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1.
Dec 26, 2013 11:54 AM ET

I'm not sure...
by Derek Roff

I appreciate your articles, and your efforts to explain building science concepts to us. I'm not convinced that your new definition of heat, which contrasts with all the textbooks and references that I have seen, is really moving comprehension forward.

2.
Dec 31, 2013 9:01 PM ET

Response to Derek Roff
by Bruce Palmer

What, specifically, is the contrast between Allison's admittedly compact definition and those of the textbooks you refer to?

3.
Jan 2, 2014 12:50 AM ET

Question
by Ron Keagle

Allison,

I too am a bit confused by this definition. You say that heat is a measure of how much thermal energy transfers from one object to another because of a temperature difference.

Then you emphasize that heat flows only when there's a temperature difference, and it naturally flows from a warmer body to a cooler body.

When you say that “heat flows only when there's a temperature difference,” it follows that heat does not flow if there is no temperature difference. The distinction of heat that is not flowing shows that heat can exist without flowing. Yet how can heat exist without flowing if flowing is what defines heat?

4.
Jan 2, 2014 3:55 PM ET

variations on heat
by Derek Roff

Responding to Bruce, the term "heat" shows up in lots of fairly basic equations, many of which are relevant to building design at one point or another. For example, the BTU is only a meaningful measurement unit, because we have a definition for the [specific] heat of water. The definition of BTU is incompatible with Allison's definition here. So are the classical laws of thermodynamics.

I can understand what Allison means in his new definition, and I can guess why he chose it. He wants to communicate to readers a more active and functional experience of how heat moves in a house. But I think equating heat and heat flow adds confusion, rather than reducing it. Will it not be confusing to readers, to suggest that adding insulation to a house will reduce its heat? That a really well-insulated electric water heater, that is up to temperature and idling, has virtually no heat?

According to quantum theory, we can't determine whether Schroedinger's beer is cold or not, until we open the cooler. I don't think we need similar confusion when discussing building science concepts.

5.
Jan 2, 2014 6:55 PM ET

It's basic physics, not a new definition
by Allison A. Bailes III, PhD

What I've stated above is just basic physics that you can find in just about any introductory physics book. I haven't redefined anything. Heat flow is analogous to work. It's a transfer of energy, just as work is.

And speaking of work, there is an exception to what I said above about heat flowing only when there's a temperature difference. When work is done on or by a system or when there's a phase change, you can have heat flow without a temperature difference. Building enclosures, however, usually don't do work or have work done on them, and few have phase change materials to simulate the effect of thermal mass.

6.
Jan 2, 2014 7:01 PM ET