A/C strategy

[saichele]

Nothing to do with Gambling...

Anybody have any conjectures on whether it's better to turn the AC off when you go to work or not? When I come home, it results in a 'long burn' of about 30-45 minutes, during which time I can just imaging the meter smoking out at the side of the house. Or, I can let it go duringhte dya and not have to think about it.

Steve

 

[wahoowad]

get a programmable thermostat and set it a few degrees warmer during the day so it will run less. Then have it set to drop the temps back down a bit while you are home.

I need to follow my own advice. How much are basic programmable thermostats?

 

[Eric Johnson]

They're pretty cheap, wahoowad. You can pay over $100 for a really fancy one, but the basic models start at around $20, I believe. Last winter I had trouble finding double-pole 240v models, but everything else is readily available.

My strategy for coping with the heat in recent days has been to (finally) get around the cleaning out the basement. I haven't found the previous owner's long-forgotten stash of cash and jewels (yet), but I did come up with a bunch of interesting artifacts from long ago, including a nice iron fireplace poker and some old knob and tube wiring.

 

[saichele]

I looked at that (had one at the old house) but the cost runs up fast with the fancy pants furnace we have. (Still crappy ductwork, but a fancy furnace) It's a 'dual stage' with AC, and I couldn;t find anything under $100 when I went looking last year.

Steve

 

[Sandor]

What do you keep the thermostat set on?

What is your indoor humidy level? This is important.

 

[saichele]

about 75 at night, 80-82 daytime. Humidity stays around 50-60%, although it's not managed for that specifically.

Steve

 

[tradergordo]

Every air conditioner dehumidifies the air, a good air conditioner should be a good dehumidifier. I also do the programmable thermostat, 77 when I'm home and 83 when I'm not.

 

[Roospike]

I work from home so I'm here all the time so , 72° 27 -7 . Older 100+ year old 2 story home ( remodeled ) no way for central A/C so we have 5 wall A/C units ( like window units ) 2 down stairs and 1 in each bed room up stairs . The 2 down stairs run 24 -7 and the 3 up stairs run only at night set @ 73° #1. older home 1800 sf #2. Five wall A/C units #3. running A/C's at 72° #4. Family of 5 #5. some one home all the time. Your thinking HIGH electric bills right . In the spring and fall our electric bill runs $60. - $75. And The mid summer our Electric bills run $90. $125. ( gas water heater only $25. - $32. year around ) It pays to button up your home. We had the programmable thermostat in our last home ( modern 70's style ranch- 1500 sf ) with central A/C and heat . We droped our A/C-electric bill $40. a month with the programmable thermostat. And our average electric bill in the summer in that home with central A/c was $180. - $220. a month AFTER the programmable thermostat.

 

[Sandor]

I like to shoot for an indoor humidity level of 50% or below. Anything above that will encourage mold/mildew growth. Anything above 60% and things start to feel cool and clamy and bathrooms will start to funk.

The last several homes had a/c units that were too big. Did not run long enough to effectively dehumidify to the 50% range. I live by the Chesapeake Bay and ITS HUMID. Mold is a huge issue around here.

The solution I found was to use a small Energy Star window unit. Picked up a 9000 BTU 10.7 EER unit for like $125 at Lowes three years ago. Set the pup at 73 and let it run. Amazing how much moisture it pull out of the home and is cheap to run. No ductwork losses! On low/mid eighty degree days, thats all thats needed for the entire home.

Today its 102F outside with a dewpoint of 80.

Inside the 1500 sq ft rancher I'm in now, the humidity is 47%. The temp is 78. The window shaker kept the home below 78 until about 11 this morning. The big unit will cycle to about 9 tonight. The window unit runs nonstop and is set at 73.

To address your question about thermostat settings, I would leave it at 78. Trying to cool the home when you get home at 5pm when its the hottest out just does not make sense to me. The unit is certainly the least efficient at this time.

Also, get a small digital weather station with the remote sender that reads temp and humidity. See what your home sits at. There is a big comfort difference between 50 and 60 percent humidity. You may find if you dry it out inside, you can be comfortable with a higher thermostat setting.

