Properly designed vs. oversized

Voyager

This is how you tell the difference between a properly designed boiler and in-slab hydronic system and an almost certainly oversized forced air heating system on a day that is 15 degrees colder than the design day for the area. Thankfully, the properly designed system is only in my workshop and I can only blame myself as compared to the commercial contractor that designed and installed my house system. 😂

Solid_Fuel_Man

-32F here in Maine today. Good day to test, I design for -40 in this area. 

Is your slab just in need of an outdoor reset tweak? Or is the boiler actually undersized? Pretty hard to undersize a boiler for the majority of residential systems. Same can be said for forced air. 

hot_rod

There is usually a 10- 15% fudge factor in load calculations, if you used the software or manual J based formulas?
Is the boiler running non stop at 100% output and not keeping up?

Properly designed, and not keeping up, shouldn't be in the same sentence

fentonc

I'm also curious if the boiler actually fired all day, or if the combo of radiation and water temp just doesn't output enough heat at that outdoor temp. We had an almost-exact design temp day here last week, and my boiler fired for 23% of the day while the circulator ran (so one of the 3 zones was calling for heat) for 60% of the day, and that's with the supply high limit lowered all the way down to 160F (the lowest I felt comfortable going with my non-condensing boiler). I'm pretty sure my boiler could heat my house if it was -100 outside.

ChrisJ

hot_rod said:

There is usually a 10- 15% fudge factor in load calculations, if you used the software or manual J based formulas?
Is the boiler running non stop at 100% output and not keeping up?

Properly designed, and not keeping up, shouldn't be in the same sentence

I think I'd be ok if my system lost 1 degree during extremes but I wouldn't be happy with 5 or 6 degrees.

I'd rather it keeps up and a little extra to be honest. People do come and go and that means opening doors and a door being open even for a few seconds makes a huge difference when it's -15F out.

@Voyager Where are you located?

Voyager

Solid_Fuel_Man said:

-32F here in Maine today. Good day to test, I design for -40 in this area. 

Is your slab just in need of an outdoor reset tweak? Or is the boiler actually undersized? Pretty hard to undersize a boiler for the majority of residential systems. Same can be said for forced air. 

My workshop is 32’ x 48’ x 14’ high ceiling. It has a 5” slab with 2” of foam insulation underneath. Unfortunately, I was away when the contractor poured the slab and backfilled and they did not insulate the edg of the slab which is exposed fully on one side and partially on the other three. This contributed a surprising about of heat loss when I did the calculation. And estimating air exchange rate was just a guess as I did not have an infiltration test done and just guessed what the building would be with the 12’x12’ overhead door and such.

I did my own heat loss calculation using a spreadsheet, but did compare it to one online package and got similar results. I designed for 70 F inside on a 0 F outside day and got about 38,000 BTU/hr heat loss. I selected a Triangle Tube CC50s 40,000 BTU/hr boiler, which to my dismay I see has just been discontinued.

Do I have the boiler tuned optimally? Almost certainly not as this was my first rodeo in regard to designing and installing a heating system. I did it myself as a retirement project (I am a retired electrical and structural engineer) mainly for the learning experience and fun of doing it.

My first post was somewhat tongue-in-cheek, but I think it does somewhat confirm that my design assumptions were pretty close. I designed for a 70 degree delta T and last night had 75 to 80 degrees delta T and the boiler isn’t keeping up which is no surprise if the design rules are accurate. Also, there is a lag in a large slab like mine that simply can’t be overcome by a standard control system. It would take a pretty good predictive control system to deal with what is probably at least a 6-8 hour lag before a call for heat and seeing the response to that at the thermostat.

For comparison, my house is log construction, about 4,000 sq. ft. of heated space and has three forced air furnaces totaling 225,000 BTU/hr (125K in the basement, and a 50K in each wing’s attic). So, the workshop has about 26 BTU/square foot and the house has about 56 BTU/square foot which I suspect is well oversized, though I have never done a heat loss calculation on my house. However, in fairness, most of the heating is done by the main furnace as the two attic furnaces only heat the upstairs bedrooms and loft and the main furnace heats the finished basement and first floor which is probably 2800 of the 4,000 sq. ft. So, a more fair comparison is probably 125,000/2,800 = 45 BTU/square foot.

