Competition: Nest Learning Thermostat: Black Box Analysis

Since Nest is the only competing product you don't have to take a loan in the bank to own (well, maybe just a small loan), it was interesting to get a first hand experience with it. So, I bought it and installed next to one of DZ sensors.

I am reluctant to talk to my competition because the amount of information they can extract out of my questions significantly exceeds the amount of information they can extract of my most honest answers to their most detailed questions. --GT

Well, the experience was definitely interesting.

The Excellent

The most impressive (from usability standpoint) thing about the installation process is how they implemented pairing the device with the online account. I created the account (took a split second) and several seconds later, when I turned  to face the thermostat (less than a meter away), it was already displaying the message asking whether I want to associate it with the account I just created. Under the wraps, it is pretty simple to someone in the trade (they probably matched the WAN IP to serial number and account name to the IP it was created from), but nevertheless very impressive. Definitely karma bonus for creativity.

The Good

• No-brainer installation for someone with hands growing out of shoulders.
• It was impressive that it correctly determined wiring.
• It was really simple to configure it to work with the existing system (those who know how many variations of thermostat wiring and systems are out there will be definitely impressed by this).
• Upon connecting to WiFi, the device immediately downloaded the update.
• There's just a few seconds latency between the device and the web app.
• Control algorithm seems to be smarter than just a simple hysteresis loop, will see how smart later.

The Neutral

• Temperature displayed is the setpoint temperature, not the actual temperature.
• Both setpoint and actual temperature display resolution is 1°F and 0.5°C, this is not sufficient for some conditions (good example: the room with little air getting to it, while the other room next to the HVAC unit gets more than it bargained for). Making this happen, though, will destroy the "Apple" aesthetics.
• Not sure how successful will be WiFi connection when a DHCP server is not present. Too lazy to try, hope they did something smart.
• Initially, I thought that the device was blind as a bat and doesn't sense presence right, but then realized that it's just doing it in its own way.

The Bad

• It was quite painful to enter a 21 character passphrase for the wireless network.
• It took two reboots and about 10 minutes to download and install the update.
• There is no indication of how close the thermostat is to calling - itchy fingers *will* try to bump the thermostat if they feel too hot or too cold.
• Settings change sensitivity is, unexpectedly, extremely high compared to setpoint change sensitivity - the latter is less than 1:1, and the former is almost trigger fast. Uncomfortable, and is a violation of the principle of least astonishment.
• There doesn't seem to be a way to change the hysteresis from the default. This will cause short cycling for smaller rooms, and stale air for bigger.
• The maximum "away" temperature setting for cooling mode is just 90°F. Folks, this is not enough for hot climates - I *work* comfortably at 90°F, and won't be afraid to set the away temperature to 100°F on the second floor.
• Actual temperature is not easily visible over the "grill" (and for °C, good luck trying to distinguish "22.⁵" and "22°").
• Web app and mobile app don't honor the °C measurement unit for ambient temperature. While we're at that, why don't they display other data available from Weather Underground (which is their data source)? (The weather is displayed as a background picture)
• Standard 18 AWG thermostat wire doesn't fit into the base, had to use thinner wire. I had a patch panel for wiring so it wasn't a problem, but good luck doing this if all you have is the cable sticking out of the wall.

The Ugly

• Fingerprints all over the glass.
• Guess what two users tried to do (independently from each other) when asked to change the setpoint on iPad app. Correct, they tried to replicate the circular movement that it takes to change the temperature on the actual device. Instead, they were presented with ancient up and down arrows. Come on, folks, *I* did better than that, gesture detection is not that complicated.
• Entering several spaces in the passphrase was most excruciating. Hint to Nest developers: it is possible to use all that nice space between the alphabet and done/cancel/backspace symbols that you already have, and plant some spacebars right there. Yes, in every shift mode. Won't hurt. Took quite a while to figure out that those spaces are currently just for decoration and aren't functional.
• And it was completely infuriating when after spending about two minutes of entering the passphrase the thermostat happily reported "failed to connect" (it was a transient failure) and... displayed the EMPTY prompt again.
• Let me just say this... Don't even try to use their webapp on a mobile phone. Their "beta" is not Google's "beta". More like "alpha". At $250 plus shipping a pop.
• Where is my Android app? Right here: Nest Mobile. Pretty basic, though, nothing to write home about.