 

[jabush]

I set mine at 79 and leave it alone. It stays a little cooler downstairs, which is where we spend most of our time. Also, lots of ceiling fans, on low, keeping the air moving. If you shut down the system or play with the settings, all the stuff in the house is holding heat. IMO if you can set it and leave it, over all your system will have to work less to maintain a constant temp.
Oh...humidity stays around 50 percent.

 

[drizler]

If you are looking for a programmable thermostat just go to EBAY. There are usually a pile of them on there in new surplus condition. I put em on both my boiler zones 10 years ago. More recently I had to hunt all over to find a millivolt model to work with my corn stove as there aren't many out there like that under $100. I did find one though for under $60 brand new. For a more standard type heater I bet you can get one of the honeywells for $35 if you can orgo the fancy backlit glow in the dark panel. The cheaper standard lcd types work fine and will turn your furnace up and dow at least a few times a day. Mine have worked well for a decade with no issues and took all of 15 minutes to install with just the 2 low volt wires for the other stat. The hardest part is figurin out how to program the thing.

 

[Rhone]

I purchased a programmable thermostat and didn't pay the extra for the fancy lit screens. That's something, could I go back I'd change. Could be the lighting/location of mine but I find it difficult to read the panel and everytime I'm at it trying to see how warm it is inside or trying to do something I just wish I could hit a button and it would light so I don't have to bob my head around like I'm trying to avoid punches to catch the right angle to see what I'm doing. I got this one for $50. It's made to travel, with a mounting plate you hook all your wires to, and then you simply snap on/off the thermostat. It's intended to take off the wall, bring it to a chair, program it, and then snap it back to the wall. That would probably solve my light issue, but I'm too lazy and do it on the wall.

I ran the numbers for my house, using your electricity rates and just turning up the AC by 2 degrees for 8 hours while I'm away will save me $26 for the year so think about how much you're saving by shutting it off for those 8 hours. That's probably conservative. AC's are least efficient running during the day and most efficient running at night, my guess is you're doing it the best way saving the most money, and I think shutting it off during the day and turning it on at night is less wear & tear than keeping it running, and avoids having your AC running at all when it would be least efficient. Only get the programmable thermostat if you want the convenience, it will let you turn your AC on 1/2 hour before you come home so you don't have to enter a hot house and it doesn't forget to shut your AC off when you leave.

 

[cbrodsky]

We got the backlit honeywell - very nice unit. I'd agree w/Rhonemas that after having the previous generation in our last house, I hated not being able to see anything at night and then turning a light on to check temp, time, or adjust anything. Worth a few bucks more for sure.

The usage feature is also nice to look for on a thermostat - tracks how long it's calling for heat each day, week, and since your last reset of it's counter. A great tool to track how effective your fires are if you're still supplementing w/central heat. And generally very useful to see how effective different programs are at minimizing use.

The one problem with the Honeywell is that it is too smart for it's own good - it tries to adjust it's recovery time based on how long the previous 7 days took to get to your setpoint. That is, instead of saying "turn on the heat at 5PM" you are really telling it "figure out how to make my house 70 degrees at 7PM when I get home." It decides when it should turn on. If you have inconsistent fires that sometimes burn longer than others, then it could be thrown a bit - it's basically trying to automatically adjust seasonally so that in the dead of winter, it would take longer to recover, and would start earlier, but in shoulder seasons, it'll learn that it doesn't really have to start much ahead of 7PM. Fortunately, this more advanced control method can be disabled if needed.

-Colin

 

[begreen]

I love the backlight feature and use it all the time instead of turning on the hall lights to read the temp. FWIW I've gone from White Rodgers and Honeywell to Lux. They seems to do very well at a better price. I have a couple Lux backlit thermostats that might be up for sale now that we're changing systems.

 

[saichele]

The trick is finding one that handles the 2-stage burner on the furnace. It's a Trane 1400 XL, nice unit, but just about everything I've found at normal retail stores is only good for one stage. I asked the local dealer, they wanted $450, and wouldn't sell it to me unless they installed it.

Wasn;t an issue last winter because someone was home most of the time. This winter the house will be empty about 20 hrs/wk, so it might be nice to have, but probably not $450 nice.

