Vaporstat question

wildrage

I bought a vaporstat for my 1 pipe system in a large Victorian home. Got it to more granularly control pressure and upgrading from a pressurol. OZ/IN2 on the differential sort of threw me off.  Looks like 16 = 1 PSI.  Anyway, I want to try running as low as possible then inching up if required. 

My proposal for initial setting is .8psi for the main / cutout and 4 ounces for the differential. Based on what I read, this means the boiler will cut off at .8 PSI and back on at roughly .25 PSI.  Is this too aggressive?  Again, I’d like to start low and come up higher if needed. 

Thanks!

Jamie Hall

The graduations on your vapourstat are, as it says, in ounces per square inch. So 8, for example, is 8 ounces per square inch, or 0.5 pounds per square inch.

My own opinion -- and others may, and do, differ -- is that one pipe systems run quite satisfactorily if the pressure can be limited to around 1.5 to 2 psi. Unlike true vapour systems, there is no functional reason to keep the pressure lower than that. Your new vapourstat won't go that high, however, so I suppose I'd try it at 8 ounces cutout initially, but expecting that it may go higher if that makes the boiler cycle on pressure too much.

ChrisJ

Jamie Hall said:

The graduations on your vapourstat are, as it says, in ounces per square inch. So 8, for example, is 8 ounces per square inch, or 0.5 pounds per square inch.

My own opinion -- and others may, and do, differ -- is that one pipe systems run quite satisfactorily if the pressure can be limited to around 1.5 to 2 psi. Unlike true vapour systems, there is no functional reason to keep the pressure lower than that. Your new vapourstat won't go that high, however, so I suppose I'd try it at 8 ounces cutout initially, but expecting that it may go higher if that makes the boiler cycle on pressure too much.

The reason I limit my system to 4 ounces is noise.
At anything higher than 1/4 PSI I find it annoying and very noticeable. Below that vents remain quiet.

As far as actual function I'd say higher makes it more likely to blow rust or debris into a vent and cause it to leak.

Other than that I've got nothing.
I've yet to see anyone provide actual differences in fuel consumption between really low pressure and higher pressure.

wildrage

ChrisJ said:

Jamie Hall said:

The graduations on your vapourstat are, as it says, in ounces per square inch. So 8, for example, is 8 ounces per square inch, or 0.5 pounds per square inch.

My own opinion -- and others may, and do, differ -- is that one pipe systems run quite satisfactorily if the pressure can be limited to around 1.5 to 2 psi. Unlike true vapour systems, there is no functional reason to keep the pressure lower than that. Your new vapourstat won't go that high, however, so I suppose I'd try it at 8 ounces cutout initially, but expecting that it may go higher if that makes the boiler cycle on pressure too much.

The reason I limit my system to 4 ounces is noise.
At anything higher than 1/4 PSI I find it annoying and very noticeable. Below that vents remain quiet.

As far as actual function I'd say higher makes it more likely to blow rust or debris into a vent and cause it to leak.

Other than that I've got nothing.
I've yet to see anyone provide actual differences in fuel consumption between really low pressure and higher pressure.

Yea, that's my reasoning too. Seems that once mine goes over say - 1.25 PSI I get hammering in my mains. Current Pressurol only goes to .5 with a 1 differential, putting me at 1.5, just above that. I've got the radiators all sorted out, but the mains will start to hammer at the peak of the cycle, right before the cut-off. With a thermostat say, set to 65, the temperature is going up to near 70...so I'm hoping that better control with the cutoff will help with all that.

EBEBRATT-Ed

@wildrage

When you install the vapor stat keep your pressure control for a back up

gfrbrookline

That is a huge setback for steam heat, we generally run 2 degrees or less, in many cases constant. The material your building is made of can have a huge impact as well. What I found in my brick building is it actually cost more to run with a 2 degree set back at night than it does to keep a constant temperature because of the thermal mass of the brick.

ChrisJ

gfrbrookline said:

That is a huge setback for steam heat, we generally run 2 degrees or less, in many cases constant. The material your building is made of can have a huge impact as well. What I found in my brick building is it actually cost more to run with a 2 degree set back at night than it does to keep a constant temperature because of the thermal mass of the brick.

