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heat can't keep up at night
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John Ketterman_2
Member Posts: 12
I started the thread about what a design day really means. Here's my problem.
I did the calculations and chose the Munchkin 80 boiler myself. After three years of no sweat, this year we got close to the design day, -10F. I did a good job: on the average, the boiler should handle a 65-degree day. But that "on the average" is the kicker.
On Sunday the minimum was -5F, the maximum was 1F (67 ddays). This is 8 ddays warmer than design. If you look at gas consumption for the whole day, you can see that the boiler drew about 85% of its max capacity, so it should do fine on a -10F day (75 ddays).
Here's the problem. During the half-day 10p to 10a, the boiler was going flat out all the time---thermostat shows full 12 hour call for heat; gas meter shows that boiler is drawing its full quota (80,000*12 BTU). But it could't keep up! The house cooled several degrees.
In the daytime, however, there was no problem. The house heated back up, and the stat even stopped the boiler for a couple of hours. That's how the net gas consumption ended up being 85% of the maximum.
So based on average daily consumption, the house can handle -10F weather with no problem. But based on nighttime consumption, the boiler is under capacity.
Being an amateur homeowner, I apparently "over-right-sized" the boiler. On a design day, the house will get very cold at night. True, it will catch up in the daytime, but on the average, the house will be cold.
My wife is not happy with me.
I did the calculations and chose the Munchkin 80 boiler myself. After three years of no sweat, this year we got close to the design day, -10F. I did a good job: on the average, the boiler should handle a 65-degree day. But that "on the average" is the kicker.
On Sunday the minimum was -5F, the maximum was 1F (67 ddays). This is 8 ddays warmer than design. If you look at gas consumption for the whole day, you can see that the boiler drew about 85% of its max capacity, so it should do fine on a -10F day (75 ddays).
Here's the problem. During the half-day 10p to 10a, the boiler was going flat out all the time---thermostat shows full 12 hour call for heat; gas meter shows that boiler is drawing its full quota (80,000*12 BTU). But it could't keep up! The house cooled several degrees.
In the daytime, however, there was no problem. The house heated back up, and the stat even stopped the boiler for a couple of hours. That's how the net gas consumption ended up being 85% of the maximum.
So based on average daily consumption, the house can handle -10F weather with no problem. But based on nighttime consumption, the boiler is under capacity.
Being an amateur homeowner, I apparently "over-right-sized" the boiler. On a design day, the house will get very cold at night. True, it will catch up in the daytime, but on the average, the house will be cold.
My wife is not happy with me.
0
Comments
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very curious?
what type of emitters are you using?
what are your indoor nighttime lows?
are you using more hot water at night than in the day?
basement warm? pipes insulated? bond insulated?
got snow on the roof?0 -
If the boiler runs
non stop and still falls behind, sounds like you either need more boiler output of perhaps some supplemental heat for those periods of below design.
You might size up the boiler if the piping and emitters can handle the extra output. Possibly tweak the output of the boiler
Maybe a blower door test, and some infrared pics of the outside, to assure the house is not leaking more then you estimated in the original calcs.
hot rod
To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"0 -
And
any night setback? Not that night setback has a place in your setup, but I find if you do set it back five degrees you stand a chance... I think the sizing is correct in that this is the time you want the boiler to run flat out.
You must have pretty decent solar gains too, am I right?
If your wife is not happy with you, it may not be the boiler. 0 -
Some inexpensive solutions beckon...
Bigger radiators or a large buffer tank would allow you to store BTUs and help the house flywheel through the night.
Another option is to go to energystar.gov and get a blower door test done. Identify the worst leaks, and your design-day load may drop to the point where the boiler can keep up at night.
Lastly, there may be some low-hanging fruit left re: insulation, where simple steps like putting insulation on the basement walls or ceiling saves just enough BTUs to make it through the night... never mind insulating crawlspaces, etc.0 -
easy solution?
heavy or flannel curtains for big windows in house! door walls too.0 -
> what type of emitters are you using?
Mostly cast iron rads, new panel rad in the extension.
> what are
> your indoor nighttime lows?
65F. Stat is set at 69. Not a disaster but not ideal.
