heat loss software

superdave

What do you think about the slant fin soft ware? I had a supply house do a heat loss I thought it seemed light. I used the slant fin software I needed about 70% - 80% more BTU for this job. The building is brown stone in Beacon Hill Boston Ma. with old windows single pan and 12" of brick with 3/4" strapping and board/plaster no insulation. The supply house was about 16BTU per square foot the slant fin came in about 30BTU per square foot. I do not know if I am using the software program wrong.  ( I am using 0 degree outdoor temp. 70 degree indoor.) Thanks 

Brad White

I agree with you

30 per SF is more in line as a check figure than 16.



I recently did an assist/check calculations for a small radiant job on Beacon Hill. The space was a walk-out basement, so partially below grade. The radiant at 30 was not enough for design days so was supplemented with some of the existing cast iron radiation.



If your spaces are above-grade and amortize that heat loss over more SF, 30 seems reasonable, but on a specific room basis (more exposed wall and glass and net room SF not counting interior hallways, etc.), you may well find yourself above 40 BTUH per SF in my experience.



We know you cannot insulate and storm windows are only allowed on the interior so air sealing is your friend, the only tool you really have. So we admit defeat and have higher BTUH per SF check figures than your supply house has. I suspect they made assumptions of insulation values being rational. Can you check their inputs? They may also have used incorrect SF numbers as a divisor, who knows? But it is off significantly in my experience too.



If you like, bounce them by me for a sanity check.

superdave

heat loss size

I have check the room sizes both are in same ball park some are off by 10 square feet or less. I also called the supply house and double checked that they new about old windows and 12" thick brick with no insulation. They did change a little went roughly from 16 BTU per square foot to 20 BTU per square foot. That is about 30%  more heat then there first heat loss. By the way I had my guy's already rough in for the first heat loss and it is board/plaster. This is what happens when you do not double check others work.  

icesailor

Heat Loss Software:

I've used the Slant-Fin software and the IBR calculation manuals that Slant-Fin came from. I've never ever had a problem.

Some experience is required when using these programs. Knowledge of what you are dealing with is very important. Where you really get in trouble with these programs is infiltration. An  insulated building requires a lower factor and an uninsulated building requires a much higher infiltration factor. High enough the throw a room number right out the window with all the heat you were planning.

When I do a calculation, I do the room calculations and measure the radiation installed in the room. I know that the radiators in the room worked, and that the radiator kept the room warm. If the BTU calculated loss is way below what is installed in the room and your calculation don't come somewhere near. someone didn't use the right numbers.

I bought the IBR course, many years ago and figured it out for myself. Because one supply house was so much higher in their calculations than another. When computer programs first came out, I tried a few. It was easier to do it myself because I could nuance the problem areas.

If you really want to be a heating pro, do your own calculations. You will get a whole new understanding of what you are trying to do. And when you get called on a problem job installed by others, you will know just what is happening and you will look at it with true knowledge.

tim smith

Re heat loss etc

I just finished a load calc on 8500 sft in Seattle. no insulation in walls, R30 attic, 1400 sft single pane glass. just about 26btu /ft . 2 floors mostly over unconditioned basement.

superdave

thanks for all your time

I know what you both mean. Most of the time I do my own heat loss and never had any problems. My supply house told me they would do it and give me a cost of stock to save time. I think now I know why they came in at a lower $$. I hare allot about how so many heat losses are done with over kill. I am just tiring to see if I need to go back and open up walls floors and ceilings. Or  am I OK with there heat loss, they are standing behind there heat loss numbers and saying it is my software that is bad.   (One room for example is 12'x15' ceiling 9'   24' of old window one 12' out side wall 12" thick of brick and 3/4" of strapping and board/plaster with no insulation and with ceiling of R30, floor under is heated, cold portion wall 15'   they said 3,200BTU   My software is at 5,200BTU)  What do you think! 

Brad White

What do I think?

For the room you described, I get a net heat loss (no safety factors) of 6,468 BTUH, just under 36 BTUH/SF.



24SF glass x 1.13 x 70 =      1,898

96 SF net wall x 0.3 x 70=     2,016

180 SF roof x 0.04 x 70 =         508



Sub-total for transmission alone, no infiltration, I get 4,418 BTUH



I took infiltration at 1.0 ACH which comes to 27 cfm or 2,050 BTUH. Total 6,468. 



Now, the reason my numbers may be higher than yours is that when measuring the exterior wall, I add for the structure above, the exterior wall within the structural thickness. In any building you have to account for that or you miss broad stripes of wall. So instead of 9' high walls, I used 10', then subtracted the glass area.



I think the lesson here is to have in your head some decent check figures. You KNOW that 16 BTUH per SF is too light. As stated and demonstrated above, 30 to 40 may be more in-line. Not a calculation method but just a sanity check.



As for the roughing in, do not despair especially if you are talking radiators. 1/2" PEX or copper can easily carry 7,500 to 10,000 BTUH as one example.

superdave

thanks for looking

The one thing I all-ways do on Panel radiators is home run pex to a manifold in a closet so each radiator get the same starting temp. But it looks like I need to open up wall, floors, and ceilings to make the needed adjustments. This is what happens when you rush through and use a supply house that is just tiring to make a sale. I all-ready know the answer to this question but going to ask anyway do you think I need to change the rough?   Thanks David

Brad White

That is what I was hoping to offer

that your pipe sizing as roughed MAY be perfectly fine for a larger heat loss than you are thinking. I work near Downtown Crossing so if you want me to take a look as a courtesy, write me off-line and I will see what I can do. No obligation, just another pair of eyes. I am actually in the office today if you are around.



