Say A/C experts... True efficiency

Boilerpro

Something that has been rattling around in my brain for a long time and bumped into similiar idea in Dan's radiant heating book in the chapter on radiant cooling. I have always had serious doubts as to the claim that central ducted air units are more efficient than window units (I know... ugh) or even ductless systems. From what I understand, the SEER ratings of central air units do not take into account the power used by the ductwork fan which also generates additional heat for the compressor to dissipate. In window units, this is accounted for and in ductless systems I imagine the circulating fans are very small. Of course all of the ductwork losses to unconditioned spaces (especially lets say a hot attic)and the results of increased air leakage from the structure due to pressurization and depressurization of different spaces in the structure are also not accounted for. I continue to find that homes that use reasonably efficient window units (SEER 9 +)with good natuaral air circulation almost always have much, much lower cooling costs.


Boilerpro

Floyd

It's kinda like....

replacing a floor furnace with a central heat system!
The system efficiency can be much higher but the fuel
bills will always go up!!!!
Now you are heating the whole house instead of just the
center of one room.
If you take a thermo. and walk around a house with a
window shaker in it you will find at least 4 or 5 degrees
variation. Now if you take and try to cool the whole house down
it will take more electric.
Now as far as the SEER goes, you will find that the rates are different
for different air handlers or furnacesm that is because of the blower
motor and is the reason why all of the very highest eff. units are
using ECM motors.
Also, concerning the ductwork issue.... that is why it is extremely important
that the integrity of the ductwork is taken into consideration and it is well
built and insulated!!!!
I have also installed a number of ductless units and feel that they do a
very good job... in certain situations. Also there are some very poor
quality units out there. I stick to the Mitsubishi unit, they are top quality
and perform above and beyond their ratings.

Just my 2 cents!!!!

Floyd

Boilerpro

Floyd

> replacing a floor furnace with a central heat

> system! The system efficiency can be much higher

> but the fuel bills will always go up!!!! Now

> you are heating the whole house instead of just

> the center of one room. If you take a thermo.

> and walk around a house with a window shaker in

> it you will find at least 4 or 5 degrees

> variation. Now if you take and try to cool the

> whole house down it will take more

> electric. Now as far as the SEER goes, you will

> find that the rates are different for different

> air handlers or furnacesm that is because of the

> blower motor and is the reason why all of the

> very highest eff. units are using ECM

> motors. Also, concerning the ductwork issue....

> that is why it is extremely important that the

> integrity of the ductwork is taken into

> consideration and it is well built and

> insulated!!!! I have also installed a number of

> ductless units and feel that they do a very

> good job... in certain situations. Also there are

> some very poor quality units out there. I stick

> to the Mitsubishi unit, they are top quality

> and perform above and beyond their

> ratings.

>

> Just my 2 cents!!!!

>

> Floyd

Boilerpro

Floyd, I understand where you are coming from...

However, well built insulated ductwork is not the norm from what I have seen. If insulated, usualy only a couple of inches of fiberglass on attic ductwork. I still have "window shakers" in my own home and have very good air circulation so temperatures don't vary too much, Other than it tends to be cool in the room with the A/C. I can cool our well insulated 1906, 2800 sq ft home with 700 sq ft of glass with 1.5 tons a/c. Keeping the house about 75F to 78F it only costs about $60 in the worst month of our wonderfully humid northwest Illinois summers. I am getting ready to install central air from the attic down, and I am very curious what will happen to our summer electric bills.

Boilerpro

Brian (Tankless) Wood

Hi Boilerpro

This will probably be a bit more costly going in, but have you considered the chilled water approach of MultiAqua.

I have'nt installed any of these myself, but it really is true zoned AC, with t/stats for each mini air handler.

It's like having window shakers in each room without the noise, but with total control.

No refrigerant handling either. And then, when you are happy with it, it becomes another value-added service you can offer clients.

Just food for thought.

Swampster in humid-land.

Floyd

If you keep...

your house at the same temps and do a good job of insulating
the ductwork, you should be well pleased with the central system.
I have seen a ton of lousey ductwork, whether it is ductboard or
sheet metal. Make sure if you use ductboard in an attic that you
use iron-on tape instead of stick tape!!! If you do sheet metal make sure
of the fit and seal it with mastic.
Also you will want to go with a system that is a bit bigger than 1.5 ton.
One, because you will now be cooling the whole house, and
two, because the really small air handlers have such a small fan/blower
unit, that they have a hard time moving enough air.
I usually will go with a bit bigger air handler and a smaller condenser,
which can be done as long as the sizes aren't too different.

Again just some 'stuff' I have figgered out over the years.

floyd

Andy Michl

There is a product that Honeywell and Enalis are promoting that checks the complete system at the same time. Monitors check the airflow, a.c charge, outside/inside temps, temp rise/drop at the airhandler. After all the data is collected it will tell you if the system is short on return air, supply air, heat loss/gain thru the duct system on each branch run, and the charge on the ac system. The only real doubts I had about the product is the air flow hood on the return side is designed for 500 cfm and above. Most residential is well below that. However this is one of the first products I have seen to test the feild operating effiency of forced air systems. It is a good step in the right direction. The link is www.honeywell.com/yourhome/ I think you will find it interesting. They claim to be able to put a seer rating on the equipment in the feild, and some utilities are giving rebates to consumers that use the system.

don_9

efficiency

Boilerpro it is what it is. the heat from a fan is so low
on a residential unit that its not a factor.The Ideal system when it come to ductwork and losses is to installed it inside the envelope,then it is no longer a factor.But
that never seen to be possible.If you duct seal and used r6
flex line or 2 inch insulation it no longer a issue.you will find most of your losses right at the airhandler door panels.I would have to agree with you a self contain unit would be more efficent.but when they dont change the airfilter or have the coils clean as you know the efficency rate is reduce any way.AS they say if you want efficency you have to give up some capacity,and if you want capacity
one must give up a little efficency.I have yet to hit the
bullseye. don

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