What size vents do I need on my mains?

joe7

I have a one pipe steam system.  The main is 2”.   the returns are 1 ¼”.

One main is 50’ the other is 25’

This is a 2 floor,  4 family house.  the 50’ main has 8 pipes rising from it to radiators while the 25’ main has 5.  At the very end of both mains are 2 risers.

Also, where and how should they be installed?

One last question: I’m trying to figure out what this particular part of the system is for.  The size of the first part of the return on the 25’ main is 2” (as opposed to 1 ¼“ like the rest of the return)  and it has a large valve. The hole is plugged. Close the floor, it transitions to the regular 1 ¼” – see picture

Thanks.

nicholas bonham-carter

Unused radiator valve?

For main venting, you can't go wrong with gorton 2's on each main, if you have the headroom. The longer one may need 2 of them on an antler. I would rather have too much venting than too little. A 0-3 psi low-pressure gauge will show you the back-pressure of venting which should be 2 ounces.

That fitting looks to have been a radiator valve, whose radiator has been removed, and the supply plugged.

Are your supply pipes insulated with fiberglass, so all the steam gets to the radiators?--NBC

joe7

NBC

you write: A 0-3 psi low-pressure gauge will show you the back-pressure of venting which should be 2 ounces.  What would it help me to know the back-pressure?

Also, why would there by a radiator valve in the basement – installed on the return?

Thanks.

nicholas bonham-carter

Back-pressure of venting

When the main venting is inadequate, you will see how high the pressure gets, as the fuel company labors to squeeeze the air out of the radiator vents, on your dime.

When you have enough main venting, the resistance to the escaping air is very low, and so is the pressure at that time. Good main venting results in all the main pipes filling with steam quickly with less run time. When they are full of steam, the main vents will close, and then the steam begins to rise up into all the radiators at the same time.

As far as I am concerned, any well-vented system should run properly at 6 ounces or below.

Only when recovering from short setbacks of less than a day, can the fuel company make some more money on you, so keep the temperature constant, even at 66 degrees.--NBC

joe7

a

Are you saying that changing the temperature to different levels morning/night negatively impacts the fuel efficacy?

NYCLandlord

same here

Yes, Nicholas, what are you saying?

I would think that a temp set back of 5 degrees in the afternoon for 4 hours and pay for the catch-up would still be less gas then to leave it without the setback.  I have 60min cycles so I save 4 fire-up cycles runing 20min each, thats 80mins of full on gas.  This vs. a longer catch-up run time of ie: double from 20mins to 40mins of run time.  I am still ahead of the game by 40mins of full on gas.

This is just afternoon, at night, this savings is doubled.  Am I missing something?

nicholas bonham-carter

setback results

i believe that steam systems are more economical when set to a constant temperature. regaining temperature after a setback is like acceleration when driving a car. the high mpg driver tries to keep a constant speed, and when he does have to accelerate, he presses on the pedal with the lightest touch, as more fuel is used gain speed. steam systems have a high inertia, and like an ocean liner do not respond easily to changes in speed or settings. a building with the envelope in good condition, responds better to the constant temperature. even better would be a modulating burner which could switch to low fire when the pressure has been established during a call for heat.

when the system is in perfect condition, the temperature can be set lower than the standard 70 deg, as there has been no cool down period to make people feel cold. obviously, if the building is a church, used only once a week, then a setback will save some money.

maybe the following experiment would confirm or deny this:

1.note the time, turn off the boiler, and read the gas meter, and wait 6 hours.

2.note the number of minutes of the off period, and turn on the boiler.

3.watch for the thermostat to be satisfied, and note the time, and the meter reading.

4.keep the temperature set constant for another period of time, and note the meter reading and the time.

5.finally compare the gas consumption, per minute of the makeup period with the constant period.

continuing the car analogy, a system without proper venting is like a car with dragging brakes, so more fuel has to be burned to compensate. if there are several dry returns, you want a very similar low venting resistance [back-pressure] on each, so the mains completely fill with steam before any riser starts to fill. this is because the standard hoffman 40 has a higher resistance than the mains. if you have a tall building, then you can put a higher capacity radiator vent on the very top of each riser to get the steam up to the top more quickly.

anyway it's just my 2cuft.--nbc

NYCLandlord

Worth a try

I see you point about the driving a car. We all can agree that if youre going to drive a 500 mile trip, Less gas is used if you go constant all the way at 60mph, vs 90mph at some points, then 30mph in others. Using this analogy, would driving 500 miles at a constant speed use less gas then driving a shorter distance at varying speeds. This feels like back in high school math. With this question, the big factor is how much shorter is the trip.