> are you using more
> hot water at night than in the day?
For domestic hot water we have a separate water heater, not using the Munchkin.
> basement
> warm? pipes insulated? bond insulated?
Yes, basement is ok, it's within the envelope, so insulating the pipes wouln't help. I don't know what a "bond" is.
>
> got snow on the roof?
A thin layer only. Usually that helps insulate.
> You must have pretty decent solar gains too, am I
> right?
Apparently so, judging from these observations.
> If your wife is not happy with you, it
> may not be the boiler.
All I know is, she said it wasn't big enough.
And in response to questions by others: it's blower tested and sealed up tight. The problem is that it is an old brick house, so it's not really thermally insulated at all, except for the attic which is properly insulated.0 -
> non stop and still falls behind, sounds like you
> either need more boiler output of perhaps some
> supplemental heat for those periods of below
> design.
>
> You might size up the boiler if the
> piping and emitters can handle the extra output.
> Possibly tweak the output of the boiler
>
>
> Maybe a blower door test, and some infrared
> pics of the outside, to assure the house is not
> leaking more then you estimated in the original
> calcs.
>
> hot rod
>
> _A
> HREF="http://www.heatinghelp.com/getListed.cfm?id=
> 144&Step=30"_To Learn More About This
> Professional, Click Here to Visit Their Ad in
> "Find A Professional"_/A_
0 -
> what type of emitters are you using?
>
> what are
> your indoor nighttime lows?
>
> are you using more
> hot water at night than in the day?
>
> basement
> warm? pipes insulated? bond insulated?
>
> got
> snow on the roof?
0 -
> any night setback? Not that night setback has a
> place in your setup, but I find if you do set it
> back five degrees you stand a chance... I think
> the sizing is correct in that this is the time
> you want the boiler to run flat out.
>
> You must
> have pretty decent solar gains too, am I
> right?
>
> If your wife is not happy with you, it
> may not be the boiler.
0 -
> any night setback? Not that night setback has a
> place in your setup, but I find if you do set it
> back five degrees you stand a chance... I think
> the sizing is correct in that this is the time
> you want the boiler to run flat out.
Forgot to answer this one. No night setback in the stat, but in effect we're getting night setback. No problem with that at night, the problem is that is is cool in the morning and much of the day. A right-sized boiler doesn't recover quickly from voluntary or involuntary setback.0 -
IR gun
John, if you don't have an infared gun thermometer you might want to get one. Go hunting inside for cold spots and outside for warm spots. You may find some quick wins.0 -
Any fireplaces? Without a good damper and reasonably tight-fitting doors, old fireplaces can be gigantic heat suckers...0 -
John, if you're cold for a night every three years, that should be worth it the other 99.908% of the time you are getting truly maximum efficiency.
also, you can't really measure boiler output in degree days. boiler output is measured in BTUs/Hr for a reason. what's your max load in BTUs/hr? What water temps do you need at your emitters at design, and are you getting it?
Given your note that this house is not really insulated, I would wager that you're right that you undersized the boiler. But as others have noted, there may be steps you can take to address heat loss rather than upsizing the boiler.0 -
> Bigger radiators or a large buffer tank would
> allow you to store BTUs and help the house
> flywheel through the night.
Think about it. It's one thing to use a buffer tank to reduce short cycling, but to store heat in the day for use at night?
Let's make up some numbers. The OP says the heat goes off during the day for a couple of hours. So let's try to tun the boiler during those 2 hours, and save that heat: 160,000BTU. Say this heat is released by cooling the buffer water by 20F. So that's 8,000 pounds (1000 gallons).
A large tank for a residence.
Next, how will the OP use a buffer tank to store and release heat, given that the boiler is running all the time and so the water won't have a chance to cool?0 -
I'm not advocating the buffer tank idea, but remember you are only trying to store the difference between what the boiler can produce and what is needed during this 12 hour period, not the full load. If he's only, say, 5kBTU/hr short during these periods, that's half the tank you're talking about.
