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.PDFPlease 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