Radiant Barrier (Dallas, Howe: rentals, insurance, homes)

[lh_newbie]

Radiant barriers shouldn't even be looked into unless you've already done three things (assuming you have a vented attic space with "ceiling" insulation):

1. Increased attic insulation to R-49 as recommended by DOE
2. Have adequate ventilation in the attic - meaning plenty of soffit vents and ridge vents.
3. Sealed/insulated ductwork

Realistically, if you have these things completed, radiant barrier is basically not needed. Save the money you'd spend there and put it into your next HVAC replacement, buying the most efficient unit you can afford. On any home 10 years old or older - you will most likely see a 50% decrease in your peak summer cooling bills if you do these items (and the HVAC). We did this. Our heating bills are down over 30%; cooling bills down over 50%. And we still have crappy, single-pane aluminum windows in most of the home. Please summer cooling bill for a 1976-built, 2576 sq ft home in 2008: 1,529 KwH or $220 - and we keep our AC at 75 degrees. No radiant barrier at all - and we don't have the most efficient unit on the market - we have a dual-speed, 16-SEER unit (13 SEER is the federally mandated minimum - I've seen units as high as 21).

Brian

[loves2read]

radiant barrier does help--the three items you mentioned have the more efficient ROI though and are just easier to do as a retrofit

I know that installing a higher SEER unit is supposed to also provide significant savings but some studies I read said that under high-heat conditions the efficiency of the A/C unit to actually operate at that SEER rating is usually significantly reduced--so that a 16 SEER rarely operates at that level once the temp gets above 95 or so--of course A/C with lower SEERS are also operating at reduced efficienty as well...

[loves2read]

NRGPro--have you been in an attic that has had radiant barrier foil or decking installed...
I have and I can tell you the attics are cooler than homes W/O radiant barrier

[lh_newbie]

Originally Posted by loves2read

radiant barrier does help--the three items you mentioned have the more efficient ROI though and are just easier to do as a retrofit

I know that installing a higher SEER unit is supposed to also provide significant savings but some studies I read said that under high-heat conditions the efficiency of the A/C unit to actually operate at that SEER rating is usually significantly reduced--so that a 16 SEER rarely operates at that level once the temp gets above 95 or so--of course A/C with lower SEERS are also operating at reduced efficienty as well...

SEER ratings are standardized. They are measured at 75 degrees. Since the outdoor unit exchanges heat with the surrounding air, of course the efficiency goes down as the external temp goes up (higher air temp means less differential temp between air and heat exchanger temp, so the air will absorb heat at a slower rate). And as you state, a 16 SEER unit is still more efficient than a 10 SEER unit at the same outdoor temp - what you compare is the relative efficiency with SEER, not absolute efficiency. It's also important to ensure your outdoor unit isn't sitting in the sun (and getting heated up - since that decreases efficiency).

I have seen some new systems coming to the market that even include a "misting system" on the outdoor unit. Some folks put up misters around their patios and turn them on when it's hot outside, lowering the ambient air temp by 10-15 degrees (unfortunately, raising the humidity as well). Since the outdoor AC unit doesn't care about humidity, it totally makes sense to me. I am contemplating setting up a small relay, hooked to a hose and a couple misters around our compressor. Since we have a 2-speed compressor, I'm thinking it would be cool to have the "high" mode also trigger the misters. Yup, I'm a tinkerer. I have a clamp-on ammeter (measures current through a cable) that this summer I'm going to connect to the feed into the compressor, kick it on high, then while I'm monitoring amperage - using the hose, throw a light mist around the compressor to see if the amperage drops to determine if it's worth my time/energy to build an automated system.

[dixierambler]

Originally Posted by lh_newbie

I am contemplating setting up a small relay, hooked to a hose and a couple misters around our compressor. Since we have a 2-speed compressor, I'm thinking it would be cool to have the "high" mode also trigger the misters. Yup, I'm a tinkerer. I have a clamp-on ammeter (measures current through a cable) that this summer I'm going to connect to the feed into the compressor, kick it on high, then while I'm monitoring amperage - using the hose, throw a light mist around the compressor to see if the amperage drops to determine if it's worth my time/energy to build an automated system.

