Author Topic: Solar hot water heater – Data Logging  (Read 7715 times)

0 Members and 1 Guest are viewing this topic.

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Solar hot water heater – Data Logging
« on: March 23, 2013, 06:34:27 AM »
Part 1

Solar hot water heater – Data Logging - background.

I was inspired to construct my ‘batch type’ (an American term I gather) solar hot water heater in the early part of 2006 after reading an article in the Homepower magazine (also American).

I decided to build it with non-ferrous materials for the following reasons:-

a)   I did not want to spend any money on maintenance,
b)   I wanted it to last for 100 years and more with a caring owner,
c)   The materials were available locally,
d)   a, b and c, mean a potentially good re-sale value,
e)   it was transportable in one-piece by truck equipped with an hydraulic lift, and
f)   I am technically gifted to the extent that I could make it myself.

The basis of the design was a single stainless steel sheet measuring 8 feet (2.4M) x 4 feet (1.2M) which was to form the internal floor of the heater box. Thereafter the framework was to consist of stainless steel angle which was pre-drilled and tapped for bolts to hold the enclosing stainless steel side panels. The interior walls and floor were lined with Isotherm which is a high quality form of polyisocyanurate. After lining, the panel seams were taped over with aluminium sticky backed foil. The final top covering was done with four sets of double glazed panels.

The internal pipe work consists of 42 mm diameter copper pipe arranged in a Zig Zag fashion. The water inlet is at the bottom low side of the box and the outlet on the upper high side. Water supply is direct from the mains at ~ 60 psi so this means the true boiling point is ~ 1480 Celsius. The box almost faces due South.

The heater box was constructed on my carport floor as was the pipe work. A simple jig was constructed so that the entire pipe work assembly could be moved back to front, and up and down, so that soldering was a carefully controlled good quality job. After this was done it was pressure tested for leaks (which there were), corrected, and finally passed when no leaks were present.

The pipes were fitted into the box, and, with the aid of some soft drinks, I persuaded a local road repair contractor to use his truck crane to lift the heater box onto my carport roof where support mounts were already in place. This job was well prepared in advance and only took five minutes.

Thereafter it was a simple task to connect up to the water supply and distribution  piping to the kitchen and bathrooms.

During the construction phase I had obtained some small battery operated LCD temperature readers (in Celsius) to monitor the ambient temperature, and a special umbilical wire type to fit into a copper block mounted on the outlet pipe inside the solar box to measure water temperature.

And it all worked very well indeed!

I recollect the Homepower magazine mentioning that one could amortize capital expenditure against utility bills over a four-year period.

I did take the opportunity to estimate the capital cost (not including tools and consumables) which came to – HK$7,000 or US$897. So divide that by four years and three people and you have the cost per person. The hot water usage covers showers, dish-washing and other occasional cleaning uses. The savings against electric hot water heating are significant.

The all up weight was measured at 450 lbs or 204 Kg including water.

Water capacity I have recorded as 7.6 gallons or 34.6 litres. (I need to recheck this and will post a revision if necessary).

After being a “happy chappie” at this point I always wondered if the solar heater box was efficient in terms of heat production. Could more efficiency be gained, and was heat being lost? Observing heat or temperature with the human eye is impossible without tell tale instruments and, by this time, I had become an Otherpower Forum member and was taking more notice about all sorts of things being posted on the Internet.

Quite by chance, I came across a website selling an eight sensor PCB interface with software for logging temperature so I purchased a set.

Data Logging Temperatures

At first I did not know how or where I should install eight sensors so I opted for five which were:-  the Inlet pipe, Centre Pipe, Outlet Pipe, Internal Air and Ambient Air – a total of six. To fit the sensors onto the copper pipes I had to close down and empty the system so that I could solder on some more rectangular copper pieces pre-drilled to accommodate each sensor which is like a TO18 shape transistor.

This was done and the sensors were held in place with heat conducting compound and covered by a wooden ‘bridge’ to avoid direct sunlight.