Steve

 

[Mo Heat]

I love the backlight feature and use it all the time instead of turning on the hall lights to read the temp. FWIW I've gone from White Rodgers and Honeywell to Lux. They seems to do very well at a better price. I have a couple Lux backlit thermostats that might be up for sale now that we're changing systems.

I bought a non-back lighted Lux in CA about 8 yrs ago. Brought it to MO because I liked it, but the last two years it seems to loose its mind two or three times a year. This time it was the day after I left on vacation and Mother Mo Heat was about to dial 911, due to a heat wave in St. Louis that had hundreds checking into hospitals, by the time she finally reached us in the mountains where our cell phone wasn't working well, so I could talk her through a reset and readjustment on the phone. No easy task with Mother Mo Heat's technical abilities and Mo's waning memory.

BeGreen, I might be interested in one of your back-lit Lux units if price and shipping isn't prohibitive.

 

[vgrund]

I've been away enjoying the summer but it is good to be back to this forum.

AC... Some may recall the problems I had with my house being underinsulated and leaky as I posted here about it. I fixed these as must as possible with the heating season in mind ($$$$ propane bills), but obviously it helps year round. I had ~ 30% lower electric bills this summer.

I have central AC for 3600 sq. ft. It is split into 4 zones with programmable thermostats (upstairs bedrooms, 1st floor master, living/kitchen/family rooms, home theater). Programmable thermostats are easy to add to such a system. Any regular Lux or similar model will do. It's just 4X as expensive (one for each zone). It wasn't quite as easy before my energy improvements, but now I can easily defeat gravity and make my upstairs bedrooms zone cooler than the zone below it. So, the golden rule about fixing efficiency applies here as well.

There are more permutations with programming 4 zones. In general, I try not to let my second floor get above 78 because it takes forever to cool if it gets too hot (pushing heavy cold air up 2 floors from the basement). I cool the master bedroom during the sleeping period and general spillover from cooling other zone sufficies during the day. I cool the living/kitchen/family area until about 8 PM, when it goes to 80 (essentially off because spillover from other zones keeps it below that cutin temp). The theater I keep at 78 during the day and then drop to 76 around 6 PM. By the time we head up to watch TV or a movie it is comforably cool, in fact sometimes too cool.

Get programmable (a) programmable thermostat(s). You'll have no end of entertainment finding the ideal program for your family.

Victor

 

[Mo Heat]

... I have central AC for 3600 sq. ft. It is split into 4 zones with programmable thermostats (upstairs bedrooms, 1st floor master, living/kitchen/family rooms, home theater). Programmable thermostats are easy to add to such a system.

Victor,

Was your HVAC already set up for 4 zones and then you simply added 3 more thermostats? Or was it one zone and you created 4 zones just by adding 3 more thermostats?

I'm trying to imagine just adding thermostats to my house. But I can't see it would do much good if any one of them simply caused the A/C to cycle on, which will feed all the registers in my existing single zone (whole house) without somehow blocking or redirecting the air flow going outside the area I want to make cooler. And since my blower unit is sized for the whole house, I'd guess the fan would have problems if I stifle its output by blocking off outlets.

Maybe I'm reading your post wrong, but you seem to be implying you can just add thermostats to an existing single zone system to create multiple zones. Is that what you are saying?

 

[vgrund]

I'm saying I had 4 mercury thermostats in each zone when I moved into the house. They report down to a panel that controls motorized dampers. In other words, my forced-air system was designed with 4 zones.

What I mean is that programmable thermostats are easy to add to MULTI-ZONE systems such as mine. The only difference is that only the primary zone uses all the features of the thermostat (main on/off, fan-on, etc.). The other zones can only call for heat or cooling.

While I'm at it, I'll add that one should look for a thermostat that retains its programming when switching between heating and cooling and vice versa. That is a very handy feature whose utility increases with the square of the number zones.

Victor

 

[DavidV]

I set mine for 75 during the day and 70 at night. If I'm hot, I won't sleep. if I don't sleep I'm no good at all. Since we upgraded the hvac and started the programmable thing, my usage went from 3500 to 2900 for august. The humidity is the killer. I've been considering getting a dehumidifier. Don't have any place to stick a window unit so that won't work.

