Before I pay to have a professional heat loss calculation and design done, I'd like to do a first cut at it myself. I'm playing around with the Home Heat Loss Calculator (http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm) at Built It Solar.
Are there other resources that you would recommend to me?
Thanks,
Jeff

I find HEED 3.0 useful.

http://www.alternateheatingsystems.com/btucalculator.html

Simplistic but came up with the same numbers as the pro's for me.

Thanks, guys, I'll check them both out.

I used this one, it seemed pretty in depth and all the other ones I used appeared to agree pretty closely with it

http://www.warmlyyours.com/hlc/room/index_main

Just run my numbers through that link and it was pretty much in the same area as the others. There was somethings I liked, I could actually pick a comparison site very similar to mine.

I had a look at a pro system at the weekend, one big issue I have is wind chill. None of them seem to seriously address that They do seem to be better designed for new build and a guide for the rest of us.

Posted By Como on 02 Mar 2010 12:48 AM
Just run my numbers through that link and it was pretty much in the same area as the others. There was somethings I liked, I could actually pick a comparison site very similar to mine.

I had a look at a pro system at the weekend, one big issue I have is wind chill. None of them seem to seriously address that They do seem to be better designed for new build and a guide for the rest of us.

Wind chill is primarily a human comfort while outdoors factor. Wind effects can be a primary driver of air-infiltration, which IS factored into heat loss estimation tools.  If your place is partially earth-sheltered & fairly tight, their built-in air infiltration estimates are probably overshooting reality.

The simple-minded heat loss tools are probably also overestimating the heat loss into the earth-sheltered portion, which probably has an average temp above 50F, with R10 of rigid foam, no thermal shorts to contend with, and not much changed during design-day outdoor temps.  Using the WarmlyYours tool you can't model that as an exterior wall- a closer approximation would be to treat that wall area as insulated floor slab.

Out of curiosity, what are the various tools giving you for heat loss numbers?

10500 HDD
I used Leadville, CO as the comparison site
5500 sq ft
Average ceiling height 13ft
Double glazed storm windows
R50 in the roof
Solid masonry walls

500,000 btus seems the average

The one above was c470,000

Wind chill can drop the temperature by 30 degrees. We have no protection and it blows, very hard.

Today no wind, snow as an insulator and a high of probably 40 with lots of solar gain, something else that does not seem to be factored in. But then they look at worst case scenarios.

Posted By Como on 02 Mar 2010 10:54 AM
10500 HDD
I used Leadville, CO as the comparison site
5500 sq ft
Average ceiling height 13ft
Double glazed storm windows
R50 in the roof
Solid masonry walls

500,000 btus seems the average

The one above was c470,000

Wind chill can drop the temperature by 30 degrees. We have no protection and it blows, very hard.

Today no wind, snow as an insulator and a high of probably 40 with lots of solar gain, something else that does not seem to be factored in. But then they look at worst case scenarios.

There's no factoring in solar gain to a heat loss calc.  A heat loss calc assumes the possibility (likelihood) that the design day temps occur before dawn.  It's not the same as calculating a daily or seasonal heat load, which will have many other variables.

What exactly do you mean by " Wind chill can drop the temperature by 30 degrees"?  Is that your INDOOR temperature dropping by 30 degrees?

500KBTU/hr seems sky high unless those masonry walls are uninsulated. If uninsulated your walls would have comparable U-values to your windows, several times the heat loss of even moderately insulated walls.  The effect of wind on conducted heat loss is quite small for even a modestly insulated house, as long as it's tight, but un-insulated masonry walls have very low R-values.  You may have a high enough exterior wall temp for wind-washing to make a significant difference, whereas for even  tight 2x4 stick-built R13 walls the effect wind on peak conducted heat loss is negligible (but it can drive infiltration losses significantly.)

Even if the walls are uninsulated completely, that estimate is high by a factor of 3 at least.

I've done loads on homes with uninsulated walls. they typically top out around 35 to 40 BTUs/sq ft average, tops, in northern climates.

Nothing personal Como, but you are not even in the ballpark with how to properly calculate a heatload. As dana notes, wind chill is not a temperature effect. forced convection can drive additional heat loss from the walls, it's true, but the primary additional driver there is really infiltration.

I wish...

I have run the numbers through 4 on line calculators.

Plumber came up with the same number.

Consultant came up with same number, they used Wrighsoft http://www.wrightsoft.com/

This assumes insulation and window refurbishment.

I have been working on 70 plus with a -15 minus. So 85 degree difference worst case. Sunny and 40 today.

I don't know what to tell you. it's not possible.

I agree- insulated even to R5 there's no way it's going to hit anywhere NEAR half MMBTU/hr with an 85F delta-T.