How can that be?
Where's that heat disappearing to that a setback costs you more?

Unless you're saying your system builds pressure etc doing a recovery.

Jamie Hall

Here we go again. It does seem counterintuitive, but in any system -- not just steam -- if you are heating objects, not just air, it takes a good bit of energy to heat them up coming out of a setback. One would think that that energy would be recovered going into the setback, but... it doesn't seem to work that way. At best, though, one would use the amount of energy which one would use at the average temperature between the low and the high, instead of what one would use if one were always at the high temperature.

Also, for comfort, one has to start out of the setback before you want to reach the high temperature -- sometimes by quite a bit; perhaps an hour or more in a typical wood house and perhaps as much as many hours in a masonry building like @gfrbrookline 's.

Perhaps someday someone will have two identical houses located side by side (but not too close) and we can all gather and run an experiment on it...

ChrisJ

@Jamie Hall. There's no here we go again.

Any heat you put into an object you get back, 100%.

Energy cannot be created or destroyed.
If that's the case where's it going?

Heating up an object and letting it cool, like say a heavy cast iron radiator does not consume any amount of energy anyone on here could ever measure.


Comfort is another subject.  I keep my heat at one temperature because I like it but I know damn well I'd use less gas by doing a setback.  Lower temperature means less heatloss and it's literally that simple.


I know I'm not telling you anything you don't already know.

Jamie Hall

No, @ChrisJ , you're not telling me anything I don't know. And in fact, if one reads carefully, I mentioned that the actual fuel usage with a setback will be the same as the fuel usage would have been had one maintained a steady temperature as the weighted average temperature over the time period. All else being equal.

Which, of course, it never is.

As is so often the case, one is trying to strike a balance between comfort and efficiency in these things. If all one cared about was fuel efficiency, then clearly the best approach to setbacks would be to bring the structure to the comfort temperature while it was in use, and then shut the heat off completely until either it was time to bring it back up -- or it was necessary to avoid freezing something. This approach, in fact, works very well indeed in situations where the structure is used only infrequently, such as a church which I manage. As it happens, that structure has a remarkably good hydroair system -- and is used only on Tuesday evenings and Sundays. So... the heat is turned on Tuesday afternoon in time to bring the parish hall up to about 65 for the meeting, and turned off when folks go home. Likewise on Sunday morning. The furniture is a bit chilly, and it raises havoc with the tuning of the organ, but that's minor. The point is that it can get from about 40 or so in the wintertime up to manageable in a couple of hours of continuous running.

Clearly a setback will save energy -- I can't argue with that. How large can it be? And how much energy?
That is a mostly a comfort question, provided the system can, in fact, recover quickly. If it cannot -- a radiant concrete floor, for example, or a solid masonry building, while one could undoubtedly save a small amount of energy by turning the heat down (or off), you begin to run into how long recovery will take -- and I would argue, energy considerations completely aside, that if the recovery takes longer than a couple of hours, perhaps the setback is too large for comfort.

Then there are other considerations as well. I mentioned a paragraph ago that a setback raises havoc with the tuning of the organ in the church (tuning the organ costs as much as about a thousand gallons of propane... the vestry doesn't want to hear that) -- so one needs to balance the impact of the setback on the actual fabric of the structure and the contents, never mind the people. This is often ignored completely, but can be a significant economic consideration in some instances. There are very few things -- either structure or artifacts in the structure -- which will be seriously affected if the temperature is allowed to change slowly, provided only that it is always above the dewpoint. There are a great many artifacts, however, which may indeed be seriously damaged if not destroyed by having regular temperature swings of much over a few degrees over short periods of time (short enough so that they have differing temperatures within the artifact).

One size does not fit all...

BobC

I worked 1430-2300 for the last 8 years of my working life. I'd leave the house at 1330 and be back at 2330 and watch an hour or two of TV before going to bed. My regimen was to have the heat come up at 0515 (I got up at 0600 - old habit) and shut down at 1245. I would not turn the heat up when i got home for work, I'd just put a sweater on and have a couple of pops while watching TV.