The ‘PCB kit’ was interfaced by serial cable to my computer and the software started up – it seems to be a locked version of Visual Basic. At start up one selects the Port and makes the usual mouse click and hey presto real time temperatures appear in small boxes. No sensor, equals, no reading.

Other options allow the user to select the type of data output, frequency of sampling, and a few other minor refinements.

What I liked about this was the ‘selection for ‘Log data to’ because if ‘Excel worksheet’ is selected the software automatically opens a worksheet and data flows into a line each time a reading is taken. Later one can save the data worksheet with a name – usually the date - and thence produce a chart to provide a picture of what happened during the day.

I read the data for several weeks and was fascinated by it. The power of the sun to heat water as the sun is rising, and then when it’s overhead, is phenomenal.

And then my Data Logger stopped working!

Following are photographs showing various stages of construction and require little or no explanation.

I am sure interested readers may be curious about the data logging kit so more information can be found here:-   http://www.smartec-sensors.com/assets/files/pdf/manuals/SMTAS08N.PDF

Please note that I have no connection with the vendor.

Continued in Part 2 ------  How I got the data logger working again.

Dave in Hong Kong



David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Solar hot water heater – Data Logging
« Reply #1 on: March 23, 2013, 06:36:05 AM »
Part 2

Solar hot water heater – Data Logging - continued.

No data logger really irked me and no matter what I tried the damn thing would not work again so I disconnected it from the computer until late 2012. At this point in time my computer was becoming noisier and noisier, slow, and short of hard disk memory so I opted to purchase a new one.

The new machine was re-equipped with Windows XP and MS Office 2003. It also had no serial input ports (just USB’s) so I inserted a new card with two Serial inputs and associated software control. This at least gave me the opportunity to try out the Data Logger again.

And so I did. Everything was connected up and I selected the LogSmart software and there were the instant readings for temperature for the original six sensors. That was a surprise.

The next gamble was to select Log to “Excel worksheet” and a frequency reading every five minutes. Much to my astonishment a new Excel worksheet flashed up on the screen which indicated that the software was trying to work but no data was incoming – the sheet was blank.

This aroused much curiosity and quite by chance I right clicked on the LogSmart logo and went to Properties. In the Properties window there is a selection item for Compatibility so I clicked on this and found a tick box from which I could select various versions of Excel. I played around with this for a while and eventually after selecting Excel 2000 I discovered that the data would go into an Excel worksheet but not the date and time. I was nearly there  ----

I then went to Windows XP Regional Settings and reduced the Date and Time formats to the most basic of settings found when Windows XP is loaded from scratch. Previously I liked the date to read Thursday 24th December 2013 – nice and long winded, but now it was back to basics  - 23 March 2013.

So I tried again and Bingo the spreadsheet started working again just like it had done six years previously. It then dawned on me that the LogSmart software had a serious problem with changes to the Windows XP System Date settings. 

At this point of happiness I decided I would like the remaining two unused sensor inputs to be incorporated into the logging arrangement, but how can five sensors be fitted into 9 horizontal pipes? The answer is they can’t unless one takes the entire length of pipe and sub divides it into equal spaces which is what I did, so I now have:- Inlet (zero), 3.9M, 7.8M, 11.7M, 15.6M, Outlet 19.53M, Internal air and External air.

I have already purchased a genuine copy of MS Office 2010 and tested it and found that did not work with the Compatibility selection for Excel 2000. This time I was determined to solve the problem and deselected the Compatibility option and just let the program run without and modification, and, blow me down, it works!

I then removed Excel 2010 and reloaded Excel 2003 and ran that with LogSmart (no compatibility selected) and that works as well. So there was the answer – changing the Windows XP System Date settings mucked up the LogSmart software big time. My own unwitting fault all along.

Having bored readers to death with this saga I am sure you would now like to see what sort of charts I obtain from sunny days, overcast days, mixed sun and cloud days so I will post these as Part 3.

To be continued with charts. I have never posted Excel charts in the Forum before so this will be another new adventure in life.