I dont have any concrete numbers on how much is saved. I measured the gas consumption based on run time and not by reading the meter. However, your approach is worth trying. There must be a break-even point, it would be surprising to find that there arent any real significant differences.

PMJ

Slightly Different Take

It seems to me that the net cost to heat is in replacing the heat lost which is directly related to the average temperature difference for the 24 hours. Letting the structure cool inside overnight reduces the total loss because the net average temperature difference from inside to outside is less.



On my system I do let the night temp drop 3 degrees starting at midnight. For one thing cold radiators encourage people to head for bed. But in the morning I use the wake, leave, and return settings to step the heat back to normal one degree at a time over 6 hours. Even though the inside temp is actually below normal all that time it is not noticed because the radiators are always warm(not blazing hot) and the live heat is most comfortable. Everyone likes the morning time because their bathroom rads are all gently warm. The most I let the boiler run on the coldest days is 10 minutes on and 10 minutes off which assures the warmup is slow and even. If it is warmer out the percentage on allowed is even lower. The net of it is that the house spends now about 12 of the 24 hours at a lower inside temp which means a lower total loss to replace then if I had left it constant. The fact that I bring it back very slowly means that there really is no significant "acceleration". Even being off the 6 night hours the 460,000 btu input boiler is only about 20 minutes to steam in all radiators from call on the first fire. I have tweaked this system for 20 years and watching the bills I'm quite convinced the setback saves money.



If I lived where it was colder (nights here generally in the 20's) I would set back more but the house barely drops the 3 degrees in six hours at 25 outside so we'd still have cold rads most of the time at wake time if I did.

nicholas bonham-carter

Setback methods

Your staged return to normal temperature is a good principle to follow, and probably mitigates the acceleration factor.

Since you have studied, and tweaked the system, then why not keep track of the runtime of the various temperature periods, and post your findings here, as setback is a frequent point of discussion here.

In my case, a setback has resulted in much more boiler activity, than simply maintaining the same setting.--NBC

SWEI

setback measurement

Another case where measured air temp does not accurately reflect what occupants perceive.   Your "live heat" is increasing MRT before air temperature.  This phenomenon allowed old, uninsulated high mass buildings to "work."

nicholas bonham-carter

List of things to be done

You could redo the supply piping yourself, but in the spring, so having the boiler out of service for a week or so will not be a problem. I would use a drop-header which will be easier for the novice to install. In the meantime, I would wrap the pipes with fiberglass insulation, to make the steam a little better in quality.

Getting some main venting is most important. If the supplies come back close to the boiler, then that is where they should go. If there are no plugs where they once were, then the drop from dry return to wet could be drilled and tapped. This is another job for the spring. As a temporary fix, try to put a faster vent on the last radiator on the main, and slower vents on all the others. A gorton d would improve things, with Hoffman 1-a's on the rest.maybe you will discover the plug where the main vents were.--NBC

Mark N

Boiler on and off

PMJ, how do you get your boiler to run 10 minutes on and 10 minutes off in cold weather. What control are you using to cause that to happen. I have a small 1 pipe system and in cold weather my system run a 20 to 25 minute on and will stay off for 1 to 1.5 hrs.

PMJ

Data Etc.

I'd like to pursue this. My concern about the data you ask for is that it is very difficult to get 2 periods with the same indoor/outdoor temperatures and sun input conditions - especially the shorter they are. We are looking at what are single digit percentage differences so comparing say two 24 hour periods will be tough to do. The demand won't be the same. The main reason for my setback is that it is more comfortable living. Sleeping is better a little cooler and guaranteed warm rads in the morning is just nice. But I do believe I save a few percent too - I will pursue getting the data.



