Munchkin sudden rise in gas consumption

.

This is our first winter with a Munchkin (80M) so I've been monitoring it closely. Gas consumption has been rather precisely proportional to the degree-days, at 0.20 (+/- 0.005) therms/degree-day. Just this last week it varied for the first time, jumping 10% to >0.22 therms/degree-day.

I can't think of any good reason. Water temperature is always under 130, so it can't have stopped condensing. The weekly period doesn't include Thanksgiving so nothing unusual happened to throw the reading off. The view through the porthole is the same as always, no noticeable change in flame color. Vents are not blocked, we haven't changed thermostat settings, and nothing else is out of the ordinary. It's been a little colder last week than before, but not dramatically so (25-35 degree-days each day, compared to 15-30 in previous weeks).

I will call my contractor, but I think this was his first Munchkin, so I want to be prepared to point him towards possible solutions. This is a subtle one and I am not sure he'll find it immediately.

Dan Peel

Fuel increase

One of the first things to check will be the condensate drain. Be sure it is draining away and not backing up in the unit. Dan

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Mark Walnicki_2

Not my area of expertise

but I have to wonder if there's any problem at all. First glance & gut instinct tells me no.

I'll agree that, statistically speaking, a 10% jump sounds like a lot. But I've never been a fan of statistics or percentages, anyone can take any number and turn it into whatever they want to get whatever implication/result they want. Not that I'm not impressed with your monitoring, I should be on top of things like that here!

The first thing that came to mind when you mentioned monitoring fuel usage vs. degree days was my handy-dandy, well-worn copy of the "Burnham Heating Helper", Chapter 7, 'Fuel Consumption & Energy Cost'. I believe it may be available on-line, but I will provide the first part of that chapter here:

"There are several ways to calculate the operational cost of a specific boiler in a particular location. The accuracy of each will depend on the attention one gives the many variables.

Two popular methouds are the "bin" and "degree-day". Though the "bin" method has the potential to be more accurate, it is more complicated when necessary weather data is not readily available. Discussion will be limited to the the "Degree-Day" method.

The "Degree-Day" method is not without controversy. Historically, the reference temperature is 65*. This assumes that a building with average insualtion and a thermostat set at 70* will cause a boiler to begin operation when outdoor temperature falls below 65*. Overlooked variables could be sunshine, wind, heavier insulation, different thermostat setting."

The last line sticks out most for me. At this time of year the hours of daylight are getting shorter, hence less available hours of sunshine & here in upstate NY the hours of sunshine have been even less with various storm systems trying to take hold. And it's certainly been a lot windier more of the time vs. the same time period last month.

Just my thoughts, I'm curious what the Munchkin experts have to say...

hr

Any other gas appliances

in the home?

Does it provide DHW? Any increase in DHW use or has the incoming water temperature to the DHW dropped.

Was a combustion analyzer used to set up and check burner operation? Might check it again with an analyzer.

hot rod

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J.C.A._3

I agree with ,

Hot Rod on this one. Get the instruments on it before passing judgement. Eyeballing a flame is NOT the way to check such a precisely controlled fire. The variables are in the manual and are easily attained by using the proper combustion analyzer. Water temps. also will play big into this. The ground is getting alot less sun this time of the year and those feed pipes are getting mighty cold down there. Chris

Mark Eatherton1

Every one knows its Windy....

And windy has dark green eyes, the color of stormy skies...

Without knowing your flue gas analysis at the time of commissioning, it's virtually impossible to blame it on the appliance...

My guess is that it is related to subtle changes in exposure conditions, primarily wind induced infiltration.

Has it been windier than usual?

ME

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Plumbob

(a) I will check the condensate when I get back home. What happens if it stops draining? Wouldn't it trip a sensor of some kind and shut the boiler off?

(b) I agree that there can be variations due to sun/wind etc in the therms/degree-day ratio. It has not been more cloudy or windy than usual, I haven't seen a swing this big in the ratio before, so I would like to check out possible sources of problems suggested here, but sure, it could be just a fluctuation.

