Comments on: Nest Thermostat Data Unveiled at ACI Conference

By: Brian Butler

Brian Butler — Sun, 05 Jul 2015 20:55:08 +0000

In reply to Dale Sherman. I wonder if Nest is doing any
I wonder if Nest is doing any actual blower door testing on a few sample homes to dive deeper on these questions...?

By: Brian Butler

Brian Butler — Sun, 05 Jul 2015 16:55:08 +0000

I wonder if Nest is doing any
I wonder if Nest is doing any actual blower door testing on a few sample homes to dive deeper on these questions...?

By: John C

John C — Sat, 23 May 2015 15:02:35 +0000

All I

All I can say is that Nest called 20-30% aux in my well sealed, tight ducted HP house with new split HP, when the outdoor temp was in the 30s (which are a lot of hours in my mid-atlantic climate), yet my balance point is 22-23°F.

My old Honeywell VisionPro never called aux above 25°F. My Ecobee has a lockout there, and no problems.

The interesting question for Blasnik re the last graphs showing aux usage is how much of the problem is the HP and how much is the controller....the Nest.

If you see the home using a huge amount of aux, but the compressor is only running 10 hours a day....I think that is a smoking gun at the nest.

Typical day in the 30s, my nest would run my compressor for 15 hours/day, and call a lot of aux. The other stats would run the compressor 20 hours and no aux. Below balance point, the Honeywell would run the HP 100% duty, and strobe the aux, the Ecobee runs ~95% cycle, and the nest ran an 80% duty cycle on the HP, making up the lost output with more aux.

Seems like a pretty easy analysis for Blasnik to do, HP cycle time versus temp.

He could regress HP and aux runtime versus outdoor temps (and clean up the data by cutting high outdoor wetbulb). And then compute a balance point for each system, and determine how much aux nest was calling above, say balance point+5°F. That is, how much is totally wasted by defects in the control algorithm.

And then prob get fired.

By: John C

John C — Sat, 23 May 2015 11:02:35 +0000

  All I
  All I can say is that Nest called 20-30% aux in my well sealed, tight ducted HP house with new split HP, when the outdoor temp was in the 30s (which are a lot of hours in my mid-atlantic climate), yet my balance point is 22-23°F.    My old Honeywell VisionPro never called aux above 25°F. My Ecobee has a lockout there, and no problems.    The interesting question for Blasnik re the last graphs showing aux usage is how much of the problem is the HP and how much is the controller....the Nest.    If you see the home using a huge amount of aux, but the compressor is only running 10 hours a day....I think that is a smoking gun at the nest.    Typical day in the 30s, my nest would run my compressor for 15 hours/day, and call a lot of aux. The other stats would run the compressor 20 hours and no aux. Below balance point, the Honeywell would run the HP 100% duty, and strobe the aux, the Ecobee runs ~95% cycle, and the nest ran an 80% duty cycle on the HP, making up the lost output with more aux.    Seems like a pretty easy analysis for Blasnik to do, HP cycle time versus temp.    He could regress HP and aux runtime versus outdoor temps (and clean up the data by cutting high outdoor wetbulb). And then compute a balance point for each system, and determine how much aux nest was calling above, say balance point+5°F. That is, how much is totally wasted by defects in the control algorithm.    And then prob get fired.

By: Richard Parker

Richard Parker — Thu, 14 May 2015 15:49:16 +0000

There is no question that
There is no question that running a coil in cool mode will lower the humidity even in a very leaky house. This is easily demonstrated down south and has been for decades even with mercury bulb thermostats.

However indoor units installed in crawl spaces and attics are guaranteed to be very leaky; this is SOP by builders in the south and the midwest. Running the air handler fan continuously or in a random circulating mode (recently enabled by smart thermostats)is also common which will always dry out a normally wet evaporator coil increasing the humidity.

