System 2000 oil boiler cycling on/off, what is normal?
Hi,
I have a system 2000 oil boiler (EK2) - which supplies hot water to two separate air handlers (first co) for heating.
The system is appropriately sized AFAIK, as in the last few winters, at around 0F (which is the design temperature for my region as far as I know) it can just about maintain 69F running around 100% (depending on sunshine) of the time.
Once the house is up to temperature, with normal outside temperatures, the air handlers run on/off (independently directed by thermostats) for short periods. The oil boiler is designed to return to cold, and controls the air handlers so they keep blowing air to use the residual heat efficiently. That's all as expected.
The problem is early morning warm-up. Probably caused by the house being open plan, the upstairs heats up quicker than the ground floor (hot air rises), and the system spends a lot of time running only the ground floor air handler. On top of that we maintain cooler bedrooms upstairs anyway. As the boiler is (necessarily) sized for both air handlers' combined output, obviously it has to cycle on/off to accommodate. So with only one air handler continuously asking for heat, it switches the burner on and off.
I've been trying to count and it seems to cycle on/off around 10 to 12 times per hour. That's every 5, 6 minutes! As these boilers are relatively "lightweight" and have minimal water contents, the high heat output quickly reaches shut-off temps and the burn is interrupted. Water keeps flowing, air handler keeps blowing, and once the water has cooled off a bit it starts the burner again.
My question:
A) How bad is this? Obviously more wear and tear and probably inefficient?
B) How to avoid this? I can't be the only one with two air handlers on one large boiler. Do cast iron boilers cycle less because of their thermal lag? Is there a standard way to make this system more efficient, like a buffer tank, or would that defeat the whole purpose of the System 2000 returning back to cold? My previous house had a big old boiler that was kept 'hot' continuously, servicing two air handlers in mostly the same setup. But that was quite wasteful in summer, as it kept the boiler hot just for hot water.
C) As there are very few modulating oil boilers, what would the better design be? Big buffer tank? Two oil boilers separate, each sized appropriately for their respective air handler's max heat output? Are there any two-stage oil boilers out there, or would that require a switch to another fuel, like propane?
Thanks for any insights!
Waldo
Comments
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So it's turning off and on from high limit under approx. half load? Is this an EK1 with digital manager? there are adjustments.
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I see that it is an EK2. Questions: Digital manager? There are adjustments. Does the burner cycle off and on from high limit when both air handlers are calling? Because of low water content (EK2 holds 4 gals. of water) burner cycling from high limit under partial load is normal, however you may have more fire than you actually need. Also, first floor may be taking too long to heat due to insufficient water temp. or air flow.
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@wvrlem Can you tell me what's turning the boiler off? Is it the manager turning the boiler off on temperature? Or is it running to high limit? Are you saying the 1 floor fan coil system isn't putting out enough heat?
Robert W.
Energy Kinetics
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Need to tell us what the indicator gauge and the manager look like when it shuts off.
- Is there still a call for heat?
- Is the burner light still on when it shuts off?
- Is the return temp indicator maxed?
- Is the boiler temp dial at like 215 or less?
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Sounds like the first floor air handler is too small for a night time setback.
1 -
Thanks for the replies - There is a continuous call for heat (for 1 of the 2 zones).
To be exact:
In the morning, I scheduled both air handlers to come on at the same time. System runs stable for an hour or so; oil burner on continuously, water temp around 175, return around 140/150. This can go on like that for hours, if needed. But once the second floor is warmed up (usually that warms up first) the ground floor keeps calling for heat. Our bedrooms on the second floor are kept cooler, and as I said it is open plan so some of the warm air shoots up to the second floor.
So for the next hour or so, zone 1 (ground floor air handler) keeps calling for heat. As that zone can only output so much BTU (I think, depending on air/flow and water temp, up to max around 100.000 BTU or so?) the boiler temperatures keep increasing and at some point the boiler shuts off once the return temperature reaches 170 F. (on the led's on the digital manager).
The burner stops, the burner light is off, the call for heat is still on, the zone is still active, and pump and air handler still run. Water temperature slowly goes down as the air handler sheds the heat and once return water temperature is around 140 or so the burner starts up again.
I've also tried to reduce the high limit, (Factory set at 205/215, but the air handler says it is supposed to work with max 180F supply) to, say 190 and in that case the high limit shuts down the burner before the digital manager does (you can hear it click). The burner light stays on but the burner is off and once the supply water temperature is below some temperature the high limit clicks back shut and the boiler starts burning again.
But in both cases, the burner cycles; it just is triggered either by the return temp > 170 (digital manager) or supply temperature >190 (or what I set the high limit on).
Unfortunately there is no way to push the ground floor air handler to push out the full 170.000 BTU the EK2 makes, as far as I see. Air handler supplies warm air to the ground floor at around 125/130 F.
So the question is: is that normal for this system, to cycle every 5,6 minutes when heat demand for the house is roughly 50% of total power?0 -
Your ek-2 boiler doesn't know only half the house is calling for heat. It only knows on or off and It's sized for the entire house. If your 1st floor air handler is sized correctly, the filters are clean, and your coil is clean, then your air handler is stripping the correct amount of heat for that floor. So yes the boiler will cycle on and off as needed.