The Verdict

Short version: Meh.

Long version:

• Hardware looks to be decent (though, just like I suspected, there's not much stainless steel, it's mostly plastic).
• Embedded software (on the thermostat itself) is perfect as far as usability is concerned, but passable as far as climate control is concerned (no comments about learning ability, that'll be covered later).
• Web front end is definitely in alpha stage. Let's hope that they are planning to advance it, or at least make it work right on a wider variety of devices.

Applicability

All the information above is pertinent to model Diamond-1.10, display software ver. 1.0.4, base ver. 3.5.2/1.1, as of January 5 2012.

Honeywell RTH7500: Long Term Verdict

Surprisingly, the most annoying feature of this thermostat turned out to be lack of programmable hysteresis, a.k.a. deadband.

This particular one, installed in this particular location, allows runtimes as short as three bleeping minutes - whereas the time required to get into more or less efficient operating mode is no less than about five minutes for furnaces and about fifteen minutes for an A/C or a heatpump.

Likewise, there is no minimum run time protection (sometimes called short cycling protection).

In other words, this thermostat will make your unit work much less efficiently than it is designed to, and the only way to prevent that is to put the thermostat in a place where the temperature changes very, very slowly - like a closet or a thermally insulated box. Which is not quite that practical.

So, thumbs down, no go.

Likewise, if I ever have to select a thermostat again, I will pay particular attention to presence of programmable hysteresis and minimum run time.

The Competition: Advanced Temperature Control

Doesn't quite look in the same weight category as DZ, but it is. DZ, despite being all primitive and DIYy, is limited only by hardware. Give it commercial class hardware - get commercial class performance.

Just give me a second to finish the UI, all right? :)

Speaking of which, they have a nice touch screen as well.

(Image: Control4)


UPDATE (2012/02/22): All links are gone. Cursory search on their site doesn't produce anything close to original results, so I've decided to just leave them as is, for those with enough time to investigate. Oh, and by the way, DZ has a shiny UI now as well.

The Competition: ENV-VST-C

Apparently, doesn't support zoning per se. On the other hand, lots of interesting features, and pretty complete documentation. Along with other interesting things.

Some things in it are hilarious, though - I'm still waiting for feedback from a HVAC expert on some of them, will publish conclusions when I get it back.

In any case, merits thorough investigation. I don't think you can buy it though - let me know if you learn otherwise.

(Image: AMX)

The Competition: Honeywell Prestige HD

The best things to do with competition are to know them and to respect them.

Here's what our competition is, sort of:



Go read the Honeywell Touchscreen Thermostat and Portable Remote Review and keep in mind that there is a subtle distinction between Prestige HD and Prestige SD (about a hundred dollars or so).

Then go do some shopping (zoning system not included) and hopefully come back - if not today, then in a few weeks or months when the GUI (and other unannounced bells and whistles) is back to its former glory and beyond, for the price of Prestige with comparable feature set is steep indeed.

By the way, DZ is going to look nothing like Prestige :)

UPDATE: This is what it looks like. This is what it looks like :)

Favorite quote from the Homeowner Brochure (emphasis mine):

You can even name each of your zones on the Portable Comfort Control by having your contractor customize it with more than 60 different naming options - upstairs, master bedroom, office - even wine cellar and home theater!

(Image Credit: Gizmodo.com)

FAQ: Thermostat Sensitivity

Q: Default thermostat settings cause too much of a temperature swing, how do I make my thermostat more sensitive?

A: You increase the value of P for the PID controller associated with this thermostat. Default value of P (1.0) corresponds to a deadband from 1°C below the setpoint to 1°C above. Increasing P to 2 will cause that to change to a range from 0.5°C below the setpoint to 0.5°C above.

Likewise, if you want to dumb down your thermostat because the HVAC switches on and off too often, you need to decrease the value of P. However, be careful, for short cycling (the HVAC term for this phenomenon) may have different causes - but you'll be able to easily see the cause for them on charts DZ generates.

Q: Will there be a UI control for that?

A: Yes.

