Heat loss calculation for superinsulated building

GroundUp

I have commandeered a stack of new walk-in freezer panels with enough walls and ceilings to make a 33x62x10 building. For those not familiar, these are similar to SIP panels and just lock together via tongue and grooves with camlocks. I worked for a company in high school that dealt these coolers and freezers to grocery stores, liquor stores, etc and I was on the install crew so I'm well versed on that part, however the fine print such as heat loss is not something the MFG provides, although they spec and provide the cooling equipment with the box. The only info I've gotten from them is that the panels are all R44 closed cell foam. These particular panels are structured entirely of foam, there is zero wood in them whatsoever- only the foam and 24ga steel sheathing on each side, so in order to support the roof trusses I'm leaning towards hand framing a 2x4 interior wall around the perimeter which I'd fill with R13 glass. No thermal bridge and R57 walls ought to leave me with a fairly easy to heat building, save for the overhead doors and windows.

I would love for this to be a radiant slab application, but I'm afraid the floor will never be "warm" anyway so I am open to suggestions on that part, maybe a low mass like radiant ceiling? Manual J does not give an option for anywhere near this R value, nor can I figure out how to work an overhead garage door into the equation. I can get R18.4 overheads readily, so that is the plan for right now. This will be mostly a heated storage garage for vehicles and ATV/snowmobile/lawn tractor/skidsteer type items so I can have my shop back in these lovely MN winters. I have a wood boiler in place that currently heats my house and shop via insulated underground lines, and I will tie this new building in as well. The boiler is getting swapped this fall anyway and at that point I would like to make a couple changes there as well, with a plate exchanger within the boiler cabinet and constant circulation only through it and the loads circulating only on call for heat to minimize ground loss. Despite having buried top dollar pipe, there is still a ~150,000 BTU a day ground loss with constant circulation 350 feet round trip to my house so it does add up. Not that I would really need to have a heat loss for the building, as the wood boiler doesn't care, but I would like to know what I have and especially if I go with something like a radiant ceiling it will become more of a necessity. Tried SlantFin as well and can't even come close. Regardless of heating method, I'll probably just have a line voltage stat to spin a 15-58 and pull glycol through a mixing valve from the plate and run it through the system. Yes, it'll be cold for a minute after sitting idle in the underground lines but I don't care. Please excuse my rambling, I over-explain things to avoid answering a million questions later on. Anybody have a good way to calculate the heat loss? TIA!

Zman

A friend of mine built a similar building as a garage that he and his wife parked in every day. The issue he had was ventilation. Every time they parked the snow covered cars, the room clouded up. He ended up installing an HRV to deal with the problem. I wonder if a HRV with duct mounted fan coil off the wood boiler would do the trick. You could trigger the HRV based on space humidity and let the coil heat the space on recirc mode the rest of the time.
Here is an approximation of your heat loss. Your building will be tighter so you may want to tweak the ACH number.

STEVEusaPA

Excellent insight Z (I forget if you spell it Carl or Karl).

Instead of constant circulation underground, maybe install a buffer tank to the building. Let your heat source charge the buffer tank (could even have a solar coil) as needed, let the buffer tank supply the zones to heat the building

GroundUp

That's awesome @Zman , thank you! Will have a little less glass and door but very close. As for the humidity issue, I have the same problem in my 2x6 R19 shop with 288ft of R7 overheads. Regular daily snow isn't so bad in there, but if I leave the truck outside and the bed fills up or I bring the Bobcat in after plowing it gets to be a sweaty mess. That's got a radiant slab and a lot of steel so when it gets nasty I can just leave the overhead door open for a minute and it dries out nicely without losing a ton of heat. I was planning to drop an HRV on a humidistat in this new building, didn't even consider the hot water coil idea. Interesting idea, I'll have to ponder that- however I am pretty determined to keep it radiant. Daily vehicles will still be parked in the shop, so the snow melting load in this freezer will be pretty minimal.

GroundUp

STEVEusaPA said:

Excellent insight Z (I forget if you spell it Carl or Karl).

Instead of constant circulation underground, maybe install a buffer tank to the building. Let your heat source charge the buffer tank (could even have a solar coil) as needed, let the buffer tank supply the zones to heat the building

It may have gotten lost in my ramble, but the constant circulation ordeal has already been remedied without a buffer tank. The boiler needs to burn 24/7 and can only shut down so tight, so the plate exchanger in the cabinet will always be hot and circulation loss minimal. Let's call it an "on demand" system with the boiler itself being the "buffer" as the tank holds 180 gallons itself

hot_rod

The floor will always be ambient temperature when heated. so with snow cove red vehicles I think radiant floors are ideal.

