primary/secondary?

JSPAK

on the design i put in my first post there was no return water protection valve controls...the contractor doing the job is designing this ... i feel that this protection is missing .... when the water in that loop is circulating at 120 and lets say it got a 2 degrree diff ... hits 118 injection pump comes on (remember its not a variable speed ) whatever that pump is putting into the system has to be taking out ..... 190 out 118 in ... any suggestions as far as what kind of protection to put on there would be helpful (i personally think the pipng needs to be changed .....put a blending pump in and inject off that line and return to that line with a vairible speed injection pump ... monitor the return water to boiler and never let iit get below a certain temp

JSPAK

primary/secondary?

just curious.i used to install boilers about 20 years ago so i am familiar with the different systems and and some of the problems they can cause if installed incorrectly . i now work for a school system in the maintenance dept.and we leave the installation up to the contractors .well this one contactor is replacing the 2 watertube boilers with 2 cast iron smith boilers and piping it as a primary secondary .. heres the basic way he's piping it ... the system used to be a mixing valve about 75 feet away from the boiler .. he will be using a heat-timer control .the main loop is 3"pipe and the injection piping is 2 1/2 piping . injecting pump only comes on when temp gets below setpoint. and depending on oa we could be running 120 degrees in the loop .120 degree water being introduced into a 180 boiler doesnt sound like a good idea ... maybe i am wrong but better safe than sry
http://img.photobucket.com/albums/v511/soak123/boilers123.jpg

Al Letellier_9

P/S

Sounds like a plan to me. This is done a lot in the industry today, and properly sized, this will protect the boilers more than that old mixing valve. Heattimer makes great controls and it seems like your guy knows what he's doing. It is a great way to stage fire your boilers and rotate the lead/lag for equal run time. Depending on how he sized the boilers, you will only run one on light demand days. The savings can be quite significant.

Cunner_2

P/S

I wouldn't totally rely on the P/S to protect the boilers in that application when running an aggressive reset schedule, in the shoulder months ( fall-spring ) your 120 system water make trouble with the boilers, ie boiler condensation and thermal stress. P/S will sure 100% flow through the boilers but may not totally protect against temp. I see many of the CI manufacturers are now recommending boiler by-pass pumps and I believe one of them now offers a return temperature control package. I've seen more than a few commercial CI boilers fail that were piped P/S but showed signs of condensing, just food for thought.

Brad White_9

I am finishing a design on an elementary school

not unlike what you describe: A single 1956 Fitzgibbons Fire Tube steam boiler, all of which output goes to (2) shell and tube HEX then to a set of pumps serving original and addition loads. No steam leaves the boiler room; it all goes to hot water. (School was steam at one time I was told but the HEX's seem to be as old as the boiler.

It is incredible that in 50 years they had only one day of school lost that anyone remembers due to boiler failure -due to tube leaks- and only a couple of years ago. A re-tubing took care of that and dropped the therms useage from 80,000/year to 60,000/year. We will see what the new boiler system will do over time, but currently and to date they have run 200 degree water without reset. ("No complaints that way!")

The new system will be a pair of Burnham V-1118's as basis of design with the return water protection valve controls just as you describe. Each is sized for 2/3 capacity should one fail or be serviced they can still hold school.

The system output of these HWR protection valves forms the primary or boiler loop. The secondary or radiation/Unit Ventilator loop is decoupled and a valve injects for deep reset fully adjustable. The boiler loop will be maintained at 200-140 full range and the secondary at 200-100 full range, all adjustable. Secondary pumps are on VFD's using DP control.

We could not use condensing boilers because the school is a water works per the state and the well is right there. We cannot dispose of combustion condensate in that septic system as it is considered industrial waste, however mild and even if neutralized (in case anyone asks!)

Goes to bid in a few weeks for a summer project. I will post pictures.

Anyway, I mention all of this because of the parallels in the design, so yes it is a proven concept not too foreign.

Brad

[Deleted User]

If you are

going to maintain temperature in those boilers, I would install a blending pump on each.

Cunner_2

Return Protection

Are you using the RTC's from Burnham or your own design? Just curious, I see the return temp and boiler flow becoming a huge issue with the vast improvements in building management systems. Seems like there is a big gap in communication between the Energy Managemnt Companies and the Boiler manufacture's.

Brad White_9

Manufacturer versus ATC

We have specified the Burnham RTC as an acceptable means and method to what is a generic concept (modulating valve enforcing a minimum HWR temperature to the boiler). This is a public job so must be competitively bid. We describe the sequence and if they use someone else (Buderus or DeDeitrich) they have to get her done. If Burnham and their RTC it is certainly acceptable not to mention our preference.

For controls we specify the "what we want to happen" and allow the contractor to determine the means and methods. However it always goes with a burner-boiler package of controls that will "do it all" including pump sequencing by default. In such cases, the central DDC system (new to this job as it replaces pneumatics) will still do Start/Stop/Enable, Alarm and Monitoring of Setpoints.