The thermostat automatically went from 67 to 57 at 1245 and up to 67 at 0545. It took a while for the boiler to get things comfortable but thats why I had a sweater or sweatshirt on. I knew that setback was deep but it was also for enough time that the system didn't chase it's own tail. When I retired in 2009 the thermostat went from 62 t0 67 at 0515 and back down to 62 at 2130 and my fuel consumption didn't change much, I track my fuel use from year to year. As I get older I feel the cold more so i keep it at 70 during the day and 67 at night and again I didn't notice fuel usage going up much - certainly not enough to make a difference.

When you look at all the book cases and shelves of records you can see there is a lot mass in the house (also a 500# 1908 safe in one corner of the dining room acting as a printer stand). It takes energy to swing all this stuff, if you walk by that safe a couple of hours after the heat comes up you could feel it drawing heat away from you. I agree with Jamie that you have to realize it takes energy swing that mass, especially when your in an old house that isn't exactly tight.

Bob

ChrisJ

BobC said:

I worked 1430-2300 for the last 8 years of my working life. I'd leave the house at 1330 and be back at 2330 and watch an hour or two of TV before going to bed. My regimen was to have the heat come up at 0515 (I got up at 0600 - old habit) and shut down at 1245. I would not turn the heat up when i got home for work, I'd just put a sweater on and have a couple of pops while watching TV.

The thermostat automatically went from 67 to 57 at 1245 and up to 67 at 0545. It took a while for the boiler to get things comfortable but thats why I had a sweater or sweatshirt on. I knew that setback was deep but it was also for enough time that the system didn't chase it's own tail. When I retired in 2009 the thermostat went from 62 t0 67 at 0515 and back down to 62 at 2130 and my fuel consumption didn't change much, I track my fuel use from year to year. As I get older I feel the cold more so i keep it at 70 during the day and 67 at night and again I didn't notice fuel usage going up much - certainly not enough to make a difference.

When you look at all the book cases and shelves of records you can see there is a lot mass in the house (also a 500# 1908 safe in one corner of the dining room acting as a printer stand). It takes energy to swing all this stuff, if you walk by that safe a couple of hours after the heat comes up you could feel it drawing heat away from you. I agree with Jamie that you have to realize it takes energy swing that mass, especially when your in an old house that isn't exactly tight.

Bob

And yet Thermodynamics says this is impossible, no?

Jamie Hall

The raw simple thermodynamics says -- as I said -- that one will save energy. Unfortunately, first without getting a lot more involved and considering specifics, it doesn't say how much (that's why I want my experiment with two identical structures in the same location!). Perhaps more important, it can't tell us anything useful about what the perception by the critters -- including humans -- occupying the space is.

As @BobC noted, you walk past a big cold hunk of iron you feel the cold -- though the air temperature has not changed. You walk past a big warm radiator, you feel the heat -- though the air temperature has not changed. I've heard it said that with forced air one needs to keep the thermostat warmer than with big radiators -- I've only lived with forced air in one house, years ago, but I suspect that the remark is true, since the container you are in -- the room -- is cold, even though the air isn't.

In another thread we are talking about fireplaces -- and all the advice is that fireplaces waste heat (and indeed, a good many of them do -- though not all). But which seems more comfortable? Being in front of a nice fire in a fireplace with the room at say 65, or in front of a dead fireplace (let's have a needlepoint screen for it anyway) and the room at 70?

ChrisJ

Jamie Hall said:

The raw simple thermodynamics says -- as I said -- that one will save energy. Unfortunately, first without getting a lot more involved and considering specifics, it doesn't say how much (that's why I want my experiment with two identical structures in the same location!). Perhaps more important, it can't tell us anything useful about what the perception by the critters -- including humans -- occupying the space is.

As @BobC noted, you walk past a big cold hunk of iron you feel the cold -- though the air temperature has not changed. You walk past a big warm radiator, you feel the heat -- though the air temperature has not changed. I've heard it said that with forced air one needs to keep the thermostat warmer than with big radiators -- I've only lived with forced air in one house, years ago, but I suspect that the remark is true, since the container you are in -- the room -- is cold, even though the air isn't.

