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All questions about time & measures (distances, length, surface...) for SWater heating  RSS feed

 
Xisca Nicolas
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I have a few questions that could all be grouped in one theme,
...and some folks might have the same questions with another location problem...

That is about the relationship between those 2 parameters: time and dimensions.
I guess that when one diminish, the other must rise!
Are there some rules to follow about adapting them one to the other?
The heat depends on the surface the sun strikes AND how long it receives sun.

Let's put apart the unpredictable, of course some days are more sunny than others.

Example: I get a plan that is made to work all day long, and my place is less sunny.
How much must I increase the surface if my place is half as sunny?

 
Xisca Nicolas
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Now my case:

I live in a sunny place but in a valley and the house is below a cliff, facing WNW.
Sun comes at 2pm...
35' above, Sun comes before 9am...

So, I think that it is much too much when you wait for hot water down there!
1) What is the reasonable distance between the hot water tank and the taps?

What can I expect if my system starts working in the afternoon? 4 hours in winter, more in summer...
 
Bob Ramlow
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Location: Amherst, Wisconsin
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Most solar water heating systems are sized so that they provide the target amount of hot water in one full sunny day. The size of the collector array will depend on the climate. this is the most efficient and least cost arrangement. If you have less than a full day of sun on the collectors, then you have to have more collectors to provide the desired amount of hot water.

Distance of the collectors from the heat exchanger and storage tank does not make that much difference. The piping has to be well insulated in every case, and the heat loss from well insulated piping is not that great.

Bob
 
Xisca Nicolas
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Hi Bob, thanks for coming.
Sure, less sun, more collectors...
I would like to be more precise about the ratio:
Does a half day of sun mean exactly double collectors?
Is it less because it will heat more in the afternoon than in the morning?
Also I guess it is less because part of what is happening during the day is for maintaining the heat.

I am not convinced that the pipe distance has so little importance, even with good insulating.
Don't you think that the shower temperature might go up suddenly when arrives the real hot water from the tank!?

Is it possible to heat the water in the sunniest place, and (as it is higher than the house)
send it to a container near the house?

I have always seen the container above the solar system, as the hot water goes up.
But then, why not send the hot water to another tank?
 
Bob Ramlow
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In warm climates where it never freezes, it is possible to have a direct system where the domestic water actually goes through the collector. In most climates a solar fluid of some type goes through the collector and a heat exchanger transfers the heat from the solar fluid to the domestic water. If you are talking about systems in non-freezing climates, then distance does become more of an issue. My book talks about this subject in detail.

Regarding the size of the array, the sun is the same whether it is AM or PM, it is the hours that the collector is exposed to the sun that is important. Lets say that with one collector exposed to the sun for a whole day it will produce 40 gal of hot water. If you only expose the collector to 1/2 a day's worth of sun the collector will only heat 1/2 as much water. This gets a little more complicated depending on which type of system you choose, so I suggest studying my book.

Bob
 
Xisca Nicolas
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Yes true, I am in a non freezing climate...
Here we can have black pipes warming water and it's done.

whatever the system is, and even if the water is heated thanks to the grid...
there is still something I do not understand...
when the water is in the collector, for stocking until use,
then I talk about the length from the reservoir to the shower.

How much water is hold in 10m or 35 feet of pipes
Even if you insulate the pipes (and without even speaking about copper price...)
- It spoils a lot of water before you get the right temperature
- It is not nice to be waiting for hot water that long
 
Jim Lea
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Location: Southern Sierra Nevada's
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Xisca,
What is the inside diameter of your pipe? A 1/2 dia pipe that long has approx. .35 gallons. By my calculation. May not be waisting as much as you think.
Hope this helps,
Jim
 
Xisca Nicolas
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I collect a bucket of water each time I take a shower
(or else the water goes to the same place!)
That is 2 or 3 gallons...
35 gallons is a looooot!

I have even removed the hot water from a tap just because it is 4m from the water heater and that I thought hot water was just coming when my hands were washed and cleared!
 
Bob Ramlow
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Xisca, with a direct solar water heater in a non freezing climate, then distance certainly is an issue. Posts below give you an idea of the volume of water in a pipe. Make it as short as possible.

Bob
 
Xisca Nicolas
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And distance is also an issue in freezing climates. Even more.

What's about having the heating system anywhere,
where it gets the more sun,
and then send hot water to an insulated tank in the house?

I do not understand why everybody stocks water near the heating system.
I understand it only when only the roof is available for the system.
 
Bob Ramlow
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In a freezing climate a solar fluid is heated in the collector and is typically pumped to a heat exchanger where the solar heat is transferred to the domestic water and that water is stored in a storage tank. There is little heat loss in the solar piping loop if they are properly insulated, so distance in this loop is not critical. I have a 30+ year old solar water + space heating system here in Wisconsin that is 100 ft. from the heat exchanger and it works fantastic.

Now, the distance from the solar storage tank to the back-up water heater is much more critical - you want these close together because when you use hot water, solar preheated water flows from the solar storage tank to the back-up heater and if the distance is long and the draw is small, then the preheated water never gets to the back-up water heater.

So the distance is not critical from the collectors to the heat exchanger but is critical from the solar storage tank to the back-up water heater.

Bob
 
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