Navitron Renewable Energy and Sustainability Forum

BIOMASS => General => Topic started by: bovnet on March 18, 2011, 05:27:57 PM



Title: differential controller
Post by: bovnet on March 18, 2011, 05:27:57 PM
Hi,

Im using a small differental control for the stove pump. Any pointers as to what min and max differentials to use ?

Steve


Title: Re: differential controller
Post by: Ivan on June 23, 2011, 12:58:32 AM
I think there's a critical temperature to prevent ...now what's it called..... back end rot or something. Lukewarm water isn't good for boilers, so minimum temperature at boiler of 45C, I think.


Title: Re: differential controller
Post by: bovnet on June 27, 2011, 09:51:46 AM
Yes got a mixing valve to quickly bring the boiler up to 61c drawing return water from high or low points on the tank as required. Was after pointers for the switch on switch off differential between tank and boiler.


Title: Re: differential controller
Post by: Brandon on June 27, 2011, 10:08:41 AM
bovnet, what mixing valve are you using? have you allowed the system to fail safe to gravity (with adequate heat loss) circulation?


Title: Re: differential controller
Post by: bovnet on June 27, 2011, 10:12:23 AM
Yes as my tank is below the stove i have a gravity safety circuit with flat plate heat exchanger and mains cold water to cool operated by a manual capillary valve.


Title: Re: differential controller
Post by: Brandon on June 27, 2011, 11:04:02 AM
and as I asked, what valve are you using?  Do you have any diagrams or schematics?


Title: Re: differential controller
Post by: bovnet on June 28, 2011, 06:14:31 PM
http://www.heatweb.com/xcelinstall.pdf page 19


Title: Re: differential controller
Post by: Brandon on July 03, 2011, 10:14:33 PM
hmmm, plumbing by numbers eh?...

In that instance, I would control the circulating pump with a flue stat, then it will only run when there is heat to be had.  I see no real need for TDC in the schematic shown.


Title: Re: differential controller
Post by: bovnet on July 05, 2011, 12:23:48 PM
Knew there was some kind of jibe coming.

There are certain stoves where that really wouldnt work.

It doesnt answer my question in any way at all.


Title: Re: differential controller
Post by: Brandon on July 08, 2011, 10:36:16 PM
bovnet,

sorry that was not intended as a jibe

Can you further explain "There are certain stoves where that really wouldnt work."

I am trying to be helpful, and constructive.  You are after advise, I am trying to give it.  I honestly do not see why you would want to complicate things by using a TDC.

An explanation of your thoughts and logic would be helpful, so that we can understand what you are trying to achieve.

Brandon


Title: Re: differential controller
Post by: bovnet on July 09, 2011, 08:41:38 AM
The issue isnt weather to use a differential controller or not  its installed. Im after any rule of thumb, methods of reaching best settings on a differential control. the same i guess will apply to solar. What effect does the pipe length have for example ? or it is just observation of startup and stop. The situation i dont want is on cooldown drawing heat from the tank into pipe work. Do people just use defaults ?

Certain stoves self regulate depending on the water temperature. I cant see one of these damped down been able to spring into life and operate a flue stat.

My set up works really well. Someone runs a bath, then a short time later the stove springs into life.


Title: Re: differential controller
Post by: Solal on July 10, 2011, 04:29:55 PM
I assume only one sensor  is fitted sensing  hot  flow ( say 70c) from the stove and when the set  temperature is reached  the pump  is energised.
A differential  of say  5  degrees  and  then  pump off.


Title: Re: differential controller
Post by: bovnet on July 10, 2011, 05:10:44 PM
no 2 sensors, one on top stove outlet and one on the return to stove at the tank outlet. A backup pipe stat at 85c is also on the stove outlet


Title: Re: differential controller
Post by: Solal on July 10, 2011, 05:15:54 PM
What does the return  sensor  do?
I would fit  S2  to the cylinder at the  stove flow input level. And  TminS1  set  to 60c at the stove. Having it lower  is pointless  as I think you have a termovar fitted.
And TmaxS2 set to say  80c. And  a 5 degree  delta T.