Heat Loss Calculation Data?

[Sawyer]

I am sizing for panel rads.

Would I be correct assuming that window sq/ft area entered into a heat loss calculator should be subtracted from the wall area and then this new total wall area entered in as total wall area?

If I do not do it this way it seems the calculator keeps the initial total wall area and calculates the loss for this plus the loss for the windows.

 

[tom in maine]

I never usually deduct the windows and doors from the walls unless there is a very large area involved.
The difference is not that much more.

It keeps things simpler and gives me some fudge factor in case I missed something.

 

[Floydian]

Hi Sawyer,

what program are you using?

The academic(free with book) version of Siegenthaler's software is set up so you enter the total wall area without subtracting for windows/doors. When you enter the window area and values it automatically adjusts.

You could double check the software also. area / rvalue x delta t = heat loss

Are you going to use TRV's on the panel rads with constant circulation?

Noah

 

[jimbom]

I always removed the door and window area. The final heat load is going to be plus or minus a certain amount for a certain level of confidence. Why not have that +/- on the most accurate calculation?

 

[Sawyer]

The room is 20’x28’ with 9’ wall and a 6/12 cathedral ceiling. To correct for the 6/12 ceiling I am using 10.5’ walls rather than 9’ walls. Total exposed wall area is 798. There is also a 20’ heated wall to kitchen which I am not using in the loss calculator. I have 320 sq. feet of window area (triple pane) in the living room. The window area is significant.

I am using Uponor’s Design calculator. 18,135 BTU/hr loss @ 69* design, 9116HDD. Build It Solar, 16,870 BTU/hr. I did notice this figure only went to 18344 when I used the full wall area which changed much less than I suspected. Maybe whether window area is subtracted or not does not matter much with a well insulated wall. When I used Slant Finn I got 32,000 BTU/hr loss!

 

[Floydian]

A couple more things...

Are you adjusting your whole wall/ceiling r-value counting the framing factor? I think a 15% percent framing factor is normal when figuring whole assembly r-values.

And the real X factor in heat loss calculations is the air exchange rate unless you have had a blower door test done. They cost a few hundred bucks and are becoming mandatory in new construction is some places.

Noah

 

[Sawyer]

Hi Sawyer,

Are you going to use TRV's on the panel rads with constant circulation?

Noah

Noah, I was planning on using the wall thermostat with a pump for zoning. I am thinking this should work good in this room. In your experience do you feel a TRV would give better "felt" control??

 

[Sawyer]

A couple more things...

Are you adjusting your whole wall/ceiling r-value counting the framing factor? I think a 15% percent framing factor is normal when figuring whole assembly r-values.

And the real X factor in heat loss calculations is the air exchange rate unless you have had a blower door test done. They cost a few hundred bucks and are becoming mandatory in new construction is some places.

Noah

"
Are you adjusting your whole wall/ceiling r-value counting the framing factor? I think a 15% percent framing factor is normal when figuring whole assembly r-values."

Noah, I used the R20 value for the walls where the ceilings are R44. I would guess this would cause the calculator to give me a slightly higher loss that the actual ceiling. I should probably run with an adjusted ceiling area and walls at 9'.

I used .3 for air exchanges. All outlets, windows, doors, and penetrations were foamed, then the walls were sprayed with adhesive cellulose insulation. Do you think this is a proper factor for infiltration?

 

[Sawyer]

Using Uponor’s Design calculator, all exposed surface are included without subtracting for windows. 9 foot walls rather than 10.5’ walls and allowing .15 for cathedral slope in ceiling the room calculated at 16,996BTU/hr loss @ 69* design, 9116HDD. I think this will be a good figure to use for sizing panel rads.

 

[Floydian]

Sawyer,

All I can offer on TRV's in what I have read about them. Mostly from Heaterman here, and the pros over at The Wall. I would say from my research that TRV's win the comfort control game without using electricity, but obviously they can't tell your circ when to come on so that's an issue.

I ran some numbers in my calculator assuming:

600 sq ft of ceiling at R40 (r44-4 for framing)

triple pane windows R5? Good choice on the triple panes BTW. $$$ but big plus in the comfort game!

