American Standard boiler and outdoor reset: Am I doing this right?

OldBoiler65

Hello folks, I'm here looking for any helpful tips you may have. I've been running this 1965 American Standard G210 for the past two winters. Just looking for any way I can dial it in better or if I already reached the limit for improvement. I am using a Taco PC700-2 outdoor reset and a Taco SR501EXP relay. The boiler only has a high limit as original equipment, and it is in place and working. I found out about the PC700-2 and thought it would be a good way to control the boiler more precisely. It's been working fine this way for the past two heating seasons. But I do still get some short cycles. The boiler temp sensor is installed on the return pipe, and I wrapped it with insulation. Last winter I installed a Tekmar 518 thermostat in place of my old Honeywell mercury t-stat. I have it hooked to its own outdoor temp sensor also. I have been playing around with the differential settings ect on the PC700 but its trial and error. Still slowly getting the grasp of how it works. Yes, I know this boiler is oversized and outdated, but it does work good till I get something else. The house is a 1920 bungalow around 2500 sq feet with a full basement. Boiler is running several cast iron radiators.

Ironman

I didn’t know that you could connect an outdoor sensor to a 518. If so, does that influence the stat? And if so, you shouldn’t have that and the PC 700 both trying to work off of outdoor temperature.

What’s the CPH rate on the 518?

OldBoiler65

Ironman said:

I didn’t know that you could connect an outdoor sensor to a 518. If so, does that influence the stat? And if so, you shouldn’t have that and the PC 700 both trying to work off of outdoor temperature.

What’s the CPH rate on the 518?

Thanks! I started thinking that myself. I'll bet it does influence it. I got carried away with gadgets and hooked an outdoor sensor to the 518. Think I will unhook it and see what happens. Couldn't find the CPH rate yet, just that it has auto cycling.

STEVEusaPA

Best thing you could do for energy savings is to tighten up your building envelope.

OldBoiler65

I agree, it really needs tightened up. Working on it a little at a time.

OldBoiler65

Alright, I'll get some pipe insulation for it. All I had was the wall kind at the time.

Ironman

I believe that the sensor connection on the 518 is for a radiant floor sensor, not an OD.

OldBoiler65

It could be exactly that. I seem to remember it having a setting for outdoor in the menu. But I'm going to unhook it anyway. Thanks for the help!

Teemok

518 will display OD temp. I'm not sure it does anything with that info. What are your design settings? Lowest OD temp, highest OD temp and warm weather shut down, Lowest and highest return water temp.?

Teemok

PID thermostat control of a control doing ODR might be an over complication. Long firing times (read not cycling) requires firing rate staging or variability. I'm betting you don't have that. The very small percentage of efficiency gain achieved by lowering the water temperature might be negated by causing more short cycling. You don't want to condense your combustion by products (exhaust). ODR can help with indoor comfort in that you can control indoor over shooting and at the same time experience less undershooting when it's very cold out.

OldBoiler65

Teemok said:

518 will display OD temp. I'm not sure it does anything with that info. What are your design settings? Lowest OD temp, highest OD temp and warm weather shut down, Lowest and highest return water temp.?

I had the PC700-2 set close to the factory settings at first. All temps Fahrenheit. Boiler start 75, Outdoor start 75, Boiler design 170, Outdoor design 10, Boiler min 140, Differential 20, and I had warm weather shutdown off.

OldBoiler65

Teemok said:

PID thermostat control of a control doing ODR might be an over complication. Long firing times (read not cycling) requires firing rate staging or variability. I'm betting you don't have that. The very small percentage of efficiency gain achieved by lowering the water temperature might be negated by causing more short cycling. You don't want to condense your combustion by products (exhaust). ODR can help with indoor comfort in that you can control indoor over shooting and at the same time experience less undershooting when it's very cold out.

Should I use a more simple thermostat than the 518? I had a new old style mercury stat with it before. It seemed to work alright after playing around with the heat anticipator.

Teemok

PID works on the principle of adaptive pulsed on and off intervals. It (short cycles) as it approaches the set point so it doesn't over shoot. It learns from the past. You might be able to turn it off or make the setting so it is effectively turned off. I'll look it up. The ODR curve can help prevent overshooting. Two things adapting can cause problems. You want your boiler to fire in long cycles. On and off is inefficient. Your numbers look safe. Widening the diff would make it fire longer but also be off set point for more of the time. It's a comfort vs efficiency game of adjusting settings.

Teemok

518 says pwm (pulse width modulation) That may or may not use PID. I see no adjustments. It's a good thermostat. On other PID stats I've used had adjustments. I would watch what it's doing as it approaches set point. The boiler control will prevent some short cycles as it rides its diff. As long as the boiler doesn't cool down and then fire for a short shot then cool again. Flame on and off is one cycle and cold to hot is another. Cold to hot is more of the efficiency killer than flame on and off.

Steamhead

The manual for this unit is rather ambiguous, but ISTR every ODR control I've ever used says to put the boiler temp sensor on the supply pipe leaving the boiler, not the return line. This way it monitors the actual boiler temperature.

Teemok

I've seen It on both. On return it heats up faster using the boilers operator temp till the return gets warm. The numbers are just lower and it plays boiler minimum return temp. guard.

OldBoiler65

Great information. From memory, it's been since this past spring that I had the heat on full time. But I seem to remember getting it to fire in good cycle times. Only it would come back on and fire for a couple minutes or more then shut off for a while till the next cycle. This is the 518 approaching the set point I assume. Didn't seem to do this from cold to hot. Thanks again, I'm a hardcore DIY guy but this is all new to me and I really appreciate the help.

The Steam Whisperer

One other thing to consider is that if you have a single zone high mass system..ie converted gravity radiators.... the system already naturally resets itself due to the thermal mass preventing the system temperature from getting very high most of the year.

OldBoiler65

Steamhead said:

The manual for this unit is rather ambiguous, but ISTR every ODR control I've ever used says to put the boiler temp sensor on the supply pipe leaving the boiler, not the return line. This way it monitors the actual boiler temperature.

Would it be better if I moved it to the supply? I can do that easy enough.

Teemok

The ODR boiler control might cycle the boiler more on warm up when on the supply. (supply hits set-point while the return is still warming up. On the supply is tighter temperature management at the cost of a few more cycles. 6 or 1-1/2doz. Some conditions could have the return water coming back cooler than the boiler minimum. If want to assess/ find condensation points by controlling outlet temp. the supply works.

OldBoiler65

Sounds like a plan to me. I'll give it a try and see what happens. I think I have a pretty good idea how the ODR works now. This forum is a great wealth of knowledge.