One-Pipe Cast Iron Radiators Overheating with TRV installed

TheRookie

Stats:

-15,000 SF masonry building (1930's)

-30 HP boiler (new)

-Gravity return condensate system (existing with new FW pumps)

-One-pipe parallel flow up feed system

-Wet return

-Existing cast iron radiators equipped with new electronically actuated TRV's (Macon controls)

-1 PSI - 4 PSI cut in/out (I'm going to lower this)

-New main line air vents

-New thermodynamic steam traps at main condensate return line.



I zoned out the building with thermostats, on a call for heat the actuators open and the vent whistles as it is supposed to. 



Problem is when there isn't a call for heat the radiators still put off a tremendous amount of heat and are cooking the building occupants. 



How can the radiator heat when air isn't leaving it? 



The contractor completely isolated the air vents from the system by manually closing the actuator valve upstream of the vent.  Still heats up, just a little slower. 



Building occupants are having to use the ol' double hung gate valve to keep cool, not good for the energy savings the building owner wants with a modern boiler. 



Any thoughts? 



Thanks in advance guys and let me know what I left out.



-Shawn

Enreynolds

Comments/Questions

{15,000 SF masonry building (1930's)}  What is the connected EDR

{-30 HP boiler (new)}  Was this new Boiler sized to the EDR

{-Gravity return condensate system (existing with new FW pumps)}  I am not sure I understand: is this gravity return or or does it have a condensate receiver and pump

{-1 PSI - 4 PSI cut in/out (I'm going to lower this)} This will save you money

{-New main line air vents}  If your Main vents are whistling, you need more main venting

{-New thermodynamic steam traps at main condensate return line.}  This is the one that most concerns me.  It sounds suspisiously like a master trapped situation.  Shawn, to you have any of Dan's books on steam heat.  It sounds like you might benefit from the Lost Art Of Steam Heating.  It might also be beneficial to post some pictures of your system and the offending radiator.  Take them from a ways back so the piping can be traces, and from as many sides as possible.  You will find some help here.

Eric

Paul48

Do

The radiators go to zero pressure, and do the TRVs have a vacuum breaker?

TheRookie

Response to Enreynolds

-Connected EDR will take me a second.  Designed it two years ago.

-Boiler size was based on how much steam could be condensed (EDR) plus a pick up factor.  I want to say around 30%

-The condensate flows via gravity to a condensate receiver tank which is equipped with a redundant feed water pumping system controlled off the boilers level controller

-As far as the cut in/out the boiler manufacturer (Hurst) is leery of lower settings but we're going to try it anyway.

-This project is 4 hours away and I am relying on second hand information from the contracting crew.  I will ask how the main vents are acting and whether or not there is audible whistling.

-I do have the lost art of steam heating and essentially lived with it throughout the design of the upgrade, possible I missed something though.

-I'll track down some photos.

-Problem is... all of the radiators are offenders. 

TheRookie

Radiator pressures

As far as the radiators pressure.... I am at a loss on that.  Yes?  At least with respect to the atmosphere.  They would have to such that the condensate would return correct?

TRV's have integral vacuum breakers

TheRookie

Connected EDR

My notes show that the connected EDR is around 2500.  

TheRookie

Photographs

Standard radiator installation (prior to install of TRV) attached.



Any other photos I should track down?

Rod

TRVs

Hi- These are the TRV units (with electric actuator) you're using?

- Rod

TheRookie

TRV's

Those are the models.

I had a bid alternate for these models vs. a built up model and the Macon controls made most economic sense.

TheRookie

TRV's

Except the actuators are electrically controlled via space thermostat.

Paul48

I'll

post this, to make my question clearer(or maybe not :P) http://www.fiainc.com/documents/10-08Canyoureallycontrolaone-pipesteamsystem.pdf

TheRookie

I

think your onto something. 

I do not believe the boiler is controlled off space demand.  Which means that the radiators are not at zero pressure when satisfied. 

I have already sent a feeler to my temperature control contractor to determine how hard it would be to prevent the boiler from energizing if there isn't enough heat demand in the space even if the pressuretrol is calling for it. 

Rod

Overheating with TRVs

Hi Shawn-  With the whistling and the comments: "The contractor completely isolated the air vents from the system by manually closing the actuator valve upstream of the vent. Still heats up, just a little slower." and the comment: "all of the radiators are offenders".

it would seem to me that the boiler maybe running at too high a level of pressure and even though the TRVs are closed, that the high pressure is compressing the air in the radiators enough so that steam is entering them. Do you have a gauge reading on the actual maximum pressure the boiler is operating at now?  I'm wondering if the boiler may be actually going higher than the set 4 PSI.The settings on the pressure controls are notoriously inaccurate and it is better to set them by actual pressure gauge reading.

Where is the trap located on the condensate return line?

- Rod

Paul48

I

hope it helps you out. Like a lot of the guys here, I file stuff away that would only be of interest to the obsessively insane. Then it's like that tool, you know you have it, but where did you put it? Keep us posted and Good Luck.

Rod

Need Zero Pressure for Vacuum Breakers

Paul- Good point! The system has to go to zero pressure for the vacuum breakers to open so that the radiators can fill with air.

- Rod

Paul48

Pressure Drop

Gauge the pressure at the boiler and at the most remote radiator in the building. The difference is how much pressure you need to get steam to the whole building.Any more than that is wasted money.

Paul48

hmmm

obsessively insane.....or insanely obsessive? Anyway, I couldn't hold a candle to Rod's library.