The panels must be 6" thick to get R-44? Are they built for exterior use?

GroundUp

hot rod said:

The floor will always be ambient temperature when heated. so with snow cove red vehicles I think radiant floors are ideal.

The panels must be 6" thick to get R-44? Are they built for exterior use?

Think so? I was having a little bit of reservation on the floor idea in case I wanted to heat it up quickly as it will likely be set to 45 degrees only. There may be an instance where I want to bring it up to 70 to drink beer or something lol. I suppose I could hang a 50k unit heater and pipe it in series before the mixing valve and run them in tandem.... Hmm. Low GPM and high Delta T but the plate won't care. The panels are 5-1/2" thick like a 2x6 wall, I thought 44 seemed high but that's what they say. Apparently the high density foam has a slightly higher rating than regular closed cell. The sidewalls are rated for exterior use, but the flat ceilings we always put a rubber membrane on them. This one would get wooden trusses with a 4/12 pitch and ribbed steel on the roof as well as the sidewalls to match my shop.

My old boss, the guy I'm getting the panels from, has a 40x60x16 at his place that we built the same way about 8 years ago. His is wood rail (built like typical stick frame w/ studs at 16" OC) where this one of mine is foam rail, but similar deal with the exception of thermal bridging from the studs. He uses it as an airplane hangar and loves it. We own some hunting land together up north and built a 16x28 garage the same way, except that one is cooler panels so only 3-1/2" thick. Opened the door on 4th of July last year and there was still snow on the floor from February when we were up there snowmobiling haha. He's the biggest restaurant equipment dealer in the state, so once in awhile he comes across deals on these types of things. This particular truckload of panels for me, all I have in it is the trucking costs and a few bucks for the man as legwork compensation. Let's just say the concrete slab is going to cost triple what I paid for the freezer- I couldn't pass it up

hot_rod

For me anyway, radiant floor heat is a must if you ever plan on spending time on your feet in the space. No other heating method can provide that comfort for a slab on grade.

I'd insulate and tube the slab, for future use if nothing else.

Sure a Hot Dawg would be a "dragster" heat emitter and move some moisture. if you want warm "now" hard to be a forced convector.

Since you have a wood hydronic source, a HW coil and radiant floor would give you options for now and later.

Most common in farm country shops around me is an old truck radiator connected to an OWF. Your choice of 12VDC or 120V fan

I'm in the process of building a TC truck camper for my truck with SIPs, instant walls. A SIP manufacturer near me will sandwich whatever materials you take him. I went with FPR as the final outer layer.

GroundUp

Slab would be insulated regardless of heating method. Never said anything about a Hot Dawg..... The whole truck radiator thing is old news around here now that unit heaters have become affordable, I install 20-30 a year- often coupled with radiant floors, as the majority of my jobs are sheds/shops and the majority of that majority have outdoor boilers. For example, my road is 4 miles long and has 11 houses on it. 9 of those 11 have outdoor boilers. I have the radiant floor/unit heater setup in my shop and love it, I just like to monkey with things and see how different setups perform on my own dime instead of experimenting with customer systems. I've done a handful of radiant walls and ceilings but in all honesty, haven't spent enough time in the space afterward to judge comfort.

I push the radiant floors hard for my jobs, but many are scared away by the cost and the fact that "the heating guy" around here for the last 100 years still to this day has no understanding of hydronics and has built a number of crappy systems which obviously homeowners hate and it gives the radiant slab a bad reputation. I'd like some more experience in the wall/ceiling area to use as a substitute when they shoot the slab idea down, so no better place to monkey with it than my own home. Just thinking outside the box is all!

Other than melting and evaporating snow, I couldn't really care less if the slab is above ambient temp- this building will serve 98% of its life as a simple heated storage building so any floor standing instances will be few and far between

hot_rod

Cost wise I'm not sure a ceiling or wall would be cheaper if the slab is already part of the plan. They all need insulation, and tube. walls and ceilings that I've done used aluminum transfer plates, so that cost factors in as well as more labor than rolling tube for a slab pour.

The main deciding factor is how the space is used, for equipment storage there is not a lot of advantage. If you or somebody down the road plans on working in there slabs heat rules. There are some 18"on center shop designs that are workable, if perfect foot comfort in not required.