Finally I have seen more homeowners buy Nest thermostats simply for the remote control, cool factor and a perceived "savings" (rarely demonstrated)while employing them with bad hvac installs, low refrigerant, dirty coils and leaky envelopes.

By: Richard Parker

Richard Parker — Thu, 14 May 2015 11:49:16 +0000

There is no question that
There is no question that running a coil in cool mode will lower the humidity even in a very leaky house. This is easily demonstrated down south and has been for decades even with mercury bulb thermostats.    However indoor units installed in crawl spaces and attics are guaranteed to be very leaky; this is SOP by builders in the south and the midwest. Running the air handler fan continuously or in a random circulating mode (recently enabled by smart thermostats)is also common which will always dry out a normally wet evaporator coil increasing the humidity.     Finally I have seen more homeowners buy Nest thermostats simply for the remote control, cool factor and a perceived "savings" (rarely demonstrated)while employing them with bad hvac installs, low refrigerant, dirty coils and leaky envelopes.

By: David Holtzclaw

David Holtzclaw — Thu, 14 May 2015 06:54:48 +0000

Thank you Allison for posting
Thank you Allison for posting this. The “conditions when the air conditioner is running” slide makes me wonder if “residential economizers” might make more sense now? As I understand it, residential economizers were thought to never be cost effective as residential loads are driven by envelope loads not internal loads as it typically is in the commercial sector. But these new data makes me wonder. From my experience, my clients in cold climates overuse their AC because of comfort – they HATE being the slightest bit hot, but can tolerate 60F indoor dry bulb all winter – (like Vermont). For cold climates, it seems like economizers (or windows) might work. Or, now that more and more homes have mechanical ventilation, some control scheme were more ventilation is added when outside T is lower than inside T instead of firing up the condenser (or the windows are opened :-).
For cold climates, these numbers (30%, 13%) could lead to real savings. Was this discussed? Any thoughts?

By: David Holtzclaw

David Holtzclaw — Thu, 14 May 2015 02:54:48 +0000

Thank you Allison for posting
Thank you Allison for posting this. The "conditions when the air conditioner is running" slide makes me wonder if "residential economizers" might make more sense now? As I understand it, residential economizers were thought to never be cost effective as residential loads are driven by envelope loads not internal loads as it typically is in the commercial sector. But these new data makes me wonder. From my experience, my clients in cold climates overuse their AC because of comfort - they HATE being the slightest bit hot, but can tolerate 60F indoor dry bulb all winter - (like Vermont). For cold climates, it seems like economizers (or windows) might work. Or, now that more and more homes have mechanical ventilation, some control scheme were more ventilation is added when outside T is lower than inside T instead of firing up the condenser (or the windows are opened :-).  For cold climates, these numbers (30%, 13%) could lead to real savings. Was this discussed? Any thoughts?

By: Nate Adams

Nate Adams — Wed, 13 May 2015 19:50:32 +0000

Switching gears to a Building
Switching gears to a Building Science perspective, while the RH and run time bit is interesting, there is a lot we don't know as Dale S. and Sean L. commented.

The biggest factor there is probably duct connections to the outdoors. In your experiment on your own family, Allison, you found that running the fan bumped RH because it sucked in more outside humidity through leaky ducts.

Could the same be true here even with equipment running: duct leakage to outdoors pulls in more moisture than the equipment takes out?

I'd be curious how the numbers hold in a reasonably tight home with reasonably tight ducts. Crappy houses perform crappily...

By: Nate Adams

Nate Adams — Wed, 13 May 2015 19:43:52 +0000

I'm very thankful Michael
I'm very thankful Michael Blasnik got Nest to allow this data to be presented.

Echoing Andrew McDowell, the next question is how can we use this information to help consumers? How can we sell more jobs with it?

This is off topic a touch, but at the ACI keynote less than 10% of people raised their hands when asked who was a contractor. There is a sales problem behind that. All the specialized knowledge in the world doesn't matter than much until it's applied in the marketplace. Food for thought.