Dark roof/light roof... heating/cooling...Best of both worlds!

Cecil's Columns/Staff Reports
21

Una

I am not sure of old name, but I was here long ago and then you started charging and I just never got around to paying.

First off, I know my quip about “school of” sounds a little personal since you helped research the article but I was only trying to be cute. I respect and appreciate the work Cecil and Staff do and did not intend to diminish your work. It was a well researched article and I am only picking at nits.

First point:
I was referring to the questioner where he referenced an old column which states:

This is misleading since polished Al actually absorbs slower than white paint. It reaches a higher temperature since it also radiates energy slower. Once we bring up the physics of outer space, it has to be explained properly and it wasn’t. On a roof in atmosphere it is much more complicated so it is best not to even reference the old column. Since it was referenced it should be explained that (a) yes, surface properties can make a big difference, and (b) when you add convection the rate a surface radiates is less important and the rate it absorbs is more important

The Al referenced in the column was from the space reference, and of course this surface will not exist on a roof. It will quickly corrode and commercial Al roofing materials are coated or anodized and will have different properties from polished Al.

Second point – The questioner asked about paint and did not seem to be talking about roofs at all, but the answer and research is mostly about roofs so I stuck to the roof. For walls, I think insulating is harder but planting foliage is easier so my response would again be a guarded “yes, but” in that paint could affect HVAC costs but there are other, first line, options (overhangs!, foliage, …).
Back on the roof: I did qualify that a lighter color surface can be helpful if insulating is not practical but if insulation is practical it should be the first line option. And let me be clear that a well insulated attic includes insulation, proper ventilation, effective sealing of openings, and proper isolation of any ductwork.

Another point I was careful to make is that a lot of the activity on roof coatings is targeted toward commercial buildings. They are applicable to many single family homes with insufficient attic space, but it is appropriate that in answering the question, and referencing specialty coatings, that Cecil also make clear the distinction that his answer is highly dependent on roof configuration, insulation, etc.

22

Not infinitessimal, though a very rough back-of-the-envelope gives it something on the order of 1/100 of 1%. But the total effect also includes energy efficiency – remember, by the 2nd law of thermodynamics, air conditioners put more heat into the environment than they remove from the space they are servicing, always and unavoidably.

23

I live near Boston (and recently re-roofed in light-colored shingles). I doubt that this increases my heating bills, as the Master suggested it would because my roof is usually covered in snow in the winter, which is whiter than any roof I’ve seen.

I have a unheated, well -ventilated and insulated attic with solar hot water collectors on the south (rear) roof of the house (built when Carter’s energy conservation credits were still in effect) The snow on the front (north) doesn’t melt, due to the deliberately optimal solar alignment (neither does the driveway and front yard – an unanticipated and very annoying side effect – my driveway is still thick with ice when everyone else’s has melted. Grrr…) The snow on the back also persists, except in the immediate vicinity of the collectors – a testament to its albedo

For most houses in Boston suburbs, I’d guess that snow largely negates the color of the roof in winter. A full ventilated attic is common here, because it has benefits. True, many kinds of traditional local architecture have steep roofs to shed snow, but those older houses have often been expanded with dormers (reducing the pitch)

24

QUOTE=Elendil’s Heir;12324769]Way to win friends and influence people, Alexov. :rolleyes:
[/QUOTE]

I’m sorry if I sounded curt but I did start off this post with the intention of drawing attention to what is a very effective and cheap way - in the long term - to both heat and cool a house, but noticed in the subsequent entries that it seemed that others had hijacked it and were now talking about something quite different. I had foolishly imagined that a few people, perhaps, would express interest in it, but no, it did not happen. This, to my mind, is not particularly good manners and it happened before with some other post I started some years ago.

In the original post, I indicated that heat recovery ventilation would not work in the winters of climates like NYC’s, which are very cold in winter. During spring and autumn and summer, however, it might be quite good.

I also gave what I thought was enough info (short of a direct plug which could be seen as an attempt to get a free advertisement! ) to enable anyone to find, on the internet, the people who make this system . I have no commercial or other connections to them whatsoever.

Given that there are probably many millions of houses in large parts of the US, for example, that do not have very cold winters, then possibly tens of millions of you could benefit from it. Must be something wrong with that, I guess, since people, apart from MeDrewNotYou ingored the idea.

Ps, while it would be nice to think I might influence a few people into looking into it, the purpose of my second post was not to win friends. Sorry!:smack:

25

You may want to consider that the climate ranges of the United States, and I’m not just talking about the incredibly small area of NYC, have wide enough temperature swings that the system you described is not a viable system. I’m especially concerned about the summer cooling aspect - I find it difficult to imagine a house where the loft/roof space is cooler, even in the depths of night, than the ambient air at ground level. Between the fact that the heat has risen through the house and that the loft/roof will have a thermal load to dump over time, I don’t see what advantage the system has over opening windows.

26

While reading your post my eyes darted to check your Join Date, your post read like astroturf. This phrase in particular blew my detector:

Additionally, this forum is intended to discuss Cecil’s columns. If you want people to discuss this HVAC system, you’re in the wrong forum. The faux pas were all yours.

27

Madman2001 said:

Not really. If the energy being reflected is reflected in the visible spectrum, then it is mostly going through the atmosphere. If it is being reflected in the IR spectrum, then it will be trapped and heat the atmosphere.