Pulse, Reloaded

Once upon a time, there was an overheating video card. It begat the Pulse project, the hardware health monitor. Later, overheating house begat DIY Zoning, and since its inception, Pulse started to wither away into oblivion - a few years later I marked its status on SourceForge as "inactive", and today, there's not even a web page for it.

However, recent emergence of Android changed a lot. For a long time, lack of hardware support for DZ was a showstopper - nobody wants a zoning system that needs a computer in order to operate it. Smartphone, however, is a completely different deal.

Almost exactly a year ago I started planning for it. A month ago, I got my hands on the hardware. Today, I can say with confidence that G1 can deliver, and it does make sense to implement a control system with a mobile interface based on Android platform.

One of the lessons of DIY Zoning development was that it is a bad idea to have a monolithic system - I had to split it up three or four times before I was happy with the distributed features of the whole system. Not to repeat the same mistake, the application will be more generic than just a zoning system controller.

Hence, hereby the relaunch of the Pulse project is announced.

It'll be a short while before the feature set is established, the project site is again complete with content, and version control system will have the code - I just don't want to release half-baked barely functioning code prematurely, it is still in the works. It's just that privately expressed interest towards the project exceeded the critical mass recently, and I thought you folks would like to know what I'm working on.

Stay tuned.

Who Needs A Thermostat, Take Three

There is a new application for Google Android platform, AutoHTN, which, among other things, purports to control the home HVAC.

Told ya...

Who Needs A Thermostat?

I've been pondering about this question for a long, long time - starting in about 2001 when the only way to control DZ available was a debug panel, and last time in an essay about SWMBO Compliance Certification (Squeezebox is still a good candidate), but it seems that there's been a new development that might if not put an end to the fruitless search, then significantly widen the options available.

I'm talking about Android.

It remains to be seen how viable the platform is and how many hardware manufactures will jump on the bandwagon. But for now - having worked on different Google APIs (Checkout and Calendar in particular) I can say that it's sure going to be a hell of a fun ride, and I'm about to get busy installing the Android SDK and tinkering with it to see how well can a user interface for a HVAC system work on a cell phone.

Now, who needs a thermostat on the wall, really?

Informal Review: Honeywell RTH7500

Following up the RiteTemp GMPG808C review...

This thermostat is actually simpler to describe. It has no character. You don't notice it.

Actually, one might take it as a compliment - this is exactly what you want from an appliance - all you need of it is to perform its function and not struggle for getting a piece of your attention all day.

But it'll sure make you work to get to that point and will punish you if you try to upset the status quo.

First of all: don't lose the manual.

The rest of installation is simple - just follow the installation manual. It would be a good idea to read all of it beforehand - there's a couple of quirks you need to be aware of, in particular, configuring the thermostat to work with your exact HVAC system configuration.

Configuration takes a while - again, it's better to have the unit on the desk before you, and not in th wall cradle, when you do it. Can't do it without the manual - options are numeric. Did I mention - don't lose the manual?

That's basically it - unless you are really off with setpoints and schedules, you won't have to touch it again.

A few observations:

• It is nice to be able to move period boundaries. Different people, different schedules.
• You may want to think twice if you really want to use the "recovery" option (the one that makes sure that if you set the period starting at 9PM having setpoint of 78°F, you will have the room at 78°F at 9PM, instead of HVAC unit starting to struggle to cool it down at 9PM) - this option will throw a wrench into your energy savings if you are on a time of day usage plan. The worse is your HVAC (or, should I say, the more properly it is sized), the less useful this option is.
  
• Have to imprint it in your mind that all you need to do to change the temperature temporarily is to press up/down arrows a few times. There is no need to press "hold" - this makes the thermostat hold the temperature forever. Kind of counterintuitive in the context of other interaction patterns - closure is expected, but missing.
• I absolutely hate the fact that the only way to see the screen in the dark is to actually press the button, and, it does something just as you press the button.Watch what you're doing. The only way not to screw things up is to learn what button is idempotent when pressed twice, and find it in the dark (oh, by the way, it is not the temperature up/down arrows... they invoke a "temporary temperature change" context, which you have to explicitly get out of or let it time out - of course, not before the light goes off). Or just forget it and switch on the lights - to me, this option eventually won the argument. In other words, if you're specifically looking for a backlit LCD thermostat, have a chuckle and move on.
• Summarizing the above, one could say that the user interface design violates the principle of least astonishment and thus may not be well suited to people who still have their VCRs blinking at 12:00.
  
