I've got some wild temp swings between an office, machine
room, and production room (and the bathroom is almost
always too cold 9 months out of 12). This part of the
building has its own separate 1.5 ton heatpump for these
areas, but it's on one thermostat in the office.
Active zoning should take care of those temp issues, and
the air-handler/heat exchanger is down below in a nice,
easy-access crawl space. All the ducting is simple to get
to as well.
The folks who do the retrofit bladder system for zoning
want a MINIMUM of $7K. It appears I can get a computer good
for four zones, four stats, and the various dampers for
probably around $700-800.
Seems simple enough, but I always approach such things with
Has anyone done this? Any overlooked "gotchas"? Any
suppliers/brands better than others?
Given that the tiny machine room will probably call for
cooling when nobody else does, there might be too much back
pressure on the fan, as the duct in that room probably
represents less than 5% of total system airflow capacity.
(I might put in a larger duct and vent.)
I still might also need a bypass damper. Are those
"passive" (too much pressure opens a spring- or weight-
loaded damper); or are there active ones controlled by the
I thought perhaps a variable speed blower might be the way
to go, but that means a new fan, and still a likely chance
for a coil freeze or overheat, unless the computer has the
added smarts to run the blower longer and the compressor
It'd be nice if the system was smart enough to use
(recirculate) the waste heat from the machine room first,
before calling for heat from the heatpump.
A central computer where I could add functions or modify
standard heating/cooling "events" would good. For example,
I'd like to start the blower for a while first to
redistribute the air before switching on a compressor, or
perhaps periodically run the blower for all zones just to
recirculate the air. (I do that now manually. This alone
helps quite a bit.)
And, a central computer with a heatpump "anti-slump"
timeout would be good too.
If anyone's done their own zoning on a forced-air system,
I'd be interested in hearing your experiences, suggestions,
and recommended DIY-friendly HVAC suppliers.
Thanks in advance,
Not to get all over you but it works this way:
If it sounds to good to be true ($700-$800).....
it probably is ($7k)
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.
Maybe you missed a few items...
- That's PARTS ONLY that I obtain (CPU, stats, dampers), I do the 2-3 days labor
dialing in... (And oh yes, I know the building well -- I designed it, had it
but did all the electrical and was on site everyday. Short-sighted at the time,
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
parts budget, nor is there a home office and staff to fund. I don't at all
their asking $7K, it's just that I'm willing to investigate this further on my
given that I have some appitude for this stuff.
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
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
would be treated gently.
Not sure why the energy bill would be higher... Can you give me more background
Thanks for your reply, and any added advice you might have.
Nope, actually I didnt miss any items.
There is no "dialing in" on the system. It has many settings. They get
set properly. No guessing. It doesnt matter how well you know the
building or that you "built it" etc. That has nothing to do with
installing a zoned system properly. Your EE'ing counts for nothing
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.
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.
There is NO cpu that will "baby" your compressor. Try telling your cpu
manufacturer that you want a free new compressor because their cpu
didnt take care of your compressor. There also are not "events" you
can put in to "treat your system gently".
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.
If you have the "money to burn" then have a stab at it and watch the
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
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
getting my own 6x6 industrial controller and programming the whole thing
run the zoning controls (dampers, stats, CPU) NOT CONNECTED to the ductwork, but
in the shop. Emulate conditions; see how the added programming is working. Next
the stats into the spaces, dampers still not connected, and see if everything
Seems that many of the systems done by "professionals" relies on a lot of
-- I've observed much HVAC nonsense, both in residential and commercial
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.
Maybe, maybe not; I do have the advantage of having been in this space for 15
I know its thermal (and other) quirks; I know that at one time the coil froze
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
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
crawl space and look!). Freezing is now a far more rare occurrence.
Only that I'm generally conversant in new areas and understand much of the
design logic. But you don't know me, so that's a fair statement -- and I know
you mean. I've rolled my eyes at amateurs in my fields as well.
Gee, I thought I covered that: back pressure, insuffient air flow over the coil
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
Certainly makes sense.
Agreed. Not their responsibility.
Specifically, I was considering a longer fan runtime after the set temps had
reached, and also a longer antislump interval, given that such a system will
to short-cycle because through zoning we're changing the entire design load "on
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
the machine room. So "extra" time on the machine room could go into the
Also, programmatically, it'd seem that increasing the fuzziness of some of the
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
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
itself might get me 80% of what I'm looking for -- I do that manually now, but
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
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.
Could not agree more. I've seen the same. The difference is that because I own
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
would care as much as I do, and would be willing to follow through as carefully.
Let me guess... you're an HVAC guy and hate it when consumers do their own
That's fine. Do what I do in my fields and (a) offer to eval for a consult fee
you'll need to provide your credentials and a reference list); (b) smile and
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
stab at the original questions, if so inclined?