Or, more conventionally, the black surface absorbs the visible light, heats up, then radiates heat in IR. Same diff. Same result. Greenhouse effect.

Reflecting the energy in visible light is the attempt.

Alexov, welcome. The typical process here is to combine comments on one column in one thread. So if there are different aspects to discuss, they will be in one place. That may mean your comment gets less attention than you think it deserves.

As far as the specifics of your post, I think Una has addressed them directly. Humidity control is a big factor.

28

First, the “heat recovery system” you are describing has existed for decades, it is quite common in commercial, institution, or industrial buildings but I have seen it in some residential settings. Here at work, we call them transfer fans, they don’t reclaim hot air from the attic space but from high ceiling spaces, skylights, cathedral ceilings, etc… In the winter they recirculate the heat into the building and in the summer they exhaust the heat and humidity outside.

This makes no sense, why wait for your “roof space” to cool down to pump air out of it? Why not draw cooler fresh air straight from outside or from cooler interior areas?

As others have said, If you’re interested in conserving heat and energy, insulation is the most important.

29

Why stop with white roofs? This article discusses painting your driveway white as a way to offset your carbon footprint.

Joe

30

Yes, there is a paint that will reflect heat.

I used to work for Sherwin Williams when this product first came out. They did a demo where they coated one side of a board with it, then put a heat lamp about a foot away. The side facing away from the lamp stayed cool to the touch even after a few hours under the lamp.

31

Did they test a control, i.e. an unpainted board, to prove it did get hot on the far side?

32

Yes they did. There was a definite difference in temperatures from the painted board VS the unpainted board. We even busted out the infrared thermometer to test the difference between the two. I can’t remember what the numbers were, but the stuff works.

33

Silly me for assuming that somewhere in the US, there might be a similar climate to that of the Mediterranean, which is what we have here in Melbourne. In summer, you can open your windows but if you happen to live near a busy road, you might enjoy getting a cooler house without that noise and those fumes.

Someone else on this thread has accused me of trying to get in a sneaky advertisement on behalf of the company that makes this system; utter rubbish, but can I prove that? No, so the accusation will stick. This is the modern world?

Someone else has said that since their roofspace has a wintertime temperature of maybe 50F, how would this system help them? Meaning that it would not.

How it might help is that the 50F in the roofspace can be pushed inside the house, so your gas/electric heating doesn’t have to heat up from 0 or whatever. Your heating bill should be less. But consider what your roofspace might be in spring or fall.

And yes, to those of you who point out that this is not a new idea, I would very *very *surprised if this hasn’t been done before, long ago, when fossil fuels were very very cheap. Maybe we could look at the idea again? Maybe there could be advantages.

No, not according to you experts. So, I give up. Too much negativity in this place. Better I stick to reading my emails from Cecil, whose recent item about painting roofs as a means of saving energy prompted me to start a thread based on another system which seems to work very well in our very unusual climate. Outside today, it’s about 23C but inside it’s already 26. Haven’t turned on the gas heater all year.

34

Lestrade, if my joining date is of any relevance at all, and you think it is so bad that I even dared to mention a commercial system that might be beneficial to many people, then I hope you have the nerve to slander Cecil also after you read his comments on this item: http://chicago.straightdope.com/sdc20100415.php
Please, hop right in and give him the benefit of your thoughts… Start your own thread for the purpose?

35

You need to step back and take a deep breath. No “accusation” is sticking.

My HVAC recirculates air to heat it, through a return duct system. This sort of system is the predominant one in this country. Fresh air typically enters via leakage and dedicated air changes from the occupants.

What you need to understand is that there are some fatal flaws in the system you’re talking about. This is not a character flaw or something you need to take personally. And there is a potential communication issue; you have not explained your system very well - for example, you still haven’t addressed how the loft air is cooler than the ordinary ambient air in the summertime. I think that’s a critical flaw in the system right there - is the reason because of automobile exhaust? How close does a house have to be where automobile exhaust enters a window but won’t enter the loft via the soffits and vents? You see, there are some questions we’re trying to get answer to in order to understand why you say this system has value over a conventional system, and you’re not answering them.

36

Yeah, doesn’t a ceiling fan do basically the same thing?

37

Consider that the system described filters the air from the loft space before pumping it into the house, where as very few windows have filters across them. Well, okay, screens, but not HEPA filters, which is what his described system uses.

38

Not really, the air is removed, filtered, mixed with fresh air, and then recirculated to other areas or rooms that require heating.
A ceiling fan merely blows the warmer air at the ceiling down to counteract the natural convection in a single area or room.

39

Alexov, I’m sorry, I was unclear. I was attempting to explain one potential reason that the focus of the thread wasn’t where you wanted it. I entered an emotionally situation and didn’t give sufficient explanation leaving room for misinterpretation.

I mentioned your join date as that’s often a useful way to identify spammers, they tend to join solely to create their thread and that’s reflected in their join date. You don’t fall into this category, your post was in no way astroturf and, honestly, I apologize acting like a jerk; it was not my intention.

40

Never mind attics and roofs, I recently read about some new interior panels being developed. They look like standard drywall but have a wax core; put them on your studs and paint them as you would drywall. As the room’s temperature rises, the wax turns to liquid and absorbs the heat, cooling the room.