Sunday, August 12, 2007

OUCH! This Is Not Design

This is a kind of engineering I'm trying to avoid: Window A/C Keeps Car Cool.

Feel free to peruse the Digg article for trivial criticism.

Meanwhile, instead of joining the crowd in bashing the guy (totally deserved, I must say) I'll try to be constructive and talk a little about why I claim DZ is not a hack like that.

First of all, two projects (let's call the other one The Window Hack, TWH for short, from now on) solve different tasks, though on surface they may seem to solve the same - inadequate cooling.

TWH is supposed to solve the problem of a HVAC unit, perfectly good by design, but poor by execution, that keeps breaking and sucking money. In other words, it addresses the problem of financial delinquency. With many side effects, not the least of which are the aggravation of outbound cash flow (air drag => $$$ for extra gas) and consumer safety (imagine where that box flies in case of a collision, or if it is simply torn off by the air stream at 70mph).

DZ, on the other hand, is aimed at solving a problem of inadequate HVAC design. Moreover, it solves it in a scalable way that allows to start getting immediate improvements with very little investment, and keep investing into hardware and getting tangible benefits all the way up to the sky.

First of all, you can just install the sensor network and stop right there. Analysis of what you will see may just as well allow you to make adjustments to your home infrastructure in order to bring it to your home comfort requirements.

Then, you can run DZ in passive mode and never touch the HVAC - gives the skittish ones their piece of mind and improvements in home comfort.

Or, you can just go all the way and reap the benefits.

In any case, amount of improvements you get is proportional to your invesment - would it be your time or your money.

Breaking it down to components -

You can start with adding a $10 R/C servo and little labor to get a simplistic motorized register. Like I was saying before, this solution was good enough to work for two years without any necessity to improve it.

Or, you can go for an industrial grade modulating damper - the first Google hit for such a thing that has a price listed puts it at $180.01. I suspect that the actual price will be significantly higher - usually, you have to log in to see the price, and I'm afraid that not everybody would be able to even get an account, it may be restricted to certain audience. Consequently, even that price, whatever it is, is subject to markups all the way up before you are told the final figure.

But if you want to use an industrial grade damper with DZ and can afford it - be my guest, it is not only possible, but accounted for in the system architecture. Oh, and you can have a mixed set of dampers at the same time, so you don't have to spend all that money at the same time.

Same is true for the HVAC unit - DZ can work with a crappy 30 year old HVAC (and, in fact, it did for two years) and allow you to extract significant home comfort improvements even out of that monster. But if you cough up some cash and install a state of art, multistage, variable speed unit (that'll cost you somewhere north of $10,000) - it will happily recognize the features available and will allow you to squeeze even more use out of that.

Bottom line: you get what you paid for. But, you can spend a cent at a time here and there and keep getting returns on what you spend with even minor investments - you don't need to get a loan in the bank to make that happen.

Monday, August 6, 2007

Doctor, it hurts when I walk this way, or HVAC Checklist

Free Idiot Test - $5
Patient: Doctor, it hurts when I walk this way...
Doctor: Don't walk this way, then...

Buying a house is a major pain.

What I was talking about, again? Ah, the usual complaints people have about the house they just bought.

  • A particular register is too noisy.
  • Return air grill is too noisy.
  • Air handler is too noisy.
  • Condenser is too noisy.
  • A particular room is too cold or too hot.
  • One floor is hotter than the other.
  • A room feels stuffy when the doors are closed.
  • A/C can't keep up with the heat.
  • Heater can't keep up with the cold.
  • Air in the house feels musty.
  • There are dust traces outside of registers.
  • Bathroom walls stay moist forever.
The list becomes pretty long pretty fast, but it can grow significantly longer.

For one single reason: people don't pay attention to HVAC. They think about anything and everything except HVAC. And realize they're in trouble just as the train has just departed.

So, how this can be fixed? And who is in a position to fix it? Unsurprisingly, people who can benefit from this, at the same time helping potential victims avoid being trapped - realtors and, to less extent, HVAC servicemen.

It's a double edged sword, though - for realtors, HVAC is just one more hoop to jump through. For both the buyer's and seller's agents, this is an obstacle on the road between today and the moment they cash the commission check. It would take a person of high integrity to step away from otherwise inevitable financial gain - but wait, we're getting into old good argument about reputation...