Again, my post was somewhat in jest as I didn’t have much else to do on a -15 F morning as a retiree. 😁

Voyager

hot_rod said:

There is usually a 10- 15% fudge factor in load calculations, if you used the software or manual J based formulas?
Is the boiler running non stop at 100% output and not keeping up?

Properly designed, and not keeping up, shouldn't be in the same sentence

Yes, it is running pretty well nonstop and most likely not keeping up due to the normal lag of a concrete slab heated structure. It will overshoot by 5 degrees later today as it is supposed to warm up fairly quickly into the low 20s and a 5” concrete slab simply can’t manage a 35 degree swing in 12 hours time.

See my later reply for more details.

Voyager

fentonc said:

I'm also curious if the boiler actually fired all day, or if the combo of radiation and water temp just doesn't output enough heat at that outdoor temp. We had an almost-exact design temp day here last week, and my boiler fired for 23% of the day while the circulator ran (so one of the 3 zones was calling for heat) for 60% of the day, and that's with the supply high limit lowered all the way down to 160F (the lowest I felt comfortable going with my non-condensing boiler). I'm pretty sure my boiler could heat my house if it was -100 outside.

That may well be as I have no way to monitor the operation of the boiler. I wish that either Triangle Tube made that available (I asked and they don’t) or Honeywell from my wifi thermometer. They have the information as they send me a monthly report as to hours of operation, but they don’t provide access in real-time to the user which is a shame.

All I know is that every time I checked last evening and this morning, the thermostat shows that it is calling for heat. However, I can’t say the boiler ran 100% of the time as I have no way to track that unfortunately.

Voyager

ChrisJ said:

hot_rod said:

There is usually a 10- 15% fudge factor in load calculations, if you used the software or manual J based formulas?
Is the boiler running non stop at 100% output and not keeping up?

Properly designed, and not keeping up, shouldn't be in the same sentence

I think I'd be ok if my system lost 1 degree during extremes but I wouldn't be happy with 5 or 6 degrees.

I'd rather it keeps up and a little extra to be honest. People do come and go and that means opening doors and a door being open even for a few seconds makes a huge difference when it's -15F out.

@Voyager Where are you located?

This is a workshop so temp control isn’t that critical. I suspect I could turn up the water temp and it would keep up better. I think I have the high limit set at 100 F and probably could go higher without risking the slab. If it stays cold, I may experiment with the upper temp just for grins, but this isn’t a critical structure.

My house is toasty warm and the furnace keeps up just fine and even recovered quickly from the nightly setback. I don’t think it took even 30 minutes to warm from 64 back to 72 this morning even at -15 F, but thankfully with no wind to speak of.

I am located in northcentral PA literally within sight of the NY border.

Solid_Fuel_Man

The 100 degree high temp is your limiting factor. For refrence a slab can handle water temps as high as 125 in my experience. Not that you should ever need temps that high. 

So for proper design, you need to tweak the curve. 

I've designed, installed, and controlled many heated slabs. My findings have always been that the better insulated the structure is the more stable and predictable the inside temperatures will be. High mass radiation simply doesn't respond like low mass emitters like forced air, or fin-tube. 

You can retrofit slab edge insulation. I like to cover the exposed blueboard with PT plywood, metal, or composite decking. I've also had ugly slab edges spray foamed. 

Voyager

Solid_Fuel_Man said:

The 100 degree high temp is your limiting factor. For refrence a slab can handle water temps as high as 125 in my experience. Not that you should ever need temps that high. 

So for proper design, you need to tweak the curve. 

I've designed, installed, and controlled many heated slabs. My findings have always been that the better insulated the structure is the more stable and predictable the inside temperatures will be. High mass radiation simply doesn't respond like low mass emitters like forced air, or fin-tube. 

You can retrofit slab edge insulation. I like to cover the exposed blueboard with PT plywood, metal, or composite decking. I've also had ugly slab edges spray foamed. 

I agree and may do more experimentation as my curiosity warrants. I don’t run the shop that warm, generally 60 to 65 depending on what I am doing and prefer not to stress the slab more than necessary. If this was a residence, then I would definitely crank up the temp for more heat output and faster response to dropping temps.

