Posted By engineer on 28 Apr 2012 09:36 PM
Zoning lets a single system separately condition different sections of a home. Each zone has its own thermostat, and motorized dampers direct air only to rooms within the zone whose thermostat is calling. A two floor house works much better with a zone for each floor. A two stage system runs in low stage when just one zone calls.

That makes sense and I have always wanted a controlled system like that.

My compressor is 21 years old but my air handler is 4-5 years old and does vary the speed of the air.  It also has an electronic filter.

When we replace the compressor do you think we can keep the air handler?

Doug

A couple of you asked me how much of a DIY person I am.  Some facts:

Engineering degree.

Built a dune buggy in early years.

Robotics hobby, lead engineer for a robotics FIRST team, we came in 3rd in nation over 1500 teams.

Have dug deep into my corvette engine.

Laid floors, rebuilt walls but not my strength.

Designer at heart but like to do research first.

Never done AC units, but willing to try anything that makes sense.  Have respect for experts and would have them do certain areas.

Can fix almost anything if I put my mind to it, my wife expects it.

Son and daughter crashed their cars and together we rebuilt them.

I hope that answers to some degree what people asked.

BTW thank you all, this has been extremely helpful.

Doug

You should be able to replace the compressor and retain the airhandler, but that begs the question of whether the present system is a "matched" combination, that is, a compressor section and airhandler model number pairing approved by the manufacturer. Matched combinations are the only ones guaranteed to deliver rated efficiency. What you have works, but it is hard to say how efficiently. Correctly charging an unmatched pair is a bit uncertain, though a competent tech can get it close enough.

Given your background, there's nothing stopping you from wading in up to your armpits in this stuff. The legal barrier to working on your own equipment is quite low - must possess an EPA card in order to posses refrigerant or work on refrigerant system. Get the card by sitting through a 1 day class and taking a can-you-fog-a-mirror multiple choice test.

Posted By DougLeppard on 28 Apr 2012 10:30 PM

Son and daughter crashed their cars and together we rebuilt them.

Rebuilt the car, not the kids, right? 
Just kidding.  I hope they are ok.

Posted By geome on 29 Apr 2012 10:36 AM

Posted By DougLeppard on 28 Apr 2012 10:30 PM

Son and daughter crashed their cars and together we rebuilt them.

Rebuilt the car, not the kids, right? 
Just kidding.  I hope they are ok.

Well that proves that I am a real engineer, can't construct a good sentence.  Both kids did fine.  My son came around corner too fast hit water and hit a tree and sent the tree about of foot or so directly in the middle of the grill.  So as part of the learning opportunity we rebuilt the car and we both learned a lot.

My daughter a blond twin, would often forget she was driving and space out and she took out a sign on the side of the road that said "Caution construction zone".  She came home with the front quarter panel of her car in the trunk.  We also had a learning time rebuilding that.

Doug

I want to thank everyone that gave input, this has been a real learning experience.  I have come to a conclusion and direction.

Looking up the info on my 21 year old compressor and my 7 year old air handler I can see that will be great savings to just upgrading the compressor.  Right now it says it is a 9.4 seer and if I go to a 16 according to info on the web I may experience 45% savings.  Also if I work on a multi zone in the house that will save plus making sure that the ducts are insulated.

Geothermal is much more expensive and possibly may not have the ROI for fast enough payback.

Also my dream in the past was to have individual room control, so I am playing around with a room by room control.  Often we have only one guest upstairs and sometimes it is filled, so this would save by selective conditioning.

I am now doing the research, have found the duct dampers and found the temperature sensors, what I have not found is the right controller.  What I need is an 8 zone two stage controller of the AC and dampers.  I am capable of designing one if need be with my background in electronic engineering.

Or I might end of having two zones upstairs and downstairs but AI thought I would go for the dream until proven I cannot do it.

So input of this would be appreciated.  Anyone know of a controller for 8 zone two stage HVAC?

Doug

There are a number of zone boards out there theoretically expandable to 8 zones You'll have a heckuva time making that work using ductwork. The max I'll do is 4 zones, and that only with equipment able to drop to 50% or lower capacity at low stage, and very careful duct design.

The reason what you contemplate won't work is that the system has a minimum airflow at low stage, in round numbers approximately 225 CFM per rated ton. In other words, a 3 ton system will need to flow 600-700 CFM at minimum. An individual room might need only 80-100 CFM, and the ductwork might support 150-200 CFM max. Therefore 400+ CFM needs to go somewhere, either dumped or bypassed. Dumping it elsewhere over-conditions another zone(s), bypassing it back to the unit may ice the coil or short cycle the compressor.

The only way to control 8 zones with one system is to chill water instead of air...system operates to maintain a storage tank temperature, and each room gets its own hydronic coil... complex and pricey.

There may be an Asian minisplit manufacturer whose inverter-driven variable speed compressor might support 8 heads, but that won't be cheap or easy, either.

