Tuning for Efficiency Dual Zone A/C System in Home

[javacontour]

OK guys and gals at BITOG, the new javaContour pad has 2700 square feet of living space and two HVAC units, one for upstairs and one for downstairs.

During the day, since oilBabe has the summers off, the whole house is likely used. While at night, everyone sleeps upstairs.

So are there any tips to setting the thermostats both upstairs and downstairs for the home?

I'm looking at keeping the home at about 72 at night, and about 75/76 during the day.

The upstairs is likely going to get hotter, being closer to the roof, heat rising, etc.

So are their any guidelines on how much one can set thermostats during different parts of the day for best system operation?

Is there too much temperature change. I.E. what would be the max one would want the downstairs to rise at night before it would be more costly to drop the temperature back down rather than simply maintain that temperature 24x7.

Thanks!

 

[TooManyWheels]

The formula you are looking for is simple - If you aren't using a zoned portion of the house - Turn it off. Your unit will always spend less time running overall than if you had tried to maintain a temp while you were gone. It will also be more efficient because it will not always be in the high-current-draw startup mode.

 

[oilyriser]

The upstairs unit will likely try to cool the whole house, since cold air sinks, and the lower level will end up cooler than the set point on the upstairs thermostat.

Is there any way to sleep downstairs in summer?

 

[javacontour]

Originally Posted By: oilyriser
The upstairs unit will likely try to cool the whole house, since cold air sinks, and the lower level will end up cooler than the set point on the upstairs thermostat.

Is there any way to sleep downstairs in summer?


That would only fly with the folks in an emergency, such as we couldn't condition the upstairs. All the bedrooms and the kids loft is upstairs, so all their games, etc are up there.

I was thinking that I'd always set the lower unit at a higher temp than the upstairs, knowing the heat would rise and the cold air would fall, running the smaller unit more is more efficient, etc.

(And of course, keeping this trend in the winter program as well.)

I may look at dropping the lower temp from 5pm until 8pm when the kitchen is in higher use, and then let move to the night portion of the program somewhat early.

There are four periods on the thermostat, morning, daytime, evening and night.

We want to use the whole house, but use energy in a wise fashion. (relatively) We have five people, two teens, two adults and my soon to be 10 year old daughter, so some space and privacy is required.

 

[duaneb9729]

i would run your furnace fans all the time during the hottest part of the summer and the coolest part of winter, and if it were me i would run them all the time year around, except when the windows are open.

in the future upgrade your furnaces to two or three stage heating with a dc drive variable speed motors.

if your looking to save money try your thermostat settings around 74 or 75 degrees and perhapes 78 during the day.

with that being said with a/c i tend to go more by feel, if the house feels close or clamy i tend to over ride the programed settings on the thermostat and lower it a degree or two to take out the humidity.

when you do have your system replaced make sure you have a heating and cooling load calculation most equipment tends to be over sized

Sincerely
Duane

 

[javacontour]

At least it's relatively efficient equipment. From what I can tell, stuff made after 2006 has to have a SEER rating of at least 13.

It's all new, so chances are it will be here as long as we are. We only plan to be here about 10 years until my daughter gets out of H.S. and then move into a smaller place, closer to where oilBabe works to stay there until retirement in say 20 or so years from now.

Kids can't move back home if we don't have the larger home for them to return to.

 

[eljefino]

Can you put a door in your stairwell?

Energy is used maintaining a temperature delta between inside and out. If the inside temp gets closer to the outside for a few hours, less is used... period... even if the HVAC has to fight harder to regain the temp later. Graph out inside vs outside temps for every hour of the day, the area between the two lines is your bill.

 

[Tree Hugger]

My house (2400 sq ft.) had a single HVAC unit for the first 10 years. We could never satifactorily heat or cool both levels. Never. I bought oil filled radiators for the upstairs bedrooms, so it was OK in Winter, but Summers were always too hot upstairs.
When it came time to replace the unit, I went with two systems, one for each level, and added two returns. Now both levels are perfect. We run the temps that feel comfortable to us, which turns out to be 75 for the Cooling and 73 for the Heat, and run the fans on continuous during the morning and daytime cycles.
During experimenting for the first three months of the new system, we found, contrary to expectations, that there is virtually no exchange between levels, despite a large central open stairwell. We also found that setbacks worked very well on the Heat(65 when not occupied), but not very well at all on the Cooling (at any setback at all).
We found it not only more effective, but also cheaper to run the Cooling at a constant temperature 24/7.