Point being though, the contractor owns it all and has acceptable choices in the "How to Do It" department.

Yes, there is a gap but we like the idea of the boiler control panel being autonomous to the DDC system. In case of bus or network failure, life can go on.

JSPAK

BTW forgot to mention

there will be no blending pump on the boilers ... boiler water is maintaned at 180-190 degree water with no movement ... only movement will be when injector pump comes on (and injector pump is one speed and not variable).

Will_5

excellent

Great response Brad, I like your thinking. I wish more of the engineering community would think that way and start bridging the gap between boiler control and system control. Looks like you are certainly progressive and ahead of the curve!!!

JSPAK

looking for answers?

what i need is imformation on what to look for as far as protecting the boiler from that 120 degree water. making sure the contractor has installed all the nessary safeguards.any links would be helpful ty

Unknown

heat-timer is a great product. we use the platinums at work everywhere we install boiler or even do work. the way they work , you probably wouldnt need to worry about thermal shock because the staging on the controls is incredible. mild days you wont even see 180 degree water. it sounds like he knows what hes doing, but hey i wouldnt be using cast iron boilers anyway. RBI's and Heat-Timer make a system very merry.

Brad White

The way your diagram reads

I see nothing interfering with 120 degree or colder water hitting the boiler. You need a bypass or other form of automatic intervention. The boiler pump in your diagram can only draw from the main loop through the boiler. Unless you have a low limit on the main loop (defeating outdoor reset) you will see whatever temperature is in the main loop.

Rich Kontny_3

To Bad

I would have liked to see more than just the two boilers,years ago we did an eight story HUD financed elderly housing project and the specs called for 14 Triad Boilers. These were very simple residential boilers with a sequencer to alternate and pull in additional boilers as conditions got closer to design temp. (about 20 below)

Two of these boilers were used as priority boilers for domestic hot water using a heat exchanger arrangement. Over the years I see more and more primary secondary piping arrangements as the modular concept makes great sense.

Due too the simplicity of these boilers they were easy to maintain and you could isolate one without disturbing the overall output unless you were having design temp. conditions.

The only thing I would do different today is have dual fuel or multiple fuel capabilties.

Rich K.

Make Peace Your passion!

JSPAK

I TOTALLY AGREE

there is nothing stopping 120 degree water from going into boiler .. the new boilers are getting put in now as we speak .... one of the watertube boilers still running and maintaining temp. soon as the new boiler is up and running they will be removing the second one .... first boiler failed because of inacessable leak in tube

Mark Hunt

That is not P/S piping

and that set up will be nothing but a nightmare.

You have 1.4 million btu boiler that will only have the injection pump flow rate through if it is piped as per the attached diagram.

I attached a quick sketch of what it should look like.

Mark H

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Brad White_9

That is exactly

what we have been saying- that you need such a control or the boiler will likely suffer.

See the attached.

EDIT: I had not seen Mark Hunt's post below with his diagram. Similar concept (identical in principle) so we are both on the same page.

Cheers!

Brad

JSPAK

ONE LAST QUESTION

first i want to thank you all for all your input . my question is that when this does fail is there any danger to personal in the immediate vicinity of the boiler room ?

Brad White

I was next to a boiler once that suffered defeat

by circulation of cold return water to a hot boiler on startup.

The sound of cast iron braking is a very loud "tink!" then an expanding pool of hot water at our feet.

Now, I had been told that the boiler had already cracked some days earlier (which is why I was there) and had "healed" upon cooling when expansion stresses changed. Thus this was the re-opening of the crack upon heating so I cannot deem that a catastrophic failure.

I suppose it could be more dramatic but really do not know for certain. My cautious side says it is possible but I am also not given to being alarmed at everything.

If you have concerns, state them in writing (possibly retaining this thread and printing it out). Make your case for the record and get in writing that such an occurance would not occur and/or that all reasonable means were taken to prevent such an occurance.

archibald tuttle

all right I'll bite.

Mark and Brad,

neither of your diagrams seems to indicate a simple primary/secondary setup as I understand it which is that the boiler connections to the main loop are undertaken similarly to the heating load connections in Brad's diagram. If one figures the pressure drop and relative pump strengths of the boiler, primary, and load pumps that some bypass is a built in part of that kind of primary secondary approach.

Although you may be circulating 190 from a boiler secondary, it will cool on a bit of mixing on entering the primary loop and then that mixed feed will be drawn into the secondary load loop and returning water at a significantly lower temperature on startup would be warmed by water bypassing the secondary load because the few inches of primary pipe between the feed and the return provides very little pressure drop meaning that a fair deal of primary temp water will continue around the primary circuit thus warming the reutrn water. (not in the original diagram that started this thread, which, as Mark pointed out, is not true P/S). Unless the pipe and pump sizing is overdone on the secondary load, you should be able to avoid cold return, n'est ce pas ??? Maybe if you have a bunch of cold loops calling all at once this could be a problem, maybe a brainy controller would wait for a called loop to meet a certain return temp before starting a second. Or maybe even using two pumps or a two speed pump that engaged higher circulation to the loop only after attaining a certain return temp.

