Pushing the envelope with a pressuretrol

ChrisJ

Someone recently emailed me asking a question which made me question my self.



My mercury style pressuretrol is set as low as I could get it to work.  It cuts out just above 1 PSI and back in at around 1 or 2 ounces.  I did this using my mouth and my 3 PSI gauge.  I have also tested the system using my king valves and it reliably trips every time.  If I recall there was a mechanical limit to how far I could adjust it so I stayed away from that.



Should I have any concern running this pressuretrol at these pressures?

Abracadabra

pressuretrol

I'm not sure that they are reliably repeatable at that low a cutin.

Leepoll

What Happens

So what happens to the cycle? If I set my non- mercury Pressuretrol down to 1 psi on main and .5 on diff whats the damage risk? Wll the system run and not shut off potentially? Will it have a hard time triggering a cut in if it's set too low. I ran it tonight for about 20 minutes and it seemed to be working.

ChrisJ

cut-out

I would say I have the same concern. If the cut-in varies slightly or even gets stuck off I can deal with that if that is the "maybe".



What I cannot deal with is the cut-out sticking. Its kind of important to me.

Mike Kusiak_2

Close to the limit

If you are concerned about the repeatability of the pressuretrol settings, then why are you setting them so close to the edge?



 As I recall, during normal operation you never build enough pressure to hit the 1 PSI cutout limit anyway, so what does it matter if you set them a bit higher? If you set to 1.5 PSI off, .5 PSI on the operation would be more reliable, and it would still make no difference during typical operation.

ChrisJ

Pressure

Hi Mike,



You are correct in that I do not build pressure during normal operation.



However, I am starting to experiment with night time setbacks. I have no idea how the system will react on a cold morning during recovery.



I think I will take your advice and adjust for 1.5PSI cutout .5PSI cutin.

Mike Kusiak_2

Optimized system

Seems like you have your system tweaked really well as far as venting and firing rate. You are generating all the steam the system can condense, with no excess to cause the pressure to build to the cutout setting.



If you start cycling on pressure with the setback, I would reduce the setback to the point where you still can avoid the cycling. Any savings you might achieve by the setback would be counteracted by losses of rapid cycling.

ChrisJ

pressure

Mike,



I just got done adjusting for 1.5PSI cut out and 0.5PSI cut in. The pointers still don't indicate correctly but I'm assuming this is pretty typical?



I'm hoping to get a 3 degree setback without cycling but I want to see how the 2 degree setback behaves this weekend first. We are suppose to see a low of 12F Sunday.

ChrisJ

1.5PSI

Mike,



Should 0.5PSI to 1.5 PSI definitely be ok?  I ask only because this pressuretrol is technically spec'd for 2 PSI minimum.  I had it cycle a few times with the king valves shut last night and it certainly seemed ok.  Then again it seemed fine when it was a hair above 1 PSI.



I'm planning on buying a vaporstat down the road but cannot afford it right now.

Mike Kusiak_2

Low pressure settings

I think you will be fine at those settings. You are lucky to have the mercury switch version as they seem to be much more reliable and repeatable at low settings. The microswitch type are more problematic, as is the case with the new microswitch vaporstats.



Since you were operating reliably with the 1 PSI and 2 oz settings, the 1.5 PSI and 8 oz thresholds should give a comfortable margin of safety. The pressuretrols are calibrated at the full scale settings so they are notoriously inaccurate at the lowest settings, which is probably why there are no markings below 2 PSI. Since you are calibrating with known pressures at your present settings you should be fine.



Did you reach the 1.5 PSI cutout at the end of setback recovery this morning?

ChrisJ

Pressure

I don't think so.

I didn't go and check the boiler during the recovery, however all of the Hoffman 1As were quiet.  No hissing or clicking so I assume this means pressure stayed pretty low as the radiators didn't even get steam to the vents.

ChrisJ

3 degree setback

Mike,



Did 66F all night long and 69F in the morning and the system did not go higher than 0.5PSI.  It was 26F this morning during the recovery so I need to see what it does tomorrow morning when its around 11 degres out.  That should the first real test of the system.

Mark N

Recovery time

Did you time how long the boiler ran when recovering from the set back? If so how long was it. Was there any overshoot? If so how much was it. What is the duration of your set back.

ChrisJ

overshoot

I had 1 degree of overshoot at the end.



As far as time not entirely sure, the system was running when I woke up as I have adaptive recovery enabled. I would say 35-40 minutes is a really good guess though.



I'll try to get up before she fires up tomorrow morning.



Duration of setback on weekends is 9:30PM - 9AM. Weekdays I am doing 9:30 PM - 6AM.





Do you think this setback is saving me anything?

Mark N

Objective?