(c) We do use gas for hot water, cooking and drying. I subtract the summer use baseline before calculating the ratio, but of course if something unusual happens (guests taking showers, turkey in the oven, lots of washing) that would throw the calculation off. Nothing like that this last week to my knowledge.

(d) My suspicion is that a combustion analyzer was not used. (There's no plugged hole in the PVC vent...is that a bad sign?) I will ask that an(other) analysis be done.

hr

How's she fire up?

A woosh type of light off can indicate a plugged or slightly plugged condensate drain. That rubber trap on the back may be squeezed close or near closed.

Find a bloke with a combustion analyzer, hopefully one with a printer to leave you a print out of the performance and readings.

Make sure the test at low fire and high fire. Sometimes gas adjustments need to be made to bring the low fire CO into tolerance. Call the factory or a sharp rep, if this is the case.

hot rod

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hr

I wonder that a HO

couldn't monitor efficiency by adding a thermometer to the flue near the boiler.

I notice the flue gas temp on my analyzer runs doggone close to the temperature on the digital Munchkin readout.

I would suspect watching this temperature would give a close idea to performance. Seems if flue gas temperature goes up some of that energy is slipping through your fingers. Or the Munchkin's fingers

Think I'd get one of those Azel dual thermometers and insert one probe into the flue and strap the other on the supply outlet at the boiler. This thermometer will capture high and low numbers for you to do some data collecting.

Can't beat the price. Handy for checking all sorts of delta T's at radiant manifolds, boiler HXers, indirect tank coils, etc.

http://www.azeltec.com/

hot rod

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larry

Heating Degree Days...

How are you calculating heating degree days? There are two methods - an averaging method and a high-low method. The averaging method will be much more accurate. Also, an on site weather station will give the best data as there can be significant variations between a NOAA reporting station and your location (I can travel 7 miles south of me in the winter and see 3 to 5 degrees of temp variation at times). As mentioned by others, other parameters (wind speed and direction and solar radiation) will also play a role.

A couple of years ago I plotted system runtime as a function of heating degree days for an entire winter. I easily saw 10% variations, but the overall trendline was very clear.

.

This is a good point also. I am uing the same degree-days used by the gas company, i.e. those at the city's airport. And of course, they use high-low.

The point is not that this is correct for my home, but that it is 'official' and carefully measured. Certainly there can be days when my home sees the same weather as the airport, and days when the two differ, leading to random variations. I am not seeing the 10% variations you mention, other than this last week, because I'm doing it by the week, not by the day, which evens out the randomness.

PS No obvious problem with condensate, it is coming out. The boiler does make noises when it starts up, but I wouldn't know what defines a "whoosh" in this situation. I will arrange for a combustion analysis.

jerry scharf_2

Just a thought

Hi,

You said it got colder, but the water temperature is the same. If you are running with outdoor reset, which the munchkins usually do, the water temperature will go up as the outside temperature drops. This will increase the return water temperature and decrease the boiler efficiency. This is an expected situation in all conedensing boilers.

There are other funny things like was the week windier causing more infiltration. I've never seen how accurate the degree-day calculations are, and I would expect them to be sensitive to microclimates as well.

jerry

.

> You said it got colder, but the water

> temperature is the same.


I didn't say that. I said the water was always under 130.

Tom Anderson_2

Infiltration

Keep in mind that infiltration, always a large piece of your energy pie, will vary quite a bit, according to the square of the difference between outside/inside air temperatures.

In plain english, a given infiltration rate when outside temp is say, 20F below interior temp, compared to outside temps at 40F below interior temp, will be about four times greater. Infiltration rate is non linear with respect to temperature differences.

Just something to ruminate on as the winter progresses.

Marty_2

Another thing to consider is whats the actual heat content of the gas ? the heat content does not remain the same year round propane would bounce around even more.

Mark Walnicki_2

weather data

I've found this to be a very neat, comprehensive site. The link is just a random one I had stored on my computer for data around here. You should be able to get to your area's data fairly easily.

http://www.wunderground.com/history/airport/KALB/2001/4/14/MonthlyHistory.html