Thanks in advance,
You might use a $100 Norhtec 2.5-watt mcjrxs 486 clone with Ubuntu linux
(free) on a $10 1 GB compact flash ram, with a DS9490R USB-1-wire adapter
and some $2 Dallas DS18B20 12-bit 1-wire temp sensors and a $48 Systronics
8-1 output board with OWFS, and program it in bwbasic.
You can calculate dewpoints and economize with a humidity sensor like
Aagelectronica's $48 TAI8540D and a foamboard damper made with a $10
used windshield wiper motor, and ventilate as needed with a $300 GE
8002 CO2 sensor.
Don't hold your breath, waiting for Bubba's constructive help :-)
You designed this building and nmade a serious error when designing the
heating and cooling. You now wish to correct this error. You claim to have
an engineering background.
Ok, it doesn't work, you do not seem to have much knowledge about heating
and cooling, and you want it fixed. Your options are to hire someone
knowledgeable (a civil engineer) or head to the library. If you hire an
engineer, expect him to visit the building. You will not get good advice
without such a visit so internet advice won't be much help.
The pro hired by the general to do the HVAC did the HVAC design and made some
errors. Better than some, worse than others -- all around, a C+ (he did install
very quiet systems -- high marks for that).
My mistake was not getting way more technical knowledge about such systems, but
consumers would balk at involvement at that level. I don't mind, but was out of
at that point.
The later freezing problems never were identified by two other pros -- had to
out that one out myself. (The original guy had gone out of business.) So far,
not exactly smitten with the pros in this field. There must be good ones...
Pays the bills with long-time repeat customers. :)
It's not really broken, but some things have become inconvenient and it'd be
to optimize them.
Will all respect, this isn't rocket science (though large building HVAC may be
close) -- it is a highly-skilled trade with its own particular language and
practices; I'm looking at visiting a subset of the trade for a while, if I can.
cookbook advice I'd not take from a Netnews group in any case, at least not
second-sourcing that advice.
Such postings can, however, lead to previously unknown vendors, along with
and phrases that suggest additional lines of research.
But thanks to all the (apparently) turf-guarding HVAC guys for their replies;
not exactly the info I was looking for that in itself has been useful.
Honestly Frank, it seems that what you are trying to do is RE-Invent
the wheel. There are several very good zoning systems out there. Use
Yup, I see it everyday. REally sucks when you(me) are one that knows
how to do it right.
Depending on the crawl space, I might not either. Why on earth people
put one of the most important systems in their house down in a hole,
under a house or up in a dark hot attic, I'll just never know.
But you asked why would it damage a blower or compressor. Because it
will. Thats why.
Ive got 27 years experience in the field. You'll just have to respect
and understand why I wont give that info out freely.
Yup, you can dump it into a conditioned space or dump it back into the
return and lower the return temp. This requires a freeze stat on the
coil. Again, all the fan runtime and stuff you want to change is built
into and adjustable in most zone systems.
Nope. A proper load calculation will give you exact design specs on
what equipment should be used. Its to be done on every system
installed however many guys skip this step.
Thats what contracts are for. They spell out what they will do. You
ask for additions to the contract if you like. Anything within reason
a good hvac company would grant. A good company will want it done
right too. Some of us do still have pride. Unfortunately, you have to
do a little homework to find that right company. The same as looking
for a new car, house, plumber, doctor, lawyer and accountant. Some bad
and some good.
Yes, I own my own HVAC company. 25 yrs. 2 yrs I worked for a large
outfit. Basically just crooks.
Sure, some consumers bug me. Especially the ones that do it themselves
then call me and try to get it straightened out for free or want all
kinds of free advice. All in all though, if it werent for the do it
yourselfers out there, Id probably have a lot less work. Seems Im
always fixing up the messes out there. Puts food on my table.
Sure, get an out of the box zone system. Many out there and many work
very well without re-inventing.
Frank, I'm with you on this one. Got three estimates to replace an old heat
pump along with an eclectic furnace. Prices from highly advertised
companies were, $ 8,500, $ 9,700 and $ 10,200.
Got hooked up with a 'friend of a friend' who would do the same installation
(all Carrier equipment). Total bill came to $ 2,400 and the installer made
about $ 150 per hour for his on site labor. Lots of overhead and profit in
Hi Ivan -
Good story, and that's my "casual read" on the business side of HVAC. Nothing
with high profit, if that's what the market suggests. But if one has another
workable route, as you did and as I might, that should be okay too.
How's that Carrier system working? They had the variable speed system I *should*
have gotten originally to better support zoning. Got talked into using another
for HVAC who carried York. My mistake, and I accept that responsibility. Mostly
two systems are fine, but some of the usage patterns have changed.
Thanks for the anecdote,
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