Regardless, since you're already probably at a max water temperature requirement under design conditions, this isn't likely to be a very good solution, since you'd need hotter water for effective storage.0 -
Good Point
But as Rob indicates, the issue is not capturing the full load... the issue is the 4 degrees that the inside house temperature is dropping during the night. Any heat loss program should be able to tell you what BTU difference 4 degrees makes. I doubt it amounts to very much.
If we can just use straight extrapolation and the boiler output can maintain a 65DDay heat load just fine, whereas a 69DDay load is beyond it's reach, 4/65 amounts to about 7% of boiler output or 6kBTU/h. Storing 60kBTU (for 10 hours of heat) is a bit easier than storing the 2x you were envisoning. Plus, you can run a wider ΔT than 20 given the Munchkins DWH mode.
A simpler solution may be a small (20 gallon?) electric water heater piped in series with the header and on a setpoint that is activated whenever exterior temps drop to 0°F. If the projected 6kBTU/h load is correct, a 2kWh element would cover the heat loss that the Munchkin cannot.
Lastly, you could always zone the system to the point where certain areas of the house are "sacrificed" during marginal days.0 -
not stupid but
Just had a question what temp are you running the system at and does this munchkin have a vision kit on it ,if so you may be able to boost the boiler output as for a call for domestic hot water which would on some m80 give you a extra i believe 10 ,000 btus you would have to check with htp but it might help peace and good luck clammyR.A. Calmbacher L.L.C. HVAC
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating0 -
Or.....
Buy your wife an electric mattress pad and nice new slippers and proudly tell you're the first person in North America to perfectly size a modcon boiler.
Congratulations! ;-)0 -
why yours?
I'd be real intersted in knowing all the details? not that I'm really asking for all the details. but you are the first here I've heard of that has met load with boiler.
every other heat calc here suggest 50% or more over kill, so this is interesting.
did you use software or pencil and paper? maybe infiltration is killing you?
food for thought!0 -
> you may be able to boost the
> boiler output as for a call for domestic hot water
Yes, excellent point!. I would have to put in a couple of wires into the connector, and short them manually to simulate a DHW call, at the same time keeping the central heating circulators running since I don't actually have DHW. I would also need to give the DHW call the maximum quota of 30 min per hour.
It makes me a little nervous to do this, but I think I can do it. Would anyone happen to know how I add wires to the connector. I mean, there's a tiny metal female that you solder the wire to, and then you pull the wire through the plastic connector and the metal female clicks into place in the connector...I don't know what kind of part that female is and where to get it.0 -
I didn't use a heat calc. I trust actual data over theoretical calculations. I calculated the BTU/degree-day of my old cast-iron boiler by dividing the gas usage on my winter bills by the degree-days (also shown on my bills). I then reduced the number 30% to allow for the increased efficiency of the Munchkin (that's a fudge factor right there, of course), and multiplied by 75 for the degree-days in a -10F design day. Then I divided by 24 (numbr of hours in a day) to get BTU/hr.
I came up with something like 78,000BTU/hr. Any sane person would say, go one size higher, but I went for the 80,000BTU model.0 -
check your parameter guide
don't use munchkins so I cannot comment for sure.
But I know other boilers using the MCBA controller have a boost feature for the heat cycle too.. (parameter 11 I believe)0 -
Sounds like you just missed
on your numbers. It happens, I've done it and I'm sure others have also.
If it were a customer of mind I would bite the bullet and make the needed changes.
I doubt you will, or should, try to fool the 80K into believing it's a 100K boiler
hot rod
To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"0 -
Look For Over Looked Heat Loss
Like open regersters and unplugged filter grills on attic central AC systems or even uncovered wall units.0 -
No documented boost parameter. But there are some undocumented parameters that we're supposed to leave alone. I wouldn't know which one to change.
What's MCBA?0 -
windows
Are your windows single, double, or tripple glazed. And do they have curtians or shades to cover them at night. Even with no drafts, the heat loss thru windows is incredible. Put yuur hand behind a drawen shade in front of the glass and feel the difference. This might be all you need for the few cold nights.0 -
insulate?
any chance you can add insulation anywhere?
check all doors & windows for good seals, caulk.
Is the entire house cooler in the morning?0 -
MCBA
It's a boiler control used by various manufacturers such as Burnham, Olsen, Weil-Mclain, Cleaver Brooks, Triangle-Tube/ACV.
