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Garage_Hermit

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Reply with quote  #51 
@Willie,

Quote:
a good differential thermostat is already a "PWM" device, albeit a slow one


Yes, guess U R right, sort-of !  In the sense that it proportionally affects the duty cycle of the valve...  Open for so many percent of the cycle, and closed for so many percent of the cycle.

(I guess "cycle" for such a valve would be defined as "relative change in gate position during one 24-hr period"...).

so like U say, somewhat slow...

Slow or not, as said previously, this is the control principle on which hydronic floors etc. have operated for years... thermostatic control.

And as commonly announced, turning the thermostat down by 1°C will save around 10 percent on heat-expenditure...

https://customer.honeywell.com/en-US/Pages/Category.aspx?cat=HonECC%20Catalog&category=T100R&catpath=1.2.22.15.9

===========

Where the novelty comes in, is that adding variable speed pumping puts icing on the cake - as seen, the thermostat drives the valve and the valve causes the temperature change (in the case in point, reduces the supply to the room loop).  (if the load-demand is reduced sufficiently, (i.e. several rooms cut in one go etc. because we are going off to the country for the weekend), then presumably the boiler adjusts its own setting also...: after all, nobody in his right mind would expect a boiler to continue running at the same regime, even though the load had been turned down...) [biggrin]

(danger - parenthesis...)
yet - since we are at it - nobody blinks an *eyelid* if the *PUMP* continues running at *its* speed, even when the load has been turned down... [redface]
(end of parenthesis...)

So to recap, our constant speed pump does not know anything about the size of the load - it just carries on as normal, doing its job, namely, outputting 100% of its rated POWER... (and incidentally, consuming 100% of its rated *consumption*...).

Whence the utility of having a variable speed pump (BTW, even though I've got nothing to sell (such as pumps...) I was really glad U recognized said utility !

But U say,

Quote:
I'm not too sure how you would control it unless someone has designed a variable-output thermostat


Wel, that is the beauty of the whole idea - a variable speed pump will *sense* the load difference (it is pushing against a partly closed valve, so the pressure just went up some...).  In this case, the pump will reduce its revs, to drive the circuit at lower pressure. In cutting the revs, it is reducing its power output, and its energy: instead of using 80 watts, it might only be using 25W.  Therefore a big energy-saving...

If that pump is running for months at a time, that could be a significant dollar saving...

I guess that whether the pump just drops down to one of several pre-set speed settings, or whether it can adopt an infinitely variable speed adjustment, depends on the pump and the price U paid for it.

Reckon this is enough for one post, I'll consider the advantages of VS pumping on the solar (primary) side of the circuit when I get some time off...

G_H


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cwwilson721

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Reply with quote  #52 
Quote:
Originally Posted by stmbtwle
...

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.....


That's what we're doing, figuring out what "off the shelf" components can be used. So far, the winner is a fan controller.
stmbtwle

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Reply with quote  #53 

Actually a "cycle" to me was one on-off cycle. The "pulse rate" and "pulse width" will vary on demand.   It might be once a day or once in 5 minutes, just like my AC, or my water pump.

Controlling the fan/pump speed is the easy part; how do you "control" the controller?   Are you using some sort of differential comparator? 

I'm still trying to figure out how this works...  From what I gather you have one pump supplying several sectors each with its own valve, which may be opened or closed by a thermostat.  Are the valves proportional or are they on-off?  In either case I think you would need a pressure-sensitive pump which is probably what was described earlier.    

I've discovered that (at least some) centrifugal pumps ARE pressure-sensitive.   Cut off the flow and the power draw goes DOWN.  Not completely as there is still friction and fluid swirling around in the pump, but it DOES go down.   I checked a few minutes ago with a small AC fountain pump.  At free-flow it draws 23 watts (per Kill-A-Watt).  With the discharge capped, power draw was 15 watts.  I'm sure any engineer can explain it.

I can't speak for YOUR pump, but it might be worth checking.

_________________________________________________________________-

Another approach might be to give each sector its own pump (apparently some systems do).  Probably the valve controls already installed could control a pump instead (my differential thermostat controls a valve AND a pump with the same wire).  When a sector needs heat the thermostat turns on its pump instead of opening the valve.  When the sector doesn't need heat the pump is off.  When they are all off there is no power draw, instead of a single pump working against closed valves.


I guess it all depends on how much money you want to spend to save a few bucks in electricity.  An 80w pump running 24/365 will draw about 1.9 kwh per day or about 700 kwh per year.  At my electricity rate that's $70 per year.  If I can cut that to 25w 50% of the time, I've reduced my cost to $46/year.   I've saved $24.  If, say, I only run the system 6 months, I've saved a whopping $12.  In a year.  Really significant.  How much was that VS pump again? 


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Willie, Tampa Bay
cwwilson721

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Reply with quote  #54 
OK...Think of it this way:

If you speed up or slow down the fan in a hot air system (using a collector that requires a fan to operate), depending on the heat being generated in the collector, you increase efficiency. If you turn the fan off, efficiency drops, because of no air being moved. So, you use a VARIABLE SPEED CONTROL to increase efficiency. Makes sense, right? If you're moving air too fast through the collector, you're dropping efficiency. If you move it too slow, you lose heat out the glazing/etc, and lose efficiency. A VS Controller for the fan can change the fan speed depending on the conditions present at the time it is 'on'. Increased efficiency is the result.

