Short Cycling Triangle Tube

CapeCod

I recently completed a major renovation which included removing my forced air furnace and water heater, replacing it with a Triangle Tube PE110 with the internal water tank.  I knew it was oversized but liked the fact that I could clear up a lot of floor space in my basement.  I did inquire about the possibility of short cycling but the contractor told me something like "that is the beauty of a mod-con, it will adjust to the heat load".  Well, the contractor is gone, stopped answering emails and phone calls, and now I am experiencing my first winter with the new system.  He did a nice installation (except for a leaking radiator valve I recently discovered) and I like the boiler with the Trimax controls but obviously not happy with the customer service especially after spending so much money.  No, I don't have a heat loss calculation either.



At the beginning of the heating season a couple months ago I noticed it was short cycling quite a bit.  I started a log to quantify it and began studying the manual.  I realized that the installer just left the default reset curve and left the default "cold day" setting at 0 when my climate is more like -15 so I started playing with that and it seemed to help.  With the settings he left me, I was getting something like 1 to 2 minutes per burn.  After adjusting the reset curve, adding a few minutes to the post pump circulation, and increasing the CH Call Block to 15 minutes, I was able to get more like 5 or 6 minute burns.



Can anyone suggest any other levers to alleviate the short cycling?  I suspect my boiler is probably twice as big as it needs to be.  I have panel radiators and two zones.  I do plan on adding more radiators in the future but would like to avoid add mass to the system at this point (out of money).  Is it possible to cap the high end of the capacity (make it a 60K boiler instead of a 110k boiler) and still modulate down?  Any other ideas?  Thanks in advance!  I am going to try to attach a spreadsheet I made with all the parameters I have adjusted and the resulting "minutes / ignition"



In case the file doesn't work, data is below.



Column Headers are (date, ignition count, hour count, min / ignition, ODR Low Setting, ODR High Setting, Cold Day Design Temp, Warm Day Design Temp, Avg temp that particular day, Target Temp derived from slope of curve, post pump time, CH Call Block Time)



11/14/2012    3520    95    1.50    104    160    0    64    35    129    5    10

11/15/2012    3600    99    3.00    104    150    0    64    36    124    5    10

11/16/2012    3680    102    2.25    98    148    0    64    40    117    5    10

11/17/2012    3720    105    4.50    94    148    0    64    42    113    5    10

11/18/2012    3820    110    3.00    94    148    0    64    42    113    5    10

11/19/2012    3940    114    2.00    90    148    0    64    45    107    5    10

11/21/2012    4060    118    2.00    90    148    0    64    50    103    5    10

11/22/2012    4140    120    1.50    90    148    0    64    60    94    5    10

11/25/2012    4380    138    4.50    94    148    -15    64    35    114    5    10

11/26/2012    4480    146    4.80    94    148    -15    64    32    116    5    10

11/27/2012    4560    153    5.25    94    150    -15    64    30    118    5    10

11/28/2012    4640    160    5.25    92    150    -15    64    30    117    5    10

11/29/2012    4700    164    4.00    92    150    -15    64    40    110    5    10

11/30/2012    4760    167    3.00    92    150    -10    64    45    107    5    15

11/30/2012    4780    169    6.00    92    150    -10    64    45    107    5    20

CMadatMe

Going to Need

That heat loss as well as comparing the rads capable btu/hr output at different water temps to find a curve. From there your going to need to add a buffer tank to the system or live with the short cycling.



Playing with the curve will not stop the short cycling.

CapeCod

Playing with the curve will not stop the short cycling

it may not stop it but it certainly has a positive effect, right?  Also, blocking the call for central heat and forcing it to wait 20 minutes before coming on again definitely helps and so far I haven't notice any major under or overshooting of room temperature.



By the way, is there any kind of rule of thumb definition for short cycling?  Or is it like the definition of pornography...you know it when you see it?



I will probably try to do a heat loss at some point but the damage seems to already be done...the boiler is too big and now I need to find a way to improve it.  I had a feeling the right thing to do is add a buffer tank but I really don't have the money to spend on that now.  From what I understand, the heat loss is just a theoretical starting point anyway and would have to fine tuned to take solar gain, insulation, windy days, etc.  The fine tuning I am doing now seems to be helping, just wondering if there is anything else specific to the Trimax controls that I could try.

cattledog

Achieving Longer Burn Times

You are correct that you are moving in the right direction with lower target temperatures. Compare the data from 11/16 with that of 11/29 which were both days with 40 average temperatures. Outlet water temperatures were 117 and 110 and run times increased with the lower temperature. Chris is right that heat loss and radiator performance data may get you where you want to go quicker, but it looks like you can explore your way down to lower temperatures. Be prepared to bump things up if you get cold weather and can't achieve set point. Or, if your wife complains ;-)



There is another approach suggested by the increased run times (at the same water temperatures) with longer blocking times. You said there was no major undershoot or overshoot, so it may be possible to lengthen the run times from the control side. Please describe your thermostats and the control parameters. If they are on/off you may be able to open the set point differential. If they are PWM or proportional you may be able to decrease the cycles/hour (increase cycle length) or modify the regulation band.

