Digital t-stat

[Eric H]

The old Honeywell t-stat that controls the circulators for my floor heat wasn't coming on everytime. I was just going to replace it with the same model but the local supply house wanted $80 for it so i decided to shop around. In the Grainger catalog I found a digital Electronic Temperature Control for $79 so I bought one. I installed it today. Set it for make at 33* with a 1* differential. Seems to work great for this application.
This is the one I bought: http://www.etcsupply.com/ranco-etc111000000-digital-temperature-controller-p-86.html
There is also a 24 powered version that the sales guy said I could use: http://www.etcsupply.com/ranco-etc112000000-24v-p-102.html

I bought mine at Grainger for $79 plus shipping. The sites above are cheaper and I think I saw them for less money on Amazon.

 

[Buzzie8]

I wonder if I could use them for my doors? There is a huge differential in the T-stats I have right now.

 

[MEP001]

I might have to try one for the weep system. The refrigerator type I've always used has a 5-degree minimum differential, which means the weep stays on until it gets above 40°.

 

[Greg Pack]

Had a buddy of mine that put his ACW in OOS mode when it got too cold with one of these,

Why not use output #2 of your weepmizers?

 

[Eric H]

Why not use output #2 of your weepmizers?

I am already using outout #2 to control the automatic switchover to hot water rinse @ 27* in the bays.

 

[pitzerwm]

Expand the output #2 with a PLC or relay to control everything.

 

[Eric H]

Expand the output #2 with a PLC or relay to control everything.

Can I use a PLC to turn the circ pump on at 33* and the hot water switchover at 27*?
I do not know anything about PLCs. I should really figure it out. I am already doing just about everything I want to do using t-stats and relays.

I would really like to be able to actuate the changers to give refunds thru my cell. When my 78 year old weekend guy finally retires I'm sure it will get a lot of use.

 

[MEP001]

Can I use a PLC to turn the circ pump on at 33* and the hot water switchover at 27*?

Not from the output of the WeepMizer, but you can with a single temperature probe to the PLC. Each output can be programmed with a different parameter.

 

[pitzerwm]

Why can't the weepmizer trigger a PLC

 

[MEP001]

It can trigger a PLC, but only at one temp since it's just opening or closing a circuit. If all you're telling it from the Weepmiser is when the temp drops below 32°, there's no way for the PLC to know when it gets to 27° and to do something else.

 

[soapy]

I have been using the digital thermostats for years on my boilers. Ranco is one brand I use. I get mine at Johnstone supply. They have held up very well.

 

[Waxman]

Can you explain why the 1 degree variable saves money on gas burned/not burned?

I'm just not that bright.

thanks!

 

[MEP001]

I don't see where anyone said it does; I'm sure it's more about keeping an accurate temp.

 

[Waxman]

Hmmm. Okay. I thought that there must be a cost benefit to having the slab stay a more constant temp rather than lots of warming and cooling in a wider temp. range.

 

[Eric H]

From this website:
http://www.pmmag.com/Articles/Column/2accc815e0a8c010VgnVCM100000f932a8c0____
This is the portion of the article that answers your question:
What is differential anyway? Chip says, “Well, first you need to specify what control you are talking about. For a high limit-type control where the device is carefully calibrated to switch off (open the switch) at a specified maximum temperature, differential is the ‘difference’ between when the control opens the switch to stop the heating of the boiler, and the temperature where the switch turns back on because the boiler water has cooled below the set-point minus the differential.

“For instance, let’s say the boiler limit control is set to 180 degrees F and the differential is 20 degrees F. When there is a call for heat and the water temperature is, let’s say, room temperature, the control will turn on the energy source (gas, oil or electric) and continue to allow the boiler to heat until the water reaches 180 degrees F. At that time, the switch opens, turning off the energy source. The boiler water begins to cool. When the boiler water temperature drops to 160 degrees F (180-degree F set point minus 20-degree F differential), the switch will close and the boiler will begin to heat again.


So in my application (floor heat circulator pump) I want the pump to turn on at 33* and turn off at 34*, a 1* differential. The burner on the boiler has a preset differential of 5-10*, the manufacturer sets it. If the burner had a 1* differential it would turn on and of constantly, this is called short cycling. Short cycling is not only hard on the equipment it is also extremely inefficient. Generally the longer a burner runs the more efficient it gets.

 

[Waxman]

Still not getting it.

Is your circ. pump going to be short cycling then?

 

[mjwalsh]

Still not getting it.

Is your circ. pump going to be short cycling then?

Welcome to the world of automated temperature controls. It is a balancing act to some extent. Ideally, you would have the "where with all" to observe exactly via logging to see where the temp is not maintained &/or where something is cycling more often than desired. A good chunk of our PLC programming & logging for our new dog wash was dedicated to just those abilities. In my opinion, it is better to have the capability to easily change & tweak the differentials, ranges, & alerts (alarms) than to be stuck with some weird huge 20 degree swing by the time the boiler catches up etc. Probably in that scenario you would over compensate the high temperature too much & that could effect the efficiency. Within our laundromat commercial clothes dryers there is a PC board that is dedicated to modulating from hi to lo flame to maintain the temps which helps both efficiency & accuracy. On our boiler sytem we have smaller boilers that fire in sequence based on the current demand or need so only a portion of our boilers are firing ---- this helps efficiently ---- but not possible with too crappy of temp controls.