I would really be interested in the results of your experiment. Like you said, makes sense to me. Sort of a hybrid residential chiller system.

As for radiant barriers, I agree that in order for them to provide top performance, increased insulation and ventilation are prerequisites. But even without these prerequisites, radiant barriers can provide some minimal to moderate improvement over attics without radiant barrier.

Alternatively, there is now quite a bit of new evidence coming from building science promoting sealed attics as being more efficient. There seems to be solid evidence and science supporting it, but I think most of this is being driven by the spray foam industry. Just another alternative to consider.

[sonnytris]

I agree and I also will purchase the radiant barrier 48 inch foil and install it with one guy helping me? I see a small draw back and that is that i do not have the ridge vents? will the hat air from soffiets and thru the back of the RB foil get the air thru my static hawk vents? It has to go somewhere and hot air will find its way to the closes vent? right
will appreciate any help prior to me doing this
sonny in corpus

[loves2read]

think it all depends on prevailing winds--you could install a solar power tubine or roof mounted wind turbine--make sure it has the widest opening you can get--that moves more air volumn

check out gardenweb.com for remodeling HVAC, and house building forums about installing mister for outside AC units--some posters have done that and discuss how to do it
same with the radiant barrier info/wind turbines...

[NRGpro]

Most everyone on here seems to be pretty open minded and not opinionated...I hope I come off the same way. It's going to take an open mind grasp what you will digest below:
I don't how much time anyone has spent in the energyconservation, insulation, hvac, solar, energy manangement or building industry but I've been a licensed contractor since '78 starting the frigid winters of Michigan and moved to the desert 29 years ago. My background is extensive in all the above fields.
I'll start with a broad but compelling opinion: Much of what everyone hears about saving energy is either wrong, misapplied or installed in the wrong climate.
Anyone in here raised in a cold climate? A show of hands? Ok, you, over there...remember growing up as a kid in the winter? Watching it snow outside? Remember what you had to do before going outside? Right, put on sweater. Really cold? A jacket over the sweater. Insulation, works great! The R factor resists (keyword here), the heat flowing out of your body so you can play all day. More is better right? So is deeper insulation in your attic? DEPENDS ON WHERE YOU LIVE.
Next question, would you do yard work in Dallas wearing a sweater or a down jacket? Perhaps a wool hat? No? Why not? Don't you want to keep the heat out with insulation? INSULATION RESISTS, STORES THEN RERADIATES HEAT INTO YOUR DALLAS HOME FOR HOURS AFTER THE SUN GOES DOWN.
Want proof? This is the perfect time of the year to prove many of the above and below listed personal observations and physics.
Springtime...great weather...cool nights and just starting to get warm as the sun gets higher in the sky and stays up longer. Everyday more and more infrared radiation beats into your attic insulation. If you are not using your A/C by now you soon will be.
Your homework (and proof) is simple: You don't even need a thermostat, pen or paper to graph it but if you did, you would really be surprised.
When you get home from work (twice per week), go up in the attic at 6, 7, 8, 9 if you can and feel the attic temperature. It's cool outside. Touch the roof, there's your proof...it's almost cold from deep space irradiation.
But the attic is warm??? Where is is this mystery heat coming from? Stick your hand down inside the insulation...it's warm.
Insulation, having a resistance to heat, has been storing it for you all day, just to make your A/C run longer and your home more uncomfortable. Here's a real wake up call for you data collection types: Get a thermomter or digital thermometer from Radio Shack and measure the hottest air in the attic...get the hottest temp you can record. Now place it 1" below the surface of the insulation about 2-4 pm. You will find the insulation to be 25F to 30F hotter than the hottest attic air temp you have recorded.

