Anyone using one of the "Variable Setpoint" circulators?

[webie]

...
When you add well insulated storage it will hold its temperature unless water is exchanged with a load. By running the boiler 24 hours a day all of the heat load will be supported by the boiler. It will be as if you do not have storage. I don't see that it will help you any. If you change the way you use your boiler you could benefit from storage.

I like storage, I also like starting a fire in a Seton design boiler, I often get to light one, my everyday boiler is a large Essex.

If I understand Pat's goals correctly, he wants to use storage to eliminate short-cycling of the boiler by isolating the load from the boiler with some storage. The boiler would fire when storage gets less hot enough and would idle when storage gets more hot enough. Gasification boilers with storage normally run one burn with maybe some short cycling at the end, a Seton type boiler would allow multiple one hour or so burns, each yielding 150,000 btus or so, spaced in time by hours.

The trick will be to get the boiler to stay off until the top of storage is cool enough and then stay on until the bottom of storage is hot enough.

--ewd

Exactly !

Now that I have had a few beers and am thinking irrationally !
I am basically thinking what you really want is to increase the water capacity of your boiler . More burn time on and then more off time .
Skip all the electronics and just use your aquastat on your boiler , Just plumb your storage in reverse , heat from the bottom up , instead of the top down .
( Hot out of the top of storage tank to cold return of boiler and from hot boiler to bottom of storage tank )
The Plan . Top of the tank is 150 there is a call for heat , tank charges from bottom up till it hits the top at 190 and boiler kicks out then house cools tank from bottom up . when top of tank cools back to 150 cycle starts over , Massive thermo mixing in storage will occure . Basically work like a Giant water heater with a coil for home heating .
Ok I am ready for some one to blow a hole in this plan .
webie

 

[sgschwend]

P.
I had an idea that you could try without changing what you have now. If you like it you could use it that way or implement it in a more permanent manner.

Change your load thermostat (the house thermostat) hysteresis. If you increase the house thermostat hysteresis the run time demand on the boiler will increase and it will run longer.

I think that is what you are trying to achieve?

or You can do the same thing by increasing the boilers set point aquastat hysteresis.




In case you are wondering what a hysteresis adjustment does:
The set point is a very specific setting, in order to guard against a rapid on/off cycling of the heater the thermostat or aquastat has a built in amount of temperature delay or hysteresis.

In the damper circuit the damper is opened when the boiler temperature is below the set point but closes when the set point is reached. The boiler would probably overshoot temperature some but eventually the temperature of the boiler would drop. It is not desireable for the damper to open again as the temperature reaches the set point so on the downward direction the damper is switch open at a termperature that is several degrees below the set point. This number of degrees is the hysteresis, by adding more degrees the boiler will need to run longer to reach the set point.

Mechanical thermostats and aquastats have an adjustment for this, it is normally locked down or sealed with some adhesive. Honeywell sell aquastats with a 5 degree difference and an adjustable 5-30 degree difference.




here is a link to the boiler control I am using.
(broken link removed to http://www.dwyer-inst.com/Products/Product.cfm?Group_ID=622)

 

[patch53]

P.
I had an idea that you could try without changing what you have now. If you like it you could use it that way or implement it in a more permanent manner.

Change your load thermostat (the house thermostat) hysteresis. If you increase the house thermostat hysteresis the run time demand on the boiler will increase and it will run longer.

I think that is what you are trying to achieve?

or You can do the same thing by increasing the boilers set point aquastat hysteresis.




In case you are wondering what a hysteresis adjustment does:
The set point is a very specific setting, in order to guard against a rapid on/off cycling of the heater the thermostat or aquastat has a built in amount of temperature delay or hysteresis.

In the damper circuit the damper is opened when the boiler temperature is below the set point but closes when the set point is reached. The boiler would probably overshoot temperature some but eventually the temperature of the boiler would drop. It is not desireable for the damper to open again as the temperature reaches the set point so on the downward direction the damper is switch open at a termperature that is several degrees below the set point. This number of degrees is the hysteresis, by adding more degrees the boiler will need to run longer to reach the set point.

Mechanical thermostats and aquastats have an adjustment for this, it is normally locked down or sealed with some adhesive. Honeywell sell aquastats with a 5 degree difference and an adjustable 5-30 degree difference.




here is a link to the boiler control I am using.
(broken link removed to http://www.dwyer-inst.com/Products/Product.cfm?Group_ID=622)

Hi Steve, first off, I really appreciate you, and everyone else, helping me trying to figure something out for my new system.

I would rather not do anything to my indoor thermostats, I would rather change the something on the boiler. I know how an aquastat works, but thats about it. I have mine set at a 20 degree differentail (shut off at 185F, back on at 165F) currently. It has the 5-30 degree differentail. Never heard of "hysterisis" before ? When you talk about adjusting the hysterisis, do you mean adjusting the aquastat?