In the mean time, can we agree about the straight heat loss side of things? The loss calculation is strictly a function of the inside and outside surface temperatures right? There is an active weather station less than a mile from me so all the daily HDD data is available. It is easy to get total HDD demand for the exact dates on my bill and then calculate the cubic feet of gas/HDD required for my structure. For me it is running about 38 CUFT/HDD. Comparing warmer and colder months it seems to stay fairly constant. So for every degree I reduce my target in theory at least I need to input 38CUFT less/day. Not much as I said before but in Cleveland where it is not so cold each degree is looking like a 4% reduction or so.



From there we can move to the question of the efficiency of the steam system itself which I am much more interested in and the relationship to setback. I am not sure that this thread is the place to do it. I am not a contractor but a mechanical engineer. I run a 6 million BTU/HR low pressure steam boiler at my business for process steam and tweak my home system. I see lots of discussion here about venting and I admit I'm missing something. In the process of returning my system to vapor/vacuum I removed all the vents. I have just one opening to the atmosphere in the whole system - a 3/4" solenoid valve on the dry return right over the drop to the wet return. It closes tight when the burner is off and opens when the vacuum is gone controlled by a pressure sensor right next to it I have set at as best I can tell about 1/8 of an ounce. Never hear a thing coming out of it. My system runs on full fire with no measurable pressure anywhere. Steam flies to the most remote radiator in a minute or so from the call when there is vacuum. The whole thing is dead quiet. My feeling has come to be that pressure is the enemy and air hissing out of vents means there is resistance to steam flow in the pipe and the vent hole isn't big enough.



Anyway, I am thinking that the real efficiency of steam systems is dependent on the average length of time it takes from the call for heat to steam at the radiators which has much to do with venting/vacuum/pressure and is maybe what you are referring to as inertia? I'd like to discuss it more. Not sure what thread is the best place.

PMJ

Boiler Control

Mark,



Controlling the cycle was my most important improvement after vent damper and vacuum(which is tough on 1 pipe). I use a PLC (programmable logic controller) and discussed it a bit in another thread on vapor/vacuum. What I noticed was what you describe - your system runs full out and overshoots which results in a long off period/colder pipes and rads and then longer waits for steam at next call for heat. I used the PLC to even out the steam delivery - that is turn the burner on and off by different schedules inside a single call for heat. That is the thing about steams systems - you need a really big boiler to heat up a dead cold system so that it can deliver steam where you want it in a reasonable amount of time - but then that boiler is way more than is needed once everything is hot for continuous running on cold days. I don't need 1/2 my boiler to heat the house at -20F outside but I do need the whole thing to get going when everything is dead cold. My solution was to cycle it on and off all during the same call for heat on my own schedule which really evened things out.



I can go into more detail about the device and the program if you wish. It only cost about $100. and the software is free. It would take some doing to get used to ladder logic (I do it extensively at work) but if there is interest it is great fun.



Peter

Mark N

Boiler Control

Peter,



Ok that makes sense now. I use a Honeywell FocusPro 5000 tstat and it actually maintains very even heat throughout the house. I keep the house at a constant 70 from November to April. I never experience overshoot. My boiler is well matched to the amount of rads I have. I think there are many here who would be interested in learning about the control system you are using. Start a new thread explaining it.

PMJ

Boiler Control

The overshoot I mean is in 10ths of degrees and won't be seen on a tstat reading whole degrees.  Even an oscillation of 1/2 a degree over to 1/2 a degree under the set point can result in 1-2 hour off periods and rads that return all the way to room temp. If it were possible to match the heat lost to exactly what is supplied in the rads continuously they would be slightly warm all the time. This probably sounds like splitting hairs but I found it so easy with this control method to just  "goose" the rads and stretch the time from call to satisfaction into maybe 3 hours or even longer depending. Just an easy slow continuous climb from the bottom to the top of the dead band of the tstat. 3 on/off burner cycles per hour and rads just middle warm the whole way and well, just nice.



Question: If your temp control is even enough now, what is your reason for being interested to change the firing? Just curious. I can start a new thread to discuss the control details.

SWEI

inertia

is the flywheel effect from the volumes of water and metal in the system.  Changing the 'speed' of a big flywheel is hard.  Keeping it at a relatively constant 'speed' is not as hard.  Hard burns fuel faster.

