Posted by schooner on January 28, 2006, 8:05 pm
Few links:
http://www.hobby-boards.com/catalog/main_page.php
Lots of good info here on what it is, how it works, etc.
http://www.aagelectronica.com/aag/index.html?target=p_1.html&lang=en-us
http://www.digitemp.com/documentation.shtml
http://www.maxim-ic.com/products/ibutton/
When I get some spare time I plan to put together an app for logging BTUs
from a solar air collector.
> Check out the OneWire temp sensors if your looking for a simple solution.
> geogeek wrote:
>> I'd like to track the number of btus that enter my house through my
>> solar hot water system daily. Besides recording the change in
>> temperature each day and doing a little math, what are my options? I
>> use a Tekmar 155 controller. This units gives me delta T hours, which
>> I don't think is very useful (am I wrong?)....
>>
>> Any help or advice would be greatly appreciated.
> An accurate measurement of flow rate is one of the biggest problems
> here. If you have an AC pump connected to a differential controller,
> you could make a fairly educated guess as to your flow rate. If you
> know the amount of time the pump is on, and the Delta T, BTU/hr is a
> straightforward calculation:
> Pumping Time per day (minutes) x Gallons per minute x 8.77 lb per
> gallon x Delta T (degrees F) x 0.87 BTU/lb °F = BTU per day
> The density and specific heat factors are for 50% propylene glycol. If
> you are pumping water, the density is 8, and specific heat is 1.0
> However, if you have a DC pump powered by solar panels (as is my
> system), an accurate estimation of flow rate and pumping time is
> impossible. A flow meter is the only way around this problem. I have
> yet to find a good inexpensive one. If anybody knows of one, please
> let me know.
> One of my goals it to see if I can get a PIC controller, interface it
> to temperature sensors and a flow meter, and voila... BTUs / day.
> Steve
>
Posted by Gary on January 29, 2006, 5:21 pm
schooner wrote:
Hi,
...
>
> However, if you have a DC pump powered by solar panels (as is my
> system), an accurate estimation of flow rate and pumping time is
> impossible. A flow meter is the only way around this problem. I have
> yet to find a good inexpensive one. If anybody knows of one, please
> let me know.
I've been looking for an inexpensive flow meter as well. The cheapest I have
found (not that cheap) are:
GEMS paddle wheel flow meters: http://www.gemssensors.com/index.asp
Dwyer has a couple: http://www.dwyer-inst.com/
Look for the RMV series and the HF series,
or the UV or VFC visual venturi meters.
Omega has some venturi meters: www.Omega.com
Look for the Fl46302, FL45101, ...
Beware that some of these meters might have too much internal pressure drop, or
not enough temperature capability for some solar applications.
----------
Omega.com also has a pretty good writeup on flow measurement:
http://www.omega.com/techref/flowcontrol.html
and, http://www.omega.com/techref/table1.html
-------
DIY flow meter?
Since most of flow meters are based on the pressure difference caused by a
disruption in the flow (e.g. an orifice or venturi), I am wondering if one could
do a cheap version by: 1) create a suitable disruption in the flow using a
standard plumbing fitting(s), and 2)install pressure taps upstream and just
downstream of (or at) the disruption, 3) Then measure the pressure difference
between the pressure taps to get the flow rate.
What could the standard pipe fitting to create the flow disruption be? Maybe
two reducers installed back to back to create a crude sort of venturi? This
would not have the nice pressure recovery of a real venturi, but still would
have the low pressure area at the constriction?
Maybe a homemade orifice plate soldered inside a fitting (a coupling?)?
How would you measure the pressure difference? Maybe a Magnehelic pressure gage
could be used to measure the pressure difference -- these are $0 new from
Dwyer, but are commonly available on ebay much cheaper.
http://www.dwyer-inst.com/htdocs/pressure/Series2000Intro.cfm I have a couple
of these -- nicely made -- lots of uses.
It would have to be calibrated -- this could be done very accurately by timing
flow into a bucket of known size.
Gary
>
> One of my goals it to see if I can get a PIC controller, interface it
> to temperature sensors and a flow meter, and voila... BTUs / day.
>
> Steve
>
>
--
Gary
www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects
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Posted by daestrom on January 29, 2006, 6:07 pm
> schooner wrote:
> Hi,
> ...