Wall r value I entered R17 assuming 2x6

I am guessing a design day temp of -30* F and 70*F inside temp so 100*F delta T

5880 cu ft, .3 ach Natural

and assuming heated space below

Here is what I came up with:

Heat loss of 13,887 btuh. I think the slant fin program is way off but they do sell heating systems so.....

Good luck,

Noah

 

[Frozen Canuck]

George: I agree with Tom.

It is very typical not to subtract windows & doors unless, like Tom said the area is significant.

One should keep in mind not only design conditions (worst day) but those rare occassions when it is worse than design temp for a long period.

As an example here typical design temp is -40, however there are those rare times (thankfully) when it is colder than design temp for a week, say -45 or -50 sometimes colder, in this senario if one has allowed nothing in excess of the -40 design temp, well then your structure looses heat even though your system is running flat out. No one will be happy.

Rather than trying to "nail it", do your typical calcs with your design temp & keep in mind that having a performance buffer above design temp is a good thing, nothing wrong with a system operating at 75% & satisfying the load while having that 25% still in reserve just in case. Matter of fact many professional designs are done just like that.

BTW I prefer TRV's to have that constant feeling of warmth as opposed to the on/off of other systems of control, just how I like it not saying how you should do it.

 

[Sawyer]

George: I agree with Tom.

It is very typical not to subtract windows & doors unless, like Tom said the area is significant.

One should keep in mind not only design conditions (worst day) but those rare occasions when it is worse than design temp for a long period.

As an example here typical design temp is -40, however there are those rare times (thankfully) when it is colder than design temp for a week, say -45 or -50 sometimes colder, in this senario if one has allowed nothing in excess of the -40 design temp, well then your structure looses heat even though your system is running flat out. No one will be happy.

Rather than trying to "nail it", do your typical calcs with your design temp & keep in mind that having a performance buffer above design temp is a good thing, nothing wrong with a system operating at 75% & satisfying the load while having that 25% still in reserve just in case. Matter of fact many professional designs are done just like that.

BTW I prefer TRV's to have that constant feeling of warmth as opposed to the on/off of other systems of control, just how I like it not saying how you should do it.

I will allow for a buffer, we have unfortunately hit spells of -30 to -40 night time temps and that is when I want to be inside and warm.

Perhaps I do not understand the TRV's, when I went to http://na.heating.danfoss.com/PCMPDF/operation_princip_facelift.swf it appeared the TRV opened and closed also.

I then looked at Diversionary Piping at http://www.pmmag.com/Articles/Column/823dc940b9fc7010VgnVCM100000f932a8c0____ and saw that I could use the thermostat as a master. I see I could also go to a manifold/home run with a master controlling the circulator.

 

[Frozen Canuck]

Lol, yes George I like being inside when it's -40 or worse, it is a good thing to do. Beats the heck out of being outside.

Perhaps Steve or someone else with more exp will pick up on this thread & answer specifics on system design.

From what I have seen these TRV's work best when installed as described in your second link from pmmag, in a manifold or home run piping setup with small variable speed circs so that each zone/room has its own circ & a t-stat controlling it. The article does caution against using this setup in series for good reason.

IIRC & please be advised this is just from memory, the t stat controlled the TRV & the delta P pumps responded to the change in pressure by speeding up/slowing down when the t stat opened/closed the TRV.

When piped & controlled like this it allowed for very small variable speed circs to satisfy loads as all zones were in a constant, albeit slow state of circulation during the heating season.

Or you could skip the TRV's & use EVA's as stated in the article with the t-stat controlling the EVA.

Hopefully someone better at controls will pipe in on this.

 

[heaterman]

All I can offer on TRV’s in what I have read about them. Mostly from Heaterman here, and the pros over at The Wall. I would say from my research that TRV’s win the comfort control game without using electricity, but obviously they can’t tell your circ when to come on so that’s an issu


There are lot's of ways to turn your system pump off and on ranging from a simple room stat/pump relay to an outdoor sensor etc etc. A true variable speed circ like a Wilo or Grundfos will dial itself down so low that it does not matter if it is running or not from either a power or circulation standpoint. I know Wilo recommends leaving power on to their larger circs and provides options to let the circ idle down to nothing based on whatever input you choose.

A good variable speed circ running rads and TRV's is so darn simple almost anyone could install that system.