Dave in Hong Kong


« Last Edit: March 23, 2013, 06:43:47 AM by David HK »

SparWeb

  • SuperHero Member
  • ******
  • Posts: 3308
  • Country: ca
    • Wind Turbine Project Field Notes
Re: Solar hot water heater – Data Logging
« Reply #2 on: March 23, 2013, 08:55:32 PM »
David,
Firstly thanks for the "inaugural" posting of this data-logging forum section.  Most worthy!

Despite the emphasis on data-logging, I would appreciate more details of the enclosure and tubing that was built.  Also left to my imagination,  the performance you have been able to record.  Supposing that your (2.4m)*(1.2m)= 3 m square area collects sunlight face-on, roughly 3 kW input power.  I can't go far from there because I would like to know (if you know) the flow rate and the temperature gradient through the pipes!

BTW:  Gary Reysa likes seeing detailed projects like this, particularly when the builder has gone to all the trouble of measuring the performance (and is willing to share the data).  You can find numerous examples at his website www.builditsolar.ca.  (No I don't get a commission for promiting it)   :)

Thanks for letting me know about Smartec.  Nice board, I'll read a bit more about it (and their sensors).
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Solar hot water heater – Data Logging
« Reply #3 on: March 23, 2013, 10:02:27 PM »
Sparweb,

Thanks for the note.  You mention flow rates so my first response is that I don't know. Remember this is a "batch" type heater and not a low pressure recirculating type. I assume you understand the difference.

I can email you a host of jpeg photographs from the construction era if you would like them. The folder size is 2.34MB.

Likewise, most of my recent data logs are between 20 and 30 KB, and I have a particularly interesting one of about 173KB modified by a whizz kid on the Excel Forum. This contains a mouse controlled slide bar with pointer indicator and and data display box that changes as the pointer crosses over each data entry. This is quite an advanced use of the power of Excel. I cannot put it on this Forum as the file exceeds the 100KB limit which is a loss to those who may wish to see it.

Please let me have some more one-liner questions and I shall endeavour to answer with knowledge available.

I'll send you a PM with my e-mail. If you can reciprocate I will send back various photographs and other information.

Dave in HK

SparWeb

  • SuperHero Member
  • ******
  • Posts: 3308
  • Country: ca
    • Wind Turbine Project Field Notes
Re: Solar hot water heater – Data Logging
« Reply #4 on: March 23, 2013, 10:22:53 PM »
Okay,
Exchanging the info shouldn't be too difficult, and I'll send a message to you shortly.

Thanks for reminding me it's the batch style - I should have asked the question a little differently. 
I also assumed that there is a pump somewhere in the system, giving a known flow rate without any measurements.
How long does a cycle take, and what temperature inputs/outputs does it achieve?
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Solar hot water heater – Data Logging
« Reply #5 on: March 23, 2013, 10:34:15 PM »
Sparweb,

Perhaps its me doing the misleading. There is no pump nor circulating system. This is still planned as phase 2 if I ever get round to it. The water in the box is what is heated and that's it.

This is drained off on demand and blended with cool water as required. In the summer the water is damn hot and I have seen 116 Celsius on the LCD displays - remember the system is pressurised to 64 psi so true boiling point is around 147 Celsius. It frightens me when I see temperatures this high.

At such high levels of temperature only a small amount of water is bled off to blend with cool water for showers and dish washing so its rare that we do not have enough warm to hot water on demand.

Trust this clears things up.

Dave

SparWeb

  • SuperHero Member
  • ******
  • Posts: 3308
  • Country: ca
    • Wind Turbine Project Field Notes
Re: Solar hot water heater – Data Logging
« Reply #6 on: March 23, 2013, 11:32:21 PM »
Aha, now I see.
I thought you were storing the hot water in a tank, and circulating it through the panel.  Now I can figure this out:

The total volume is about 35 Liters, or 35 kilograms.   The specific heat of water is 4.187 kJ/kgK.

Raising the temperature of the water from 15C to 65C (from your graph posted to the Pub) is 50K.