In another thread we are talking about fireplaces -- and all the advice is that fireplaces waste heat (and indeed, a good many of them do -- though not all). But which seems more comfortable? Being in front of a nice fire in a fireplace with the room at say 65, or in front of a dead fireplace (let's have a needlepoint screen for it anyway) and the room at 70?

Of course if you walk past a big cold object you feel cold, it's sucking heat out of you.
That does not indicate any loss in efficiency though. Like I said previously, I maintain 1 temperature because I want to. My argument is that setbacks waste energy because I cannot see how that's possible according to the laws.

Am I misunderstanding the laws of thermodynamics? It's very possible, but help me if I am.

In regards to forced air, it's my understanding in a modern structure, properly insulated (2x6 framing, decent fiberglass or spray foam etc) that forced air will warm the walls plenty and you will not feel cold. But obviously the walls will be cooler than you, so you will still feel something.

Just not the same as in a house like mine if you were to attempt using forced air in it.

Jamie Hall

Nothing wrong with your thermodynamics, @ChrisJ . On a first cut level, the energy requirement to maintain a constant temperature is linearly proportional to the temperature difference between a the warm space and the cold exterior space and to the thermal resistance of the enclosure. All sorts of interesting mathematical complications start to arise when one gets to real world applications -- from simple stuff like convection in the boundary layers (which can be pretty straightforward, actually -- and should be accounted for in a full Manual J calculation) to interference due to radiant heat transfers, which can get real messy (there's a reason that thermodynamics wonks like "black"" surfaces...).

When you start adding dynamic effects -- such as changing the temperature of either the warm or cold space -- you start having to add in effects from heat capacity in the enclosure. Just one example -- badly oversimplified. Let's suppose you are dealing with an enclosure which has a relatively high conductivity and low heat capacity inner barrier -- let's say sheetrock -- then a space filled with insulation -- doesn't matter what kind -- then an outer barrier which has again a relatively high conductivity -- but a very high heat capacity. As it might be a brick wall. At a steady state, there will be a linear drop in temperature through the first barrier, a steeper linear drop through the insulation, then again a linear drop through the second barrier. Now raise the interior temperature. Eventually, of course, it will all stabilise again with nice linear drops -- but what happens in between? The interior barrier -- low heat capacity -- will warm quickly, as will the insulation, but the inner face of the outer barrier will warm much less quickly, so there will be a steeper gradient through the inner barrier and the insulation -- more heat transfer than would be expected (effectively one might say that now you are transferring heat at the rate you would expect were the outer barrier not really there -- not really correct, but sort of). That additional heat loss will taper off as the outer barrier comes up to temperature, and the extra heat will be stored in the outer barrier. But now... what happens when you reduce the space temperature? The gradients in the inner barrier and the insulation will be less than would be expected at steady state, since the outer barrier is now warmer than it would be at equilibrium, so the heat loss from the space will also be less -- but the heat loss from the outer barrier, which must be to the exterior, initially remains the same as it was at the higher space temperature. So the extra heat added to the outer barrier is not recovered to the interior, except by the reduction in heat loss from the inner space. So the question becomes -- is that reduction in heat loss during the temperature fall the same as the increase in heat loss during the temperature rise?

At which point your friendly thermodynamics wonk -- not me, not me! -- will happily begin scribbling differential equations and eventually come up with an answer and a happy grin. And the answer will be different for different combinations of barrier materials and dimensions and temperature differences and rates of temperature change...

Sigh.

EBEBRATT-Ed

It's the flywheel effect.

When you heat any building it's not just heating the air in the building your heating the walls, floors sheet rock wood furniture carpeting etc.

You lower the temp on set back and those items start giving off their heat to the air as the building looses heat during the set back.

When you warm the building coming out of set back the air gets warmer and the flow of heat also goes into the walls furniture etc and has to warm them back up.

A masonary building is a huge heat sink


A walk n freezer at 0 degrees full of product will stay cold and loose temperature gradually if the compressor quits because its full of frozen product

Fill a walk in box with unfrozen product and it takes a long time for the box temp to come down because it has to freeeze the product as well