My calculation were out by a mile!

tom_49

Constantin,

I too use Hvac-Calc and find it to be on the "slim" side.

I just did a take-off on a house we will be doing for a progressive ( if you can believe it ) builder. It is following the LEED (sp?) program. I dont know the specifics about the LEED program , but based on the R-values given to me, I cant believe the #s that it calls for.

The house is 3,080 sq ft. 2x6 const., low-e windows, it will be insulated w/ nuwool.

heatloss = 40,000 btu @ 0o design.
heatgain = 23,000 btu @ 90o design.

Those seem a little low to me, but I reviewed all my inputed info and thats what it says.

2 tons of cooling, for 3000+ ft. of living space?

I will have to put in 2, 1 1/2 ton units seeing thats as small as I can get. As far as the oil boiler goes, I think the smallest I can get is the Viessmann vito 200 ( 77,000 btu ). Maybe I should think about LP and a mod/con. What do you think?

Tom

Uni R_3

Just how inaccurate is the manual J?

59 HDD today so 6°F average

Stated Manual J - 55K @ 0°F

Min boiler modulation for Prestige 110 is 30K input

1°F setback (to help boiler runtime)

The boiler isn't running hard enough for continuous operation.

Can the true heatloss actually be that low, or am I not getting the minimum modulation that it says on the boiler plate?

NG is cheap and abundant here in the Toronto area and you never hear complaints about the quality of gas.

I'm not sure what affect the outside temps have on the clockings. I would tend to think the gas would be denser and understated by the meter, but I'm not sure.

I thought I'd be modulating when it was 25°F out or less based on 45K which I felt might be the true heat loss.

I'm curious why I'm out so much.

----- ----- ----- ----- -----

If you look at the graph the electrical load cycles on off and outside of initial draw the load never rises. The boiler cuts out when target return temp is achieved - the full drop is when the t-t is satisfied (and 1° setback is the only time this happens). Bottom line, the minimum firing rate is less than the load of a less well insulated but tighter brick home 1975 vintage with 2400 sq ft.

The HDD's today were 59, just 6°F on average above design temp of 0°F. Could it be that the it's all clocking error and that the house needs are met at the coldest parts of a 59 HDD day by the net heat from burning only 30 MBH?

The boiler usually clocks at 40-42K. The lowest ever clocked was 38K. Clocking is typically 3.8 turns of the 0.01 M3 dial - sorry we're metric, which converts to just over 40K. It makes it very simple for timing the dial movement exactly.

What would you pros recommend a homeowner do in this case?

Should I contact Triangle-Tube and ask them about it? Should I call my installer back and ask him about it? Should I even worry about it? Do you pros actually clock min and max firing rates when you install an M-C boiler?

(amps are used because the watts fluctuate with the voltage)

Perry_3

A common situation

I don't think the codes or the Mfrs have caught up to the issues with how the mod/cons work and how inacurrate the heat loss estimation is - which causes boiler oversizing.

The heat loss calc for my house was in the range of 60,000 BTU/Hr. In actuality is is probably in the mid 40's.

Just a general tracking of the issues seems to indicate that the heat loss calcs are about 1/3 conservative. 10% I could understand - but 33% does not seem to work well for mod/con boilers.

The minimum firing rate issue also has to be understood. I immediately recognized that a boiler with a 30,000 or so minimum firing rate would not allow me to gain the non-cyling advantages of a mod/con. I installed the Viessmann 6-24 that has I believe a minimum firing rate of about 22,000. That has proven to be too much for any weather above 20 F, and even for 15 F weather on a sunny windless day (solar heat gain in my house).

Along with better calculation methodologies... we need mfr's of quality mod/cons to step up to the plate with smaller mod/cons. Most Mfr's could make a unit 1/2 of their current smallest size - which would work very well as that is really about what the market really needs.


Perry

Constantin

Hmmm...

For one, I suspect that the Manual-J tables were developed to cover an installers rear, just as long as he/she followed the instructions. Thus, the calculations would tend towards "cautious" end, i.e. making assumptions towards the lowest common denominator in terms of construction quality.

Another factor in your home is thermal mass. Bricks soak up external/internal heat quite nicely. The brickwork may be in much better condition than Manual-J assumes for, reducing your infiltration load. I presume you accounted for infiltration using a blower-door test, not just guess-work, right?

I wonder to what extent seasonal efficiency of boiler plants is accounted for in the Manual-J calculations. Right-sized Mod-cons don't fall into that trap the way that non-mod boilers and furnaces can. Even staged equipment cannot respond as intelligently as a modulating piece of equipment can.

Lastly, what program did you use to calculate the heat loss? I used HVAC-Calc to good effect, coming within a kBTU or two on a design-day. Maybe some calculators are more conservative than others?