(4.187) * (35) * (50) = 7327 kiloJoules

The panel was exposed to the sun from 10AM to 2PM (4 hours = 240 minutes = 14,400 seconds)

1 kJ = 1kW * sec        so         1 kW = 1kJ / sec       

7327 kiloJoules / 14,400 seconds = 0.5 kW

This result mashes together a lot of factors and can't even be considered an average input, because the rate of heat being radiated away increases as the panel gets hotter.  Basically the panel becomes  inefficient when it gets hot, even if it starts out efficiently in the morning.  You already mentioned that the panel is shaded, but I wonder if it's being tracked to face the sun or not.  You've posted photos of your tracked solar PV in the past, and I don't believe the water panel was on the rack.

These numbers from a no-flow situation shouldn't be discouraging.  If this solar heater were to be hooked up to a water system continually circulating through, the wide temperature differential would significantly improve the efficiency, and the lower surface temperature of the panel, despite the insulation, would reduce losses too.  I expect that once your project enters Phase 2 you will see even more benefit from the panel!  Collecting data from this stage of the project will provide a valuable lesson on the effect these changes to your system will have.
Good luck!
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Solar hot water heater – Data Logging
« Reply #7 on: March 23, 2013, 11:46:04 PM »
Lets see if Sparweb's excellent suggestion has worked. A selection of different days showing what the weather does to solar water heating.

7102-0

7103-1

7104-2

7105-3

7106-4

David in HK

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Solar hot water heater – Data Logging
« Reply #8 on: March 23, 2013, 11:59:27 PM »
I never seem to get things 100% right with picture posting, but for clarity on the above:-

First chart - a cold front arriving from North China - everything falling.

Second Chart - with self explanatory comments.

Third Chart - the second again except that a very bright whizz kid in the Excel Forum has gone to town on it and added a slide bar (top). this is mouse cursor controlled, and as it moves a blue drop line indicates the data line being read, it also automatically changes data in the box. This really does show the power of Excel for those who know how to use its very advanced features.

The jagged dark blue line shows coll water going into the pipes to replace hot being taken out.

I can promise some spectacular charts once Hong Kong reaches July and August. From 0830 am the temperatures in all pipes almost rise vertically.

That's about it folks. If you have any questions please post them.

David in HK

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Solar hot water heater – Data Logging
« Reply #9 on: March 24, 2013, 12:04:52 AM »
Sparweb,

The solar heater is only partly shaded in the winter time. In mid summer its never shaded.

There will be a substantial difference between your calculations now and in mid summer.

I would never even think of this as a tracking system - too complicated and dangerous. Imagine a burst pipe at 116 Celsius!

Dave

SparWeb

  • SuperHero Member
  • ******
  • Posts: 3308
  • Country: ca
    • Wind Turbine Project Field Notes
Re: Solar hot water heater – Data Logging
« Reply #10 on: March 24, 2013, 12:30:08 PM »
Quote
...I would never even think of this as a tracking system - too complicated and dangerous. Imagine a burst pipe at 116 Celsius!

Indeed!  But I have seen a tracked hot-water panel, once in Home Power magazine.  Also given your talent with tracking electronics I didn't want to rule out the possibility.

One more suggestion about Excel spreadsheet graphs:  If you double-click on the time numbers on the X axis, you should be given a dialog box, allowing you some control over the density of numbers listed there.  At the moment it's hard to read (of course you've noticed).  To solve this you need to space out the time "data labels".  In the SCALE tab, look for "number of categories between tick-mark labels".  Try 15-minute spacing.  If your data readings have been recorded every minute, then give the dialog box "15" categories between tick-mark labels.  Also try the same figure for the tick marks themselves.  If that doesn't clarify the x-axis enough, or cleans it out too much, you can probably adjust as you like it.  Also helpful is to edit the format of the time, in the other tab, so that you can see just HH:MM instead of a long  DD-MM-YYY_HH:MM:SS   super precision time is not necessary in the graph, and remains in the spreadsheet as accurately as it ever was.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Solar hot water heater – Data Logging
« Reply #11 on: March 24, 2013, 04:21:05 PM »
You're quite right about the plethora of options to mess around with the way raw data is presented in any form including my charts shown above.