What are trying to achieve with your set back economy or comfort or both? According to the PSE&G website every one degree of setback will save you 3%. But that is for a constant set back, so 12 hours would be like 1.5%. I've been tracking my gas usage ever since I had a new boiler installed a little over 3 years ago. I myself don't use a set back I leave the tstat at 70 from November till April. Keep good track of your gas usage and factor out what you use other things like heating water, cooking and clothes drying. That usage is best determined by how much gas you use during the non heating months. You may be underwhelmed by the savings.

ChrisJ

both

I like to sleep in the cold and I was hoping to save a little something at the same time.

Jamie Hall

And you won't even

save that much, as it really does take more fuel to raise the temperature than it does to hold it.  We have seen this discussion going on on the Wall for years, with no definitive conclusion... except that deep setbacks (which usually means over 5 degrees) on a daily basis seem to be generally regarded as bad news.

ChrisJ

ok

You convinced me.



I changed my programming to 67F at night 69F during the day. This will allow me to sleep in a cool house yet not too cool. 66F seemed a bit chilly last night overall and its not worth being chilly if I'm not saving anything.



I have to assume I'm not losing anything in the end and maybe do save something, even if its 10 cents a month.



I don't know if its just me, but I love waking up to heat. In fact the heat wakes me up before my alarm clock goes off.

Mark N

Savings

The mostly mild weather this winter so far has probably saved more money than you will save with any set back. I'm on the equal pay plan for gas and electric, my plan starts in August I'm $371 in the black right now.

malex

Another approach

I am experimenting with setbacks so the system doesn't have to fight the cold (raise the temperature when it is the coldest at 5:30 in the morning. Instead I do this: at 2:30am I let the tstat drop from 70 to 68 as it is getting colder outside. I do NOT raise it back to 70 in the morning when it is still cold. Instead I raise it to 70 at 1pm when the sun is helping me to heat the house. I do this not to save money but to avoid any noise in the morning as the boiler is trying to raise the temp or even keep it at 70 when it is 11F outside.



But I am thinking this should maximize any savings as it is really the temperature difference inside and outside the house that is costing money to maintain.



68 is still a comfortable temperature and I really just wake up and leave the house so it seems unnecessary to raise temp back to 70 just for that. Other people may have different needs but this seem to work for me. Any thoughts?

malex

Another approach

I am experimenting with setbacks so the system doesn't have to fight the cold (raise the temperature when it is the coldest at 5:30 in the morning. Instead I do this: at 2:30am I let the tstat drop from 70 to 68 as it is getting colder outside. I do NOT raise it back to 70 in the morning when it is still cold. Instead I raise it to 70 at 1pm when the sun is helping me to heat the house. I do this not to save money but to avoid any noise in the morning as the boiler is trying to raise the temp or even keep it at 70 when it is 11F outside.



But I am thinking this should maximize any savings as it is really the temperature difference inside and outside the house that is costing money to maintain.



68 is still a comfortable temperature and I really just wake up and leave the house so it seems unnecessary to raise temp back to 70 just for that. Other people may have different needs but this seem to work for me. Any thoughts?

ChrisJ

malex

I have also considered this but it will not give me the benefit of waking up to heat rather than my alarm clock.



I am also experimenting between 1CPH and 2CPH though I don't think this has anything to do with the setback just overall comfort.

haaljo

"not to save money but to avoid any noise in the morning"

".... Instead I raise it to 70 at 1pm when the sun is helping me to heat the house. I do this not to save money but to avoid any noise in the morning as the boiler is trying to raise the temp or even keep it at 70 when it is 11F outside..."

What kind of noise? No setback means less noise maybe more money. Natural gas at $1.50 gallon oil equivalent makes the later a lot less important to me.

Raising setpoint @ 1pm instead of an hour before you get home doesn't make sense to me as no one home to hear noise. Sun will heat house from 1-4 whether you have boiler on or not.

malex

Rationale

IN the morning when it is the coldest, say 20 degrees, I found by using setback that the system would make a lot of noise as it was raising trying to raise the temp from say 65 to 70 (taking the inside outside diff from 45 to 50 degrees). The noise was in the form of very loud vents (one rad sounded like a tuned boat horn) as the rads where condensating like crazy at that temperature and this was at 6am. By not fighting the temperature, and instead letting the inside temp drop when it was the coldest outside I am minimizing the increasing diff in inside /outside temp as it is getting colder during the night.



When I bring it back to 70 I don;t think really matter but the sun is directly on the house at1 and by 4/5pm it is behind the trees and I feel it cooling down. Feel free to disagree but it seems to be working well for me. No more noise in the morning and I can sleep until the alarm comes on instead of the vents.