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Garage_Hermit

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Reply with quote  #41 
Nice, Carl !

At first, was off to chew U out as we are talking hydronics[biggrin]  but on second thoughts, that is a really great link!  especially for a non-electronics person like me...

In any case, since at end of the day we are talking about the "M" for motor, then it ought to work just fine for a variable-speed DC PUMP also...

(Think I'll cut & copy your link and start a new thread under AIR & FANS...)

Most important, it gives a good starting point to explore the possibilites for other control circuits, because the www bit is a REALLY great site , I just checked it out !        http://www.circuitstoday.com/


(and what do we find on the very first page, but.....

PWM Control using Arduino – Learn to Control DC Motor Speed and LED Brightness

this thread is finally getting interesting [redface]

Thanks again,

G_H
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cwwilson721

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Reply with quote  #42 
DC Fan...DC Pump...They're both motors, should be "interchangeable"

That was the closest I could find, anyway
Garage_Hermit

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Reply with quote  #43 
Thanks again, Carl !

Meanwhile, I found THIS...

http://www.redrok.com/misc1.htm#diftemp


Quote:
Walter Pearson built a working Diode sensor based Differential Temperature Controller. He drives a water pump in a solar thermal water heating application.


PHEW !

( I might be offline for a few weeks while I get to grips with this [rolleyes] )

=============
otherwise, here is an off-the-shelf model, for 89 Aus dollars. (= 82 USD)
http://oceancontrols.com.au/CET-031.html

another one here, price 85 E (= 113 USD) with a very informational booklet...
https://www.cee.siemens.com/web/sk/sk/priemysel/technologie-budov/katalogove-listy/Katalogove_listy_30003999/N3344en.pdf
[image]
G_H
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cwwilson721

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Reply with quote  #44 
Unfortunately, the oceancontrols one is a AC and just on/off (which a regular differential controller does)

"
Control Output:One SPDT relay outlet, 1 HP(16A resistive)/250Vac"

Not variable
Garage_Hermit

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Reply with quote  #45 
Yeah, I think I get you on the OCEAN model, just a ON/OF signal to a switch.

so not a continuously varied flow, but an ON / OFF flow,

a bit like U would get from a snap switch I suppose...

However, the snap switch would turn the pump ON when the collector output gets to a certain level (say, 112°F), and turn it off at (say 140°F).  (which is not variable flow) (it is permanent or continuous flow).

But the snap switch does not know the temperature of the tank...
========================

Whereas this OCEAN will turn the pump ON depending on the *difference* between the collector output and the tank output -- which is a lot finer control. The pump is still being knocked ON and OFF, like you say, but it will presumably be more rapid, staccato-like.  Not sure if this qualifies as "variable flow" though...

The SIEMENS unit operates the same way as the OCEAN...
i.e. ON / OFF to a relay to turn the pump On and Off...

However, I suspect that because it uses two outputs with different levels, that this could be used to produce a form of PWM control, to give a genuinely variable speed control, but I'd prefer to have an expert give his opinion on this one...

G_H

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stmbtwle

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Reply with quote  #46 
I'm not sure there's much advantage in a speed control in a hydronic collector.  Whether you cycle the pump 10 times a second or 10 times an hour, the flow rate is still effectively reduced.   Is the variable speed control actually more efficient? Has anyone done an objective test?

In an air collector maybe, for noise and comfort reasons.

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Willie, Tampa Bay
Garage_Hermit

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Reply with quote  #47 
@ Willie,
I expect that these people have done some tests --
they claim to have over 3 million of these things in circulation...
(Of course, one never knows how objective their testing was...)
[1366709467370]
According to the claims out there, variable flow is more efficient than on-off cycling or constant flow, and is in particular better suited to installations where the pipes have to handle varying temperatures.

This model has a self-adapting mode that is claimed to be effective in 80 percent of situations.

G_H

(BTW, I have no links to this company or any other)

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stmbtwle

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Reply with quote  #48 
Oops my mistake, it seems I've misunderstood what you have been talking about (again).  I finally found that pump and it appears it's designed for a floor-heating system (something few of us have or need here). The variable speed there is probably a good idea as it should help maintain a constant temperature.

I was talking about a solar domestic water heater.  Seems I've been comparing apples to oranges.   Sorry.

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Garage_Hermit

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Reply with quote  #49 
updated for typo's
=============
Willie,

No need to beat your breast too much !

