(Nest Thermostat) HVAC Wiring Questions

[GlockSpock]

Make sure electic heat is not running during air conditioning. HVAC/R tech for quite a few moons.

How?

[GlockSpock]

Dang it , now you have me on the hunt for a new gadget. There goes some gun money .......

Yeah...I have been told I do this by multiple people.

[Guest 6.8 AR]

Air won't be very cold coming out of the ducts, and your electric meter would be about to take off.

[GlockSpock]

Air won't be very cold coming out of the ducts, and your electric meter would be about to take off.

Well...honestly one of my first thoughts was that the air didn't seem as cool. However, I chalked it up to be one of those things you don't really notice much about until you really start thinking about it.

Besides the meter and les than scientific method of feeling the temperature...any other ways to check this?

[GlockSpock]

Yeah...something does seem off. Supposedly it is cooler outside (somewhere between 69 and 75). Thermostat is set to 76. Currently showing 80 on the indoor temperature and is down from 82 or so from 1.5 hours ago.

I never really payed attention to heating and cooling time with the other temperature because I typically left it at around 74 all the time.

What is typical cooling time per degree in an 800sqft house? 1 degree per hour? 4 degrees?

[Guest Cazador]

Post a picture of your system so we can tell what we are dealing with. If you have a dual fuel system that is a heat pump with gas secondary then you should not have electric heaters in it. If it is some bastardized system someone did a presidential solution to some pictures will help.

You will need a secondary heater for a heat pump. Below 25 degrees the heat pump will not make enough heat to heat the house. Below 40 degrees { depending on humidity and a couple other factors ] the unit will go into defrost mode. Defrost mode= The outdoor coil has reached 29 degrees and set the defrost sensor. On a timed cycle between 30 and 90 min of run time the circuit will activate defrost. The reversing valve will energize switching the unit into air conditioning and the out door fan will shut off causing the temp and pressure to build in the outdoor coil causing any ice to melt off. When the OD coil reaches aprox 60 degrees  or 10 min , which ever is first, the cycle will terminate and go back to heating. During the defrost cycle the second stage of heat is turned on to counter act the effects of the system being in airconditioning mode. In your case the second stage is gas heat.

[GlockSpock]

Post a picture of your system so we can tell what we are dealing with. If you have a dual fuel system that is a heat pump with gas secondary then you should not have electric heaters in it. If it is some bastardized system someone did a presidential solution to some pictures will help.
You will need a secondary heater for a heat pump. Below 25 degrees the heat pump will not make enough heat to heat the house. Below 40 degrees { depending on humidity and a couple other factors ] the unit will go into defrost mode. Defrost mode= The outdoor coil has reached 29 degrees and set the defrost sensor. On a timed cycle between 30 and 90 min of run time the circuit will activate defrost. The reversing valve will energize switching the unit into air conditioning and the out door fan will shut off causing the temp and pressure to build in the outdoor coil causing any ice to melt off. When the OD coil reaches aprox 60 degrees  or 10 min , which ever is first, the cycle will terminate and go back to heating. During the defrost cycle the second stage of heat is turned on to counter act the effects of the system being in airconditioning mode. In your case the second stage is gas heat.

 
Pictures!















Edited September 5, 2013 by CZ9MM

[GlockSpock]

Also, lets talk about humidity and HVAC. I've read that having a higher relative humidity makes it more difficult for your HVAC to adjust the temperature inside. My nest tells me my relative humidity level, it's currently at 56%. I've read the 45% is probably the more optimal relative humidity level for comfortable temperatures inside.

 

Nest as a "Cool-to-Dry" setting, which means it mumps AC into your house to reduce the relative humidity. It also warns this can get quite expensive, although I don't see any statistics or settings regarding what humidity level it attempts to keep it at.

[GlockSpock]

Well, first status report in! My utility allows us to view near real time usage via a web interface. 
 


I know it is far from scientific (give me a few more months and I'll have cold, hard statistics). However, I think so far this is a good sign. Nest was initially installed on September the 2nd. You can of course see the avg, max, and min degrees F of the outside temperature. Monday was when I first installed it (in the evening), and it saw the lowest usage amount for the shown period as of that date. Then, Tuesday, it showed a lower usage amount for the shown period. It is possible that Wednesday is not a complete usage yet (as in, the next time the usage is "pushed" to the server it could update). However, comparing Tuesday, September the 3rd to Wednesday, August the 28th is a very good sign. Both of them had the same average outdoor temperature, but usage was 64 vs 29. That's of course also dependent on other things, such as washer and drier usage, etc etc, but I think it is a very good sign starting off!