Could you somewhat explain how the Dwyer works?

thx, Pat

 

[sgschwend]

Yep, the difference is the hysteresis.

Set it to 30 and drop the 185F to 180F. Then see how many more run minutes you get and how much the overshoot increases. If you max is OK or lower than you want then up the 180F set point, that should increase the run time even more.

The Dwyer works just like the aquastat it has a thermistor probe that would be located in a thermal well or strapped to the boiler output tube (I would put it as close to the front as possible so you could take advantage of some of the other features such as starting and stopping the boiler's circulator. It has a digital display that shows the measured temperature (other things are displayed too, but not as essential).

There are a lots of programing features that are selected with the buttons on the front. For the most part to emulate the Honeywell you are using the set point would be entered and then a difference value you desire can be entered, all with digital accuracy. The setting ranges are much higher than the Honeywell. Programing those two numbers would be all that is necessary to replace the Honeywell. To make it easy all settings have a default value so that the device will work right out of the box. The relay switches have easy screw type connectors in the rear of the unit.

The second channel can be program as a cooling loop, which is what a circulator controller needs to do. The set point when reached will turn the circulator pump on. You can also add a second temperature probe and independently control a second loop, such as if you wanted to measure the storage temperature and switch on a different pump or fan or any other device.

Glad this is helping

steve

 

[patch53]

Yep, the difference is the hysteresis.

Set it to 30 and drop the 185F to 180F. Then see how many more run minutes you get and how much the overshoot increases. If you max is OK or lower than you want then up the 180F set point, that should increase the run time even more.

The Dwyer works just like the aquastat it has a thermistor probe that would be located in a thermal well or strapped to the boiler output tube (I would put it as close to the front as possible so you could take advantage of some of the other features such as starting and stopping the boiler's circulator. It has a digital display that shows the measured temperature (other things are displayed too, but not as essential).

There are a lots of programing features that are selected with the buttons on the front. For the most part to emulate the Honeywell you are using the set point would be entered and then a difference value you desire can be entered, all with digital accuracy. The setting ranges are much higher than the Honeywell. Programing those two numbers would be all that is necessary to replace the Honeywell. To make it easy all settings have a default value so that the device will work right out of the box. The relay switches have easy screw type connectors in the rear of the unit.

The second channel can be program as a cooling loop, which is what a circulator controller needs to do. The set point when reached will turn the circulator pump on. You can also add a second temperature probe and independently control a second loop, such as if you wanted to measure the storage temperature and switch on a different pump or fan or any other device.

Glad this is helping

steve

So Steve, are you saying w/ the Dwyer it works like an aquastat only the hysteresis can be set to a much wider range?

In other words, instead of the only 30 degree differential that the aquastat will allow, I could use the Dwyer to get lets say a 50 degree differentail? And the Dwyer would completely shut down the boiler circulator at a set temperature and turn it back on again at another set temperature? I would think you would have to keep the circulator running at minimum speed at all times to keep removing the resdiual heat off the boiler to keep it from getting too hot and blowing the pop-off? Not sure I understand how that would work.

Thx, Pat

 

[sgschwend]

To adjust the difference on your Honeywell difference setting you will need to remove the outer cover.

If you are running 24/7 start and stop control over the circulator would not be that important. With storage many users want the machine to know when the fuel is gone and turn itself off after the heat has been recovered or sent to storage.

The circulator would restart if the boiler temperature returned above the set point.

The TSS2 is a nice dual thermostat, my documents show the difference maximum is 20, when programing in centigrade the maximum difference would be 20C or 36F, when programing in Fahrenheit the difference max is 20F.

There are other models that work in a similar way with different specs. Such as the TCS series. The TCS series uses a thermal couple and can measure very high temperatures such as inside the boiler or flue, up to 999F. Or even other brands that perform the same way but with their own specs.

I use the TSS2 to control the damper and draft fan using the heat control, and the circulator using the cold control. I also have a TCS measuring combustion temperature that I use to turn the draft fan off when the fuel is gone. In all cases if the boiler reheats then the system will cycle back on.

It sounds like other folks have contribute the value of a multi speed ciculator, that is an interesting and useful option too.

 

[patch53]

Thanks Steve, I think with my aquastat set at the 30 degree differential I can get the system to work about how I would like it. The Taco Δ T circulator should work well for this type of set-up, and with the Grundfos Alpha running the house zones I should have a fairly energy efficient system. I won't be installing any of this until after the heating season is over, and I'll probably end up changing a few things as I go anyway.

I just want to get away from having the Seton cycling on and off 20-30X/day. Hour long burn times 4-6 X/day would be a much better way to run the boiler.

Pat

 

[sgschwend]

Sound good, are you going to up your difference now to see what it does?