Hydronic Baseboard Altitude Derate?

eltigraska

Is there an altitude derate for hydronic baseboards?



Sterling gives a generic altitude factor table for "convective heat value at varying altitudes," but no other manufacturer (that I have seen) publishes any altitude derates. I have called and talked to a few other manufacturers/reps that say there is no derate for hydronic baseboards. In the past I have used the sterling derate just to be safe (even on other manufacturers), but is this really necessary, am I just oversizing?



Thanks

icesailor

Altitude Derate:

I don't understand why you would need to de-rate a closed hydronic system if the internal pressures are equal.

In Denver CO, water is supposed to boil at 194 degrees at the atmospheric pressure that equals the atmospheric level. If you put water into a pressure cooker at sea level or in Denver CO, and you heat and pressurize the water to 3#, it will be boiling at about 215 degree F.  In a closed water system like Hydronic baseboard system, it shouldn't make any difference. If the water temperature in the system is set for 160 degrees, it shouldn't matter where it is. It will still be 160 degrees.

I may be wrong. Tell me if I am.

eltigraska

baseboard derate

I agree that there wouldn't be any derate on the water side. My understanding from the Sterling table is that the derate would lie in the air density differences affecting convection. My confusion lies in the differences in what different manufacturers are saying and if the air density differences truly affect hydronic baseboard outputs.

icesailor

Deration:

I guess I see the concept, I'll have to get my mind around it.

Like an aircraft flying at 5,000 feet sees less air resistance than it does at sea level. Because the air le less dense and there are less air molecules to heat at 5,000;. The same would then apply to warm air or air conditioning.

Interesting thought.

Gordy

deration

http://www.engineeringtoolbox.com/air-altitude-density-volume-d_195.html

icesailor

Elevations:

I understand how it works taking lower atmospheric pressures into gas mixers or blowers.

I don't quite see how much changes when you run 160 degree water through a fin tube and there will be any appreciable difference in the incoming volume of air and the volume coming out or the velocity of the air.

Gordy

Your exactly right

Not enough to worry about at 5000'. If your paranoid raise AWT to 170, or add more base board No?

eltigraska

Derate

Thats pretty much what I've always done, take the conservative approach and just add a bit more baseboard. Sterling does call for a 15% derate in copper-aluminum units at 5000' so not its certainly not inconsequential. The problem is I'm designing at 8000' (~23% derate) and have a geothermal system so my water is around 110F without much room to increase that temperature. The end result is a lot of baseboard, even using units designed for low temp applications. I'm not opposed to designing the system that way, but I'm just curious if anybody else had looked into it in depth and come to any conclusion one way or the other.



Thanks for all your thoughts so far guys!

SWEI

Take a look

at panel radiators, perhaps?

eltigraska

panel radiators

The architect doesn't want them.



At this point i'm more just curious about an altitude derate on hydronic baseboards in general than about the design for a specific project.

SWEI

Architects

often have to argue with interior designers, once the baseboard limitations to furniture layout are brought up.  The winner is radiant ceilings, budgets permitting.

icesailor

De-Rate AC:

In that case, how much do you de-rate an AC unit? Same type of HX.