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  1. #1

    Question

    Group,

    I realize that this is a "DIY" question, but I couldn't find any other place to ask this, that seemed to fit.

    I'm interested in creating a home brew zoned heating/air conditioning system, but I can't seem to find any information anywhere about the heating/cooling system in my house.

    I've just got two basic questions that I can't seem to find ANYHWHERE on the internet, and would really appreciate someone's help.

    1) My unit isn't designed for a zoned hvac, I don't think it has to be, right? (I intend on putting in a barometric pressure relief bypass duct, as well as the dampers required, these parts I understand and can do without any problems.) I'm mostly trying to understand what the wires coming from the control unit inside the HVAC unit do. The wires are marked with, "R", "C", "Y", "G", "W". My thermostat's manual (that was previously on the unit) says:

    C: Optional, this will allow thermostat to pull power from HVAC unit, if not connected thermostat will use battery power.
    R: Heat Power
    W: Heat
    Y: Cool / Comp
    G: Fan

    If I'm correct the following wires perform the following functions, (Please verify!),

    C: This is the power leg (getting that information from the manual, I assume it means that it's the common, but I'm not sure, it says, "if connected the thermostat will draw power from the c wire"), I'm not familiar with this one. Is it 24VAC, or the common for the 24VAC?
    R: Heat, I'm not understanding why there is two heats. (After re-reading the thermostat manual, I suspect this wire is the incoming 24VAC to connect to the W terminal for heating and to connect to the Y terminal for cooling.)
    W: Heat leg. Connect 24VAC to this leg when you want the unit to heat.
    Y: Cool leg. Connect 24VAC to this leg when you want the unit to cool.
    G: Fan, connect 24VAC to this leg when you want the fan to run.

    Also, if the W wire has 24VAC, the Y wire shouldn't have 24VAC, and should be "floating" (Nothing connected), is this correct, (of course oposite for cooling, Y at 24VAC, W at floating)?

    Also, I assume it would be bad for the unit to have the follwing situation: Outside temp is around 100F, inside is at 72F, temp rises to 73F, system turns on, cools down to 72F. This would mean the system is turning on and off very frequently, right? So, should the system be designed to say cool until 70F, then turn off, then wait till it becomes 75F before turning on? Or does the HVAC unit deal with this sort of thing, and setup delays on it's own?

    Second situation which would be a problem (I think), Outside temp is 100F, high noon. Inside temp is 72F, Temp rises, HVAC unit cools, .... night time comes, Thermostat switches to heat if temp falls below 70F, is this a problem for the unit? IE, Can the unit switch between heat/cool on a per day basis or should this be reserved for a per season basis? The reason I ask is becuase on every thermostat I've ever seen, this is a physical switch, NOT electronic, even though the thermostat is electronic.

    Is there ever any time in which you might want the W or Y to be 24VAC and NOT the fan? I realize that there is a possibilty that you'd want the fan on only, no heating/cooling. I assume this would damage the unit, but I'm not sure.

    MUCH Thanx in advance!
    Knightofoldcode,
    David Bussanmas,
    David@Bussanmas.com

  2. #2
    Group,

    Just wanted to clarify some things.

    I realize this is a "DIY" question, and that I'm NOT a HVAC tech. However I suspect the purpose for the site rule of no DIY'ers is for one main reason, HVAC techs need to make a living too. To my defense, I'm not stealing any business from any HVAC tech. I currently have a local HVAC tech and use that company for all my needs, but this is a little different. (If I was retrofitting my unit to work with a aftermarket zone system, I wouldn't need this info, just match up the letters to the zone unit, and the HVAC unit, so it's obvious I'm not attempting to bypass a HVAC tech coming out to setup a zoned system, I could do that without any help.) I'm trying to understand how the electrical portion of the HVAC unit works, nothing else. I intend on creating a interface to interface my already installed alarm panel with my HVAC system. (My alarm panel has a keypad in every room, as it's a alarm panel, whole house audio, and home automation, all in one, and soon a zoned HVAC system.)

    Also, this sort of information OUGHT TO BE IN THE BLOODY MANUAL, but it's not. I've looked. The Thermostat's manual gave me more information on what the wires are for!

    Again,
    Thanx in advance,
    Knight.

  3. #3
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,789
    Zoning instructions are with zone control systems, they don't come with the furnace or a/c.