Come to think of itt, last year I was working with some people trying to upgrade an uninsulated slab-on-grade masonry building twiceabout 10,400 square feet with 22' walls in the larger wing, 15' walls in the rest, R12 insulation in the taller attic space and R20 in the lower, with about 800-100square feet of single-glazed+ interor storms. It was running ~200-250KBTU/hr (measured with the existing heating plant) at a delta-T of 65F. It's a cavity-wall 8" block+ brick structure, but even with the air space of the cavity included IIRC it was around R2.25 for the clear-wall sections (calculated). Como has 30% more delta-T but less than half the wall area, and allegedly higher R values. If we assumed similarly crappy construction on Como's place it'd still come in well under 200KBTU/hr with an 85F delta.

500KBTU of heat lss being a 3x overestimate for a 5500' building with uninsulated 13' walls does indeed sound about right, as Rob suggested. The folks with the 10,400' building must have used Como's consultants to design the heating system, since there was 1.5MMBTU of ~80% gas burner heating the place (5x oversized for the load, even before building envelope improvements were made.)

Plugging in a 60 x 92 foot building with 13' walls, 5500' of R50 ceiling, 500 square feet of R2 glazing, R10 walls, and 50' of R5 doors into some other cheezy li'l caculators I have on my machine here at work, with an 85F delta-T it comes in at ~270KBTU/hr if the infiltration rate is 2 air changes/hour, and has to rise to a very breezy 4 ach to hit 500K. I s'pose if it leaks like a barn you could hit that level of heat load in a stiff wind.

But I'm more curious about the numbers Jeff came up with, given his earth-sheltered configuration. If it's calculating more than ~35KBTU for a delta-T of 60-65F ( typical for Kentucky) on a sub-2000 foot earth-sheltered building that size I'd be skeptical. Reality is probably under 25K.

The glazing will be more like R5. Double glazed storm windows plus the original signal pain. There are 50 odd windows , about 1000sq ft.

The walls are the big issue, a single wythe is .44. We have a mixture of 2 and 3 wythes. Plus plaster on to brick.

I will go and paste the result from the last one.

Room Floor Area 5500 Sq. Ft.

Estimated Coverage 75.0% , 4125.0Sq.Ft.

Desired Inside Temperature 70 °F

Design Outside Temperature -14 °F

Existing Heat Sources 0 Watts

Total Heat Loss 446171.0 btu/

I will repeat that it is not possible to have a heat load that high if you actually have any walls. If you persist, I would definitely recommend you use at least 3 staged heat sources so you stand a chance of running the system without massive short cycling, and I'd be surprised if you ever ran more than 2 simultaneously unless you had a startup condition in january sometime. I'm not trying to sound like a jerk, though I might be anyway, but seriously, please heed my advice. the cost will pale in comparison to your fuel bills anyway.

If you are using R5 windows, your window load is about 17k BTUs/hr. Even with crappy windows it would only be about 35k. 5500 sq ft of R30 floor and ceiling might give you 20k if you derated heavily for poor installation. worst case you're at 50k here. that means you have 400k in wall and infiltration losses. A ridiculously high infiltration load could yield another 50k and I will stress the ridiculous there as that is 50% more than the largest ACH rate I would likely specify, ever, under any normal condition, though leaky to the extreme and window to the extreme... maybe.

so 350k for wall? if I gave you 10' walls, 55x100, 3100 sq ft minus the 1k in windows is about 2k square feet of wall. R2 walls? No way. the air film alone is almost R1. and that's R2 shifting way more load to the other components than you are; your numbers are counting it even lower.

He could have a load like that...if he moved one of those Tiki huts to my place on the lake!

Posted By BadgerBoilerMN on 03 Mar 2010 07:31 AM
He could have a load like that...if he moved one of those Tiki huts to my place on the lake!

Naw, all it takes is bunch of missing bricks- like maybe 25% of 'em- it'll be leaky enough... 

But seriously, insulating the walls would be cost effective, even if the heat loss estimate is from mars, the real number is still significant.

Do you have the fuel use bills from last heating season?  It's pretty easy to put a stake in the ground for the whole-house heat loss using season heating degree days & fuel use, if the raw efficiency of the existing heating plant is known (or estimable). It's harder if you've been supplementing with wood stoves, etc., but if you also know how much wood you went through you can still get pretty close.

We will be reviewing the bids tomorrow, so I will have a better idea. I will report back, we should have 34 proposals.

The building has never been heated properly. There were 4 forced air propane furnaces when we bough it, badly installed etc but still cold.

The walls are the big problem, we are restricted by both practicality and the Secretary of Interior standards, it is a historic building.

Heating will be hydronic, a biomass system Propane would bankrupt us but we will have a back up boiler for when we are not there to keep it from freezing.

I have tried all sorts of assumptions, but I still come out with a minimum of 350,000 and that is assuming insulation I doubt we can achieve. I am working on -15 but it can go down lower.

A more normal winter would be 20 ish in the day and 0 at night, this week we are 40 and 20.

David

Quick question on wall R values. Our house is also earth sheltered. Approximately half of the walls are 10" thick poured concrete with 2" of rigid foam insulation on the outside, with all except the top 18" underground. Should I use an R value of 10 (just the foam) or should I increase the R value for the concrete and the earth sheltering? Thanks.