I had thought about retrofitting edge insulation, but the workshop costs so little to heat now that it hasn’t been worth the bother.

Yes, the response time is the biggest issue and no easy way to overcome that as it is simply physics. By noon, our outside temp was up to 0 F (ignore the temp in the picture as I have no idea what location Honeywell pulls that from) and the boiler has now turned off. It likely won’t fire again until well after sunset tonight and the shop likely will overshoot to 68 F or so as the slab releases the heat the boiler has been driving into it all night.

fentonc

I really wanted accurate data, so I built my own little monitoring system that monitors the 'circulate' and 'burn' status LEDs on my boiler, along with the supply and return temperatures for every zone, so it can keep a running estimate of how much fuel got burnt, cycling behavior and how much heat actually got transferred into each zone. I do think you probably have a 'failure' of the control algorithm and response time of your slab rather than the actual heat output of your boiler, but 'put on a sweater' is a perfectly fine solution. Given such a long response time, I think you could probably build a control system that used forecast temperature data to maintain a more even temperature throughout the day via some kind of 'anticipating outdoor reset' scheme, but aside from being a fun project, it would probably be unnecessarily complicated.

Voyager

Yes, I have thought about this given how cheap Arduino and similar systems are, but my curiosity isn’t high enough to justify that and my days as a controls engineer are 30 years past. ODR certainly is a helpful addition to a heating system, but with the slow response of a large thermal mass, the only way to deal with that is a weather based predictive control system that can greatly shift the heating phase of the boiler. I have thought about playing around with my programmable thermostat and just doing something basic like setting the temp setpoint to say 65 degrees from noon to midnight and then 60 degrees from midnight to noon. This would put about a 6 hour phase advance to the heat output and might help offset the slab lag, but in all honesty it just isn’t worth the effort for a workshop. 😁

I do expect to see more weather based HVAC controls as we try to eek out the last bits of efficiency while maintaining reasonable occupant comfort.

Kjmass1

I'd be curious how an Ecobee thermostat would work. In general, it knows the time to temp across all temperatures bands. So if the weather says it will be 0 degrees tomorrow, and it takes 8 hours to raise the temperature, it would start 8 hours early. You also get all the spreadsheet data as well to dig around with.

Daveinscranton

Depends on how you view entertainment.  I amuse myself no end with heat.  I know.  I should get a life.  I once tried a 4500 watt electric hot water heater on 2,300 square feet of well insulated house with terrific solar gain that had an additional 2,300 square feet of basement shop.  North eastern PA.  Worked mostly.  Had to keep an eye on the weather channel and turn on the tank 3 days ahead of bad weather to heat the slab.  ICF construction.

The reason I did it was because most everyone was trying to sell me a 250,000 btu boiler “to be on the safe side”.  I did eventually put in an 80,000 btu mod/con Munchkin.   Loved that thing.   Alas, it died at age 14, with all its design flaws, I still loved it.  $7 actual maintenance cost in 14 years. 

My actual heat requirement last night at -10 degrees F was under 40,000 btu an hour.   I have a Triangle Tube Instinct cranked down to 31%.  Works fine.

Voyager

Daveinscranton said:

Depends on how you view entertainment.  I amuse myself no end with heat.  I know.  I should get a life.  I once tried a 4500 watt electric hot water heater on 2,300 square feet of well insulated house with terrific solar gain that had an additional 2,300 square feet of basement shop.  North eastern PA.  Worked mostly.  Had to keep an eye on the weather channel and turn on the tank 3 days ahead of bad weather to heat the slab.  ICF construction.

The reason I did it was because most everyone was trying to sell me a 250,000 btu boiler “to be on the safe side”.  I did eventually put in an 80,000 btu mod/con Munchkin.   Loved that thing.   Alas, it died at age 14, with all its design flaws, I still loved it.  $7 actual maintenance cost in 14 years. 

My actual heat requirement last night at -10 degrees F was under 40,000 btu an hour.   I have a Triangle Tube Instinct cranked down to 31%.  Works fine.