I have data for the previous year that I can compile into statistics based on average temperature. I can then compile statistics based on average temperature after I've installed the Nest. That should provide me with quite accurate savings estimates.

[Guest Riciticky]

Trust me. If you don't know what is going on, call a hvac tech. There is a myriad of things that could be wrong. If one wire is in the wrong place, it could more than double the electric bill. You need a volt meter to ck.

[Guest Riciticky]

If there is programming involved, a single mistake could cost you a lot.

[GlockSpock]

A bit more "statistics" that I'm using to hype myself up over this:
 
What I've done is exported all available data from my electric usage, sorted it all by average temperature and then sub-sorted it by usage. I have this to show:
 
The following is for all days with an average external temperature of "77", with the high and low following the average temperature. I've sorted these records by usage, and as you can see the "Nest" day falls into 7 of 16th place in lesser usage.
 
 

6/21/2013	32	Kwh	 $2.87 	77	87	69
7/25/2013	32	Kwh	 $2.83 	77	87	66
6/20/2013	35	Kwh	 $3.14 	77	87	69
8/12/2013	38	Kwh	 $3.35 	77	87	72
7/26/2013	39	Kwh	 $3.45 	77	88	66
8/13/2013	39	Kwh	 $3.44 	77	87	73
Nest	        39	Kwh	 $3.44 	77	86      73
8/20/2013	41	Kwh	 $3.62 	77	85	71
7/28/2013	44	Kwh	 $3.89 	77	85	70
8/5/2013	45	Kwh	 $3.97 	77	87	68
5/31/2013	46	Kwh	 $3.98 	77	85	70
7/27/2013	49	Kwh	 $4.33 	77	86	72
9/1/2013	49	Kwh	 $4.32 	77	84	73
7/8/2013	50	Kwh	 $4.42 	77	87	72
8/3/2013	52	Kwh	 $4.59 	77	84	69
8/27/2013	62	Kwh	 $5.47 	77	89	66

 
The following is for all days with an average external temperature of "80", with the high and low following the average temperature. I've sorted these records by usage, and as you can see the "Nest" day falls into 1 of 9th place in lesser usage.
 
 

Nest	        29	Kwh	 $2.56 	80	90	73
7/16/2013	35	Kwh	 $3.09 	80	90	72
8/4/2013	36	Kwh	 $3.18 	80	89	73
8/30/2013	48	Kwh	 $4.24 	80	90	75
8/9/2013	50	Kwh	 $4.41 	80	90	72
8/10/2013	50	Kwh	 $4.41 	80	88	73
7/15/2013	53	Kwh	 $4.69 	80	88	71
6/11/2013	54	Kwh	 $4.84 	80	91	71
8/28/2013	64	Kwh	 $5.65 	80	90	70

 
The "77" doesn't impress me as much, however, the "80" excites me quite a bit!

Edited September 6, 2013 by CZ9MM

[Guest Cazador]

b y the pictures you posted you do not have a dual fuel system. It is a standard 2 ton heat pump with a 10 KW supplemental heater in it.

I have been in the heat and air business for 28 years. I will tell you that the most economical way to operate a system is to set the temperature on your thermostat and leave it alone. If you live a very structured life where you get up in the morn, leave for work, return home and go to sleep at the same time every day you will not see major savings in your electric bills. If you are programing for these times and setting temps drastically up and down it is almost self defeating. Reasoning for this...Day time high temp of 94 degrees. If you set the temp to 73 degrees for when you wake up and 80 when you leave for work then back to 73 when you return home. When you leave. Your house will gradually warm to 82 degrees. Everything in your house [ walls, floors, furniture, cabinets......everything]  will be 82 degrees and the humidity will also be higher. When your stat calls for it to start cooling for your return it will do so at one of the most inefficient times of the day. The functions of an air conditioning system are to cool, clean and dehumidify the air. The first thing that makes your home cooler is the dehumidifying. Until the relative humidity is lowered cooling can not take place. You are doing this at the worst time of the day for an air to air exchange system. It's pretty technical why due to the properties of the chemicals used in the system and the electrical needs to compress high temp gasses to condense them and the amount of energy used by an electric motor in a hot environment verses a cool one. If you are going to set back the temp I advise no more than 5 degrees and use heavy curtains on all the windows and keep them closed. If you really want to save some money set your temp to 78 degrees and adjust to it. 68 for heating. If you don't run the a/c in your car on super freeze it wont take you long to climatise to it. Your system will run enough to keep the humidity level down which will make it feel more comfortable. 