Mark N

Boiler Control

Peter,



I just find it very interesting. You have a 2 pipe system designed to run in vacuum. The vents for 1 pipe naturally induced vacuum are no longer made and converting to a Paul system would be a major undertaking.

PMJ

Inertia

Question: doesn't a boiler transfer a constant percent of the available heat in the gas to the metal and water in the boiler and lose a constant percent up the stack whenever it is firing? And all that heat that didn't go up the stack stays in the house when the damper closes. It may not be exactly where I want it but it is in the house.



It does seem that the total BTU's lost by the structure in are replaced by all the BTU's the boiler gets from the gas that don't go up the stack during the firing. Are you saying that  the ratio of what is lost up the stack vs what stays in the house varies somehow in the boiler itself based on something in the rest of the house?



I did pull together some numbers. I remembered that I do run constant 70 degrees in the fall when the boiler runs so little there would be entire mornings with the boiler never coming on. I ran this way from 10/17 to 11/15 and used 25,800cuft. There were 669 HDD in that period with a 70 target temp. This is about 38.5cuft/HDD. From 11/16 to 12/19 I ran the setback way with a setpoint of 69 from noon to midnight off till 6am and stepped back to 69 by noon. In this period I used 34,600CUFT and there were 950HDD. This works out to about 36.4cuft/HDD. Running continuous shows a higher gas consumption/HDD by about 5%. We are talking single digits here but I don't think the setback way will actually be worse.

Jean-David Beyer

doesn't a boiler transfer a constant percent of the ...

available heat in the gas to the metal and water in the boiler and lose a constant percent up the stack whenever it is firing?



I would say no. The transfer from the flame to the flame side of the heat exchanger depends on the difference between the flame temperature and the temperature of the flame side of the heat exchanger. It probably also depends to a certain extent on the speed of the flame across the heat exchanger. It also depends on the difference between the fire side of the heat exchanger and the water side. And then it depends on the temperature difference between the water side of the heat exchanger and the water there. It probably also depends to a certain extent on the speed of the water across the heat exchanger.



One of the advantages of a typical mod-con boiler is that it tries to arrange that the temperature of the water entering the heat exchanger is as low as possible. The lower that water temperature, the greater the flow of heat from the flame to the water.

PMJ

doesn't a boiler transfer a constant percent of the

I'm sure you are right that these various temperatures are not all exactly the same at all times so the transfer is not always exactly the same. I guess I didn't mean to imply as exact as all that. But then, isn't that what the rating is for - an average you can count on overall from normal operation of the machine - operation that includes starting up and flat out running? Seems to me that for calculation purposes everyone just says the output btu's are what is transferred whenever full fire is on -  obviously a little over sometimes and a little under other times.

Mark N

Heat transfer

This is a steam boiler. No water leaves the boiler until it turns to steam. In a hot water boiler the pump kicks on and the water starts to circulate and cooler water is returned to the boiler. In a steam boiler the only circulation going on before it starts to steam is by convection. Once it starts to steam the water is at 212 degrees and all the heat input goes into turning the 212 degree water into steam. The amount of condensate I would think has no effect on steam production and heat transfer to the water.

PMJ

Heat Transfer

I get that ok Mark. But heat that warms up the water before steam is made is still in the house - it isn't totally lost like what goes out the stack. It isn't where I want it - but it isn't outside either. I'm only saying that the rating is a pretty good average number for what stays in the house when full fire is on.

Mark N

AFUE numbers

I think they obtain their numbers in a steady state condition. Once you boiler is up to full steam they are I would think quite close.

PMJ

AFUE Rating

The ASHRAE handbook says that the AFUE rating differs from true thermal efficiency in that it is not steady state peak measure of efficiency but rather to represent the average, season long average efficiency of that piece of equipment including operating transients. Or so Wikipedia quotes it as saying. 

SWEI

right

The water mass comes into play whenever the boiler fires up from recovery.  The higher the mass (of water and iron, mostly) the longer it takes for the system to get up to temp -- or to lose temp once the boiler shuts off.  By pulse-width modulating the boiler, cycle timers control average hourly output.  Thermal mass averages out (performs low-pass filtering on) the on/off cycles.