Posted by *Kevin* on February 24, 2006, 10:52 pm

<snip>

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:

<snip>

Perhaps a small turbine water meter with a counter might work.

Posted by *Steve Shantz* on February 24, 2006, 11:32 pm

Kevin wrote:

*> <snip>*

*> 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:*

*> <snip>*

*> Perhaps a small turbine water meter with a counter might work.*

Kevin,

I agree whole heartedly about the small turbine water meter. I've got

one in my water softener. But can they be purchased? And can they

take the heat?

As for the AC pump connected to a differential controller... I've got a

DC pump connected to a solar panel. Won't work for me.

Also, to critique my earlier idea about measuring the pressure drop

across the pump...

The flow rate would be somewhat proportionate to the pressure drop,

(especially in the moderately low flow rate in my system) but the

proportionality constant is unknown. Knowing just the pressure change

across the pump isn't quite enough to calculate GPM.

One could make an educated guess based on delta Temperatures at noon on

a sunny day, but even this is not really accurate, as the temperature

and efficiency of the system would have to be factored in.

I like your turbine idea best.. if available.

Steve

Posted by *daestrom* on February 25, 2006, 5:37 pm

*> Kevin wrote:*

*>> <snip>*

*>>*

*>> 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:*

*>>*

*>> <snip>*

*>>*

*>> Perhaps a small turbine water meter with a counter might work.*

*> Kevin,*

*> I agree whole heartedly about the small turbine water meter. I've got*

*> one in my water softener. But can they be purchased? And can they*

*> take the heat?*

*> As for the AC pump connected to a differential controller... I've got a*

*> DC pump connected to a solar panel. Won't work for me.*

*> Also, to critique my earlier idea about measuring the pressure drop*

*> across the pump...*

*> The flow rate would be somewhat proportionate to the pressure drop,*

*> (especially in the moderately low flow rate in my system) but the*

*> proportionality constant is unknown. Knowing just the pressure change*

*> across the pump isn't quite enough to calculate GPM.*

If the flow is very slow, the differential pressure needed is proportional

to the flow rate (laminar flow conditions). But that is *very* low flow,

and you probably don't want to be operating in that range anyway. For

turbulent flow, the differential pressure is proportional to the flow rate

squared. So...

Flow = K * sqrt(dP)

*> One could make an educated guess based on delta Temperatures at noon on*

*> a sunny day, but even this is not really accurate, as the temperature*

*> and efficiency of the system would have to be factored in.*

If you can find just *one* flow-rate versus differential pressure data

point, you have it made. But keep in mind that the exact constant will

change with the viscosity of the fluid (ratio of water/glycol as well as

temperature), and any degradation of the pipe interior roughness

(scale/corrosion build up). So it's best to recheck your 'calibration'

every year or two.

*> I like your turbine idea best.. if available.*

You might try these folks. I've worked with them and they probably have

something that suits your needs. Of course, price varies with accuracy

needed ;-)

http://www.gemssensors.com/TOCProducts.asp?nContentsID=5

Then you have to interface it to 'something', either a recorder, or

datalogger, or computer....

daestrom

Posted by *Steve Shantz* on February 25, 2006, 6:47 pm

daestrom wrote:

*> If the flow is very slow, the differential pressure needed is proportional*

*> to the flow rate (laminar flow conditions). But that is *very* low flow,*

*> and you probably don't want to be operating in that range anyway. For*

*> turbulent flow, the differential pressure is proportional to the flow rate*

*> squared. So...*

*> Flow = K * sqrt(dP)*

*> > One could make an educated guess based on delta Temperatures at noon on*

*> > a sunny day, but even this is not really accurate, as the temperature*

*> > and efficiency of the system would have to be factored in.*

*> >*

*> If you can find just *one* flow-rate versus differential pressure data*

*> point, you have it made. But keep in mind that the exact constant will*

*> change with the viscosity of the fluid (ratio of water/glycol as well as*

*> temperature), and any degradation of the pipe interior roughness*

*> (scale/corrosion build up). So it's best to recheck your 'calibration'*

*> every year or two.*

Fluid dynamics is never quite as simple as I wish it would be. I

should have known better!

*> You might try these folks. I've worked with them and they probably have*

*> something that suits your needs. Of course, price varies with accuracy*

*> needed ;-)*

*> http://www.gemssensors.com/TOCProducts.asp?nContentsID=5 *

Excellent source. $9 for a turbine sensor that goes up to 4 GPM.

Handles temps up to 100 dC.

*> Then you have to interface it to 'something', either a recorder, or*

*> datalogger, or computer....*

I'm thinking about using a PIC to interface with temperature and flow

sensors, and interface to a PC. It would be a good learning project.

I just need to find some time. So many other cool things to work on!

Steve

Posted by *Kevin* on February 25, 2006, 11:27 pm

*> daestrom wrote:*

*>> If the flow is very slow, the differential pressure needed is *

*>> proportional*

*>> to the flow rate (laminar flow conditions). But that is *very* low flow,*

*>> and you probably don't want to be operating in that range anyway. For*

*>> turbulent flow, the differential pressure is proportional to the flow *

*>> rate*

*>> squared. So...*

*>>*

*>> Flow = K * sqrt(dP)*

*>>*

*>> > One could make an educated guess based on delta Temperatures at noon on*

*>> > a sunny day, but even this is not really accurate, as the temperature*

*>> > and efficiency of the system would have to be factored in.*

*>> >*

*>>*

*>> If you can find just *one* flow-rate versus differential pressure data*

*>> point, you have it made. But keep in mind that the exact constant will*

*>> change with the viscosity of the fluid (ratio of water/glycol as well as*

*>> temperature), and any degradation of the pipe interior roughness*

*>> (scale/corrosion build up). So it's best to recheck your 'calibration'*

*>> every year or two.*

*>>*

*> Fluid dynamics is never quite as simple as I wish it would be. I*

*> should have known better!*

*>> You might try these folks. I've worked with them and they probably have*

*>> something that suits your needs. Of course, price varies with accuracy*

*>> needed ;-)*

*>>*

*>> http://www.gemssensors.com/TOCProducts.asp?nContentsID=5 *

*> Excellent source. $9 for a turbine sensor that goes up to 4 GPM.*

*> Handles temps up to 100 dC.*

*>> Then you have to interface it to 'something', either a recorder, or*

*>> datalogger, or computer....*

*> I'm thinking about using a PIC to interface with temperature and flow*

*> sensors, and interface to a PC. It would be a good learning project.*

*> I just need to find some time. So many other cool things to work on!*

*> Steve*

Apparently the this discussion thread happened many times before and someone

decided to produce a product to solve the problem.

http://www.istec-corp.com/5-60-7.htm

Kevin

> <snip>> 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:> <snip>> Perhaps a small turbine water meter with a counter might work.Kevin,