HVAC Tips to keep your house cool in summer

[jim hardy]

°F to °C
Subtract 32
Halve it
Add 10%
Ans is 1% low, "Good enough for Government work!"

i think it's exact if i add 11.111111111 etc % (1/9 ) , just got to get that implanted in cerebellum...

 

[Sherwood Botsford]

1. When we had to redo our roof we replaced grey shingles with white painted metal. The attic space doesn't get nearly as warm.

2. On the other section of the house with steeper pitch, we increased ceiling insulation to 18" and added some roof peak vents. If the attic space is warmer than outside we get convection from the eaves vents thorugh the peak vents.

3. Part of the house is over a basement. Another part is 2 stories. Open the upstairs and downstairs windows and we get convective flow.

4. One end of the house is in a grove of spruce. Some roof never has sun on it.

 

[Laroxe]

I wonder if just thinking in terms of the temperature is a good idea when what we want to alter is our comfort. I always have the window in the top room open and have all the internal doors open, I open windows on the ground floor that are in shade and get a sort of chimney effect, moving air cools our bodies better, if the air is still we simply drown in our own sweat.. I also use fans, a good idea is to place one of those electronic mister's in front of it that,s sitting in iced water, the fine mist evaporates almost immediately and significantly cools the air. Putting any evaporating surface in the airstream of a fan can help. Moving air and water features characterised Moorish architecture. I've even built coolers from old computer parts with a Peltier unit, these are cheap and great to play with but you need a good insulated heatsink for the side which gets hot and they can only be on for short periods before you change the cooling material. There are lots of video's on you tube about using Peltiers but the higher wattage ones are best, say around 100 watts, my own view is that Peltier units are proof that magic works, they are fascinating and I can't make any sense of the science. You tube even has ideas for coolers just using iced water.

 

[anorlunda]

I still have to double °C subtract 10% and add 32. Getting pretty quick at it .
Dont have a similarly simple algorithm for the other way though.

Live in a place where the temperature hovers around -40 and you'll never have to do a conversion again.

 

[jim hardy]

Live in a place where the temperature hovers around -40 and you'll never have to do a conversion again.

This Florida Boy once went to Quebec's Winter Carnival where that was just about the day's high temperature..
I looked like the Pillsbury Dough Boy , wearing every piece of wool that i own,
much to the amusement of the locals who were walking around with open jackets and no earmuffs or gloves , sipping from bottles.. I was amazed their champagne didn't freeze
As i was contemplating 'White Fang' and Jack London's description of freezing to death in the North Woods,
one Quebecois youth taking note of my bulky "layered" and dazed look said to me "C'mon man, it's only 40."
I just knew he meant +40 Kelvin.

 

[dLouie]

Although I do have an A/C unit, it's a bit small at 600 watts, so I do have to be mindful of heat sources.
I discovered last week that one room in particular got much warmer than the rest of the house, did some IR thermal scanning and found it was mostly due to a single window. It's 2 m², and by my rough calculations accounts for 25% of my total heat flow. So I hung a large aluminized tarp to shield it. It seems to help a lot.

Today it's supposed to be 99°F/37°C, so I may turn on my attic fan. It's a 12 volt experiment left over from last year, and isn't permanently wired.
Currently, it's about 9 am(savings time, so 8 am in real time) in the morning, and the temperature outside is the same as in. About 72°F/22°C.
Attic temperature is 70°F/21°C, so it appears I have a bit of time left.*
Crawl space temperature is a surprising 67°F/20°C. I'd have thought it would be much cooler than that.

*Done!

We find the aluminized tarp is very effective here as well.

 

[OmCheeto]

We find the aluminized tarp is very effective here as well.

Just talked to my sister in San Diego last night. She said she's going to install a silver "TPO" roof this summer.
I didn't know what that was, so I googled it: Thermoplastic Olefin
Basically, a high end aluminized tarp.

 

[OmCheeto]

I ran a garden hose up to the roof and placed three yard sprinklers along the peak.
Around noon and a a couple times mid to late afternoon i turn them on for five or ten minutes.
I see steam coming from the hot shingles and feel a slight difference in radiant heat inside the house.

I'm not instrumented so it's un-scientific

Just ran the numbers, as I can't find my numbers from last summer, and like you, it made a difference:

It would require about 10 gallons per hour to negate my roofs solar input, worst local case.

but it's quite a visual effect and the talk of the neighborhood.
...

If you're not the talk of the neighborhood, you're not doing it right.

 

[sophiecentaur]

Just ran the numbers, as I can't find my numbers from last summer, and like you, it made a difference:

It would require about 10 gallons per hour to negate my roofs solar input, worst local case.

I think you must be using some pretty pessimistic parameters - you don't need to have the roof surface a lot cooler than at its worst in order to get a subjective improvement, I'm sure. If you talk in terms of 1kW / square metre over half of the daylight period, would you really need to evaporate 50l of water? (Sorry but I find Imperial stuff very confusing) 50l is a significant cost every day when you're on a meter. But I guess it would compete well with AC running co

Edit: I was well off-beam about the cost of the water. As an emergency measure it could be excellent value. I could even try it if the coming Summer is as hot as the last one.

 

[gmax137]

. If you talk in terms of 1kW / square metre over half of the daylight period, would you really need to evaporate 50l of water? (Sorry but I find Imperial stuff very confusing) 50l is a significant cost every day when you're on a meter.

Please check this, it's easy to mess it up.
Let's assume a roof area of 85 $m^2$ and 6 hours per day, at $1 \frac {kw} {m^2}$. Then the water evaporated will be about:
$$
85 m^2 \frac {1 kw} {m^2}
\frac {3413 Btu} {kw-hr}
\frac {6 hr} {day}
\frac {lbm} {1100 Btu}
\frac {US gal} {8.3 lbm}
= 190 \frac {US gal} {day}
$$

[Please excuse the odd spacing, I am just now learning LaTeX.]
This seems kind of high, doesn't it? This is 8.5 liter/day, per square meter. I'm not sure what area and time you used @sophiecentaur, to get your 50 liter value.

 

[sophiecentaur]

'm not sure what area and time you used @sophiecentaur, to get your 50 liter value.

Haha - I was just using @OmCheeto 's value of 10gallons as a starter. I should have done my own sums.
I must say, your 190 (albeit tiny US) gallons per day feels more likely. There would be one unpleasant consequence of such a large amount of water over my roof: we have very hard water here and the roof tiles would soon be white with limescale.

 

[OmCheeto]

I think you must be using some pretty pessimistic parameters - you don't need to have the roof surface a lot cooler than at its worst in order to get a subjective improvement, I'm sure.

As you can probably infer from my slowness in response, I'm having trouble coming up with a justification for that number.

As with all thermodynamics problems, this one is giving me a headache.

ps. In my defense, I did say:

...my roofs solar input...

Looking at the google Earth image, I'd say I'm quite lucky in the summer.

With the exception of my eastern neighbor's roof length, all number are heights.

Guessing my A/C bill in the summer would go up if all my neighbors cut down their trees.