• There is no apparent way to adjust hysteresis, so if you are big on energy savings, you'd better consider thermostat that can do that - GMPG808C is not the worst other choice.

That's basically all. I can make an educated guess (but it is a guess nevertheless, please let me know if it is correct) that other thermostats of the same product line are probably identical to this except for different scheduling options:

• RTH7500 supports 7-day programming (for $100);
• RTH7400 supports 5-1-1- day programming (for $80);
• RTH6300 supports 5-2 day programming (for $60);
• RTH3100 doesn't support any programming at all (for $50).

Bottomline: brand name may be overrated and overpriced.

The only other consideration is - it's been less than a year since both Honeywell and Rite Temp thermostats have been installed, so let's see which one lives longer, and by how much.

UPDATE: No Go.

Short Take: Hysteresis in RTH7500

Frequently asked question with a very vague answer - what is the hysteresis (a.k.a. dead band) of my thermostat?

For Honeywell RTH7500, the measured (therefore not exact) typical value is about 1°C (about 1.8°F) - for the sensor located in the room behind the wall where the thermostat is.

Worst observed value is 2.5°C (about 6.3°F) - for the sensor located on the first floor (the thermostat is at the second) - this is not actually a property of the thermostat, but rather an indication of how badly the airflow was designed.

Another question - can hysteresis be controlled in RTH7500? The answer is: probably not.

If it can, there's no way to do it that is described in the documentation that is sold with the thermostat (yes, I found the manual, feel free to ask me what those numbers mean).

Short Take: Where's My RTH7500 Manual?

Exactly where you put it, dummy.

Correction: I am the dummy.

So here I am, trying to figure out the way to configure the hysteresis and, at the same time, save myself a long walk to the shelf at the second floor where I *think* I put the plastic bag with the manual and spare parts. Also, it's middle of the night, it's dark, the light switch is out of the way, everyone in the house is asleep and I don't want to step on the cat strategically placed somewhere down my path.

So I'm thinking: it's 2007, let's google it up.

Yeah, right.

I guess my patience is thinned by previous encounters with HVAC machinery and service, unlike one of this gentleman.

Mind you, all configuration settings in this thermostat are not described by words. They are described by numbers. There's no way in hell I can remember numbers I have to use once in a few months, if not years. And the paper manual is nowhere to be found. And what other companies usually put up (a printable PDF document) is nowhere to be found, either.

Nice.

Another score for Rite Temp.

And don't lose your manual, otherwise you end up with a quite expensive brick on your wall.

Update: I've found the manual...

Rite Temp GPMG8085C: Informal Review

Who would've thought that this blog would be one of the most often referred to sources of information about GPMG8085C... All right, if that's what y'all want...

Ever heard of "The Golden Triangle"? "Good, Cheap, Fast - Pick Two". So, this thermostat may just as well be the closest approximation. $20 cheaper than the next guy (Honeywell RTH7500, I'll come back to it another time), does the same job, if not better.

Comparable quality and length of DIY installation.

Installation complexity: no-brainer (YMMV). A few advices, though:

• Make sure you RTFM;
• Don't drop the wires into the wall;
• Programming is best done when the thermostat is laying on the desk before you, not when you're standing next to the wall with the thermostat on it;
• At least for me, the preinstalled battery still works after a few months of operation, may want to ignore that paranoid advice to remove it.
  

Significantly bigger and nicer backlit touchscreen than the competition has (to be completely fair, they do have a big touchscreen on VisionPro, but that one is almost twice as expensive, so no cigar), and it has a nice textured button that you can grope (English experts, give me a non-ambiguous word and have my thanks in return) in the dark without being afraid to push a wrong button and reset something.

You have to really hate your customers not to provide an option like that (example: RTH7500 needs you to press any button, and, invokes the action corresponding to that button, even in the dark. So you have to be really careful where you tread, and the fact that the screen is backlit is useless - you can't comfortably use it anyway).

