New Home Owner looking for help w/ saving money
#1
08-20-19, 03:14 PM
Join Date: Aug 2019
Location: United States
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New Home Owner looking for help w/ saving money
First time homeowner here. Purchased a brand new home. Put in a Nest learning thermostat. Getting daily reports on energy usage from my provider and frustrated by bills. $350/mo in east Tennessee. I know it's hot, but that's ridiculous. We're keeping it on 77 during the day and 74 at night and still hitting 70kwH per day or more. Unit is running 9 hours on the low side and up to 12 hours on the high. I've checked the weather stripping on all the doors, checked accessible ducts and vents for tears, loose tape, etc. Nothing. Going crazy here.
#2
08-20-19, 04:14 PM
Sound like your house is TOO efficient- quick guess
-part of large development and your "front" faces north
-no front porch
-double or triple glazed windows
-high-R-value insulation in the walls and attic
-dark roof shingles and dark siding
As long as you are outside an urban heat-island, I HIGHLY recommend using fans during the night to cool down the building
I'm in an old Pennsylvania farmhouse, and although we often have several days in the 90s with "feels like" 100 F temperatures, we generally get evening temperatures around 65-70.
So, I turn of the A/C in the evening, and chill the house down to 65-70 using cool evening air.
I HAVE found that on many warm days, it is impossible to cool the house down using A/C, but in the evening, venting the hot air, pulling in cool air does a great job of cooling down the building.
-part of large development and your "front" faces north
-no front porch
-double or triple glazed windows
-high-R-value insulation in the walls and attic
-dark roof shingles and dark siding
As long as you are outside an urban heat-island, I HIGHLY recommend using fans during the night to cool down the building
I'm in an old Pennsylvania farmhouse, and although we often have several days in the 90s with "feels like" 100 F temperatures, we generally get evening temperatures around 65-70.
So, I turn of the A/C in the evening, and chill the house down to 65-70 using cool evening air.
I HAVE found that on many warm days, it is impossible to cool the house down using A/C, but in the evening, venting the hot air, pulling in cool air does a great job of cooling down the building.
#3
08-20-19, 05:00 PM
I'm a retired energy auditor and doing part time energy consulting now. Your problem is common and there are many things you can do to reduce those costs.
First, we need to know more about your house and how you are cooling it, I'm assuming a heat pump and these are electric bills. How big is the house?
Did the builder give you any energy report information?
If not that is where I suggest you start. Check your state for energy audit programs that are free. A prime function of an audit should not be to sell you something but to point out where improvements can be made.
Bud
First, we need to know more about your house and how you are cooling it, I'm assuming a heat pump and these are electric bills. How big is the house?
Did the builder give you any energy report information?
If not that is where I suggest you start. Check your state for energy audit programs that are free. A prime function of an audit should not be to sell you something but to point out where improvements can be made.
Bud
#4
08-20-19, 05:42 PM
Member
Could be the thermostat is not wired correctly and is causing the high energy bills.
The Nest is not well liked, and has a very long history of causing all sorts of bizarre and oddball problems. I consider it the worst choice for a thermostat, especially for a heat pump.
Turning off the air conditioning at night and pulling in large amounts of outdoor air is NOT a good idea. You’ve just filled the structure full of humidity that must be reduced in order to begin to reduce the heat load.
The Nest is not well liked, and has a very long history of causing all sorts of bizarre and oddball problems. I consider it the worst choice for a thermostat, especially for a heat pump.
Turning off the air conditioning at night and pulling in large amounts of outdoor air is NOT a good idea. You’ve just filled the structure full of humidity that must be reduced in order to begin to reduce the heat load.
#6
08-20-19, 07:40 PM
Originally Posted by roughneck77
Turning off the air conditioning at night and pulling in large amounts of outdoor air is NOT a good idea. You’ve just filled the structure full of humidity that must be reduced in order to begin to reduce the heat load.
Even on a humid night, pulling in 68F air at 99% humidity helps cool the house and contents down to 68F. Admittedly, I have a less-common situation- large masonry house with 2' thick stone walls which provides an incredible amount of thermal inertia if you can cool it down and keep it cool.
At that 68F and 99% relative humidity, you have 0.017 kg/M^3 of absolute humidity. When you let that warm up to 77F you end up at 75% humidity (high side of comfortable) which is ALSO 0.017 kg/M^3.
Big point is that, moist air is great at transporting heat. As long as you don't try to cool the air below the dew point, you don't get hit with that big latent heat problem.
So, back to 68F/99% situation, cooling down a 2,600 sqft house from 77 to 74 then requires (scribble) removing about 6 liters of water- not insignificant, but also a worst-case scenario.
But, look at what happens when it DOES WORK to exchange cool air.
In a day or two, my forecast is temperature is down to 59F at 84% humidity, that's 0.011 kg/M^3. Let that cool air heat up and 0.011 kg/M^3 at 74F works out to be about 52% humidity (quite comfortable, even a bit dry if you have plants or orchids).
But, just looking at the air-latent heat, and skipping the thermal inertia of the structure and contents, exchanging air that's 60ish Fahrenheit AND is below the local dew point works reasonably well to remove heat from a structure.
Last edited by Hal_S; 08-20-19 at 07:55 PM.
#7
08-21-19, 05:11 AM
Group Moderator
Wow, never going to complain about our power bill again! We run @ 80 day and 82 night in southwest Florida [where heat+humidity was invented] and we average about $150/mo. About 2000 sq ft under air AND pool pump. 
#8
08-21-19, 08:53 AM
Member
80 day and 82 nigh
Guess I will keep my GEO thermal, we run 72 year round and we're $125 a month for the yearly average!
#9
08-22-19, 07:46 AM
Member
I completely agree with Roughneck77 Nest aren't good stats and trying to cool a house in the summer at night in a green grass state is not the best way to cool.
IMO my first thing to do is get a good HVAC company out to look at the system. 2nd would be to get the energy audit that was mentioned above.
IMO my first thing to do is get a good HVAC company out to look at the system. 2nd would be to get the energy audit that was mentioned above.