That kind of boost wouldn't work because the boiler's already tapped out.0 -
> That kind of boost wouldn't
> work because the boiler's already tapped out.
But the boiler does have a boost for DHW.0 -
DHW bump
I'm aware the the 50 can ramp up to 80 for domestic, but I wasn't aware that the 80 can. Given that the rating plate on these devices is for heating, I would never try to exceed the manufacturer's rating.
If I were in your shoes, I'd get a cheap IR gun and look for cold spots inside and warm spots outside and get the heatloss down. There has to be some quick wins on an 80K heatloss.0 -
You are correct Uni
The 50 can boost up to an 80 on a call for domestic. The 80 stays at 80.
All that you can achieve by using the DHW demand is a higher boiler water supply temp. The boiler will ramp immediately to high fire. This will not solve the issue.
Mark H
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80/100
i believe that feature does exist in the programing of the controller it is i believe when plugged into a lap top will show what the max burner fan sppeed is and i believe i ramps up beyond the rated to give more btu,s i would gather similar to the 50 .The only reason i know this is i had the local rep check out my munchkin and do a little combustion adjustments and he plugged in his laptop and noticed that my unit was programed with the higher output which he had though had been fazed out due to limiablity .I do remenber seeing a piping and wiing diagram using that feature with say 2 nd hydro air or what ever that was from HTP but you would have to do a little bit of downloading and search for it there is of course a run limit to that set up being your using the dhw circuitrity that avaiable with the vision one kit and using it,s sensor most likely in a well or strap on and a couple isoltion relay to pervent the unit from firing to it's max all the time peace and good luck clammyR.A. Calmbacher L.L.C. HVAC
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating0 -
Keeping up
I may have missed how many years the boiler has been in operation. So, have you considered, loss of efficiency through scale build-up? Take a look at the attached chart.0 -
Any chance
Your not going to full out put of the boiler ??
Are you getting 185/190 at night ??
Scott
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Give up playing with the boiler...
and start putting insulation into your home! This is just like a cat chasing its tail, untill you add insulation money is just going outside...0 -
If you mean the water temperature, it doesn't go above 155. That's normal; I'm not radiation-limited, I'm boiler-limited. The radiation emits 80,000BTU/hr at 155F, so the water can't get any hotter unless I close off some of the radiators.
How do I know the boiler is running at full output? Well, for one thing, the return temperature is 134 (the Munchkin is designed for boiler loop flow such that deltaT=20F at full fire). Second, my gas meter shows that the boiler is drawing the full 80,000BTU per hour at night (about nine and half units in 12 hours).
Actually, closing off radiators will work in an emergency. I can decide to let some rooms get cold. Then the water temperature will go up, and so the other rooms will be warmer.
In answer to another post, the boiler is only three years old.0 -
SOoooo
If you don't have enough radiaton at 155 then boost up the temp and you'll get more !! You don't have enough heat at night, you've under radiated the house. By raising the output of the baseboard by using a higher temp. you may get your house to the temperature you need.
Nothing ventured nothing gained !
Scott
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Wind
what I don't see here is the wind load. Yes, I know that in the other discussion on design temps, someone suggested that wind wasn't all that important. And I really didn't want to horn in.
However...
Some houses, particularly older exposed ones, are indeed very sensitive to wind loading. My own ark, for instance. On a still day, the boiler can hold a 70 degree differential on about a 20% duty cycle -- suggesting a horrible oversize (it's not; it's steam, sized to the EDR, and is just about perfect). However, when the wind she blows hard -- as she did the other night -- the duty cycle can approach 50% on with only a 60 degree difference. Which drives the oil company nuts (what do you mean, you're out of oil?).
Sounds to me as though that's what you're seeing here.Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
> If you don't have enough radiaton at 155 then
> boost up the temp and you'll get more !! You
> don't have enough heat at night, you've under
> radiated the house. By raising the output of the
> baseboard by using a higher temp. you may get
> your house to the temperature you
> need.
Did you understand any of what I said in the previous post?0 -
Yes, it was windy. That wasn't in my calculation either!0
This discussion has been closed.
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