I know and understand all the theory that says otherwise, but facts trump theory, every time.
Hope this helps...

 

[javacontour]

Just to revive this. We had the HVAC guy here as part of the on year check up a couple of months ago and he made some changes in the duct work. Put a couple of curved sections in going to our bedroom because it was colder in the winter. (Far away from the furnace and on the north side of the home above the garage.)

He also suggested running the fan constantly and that really helped. So we'll probably keep doing that.

 

[GMBoy]

I've got the same deal. 2 units, one for upstairs and one for downstairs. I've tried everything and came to the conclusion that it was actually cheaper to run them both at the same temp. I use 78 in the summer. I am lucky that my heating part can run either heatpump or off gas so I use what's cheaper in the winter.

 

[CROWNVIC4LIFE]

Originally Posted By: GMBoy
I've got the same deal. 2 units, one for upstairs and one for downstairs. I've tried everything and came to the conclusion that it was actually cheaper to run them both at the same temp. I use 78 in the summer. I am lucky that my heating part can run either heatpump or off gas so I use what's cheaper in the winter.


What is your average bill in the summer?..Down here my friends [2 zone unit] is around 300-350 bucks a month..During the day when nobodys home it on 78 but in the evening its on 75 or 74 as 78 he says is way 2 warm to sleep..I drop mine to 74 or lower at night as well also.

 

[GMBoy]

Originally Posted By: CROWNVIC4LIFE
Originally Posted By: GMBoy
I've got the same deal. 2 units, one for upstairs and one for downstairs. I've tried everything and came to the conclusion that it was actually cheaper to run them both at the same temp. I use 78 in the summer. I am lucky that my heating part can run either heatpump or off gas so I use what's cheaper in the winter.


What is your average bill in the summer?..Down here my friends [2 zone unit] is around 300-350 bucks a month..During the day when nobodys home it on 78 but in the evening its on 75 or 74 as 78 he says is way 2 warm to sleep..I drop mine to 74 or lower at night as well also.
Originally Posted By: CROWNVIC4LIFE
Originally Posted By: GMBoy
I've got the same deal. 2 units, one for upstairs and one for downstairs. I've tried everything and came to the conclusion that it was actually cheaper to run them both at the same temp. I use 78 in the summer. I am lucky that my heating part can run either heatpump or off gas so I use what's cheaper in the winter.


What is your average bill in the summer?..Down here my friends [2 zone unit] is around 300-350 bucks a month..During the day when nobodys home it on 78 but in the evening its on 75 or 74 as 78 he says is way 2 warm to sleep..I drop mine to 74 or lower at night as well also.



I average the same as you with spikes getting into the $400's when we have a long heat wave - which is often. My house is a 2 story 3100sf with both HVAC units being old and ineffiecient. They are the same one from when the house was built in 1996.

 

[duaneb9729]

In the future when you go to replace your equipment, look at getting a variable speed air handler or a furnace with the variable speed blower, matched to a 2 stage heat pump.

You will see major savings over the equipment you have.

I suspect you have 10 S.E.E.R. equipment in your home. To go to a 13 S.E.E.R. you would see aprox a 30% savings.

 

[brianl703]

Originally Posted By: javacontour

He also suggested running the fan constantly and that really helped. So we'll probably keep doing that.


That fan uses quite a bit of power. The one on mine uses 600 watts. Over the course of a 30-day month that's 432kWh. In the summer, you use more electricity removing the heat that motor put in your house. A 600 watt space heater gets pretty warm.

 

[GMBoy]

Originally Posted By: duaneb9729
In the future when you go to replace your equipment, look at getting a variable speed air handler or a furnace with the variable speed blower, matched to a 2 stage heat pump.

You will see major savings over the equipment you have.

I suspect you have 10 S.E.E.R. equipment in your home. To go to a 13 S.E.E.R. you would see aprox a 30% savings.


Good advice there. Your a right, the current setup is only a 10SEER. But I am told that as equipment ages the SEER goes down with it. So I guess I may be an 8 SEER now and blowing money every month. I plan to replace the units in the near future, having no problems with them yet except some noise on startup outside the house at the heatpump unit at times. I would probably get 13SEER since the price difference between 13 and 16 is a lot....too much to recover cost by any energy savings quickly.