Also your high limit should be set at 210. It is there as a safety. The manager controls the temperature of the boiler.
Robert W.
Energy Kinetics
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Hi RobertW, thanks for the reply!
Ok, I get that the boiler is "single speed", so you basically can't avoid cycling. Do you have any thoughts on the frequency that would be normal in your eyes - and not detrimental to lifespan and efficiency per se? I'm just thinking every 5 to 6 minutes is quite a lot of stops and starts…
And the 64.000$ question - is there anything you'd recommend to reduce cycling, if that would be better for the system and/or efficiency?
thanks again0 -
What would be cool is knowing actual supply and return temperatures on the water and the air. The Manager will close the zone valves if return temperature drops below 120° or 130°, depending on the option. That's obviously not happening because the boiler is making it's 170° (or is it? The burner isn't going into recycle?) return temperature operating limit. Multiple times an hour. That would direct me to air flow. EK has specs for hydro air. Is that what was used? Static pressure numbers wouldn't hurt either. The First Company air handlers have PSC motors?
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I think a buffer tank is the only hydraulic fix. Or the electrical time delay on make relay that Karl posted here?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
My first inclination would to be looking at the air flow. Why is the first-floor air handler taking an entire hour or more to make temperatures and at what outdoor temperature are we talking about? What are my supply and return temperatures at this time would be a good indicator as to what's going on in the air handler. Is it sized correctly? The recent extremely low outdoor temps some areas have had in the past weeks will expose all miscalculations in sizing. High micron filtration can restrict air flow enough where you don't notice it when its 30 outside but when its zero you'll see the difference.
Robert W.
Energy Kinetics
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The cycling is simply a function of how the system, like most others, is designed. Residential gun type oil burners do not modulate. From a financial standpoint the cure in the form of a buffer tank will be worse than the disease in the form of slightly shorter service life of electromechanical components.
Sometimes a less than ideal situation must be accepted as a reasonable compromise. If the system had a single zone a properly sized burner would not short cycle; but fuel would be wasted in heating the entire structure when not necessary, or in temperature imbalance.
—
Bburd
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Your cycle efficiency drops off quickly however when you have low loads and less that 10 minute run times. So your boiler efficiency drops and fuel costs rise. Your 85% boiler can drop int the low 70% efficiency.
You can throw your own numbers into the formulas. If you spend the bucks for for of the highest efficienct oil boilers, 20 plus year life efficiency, you want to maximize it's potential.
Chapter 3 of Modern Hydronic Heating & Cooling 4th edition has a in depth explanation and example.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
hi RobertW,
I expect the top floor air handler is a bit on the larger side for the heating demand, mostly bedrooms, where the ground floor is possibly undersized for the larger space. Not much I can do about that, I'm afraid, within my budget…
Recovery is not crazy either, around 64/65 F overnight, back to 68 in the mornings.
Air handlers get regular new filters, higher airflow ones - so no crazy high MERV rating at all.
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There is a solution for this and it is inexpensive.
In the shoulder seasons, where the boiler might get down to below 20% run fraction, thereby seriously affecting efficiency, adjust the stat for a much wider differential. I've got the FHA stats set for an estimated 2°F and the run fraction is never less than 30%. In the shoulder seasons, it absolutely makes no difference regarding comfort.
Some of the digital 'stats don't discuss differential. Just set 'em on the setpoint for steam. That will give the widest differential without explaining how they work.
Additionally I disagree with the "run fraction". If I can have a boiler that runs for 12 minutes every hour, that would be a 20% run fraction. This would absolutely NOT be an efficiency of 70% as shown on the chart provided by Hot Rod. Now, if it ran for two minutes every 10 minutes over the course of one hour, with the same "run fraction" NOW you are talking about a severe penalty. These are two completely different scenarios and the offered charts are wildly in error because of this.
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Overcomplication. The dip switches on the bottom of the manager can be set to increase return temp. shutdown, approx. 155 to 170. Set high limit back to 215, that's how Roger's engineers designed the system. Result will be that first floor will heat a little faster and will be a little less short burner cycling. An original inquiry was "is this normal?" Answer is mostly yes, but I just outlined how to minimize short burner cycling. It is not a big deal, your fuel usage is at a minimum with an EK boiler properly set up. Consult your EK digital manager guide for proper dip switch setting, I don't remember offhand.
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My first thought is why does a home with only two hydro air handlers have an EK-2? What size air handlers are they and what is the size of the piping to the hot water coils? With that much boiler output I would expect both air handlers to be 5 ton or at least 4 ton with 1" copper tubing to the coils. It must be a pretty large home.
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Yes, Large home with a 5 ton and 4 ton air handler. I thought the boiler was crazy oversized at first too but the air handlers combined output can manage the heat generated fine when they're on together (and if one alone could handle all that output, them together would not work well, no?).
And the boiler approaches like 80, 90% runtime in really cold spells around 0F; so seems to be sized close enough (if maybe a bit too big).
I came from a milder climate with a modulating gas boiler, radiators and thermostat timers and thermostatic valves. Loved that system. This has quite a learning curve.
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