some thoughts on tweaking our steam system for higher efficiency..

SmellySocks

Our single pipe steam system takes about 50 min - just over 1 hour (depending on how cold it is outside) to satisfy the thermostat which is set at 65.  At the start of the season we had main line vents added, all new radiator vents added, the system was balanced and now heats much more evenly and much faster then it did originally.  At the same time we also had our boiler serviced/inspected so I'm assuming everything is functioning properly there.



During a typical heating cycle, the system doesn't even reach .5 psi (unless it runs longer, but I've never seen it go beyond .5 psi).  After the heating cycle, it takes about 3-4 hours before the thermostat calls for heat again.



Our thermostat is a RiteTemp (<a href="http://www.ritetemp-thermostats.com/60XX/6022.html">http://www.ritetemp-thermostats.com/60XX/6022.html</a>) and I adjusted the swing to 1 degree (the default was .5).  However, it seems slow to respond to the temperature in the room.  It often feels much warmer in the room as the house heats up, yet the thermostat says it's cooler.



We have about 2000 sq ft., 2 floors and a full attic (all radiators are turned off in the attic).



From the research I've been doing, it seems as though 1 hour for the system to run seems a bit high.  So, I'm wondering if my boiler is undersized for the house (it's also quite old).  Or if there's something else going on.  I don't think it's a venting issue and most of the pipes are insulated (at least in the basement that I can see).



In an effort to shorten the length of time the system runs, I swapped out a vent on the radiator closest to the thermostat on the first floor (used a Gorton D) so it would get hot faster and satisfy the thermostat sooner.  It didn't seem to effect the overall balance of the system, and only shaved maybe 5-10 minutes off the heating cycle.



So, my question is - do you think our boiler is undersized for the house?  We plan on replacing it, someday, but for the time being If it is undersized for the house would turning off some (or dare I say all) radiators on the second floor help the system run for shorter periods on time?  We have no insulation between floors and don't mind the upstairs being cooler.



Or, is the system running as it should?  Should we look into getting a better thermostat or increasing/decreasing the swing setting so the boiler comes on more often (and hopefully for shorter periods of time)?



Finally, we have our thermostat setback 7 degrees at night for 7 hours.  Overnight, the boiler usually won't turn on again until the morning.  However, when it turns on to heat the house back up in the morning it runs for about an 1 hour and 45 minutes (this is when the pressure finally gets to .5 psi, but I've never seen it higher).  Given how it normally cycles, it doesn't seem like setting the temperature back will have any effect on our gas bill as the system runs about the same amount of time either way.  It also makes one of our vents, which is normally quiet, start to hiss towards the end of the longer morning cycle when recovering from the setback (I assume from the increased pressure - perhaps a defective vent).  Thoughts on setting the temp back vs. leaving it at 1 temperature or setting it back only 2 or 3 degrees?  I've seen so many conflicting thoughts on this..



Thanks to all who give input!

jpf321

the only way to size a steam system...

calculate the EDR of all your rads and the see what the boiler is rated for.

also do you have a domestic hot water coil inside your boiler? i've hear that domestic HW coils (tankless coils) can collapse steam inside the boiler ..



i too have a ritetemp t-stat .. my swing is set @ 0.25.



i have been running recently with a 3degree setback during the night and daytime .. i only call for 71degF in the "getting ready" time of morning 6a-8a and then from 5p-10p .. it takes my boiler 1hour to bring house up 3degs .. i believe my system is properly balanced (as to my desires) well vented somewhat insulated mains...but my boiler is ancient and inefficient



you need to also time the steam from the boiler to the end of mains. and ideally to each radiator inlet valve. this will give you an idea of how long the steam is getting to where it needs to regardless of how quickly the rads are heating the room with it.



are you running gas or oil?



no one here has ever recommended a Ritetemp t-stat, nor do I expect anyone will .. there are t-stats available (i.e. HoneyWell VisionPro 8000) which are "steam rated" basically that either have an anticipator or a setting for CPH (cycles per hour) .. ritetemp tries to use SWING as a substitue for CPH.



first step is to calculate your EDR and determine your boiler size (along with whether you have a tankless HW coil) .. and then we can tell you if the boiler is properly sized.

Jamie Hall

Seven degrees?

That's usually regarded as a bit much for a steam system -- a more typical setback is 3 to 5 degrees, mostly because of the very long runs required to recover from the setback (as you have found).  What level of setback is the best for energy economy is one of those questions to which I've never seen a really satisfactory answer -- but I would suspect that yours is a bit much for economy.



If all the radiators get hot when the system runs, even though the pressure doesn't rise I would be inclined to say that the boiler is probably adequately sized.  It might be a bit bigger, but... if you are getting even heat, and things are otherwise fine, I would certainly stay with it.  One of the constant complaints people have is that the boiler cycles on pressure towards the end of the cycle -- and it is true, it isn't as efficient doing that as just letting it run.  So... I'd be quite happy with it as it is.



Again, on the thermostat, if the house temperatures are comfortable, I'd leave it be.



But then, I'm a great advocate of if it ain't broke, don't fix it.

