Microcontrollers > Data Logging
Solar hot water heater – Data Logging
David HK:
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:
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
SparWeb:
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).
David HK:
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:
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?
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