I would not read too much into the term "hydronics" - on this site, the term is used loosely, to mean liquid versus air systems.  So under ""hydronic collectors", you get both space heating and water heating applications.

In the purist sense, hydronics means using water as a heat-transfer medium for *space* heating, and employs a boiler.

Domestic hot water for hot-water users is generally produced by a hot-water heater.

A hot water heater would not normally be employed for hydronics applications unless it were specifically certified for the purpose; this is principally because an hydronics system implies a closed loop: circulation and high temperatures etc. whereas a hot-water heater is an open-ended system - designed to cycle: cold water in, heat applied, "hot" water (generally 50°C or 122°F) heated and stored, then run off; cooling of tank contents as they are run down, followed by heating, period.  Most hot-water heaters -- unlike boilers - are therefore not designed to operate in a closed-loop system.

Therefore, by addressing "hydronic", the present thread is discussing the use of variable-speed pumping in *both* of the stated types of system - space heating, and domestic hot water.

=========
An hydronic system does not have to use variable-speed pumping; most don't, in fact.  The reason is, an hydronic installation is generally built on a zonal architecture - various parts of the house can be shut off or opened up, on demand, to manage heat requirement.  The heat source (boiler) offers a *constant* temperature. The demand is regulated by a thermostat and valves to each zone: valves are shut or partially opened to manage the load, i.e. the number of BTU's required.  So the variable flow is achieved by *valving* (pressure modulation) and not pump speed control (flow velocity),  whence the reason (generally...) not to add a variable-speed pump: cost: quite simply, a VS pump is seen as redundant...
This was the traditional approach...

However, with modern pumps (circulators) featuring electronics, the situation change somewhat, and other advantages arise, that counteract the increased cost: when zone valves are closed to reduce load, the increased pressure is taken on the valve, and the pump can sense this, and reduce its speed, to avoid wasting energy by pumping towards a restriction.  Flow sensing.  This makes for lower power consumption: the pump might only have to run at a fraction of its previous load.  These bits of savings all add up.  Pumps last longer and need less maintenance.  The pump does not have to be running at peak speed, for months at a time.

With solar, the situation is somewhat different: for starters, the heat source is NOT constant, it varies according to what the collector is able to put out...

In particular, if our solar system (being DIY) is a straight-thru system (no or few zone valves) (valves ALSO being expensive), then the controlling devices mentioned above are not present: the total flow from the collector is applied to the installation (with allowance for a buffer tank where fitted). Thus the utility of a variable-speed pump comes into its own once again.

Therefore the advantages of variable-speed pumping in a "pure" hydronic system vs a solar hydronic system can be for quite different reasons.

===========

The advantages of variable-speed pumping in a hot-water system are related: varying output from collector, but need to protect storage tank (i.e. avoid circulating hot tank contents towards cold collector).  Research shows that variable-speed pumping is more efficient than ON-OFF pumping.

In particular, even without needing to go into the in's and out's of VS pumping, a simple comparison with other fields shows that VS has the advantage over ON-OFF; for example, cruise control on an automobile is performed by variable management of the vehicle throttle, and not by turning the engine on and off...  Less energy is used by modulating the speed of a motor, rather than turning it off, allowing the load to slow down, then turning the motor on again, for reasons of simple inertia.

If you look at any system, due to nature, changes take place by progression (the sun does not JUMP into the sky, stick on some heat, then jump back below the horizon - all these things happen progressively. The tides also, of course !  A hurricane does not just APPEAR - it s born of a systematic process, and fades away likewise...

Since our collectors and our water tanks and our in-floor radiant loops do not heat up instantaneously of a morning, then our pumps should not be knocked ON and OFF neither, in my view.

G_H

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stmbtwle

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Reply with quote  #50 
Not beating my breast, more like eating crow (doesn't taste all that great either).
The looseness of the term "hydronic" is what confused me.  Anyway:

I can see the advantages of a variable-speed pump in the storage-to-floor part of the system, though I'm not too sure how you would control it unless someone has designed a variable-output thermostat.

From the collector-to-storage side of the system, I'm still not convinced.  Considering the variable and unpredictable nature of the input, I think effective speed control is going to be difficult.  Anyway, a good differential thermostat is already a "PWM" device, albeit a slow one.

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Willie, Tampa Bay
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