SmellySocks

I will calculate..

jpf321:



Thanks for your response..  I will try to calculate the EDR and see how it compares to the boiler.



I do not have a domestic hot water coil.



I am running gas.



In regards to the swing, do you think by lowering my swing .25 (as you have set) I will use more or less energy vs. the larger swing?  It certainly would be nice to have less of a swing, as it starts to get noticeably colder before the boiler starts up, but if it's at the expense of using more gas overall I can put up with the temperature swings and save the money.



I timed how long it took, during a typical cycle, for the steam to reach the end of the mains.  From the time the boiler started it took about 15 minutes for steam to reach the end of the longest main line.



Jamie:



Yes, all the radiators get hot when the system runs.  In fact, some of the up stairs radiators start getting hot within 20 minutes or less of the system firing up.



So, just to clarify, it's not necessarily a bad thing that the system never reaches pressure?  I guess I was under the impression you *wanted* to get the system up to pressure quickly and have it cycle at the end.  That makes me feel a bit better.  I also saw other people saying their systems only ran for 30 minutes and anything longer signaled a potential problem, which also made me concerned.



As for the setback, I'm going to adjust it so that it only sets back a few degrees as you suggested instead of 7.  That will also eliminate the hissing problem with our 1 vent, too (which happens to be in out bedroom).



---------



In my first post I mentioned possibly turning off radiators on the 2nd floor in an effort to make the system heat up faster (shorter heating cycle).  Assuming the boiler is properly sized, my guess is this would be a bad idea as the system would then potentially reach the point where it's cycling due to pressure and not necessary satisfy the thermostat as quickly?



Our boiler is, too, ancient and from the sounds of it we're probably as good as we can get without replacing the boiler.  I'm just curios how swing, and/or less setback on the thermostat would affect efficiency. I'm wondering if a thermostat that anticipates would be better because the system wouldn't sit running as long, trying to satisfy the thermostat, because it would anticipate the residual heat once the boil shuts off..



Thanks for you thoughts and look forward to others.

jpf321

i'm not exactly sure but ..

perhaps you can tell me better b/c you have a swing of 1.0 .. but i think that means that it will OVERSHOOT the set-temp by 1degF as well as drop 1dF before firing .. with the smaller swing you will not overshoot as much nor drop as much .. not sure if that is correct nor am I sure that I answered your question.



for example ..

set temp = 70 .. swing = 1 .. burner OFF at 71 and boiler on at 69.

set temp = 70 .. swing = .25 burner OFF at 70.25 on at 69.75



I think.

Mike Kusiak_2

Swing and cycle length

As JP points out, the swing setting determines the differential in temperature between when the boiler turns on and turns off. All things being equal, a higher swing setting will result in longer cycles with longer off periods in between. Theoretically this should result in less cycling and greater efficiency. The downside is that there is a bigger variation in room temperature, which may result in your setting the thermostat higher for comfort, thereby offsetting some of the efficiency gain. Every system is different so you may want to experiment with the swing setting for the best compromise between less cycling and less temp variation.



Remember that the exact cycle length is not as important as the total amount of time the boiler runs per day to meet the heat load of the building. If you run short cycles you will have to run more of them per day, and may actually accumulate more boiler on time when averaged over a daily basis.



Cycling on pressure is less efficient than long cycles controlled by the thermostat, so if your heating is even, do not be concerned that you do not build pressure except when coming out of a deep setback.

jpf321

pressure cycling

here is a thread where I illustrate what happens when a presumably well pressure adjusted system must recover from a 3degF setback .. the first few cycles on the chart were overnight when the temp was set at 68dF .. then in the morning the temp jumped to 71dF .. you will see that I never hit 5oz of pressure during my normal runs .. but then i pressure cycled for quite a long time during my recovery.

http://www.heatinghelp.com/forum-thread/129235/Pressure-Cycling-Illustration

Jamie Hall

On cycling on pressure, again...

I still think that your system sounds as though it's running pretty well as is.



And no, you don't necessarily want to cycle on pressure.  It is very very much worth remembering that until roughly World War II we all had coal fired boilers.  We didn't cycle on pressure.  In fact, in most vapour systems (and a good many regular systems, too) there were rather interesting contraptions which kept the coal fire going just enough to generate a very slight positive pressure (typically an ounce or two) in the system -- and they just sat at that pressure, as long as someone remembered to stoke the coal.



Our modern burners usually have only two settings: on and off.  On has to be enough to fill the system, including the piping, with steam.  However, that is going to be more steam than the system can condense once it's full.  That being so, the pressure will rise -- but you don't want that.  So you turn the burner off.  But then the pressure falls too low, and you don't want that either -- so you turn the burner back on.  And so on until the thermostat is happy.  Now, if you are so fortunate that your boiler has enough oomph to fill the system with steam, and then quietly burble along at about the same rate that the steam condenses, be happy!  Be very very happy, in fact!  That's exactly what you want to have happen in some sort of ideal world.



As to length of run overall, that depends completely on how the boiler is sized relative to the heat loss of the house, how cold it is outside, how hard the wind is blowing, and how deep a setback, if any, you are recovering from.