temperatures bring certain problems to the question.

mtnDon Miller wrote:
Is it ever winter where this will be? Freezing temperatures bring certain problems to the question.

For me, yes. I have long, cold winter, and freezing brings me quite a worry. I guess it would be mandatory to use some special gas? Or just a water and antifreeze?

Some use a pump and a drain back system. Power the pump with a solar panel.

If anti freeze is used it should be the propylene type so if there is a leak it will not poison anyone. RV antifreeze is propylene based.

Also need a back flow valve of some kind to prevent warm water rising from the tank and loosing heat in the collector.

Sorry for going slightly off topic, but decision to place hot water tank in the ground or in the house is related to general water plan of my site. So my general plan would look like this, I'm on the east facing slope, slope is first light but then it gets steep.

On top of the site there is a road, then a hedge, and here I plan to dig a big cold water storage. On top of it I would build some workshop or kind of a storage, and use it's roof to harvest the rain. Since it is above the house level, I guess water will flow down by itself, no need of a pump.

Downhill there is an underground house, it has basement, and I could occupy part of it for hot water tank. It would be below bathroom, where I need hot water. There (in the basement) could also be a wood stove as a backup for sun energy.

On top of the house will be lawn and solar collectors to heat this big hot tank. Still not sure if convection will work that way, but it does not have to, solar powered pump is part of the plan. Since cold water is above the house, it will push hot water up to the shower, right?

Water from toilet would go somewhere down, didn't think of it much so far. Is there any major problem in this plan?

Zoidberg wrote:
Collector up, storage down.

http://www.google.es/images?q=thermosiphon%20solar%20collector&oe=utf-8&rls=org.mozilla:en-US:unofficial&client=firefox-a&um=1&ie=UTF-8&source=og&sa=N&hl=es&tab=wi&biw=1152&bih=676

Silly me. Of course I meant collector down, storage up, as in the pics.

Drug Mile wrote:...
On top of the site there is a road, then a hedge, and here I plan to dig a big cold water storage. On top of it I would build some workshop or kind of a storage, and use it's roof to harvest the rain. Since it is above the house level, I guess water will flow down by itself, no need of a pump.

Definitely.

Drug Mile wrote:On top of the house will be lawn and solar collectors to heat this big hot tank. Still not sure if convection will work that way, but it does not have to, solar powered pump is part of the plan. Since cold water is above the house, it will push hot water up to the shower, right?

Thermosiphon will not work with that arrangement, so a pump will be needed to drive the circuit between collectors and tank. On the other hand, hot water will be pushed up if everything is correctly piped.

Drug Mile wrote:Water from toilet would go somewhere down, didn't think of it much so far. Is there any major problem in this plan?

Depending of how much head there is beween points of use and the storage up the hill there might be problems with appliances with internal valves that expect a certain pressure to open and admit water in (washing machines come to mind).

Drug Mile wrote:

Water from toilet would go somewhere down, didn't think of it much so far. Is there any major problem in this plan?

Worm composting toilet?

http://mtbest.net/worm_farm.html

http://www.wormdigest.org/content/view/44/2/

http://www.solviva.com/wastewater.htm

Zoidberg wrote:
Depending of how much head there is beween points of use and the storage up the hill there might be problems with appliances with internal valves that expect a certain pressure to open and admit water in (washing machines come to mind).

I think the calculation is that water needs a head 10 meters to equal 1 bar of pressure, which is considered minimum water pressure in municipal systems in many places.  So if the upper tank is 10 meters above the house you should have decent pressure. 

Here is a table including conversions:
http://www.tapshop.net/water_pressure_etc/