[GlockSpock]

b y the pictures you posted you do not have a dual fuel system. It is a standard 2 ton heat pump with a 10 KW supplemental heater in it.
I have been in the heat and air business for 28 years. I will tell you that the most economical way to operate a system is to set the temperature on your thermostat and leave it alone. If you live a very structured life where you get up in the morn, leave for work, return home and go to sleep at the same time every day you will not see major savings in your electric bills. If you are programing for these times and setting temps drastically up and down it is almost self defeating. Reasoning for this...Day time high temp of 94 degrees. If you set the temp to 73 degrees for when you wake up and 80 when you leave for work then back to 73 when you return home. When you leave. Your house will gradually warm to 82 degrees. Everything in your house [ walls, floors, furniture, cabinets......everything] will be 82 degrees and the humidity will also be higher. When your stat calls for it to start cooling for your return it will do so at one of the most inefficient times of the day. The functions of an air conditioning system are to cool, clean and dehumidify the air. The first thing that makes your home cooler is the dehumidifying. Until the relative humidity is lowered cooling can not take place. You are doing this at the worst time of the day for an air to air exchange system. It's pretty technical why due to the properties of the chemicals used in the system and the electrical needs to compress high temp gasses to condense them and the amount of energy used by an electric motor in a hot environment verses a cool one. If you are going to set back the temp I advise no more than 5 degrees and use heavy curtains on all the windows and keep them closed. If you really want to save some money set your temp to 78 degrees and adjust to it. 68 for heating. If you don't run the a/c in your car on super freeze it wont take you long to climatise to it. Your system will run enough to keep the humidity level down which will make it feel more comfortable.

That is great information! I have been running the AC around 78 this previous week. So is it even worth letting it go up to 80 or so when I am not here? I have always wondered about efficiencies and what not, I just wish that the climate was steady enough to test everything in various ways.

[GlockSpock]

b y the pictures you posted you do not have a dual fuel system. It is a standard 2 ton heat pump with a 10 KW supplemental heater in it.

I have been in the heat and air business for 28 years. I will tell you that the most economical way to operate a system is to set the temperature on your thermostat and leave it alone. If you live a very structured life where you get up in the morn, leave for work, return home and go to sleep at the same time every day you will not see major savings in your electric bills. If you are programing for these times and setting temps drastically up and down it is almost self defeating. Reasoning for this...Day time high temp of 94 degrees. If you set the temp to 73 degrees for when you wake up and 80 when you leave for work then back to 73 when you return home. When you leave. Your house will gradually warm to 82 degrees. Everything in your house [ walls, floors, furniture, cabinets......everything]  will be 82 degrees and the humidity will also be higher. When your stat calls for it to start cooling for your return it will do so at one of the most inefficient times of the day. The functions of an air conditioning system are to cool, clean and dehumidify the air. The first thing that makes your home cooler is the dehumidifying. Until the relative humidity is lowered cooling can not take place. You are doing this at the worst time of the day for an air to air exchange system. It's pretty technical why due to the properties of the chemicals used in the system and the electrical needs to compress high temp gasses to condense them and the amount of energy used by an electric motor in a hot environment verses a cool one. If you are going to set back the temp I advise no more than 5 degrees and use heavy curtains on all the windows and keep them closed. If you really want to save some money set your temp to 78 degrees and adjust to it. 68 for heating. If you don't run the a/c in your car on super freeze it wont take you long to climatise to it. Your system will run enough to keep the humidity level down which will make it feel more comfortable. 