The biggest thing I noticed with ceiling radiant is a working shop is it never really as comfortable beneath things. In the body shop I did with ceiling the owner noticed working below cars on lifts for example was not as comfortable as the shop he had with radiant floors. Or his feet under a desk or work bench. he did like the response time being a dry lightweight system.

Needs, expectations and budgets always seem to drive radiant decisions.

GroundUp

I think I talked myself back into heating the slab like was originally planned, thanks for the reassurance. Very good points made. Now to figure out a way to monitor heat actually used in the building over a given course of time....

hot_rod

The amount of heat used can be easily monitored and calculated with a BTU meter.

Basically a rotary water meter and two temperature sensors is all you need. More expensive versions will data long and have BAC or wifi connection to monitor remotely.

Even simpler is a solar differential control with heat metering function. You just need to determine a flow rate, measure or calculate it, plug that gpm into the control and slap on two sensors.

If you have 12VDC or 24VDC available, or a transformer to get it, I'll send you a control to play around with. It is not a sealed certified version, but plenty accurate for gathering BTU data.

GroundUp

Thanks, a quick Google search shows a lot of chatter of the Caleffi iSolar units- would it be safe to say these are the units you are referring to? I'm no technology whiz by any stretch of the imagination, so the more basic the better. It seems the ones I ran across were rather pricey to justify buying simply to satisfy my curiosity. Not like it's an apartment or something that I need to meter, it's simply a curiosity thing. Do you maybe have a simple budget friendly make/model that I can do some research on? This information is much appreciated

hot_rod

It is an I-solar control. Super simple to drive, 4 settings and it starts reading. We discontinued this line, Caleffi will continue to sell solar products that we manufacture, in upcoming catalogs.

PM your address and I'll send one your way. I can talk you through program when you are ready.

HVACNUT

You could do the radiant for comfort and a ductless heatpump for those beer drinking times.
Nice spot for a kegerator.

Gordy

As @hot rod said I would put the pex in the concrete anyway. It opens many doors for alternative methods of heating the space. Concrete with out pex is a missed opportunity.

I would also form a brick ledge for the panels to sit on. Ideally 6” lower than your floor pour where your conventional framed wall will sit. If this is a slab on grade of course.

That way the bottom of the conventional wall will not be a direct path for infiltration at the sill. The bottom of the panels will be lower than the bottom of the framed wall. It will also enhance your perimeter insulation detail.

Provided of course if you want to sacrifice some of that 10’ panel height.

hot_rod

I like the brick ledge idea. Maybe wrap the ledge and vertical portion with some Ice&Water stick down material since the panels may not be PT lumber? It would provide a gasket and handle the wood to concrete connection

Gordy

Most deffinetly wrapping that detail with a waterproof membrane.

I watched a bunch of these set at Berner Foods plant. For imterior cold storage, and exterior wall envelope. There is no lumber in the panels.

One detail I thought could have been done better was that top of foundation bottom of panel exterior perimeter detail. The building was red iron framed, and the panels attatched to the C channel cross members. The bottom of the panels did not sit on the foundation wall it basically hung off the fasteners to the red iron framing. However the panels could have been tall enough to allow them to fly by the top of foundation. It was an industrial application, not a whole lot of thought ever goes into envelope efficiency

GroundUp

Correct that there is no lumber in the base of the panels, I do recall though that the foam rail wall panels have a 2x6 at the very top in order to lag the ceiling panels into them. This will be slab on grade, but the whole brick ledge deal I'm not fond of. Ice and Water or not, there is a 99% chance there will still be infiltration which will destroy the aluminum sheathing in short order as it will never dry. I've been around enough of these boxes in my day to know they won't take much of a beating from soil in farm country. The wall panels utilize a groove at the base which we anchor down a "screed" to the top of the slab with a bead of butyl underneath to fit in the panel groove and I will also butyl each side of the panel where it meets the slab. Perimeter XPS foam around the slab gets raised 6" higher than finished floor as well, as we do with all stick frame buildings. Exterior stripping brings the ribbed steel out far enough to hide the foam (local mill cuts true 2" stripping). Zero chance of sill infiltration, I've been doing it that way for almost 10 years. I do like the idea of having an R44 slab perimeter, but I feel the cons outweigh the pros. Also I need a 9ft high door to get my truck in so I couldn't afford to drop the lid 6". Just got home from fighting with some radiant walls all day so maybe I'll be thinking a little more clearly tomorrow lol. Thanks for the input fellas

Gordy

I was awaiting a response before more detail. Yes you would have to implement weeps every so often just as brick in the brick ledge sill area for a drainage plane.

