Gravity Feed low pressure,Solar Hot Water systems?

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Gravity Feed low pressure,Solar Hot Water systems?

Postby BlueSky » Wed Sep 23, 2009 11:22 am

Hi Im looking to install a Solar hot water system and I am unsure of the best option.
If you have any experience with this type of situation ,I would greatly apreciate any advice ....
I do not have mains water and do not want to use a pressure pump (unless I really have too)
I have a 5000 gallon tank at the top of my property which supplys the house with gravity fed water . The bottom of the tank is about level with the ridge of my single story cottage (4m?)and sits about 20m away.
I would also like to hook up my combustion heater to the system if possible for added heating in the winter as we keep the heater going prety much non stop all winter.
At present I have a standard mains electric hot water service which sits on the ground next to the cottage. The gravity fed pressure is not great, but I am not fussy about gushing hot water and I am quite happy with the natural water savinging I get from my trickling shower. I would be more than happy if the new system produced the same pressure...
I have looked into it a bit and there seems a couple of options.....
A tank inside the ceiling (Beasly or Rannai) and pannels outside.
A tank attatched to the top of the solar pannels, all in one ,type setup.. and I think "Edwards" make a low pressure one?
I liked the look of the "Evacuated Tube" systems but think they need mains pressure?
I also get occasional frost where I live in the Adelaide Hills....

Any help greatly apreciated....cheers
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Re: Gravity Feed low pressure,Solar Hot Water systems?

Postby any_old_id » Wed Sep 23, 2009 8:38 pm

Hi.

I've seen evacuated tube systems for Gravity Feed, so that shouldn't be an issue, the only thing is for gravity feed, the HWS is above the tubes on the roof. You may have issues with height of that and your water tank (but I'm no expert there!)

You should be able to connect the combustion heater to it, you just have to be careful that the reverse thermosyphon effect doesn't happen (ie when heater not on it 'cools' the water instead). Keeping pipe runs short and insulation should help with that. Maybe a valve to shut off in summer?

Evacuated tubes shouldn't be affected by frost from what I'm told.

Good luck!

Simon.
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Re: Gravity Feed low pressure,Solar Hot Water systems?

Postby sou'westies » Sun Sep 27, 2009 10:57 pm

Our nearish neighbours have a setup like this, a solahart system with tank mounted above panels on roof, gravity fed from a tank, with a wood fired stove to boost.
It has worked well for them for at least ten years. They do have a reasonably high head to feed the system, about 5m above the solahart unit.

This would be the ideal setup as it requires no power to run, aside from charging the header tank, and this is exactly the system we want to set up as well, so I am very interested in any extra info as well.

Our plumber says it needs large diameter pipes to and from the unit to maximise flow, 19mm, or 3/4 copper at least, and high flow valves. The valves that come with mains pressure are probably too restrictive.

I'll do a bit of research with our neighbours, and talk to our local plumber some more and try and post what I learn.

Info on the net on this setup is bloody scarce, so if anyone can shed any light please do!
Cheers - Andrew
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Re: Gravity Feed low pressure,Solar Hot Water systems?

Postby BlueSky » Mon Sep 28, 2009 11:34 am

Thanks for that Andrew, yea there is very little info on the net on the "nuts and bolts" of what is required to run a low pressure gravity feed system. Theres a couple of systems as i described above that say "open system" which can be "low pressure" but its a bit vuage as to what are the limits each end.
Im guessing that the top of holding tank of the solar hot water service can be at the very least, slightly below the the header tank, but I cant be certain.
I know the Beasly/Rannai system with the tank inside the ceiling space is the more common aproach but seems a bit more complicated to install and Ive heard of difficulties with the water getting too hot and boiling so Im not sure if there is some sort of monitoring system these days to stop that.
On the Edwards site they have a diagram of the system hooked up to the combustion stove and state its a low pressure system but again I'm not sure of its limits.
The best thing would be to talk to a plumber who instals low pressure systems regularly and knows the different aproaches and their pro's and con's...I look forward to hearing more from your research and will post any extra info i find out....cheers
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Re: Gravity Feed low pressure,Solar Hot Water systems?

Postby bruce » Fri Oct 02, 2009 12:55 pm

We have had a Solar hot water system on our roof, fed by a 2000 lts water tank on a 5 meter stand. Also we have connected a fuel stove, with an inbuilt heating manifold ,to the Solar hot water tank. The system has worked well for 25 years. It boosts the Solar hot water during winter & we only need to switch the electric booster on for 1 hr 3 or 4 times a year when the fuel stove is not lit or we have no sun days in a row.
Your heater will need a hot water manififold or coil.
Plumbing from heater to Solar hot water to allow thermo syphon circulation.
Atmospheric vent on Solar hot water to stop steam pressure buildup.

hope this helps
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Re: Gravity Feed low pressure,Solar Hot Water systems?

Postby bradley.jarvis » Fri Oct 02, 2009 9:58 pm

We have gravity fed water with a 2000L header tank at about 3 meter head, the water flow is a bit slow but we don't need to run a water pump constantly(which wastes power and is noisy). We have a copper tank that is hooked up to a combustion stove to heat it up.

