Monitoring temperature in a heat store

 

Hi, I'm looking for some bright ideas. Dim ones may be fine too - it's
not too technically challenging a problem.
I'm setting up a renewable energy system in a house I'm renovating here
in Scotland, essentially to provide hot water for piped underfloor
heating (ufh). I've a wind turbine and solar panels heating a 2 cubic
meter water tank as a heat store and this feeds the ufh manifold and
also preheats the dom. hot water. I've made the tank tall (2.4m - 8ft)
and slender in order to achieve a temperature gradient, top to bottom,
and now I want to monitor the temperatures in it. This then is the
question - what are my choices for doing this temperature monitoring?
I've no experience of doing this so am starting from scratch. I was
thinking about, say, four monitoring points between the top and the
bottom - but what to use in this post-mercury electronic era? Is it
worth thinking about data loggers to do constant monitoring (that would
be nice)? What about price (I don't want to spend a fortune)? I'd
intended drilling through the tank (grp-lined osb) to just shy of the
watertight skin for placing the sensors, but maybe I could clamp them
to some of the various (copper) pipes that emerge.
The tank is in an outbuilding - could temperatures be monitored
remotely from the house? Wirelessly?
(As I'm in the UK I may not be able to access specific pieces of
equipment available in the US)

Your ideas would be gratefully received.

Season's greetings

 


Pig Sick wrote:

RS Components sell a variety of data loggers and there is a pdf file
explaining about them here
http://docs-europe.electrocomponents.com/webdocs/001b/0900766b8001b98e.pdf

or go to http://rswww.com  and search for data loggers. They don't start
very cheap at about £130 upwards I think, although RS aren't the
cheapest supplier. As for sensors, you can use thermocouples,
thermistors (non linear usually) or platinum resistance (not cheap) or
even a specifically designed chip which otputs a voltage proportional
to temperature. It really depends on how often you want to take
readings and how regularly. If you just want to do the job manually a
digital themometer and a few probes would do the job. I can't advise
you on wireless links as I know nothing about them.

Other suppliers worth considering are Farnell and their subsidiary CPC.

--
Malc

 



There are a variety of inexpensive measuring components, if you have
some slight amount of electronics skill. The price for having someone
else package things up is easily a factor of 100 (or so) on the price.
The typical example of that is a indoor/outdoor thermometer, perhaps of
the "multiple wireless outdoor sensor" flavor. Expect to pay over 100
pounds (vague guess based on passing these things by in a catalog of
overpriced things - perhaps you can find them cheaper if you search hard
enough, I have not expended any effort on the search).

A device I'm fond of for being "fall-off-a-log simple" (albeit not new
and exciting) is the National Semiconductor LM34/LM35 temperature
sensor. A cheap (5-10 pounds) digital voltmeter and a DC power supply
(or battery) yield a direct reading of the temperature (you may need to
mentally shift the decimal point, that's all). They go for less than a
pound each at present exchange rates. If you are happy just reading the
temperatures, you could have a box with a switch to read out each sensor
to the meter when interested, and this could be located in the house
with wires running to the tank.

http://www.national.com/pf/LM/LM35.html

National appears to have a production facility in Scotland, so I doubt
you'd have much trouble getting their products in the UK.

Inexpensive data logging tends to involve old computers. For those, a
digital type sensor might be better, such as a Dallas/Maxim DS18S20 (or
many others - that's an example, not a hard recommendation of the one
product you must have).

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2815

They list direct sales offices in the UK at the link below:

http://www.maxim-ic.com/company/contact/sales_offices.cfm/filter/maxdist

--
Cats, coffee, chocolate...vices to live by

 


Ecnerwal wrote:



That's the baby. I couldn't bring the number to mind. I expect that
Maplin will sell them if not CPC or RS.

--
Malc

 

I can think of a couple of options. One is to look at Omega
Engineering:

http://www.omega.com

I'm pretty sure they sell internationally.  If you see something that
you like, look around the web.  Omega charges a premium for their
stuff, most of which is private labeled for them.  You can usually
find it elsewhere.

If you want to do some electronic, take a look at the Dallas Semi
One-Wire series.

http://www.maxim-ic.com/1-Wire.cfm

These are ICs designed to daisy-chain on a single wire (and ground, of
course.)  The best configuration, however, is to run a separate power
lead.  A few years ago I designed a restaurant refrigeration
monitoring system using these devices.  It did exactly what you're
wanting to do. Hookup was via ordinary 4 conductor telephone wire.
Power, ground, data.

Dallas sells PC interfaces, evaluation kits and provides free software
(Windows and Linux).  I bought the $100 kit that contained several of
each part they make plus some i-Buttons.  Well worth the money.

Considering how cheap ordinary telephone wire is, I'd not waste my
time with wireless.  Unless you use licensed transceivers, the service
is likely to be quite unreliable because of the radiated power
restrictions.  Wired is so much simpler.  You could run Cat 5 out
there and also have a network connection :-)

A second approach would be to have the i-Bus to RS-232 interface at
the tank and hook that to RS-422 cable drivers to hustle the data back
to the house.  RS-422 drivers are very cheap and can drive thousands
of feet of telephone cable.

Yet another approach is to use a Parallax Basic Stamp at the tank.  It
has a built-in i-Bus interface.  Write just enough code for the Stamp
to collect the data and squirt it out the serial interface.  Connect
that to the RS-422 cable driver.

These guys make some nice RS-422 devices.

http://www.bb-elec.com/products.asp

My approach to monitoring the tank would be put several sensors in a
wand that could be screwed in the top of the tank and extend to the
bottom.  A length of capped copper tubing with the sensors RTVd to the
inside wall would do the job just fine.  A suitable pipe bushing and a
compression fitting would attach it to the top of the tank and bring
the wires out.

On 29 Dec 2006 03:43:40 -0800, "Pig Sick"


John De Armond
See my website for my current email address
http://www.neon-john.com
Cleveland, Occupied TN
Don't let your schooling interfere with your education-Mark Twain