The same theory should hold true in a water-based collector system: Speeding up, or slowing down the flow rate in/thru the collector should increase efficiency in the system, changing the flow rate when conditions change. Turn off the pump, no heat being collected. On the other hand, having too much flow would reduce the amount of heat being transferred to the liquid, also dropping efficiency. So, on/off not as efficient as a variable speed pump. Or, if not a pump, maybe a controllable flow (needle type) valve.

The controller part is fairly easy (a board has been made and posted about in the other thread), and should work fine for a VS Pump.

The object isn't to minimize cost of the system (even $70 spread out over a 10 year span is nothing, anyway). It's to increase the efficiency of the system as a whole. Get every last bit of heat out of that photon. 

Does what we're trying to accomplish make more sense now? (Not being sarcastic. I just think you missed the point of what is being pursued in this thread). I'm assuming you are thinking 'electrical efficiency", not "heat extraction efficiency"

Or am I missing the point? Or, if I am, I may actually be coming at the issue from the other side of the system: From the collector side of it, rather than the distribution side. Either way, a VS pump *should* increase efficiency of the system as a whole.
Garage_Hermit

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Reply with quote  #55 
@willie

I hear you 6/6 on the cost-saving issue.
However, there is more to it than simple power consumption, there is the maintenance and life-cycle-cost aspects also.

OK, the pump costs more, but it lasts longer and uses less power also...

It is neatly explained in this great link that Keith posted ages ago, as seen by 447 of us [smile]

http://www.simplysolar.supporttopics.com/post/variable-speed-pumps-6428273?pid=1278858954#post1278858954

ADDED:
and just for objectiveness/commercial fairness, here is a similar test, for a VS pump from another manufacturer...




And as Carl says, we are (so far...) only talking about the PUMP - not yet gotten onto the overall SYSTEM efficiency aspects yet...

( but getting there...)

G_H

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(1)  "Heat goes from hot to cold, there is no directional bias"
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cwwilson721

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Reply with quote  #56 
Quote:
Originally Posted by Garage_Hermit
...

And as Carl says, we are (so far...) only talking about the PUMP - not yet gotten onto the overall SYSTEM efficiency aspects yet...

( but getting there...)

G_H


That's what testing is for..at worst, we'd have an expensive pump, running at a constant rate, no change from the current DIY "state-of-the-art".

But, if it does really help, it would be 'optional'. The current DIY SOTA for Water Based systems is pretty good. This might help it just a bit more.

I think a variable speed fan in a Hot Air System may be even more beneficial. Then again, I was wrong earlier this month...It's conceivable it can happen 2-3 times a decade....lol

The VS concept, as a whole, should be valid. Differing loads, differing amounts of sunlight, differing temps in the collector(s) and 'systems' to be heated, all point to a VS solution to improve efficiency, no matter if it's Air or Water.

Is it overkill? Maybe.

Testing will tell.


stmbtwle

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Reply with quote  #57 
Right, only testing will tell.

But while we're on the subject of making it work, AND keeping the cost down:  Any small AC pump or fan can be varied with a $15 fan control from Big Box, only problem is that "controlling the controller" is still MANUAL.  So how to automate it?

Automotive thermostats are cheap and available in a wide range of temperatures.  We've already discussed using one to actuate a flap or door to ventilate a stagnated collector.  Suppose one were to connect the thermostat to a linkage operating the Big Box fan control?   There is your temperature-sensitive speed control, and you can use the pump/fan you already have!  A DC pump would require a different type of controller, but the concept should still work.  Thoughts???

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Willie, Tampa Bay
Garage_Hermit

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Reply with quote  #58 
Not wanting to put the cart before the horses... I suspect a thermostat is not the right element for the desired application: it is basically only an on-off switch, working around a setpoint...

What would be required would be a "variable thermostat" - rampleasure.net/lee/index.php/323

I am betting there is an easier way !

G_H

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stmbtwle

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Reply with quote  #59 
That's the advantage of a differential thermostat.  While it doesn't control fan speed, the "setpoint" DOES vary, according to the temperature of the storage.   As storage temp goes up, the "setpoint" for the collector goes up as well. If the storage temp goes down, the setpoint goes down to maximize efficiency of the collector.   If the collector temperature drops (cloud) the thermostat will shut off the fan/pump immediately to avoid wasting power and heat.  Some also have a high-limit setpoint so storage temperature does not reach a dangerous level.
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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
cwwilson721

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Reply with quote  #60 
I was mentioning the board here:

http://www.simplysolar.supporttopics.com/post/show_single_post?pid=1282658719&postcount=9

Attach thermal sensors, and you get variable speed via PWM.

It's a Thermostat/PWM Speed Control/Differential controller all in one, and should be easily adaptable to VS Pumps.

Depending on the temperature settings, you get variable speeds. Not on/off, like a standard thermostat, but varying speed dependant on the sensors. And can control 2 VS fans/pumps/whatever.

Now to get real details....
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