    What your asking for is basically step by step instructions, since setting up the controls for the zoning, and wiring the furnace and a/c up RIGHT and for SAFE operation is involved.

    Bypass sizing, and set up.

    Although instructing you how to do all this takes nothing away from me, it might from some contractor in your area.

    Maybe in your area they don't care.
    If thats the case, call the contractor you mentioned, and ask him how to do it.

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  4. #4
    I fail to understand how what I am doing will take any business away from ANY HVAC TECH!

    "Bypass sizing and setup" I don't understand what you mean by this.

    I already have a HVAC system installed, and am remodeling the house. the currently HVAC setup will remain, and was installed by a professional HVAC service in my local area.

    The unit has already een sized for my house by my local HVAC tech. And setup by the same company. I'm just interested in setting up a zoned system, from a home brew component based sstem. IE, I am going to create my own system and have their OWN PCBOARDS MADE FOR THIS. Therefore, I'm not purchasing anything from a HVAC location, ANYWHERE. My local HVAC company has already been contracted out to install the dampers, and relief bypass, taht's how I found out that I need a relief bypass valve.

    I'm not screwing anyone out of bussiness here. I'm looking for information that should have been provided by the manual!

    Knight.

  5. #5
    Join Date
    Apr 2002
    Posts
    11,808
    Look at the wiring diagram. On the unit for sure and quite possibly in the manual as well.

    I have no desire to assist you to smoke your transformer or the integral electronics of your furnace, or to assist you in cycling a furnace off of high limit and or freezing a coil solid.

    Concerning a thermostat system switch, where you manually select the system function to one of "Heat - Off - Cool", there are thermostats available with a function called 'Auto Changeover' that automatically switch between heating and cooling as required.

    If you want to reverse engineer thermostat differentials and auto-changeover try honeywell's site.

    [Edited by Carnak on 07-22-2005 at 09:16 AM]
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  6. #6
    Join Date
    Apr 2004
    Posts
    7,680
    I dont unserstand what manual you want. A home brew system as you call it has no manual. The low voltage designations are in the manual that came with the unit and on the wiring diagram unless industry standard letter codes are used. Control logic is generally desinged using industry standards. The instruction manual that comes with a furnace or air conditioner is written with the assumption that there is an understanding of these standards, codes, and laws and fundimentals of thermodynamics, as well as compitency in electrical aptitude, and a working knowlege of how a system works and why.

    You seem to have the electronin or software side pretty well licked, and a contractor who is willing to do the dampers and all. Can he not answer your specific questions?

    If you are using your own sensors, my question would be how do you plan on dealing with anticipation? Next, If you set the cooling for 72 on a 100 degree day and it cools off overnight, and the set point never changes, How would the the house cool to below 70? Better get a grip on how you plan on controlling the equipment. You should also know how to prevent the heat from coming on.

    No one here, sorry to say, is going to deatil a system step by step.

  7. #7
    Join Date
    Apr 2005
    Location
    Tampa, Florida
    Posts
    1,634
    Originally posted by knightofoldcode
    Group,
    ...
    1) My unit isn't designed for a zoned hvac, I don't think it has to be, right? (I intend on putting in a barometric pressure relief bypass duct, as well as the dampers required, these parts I understand and can do without any problems.)
    Um... how do you plan on determining what the static pressure of your duct (zone) branches are, what the allowable static pressure range of your system is, and setting up the barometric bypass according to these?

    That issue aside, you're better off going with a real zoning control system. They aren't THAT expensive and have all of the safeguards built into them.

    I agree with Carnak... If you really insist on designing your own system, poke around on the Honeywell site. They have an HVAC controls manual out which gets into the nitty gritty of theory, design, etc. and runs ~400-500 pages long and is a free download. You probably should be aware that a good (advanced) control system isn't as simple as on & off. The better Honeywell thermostats use calculus to determine when to turn on, when to turn off, how long should a run time be, etc, and that's not even getting into programmable thermostats & recovery ramps.

  8. #8
    Group,

    First, I thank everyone for their help, however limited it may be.

    Um... how do you plan on determining what the static pressure of your duct (zone) branches are, what the allowable static pressure range of your system is, and setting up the barometric bypass according to these?
    My local HVAC tech will do all of this. He already installed the dampers and played with the system for a while, I specifically told him NOT to install a Zone conmtroller, as I was going to create it, so taht it could be integrated into my alarm system and whole house audio system.