"But my house has vents". Sure, but like someone just mentioned, are they open? Funny how the new home inspector from the city overlooks this important item. "But I have a ridge vent". Ridge vents don't work unless there is a breeze. I know, I've tested them with smoke. We built an energy home in '91 and used ridge vents and tripled the soffit venting. In may the homeowner (and close personal friend and builder who built the house), called me up: "I just installed a pull down ladder in the garage and the attic is like an oven!
Knowing this would affect the electric bill I stopped by. The attic was 148F! I could see light streaming into all the open soffit vents around the house but no air movement? I went into my truck and got a bottle of test smoke and puffed it up under the ridge vent...nothing, it just sat there. "How could this be possible?" After thinking about the design it's basic logic:
Which fluid (air is a fluid), is more dense? Outside air at 100F or attic air at 145F? Outside air.
Which way does hot air go? Up or down? Down.
What pressure is in the attic to drive air? Aside from 5' of stack effect, virtually nothing, same as ambient.
So a ridge vent is designed to allow a less dense air to displace air with higher density (also weighs more), and fight gravity by traveling DOWN the slope of the roof to get out? Doesn't happen. Ironically, the hottest attic I've ever been in was in Dallas TX and has black roof, facing South on one wing, had silver paint under the roof deck and full ridge venting on every peak. Important to note, a burned out Home store fan was up near the peak and out of curiousity I crab crawled up the steep 8/12 pitch roof to hold my hand over the dome of the burned out fan. Hot air was pouring out but nothing...absolutely nothing could be felt exiting the ridge vent.
Listen, don't take my word for it, get on a ladder and find out for yourself.

Next: is glass transparent to infrared heat? Stand behind a window with the sun coming through...feel warm? There's your answer. Fact is, glass is amost transparent to infrared heat which means it passes right through it. And what is fiberglass made of again? And what kind of heat is most prevelant in attics in hot climates? Infrared.

Next: Radiant barriers placed up against your roof deck is the worst possible thing you can do aside from adding more insulation (sweaters in Dallas), in your attic. Fact: We have been building homes in Phoenix without any insulation since 1986. There's one now being framed that's wrapped in radiant barrier and the builder is now cutting sizes of the new units by 50%. We have been for years. Radiant barrier has to not only be designed correctly (must be dust proof), installed correctly (so it works winter and summer), and most importantly...wrap all your ducts if they are in the attic. Google "Duct Wrap" and the #1 hit is the best product ever made for wrapping ducts. HUGE benefits, even during the off cycle.

Ok, stepping down off my soap box. Anyone have any specific questions feel free to drop them by here and I'll give it my best shot.

[NRGpro]

PS: a side note on the Dallas house listed in my last post. The home owner's wife told him: "The day that silver paint was put on the house got hotter and the A/C never shut off". He dismissed it but he's not home all day. He's logical and just spent $2000 on energy saving silver paint, he doesn't want to hear the bad news.
We installed a radiant barrier correctly, installed a German attic fan, wrapped his ducting and installed a solar tube.
His home is now comfortable, the A/C off cycles are longer than the on cycles and his bill went down 34%.

Another thing to not purchase: Solar attic fans. "Up to 1250 CFM" is the claimed performance. Ever see ANY of them with test results? No? You know why? Because best case scenario, pointed South at noon the move between 275 CFM to 310 CFM. My work van will go "up to" 300 mph if I drive it off of a cliff. I imagine if a tornado would happen to find it's way over your solar fan it may move "up to 1250CFM" Really, think about it, how much power is 10 watts really going to move? Or now the really big gun, the 20 watt!!! You have thousands of cubic feet of hot, stagnant, energy consuming hot air and hot insulation in your attic and a 20 watt solar panel (hopefully pointed towards the sun), is going to cool your attic?

They sell these at the home show and the display unit is plugged into a 60watt DC converter....blows like a hurricane at the home show. People walk by and are amazed! "Yes, I need one of those" and sign up for an installation. More homework: Do a blog search on "Solar attic fan complaints" and see what you get. Even in Hawaii they don't work and it's not very hot there and really sunny. We will soon have a 110 watt unit available, stay tuned.

[scarmig]

I think the point of the soffit vents is to complement the ridge vents... hot air moves out of the upper opening, pulling in cooler air from the lower opening. Convection, basically.