>>
>> However, if you have a DC pump powered by solar panels (as is my
>> system), an accurate estimation of flow rate and pumping time is
>> impossible. A flow meter is the only way around this problem. I have
>> yet to find a good inexpensive one. If anybody knows of one, please
>> let me know.
> I've been looking for an inexpensive flow meter as well. The cheapest I
> have
> found (not that cheap) are:
> GEMS paddle wheel flow meters: http://www.gemssensors.com/index.asp
I've played around with these GEMS ones myself. Got some pretty cheap from
ebay.
But the OP should these things measure *volume* (i.e. gallons or liters per
minute) not mass flow. To get a really good idea of the heat collection,
you also need to know the mixture ratio pretty accurately.
The density and specific heat capacity of water and glycol mixtures can be
found on the 'net. To find the actual heat transferred.....
Energy Delivered = <volume flow rate>*<density>* <heat-capacity> *(Tin -
Tout) * time
(get all the units converted/cancelled out too)
daestrom
Posted by Gary on January 29, 2006, 7:43 pm
Hi,
Any thoughts on the DIY flow meter?
I bought $.27 worth of plumbing fittings this morning to give it a try :-)
Gary
daestrom wrote:
>
>>schooner wrote:
>>Hi,
>>...
>>
>>>However, if you have a DC pump powered by solar panels (as is my
>>>system), an accurate estimation of flow rate and pumping time is
>>>impossible. A flow meter is the only way around this problem. I have
>>>yet to find a good inexpensive one. If anybody knows of one, please
>>>let me know.
>>
>>I've been looking for an inexpensive flow meter as well. The cheapest I
>>have
>>found (not that cheap) are:
>>
>>GEMS paddle wheel flow meters: http://www.gemssensors.com/index.asp
>>
>
>
> I've played around with these GEMS ones myself. Got some pretty cheap from
> ebay.
>
> But the OP should these things measure *volume* (i.e. gallons or liters per
> minute) not mass flow. To get a really good idea of the heat collection,
> you also need to know the mixture ratio pretty accurately.
>
> The density and specific heat capacity of water and glycol mixtures can be
> found on the 'net. To find the actual heat transferred.....
>
> Energy Delivered = <volume flow rate>*<density>* <heat-capacity> *(Tin -
> Tout) * time
>
> (get all the units converted/cancelled out too)
>
> daestrom
>
>
--
Gary
www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects
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Posted by Steve Shantz on January 29, 2006, 8:30 pm
Best of luck in your endevour!
I would suggest that rather than adding restrictor fittings into your
line...what if you measured the pressure boost across the pump? Place
one transducer just after the pump, and one right before the pump, and
measure the differential pressure. At zero flow, no pressure drop. As
the pump speeds up, there will be an increasing pressure change across
the pump. The signal might be noisy and may need filtering, but the
idea seems good to me. If across the pump is too noisy, how about
measuring the pressure drop through your collectors? One transducer on
your out-bound (cold) pipe, and one on the the hot return pipe. I'm
not sure this would really make a difference though, as compared to
just measuring across the pump. You would get the largest signal by
measuring across the pump.
Are there any (cheap) piezzo transducers and signal conditioners that
would enable the signal to be fed into a processor?
Steve
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> geogeek wrote:
>> I'd like to track the number of btus that enter my house through my
>> solar hot water system daily. Besides recording the change in
>> temperature each day and doing a little math, what are my options? I
>> use a Tekmar 155 controller. This units gives me delta T hours, which
>> I don't think is very useful (am I wrong?)....
>>
>> Any help or advice would be greatly appreciated.
> An accurate measurement of flow rate is one of the biggest problems
> here. If you have an AC pump connected to a differential controller,
> you could make a fairly educated guess as to your flow rate. If you
> know the amount of time the pump is on, and the Delta T, BTU/hr is a
> straightforward calculation:
> Pumping Time per day (minutes) x Gallons per minute x 8.77 lb per
> gallon x Delta T (degrees F) x 0.87 BTU/lb °F = BTU per day
> The density and specific heat factors are for 50% propylene glycol. If
> you are pumping water, the density is 8, and specific heat is 1.0
> However, if you have a DC pump powered by solar panels (as is my
> system), an accurate estimation of flow rate and pumping time is
> impossible. A flow meter is the only way around this problem. I have
> yet to find a good inexpensive one. If anybody knows of one, please
> let me know.
> One of my goals it to see if I can get a PIC controller, interface it
> to temperature sensors and a flow meter, and voila... BTUs / day.
> Steve
>