Batch type solar water heater

[David HK]

I am slowly moving ahead with the construction of a solar water heater on my garage roof. I will paste photographs on the site in the near future.

However, one question. I am intrigued by the water temperature and wish to enquire if other builders have ever placed water temperature guages in the heating loop?

If yes, what sort of water temperatures can be achieved and what is the prevailing ambient (outdoor) temperature?

I live in Hong Kong and in the summer our day and night temperature is a steady 33 degrees Celcius.

Dave

[dinges]

Hi,

Pictures would be very welcome.

Currently I'm building a small batch heater myself (25l) as a tryout for a bigger one (100l). BTW, noted some days ago that the smallest US conventional water heater is 50 gallons?! We get by on 50l... easily?!

Anyhow, I will install a temperature probe; I have 2 PT100 probes lying around, one of them will be permanently installed so I can electronically measure temperature. Don't know if the final big one will have one, but the trial tank will.

Have also made some calculations on expected temperature; Q=m*c*dT; heat loss from black-body radiation of the tank. Not accounting for convection & conduction, only for black body radiation, I should get a water temperature of 99deg.C?! This is with a total solar area that is twice the 'projected' surface of the water tank. Temp.rise would be about 19deg.C/hour. This seems like much to me.

Like the original poster, I'm interested too in actual measured values of such water heaters.

Peter,

The Netherlands.

[David HK]

Hello Dinges,

I am going direct to the full size unit. My capacity will be 226 litres or 49 gallons in 8 copper pipes of 42 mm diameter. I think my maths are correct.

The straight lengths of copper pipe are 6.4 feet long with U elbows at each end. The entire unit is entombed in a glass topped box 4 feet by 8 feet.

Apologies for the Imperial - Metric mix of measurements.

Dave

[BoneHead]

I am also interested in this.

A few months back, I decided to start turning off my hot water heater except for 3 hours a day. My wife and I ended up leaving the house for a day and a half and we returned, the water was still hot enough to shower or do dishes. It stayed that way for almost three days.

The hot water heater is only a 30 gallon mobile home factory unit. For insulation, all it has is about 2 inches of R rated foam.

I wanted to build a box around two 55 gallon drums painted with temp resistant, water proof paint and then fill it up with spray foam. I don't see any reason that this can't work for a heat well. If anyone else does, please let me know.

To the OP: By what method are you building the actual heating portion of the heater?

[BoneHead]

Ah, I see. You posted it while I was messing around...lol.

[dinges]

David,

I understand; you aren't using one vessel but several smaller pipes.

This should heat up your water faster; the reverse is also true, it will cool down after sunset much faster too.

Just realized: whether one should install a batchheater or solar-collectors& separate storage vessel also depends on how you use the water; in the evening: batchheater is fine. In the morning: solar collectors with separate storage are better.

BTW, like the other poster I also noticed how long you have hot water if the unit stops; about a year ago our tank heater went defect; we immediately all showered (3 people) to make use of the water; however, the water that was left after that was still hot the next evening... Our new boiler is much smaller than the old one, only 50l, but more than enough for 3 people & normal usage; that's why I'm so surprised that you are installing such a large system (226l). Like I said, the smallest boiler available (or advised) in US is 50gallon, I read somewhere. Mine is 50liters, 3.8 as less... And I don't feel I'm short on hot water.

Have you calculated max. temperature and expected heating time of the water?

Looking forward to hearing more on the system,

Peter,

The Netherlands.

[ghurd]

Standard US water heaters are 40 US gallons for gas, 50 for electric, but 30 gallon is quite common for both types.

G-

[adelaide]

cool i use a fridge on side to contain water 500l hahah ,bit of silicon and pipe. poly pipe doesn't silicon well so use different at joining point if u use this ,poly seems to last 1 or 2 years when under polycarbonate, the joins go first and leak so i use coil now and pump and also some copper exchangers tracking the sun with cordless drill/meter of thread in chuck, hot wired to light sensor/car cent lock relay on door hinges. just have pannel lower if using convection was funny lesson for me was going in reverse at night hahah. temps in pannel go higher than 100c some times and water temps go over 70 c in adelaide australia .is so cheap to go larger so would recommend bigger collector. also if using pannel other than water body for storage is very important to make it on angles that cannot collect bubbles and block if using convection as pump. if just batch no collector put up top box and insulate box well and go wide as possible maybe consider mirror too with adjustable angle. is fun and rewarding sun/black coz really does collect a lot of watts for so little dollars.

[David HK]

The following drawings give an idea of the design concept:-

In the lower sketch the white areas represent polystyrene insulation which will be painted black.

The rectangular box faces south and is nicely covered by the sun moving from east to west each day.

We have heavy rainstorms here in the summer months so the stainless steel angle will have holes drilled in it to self drain the cabinet as required. Please note that it is my assumption that only 50% of the top side of the pipes will ever be exposed to direct sunlight hence the lower 50% being insulated.

Its meant to be a megga simple arrangement.

Any comments would be welcome.

Dave

[electrondady1]

sounds like your ahead by a decade adelaide,

 how about some photos so we can catch up!

[richhagen]

The ones I've seen use a slightly different concept.  Instead of having an insulating material coated black, they had a thermally conducting material, such as aluminum painted black and thermally bonded to the coil.  There may be insullation below that, but the idea is to transfer as much of the heat that strikes all of the surface to the fluid in the coil, so they try to conduct it across the surface to the coil using Aluminum or even copper.  One might be able to mimic this by soldering a copper coil to a copper flashing backing and painting the whole thing flat black, then insulate the back side and mount it in a box with a glass or plastic front that transmits as much of the available visible and invisible light spectrum to the inside, but minimizes the transfer of air from the inside to the outsided to maximize the greenhouse effect.  Anyway, these are just ideas based upon my observations of older versions of these type panels.  Rich Hagen