Not sure what is meant about soils. That has to do with proper site grading.

If the skin is aluminum corrosion shouldn’t be detrimental to the panel.
The ones I see are aluminum skinned.

Also hot rods input on the brick ledge detail is key.

Infiltration is usually not a problem until a period of time later when things settle, or shrink.

GroundUp

"Proper" site grading means the soil is at finished floor level where I come from. If the aluminum sits 6" below said grade, the minerals and whatnot in the soil will eat it in a matter of a couple years. Farm country, fields for miles in every direction. I don't mean to argue or anything, I do appreciate the input. However I replaced hundreds of rotten panel bottoms when I worked for this place and can assure you the aluminum would die a horrible death buried in the soil around here. Sounds like you do things differently in your neck of the woods Gordy, how is it that proper grading to a slab on grade building is achieved with the slab above grade? I'm having a tough time picturing that without a gob of exposed XPS. Always interested to see how others around the country do things

Gordy

You can make your finish grade 6” below the bottom of the panels. Compensate for this by raising the finish floor elevation to get proper site drainage.

hot_rod

Inspectors around here want to see finish grade 6"or more below any wall siding.

That is where we had to detail the exterior foam around foundation or slab edge. A metal Z flashing would cover the edge of the foam.

Certainly at overhead doors the gravel can meet the slab.

Sounds like you have a plan that works.

GroundUp

Huh, that's very interesting. I tried the steel Z flashing deal on my own shop several years ago to hide the foam 6" above my slab and down below grade (before the 2" stripping idea came along) and it was completely rotten in 1 year. Replaced with painted galvanized, it was garbage in 3 years. Replaced it then with a color matched composite and it's still holding strong. Inspections could just as well be a foreign language around these parts- aside from electrical and septic, nothing gets inspected even commercial. I called the county for a mechanical inspection on a new bank I did about 3 weeks ago and they had no idea what I was asking for. Flat fee for the building permit and that's the end of it. Maybe it's crazy and maybe not, but there is no such thing as sill infiltration the way we build and I'm content with that.

hot_rod

Galvalume is the main material around hear for barns and flashing.

I had an in-ground pool that was galvanized steel panels with a vinyl liner. The panels were in good shape, a few were rusted and corroded where they seamed together, I collapsed the panels and filled it in a few years back, been in the ground for 30 years or more.

It must be staying wet or damp to rust thru in 3 years?

Really no material last forever out in the elements, even vinyls and composites. Maybe stainless weathers best?

GroundUp

It's real heavy clay out here,and the topsoil is nearly always wet. Heavy rains will make lakes in the yard for weeks until they evaporate. I drain tiled the main yard a few years back to a man made pond in the swamp in the back part of my property which has helped tremendously. My regular M-F job as a commercial pipefitter takes place around the metro area, 80-120 miles away from home where nothing is farm related and down there I've noticed the dirt is very forgiving as far as corrosion goes. Home is a place where the closest loaf of bread is 12 miles away and everything is farmland, I say it's got to be something with the sprays and chemicals being evaporated and rained back down on the topsoil that has the corrosive effect but that's just speculation.

Different parts of the country have different ways of doing things, like natural gas piping for example. I've seen tons of folks on here and other forums yacking about black pipe being the ONLY acceptable method. MN building code lists copper and galv as acceptable, and any commercial rooftop throughout the state is piped in galvanized unless it's over 2" where it is sch 40 steel painted yellow on the outside. As long as Type L is brazed, it's accepted anywhere and used almost exclusively in medical facilities around the metro. I believe that is a corrosion issue down south where copper is never allowed on NG, but it is the standard here.

Gordy

Yup, fertilizers, and pesticides. At least the ground is cohesive soil which keeps some of it out of the aquifers

Gordy

Rhino liner the bottom 2’ of the panels I see it comes in spray cans now.

GroundUp

It'll be covered with ribbed steel down to just above the lawn with 2" XPS sandwiched in between from the perimeter insulation. Should be no issues. Side note though, Rhino in a spray can? That sounds interesting

Jamie Hall

I'm familiar with those clay soils, @GroundUp . It's not the pesticides and herbicides, although excess ammonia fertilizer doesn't help a bit. It's that they hold moisture so well, and the result is assorted acids which are really tough on pretty much any metal -- particularly if there are dissimilar metals involved (electrolytic corrosion). It's why pipelines have impressed voltage cathodic protection.

That said, the best protection is epoxy coating, carefully applied, with a polyethylene wrap. It used to be coal tar -- can't get that any more.