Enreynolds

Oversized Boiler

Based on my calculations, a 30hp boiler outputs 1,005 MBtu/hr.  Based on your attached edr assuming a  30% pickup factor, I calculate that you need 788 MBtu/hr, or a 24HP boiler.  These figures may not be correct,  but it seems that your boiler is oversized, and running  up to 4 psi will exaserbate your problems. 

Eric

JUGHNE

Same problem myself this morning

The schoolroom with the wall t-stat was 70*, the other 2 rooms got up to 84*; yes windows opened, even window ac running.  The t-stat room rad vent was very slow/not working and boiler stayed on longer a long time.  Rooms with working TRV 's overheated by not being to see a cycle to 0 PSI.  2.5 psi seemed to work itself into rads with TRV.  The T-stat room radiator is the director for the whole show and was too slow coming up to heat to satisfy wall T-stat.  I actually "heard" the problem down in the boiler room several days ago at the end of the heating cycle as the condensate returning sounded like a urinal flush valve stuck open;  vacuum bkrs finally opened and water come down 3 stories of 2 " pipe.   Well that's today's theory and I'll know tomorrow morning if this hunch is right; changed nothing but the vent repair. These TRV's never worked well until the pressure was cut down from 5 PSI to 2.5 PSI a couple of years ago.  What do you have for the "director" on  the system? 

TheRookie

Boiler Pressure

Rod, I'll definitely look into the actual steam header pressure to be sure that the pressuretrol is accurate.



As far as the steam traps, they are at the very end of the basement perimeter condensate loops in the vertical section.

TheRookie

Boiler Sizing

Thanks for the double check Erik.  I don't have my CD's in front of me be one thing I forgot to mention is that this project is at 5000 ft elevation and I believe the boiler rating was input, so I can only assume there is some efficiency derates I included.  I'll double check to be sure we're not grossly over sized though.  

Dave in QCA

Over engineered, but missed one fundamental point!

Wow!  It sure sounds like someone put a lot of thought and expense into this project to give tenants in the building individual control, with a thermostat that is like what most people are used to.  But, the engineer missed a fundamental fact.



When the boiler is off the system, pipes, radiators, etc., are all filled with air.  When the boiler starts steam begins to travel through out the system.  However, for that to happen there must be a way for the air to get out.  In your case, if a space is already warm enough, the thermostat will have the radiator vents in the closed position and since the air cannot get out the steam will not go in.   However, for the those vents that are in the open position, steam will go into those radiators, and with the pressure you're running ( I suspect you are maintaining most of the time) the radiator will heat up very quickly and put out a lot of heat.  Then, the thermostate closes the vent.  Your engineer may have assumed that this would shut the heat off, but it won't.  Since the air was already let out of the radiator and the boiler continues to run, steam enters the radiator, condenses to water, flows out of the radiator, and is replaced by more steam.  This will continue as long as steam is maintained in the system.  I think I understand the boiler to be maintaining steam if any one of the zones is calling for heat.  Thus, if you have one cool zone, the rest of the building will continue to cook. 



There needs to be some other way to control the boiler!  It needs to shut off at least once an hour.  Perhaps it could be operated by another sensor(s) that are not adjustable by the tenant.  Steam should come up no more than once per hour and the lenght of time it is one should either be controlled by the outdoor temperature or by the space that is normally the coolest in the building.  The control of the sensor operating the boiler should NOT be adjustable by the tenant. 

This might be a good application for a tekmar 279, or honeywell vision pro.  This will not be a difficult problem to solve.



Get that pressure turned down!  No higher than 2 psi max! -- probably even lower.   The existing vents should allow vacuum to be broken, but even if the vent is in the closed position, air will enter the system one way or another.  I don't think that is the root of the problem, but rather that your steam is continuously "up".

TheRookie

Boiler control

Dave,

Thanks for the insight.  I am looking into how we want to de-energize the boiler and let the system fill with air, whether its based on a building heat demand, or perhaps once an hour as you had mentioned.  Likely the latter.

Its interesting.  I lived and breathed this project for a month, purchased books, etc...  Still didn't get it right!  Steam is very tricky. 

JUGHNE

Same problem yesterday in school; corrected

This morning after 10* setback rooms were within one degree of each other.  You are very fortunate to have good vac bkrs on your TRV's.  Mine are 30 year old Danfoss RAV?? with iffy at best vac bkr, so still hear water flushing down condensate piping.  Our master control is simple HW 6000 t-stat in the one room without TRV.  Too low tech for most engineers (and what apartment would get that control anyway). 

Dave in QCA

Tekmar would be great!

There is a very large apartment/condo here in the quad cities with one-pipe steam and TRVs on the radiators.  The boiler is controlled by a cycle timer that runs the boiler a certain number of minutes out of each hour.  It is adjusted manually by the super as the weather changes. (surely wastes a lot of fuel!)  So, your idea of some kind of timer would certainly let the TRVs do their job, but I would imagine that you could do a whole lot better.



I would highly recommend using a Tekmar 279 in your situation.  The way it works is to cycle the boiler a certain percentage out of each hour based on the outdoor temperature.  It incorporates warm weather shutdown and also will keep the boiler hot without steam in the summer if you're using it to heat domesting water.  



I installed one of these myself, purchased from Pexsupply.com (real good price).  In my building it provides the only means of temperature control in a 8,000 sq ft, 9 unit building, and it does a VERY good job of maintaining very even tempertures, and has paid for itself in savings.