What kind of aquastat to turn pump on when low temp and off when high?

LegendsCreek

My wood boiler services 3 of my buildings. I want to keep the inside oil boiler in one of my less used buildings warm but not have the wood boiler pump constantly. What kind of aquastat can I put in there that I can strap onto the oil boiler return line to sense when the water reaches a low temp, then turns on the circulators for the wood boiler to bring in hot water, then shut off when it reaches the high temp (or is there a timer of some sort)? Trying to think of the best solution to keep the oil boiler water hot without running the pump all the time. Thanks!

LegendsCreek

Thanks for the recommendation but I am looking for something that straps on. Hopefully there is a solution that doesn't involve needing an immersion sensor.

hot_rod

A solar differential controller would be another option. They can be used as a setpoint or differential function. High and low limits can be set, nice digital display, and some data logging and heat energy logging.

They also have variable speed functions built in to lessen pump cycling.

It may be cheaper that two of the well style aqua stats and it is a digital control.

Max amp is typically 1, if you have high head pumps it would take an isolation relay.

Here is a manual that shows al the different arrangements.

http://www.houseneeds.com/upload/pdf/caleffi-isolarplus.pdf

warno

I can't remember for sure if the sensor can be banned to the side of a pipe or not but I have a Johnson Controls A419 that works great. Has options for high or low shutoff. Easy to use and good price.

LegendsCreek

thanks guys for the info. Warno, the Johnson Controls A419 looks like it may work but my question is can I make it turn on at a low and shut off at a high point? From the photos it looks like I can secure it to my black pipe but not completely certain.

I didn't mention that it will be controlling two pumps. One high head and the other just a basic circulator. They are wired together to the same junction box already and I need this controller to tie to and control power to that junction box.

ratio

This model is line voltage powered. It can be set for heating or cooling operation. It says up to a 30* differential, which might not be sufficient for your usage but if you change the units to Celsius you should be able to get a wider deadband. The sensor can be zip tied on to the pipe, with heat transfer paste if you have it, but some insulation wrapped around will be more helpful.

The sheet shows the relay operating the load, but I always treat on-board relays as pilot duty, meaning they operate another (cheaper to replace!) relay or contactor & that operates the load.

hot_rod

I think pretty much any sensor can be strapped on the outside, use some transfer grease as Ratio mentioned, insulate completely around it. The outside of any metallic pipe will get as warm as the fluid inside, eventually, or close enough that you can compensate fro with adjustments.

I like to use a stainless hose clamp or two to fasten the sensor, zip ties loose some tension on warm pipes after time.
Find the real narrow types as the bend around two rounds better that the wide ones. Automotive parts stores have the narrow type.

warno

Yes the A419 has a heating or cooling option. So it can turn on the relay at either hot or cold.

LegendsCreek

Thanks for the info guys. I like the idea of the the metal clamps as opposed to the zip ties.

One issue I am wondering is with the differential on all of these, including the A419. Lets say I want to turn on my pump at 100 degrees, and have it power until it reaches lets say 160 degrees. All of these controllers have a 30 degree differential. So if I set it to turn on at 100 degrees, then the max temp it will shut off on is 130 or so. Correct?

hot_rod

I used the Ranco and Penn brands brand, it, and most others should have and adjustable differential. You should be able to find spec sheets online before you buy.

Johnson Controls, Ranco, Penn, Honeywell, Azel, probably others offer these electronic setpoint controls.

SWEI

Ranco ETC is another option. Comes in a few different configs.

LegendsCreek

I am looking at Ranco right now. They seem pretty reliable and excellent price. I am now seeing any with a higher differential. I would like the option of at least a 60 degree differential but I will settle for a 30 degree if I need to,.

LegendsCreek

I agree about doing it in series, but I was hoping to not have to spend the money on 2 units. 30 degrees would work for me but I was hoping for a little more control. This is all for a never-ending wood boiler project I have been setting up on my farm. Its been almost a year doing this install and I am 98% done and this will be putting on the finishing touches.

ratio

According to the data sheet I linked to above, the A419 will do a differential of 30*, F or C. 30* C is what, about 54 degrees F?

warno

I might have missed it but why do you need such a large differential?

Steamhead

No need to over-think this with electronic units. This Honeywell unit

https://customer.honeywell.com/en-US/Pages/Product.aspx?cat=HonECC+Catalog&pid=L6006C1018/U

or this White-Rodgers unit

http://www.emersonclimate.com/Documents/White-Rodgers/instruction_sheets/0037-1209.pdf

will do what you want just fine. They both have single-pole-double-throw (SPDT) switches so you can wire them to close the circuit when the temperature falls.

SWEI

Check http://www.mydtcstore.com/ No listings, but very flexible and quite inexpensive.

hot_rod

There was a setpoint control built that allowed up to an 80° differential adjustment for the mini tube injection systems, and other unique system designs.

I remember it being built by HeatTimer under a private label to the former RTI Radiant Technologies out of NY.

If for some reason you need a wide differential range, maybe check out the HeatTimer offering.

LegendsCreek

Good info guys! I have a question about setting it to Celsius to get the 54 degrees F differential.. Will this actually work if I change it to Celsius? If I could get a differential of 50 then it would totally work for me.

The reason for wanting 50 degrees is so I can find a sweet spot for this building. I have a Central Boiler that will heat my house, my workshop and my guest house. We rent the guest house on Airbnb and if its slow in the winter then we want to be able to heat the house only slightly to keep the pipes from freezing. So i figured with the higher differential I would be able to keep the oil boiler warm by running my wood boiler pump when the oil boiler reaches a low. I want to avoid wasting BTU's on the guest house when its unoccupied and give it just the bare minimum.

ratio

The paperwork says:

Differential (dIF) establishes the difference in temperature (in F° or C°) between the cut-in and cutout values. The differential is set relative to Setpoint and may be set from 1 to 30F° or C°. See Figure 7 and Figure 8.

I read that as 30° F or 30° C depending on units. I could be mistaken, perhaps a call to tech support is in order, if no one has an extra one to check.

This particular unit has a dry contact input for a setback function that can reset the setpoint by 0-50°, again F or C. This merely moves the setpoint by a predetermined amount, but I see no reason why it can't reset itself once it hits its setpoint, effectively adding the reset offset to the differential.

NB: I like complicated controls. Rube Goldberg is my hero. There may be a better way to do this.