 

Ok, I changed the aux. heat from gas to electric in the settings. I now have two additional settings available. The first one asks when to use the heat pump compressor when the temperature outside is above: (default is always). The 2nd additional setting asks when to use the aux. heat (default is 50f or below). Sound good? It is typical for the aux. and heat pump to work when it is super cold, right?

[GlockSpock]

That's the settings on the Web GUI, it's pretty much all that there is on the unit as well. I think it is good to go. Thoughts?

[Guest Cazador]

Use compressor default, all the time.  The second stage default is good at 50, if your heat pump is working properly it should not come on until outdoor temp is between 30 and 25. Your mileage may vary depending on insulation values in the house, quality of windows and doors.

If you use the dehumidify mode you will probably be sorry you did when you get your first electric bill.  Usually a dehumidify mode consists of the unit running in cooling mode but cycling the electric heaters on and off to maintain the room temperature close to the set point. Not an economical idea unless you want to dehydrate fruits and veggies on the counter top.

[Guest Cazador]

I leave my stat set on 78 when I am home. If I think about it I will change it to 80 before I leave. When we have temps like last year in the 100's I will leave it on 80. I do not use a programmable one. Our lives and schedules are too hectic to set times and temps.

[GlockSpock]

Latest Graph:

 

 

Latest Percentages (which the graph is based upon):

 

 

The Pre-Nest data is based upon data from 9/18/2012 to 9/1/2013 and the Post-Nest data is based upon data from 9/2/2013 to 9/24/2013. Obviously the more data I have the more accurate it will be, but unfortunately I will not be able to offer true statistics for Nest savings because it is no longer the only variable.

 

As of 9/23/2013, I installed (11) 6w LED's, replacing (11) 65w incandescent bulbs.

As of 9/25/2013, I reduced the water heater temperature from ~140F° to ~120F°.

 

Therefore, since the Nest data only goes up to 9/24/2013, the average usage based upon Nest installation is a very high percentage based upon the installation of the Nest itself due to the fact that only 1.5 days of the data is also based upon LED installation. I think it is safe to conclude that the Nest will save somewhere between 5% and 15% total energy usage. If you assume that the days Post-Nest usage was higher than the Pre-Nest usage were simply anomalies (based upon dish washer usage, washer/drier usage, etc), I think it is safe to say that the Nest is saving me >7%.

 

I will update this thread with more graphs and data as time goes, but just keep in mind that those graphs and data will also be factoring in additional factors than just a Nest. However, just remember that my ultimate goal here is not to create accurate graphs regarding Nest installation, but rather to save every possible $1 in regards to my electric bill.

[GlockSpock]

 

New data, now with cold weather! It appears I will probably end up saving a higher percentage when heating compared to the cooling. Hopefully that ends up being the case. In other news, October of 2013's usage was 709 kWh, while October of 2012's usage was 790 kWh. Since I installed the new showerhead, I've also been excited to see what sort of water usage we would have.

 

Drum-Roll Please....

 

5 Units! That's down from 8 units the previous two months. Also worth noting that there is only one other month in my record of having 5 units usage. For the records I have, I have an average usage of 6.77 units of water. I will take 5 any day! Cutting 3 units of water saves me $16.65 (water + sewer charge). That's pretty nice considering the shower head I purchased was just under $9 shipped!

 

If my calculations are correct, my bill should be $122 this month for water, sewer, electric, and sanitary pickup (trash) (it is hard to calculate exact electric, TVA essentially charges different rates per month based upon usage and other things). Usually my calculations are +-$5. 

[Fourtyfive]

That does it , I'm getting one ....

[GlockSpock]

For anyone that was slightly interested in purchasing one, do it today. If you order a Nest on Amazon for $249, you get a $40 Amazon card to go with it!

 

http://www.amazon.com/gp/product/B009GDHYPQ/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B009GDHYPQ&linkCode=as2&tag=tecstu-20

 

 

 

Get a $40 Amazon.com Gift Card with Purchase of a Nest Learning Thermostat
For a limited time, get one $40 Amazon.com Gift Card at no additional cost when you purchase one or more select Nest Learning Thermostats shipped and sold by Amazon.com. To receive the Amazon.com Gift Card, add the gift card to your cart now and continue shopping. Learn more

 

Edited December 2, 2013 by CZ9MM