Zman

6 per hour

The number I here tossed around the most is 6 cycles per hour.

That would be a complete cycle every 10 minutes (on and off time). It looks like you are pretty close.

There are 3 things effecting your cycle time;

1. System mass. It takes 1 BTU to heat one pound of water one degree.The more water you have, the more energy your system can absorb and hold between cycles.More mass will absorb more energy and lengthen cycles.You could add a buffer tank, I think this would make the biggest difference.



2. Boiler on /off differential. Your trimax should be automatically going to low fire and stretching the differential out to 20 degrees. By activating call block you are effectively stetching it further.



3.The ability for your radiators to emit energy. In a perfect world your radiators would be sized to match the low fire rate of the boiler. If this were true the  boiler would run constantly at low fire until the demand is satisfied. This is not usually practical/possible in a residential system. By lowering your water temps, you are doing a good thing by making the return water colder and increasing the efficiency of the burn. Lowering the temps will have the negative effect of reducing the transfer rate of your radiators thus  decreasing cycle lengths. You will have to find a balance that works for you.



Carl.

SWEI

...the high end of the capacity

Your issue is with minimum modulation rate (16k on the PTS60 versus 30k on the PTE110.)

CapeCod

Your issue is with minimum modulation rate

SWEI - Yes, at this point the damage seems to be done.  The right thing to do was to get the next size lower and add an indirect water tank.  I actually had that quoted and it was pretty much a wash financially.  I just liked the fact that I could reduce my footprint in the basement with the PE110.  I inquired about short cycling at that time and was assured I would be OK....guess I should have done even more homework.  This warm winter doesn't seem to be helping matters.  Anyone want to swap a PE110 for a PTS60?

CapeCod

you may be able to decrease the cycles/hour (increase cycle length)

Don't know much about my thermostats, maybe I can google the model number and figure out what kind they are.  Having said that, by blocking the call for central heat at the boiler, am I not doing the same thing?



I think I may try to do a heat loss for myself to understand it better and quantify how oversized the boiler is.  I read a few threads here regarding basic homeowner calcs you can do for free.  If anyone has a good website for that please let me know.  With all the variables involved it seems this will get me in the ball park and probably help me understand the system more but I will still end up playing around with the numbers once I am done.



I appreciate everyone's the advice so far...

Zman

How many?

How many zones do you have?

Lowering the water temps should reduce the radiators output and shorten burn times.The circulator post purge starts after the t stat is satisfied.

Carl

cattledog

Short cycling

Cape--



I think that Zman and I are talking about two different conditions of short cycling, and some clarification would help.



Are the burn times a function of quickly satisfied calls for heat, i.e. the thermostat tells the boiler to stop, or are the burn times controlled by the boiler output water temperature going above the target temperature and the boiler is telling itself to stop regardless of the call for heat.



I am working under the first scenario where the call for heat is quickly satisfied and the zone thermostat tells the boiler "enough". In this case lower water temperatures and modified control parameters can help. If you are cycling off the boiler differential and are under radiated then then lower temperatures and wider control parameters won't help.



I see some potential problems with using the boiler blocking parameter rather than the thermostat parameters, and the problems can be different depending on the type of thermostat--on/off or proportioning.



In the on/off case blocking is potentially equivalent to lowering the bottom differential--i.e. it lets the room drop lower in temperature than it would normally do, but to an unknown degree., before turning back on.There may be a problem with the two thermostats, and the block may apply to both, when you really want it to apply to just the last run zone.



In the case of proportioning controllers, they usually learn from the system response and adjust themselves. If they think they are calling for heat, and don't see the system respond because it is blocked they will probably call for longer on times but.they also may call for heat with the block off or at random times during the block period, and the learning won't be consistent.



Please let us know whether the boiler is cycling on quickly satisfied calls for heat or internal over temperature. In the first case, understanding of the thermostats may give you some preferable options to using the blocking parameter.

CapeCod

How many zones do you have?