Brad White_9

Heat Loss Calculations

The core of heat loss calculations, transmission, is pretty hard to "fudge", provided you take care to assess your wall, roof and glass structure accordingly. Knowing how much framing you have and how that affects the entire aggregate wall R value is key to this.

It all breaks down to "Area x u x Delta-T".

I have not used Manual J so have more questions than observations. If the wall R (and "u") values are "given" to you such as by stating "2x4 insulated construction", does it tell you what the final number is, or is it buried in the calculation?

Anyway, I was trained to take each layer of wall construction both at framing and between framing, multiply each by it's decimal percentage of the whole to obtain an aggregate adjusted R value. Same for roof and floor construction. Glass is from tables and absent special coatings, is really an air space and air film exercise. Again, pretty hard to fudge.

So what is left? Infiltration.

(Forgive me if you have read this before

Each room typically stands on it's own as far as sizing radiation. Eventually it will see 100% of it's heat loss. Air will leak in at some time.

Added together, the sum of all rooms will never see this infiltration at once. What leaks in on one or two sides, leaks out the other. Those exfiltrating rooms only see conditioned air leaking in from rooms that have bona-fide infiltration...

Further, open plan rooms have higher infiltration potential than a host of rooms with doors that close. With warm air systems and inadequate return air as is too often the case, infiltration can accellerate at a rate I would love to know, due to mechanically imposed pressure differences.

My typical iterative solution is to calculate each room with both transmission and infiltration for radiation sizing purposes. Then, for sizing the boiler and for comparison to "sum of rooms", I take the "transmission only" and assign infiltration to the house as a whole, knowing that the factor I use for that would be about half what the sum of room infiltration would be (if that makes sense).

Again, an open plan room would have a higher factor. Isolated rooms a lower factor.

I suspect if you compare a Manual J with an ASHRAE method calculation (the method I use), but transmission only, not infiltration, that would be your starting comparison.

Absent blower door tests, infiltration can be 0.35, 0.50, 0.75, 1.0...etc. Air Changes per Hour (ACH).... Think there is room for differences in outcomes?

Uni R_3

You're missing the point...

If your Vitodens 6-24 was clocking in at between 33 MBH and 35 MBH instead of the 25 MBH stamped on your rating plate, would you call your installer, Viessmann or chalk it up to measuring error?

Constantin

Hee hee...

Brad, some day I hope to introduce you to a builder in TX that builds very tight houses (if you don't know him already) who posts regularly over at Breaktime. One of his homes had an ACH-rating of 0.058.... and his personal home heats and cools in TX for less than $100 a month.

IIRC, he likes to put the insulation on the outside, overlapping, and all that. No telegraphing via studs, etc. to worry about. Plus, there are time-honored architectual features like overhangs, siting, etc. that contribute plenty to passive warming during the winter and less heat gain during the summer.

If I were looking to build new, this is the kind of builder I would seek out. Even if he couldn't do the job due to geography, I'd fly down there to learn from him how to do it right. Then there are the luminaries on the Wall for the HVAC, etc. So many great resources that the web has allowed to connect.

Brad White_9

I am a huge fan of continuous insulation!

But 0.058 ACH? I would never hold a bean and cabbage dinner in that house, no sir.

Otherwise, my kind of builder.

Uni R_3

Constantin

My heatloss being lower than calculated doesn't actually create huge issues for me. That's good news. I used the Slant-Fin program and I use very small infiltration numbers, I don't add in joist spaces, I use extremely reduced infiltration numbers for low levels. The house tested 4.5ACH @ 50 Pas last time which sounds high but 5 is considered tight for that.

My questions all pertain to a boiler that is clocking at between 33 and 40% higher than it should on minimum fire.

Kal Row

heat loss is just a starting point...

the goal is customer comfort - and the customer's skin doesn’t measure temps, only whether the heat is flowing in or out of the body - so the heat type and natural draftyness, and humidity of the space has to be considered.

if you are using baseboard - you are trying to heat air to heat people and with baseboards that’s a long and slow trip,

if it's coils in air handlers - it's even worse cause of the draftiness, just try blowing over the top of you hand - it's cool even though your exhaling a higher temp than you skin,

big flat cast iron radiators are better cause the main component is radiant energy but they are still moving air and that part sucks - but typical cast iron rads are dead on with heat loss calcs

even radiant can be messed up by airflow, had a lady with an extended kitchen with a vaulted ceiling and a huge skylight - and the natural convection in there, make it uncomfortable - even though the floor is hot (100f hot at the tile surface) nevertheless i told her, that unless she hangs a sheer chiffon curtain across the bay window and the patio door to halt the convection - she will always feel chilly

so you really need to analyze the space and make an intelligent decision - the calcs only get you so far

Uni R_3

Brad, you're forgiven...