The water thermosyphens to the hot water tank which we have wrapped in at least a foot of wool that is stuffed into a sleeve made of shade cloth. This means that the water will stay hot for at least 24 hours(in 5degree weather) and is still warm after 2 days, the more hot water you use the less the time it will stay warm for though. We have also made lagging for some of the pipes by taking a raw sheep fleece and wrapping around the copper pipe and then using duct tape to hold the sheep wool in place.

We have only had the setup running over winter, and we are looking at backing it up with solar hot water over the summer. We are currently looking for a solar hot water panel or tubes. We also are finding it difficult to just locate a panel by itself without pressure relief valves and pumps etc. The only requirement for it is that the pipes are a big enough diameter. Our combustion stove works well with only 3/4" so that should be fine for the SHW.

I'll try and explain how we have hooked up our system below (hopefully it makes sense)

The components:
- Copper tank with 4 entry points, one at the bottom (on the side), one a 1/3 of the way up and one at 2/3 (both these are on the opposite side to the bottom entry point) and one at the very top centre of the domed tank
- Combustion stove with 2 entry point, one top and one bottom (these come out the back of the stove).
- a small feed tank with ball valve, with 2 entry points, one into the valve and one at the bottom, it also has an overflow outlet.

Location of components:
- Small feed tank is above copper tank on roof, it has an overflow outlet onto the roof
- Copper tank is below small feed tank in the roof space
- Combustion stove is in kitchen as close to below copper tank as possible

How it is connected:
- From cold water header tank to cold water taps, this is also connected to the ball valve in the small feed tank (we have 1/2" but 3/4 pipe would probably be better)
- From the bottom of the feed tank 3/4" pipe is run down to the bottom entry point of the copper tank, this is the cold water inlet for the hot water system.
- The 1/3 entry point from the copper tank is connected to the bottom entry point in the combustion stove, this should be 3/4" or bigger. This pipe should not go above the copper tank entry point and should rise all the way from the stove to the copper.
- The 2/3 entry point from the copper tank is connected to the top entry point in the combustion stove. This should be 3/4 or bigger and should not go above the 2/3 entry point and should also rise all the way from the stove to the copper. This is the hot water return, this pipe will get hot first, the 1/3 pipe will get hot once the copper tank has at least 2/3rd hot water in it.
- The top copper tank entry point is the hot water outlet and can be 1/2" pipe to all the hot water taps in the house (the bigger the better the flow, but it should not be bigger than the inlet pipe). This exit also has a tee connector that has a vent pipe come out through the roof(they are usually bent into a hook) and it can either drip onto the roof or go into the feed tank. This is very important as it makes sure that you do not pressurise the copper tank and cause it to explode.

You don't need the small feed tank with ball valve if the vent pipe is above the water level in the cold water header tank or can be fed back into your cold water header tank, otherwise if the vent pipe is below then the water in the header tank will gravity feed out the vent pipe!

This setup is quite simple and means that you don't have to worry about high pressure and pumps etc. We put it together in about 2 days and I am no plumber(I did look at similar system setups and talk to quite a few people about it before putting it together though).

To add in the SHW it would have to be plumbed up so that the entry/exit points are below the 1/3 copper tank entry point, and would have to be careful so that the thermosyphen does not draw the water through both the SHW and combustion stove. So they would be connected in parrallel not series which allows for separate loops.

Let me know if this makes sense, if not I can probably draw something up and post a picture

Thanks, Brad
Living off-grid and loving it!
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Re: Gravity Feed low pressure,Solar Hot Water systems?

Postby Gordon-Loomberah » Sun Oct 04, 2009 4:26 pm

BlueSky wrote:I liked the look of the "Evacuated Tube" systems but think they need mains pressure?


There are a mains and non-mains pressure versions of evacuated tube systems available. Here is a photo taken a few minutes ago of my hydronics heating array of 78 tubes, they are vented to the atmosphere and I have them set up to thermosyphon, so I only need 1 circulation pump- for the radiators. Its been overcast all day with occasional showers, yet the water temperature at the 2 hydronics radiators inlet pipe in the living room is 55C.
Behind the 250l tank on the right is a 1000l tank, which is to be connected when I get around it it ;) I'll also be adding our wetback stove heated water to this system sometime before next winter.
Image
I have basically the same tank with 30 tubes as on the right here for my hot water, except it is pressurised @ ~250kPa by the 5000 litre tank visible up the hill.

Gordon
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Re: Gravity Feed low pressure,Solar Hot Water systems?

Postby BlueSky » Tue Oct 06, 2009 12:43 pm

Hi Gorden,
Just wondering what brand of evacuted tube system you have there?
Does the water go through the tubes or are they the sealed type with some sort of refridgerant
that transfers the heat at the tank end?....cheers...nice set up....
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Re: Gravity Feed low pressure,Solar Hot Water systems?

Postby Gordon-Loomberah » Tue Oct 06, 2009 3:31 pm

Thanks BlueSky, the 24 tube manifolds are the sealed type and the 30 tubes on the right with the tank have water in them. My solar HWS has the sealed tubes, so it will be pressurised.
They are all from RunonSun.

Gordon
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Re: Gravity Feed low pressure,Solar Hot Water systems?

Postby stuartj » Tue Jul 27, 2010 11:05 pm

Has any one had any experience using SolarVox evacuated tube collectors. They look like good quality units for gravity feed systems at a good price?
Keen for any feedback as like to add thermosyphone SHW to gravity feed wetback system.
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