Brad

o311sta

Software oversize?

I thought I was reading opinions on here, not very long ago, that heat loss software was still on the over sized side. I will keep searching for that thread.

Kevin

icesailor

Oversize Software

This may not count for much, but, in my opinion, as long as one program, compared to another, covers the losses in some relatively equal way, it doesn't matter all that much. Because with everyone wanting to use low temperatures in hedating systems which means additional radiation, more radiation means lower water temperatures. With experience with your programs, you can fudge or adjust your results.

MNPLUMBER

Great thread

Being new to boilers and sizing ,this thread helped me out a lot, thanks! Since my last post here I've re-done my calculations on my first design.

I compared my calculations using some of the sq. ft. numbers here and I believe I'm very close. I have three upstairs bedrooms that are 12x12 or 144sqft. each with 9ft ceilings,  two new vinyl windows in each, lath and plaster with very little insulation in the walls. Northern Minnesota with a -20 degree calculation. with my calculations I decided to use one DiaNorm model 22 24x24 panel in each room which puts out about 4600 BTUH. At 30 a sq.ft. that's 4320BTUH, very close! I'm happy! I'll be running each of these 3 panels with a home run system separately off a small manifold near the boiler on one zone valve.

The rest of my system for the main level and basement I decided to just run one loop system with the living room, dining room and kitchen getting the first part of the run, the basement getting the last. This part of the system has a total of 39,000 BTUH of fin tube.  This will be my other zone, I'm well within my footage for using 3/4" piping.



Total BTUH for both zones is about 55,000 BTUH. I'm going to use a Slan Fin cast Iron boiler, the Victory series on this one because it uses a direct vent, no chimney available and I've decided against the Mod/Con on this one for other reasons.



Regarding the boiler, the 60BTU is too small. I would have to use the 90, the net on the 90 I believe is 68. Still oversized but???? What do you think, would that one be ok? Gives me a little wiggle room anyway in case I want to add more fintube.



Thanks again for this terrific forum. I have a long way to go but each day makes a little more sense.

Brad White

To your last question-

"Regarding the boiler, the 60BTU is too small. I would have to use the

90, the net on the 90 I believe is 68. Still oversized but???? What do

you think, would that one be ok? Gives me a little wiggle room anyway in

case I want to add more fintube."



I have not reviewed your heat loss calculations, but wanted to ask regarding your assumed boiler size and at what temperature the radiators were selected. This can have a huge impact on your efficiency and radiator sizing. "Stock" radiators are often selected at 180F entering water and sometimes 180F "average" water temperatures. This is a big difference in and of themselves, with the difference being 13% right there.



If a modulating condensing boiler, with 90 MBH output, the efficiency when putting out water over 140F, even to 180F, will be in the range of 85%. Once you get your supply water below 140 and return water below 120F. your efficiency will start to climb into the 90% range and up. With radiant systems having 75-80F return water, 95% efficiency is common.



I normally select my panel radiators for 140F water with a 130F average temperature. Lower than those temperatures, the radiators become too big and not as economical. But I will get condensing all the time of the year.  So please check your radiator selection assumptions, at what water temperature, specifically AVERAGE for consistent ratings.

MNPLUMBER

not using a mod/con on this one

All fin tube was sized using 180 degree water. The three DiaNorm panels were sized using 180 degree water. 24x24 type 22 panels at 180 degrees is about 4600 BTUH each.

I've tried figuring all variables, a couple dozen different options have been looked at and just as many different opinions I've received.

I believe the system will work and work well. It may not be AS efficient as using a mod/con but that's ok,  it's close.

Sizing the boiler? So far all I've come up with is the 60 is too small and the 90 is slightly too big. Too small won't work. Slightly too big will work. I don't think anyone could size a boiler exactly  to the needed output since there are so many different variables including seasons/temperatures,  zones, etc. From what I'm learning it's about getting as close as you can.

I feel I'm close on this one,  I hope! ;-)

Brad White

That is all OK, actually.

At least you know that your having the hotter water means you can handle the colder weather with ease. The good news is that you still have plenty of room to save energy and increase comfort. (You will love panel radiators, if you have not had them before you are in for a treat vs. fin-tube.)



What I would do, in short:



1) Put TRVs on all radiators. They probably come integral with them, with DiaNorm and others.  Each zone can "trim" to its internal loads (TV crowd adds heat, low winter sun adds heat, might as well not spend yours.)



2) Separate the boiler flow loop (kept at 180F to 140F minimum, usually)



3) Separate the radiation loop (kept at 180 maximum down to as low as will heat the house on a mild day.)

Given you have or will have panel radiators and fin-tube, we should assess the actual temperature needs of each circuit. Worst thing is that you will have the fin tube on its own mixing valve and ODR schedule and that is still a good thing, not a bad thing.



4) Bridge the boiler loop to the radiation loop with either an injection circulator, a 4-way or 3-way mixing valve to control the radiation loop temperature to an outdoor reset schedule. Set up the boiler with a similar control, albeit a narrower, higher temperature range plus a floating differential to reduce short-cycling.



With the above,  you should be able to reap nearly all of the comfort a mod-con will give you and wring the best efficiency from what is a good but not the top tier efficiency grade boiler.



As for size, yes, you see the dilemma! Just so many increments to go around. Maybe you can find a 75? (This is gas and not oil, right? I forgot if you mentioned, but at least with oil the firing rate can be changed within a reasonable range.)

superdave

mixing valves



What does every body think of the Caleffi motorized mixing valve (NA16469) on this Brown stone for the radiant?

superdave

mixing valves



What does every body think of the Caleffi motorized mixing valve (NA16469) on this Brown stone for the radiant?