We all have our vices. 😂

ChrisJ

Voyager said:

Daveinscranton said:

Depends on how you view entertainment.  I amuse myself no end with heat.  I know.  I should get a life.  I once tried a 4500 watt electric hot water heater on 2,300 square feet of well insulated house with terrific solar gain that had an additional 2,300 square feet of basement shop.  North eastern PA.  Worked mostly.  Had to keep an eye on the weather channel and turn on the tank 3 days ahead of bad weather to heat the slab.  ICF construction.

The reason I did it was because most everyone was trying to sell me a 250,000 btu boiler “to be on the safe side”.  I did eventually put in an 80,000 btu mod/con Munchkin.   Loved that thing.   Alas, it died at age 14, with all its design flaws, I still loved it.  $7 actual maintenance cost in 14 years. 

My actual heat requirement last night at -10 degrees F was under 40,000 btu an hour.   I have a Triangle Tube Instinct cranked down to 31%.  Works fine.

We all have our vices. 😂

I like a Kurt DX6.

Voyager

It is amazing how much heat can be stored in 45 tons of concrete. The boiler has not run for nearly 4 hours now and the temp is still rising in the workshop. The outside temp is now up to 20 degrees.

Voyager

ChrisJ said:

Voyager said:

Daveinscranton said:

Depends on how you view entertainment.  I amuse myself no end with heat.  I know.  I should get a life.  I once tried a 4500 watt electric hot water heater on 2,300 square feet of well insulated house with terrific solar gain that had an additional 2,300 square feet of basement shop.  North eastern PA.  Worked mostly.  Had to keep an eye on the weather channel and turn on the tank 3 days ahead of bad weather to heat the slab.  ICF construction.

The reason I did it was because most everyone was trying to sell me a 250,000 btu boiler “to be on the safe side”.  I did eventually put in an 80,000 btu mod/con Munchkin.   Loved that thing.   Alas, it died at age 14, with all its design flaws, I still loved it.  $7 actual maintenance cost in 14 years. 

My actual heat requirement last night at -10 degrees F was under 40,000 btu an hour.   I have a Triangle Tube Instinct cranked down to 31%.  Works fine.

We all have our vices. 😂

I like a Kurt DX6.

Vises are not my vice.

Solid_Fuel_Man

I heat with wood only. I do have a Weil Mclain ECO70 which is turned down to to 45,000 btu but it has been valved out since I used it to preheat my wood boiler in the fall. 

I heat the slab (6" thick with 1/2" pex 4" deep) once a day for 4 hours. The slab releases heat for the remaining 20 hours. Super insulated house 3200 square feet. Outdoor temp and wind have little affect. Basically I put in 7 sticks of wood if it's above zero, and 9 if it's below zero. Close the boiler door and walk away until tomorrow. 

Heating is most definatly one of my vices. 
And old cars, and construction, and mid century stuff....and....

PC7060

haha That’s too funny. 14 degrees here and I got up 630am today and hooked up my combustion analyzer to my HTP UFT80.  The numbers looked great.  The units was running at 36% with 116F SWT / 100RWT. Running the numbers I’m heating around 3200 SFT above grade and another 1600 below grade on 29KBTU. 

Yep, I’m a geek. I just can’t help it. 

Solid_Fuel_Man

99.21%!!!! Man I thought I was doing well at 97%....... 

ChrisJ

What is "net efficiency"?

PC7060

Good question. The flue gas temperature minus the incoming combustion air are the primary drivers for both gross and net numbers but the difference is whether or not the flue gas are condensed to capture the latent heat. Net assumes 100% capture of the latent heat of the water in the flue gas / gross assume none of the water is condensed. The very net efficiency high numbers need to be taken with a grain of salt since it’s not possible to condense all of the flue gases.  

Per https://www.kane.co.uk/knowledge-centre/what-is-the-difference-between-net-combustion-efficiency-and-gross-combustion-efficiency

“Net combustion efficiency calculations assume that the energy contained in the water vapour which is formed as a product of combustion is recovered and is not exhausted from the flue or stack. Gross combustion efficiency calculations assume that the energy contained in the water vapour is not recovered.”