I have just left it "as it is" for all forum readers to see what my data logging is all about. 

Apart from producing pretty pictures can the data be used for anything useful? I had though of using a temperature value to trigger a motor to cover all or part of the glass covers to prevent temperatures going over 100 C. Any other ideas?

David in HK

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Solar hot water heater – Data Logging
« Reply #12 on: March 24, 2013, 05:53:02 PM »
To make up the cast of photographs, the following shows the on-screen control panel.


ghurd

  • Global Moderator
  • Super Hero Member Plus
  • *****
  • Posts: 8078
Re: Solar hot water heater – Data Logging
« Reply #13 on: April 06, 2013, 04:17:47 PM »
Very nice Dave.
Impressive, as always.

Any other ideas?

How about a ghurd-style dirt-simple solution?

Idea 1)  Put a couple large holes on the box, with dampers and fans?
If the temperature gets too high, run the fans?
Surely that would be easier and cheaper than a mechanical device to cover the collector?

Idea 2)
A totally mechanical thermostat valve, which opens as the temp increases, thus allowing hot water to circulate via gravity feed to a cooler area?
It is not a new idea from me.  I saw a system that used a wood fired furnace to heat domestic hot water.  If the water became too hot, a (bimetalic?) valve opened allowing hot water to flow in a long loop of copper pipe (10M?).  I have no idea what was used for the mechanical temp valve.
The one owner I reacall talking to about it in detail said it stopped the 'pop-off' from 'popping-off', and he was happier after he installed it.
It was a long time ago.   That is about all I recall.

Idea 3)
Crazy.  I am just saying it to inspire more thoughts.
What if?  The top and bottom had MANY large holes.  And the holes had covers that would lift a motor, triggered by temperature.
Motor at the top and bottom.  Box or water gets too hot, and the motors open the covers allowing the air to gravity feed the hot air out, and the temperature in the box to go lower.
Could add a fan or 5 to help the temperature to go down faster.
It seems a lot easier than covering the collector to me... but I never did anything like that before.
G-
www.ghurd.info<<<-----Information on my Controller

Frank S

  • Hero Member
  • *****
  • Posts: 1622
  • Country: us
Re: Solar hot water heater – Data Logging
« Reply #14 on: April 07, 2013, 06:45:33 PM »
Very nice Dave.
Impressive, as always.


How about a ghurd-style dirt-simple solution?


Idea 2)
A totally mechanical thermostat valve, which opens as the temp increases, thus allowing hot water to circulate via gravity feed to a cooler area?
. (((( I have no idea what was used for the mechanical temp valve.)))))
The one owner I reacall talking to about it in detail said it stopped the 'pop-off' from 'popping-off', and he was happier after he installed it.
It was a long time ago.   That is about all I recall.
 

It seems a lot easier than covering the collector to me... but I never did anything like that before.
G-

for a mechanical valve a simple thermostat from the automotive industry should function well
 Thermostats can be bought in ranges from 140f on up they last for years even in water without antifreeze coolant mix and the best thing is most are designed for full open fail should be simple to come up with a suitable size that could be installed in a 2" pipe coupling or in a pipe union 
I live so far outside of the box, when I die they will stretch my carcass over the coffin

Bruce S

  • Global Moderator
  • Super Hero Member Plus
  • *****
  • Posts: 4574
  • Country: us
  • USA
Re: Solar hot water heater – Data Logging
« Reply #15 on: April 08, 2013, 08:47:34 AM »
Since we're on the subject of possibilities :).
have you tried the freeware options instead of Microsoft?
Due to work mandates, I have to use Excel 2013 otherwise would not.
The temp log plus bimetallic fan part could be built on or near bottom with greenhouse style vent on top. push cooler air up hot air out?
The workmanship on the piping is inspiring.
Thanks for the posts! I too would like more pics of the buildup.
Gary's site is also a host of great info :) and he's always answered any emails I've sent him.
Cheers
Bruce S
A kind word often goes unsaid BUT never goes unheard