    I dont unserstand what manual you want. A home brew system as you call it has no manual. The low voltage designations are in the manual that came with the unit and on the wiring diagram unless industry standard letter codes are used. Control logic is generally desinged using industry standards.
    I want a manual from my a/c unit that tells me what each wire does! It was EXCELLENT in telling me all of the other wires, motor, flame sensors, etc. But it didn't say anything about the thermostat controls. You hit it on the nail when you said, "and on the wiring diagram unless industry standard letter codes are used." I'm looking for what these "Industry Standard" codes mean!

    You seem to have the electronin or software side pretty well licked, and a contractor who is willing to do the dampers and all. Can he not answer your specific questions?
    Probably he could. However that company went out of business. I had the dampers installed about 6 months ago, and for some reason I can't seem to get ahold of that company anymore. Some have said they went out of business, others have said that he took the money and moved to a larger city. It's hard to say, and I can't get aohld of him. No one else in the city wants to help me, they keep telling me to get a commercial zone system and keep quoting me outrageious amounts for one. IE, 4,000, JUST FOR THE CONTROL BOARD. So, I'm not about to go to them for the commercial control board, I'd rather purchase one online and do it myself. I've got all the sensor wires hanging in the wireing closet as well as the dampers, so it'd take 20 minutes. Everything is already setup, and they still want 4 grand for nothing.

    If you are using your own sensors, my question would be how do you plan on dealing with anticipation? Next, If you set the cooling for 72 on a 100 degree day and it cools off overnight, and the set point never changes, How would the the house cool to below 70? Better get a grip on how you plan on controlling the equipment. You should also know how to prevent the heat from coming on.
    I'm not understanding the first question. Anticipation? Not ringing a bell, I know what the word means in layman's terms, but probably not in HVAC terms.

    "How would the the house cool to below 70?" Because the outside tempature went below 50F, cuasing the house to cool to around 60F, should the unit turn on the heat?

    "You should also know how to prevent the heat from coming on. " *IF* my assumptions are correct in the standard codes for the wires, that's easy. They have settable relays. IE, you hit this relay coil, and the wires go to one leg, hit the other coil and it goes to the other set of wires. Easy. I'm a Computer Engineer and a electrical hobbyist. I know electricity. And am VERY likly to simply scope out the wires myself.

    That issue aside, you're better off going with a real zoning control system. They aren't THAT expensive and have all of the safeguards built into them.
    It's not the expense that has caused me to desire to create my own. I'm not doing this to be a cheapskate. "real" zoning systems require a thermostat in every room. Why re invent the wheel? Each room already has their own keypad for my alarm system, whole house audio, etc, system. I want all of this integrated in with itself. I don't want 5 keypads on the wall! That's the reason I created my own alarm panel, and whole house audio system!

    I can't seem to find the information on HoneyWells site, if anyone has a link that'd be greatly appreciated.

    Knight.

  9. #9
    Join Date
    Feb 2005
    Location
    Richmond
    Posts
    480
    T-stat wire:
    R: 24 VAC Hot
    C: 24 VAC Common
    W: Heat
    Y: Cool
    G: Fan

  10. #10
    Originally posted by york_hvac
    T-stat wire:
    R: 24 VAC Hot
    C: 24 VAC Common
    W: Heat
    Y: Cool
    G: Fan
    Thank you.

    I don't understand why this is such a "trade secret".

    Much appreciation, York.

    Knight.

  11. #11
    Join Date
    Apr 2005
    Location
    Tampa, Florida
    Posts
    1,634
    "Honeywell Engineering Manual of Automatic Controls for Commercial Buildings". 518 pages. Should provide you with some good light reading.

    http://customer.honeywell.com/Honeyw...D=77-E1100.pdf


  12. #12
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,789
    What york hvac posted is in the unit manual.

    Good Luck.
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  13. #13
    Originally posted by beenthere
    What york hvac posted is in the unit manual.

    Good Luck.

    That's what I've been trying to explain! Yawl simply condone without reading my messages! IT'S NOT IN HTE MANUAL! IT'S INDUSTRY STANDARD THEREFORE NOT IN THE MANUAL. The manual assumes you know that, and I didn't! And thanks for the good luck. :P

    tpa-fl: Thank you for the link. It's funny that you figure I can't understand it, but anyways, I still appreciate it.

    I'll report back my status for anyone who might be interested.

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