Daveinscranton

I have pretty much given up trying to measure true efficiency.  Closest way I could think of was gallons of propane and gallons of condensate.  And taking into account stoichiometric relationships.  With the flue temperature as cold as possible as it exits a heated space.  More of a curiosity or intellectual pursuit unless huge dollar amounts of fuel are consumed.  Still, I like the idea of keeping the heat in the house rather than trying to heat the atmosphere.  Dry ice in the flue or weighing silica gel in the flue don’t seem practical.  Probably not very safe either.  I thought about it though…

Bruce MacNeil

A common - and serious - error when installing basement or slab in-floor is not insulating the edge of the slab. The effects of this oversight are magnified when the rest of the structure is quite well insulated.

Voyager

Bruce MacNeil said:

A common - and serious - error when installing basement or slab in-floor is not insulating the edge of the slab. The effects of this oversight are magnified when the rest of the structure is quite well insulated.

I would have to go back and check my spreadsheet to get the exact proportion of heat loss through the slab edge, but I remember being surprised at how large a percentage of the total heat loss was through the slab edge. Definitely something to consider when pouring the slab.

I have try to retrofit mine, but that requires digging on two sides of the building and the foam would stick out away from the building since the slab was poured right to the edge. Much better to place the insulation before the pour so that the sill plate would cover the edge of the insulation.

GroundUp

I just have to wonder how this workshop is insulated and sealed. Even with the poorly insulated edges, 26 BTU/ sq ft seems pretty high with a 0 degree design. I have a 40x40x14 at home with 2x6 studs walls and R19 batts/ R40 blown cellulose attic along with two 12x12 doors, one service door, and five 3x4 slider windows which will stay 70 inside with a 39k electric boiler at -30F design. I can't remember what the heat loss actually came back at, but I think it was around 20 BTU/ sq ft. Then I also have a 32x48x10 with 5" thick solid closed cell foam walls and ceiling (walk-in freezer panels) and a 9x16 door with two service doors, and three 3x3 casement windows. The heat loss there is about 17,000 BTU at -30F so about 11 BTU/ sq ft. This building is actually funny- I have 25 four foot LED lights in there and when it's above 10 degrees outside, the internal temp will actually rise a few degrees from turning the lights on and my own body heat. Above 40 degrees outside I have to open windows. Both are radiant slabs with 2" XPS underneath and around, but the 32x48 had some similar issues to you with the exterior contractor cutting off half of the perimeter foam so he could get his base trim on.

Solid_Fuel_Man

A good day for a heating guy to test design....

ChrisJ

Solid_Fuel_Man said:

A good day for a heating guy to test design....

What's "D" mean?  I'm not familiar with that on a car.

Voyager

ChrisJ said:

Solid_Fuel_Man said:

A good day for a heating guy to test design....

What's "D" mean?  I'm not familiar with that on a car.

D = Drive in an automatic transmission car.

ratio

Voyager said:

ChrisJ said:

Solid_Fuel_Man said:

A good day for a heating guy to test design....

What's "D" mean?  I'm not familiar with that on a car.

D = Drive in an automatic transmission car.


I think @ChrisJ was making a funny…

thegreatcornholio

lol! I PrOpErly DeSiGned my system that’s why it doesn’t work!😂🤣😂..look at how well this one that was done incorrectly is doing!!..wow. Your boiler needed a bare minimum 54,000 output btus period. But, at least you did it the riGht way!?..

Voyager

GroundUp said:

I just have to wonder how this workshop is insulated and sealed. Even with the poorly insulated edges, 26 BTU/ sq ft seems pretty high with a 0 degree design. I have a 40x40x14 at home with 2x6 studs walls and R19 batts/ R40 blown cellulose attic along with two 12x12 doors, one service door, and five 3x4 slider windows which will stay 70 inside with a 39k electric boiler at -30F design. I can't remember what the heat loss actually came back at, but I think it was around 20 BTU/ sq ft. Then I also have a 32x48x10 with 5" thick solid closed cell foam walls and ceiling (walk-in freezer panels) and a 9x16 door with two service doors, and three 3x3 casement windows. The heat loss there is about 17,000 BTU at -30F so about 11 BTU/ sq ft. This building is actually funny- I have 25 four foot LED lights in there and when it's above 10 degrees outside, the internal temp will actually rise a few degrees from turning the lights on and my own body heat. Above 40 degrees outside I have to open windows. Both are radiant slabs with 2" XPS underneath and around, but the 32x48 had some similar issues to you with the exterior contractor cutting off half of the perimeter foam so he could get his base trim on.