The advice here by Dana, Joe and Eric is all good.

I would consider sending one of my energy auditors to you, but I'd have to cover time and mileage. On an older home, both blower door and ductblaster tests tend to be very revealing. Alternatively, we could work on a remote basis. PM me if interested in either option.

I suggest using duct dampers on both the supplies and returns so that you aren't pressurizing or depressurizing rooms (not good for infiltration or wall moisture). Passive returns are not good enough.

I figured that there would be a minimum number of rooms to be cooled, so that the system would not be stressed. Certainly you would not want to resend it back into the unit and freeze it up like you said.

I will think through a 3-4 zone approach to see how that would work.

Thank you for putting up with my dreaming.

Doug

Posted By jonr on 08 May 2012 08:22 AM
I suggest using duct dampers on both the supplies and returns so that you aren't pressurizing or depressurizing rooms (not good for infiltration or wall moisture). Passive returns are not good enough.

Thanks for that input, I will take that in consideration.

Doug

Again 8 zones not practical but chilled water and a variable speed hydronic air handler would do it. Even 4 zones is a lot. If you get the load down to 2 tons with envelope improvements, 4 zones might be very doable.

Posted By jonr on 08 May 2012 08:22 AM
I suggest using duct dampers on both the supplies and returns so that you aren't pressurizing or depressurizing rooms (not good for infiltration or wall moisture). Passive returns are not good enough.

btw,
Choking the return is the very fastest way to ice an evaporator coil on a conventional AC. Much easier to get away with a discharge restriction though neither are good.

Doug 
  If you can get to the ductwork to make ducts and joints tighter, sure , that is good...

Q' About your zoning, in your 8-zone plan, how many runs of ducting would be in your smallest zone (sqft qnd ceiling height ) -just wondering how that was arrived at- ? 
Doug:
Zoning thoughts---- For just a higher room level, and a mid-level, and then a rec-area, and a Fla room (>?) may be a reasonable 4 zone system. 

Some OEM zone-boards are already included in Hi-Eff Ht-Pumps. Some constant plenum temperature systems work in heating, ECM-ii motor modulates by PWM signal. However, a re-programmable, or dip-switch selection can be adjusted for cooling and "like"-dehumidification at those slower CFM/ton mentioned by Curt. (by an installer's careful set up). Some OEM have a "drops blower motor by %RPM  to a "DeHumidification" mode speed, off a  select wire for the Variable ECM apps.

There are air-pressurized -both- diaphram and cylindrical pneumatic 'ram' reliable DAMPERS out there for quick retrofits. IF you can get in to the runs to a select zone (or to 3 out of 4 runs), -parallel installations into 6, 7, and 8' rounds -off of a trunk are cost-effectively done relatively as easy as making a small opening in a trunk, to reach a hand in to place an UNFOLDING damper system. This style of damper can be investigated at    arzelzoning.com 
  Arzel also carries staging and variable- like controlled equipment just for simple single stage heat pumps, but by adding the Emerson or GE Green IQ blower motor. Comfort may be about regarding some things minimally such as enough cfm for 2.5 room-volume air rotations/hourly in large-areas, and see how comfortable it is where about 8ft above flooring in cooling - to also considering over 3-rotations in smaller rooms.  You can also just buy the little air pump and solenoids and control as you please.

Some contractor of a nice organization I saw last month in WVa still (but I don't) use weighted-balancing-bypass on ht-pumps at the return air to supply at select important points. This will allow some aqpplication to reduce "chokings" and "pressurizings". This CAN be for also when zoning bypass-dampers in returns.

JOE mentioned a true concern of choking a return air - but qualified installerscan design workable- restricted air flows.

----- Previously mentioned by others
CARE- Doug, as you have continued to show - , just care about a lot "calculation" ... Dampened return airs can be found in tall meeting buildings wanting warmer high return in the winter and have "3-way-like" return grills that are lower to just above people's heads in the summer (dampened in the winter on a same rod to the high damper) to not disturb air layers in ceilings during the hotter days, (IF it/that were applicable).

That arzel pneumatic-damper system can make a single staging or multi staging heat pump or a/c or gas or whatever look very 'state-of-the-art' .  Ingram's supports and gives enough design and details with - dealing with MANY people...
Like the PHOENIX Distributing (on line) does also, sometimes will have a polit-media biased broadcast.
 
You may find a good and close-enough idea of your load studying is available from equipment sellers if you just gather the wall sizes, roof and windows and perimeter  footages

and [again] look at all your existiong ducts for leaks,

Probably in 3000 sq ft home , I think that you will find 90% is decently answered/handled about all of your comfort questions if at least 2 zones are installed.  Damper OEM's are eager to design. You may have the situation that allows add-ons after making the building better than before.
....

>< sorry my eyes were crossing
did that say check ducts?

