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Garage_Hermit

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Reply with quote  #71 
@carl

Quote:
There are mechanical/inline thermostats that shut off the flow when a certain temperature is reached. They are usually used on radiators.


I guess you are referring to these ?


[thermostatic_radiator_valve]
This looks like it is manually controlled - and this next one is controlled electronically (with manual  override possible) (about 5 times more expensive...)
[danfossvalve__44540_zoom]


Finally, this last one is a wireless version... drive it from your smartphone !

http://cdn.recombu.com/digital/images/news/M11004/1350043182_w315_h510.jpg

Irrespective of the version, they should all work OK with a VS pump, using the auto-adaptive pressure feature.

Therefore, I don't actually see the need for...
  • Quote:
    A combination pressure and temperature controller, driving VS Pumps via PWM
because the VS pumps referenced above have a built-in pressure sensor.

OK, a VS speed pump that has NO electronic pressure sensor would need some sort of controller.  But I can't see how a dual-feature controller would add any real functionality - it sounds awful complicated and would no doubt up the cost quite a bit...  Since there is (presumably) some sort of connection between the temperature and the pressure, then one channel ought to suffice, in my mind...

Anyhow, I guess what's important is that not only is VS pumping/circulation desirable, it is also best if it can be commanded by integral pressure control.  Then whether your valves are manually or electronically controlled, or manually overidden even, then the pump just adapts its speed to the pressure conditions of the circuit. 

What's also important, is, the user -- "the man in the loop" - remains in charge of the installation, deciding which zone to turn up or turn down or OFF; or decides the program setting so that the centralized electronic control manages the various zones...  And the pump just does the business accordingly...

I'll try & look at the drive-side (rather then the load) aspects in a while...

Cheers,

G_H

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cwwilson721

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Reply with quote  #72 
The "manual' version would be fine...just set it for the temp you want, and it'll shut that 'loop' off when the temp is reached.

As far as "complicated" controller goes, it's just a matter of sensors and changes in the programming. Basically, use a pressure sensor as one of the inputs instead of a temperature probe (they both use voltage as the input, so no biggie there), test/figure out what values from the pressure sensor corresponds to the desired speed for the temperature probe, and set accordingly.

Ex: Let's say low pressure reading (all loops of a 3 loop system are open) is .2v, and 60F is .2v for the temperature probe. Continued testing shows .5v is 2 loops 'off', one loop heating, and .5v equals 150F. Just test, and set the controller as the same temps as the voltage of the pressure sensor sends for the desired speed. (These are just examples. No tests have been performed)

We should be able to use the fan controller from the other thread, if we can get the probe specs (voltage spread). The amp max on it is 4A per pump/fan, so it may be possible...Except, on one circuit, we may want more flow when sensor voltage is high, and the other slower flow when sensor voltage is high (maybe sensors can be ordered that are 'reversed'? Don't know)...But that can be worked out...

The advantage to the XS FAn Controller is cheaper pumps, no need for a integrated pressure circuit, thus, can use the cheaper PWM Pump(s) on both sides.

If I can get more details on the controller, I'll post them.
And, various sensor (pressure and temperature) specs, and how/if they'll work

Garage_Hermit

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Reply with quote  #73 
Link to TACO link variable-speed circulator, as suggested by Willie...

Includes an interesting video...

http://www.taco-hvac.com/en/products/Variable%20Speed%20Delta%20T%20%2200%22%3Csup%3E%26reg%3B%3C/sup%3E%20Circulators/products.html?current_category=372#

Here it is...
[372]
Sounds like just the thing to have !

G_H

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cwwilson721

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Reply with quote  #74 
Check out the video here (the part we would be interested in is at about the 10:55 mark):

http://www.thisoldhouse.com/toh/tv/video/0,,20805187,00.html
Garage_Hermit

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Reply with quote  #75 
yeah - variable flow, to save on the power bill, sounds neat !

Course, where HE has to pay for GAS, we get our heat for FREE !

G_H

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cwwilson721

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Reply with quote  #76 
Well, cost of electricity...

Even since that would be negligible here, variable speeds would still save on wear/tear on the pump, lines, etc.

But, add in the electric savings, and maybe adding another possible 50% lifetime on the pump, and even one blown out water line, it seems worth the extra cost.

So, pressure side control is 'on the market'...now for temperature controlled VS pump...
sundug

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Reply with quote  #77 
I have been reading Tom lane's-"Solar Hot Water-Lessons learned 1977 to today" , which is a great overview of SHW from a guy who has been in the industry for decades. He says on page 10-
"The right PV module matched with the proper DC pump cannot run at the "wrong" time. DC pumps with PV modules, functioning as both the controller and the power source will outperform differential controllers used in small pressurized glycol systems or open loop residential hot water systems, especially under low sun conditions. This is due to the variable speed nature of DC pumps."
------------------------------------------------
I should add that the PV panel and pumped I bought in 1990 from Zomeworks was sold as a matched set. I also added a solid state zero degree differential, PV powered differential controller- http://www.arttec.net/Solar/9-23-02/Sept23-02.html
to make sure the pump does not run unless collector temps are above tank temps, altho I do not feel it was a problem before. Doug

 

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sundug

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Reply with quote  #78 
PV pumping provides low cost variable flow. Sundug

From Homepower Issue #126, Aug, Sept 2008  Article titled "Under control-solar water heating- SHW controllers" Page 60
 
"Parasitic loss occurs when energy is consumed or lost in order for a system to make more energy. <snip> In grid powered SHW systems, the pumps and controllers take a certain amount of electrical energy to operate. <snip> If the parasitic losses are greater than the solar energy being put into the SHW system, a net loss of energy results. In PV-direct DC systems, the pump energy losses are inconsequential because the energy from the PV module is there regardless, and at no cost. But in AC systems, a wider temperature differential is used to ensure that the parasitic losses are not greater than the solar energy gained. <snip> Since there is no utility generated parasitic power consumed with a PV powered DC differential controller, the turn off differential is lower-sometimes zero is appropriate if the pipe losses are negligible."
-------------------------------------------------------------------------------------------
 This makes it clear that PV pumped SHW systems are more efficient because they have a zero degree differential, gaining solar heat whenever collector temps are above tank temps, while AC powered system differentials range as high as 18*F, to overcome losses caused by carbon based grid powered pumps. Doug
 

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stmbtwle

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Reply with quote  #79 
Solar powered pumps if properly matched will automatically vary their speed according to input. That said, matching them to the proper panel and installation can be tricky. If the pump is undersized or underpowered, on hot days it's possible to get more heat input than the pump can move to storage, in which case the differential will rise until the input vs output stabilizes. On overpowered setups, it's possible on overcast days to pump hot water from storage to the collector where some heat is lost through the glazing.

A differential controller is sort of a quick-and-dirty solution. If the collector is warmer than storage, the pump will run. If not, it won't. If the pump is moving too much heat for the current input, the collector temp will drop until the differential drops to the setpoint and the pump shuts off. Then as the collector heats up the pump will start again, and so on. You can call this "cycling" or "batch processing", but to me they're the same. If the dead band between on and off is too close, the pump will be constantly cycling. You can reduce the cycling by controlling the pump speed, or by setting a wider dead band.

AC or battery powered pumps will not change speed automatically unless a differential-sensitive speed control is installed. This works fine but can be tricky to program, as conditions are constantly changing.

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