Theoretically, it should be a part of home inspection report, but I'm yet to see one that would address those particular issues, or even if it did - somehow a $20 register doesn't seem to register, no pun intended, when a typical house could very well cost north of half a million dollars and this is exactly how much is at stake when you are considering buying it (or so you think at the moment. Actually, the stakes are even higher - your well being is at stake). Especially keeping in mind the fact that issues like this will surface well into the process, after you have already decided to make an offer, paid inspection fees and generally are tied up pretty fast.

Another issue is that a person or a crew that will perform the inspection is not necessarily highly proficient in HVAC. Yes, they know the motions (check the supply air temperature, etc.) - but what they do may not be enough. Then again, it is applicable to every possible subsystem in the house (Gawd! Don't ask me about the state the wiring system was in at the house I live in...) So the advice here would be to actually make an extra step and pay a HVAC contractor (yes, and the plumber, and the electrician, and the roofer - the list goes on and on). I don't think you would regret this much, especially in today's market - you may be ecstatic and think you've just coaxed the poor desperate seller and made a steal, but tomorrow will come and you will see that you're already upside down with all the problems you've overlooked.

But let's take a step back and read the complaints above. All of them share one property: they are obvious. All you need to do is pay attention.

There are certain things you can do in order to make those those problems more obvious.
  • The most difficult - look for a new house during most unfavorable season. I know, it is difficult, and plans may not work this way, and it would be difficult to have extreme conditions for the heater in the middle of the summer, but at least try. According to 6 years of observations, for Arizona (actually, North Valley, but it may be good enough for all of South Arizona) the coldest period appears to be a second half of January, extending into first half of February. Hottest period is usually the second half of July - immediately followed by the humid period (one thing I can say, though, is that if you have humidity problems in Arizona, out of all places, you'd better start walking away from that house before you finish reading this article).
  • Next best approximation is to schedule a visit during most unfavorable time of day. Hottest time of day, as far as cooling is concerned is around 5PM. Don't even hope to get the coldest time of day - unless you get to spend the night at the house, which, in this favorable to buyer market, may not be impossible.
  • Spend as much time at the house as you possibly can.
  • Make sure the doors stay closed during this time.
  • Open the curtains, don't take no for an answer.
  • Shut off the fans. Even if you like them and want them. Fans may mask the problem that already exists.
  • See where the thermostat setpoint is. Don't be cheap and spend $20-30 at RadioShack to buy a decent digital thermometer, say, 63-1087 or 63-1088 (disclaimer: I haven't tried those. The one I have is 63-1032, but it is wired).
  • Listen to the HVAC noise.
  • Run the hot shower for 15 minutes and see what happens to the walls afterwards. Hygrometer would probably be useless - sensor has too much inertia.
  • If you feel particularly adventurous, you may even want to shut off the HVAC for a while and then switch it back on and see how it behaves. Keep in mind, though, that if it brings the temperature back no normal within 15-20 minutes, you have a unit that is actually oversized (unless it is multistage, which is very rare).
And, again, start paying attention.

Saturday, August 4, 2007

Google Calendar as external scheduler for DZ???

Just thinking aloud - would using Google Calendar API be a gross overkill or actually a smart idea?

Let me see...

  • Unlimited number of zones supported...
  • Unlimited number of periods scheduled...
  • Arbitrarily flexible scheduling - you want 5+2? We have it. You want 5+1+1? We have it. You want 7-Day? we have it, too.
  • Accessible from Internet...
  • Accessible from your mobile phone...
  • Relatively nice and user friendly user interface...
  • They even work on improving it while you sleep...
Actually, this may not be such a bad idea at all.

Thursday, August 2, 2007

Informal Review: Honeywell RTH7500

Honeywell RTH7500 Thermostat

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.


SketchUp Sketches: DZ Testbed

This is a contraption that can be used to test the zoning controller functionality and operation. As the moment of writing (the image above is live, so is the link) it is just a rough draft (yeah, and it's 2:30AM), but I hope you get the idea. Plug heat sources (electric bulbs will do) into big holes. Plug temperature sensors into small holes. Connect the servos to DZ output. Connect fans to DZ output. Switch it on and watch it go crazy.

Four servos may represent up to four zones.
Four fans may represent up to four HVAC units.
Dimmers may be used to simulate variable heat load.
The divider between two middle fans is missing intentionally.
All sizes in the model (fans, servos, planes) are true and correct.

Link to the model page