There's a stylus and a holder, but feel free to ignore it - fingers and/or fingernails do the job just fine. No visible scratch marks after few months of use.

7-day programmability is certainly nice, but the schedule selection is really weird - you can't set the schedule boundaries at arbitrary time, but only at one of two settings (forgot what times exactly, will update later). Kind of inconvenient, and this is probably the most annoying feature, or, rather, lack thereof. Competing device shines here - you can have your heat and cold any time.

Side note: I'm wondering why nobody figured yet that anticipation is something you're quite willing to have for a period starting, say, at 6PM, when you return from work, but not really want for the period starting, say, at 9PM - when you are on a time of day electric plan, which makes energy after 9PM three times cheaper than before. Remember, you read it here first.

If you don't need 7-day programming, there are other, cheaper Rite Temp models that offer compatible feature set, but 5+1+1 or 5+2 day programming.

I'm quite willing to forgive lack of schedule configurability for including an extremely important feature - you can manually change the hysteresis. Setting it to the maximum value makes the temperature spread quite noticeable (up to 5°F), but makes the unit cycle about three times less often than it would otherwise do. Don't have equipment to measure the actual gain, but would certainly recommend this thermostat to people who are either energy conscious and don't mind little discomfort, and to people who have grossly oversized units - you guys may suffer from temperature swings even worse, but at least your electric bill will drop like a rock because the unit won't breathe like a dog outdoors in Arizona summer anymore.

Can't say anything about humidistat - not much use for it in the middle of Arizona summer.

Another useful feature - filter usage counter. Depending on the climate, your unit may cease operating for a couple of months in mid-season, so you can afford to buy a higher quality, more expensive filter without a fear that you're wasting money (just think of how much it'll cost you to clean the inner coil when the time comes, and reconsider buying that inexpensive $3 filter).

You definitely need to read the manual provided with it in order to learn to operate - but then again, this is true about any more or less complicated home appliance - it takes significantly higher IQ to figure out how to connect the 5.1 home theater and the rest of components together without electrocuting oneself, so no big deal here.

At least all the settings have icons assigned to them, and you can figure out what is what, unlike some other designs, where features are indicated with numbers (come on, it's not 1960 anymore...)

Bottomline

Well worth the money I paid for it.

Disclaimer

God, what have we come to... Anyway - use your common sense, don't do stupid things, and read this first.

Thermostat Wars

The predominant kind of thermostat war is the one between those who understand the concept of the thermostat and those who don't. It is difficult to believe, but there are still people who don't get it. They would crank the thermostat all the way down when they feel hot and all the way up when they feel cold. I kid you not, several years ago there was a guy who came to the Residential HVAC forum with a question, "how to educate the significant other not to do that". After few days and several dozen messages, the community agreed that the only way to deal with his particular problem was to install a fake thermostat. This case is beyond repair, let's concentrate on the other.

Out of remaining, two kinds can be distilled: those that require marriage counseling and cause HR violations , and those that don't. The latter is the kind I would like to cover in this article.

The final division is the wars between the occupants of different rooms, and, those apparently happening just in the mind of a single person waging the war.

The first kind is actually pretty easy - this is what the zoning systems are for. I mean, the real ones that do allow you to set different temperature for different zones.

As for the last kind... Imagine a situation when there's a person who claims they are absolutely comfortable with a certain temperature - let's say, for the sake of argument, it's 78°F. And indeed, when put into a scientifically controlled environment, they feel just fine. But in real life...

They fiddle with the thermostat all the time. Sometimes they push it up. Sometimes they push it down. Sometimes, they claim the thermostat is not calibrated (it is). When cornered, they are claiming the temperature is not right, and demand a precision thermometer. And you know what?

Most of the time they are right.

The cause for it is trivial from a control systems engineer standpoint, but is carefully hidden in a plain view for the rest of the world.

Almost all thermostats, except the very advanced ones, are based on a very simple concept of a hysteresis. Temperature goes X degrees above the setpoint, cooling on. Temperature goes X degrees below the setpoint, cooling off. Simple?

Not quite.

