Electrical Efficiency Design Practice

[ralft]

I would like to know why the HVAC industry design practice for at least the smaller systems that I know of still seems disadvantaged from an electrical efficiency viewpoint. I am certainly NOT a professional in this area but rather a retired electrical engineer with a fair amount of hands on experience with smaller A/C systems. Why are the compressors still "canned" forcing all the motor heat into the refrigerant and then using fan energy to remove that heat. Why not use mechanical seal compressors as the automotive HVAC industry traditionally still does quite reliably. Similarly, why is the air handling fan motor always placed in the conditioned air space adding that much additional heat load to the system?If you would like to email me directly, please decipher my email from: ralft(at)hal- pc(dot)org

[.p.jm.]

Actually, that used to be common many moons ago. Then they invented hermetic ( sealed with the motor inside ) compressors, and found that they could make them cheaper.

Cost. Also, the heat gain in winter ( good ) offsets the heat load in summer ( bad ), cost-wise.

[Tony Hwang]

Hi, I am retired EE too.(digital electronics). I and you should be well aware of the bottom line dictates the product design, not science or logic. The bottom line, the bottom line, the bottom line........

[Don Ocean]

Don't forget the packaging design either. Perhaps you could be better educated by looking at Modern aircraft and spacecraft envrionmental systems. Garrette Industries Air research archives has some excellent data. Keep in mind the mighty dollar reins supreme.

[ralft]

I heard you all loud and clear BUT, my impression is that the manufacturers are very much driven by being able to claim a higher SEER and wouldn't these changes have a significant effect on that. And regarding the comment that the air handler motor adds its heat to the house air in the winter as an advantage, my reaction is to provide 2 motors on the same shaft. One in the air stream and one outside. I believe I would pay $100-$200 more for a system with those features. On a 4 ton system, I think they would save about 4% which I think would improve the SEER by 0.5 to 1 units and pay for itself in a couple of years. Are my quick calcs all wrong?

[Steve]

SEER is nothing but fluff.... the testing is done at 80F IDT, and 82F ODT. What tells the story is EER where testing is done with 75F(or 80F, I disremember which atm) IDT and 95F ODT.

Also, with the heavy use of ECM blower motors in the new equipment, the electrical usage is a small fraction of the old PSC motors, thus creating a whole lot less heat in the air handler.

But.....as an EE, if you had truly done your homework, you would know this.

[.p.jm.]

Yes. Both in the economics, and in the energy useage.

[.p.jm.]

Just to expand a bit -

Forcing the home owner / architect to design the building so as to have the unit mount half inside, half outside ? With the wall in the middle ? Not gonna happen. Plus, the quiescent motor would act then as a generator, inducing drag on the running motor. And doing all kinds of interesting things to the building power supply.

A 1 HP motor = 745 watts, aka ~ 2,500 BTU ( input energy ). Some fraction of that is going to be waste heat - maybe your 4 % ? IOW ~ 100 BTUH. Design guides suggest adding a 2 deg F rise ( or load ) for fan heat.

Compared to let's say a 3 ton system, at 36,000 BTUH - 100 BTUH is a trivial portion of system capacity and therefore EER.

[Daniel who wants to know]

The full 2500 would be applied as extra sensible heat load on the evaporator because all electricity consumed becomes heat eventually so if it is a watt-hour and it is consumed within the conditioned space it adds 3.41 BTUh to the load. In the case of the blower the air gets heated just from the friction with anything it moves against including itself. Once again putting the motor outside the envelope wouldn't do much and you have to move the air somehow so it is a necessary evil.

P.S. This is why whenever I have a box fan in a window I face it outward, Might as well send as much of the motor and friction heat directly outside as possible. Also my cousin has a tendency to run 1 window unit and a dozen fans inside the house and leave on all the interior lights which of course are populated by 100 watt bulbs and then wonder why she can't get cool and why the electric bill is so high

[.p.jm.]

Only if you look at the meta-view of ultimate entropy and chaos theory. In reality, 95 + % of the fan's input energy is expressed as desired work ( moving air ). Yes, it eventually becomes heat. However, your other option is don't move any air.

Look at the gaping hole in your theory - even in your design, still 95 % of the input energy is imparted to desired work INSIDE the structure, and thus will eventually dissipate as heat ( as the air slows down due to friction etc ), so you gain nothing on that issue.

What I said above :-) And it refutes your idea of placing the motor outside for some kind of gains. The only thing you coudl gain would be the motor waste heat as I said, ~100 BTUH out of 36,000

Is she at least cute ? :-)

[.p.jm.]

Which does not make it 'waste' heat. Only the 100 BTUH is 'waste' as it perfroms no desired work or effect. The other 2400 ( BTUH of energy input ) is CONSUMED, but not WASTED, as it does desired work.

[.p.jm.]

That's OK, no one else did, either :-)

[Daniel who wants to know]

I was actually trying to support your reply to ralft regarding why it would be foolish to put the motor outside the envelope. No harm done :)

[Alexander]

I have yet to see how it can pay for itself when the manufacturers indicate a 12 to 15 year life span and necessary expensive maintenance and repair.. Or at the very least a paid maintenance contract. Also rising costs of some energy due to decreased usage. The only real gain I see is cutting use of earths resources. The real payback Items seems to be heavy duty insulation and lots of caulk. Energy efficient windows are a joke as they have very little gain. No windows will certainly decrease heat loss. But Code demands 10% light area and I personally feel that is too little for my taste. Of course a too tight house can cause sick-house-syndrome. My advice is sell out and go native on some tropical paradise...If you can find one that the Realtors haven't developed. ;-) Without Volcanoes!

[Tony Hwang]

Hmm, If designers/engineers are given free reign, anything is possible. We don't live in ideal world, it is realistic world. Start with a economics 101. I experienced many cases of excellent, superb product killed by marketing type whose concern is only bottom line. Worst case is pharmaceutical companies. If you think they run to save live, think again.

[.p.jm.]

Y'all actually gonna let me get away with that one ??? :-)

[Steve]

You got the ball.... run with it :-)

[.p.jm.]

Otay, otay .....

In the scenario of 'two motors running one shaft', the quiescent one ( the one that's not hooked up to a load electrically for you challenged types :-) ) will indeed impart a small load, on start-up only, to the other motor.

Once up to speed, seeing as it is disconnected electrically, it is free-wheeling ( no counter-EMF drag ), and thus imputes almost zero load to the other motor.

Also, being disconnected electrically, it does nothing 'funny' or 'interesting' to the building supply it is NOT hooked up to ( at that time ).

Y'all should have jumped my shit on that one !! :-)

Where's Nick Pine when you really need him ? :-)

[.p.jm.]

Nick Pine ?

[Steve]

FCC because of radio frequency interference