Karl - I have a  total of 3 zones but one of them is in the below grade basement and so far has not really been used at all.  The second zone is the main living area, kitchen, and a couple small bedrooms.  The third zone is the upstairs which is a converted attic housing the master bedroom and bathroom.  I should mention that due to planned renovations I opted not to put in radiators in the kitchen and downstairs bathroom so I am definitely short some radiator output.  Should I engage the basement zone just for the boiler to have something to chew on even though I am not using it?



Your comment about lowering the temps gives me food for thought.  I was going the direction that lower is better so I just kept lowering the temperature until the boiler could not keep up.  However, after thinking about it more, that point will probably never come because my boiler is already firing at the lowest possible rate.  If I lower the temperatures it will only take it literally 10 to 15 seconds to bring it up to the low target temp and then shut off...hence the short cycling.  So, lower temps are not always a good thing?  Is my thought process correct?



Appreciate your other post...I was still trying to gather my thoughts to respond.  I also hope to find an hour of peace today so I can finish the heat loss calculation.

CapeCod

two different reasons for short cycling

Cattledog - I just responded to Zman and then saw that you posted something.  What I just posted is directly related to your question.  I just had the same revelation and I believe what I am dealing with is what you described in your second scenario.  The boiler is shutting off NOT because the thermostat is satisfied but because it reaches its low target temperature very quickly.  I don't know if it is truly that black and white but it certainly seems logical.  And due to planned renovations,  I am intentionally under-radiated...not enough radiator power for the house. More things to think about...thank you!  As I mentioned, I am going to do a rough heat loss today.  Just found a basic online calculator on the "warmly yours" website that seems easy enough.

CMadatMe

That's Why I Said

Lowering the water temp will not stop the short cycling. A btu is a btu and if you cannot pull them out of the boiler then it is going to reach target temp rather quickly. Buffer tank is the simple fix.

Zman

Correct

Chris,

Absolutely the best fix to short cycling in this case would be a buffer tank.

I do believe some improvements could be made by fine tuning the curves.

The data provided is flawed as it does not indicate which zones are calling.

Carl

CMadatMe

Flawed

Carl,



The entire reason everything is flawed is no heat loss, no measurement of heat emitters, no measurement of capable emitter output all before installation. The poison has been delivered and we both agree on the antidote. Without it, this homeowner most likely will end up just chasing his tail like a dog in my opinion.

Zman

Fair enough

Chris,

It sounds like he is working to that end. I do not disagree.

Carl

CapeCod

It sounds like he is working to that end.

Carl - Yes, working to that end...hoping I get there without going broke.



Chris - It took a while but I got there, thanks for the advice.



So I did the heat loss calc today and as I was doing it, I had a flashback of when the installer originally came out to do the estimate and size the radiators.  He picked them out of a Myson catalog taking some basic measurements of the room.  Pretty much what I just did.  The numbers seem to make sense to me.



I am going to attach the numbers I got room by room along with the panel rad capacity I have.  Hopefully I did the adjustment correct.  Average Water Temperature (AWT) is Boiler supply temp and Entering Air Temp (EAT) is room temp?



So, if what I did was correct, the boiler is over twice as large as it needs to be on a design temperatuere cold day (-4) which is fine because it can modulate down.  However, with the mild weather we are having now (40's) it probably cannot get down that low.  Appreciate you following me on my journey...can you check if you can open this file and see the numbers.  Does it make sense?  Looks like I should be running at significantly higher supply temperatures which means my return temps will be high and I wont't gain the condensing efficiency?

SWEI

radiators

Use the Myson data to determine the water temp at which the radiators match the space losses.  This is your system design temp.

CapeCod

correct water temp?

I think that's what I did...the third (heat loss) and fifth (rad capacity with adjustment for EAT) column are about equal at 47,000 Btu.  So does this mean that the upper setting of my ODR curve should be 215 F?



Not sure how I get the lower setting of the ODR curve based on this?

CMadatMe

Design Day

-4 is the record for Cape Cod back in 1976. I'd be more inclined to look at this for design temp and winter temps on average. Plug in some of these monthly averages as your design temp to get an understanding how much you really are going to need that buffer tank at some point. I can understanding tweaking the best you can for now but save your pennies for that buffer tank.



http://www.currentresults.com/Weather/Massachusetts/Places/cape-cod-temperatures-by-month-average.php





Are these rads like these Integrals?



http://www.hydronicalternatives.com/getattachment/26cf4861-b0c7-4935-ae42-0a1e0a3e93aa/Radiator-Promotional-Literature.aspx

CapeCod

-4 design temp

Chris - My name is a bit of a misnomer....it actually refers to the style of my house....but I am in Wisconsin so I have used anything from -4 to -15 to define the coldest day and therefore the highest point on my ODR curve.  The panel rads I have are similar to the ones you showed but probably have less output because they only have one row of plates rather than two.  I was looking to build out the least amount possible from the wall.