I've read that before, now can you go back and read my questions? If my heat loss is lower than the 45K I estimated, I really don't mind. All of my questions are boiler related. I don't think that I'm getting the minimum modulation as stated by the manufacturer. Obviously Manual J is a factor in not getting down to modulation levels, but my sole concern is if the boiler is performing to spec and how to resolve that if it isn't.

Here are the questions again:

What would you pros (or homeowners or HVAC engineers) recommend a homeowner do in this case?

Should I contact Triangle-Tube and ask them about it? Should I call my installer back and ask him about it? Should I even worry about it? Do you pros actually clock min and max firing rates when you install an M-C boiler?

Constantin

So perhaps it's the calculator?

I thought that HVAC-Calc was Manual J, 7th Ed. compliant, so I'm surprised that different results would emerge.

The heat gain and loss does not look that strange. Our house is a 134-year-old girl and has true 4" studs in the older part and 5½" studs in the newer part. Corbond in the old part, icynene in the new part. Our heat loss at 9° outdoor came out to 12BTU/ft²/hr. At 0°F, I expect about 14BTU/ft²/hr.

Given your newer construction and better windows, I don't doubt that 13.3BTU/ft²/hr is out of the question. Have you considered using foam as an insulator instead of NuWool? I ask, simply because I always worry about infiltration. Corbond not only stops that but also stiffens up the walls.

As for your heat gain, it depends on the site, I suppose, along with architectual features, like overhangs over windows (to keep the summer sun out), etc.

Our heat gain came out to about 11BTU/ft²/hr on a design day (91° outdoor, 74° indoor). I'd take a close look at your sensible/latent heat requirements and see if playing with the indoor coil is an option. Many manufacturers publish a variety of ARI-rated coil/AH/condenser combinations.

So, while your heat gain is a lot less than ours, it's not inconceivable that it's accurate. I submit, for example, that the second stage on either of our compressors did not activate once last summer and we hit design conditions a couple of times. The second stage fires up once the first stage (66% of rated capacity) can no longer keep up with the heat gain.

I believe that the new manual J (8th Ed.) accounts for tree shading in ways that the 7th ed. did not. This may explain the discrepancy between our heat gain vs. loss accuracy.

Constantin

Sorry about that...

I got confused in all your talk about heat loss that I thought your question pretained to that...

... I guess I would check a couple of things. One, what is/was the local caloric gas content on the day you clocked the boiler? The utility ought to know. You're not that high up, IIRC...

... A call to TT is a good idea, just to get their perspective. Perhaps your boiler is not set up correctly. Just as the Vitodens allows the installer to preset all sorts of things, perhaps the Prestige needs a similar massage to enable the low-end of the firing cycle.

Uni R_3

Thanks

My wife's the professional writer... I'm enlisting her to do any postings like this next time. I'm at about 260' or less and these measurements have all been at different times. The lowest measurement ever was 38K.

Thanks for the idea about calling the utility, I'll call Enbridge Gas and verify that they're in the 35,300 BTU/M3 range.

What affect would temperature have on the clocking?

Brad White_9

The Unforgiven

The fault dear Brutus lies not with the stars, but with ourselves...

If I were Triangle Tube and got a request like that, my response would be, "So?", albeit more politely. They may have suggestions on down-firing but sometimes what you have installed is as low as it goes. Hence our repeated call for smaller ModCons....

Beyond that, it all gets down to who did your heat loss calculation and how they stand behind it.

Not that it would change anything, but try it using the ASHRAE method or any other means and see what you come up with. My ASHRAE method is really just a simple Excel spreadsheet. As with any method, some judgement is required, especially regarding infiltration.

jp_2

constantine, icynene & corbond?

did you do both? wondering why the 2 materials, I understand that corbond has nearly twice R value of icynene?

Wayco Wayne_2

My experience

this Winter is based on 2 jobs I did heat loads for and I was right at the max for the boilers I wanted to put in. In another life I would have gone up a size. But in a mod con world things are a little different. I whined about the decision on The Wall and was assured by my friends to stay with the smaller boiler and be close, which I was inclined to do anyways, but a little outside support gives me confidence. Both jobs have a Prestige 110 mod con and both jobs have been trouble free, (Knock wood) even though we have been below desgn temp on several occaissions. I use Wright Draw which is based on Manual J. Just my 2 cents on the subject. BTW Brad, I read a story about a large man (about 450 lbs) who died in his sleep due to eating beans and cabbage before bed and then falling asleep in his small NY apartment with the windows closed. What this country needs is a Window ERV. Ack!