Since it has been four years since I built my shop, I went back to my spreadsheet to refresh my memory. I used R-22 for the walls (R-21 insulation + 3/4" OSB). I used R-19 for the ceiling as the contractor's document wasn't clear. It says the ceiling has R-19 faced and unfaced insulation. I am not sure if that means R-19 with different insulation types in different places or if it means R-19 faced on the bottom with R-19 unfaced on top of that for R-38 total. The latter would be what I would expect in a home in my area, but I don't think workshops have that requirement. Since getting into the attic requires taking down a sheet metal access panel, and I wasn't curious enough to do that, I just used a conservative value of R-19 for the ceiling.

I used a 60 degree delta T assuming 70 inside and 10 outside as I believe these are the numbers I found at ASHRAE for my area. I generally maintain the shop at 60 to 65 so that is still close to 60 delta T when it is 0 outside. My total heat loss computed to 40,700 BTUH. This consists of:

Ceiling - 4,851 BTUH
Walls - 5,340 BTUH
Windows (8) - 1,613 BTUH
Doors (2) - 504 BTUH
Overhead door - 1,440 BTUH
Infiltration (0.8 changes/hour) - 18,889 BTUH

for a total requirement from the slab of 32,636 BTUH or 21.2 BTUH/square foot to heat the building. Now adding in the floor losses:

Floor edge - 4,708 BTUH
Perimeter loss (4' band around slab perimeter) - 2,340 BTUH
Interior bottom of floor slab - 1,020 BTUH

for a total of 40,705 BTUH total required from the boiler.

I used the Zurn Radiant Heating Design and Application Guide as my key reference document.

ChrisJ

ratio said:

Solid_Fuel_Man said:

A good day for a heating guy to test design....

What's "D" mean?  I'm not familiar with that on a car.

D = Drive in an automatic transmission car.

I think @ChrisJ was making a funny…

Yeah I was

I've spent 80% of my driving without D being an option.

My left leg isn't broke.  Yet. 

Voyager

ratio said:

Voyager said:

ChrisJ said:

Solid_Fuel_Man said:

A good day for a heating guy to test design....

What's "D" mean?  I'm not familiar with that on a car.

D = Drive in an automatic transmission car.

I think @ChrisJ was making a funny…

I thought he was just a manual transmission man like myself. 😁

Voyager

ChrisJ said:

ratio said:

Voyager said:

ChrisJ said:

Solid_Fuel_Man said:

A good day for a heating guy to test design....

What's "D" mean?  I'm not familiar with that on a car.

D = Drive in an automatic transmission car.

I think @ChrisJ was making a funny…

Yeah I was

I've spent 80% of my driving without D being an option.

My left leg isn't broke.  Yet. 

Likewise, up until my 1994 Chevy needed to be replaced in 2014 and all I could get in a 2500HD was an automatic. Well, I think you could still get a manual with a Diesel engine, but I had no desire for a diesel and its higher cost to buy and maintain. And then my work commuter Sonata finally needed to be sold last year (I retired a few years ago and just didn’t need three vehicles) and that was my last manual car as my wife’s Equinox is automatic. I still much prefer standard shift and at least both of my motorcycles are still standards.

EBEBRATT-Ed

I found a 2007 F150 totally stripped down. Was a TN. no rust truck traded in in CT. Was in like new condition when I got it in 2016. 93,000 miles 6 cyl and best of all equipped with "a millenial anti theft device" 5 speed. As long as it runs I will never get rid of it

Solid_Fuel_Man

Oh my passion for manual transmissions is very deep @ChrisJ @Voyager believe you me! That is my 2020 work van I bought last year. Of course no manual option....and I absolutely would have bought one if it was an option! 

Off topic as we are now, I'll post a picture of the 3+OD transmission I sourced from a 1979 Mustang, machined and adapted to my 1959 Galaxie so I could have overdrive.
Colum shifted 4 speed I might add...makes for some fun having the only 4 on the tree that anyone has ever heard of. 


Had to do extensive machine work on the  column and linkage to make it all work.