 

[Sandor]

I set mine for 75 during the day and 70 at night. If I'm hot, I won't sleep. if I don't sleep I'm no good at all. Since we upgraded the hvac and started the programmable thing, my usage went from 3500 to 2900 for august. The humidity is the killer. I've been considering getting a dehumidifier. Don't have any place to stick a window unit so that won't work.

The humidity has been nothing short of tropical this year. It really has me thinking of moving to western NC.

Anyway, this is why I started to slightly undersize A/C units in the homes I built around here. Had problems with homes being cooled to 75 with humidity levels in the 60% and higher. I like to see indoor humidity levels around 50%. The difference between 50 to 60 percent is huge, and anything over 50% encourages mold/mildew growth.

I was using the dehumidifier approach to get the house drier, but they do put out a fair amount of heat. The ones that are designed for low temperature operation put out alot of heat. They are noisy too.

So, using the dehumidifier in conjunction with the A/C may negate the savings you made with the more efficient A/C system. However, the dehumidifier works great in fall, when its cool and damp.

I really encourage the use of small Energy Star window A/C units. Like 9k BTU with an EER of over 10. They are less expensive than a dehumidifier, remove lots of moisture, and do not pump heat into the home.

I am aware of the stigma associated with a window shaker, however, the benefits are too great for me to ignore.

David, do you have a digital indoor weather station so you can see exactly what your indoor humidity levels are?

 

[Mo Heat]

...Anyway, this is why I started to slightly undersize A/C units in the homes I built around here.

Sandor, You've written this a couple times, and each time I read it I wanted to thank you for sharing it. I now perceive my A/C unit in a completely new light. Where I once saw it as under sized, I now see it as just right. And it does keep the humidity below 50%, too. So anyway, thanks. This will also help me size the next one when this one poops out, likely in a couple more years.

BTW: I keep my A/C thermostat at 79*F from 11 am - 11:45 pm and at 78*F from 11:45 pm - 11 am. It takes about an hour to drive the temp down by this one degree F in my house. And it runs near constant from about 1 pm or 2 pm until 8 pm or 10 pm.

 

[BrotherBart]

Sandor:

" I am aware of the stigma associated with a window shaker, however, the benefits are too great or me to ignore."

I hear ya Virginia humidty Bro. We never used the heat pump for heat just A/C. When it crapped a couple of years ago I put a 5,000 BTU window unit down stairs and an 8,000 upstairs. I always got hacked that to keep the upstairs cool I was paying to freeze my butt off downstairs. The electric bill dropped by half in the summer and the humidity is non-existent. The one downstairs runs around two hours a day total and the one upstairs lounges along until around ten at night sucking the humidity out of the place.

And I can buy fifty of them for the price of one central air unit. In fact I can buy one a year for the cost of some guy coming out and pretending to service the central air unit.

 

[Sandor]

Sandor:

" I am aware of the stigma associated with a window shaker, however, the benefits are too great or me to ignore."

I hear ya Virginia humidty Bro. We never used the heat pump for heat just A/C. When it crapped a couple of years ago I put a 5,000 BTU window unit down stairs and an 8,000 upstairs. I always got hacked that to keep the upstairs cool I was paying to freeze my butt off downstairs. The electric bill dropped by half in the summer and the humidity is non-existent. The one downstairs runs around two hours a day total and the one upstairs lounges along until around ten at night sucking the humidity out of the place.

And I can buy fifty of them for the price of one central air unit. In fact I can buy one a year for the cost of some guy coming out and pretending to service the central air unit.

Exactly!

I have come to the same conclusion as you.

 

[vgrund]

Hmmm I never really considered the efficiency of central versus window units. I always assumed a central system would be more efficient if one is conditioning a large space. I had a few window units in a series of apartments I rented before I became a house caretaker for the mortgage company. The noise drove me INSANE. Perhaps they have improved since the 90s!

Anyway, we're about done with air conditioning for the season in New Hampshire. It only runs when I fire up the electronics and lights in my home theater! On a related point, I switched to low voltage lighting in my theater. It was previously lit by 75W R-30 track fixtures. The heat load was a problem in that space. A posted about this on sci.engr.lighting and a very nice lighting engineer suggested MR-16 low voltage fixtures which fit into the same track. They provide similar light levels, are still fully dimmable, but they emit about 30% less heat. It made a noticable difference.

Victor