He's baaaaaaack!

what it is about, just  is to give some allowances for practical zoning -

HAH

was  there- 'check ducting '


---Arzel was just interesting for to mention here since installingfor retrofitting,  even four zones, may be needing some good tricks too

Posted By knotET on 09 May 2012 03:10 PM
now how do we help the threadholder at the top?

Cease replying with incomprehensible rants would be a great start.

@engineer

You said "Most Florida homes have lots of ductwork in hot, vented attics. "

True for ours.

You said "We address this by retrofitting sprayfoam insulation onto the roof sheathing, bringing the attic and its ductwork into the thermal and pressure envelope of the home. Ducts no longer leak to the outdoors, and their heat gain and loss to unconditioned space is eliminated. "

I understand the concept but don't get how it helps. It seems to make this work well you are having to cool a larger area. Yes you save on the ducts staying cool but you have the whole attic to cool. Wouldn't it be better and cheaper just to insulate the ductworks better?

Or maybe I just didn't understand it correctly.

Doug

Insulating at the roof deck from ridge to soffits air seals the building, eliminating stack-effect infiltration. If you insulate just the ducts the attic stays warmer, increasing the stack effect drive.

When insulating the roof deck in an FL climate you can leave any existing insulation at the attic floor in place (except at the edges where you need to air seal.) This effectively adds to the total R for the fully conditioned space, and puts the ducts into an intermediate space in the thermal boundary, while FULLY within the pressure boundary. The peak temps in the semi-conditioned but air tight attic will be a few 10s of degrees lower than it would be previously, but warmer than the fully conditioned space, but the dew point of the attic air will now track with the drier conditioned space air rather than the exterior, and any duct leakage will no longer drive air-infiltration which, raises both the latent and sensible loads. With R19 at the attic floor and R19 at the rafters, with a 120F roof deck and an 80F room the ducts are now in a dry ~95F or cooler attic as opposed to a humid 115F attic, which saves over half the conducted loss, and ALL of the leakage driven air-infiltration losses and ALL of the stack effect infiltration losses.

Insulating just the ducts helps, but leaves the other significant losses in place. It's not to say that insulating and sealing the ducts isn't a good idea, only that by itself it doesn't solve the problem anywhere nearly as fully as insulating and air sealing the roof deck. You would also have to air seal and better-insulate the ceiling to achieve a similar result when focusing on duct insulation. As a retrofit it's often more time consuming & expensive to air seal the ceiling/attic floor and air-seal & insulate the ducts, than it is to air seal and insulate the roof deck. But if the ducts are very tight ceiling/attic floor performs well for tightness in blower door test it can be cheaper & more effective to insulate the ducts with foam and blow a foot of cellulose over the rest.

BTW: The 400 square feet per ton metric is a typical contractors easy rule of thumb, a rule unmerited by a careful & valid Manual-J calc, and is guaranteed to oversize even without air-sealing the house or ducts better. Even though standard AC systems of the 1980s & '90s were often sized that way, the actual cooling loads were not really that high. In a reasonably tight code-min house where at least SOME attempt has been made to seal the ducts, 800'' of living space per ton is more likely to be closer to a true straight-ahead Manual-J than 400'/ton.

But heat gain isn't a function of conditioned space floor area, it's a function of exterior surface area, and emissivity & reflectivity of the exterior materials, with particular emphasis on the performance of sun-exposed roof & windows. Two story houses have a very different heat gain characteristic per square foot of conditioned space than single story houses simply on a surface area (particularly roof area) per square foot basis. East facing windows that take all their gain during the cooler AM have much lower effect on peak and average loads than west facing windows that take it on during a hotter part of the day when the roof is already hot, etc. At the cost per ton of geothermal heat pumps, a DOE-2/BeOpt type of simulation would be a better approach to system sizing than the much simpler Manual-J. True peak cooling loads can easily shift by a ton or more with the solar reflectivity factor of the roof, or the shading & solar-gain factors of the west facing windows. Hitting or exceeding 1000' of conditioned space per ton is a pretty low hurdle to clear for a new designs that have been modeled for energy use, and that would be pretty easy to retrofit on a code-min house built since 1990 with air sealing and spot-insulation. I have no doubt that engineer's approach of insulating and air sealing gets you there- the question is whether that's the true peak load, or is it actually lower, like 1500'/ton? Manual-J wouldn't necessarily tell you, but DOE-2/BeOpt probably would. Manual-J is guaranteed to oversize too, but not by as much. If it were my money I'd model it before signing the contract (but hey, I'm nerd. :-) ) For cheaper systems the upfront cost of oversizing the system may not warrant the pencil-sharpening effort, but for ground source systems even if you paid a competent energy-use analyst to model it the cost might be worth it, especially if the building & site analysis steers you to other retrofits that can peel even more tonnage off the system size.

Dana, thank you for the explanation.   How did you learn this stuff?