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Frank Stearns Frank Stearns is offline
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Default DIY HVAC Zoning?

Bubba writes:

On Mon, 03 Mar 2008 22:19:43 -0000, Frank Stearns
wrote:


Bubba writes:

self-snips


more snips

Maybe you missed a few items...

- That's PARTS ONLY that I obtain (CPU, stats, dampers), I do the 2-3 days labor and
dialing in... (And oh yes, I know the building well -- I designed it, had it built,
but did all the electrical and was on site everyday. Short-sighted at the time, I
declined a 6 zone system and settled for two, one of which handles the rooms in
questions. Live and learn.g)

- I don't have a massive regional radio ad and marketing campaign to pay for in that
parts budget, nor is there a home office and staff to fund. I don't at all begrudge
their asking $7K, it's just that I'm willing to investigate this further on my own,
given that I have some appitude for this stuff.


After you replace a few compressors, fan motors and blower wheels,
along with a multitude of other problems with the system never working
right, refrigerant leaks and ridiculous energy bills, you might begin
to understand that "Zoning" aint for the average joe.


Well, not exactlty an average joe... extensive background with several kinds of
engineering, and a lot of practical DIY experience across many areas (including
being a multi-unit landlord for many years) -- enough overall experience to know
that each trade has its interesting twists and that it's good to get as many data
points as possible.

So why a compressor failure? Blower & fan failures? Would that be due to no anti
slump? Coil freeze? Too much back pressure?

I hope I addressed those concerns by getting a smart enough CPU that will either
"baby" the compressor or could have "events" added to its program so that the system
would be treated gently.

Not sure why the energy bill would be higher... Can you give me more background on
that one?

Thanks for your reply, and any added advice you might have.

Frank


Nope, actually I didnt miss any items.
There is no "dialing in" on the system. It has many settings. They get


Sure there is. In the various kinds of engineering I do, we routinely test;
generally at very conservative settings until we know something is going to work.
And I do appreciate the dangers of modifying a system to do a job is was not
designed to do.

What I'd probably do, especially if I'm adding programming to the CPU (or perhaps
getting my own 6x6 industrial controller and programming the whole thing myself), is
run the zoning controls (dampers, stats, CPU) NOT CONNECTED to the ductwork, but out
in the shop. Emulate conditions; see how the added programming is working. Next move
the stats into the spaces, dampers still not connected, and see if everything still
looks good.

set properly. No guessing. It doesnt matter how well you know the


Seems that many of the systems done by "professionals" relies on a lot of guessing
-- I've observed much HVAC nonsense, both in residential and commercial settings:
noise (wrong duct and/or blower size or bad layout or wrong diffusers), hot/cold
spots, short or long cycles because the thing wasn't sized correctly. and so on.


building or that you "built it" etc. That has nothing to do with


Maybe, maybe not; I do have the advantage of having been in this space for 15 years.
I know its thermal (and other) quirks; I know that at one time the coil froze way
too often (didn't blow the comp, though, knock on wood; but it did trip the
overpressure limit a few times). I mitigated that -- all on my own. Two HVAC pros
couldn't figure out what was going on (only that I should replace nearly new
hardware for no good reason... well, $$$ for them).

I finally figured out the problems by looking (the pros wouldn't even go down in the
crawl space and look!). Freezing is now a far more rare occurrence.


installing a zoned system properly. Your EE'ing counts for nothing
either....sorry.


Only that I'm generally conversant in new areas and understand much of the common
design logic. But you don't know me, so that's a fair statement -- and I know what
you mean. I've rolled my eyes at amateurs in my fields as well.


The fact that you have no idea why an improperly installed zone system
will fail a compressor, blower or blower wheel tells me you need to
leave it to someone that does.


Gee, I thought I covered that: back pressure, insuffient air flow over the coil such
that it freezes (or return air that's "overly conditioned" due to poor return
locations), etc, etc.

If you'd like, provide a high-level overview of the more esoteric aspects that I
missed.


Improper static pressure in ductwork can make a blower wheel look like
someone has bashed it with a sledghammer. Ive seen it many times.
Improper air flow through a coil will also destroy a compressor. Ive
seen that many times over too.


Certainly makes sense.


There is NO cpu that will "baby" your compressor. Try telling your cpu
manufacturer that you want a free new compressor because their cpu


Agreed. Not their responsibility.

didnt take care of your compressor. There also are not "events" you
can put in to "treat your system gently".


Specifically, I was considering a longer fan runtime after the set temps had been
reached, and also a longer antislump interval, given that such a system will tend
to short-cycle because through zoning we're changing the entire design load "on the
fly". And that's hard on everything. I was also considering a longer
minimum run interval, and dumping the "extra" conditioning into the other spaces.

I do know, for example, that the production room will tend to heat nearly as much as
the machine room. So "extra" time on the machine room could go into the production
room.

Also, programmatically, it'd seem that increasing the fuzziness of some of the zones
would be useful. A +/- 5 or even 10 degrees in the machine room would be fine.
Doesn't need to be +/- 1 degree. Production room could be +/- 3; the office would
nice a little tigher, but it doesn't matter all that much either, if it's better
for the system.

Programmatically, I'd also be looking at a logical weighting of using the blower
before calling for conditioning. (In fact, programming the blower on/off in an of
itself might get me 80% of what I'm looking for -- I do that manually now, but it's
a pain to remember to do it right.)

I've noticed in a lot of "modern" HVAC design thinking wants to hold things very
tight, perhaps too tight, unless the system is sized *exactly right* and takes into
account thermal loads from windows and other sources. Hell, around here, those
calcs are routinely blown out of the water given the number of southern windows
coupled with the wide variance of sun and cloudy days.


Its called Proper Technique, Proper Installation and a whole lot of
knowledge. Ive seen companies that do this regularly that can screw
them up. Ive seen companies that only do a few of them that screw them
up even worse.


Could not agree more. I've seen the same. The difference is that because I own the
joint I realllly want to be careful with this.

Even if I were willing to spend the $7K, I'm not entirely sure I'd find pros that
would care as much as I do, and would be willing to follow through as carefully.

If you have the "money to burn" then have a stab at it and watch the
sparks fly.
Have Fun,


Let me guess... you're an HVAC guy and hate it when consumers do their own stuff.
That's fine. Do what I do in my fields and (a) offer to eval for a consult fee (but
you'll need to provide your credentials and a reference list); (b) smile and clean
up their mess afterwards -- on an open-ended cost-plus basis.

In the meantime, as long as your responding to the posts, perhaps you could take a
stab at the original questions, if so inclined?

Thanks in advance,

Frank
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