All of these ideas are workarounds that effect a similar idea to modulated bypass return temp regulation. I have had much more luck with on-off kinds of control decisions than with modulating bypasses that require automatic valves.

And Brad, how much condensate were you really needing to drain on this job. couldn't they let it fill a five gallon bucket and have a custodian take it home and dump it down his toilet or just run the drain tube on the floor and let the water evaporate.

This is the typical deal with recursive regulation. School serves some number of kids, well of the number of 25 that makes its well a public water supply, and thus makes the school a nuisance to itself. Then everybody turns themselves into pretzels to design a septic system for the school and then they get worried about a few quarts a day of flue condensate while they have bathrooms for the entire school flushing away every day. That's not to say that the septics systems aren't reasonably designed and can't handle that, but the relative risks of the two behaviors are inverted in consideration, while theoretically more efficient heating equipment is barred. Maybe I'm am grossly underestimating the quantity of condensate representated by the small drip from the tubes relieving the exhaust on condensing boilers but this sure doesn't make any sense to me.

Brian

Brad White

Ah Brian....

In the system I designed, the boiler loop (which I call the primary because it has the higher temperature from which other temperatures are derived) indeed circulates, not unlike a reservoir of hot water, semi-limited in volume. Indeed, the system return (secondary or load return) does dilute this but that is how the load is picked up. The boilers, boiler pumps and their valves modulate to maintain that reservoir at temperature and this happens very smoothly.

When the system-side draws off load it can be a sip or a gulp but with more finesse than that. The injection valve also modulates...The result is nearly dead-nuts control on the secondary side with modest spikes in the primary side; those only tending toward the periods of low-fire when there is no down-turn room but there are minimum run-times on the burners.

Right now the steam system they have runs with Low-High-Low fire, 8500 MBH input for a 4600 MBH peak load. Take out the change of state and allow outdoor reset to flourish and you really have some improvement.

As for the amount of condensate, take a seat: The "hybrid plant" would have had one Burnham V-1118 and two (2) 2000 MBH condensing boilers which would take the lead. When in condensing mode, each of these boilers would produce between 18 and 20 gallons per hour... (one gallon per 100 MBH input in rough terms). There was not enough storage on-site. Disposal rates work out to about 30 cents a gallon...

That poor custodian would be hauling 40 such buckets a day and under cover of darkness....



As for being a water-works, this school's well also serves the town as a back-up source. The town is very sensitive regarding ground disposal as they have had several contaminated wells over the years.

We tried to make the case for surface percolation but the state and town said no. Still, the system we have designed preserves the best feature of a Mod-Con: Modulation.

See you in a couple of weeks, my friend!

Brad

archibald tuttle

challenge accepted

OK, OK, so you are dealing with 4 million btus and I'm running a lousy half a mill on the building I'm using for comparison in my mind (two teledyne-lars nee heatmaker 9600 hot water makers). So if I bottled my return, I should be coming up with 5 buckets a day. I can't believe it, so I'm going to put the outlet tubes into a bucket and keep an eye on them. Maybe since they are not modulating I am not really in condensing mode for as much of the operating time so that is my experiential bias - that I did this job just before the serious mod conds had matured.

Get what you are saying about the more relibable regulation of temperature in the secondary of the system you designed and given protecting expensive boilers from cold shock it seems iron clad, but in my experience, I have seen more failure with automated valves than with any other heating component so if I give up rock solid secondary temp but design to dilute return with pipe sizing, etc. I'd be interested to see what I could do.

Of course in most cases now I'm not worried about low return temp, although it is too bad that I plumbed my own house before primary secondary became popular. Oh well, when I have nothing better to do, like when my existing boiler gives out from the modest cold shock I subject it to, then that will give me an excuse to redo the piping in my own house. Until then, you know what they say about cobblers children.... and I have to finish the steam installation across the way. Want to come down early on the 17th and have alook, if the weather's decent?

Brian

JSPAK

wm primsec piping guide.pdf???? anyone got this file???

heres where contractor got his idea of primary secondary seems this is the perfered method recommended.

http://www.weil-mclain.com/professionals/services/Bulletins/SB0205.pdf

i was watching the system installed today and discharge from injection pump was 165 degree.....
target at 24 degree Outside air was 154 degree
return at temp sensor 2 feet from boiler was 135 degree

system was maintaining 154 +-2 degree ......even though contractor says triple duty walve wont let it shock boiler wasnt even warm out and return wont let enuf 140 or less water.... hmmmmm

if anyone has this file would be greatly appreciated if u could send to me ... jspak@snet.net