I used an online heat loss calculator where you actually input a city (rather than a design temp).  When you get done with it, it shows that the design temp for my city is -4.  Out of curiosity, I picked a city with the mildest climate possible (San Diego) and put that in to represent the kind of weather we are having now....in the 40's.  That gave me a heat loss of about 19K which is way below lowest modulation of the PE110.

SWEI

water temp

Not sure where your 215F AWT came from (Myson uses 176F for their nameplate ratings, assuming a 68F space temp.)



Whatever the source:



Dividing the 10,203 BTU/hr heat loss for the LR  zone by the 19,015 nameplate capacity gives a ratio of .537



Myson says a 65F ∆T results in 0.53 of adjusted nameplate capacity, so a space temp of 68F in that space can be achieved with 133F water in the radiator.



I'm not implying this is your system temp, but giving you an example of the process used to determine it.

CMadatMe

Sorry

Made an assumption as to location. But glad to hear you are understanding your situation. Save those pennies for the buffer tank.

CapeCod

Myson says a 65F ∆T results in 0.53 of adjusted nameplate capacity,

SWEI - Having a difficult time understanding the acronyms.  For the "select" series of Myson radiators I see correction factors in the brochure similar to what you are saying.  I have the "decor" series which have a different set...and the terminology seems to be different as well.



"select" uses  mean water to air temperature difference (assume this is what you are calling delta t)



"decor" uses AWT and EAT...Is entering air temperature the temperature of the room you want.



Attached is where I am getting the 215 F reference point from Myson.  Seems awful high compared to the other radiators.  This is supposed to be a hot water rad after all, not steam.  Does this make sense?

SWEI

inconsistent acronyms

but the intent is the same, and it's the ∆T that matters.  Nominally rating them at 215F produced higher output numbers, but you can still correct those.  Your numbers show different ratios of losses to radiation capacity for each room, so you're going to have to pick a compromise point.  Add a column to your spreadsheet and divide the heat loss by the radiator capacity for each room, then decide which room is going to get more and which will get less.  Do you have TRVs on these radiators?

CapeCod

Myson selection charts (EAT)

SWEI – so I am still a little confused as to what EAT

actually means in plain English for these Myson radiators.  I added a column like you said to get the

ratio of room heat loss to radiator capacity. 

I then scanned down the EAT = 65 F column on the Myson selection chart

and looked for the corresponding water temperature based on the ratio.



I used 2 scenarios – current state and future state.  Current state takes into account the fact

that I have no radiators in the kitchen and downstairs bathroom.  I took the heat loss associated with these

rooms and spread it out among the other rooms in that zone that do have

radiators.  Not pretty but that is what I

have now.  Future state takes into

account the radiators I will add next year after I am done remodeling. 



I think my heat losses in general are a tad overstated.  The second zone definitely seems too much

because if it were really that bad I would be freezing there.



Having said that, I am looking at using 190 F on the high

end of my ODR curve based the current state of affairs and 160 F on the high

end once I get additional radiators installed. I don't have any TRV's installed currently but perhaps that is a good idea to install them on some of the larger radiators so I can throttle them down so they match a bit better with room?

Hope this makes sense and apologize if I am boring anyone to tears with

my saga.

SWEI

ratios

are what you want to focus on during the design phase.  Getting them to converge on a value is more important to comfort than the particular value.  Once they are somewhat close, you can look at increasing all the radiation across the board, which will reduce water temps and increase efficiency.  Bathrooms benefit from a somewhat higher ratio, but the best approach is to simply increase the interior design temp for those rooms.  Re-size radiators first, then look at TRVs.  They greatly improve the situation for rooms that have considerable solar gain or are infrequently utilized.

CapeCod

short cycling resurrection

Sorry, I have to resurrect this post again.  I have ordered and mounted a few more myson radiators as well as the TRV's.  I am ready to implement the suggestions all of you gave me last year (buffer tank + variable speed pump for continuous circulation).  I had been running this by a contractor last year and now that it is time to implement I can no longer get a hold of him.  I called a normal hvac contractor out to give me a fresh quote on this and after trying to explain what I wanted to do it didn't seem like he wanted to touch it with a ten foot pole.  I had to sell him on the proposal rather than the other way around.  At least he was honest...he didn't believe the changes I was talking about would alleviate my short cycling and didn't want to disappoint.



So, anyone have any recommendations for a boiler / controls expert in the Milwaukee, Wi area?