Anti-short cycle timer?

Cosmo

I was just wondering. On a multi-zone system, and especially when low-mass boilers are used without buffer tanks or expensive controls, the oil-fired burner takes a beating from continually stopping and starting as zones call for heat. The problem is when a zone is satisfied the burner shuts off, and if another zone calls a couple seconds later the poor burner starts up again. Is there a control out there with a timer, that would not allow a start until the burner has been idle for a predetermined time, say 15min? Then this might solve the rapid start stop. It seems like this could be an inexpensive thing for those people who won't go for a nice Tekmar control. Lets see what you guys can come up with...
Casmo

ed wallace

delay timer

you should be able to pick up a delay on make relay at an
hvac supply house ICM makes a digital progamable delay timer
mfg #icm103b but it is only rated for 1 amp constant and
10 amps on start up graingers also sells time delay relays
good luck let me know how you make out

ed wallace

delay timer

you should be able to pick up a delay on make relay at an
hvac supply house ICM makes a digital progamable delay timer
mfg #icm103b but it is only rated for 1 amp constant and
10 amps on start up graingers also sells time delay relays
good luck let me know how you make out

Cosmo

That is exactly the problem

I ran into, with the low amp ratings. Buderus I think has a timer but I have never seen it and don't know if it is a stand-alone control or if it must be wired into the ecomatic control to work. Well I will keep looking, thanks for the response...
Casmo

Duncan

Delay on make timer

A company I worked for many years ago in Denver came up with the idea of a "Denver time delay".

The idea was, that when the boiler came on, the timer would delay the burner from firing. When a zone valve opened and circulator came on, water sitting in the boiler that was heated from the previous cycle would circulate, scrubbing residual heat from the boiler.

The time of the delay was calculated by running the largest zone and seeing how long it took to drop twenty degrees.

The only problem was... on minus twenty degree cold snaps, the delay was too long.

It was a good idea, but it was based only on a time setting, not a responsive setpoint control.

If your small relay won't handle the current, cascade relays: the smaller relay controls the larger relay's coil. The larger relay is rated to handle your larger current.

hr

A mechanical fix

would be better than a delay on the boiler. If a second zone calls it needs heat. A some point those 15 minute delays will prevent the room or zones from getting the heat they need to satisfy the call.

The best way would be to buffer the system and look at deep cycling the boiler. Maybe a 30 -40 degree delta T control on the boiler. That low mass could run 140 - 180 without a problem. Watch Nov. or Dec. PM mag for an article on this.

Did you ever see DVW's 100 degree buffer tank design? He had Heat Timer tweak some setpoint controls to allow a 100 degree differental setting. Now that's the way to exercise mass and buffer to the MAX.

hot rod

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Pat

anti short cycle

I know of a contractor that would use 2-stage t-stats. 1st stage opened the valve and started the circulator. 2nd stage started the boiler. You do run into the potential of a room dropping a good 2 deg before the boiler comes on, but it might help with the short cycling. Just a thought.

Jamie Hall

same kind of idea...

How about running the circulators on thermostats, and the boiler on its own (separate) water temp. thermostat? Sort of like a glorified water heater... Haven't tried it (don't do hydronic, only steam) but it's kind of like the use of a vaporstat to control to boiler in steam...

just a thought

bluenose_7

Triple

Jamie, you got it right on the money.
You must be using a triple aquastat with the end switches tied in on TT terminals. Disconnect and run the end switches to a circ relay, that is assuming your not trying to heat your domestic hot water through a tankless coil.

Cosmo

Well this is what I came up with

As I had seen, and Ed Wallace mentioned, ICM makes a 'Delay on break' control, #ICM 203. On a beckett (or most any other american burner) there are 'TT' terminals on the burner control, which in most cases is jumped (forget the tankless coils jobs). So if we placed this control between these terminals, the ICM unit will in fact break the continuity for .03 to 10 minutes before making. I like it. And the cost is less than $20. This boiler has to wait ten minutes after every call is satisfied before being allowed to turn on again. Of course when using a Tjernlund inforcer, we have to add another relay and interrupt the power (or the limit lead that runs through the lwco, and such) instead. I will try it tomorrow on my own old Vailant boiler.
Thanks for posts, more ideas welcome
Casmo

J.C.A.

Timer off question.

Oil boilers(properly tuned and setup WITH INSTRUMENTS!!!) make all of their soot on start and stop , so you are wise in trying to limit the amount of each .The problem is...the owners want their heat when and where they call for it . The best oil control innovation in the last 15 years , in my opinion is the CCT relay .(Honeywell followed the lead) As long as you have an oil valve , doesn't matter whos it is , with a simple wiring change you will have pre-purge and post purge control . I have special ordered controls ,programmed for special situations and haven't been let down yet .I had one in a church that has a 2 minute post-purge function and a 15-20 second pre-purge . It used to need cleaning at least 2 times a year , with this control it is down to a dusting every year and most of the time it doesn't even need that. Oil firing is a different animal as compared to a gas unit . (again) Proper sizing is of the utmost importance . The key is to get it to run clean as long as it is running . No foul starts and stops . Scrubbing too much heat out of a (usually ) cast iron boiler isn't the best way to do it either . Firing into a warmer boiler also adds to a clean start .If you can bring the burner motor up to speed, establish a draft and get the oil just a little bit warmer by having it beat itself warm in the fuel unit , you will get a cleaner start. I think this is a better way to go than trying to keep it from firing for a set time . JMHO. Chris.

Cosmo

Thanks Chris

I agree with everything you said. I use the new Honeywell R7184A burner control on every Beckett I install. This control gives a pre-purge, adjustable post-purge, and also interrupts the ignition after the fire lights. Otherwise I install a Riello and all that standard. I just wanted this timer for the jobs with a bunch of zones, and no expensive (but worth every penny) Tekmar control.
Thanks,
Casmo