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Bernie Riddle_2

Makes you wonder

Why the M_J hasn't been re-eveluated or upgraded. I too think it may have something to do with Delta T. I bet J is based on 20° and most ModCons probably run less than half

My Ultra avg's 4-8°> My calculated heat loss was 32K-39K btuh, My 80 is running constant fire and circ at 16,000 btu input over 20° and under is 21K-24Kbtuh

Still baffles me when people say "why don't they make them smaller"

Brad White_9

Baffled

The operating Delta-T has less to do with output than with flow. Actually they are interchangeable in a way but that gets lost in the academics of it all. If you are running 4 to 8 degrees it only means that your flow rate is higher than necessary and that your emitter temperature is that much higher (averaging 2 to 4 degrees less than your supply water temperature. (I am not sure I fully understand what you are saying, so if I missed your point, please clarify.)

Maybe your constant fire is really a sub-peak steady state? I mean, if you have an 80 MBH input against a <40 MBH load and it runs full out, something is not adding up.

When a typical house in the 1500 to 2000 SF range has a heat loss at peak in the 30 to 50 MBH range and the hours of occurance which are above minimum modulation comprise 60-70 percent of the heating season, that is why I ask for smaller ModCons.

Uni R_3

Your experience Wayne...

Enough about 'real' natural gas!!! ;-)

Wayne, do you check/clock min and max firing rates after you do an install? If so, what has been your experience in clocking the low firing rates on Prestiges?

If a customer thought that a boiler that you've properly installed was only clocking down to 40 - 42 MBH, what should they do?

bob_50

It sounds like

we are going to have to modify the way we write contracts in the future. In the past we just guarnteed some specified indoor temperature at some specified outdoor design conditions. With the new technologies we will have to guarntee that the system is operating balls out at design conditions and will modulate when design is above some other specified condition. I don't think the state of the art can accomplish those requirements. bob

Constantin

Corbond in the Old, Icynene in the new...

... the installer preferred icynene because it's easier to finish (cut). Misapplied Corbond is a bear to work with/remove. Much harder than Icynene, which just requires a long sawzall blade (if that). We also had thicker walls in the addition to play with. Between floors, we also used icynene to ensure that noise and heat stayed on each respective floor.

With all that behind me, I prefer corbond because it's stiffer and has less tendency to detach from the surfaces that adjoin the application-surface.

jp_2

thanks Constantin

the closest Corbond installer is 200 miles away, hes not real interested, the icynene salemans is trying to call icynene R7?
I may consider furring the walls and going with 5 1/2" Nuwool.

Constantin

It's not R7 if it's the icynene I know...

... what I would confirm though is if NuWool acts as a proper infiltration barrier. All the foams are pretty unbeatable at this. I maintain that the 0.2ACH this house enjoys are now 100% related to the flues (kitchen, fireplaces, HRVs) as well as the windows (1/3 of which are 134 years old).

Low/No infiltration is just so cool... watching the snow going sideways outside and not feeling a thing... priceless. In the rental apartment, we always knew which way a cold wind was blowing.

Bernie Riddle_2

Same but different

Uni and I have similar circumstances > We both have Mod/Cons that are living at minimun modulation and we both "at min modulation btuh" are way under our projected heat loss calc.

The difference is my 80 Says it has a 5-1 turndown to 16,000 btu and it will self modulate to 16K>>[and have it controlled to stay there about]

Uni's TT-p say's his turndown goes to 30,000, but his paremeter min setpoint only allows it to go down to 40K> even if you based it on DOE, it's still not 30K. I believe that was his question??

Uni R_3

Prestige - Below design and no modulation

My true heat loss IS NOT be half the Manual J. If the boiler's minimum modulation is 30K then that's a net of 27.6K at 92%. The temperature bottomed out at -4°F last night which is 4 below design for this city and the boiler was still on/off at minimum fire. Longer firings but not continuous. Not only that, it recovered from a 2° setback at starting at 3am that I stuck in there just to add load.

As stated clocking the meter shows it to be between 40K and 42K most times. The lowest clocking ever was 38K and this was when it was very cold out. It clocks perfectly normal on high fire. This boiler should be 110K high and 30K low.

The pressure elevation factor would be for 260' ASL. That means the clocking should be multiplied by around 1.008 - a few hundred MORE btu than what it clocks.. The gas company will be calling me back about any potential meter deviation for that type of meter at given temperatures and also any caloric range info that they have. Typically NG here is 95% methane. I really don't suspect any gas issues.

I'm not getting the advertised minimum modulation.

Any suggestions on the best approach to get this resolved?

Is it worth getting resolved?

Dave_4

Perhaps it's a matter of adjustment?

jp_2

wouldn't it be pressure?

the calorie content should have no effect on minimum fire, just the output at minimum fire.

i would suspect gas pressure or gas valve inadjustment.

question is, at what outside temp does the boiler start to cycle, under minimum fire?