First of all, not all thermostats (as a matter of fact, very few) will let you change X. According to some claims (google it up if you want), X = 2.5 (I suppose Fahrenheit) for mechanical thermostats, somewhat less for digital. 5°F spread is a lot.

Side note: Rite Temp GPMG8085C (and possibly other Rite Temp thermostats) will let you control hysteresis. Doesn't mean I endorse it, though - it's got its quirks. Doesn't mean I condemn it, either - it's doing a good job comparable to Honeywell RTH7500 for $20 (20%) less.

Then, the situation gets very interesting as temperatures get milder. The closer is the ambient temperature to the setpoint temperature, the more suffering there is (that'll be mornings, afternoons, and the whole mid-seasons). The reason?

Deviations of ambient temperature are sufficient to cause severe discomfort, but are not sufficient to kick the temperature at the thermostat beyond the dead band and thus to force the HVAC unit to actually do something.

Things can become really bad if the house is big enough, and the part of it where the thermostat is is insulated better than other parts - all in all, "mild" is a relative term. A typical case would be a tri-level house somewhere in Arizona.

Which is where and how it all started. Is there an answer? Yes, and it's been already implemented several years ago, but I'm not telling. It would suffice to say that if you want to find out, by this time you know where to look for it.

Imitation is the most sincere form of flattery

Here's a screenshot of a debug console for DZ, published on February 22 2002:




(also, here, here, here, here, and here, and the whole discussion around it here)


Here's a picture of a Honeywell VisionPro Touchscreen Thermostat, released several years later:



Hmm...

Shut off the A/C or leave it running?

One of the most frequently asked questions is "Should I shut off my A/C when leaving the house, or leave it running?"

You see, it's not that simple...

This is one of those classical cans of worms that a lot of people (HVAC professionals in particular) have an opinion on, but just try to ask them to quantify the problem, and the result has all the chances to be hilarious.

Suppose, you go on vacation and shut off the A/C for a month. You've just saved a lot of money, except now you have to repair the cracked deck in your sixty thousand dollars Steinway grand piano you absolutely forgot about.

Suppose, you get out to walk the dog and shut off the A/C. I will call you paranoid and probably pound foolish, penny wise (all in all, having a dog is an expense you don't really have to incur if you're so concerned about your financial well being).

Suppose, you send the kids to school and go to work at 0800. Kids get back from school at 1400, you get back at 1800. This is where things get interesting.

Pretend the house is a pool. The HVAC is the hose. The walls are the drain. The drain is constantly open. The hose is open as it is needed to keep the pool filled up.

So when you shut off the hose, the pool starts losing water. The longer the hose is shut off, the more water you have to replenish (note that this is pretty much like cooling the house - yes, there will be a point beyond which all the water is gone, and from that moment on you're purely saving money). On the other hand, the longer the hose is shut off, the less you pay.

When you come back and open the hose, the water level goes up (and the house cools down). The bigger the hose is, the faster it will happen.

In other words, the bigger your HVAC is, the more sense it makes to shut it off or adjust the setpoint when leaving the house.

But wait, this is not the end of the story yet...

The drain is nonlinear.
The hose is nonlinear.

The hotter it is, the bigger is the drain, the sooner the water is gone.
The hotter it is, the more strain is put onto the hose (this is even worse for heat pumps in heating mode, because of the balance point).
It may lead to a situation when the inflow can't keep up with the outflow.


In other words, the smaller (or worse) is your HVAC, the less sense it makes to shut it off or adjust the setpoint when leaving the house. If this is your case, bite the bullet and pay the bill. Which reminds me, by the way, that poor people pay more.

But wait, this is not the end of the story either.

The highlighted cases above are for extremes. As the weather gets milder, efficiency considerations fade because the drain narrows (not as much heat is lost or gained). For this case, the longer you are away, the more sense it makes to shut off the HVAC or adjust the setpoint.

Now, let's remember the rule: whatever you cannot measure, you cannot improve. You may spend days and nights guessing, but you will never know whether you improved the situation or made it worse until and unless you have long term trends monitoring set up.

Which brings us all the way back, right here.

PS: Inquisitive readers will notice quite a few threads dangling here. Detailed explanations will go well beyond the point of loss of interest, but those who care to find out have probably figured out where to go to get the answers.