[AC_Hacker]

BradC,

I gotta say that I am completely in awe of your scrap supply. I need to snoop around here to see if I can find a cornucopia like you've found.

Ebay doesn't look so good to me any more.

Originally Posted by BradC

Steel transmits heat a *lot* slower than copper or Brass. Wrap the HX in a wet (not damp, Dripping wet) cloth and heat the brass/copper mostly. The process of heating the copper/brass will transmit heat through to the steel.

Good advice on the brazing. Regarding heating the copper first, I also read some similar advice on a HVAC blog, describing brazing up a Danfos TXV. Thanks for that.

Originally Posted by BradC

I'm not doing anything new by any stretch of the imagination, but thus far I've spent about $300 in parts so I'm *way* ahead of the curve.

Well, you may not be pioneering any new technology, but in my opinion, being able to convert scrap into functioning, efficient HVAC equipment really is different. Not only because you are able to make what you need, that you may not be able to afford otherwise, but also because you have avoided an additional burden on the old ecosphere.

I'd say that entitles you to a magnificent trophy, so here it is:

This trophy presented to BradC
for world-class scrounging.

I think you can probably print it out and put it on the mantle, or hang it on the wall.

Originally Posted by BradC

Yep, the Nazis that regulate refrigerant here have the whole show so far closed it's almost impossible to get accredited to handle refrigerant...

Yeah, I heard that the ozone layer destruction was much more serious in Australia than in other places. I heard stories about sheep going blind, and school children being required to wear hats when playing out side at school. Is this true?

I personally take the ecology warnings pretty seriously. It's a very long way to the next habitable planet, and I'm probably on the 'Do Not Fly' list.

Originally Posted by BradC

One is a single phase ~7KW ...the other is a 3 phase ~18kw scroll...a couple of small rotaries (~14cc displacement) from window A/C's.

You're working with some pretty good sized stuff there. You must have noticed that my stock is quite small in comparison. My philosophy is to make insulation my first priority, and to make up the difference using the smallest, most efficient HVAC technology I can build myself.

Originally Posted by BradC

Right now I'm using the TEV that came with the first fan coil unit.

I'm right now in the process of designing my next unit, and I'd really like to use a TXV in it. I have a Danfos TXV that uses inserts to give it a wide range. I selected an insert for about 2.6KW. I know that cap tubes are used in units up to about 5KW, but I really want to be able to change the metering with a screwdriver, rather than the cap tube twiddling method. There's a lot of experimenting I just haven't done because of the hassle of changing cap tubes.

Originally Posted by BradC

I've just ordered some stepper driver chips and I'll build my own EEV controller to play with.My aim is to get the EEV's running, plumb in the second head and get the control algorithms stable. Then play with some PHX units in place of the existing condenser to try and get the condensing temperature down further. Also with the EEV's, I *should* be able to raise the evaporating temperature in response to load drops. Of course the closer the evaporating temperature to the condensing temperature, the better the COP. The other thing I need to look at is a dedicated submersible pump, preferably with speed control.

I think I was perhaps too quick to bestow the trophy... This sounds really interesting! I was thinking about something like this just a few days ago, how cool it would be to have automatic, programmable feedback in the metering device.

I don't know if you know about this one, but I came across a paper that was about computer modeling of the action of cap tubes. The action of a cap tube is way more complex than I would have thought, and as I recall they are able, within a certain range, to adapt to changing conditions. But programming them is pretty crude, what with cutting and brazing and all...

Originally Posted by BradC

Well, somewhat agricultural to start with, I've tried ~18M of 7/8" coil in a 208L (We call them 44 Gallon, but I think they are ~55US Gallons) drum. Worked ok-ish, but after seeing what you are up to I'm looking for a PHX.

I really like them. They can be expensive, though, especially in larger sizes. I did try to make my own heat exchanger... I bought some copper coils to make a tube-in-tube exchanger, and I realized that I had spent almost as much on the copper as a new Brazed Plate would cost, and I still wasn't sure what the capacity of the homemade unit would be or its efficiency.

By the way, earlier in this blog I published a formula for figuring the heat transfer capacity of a Brazed Plate HX. I now realize that I was overly optimistic. I have changed the formula (the final multiplyer was changed from 5000 to 1950) and it works pretty good for brazed plate HX in the 7.5 inch x 2.8 inch x (any number of plates). For other dimensions, it’s way off.

I am working on a revised approach that should simplify selection. Until then, I would advise using a program called FlatPlateSelect, and double-checking that with data from brazed plate selection charts, from more than one manufacturer.

I have gotten selection advice from seasoned HVAC technicians, completely different results from the computer program, and still different results from the charts... however, I think I’m starting to zero in on this one.

Originally Posted by BradC

Only 1 water pump as I'm using DX head units.

OK, you are using refrigerant-to-air heat exchangers, right?

Originally Posted by BradC

Ideally I'd like to be running a chilled water loop rather than DX, but I just had a quote for over $2,000 for a couple of chilled water fan coils, whereas the last DX unit I got for $20 from the recycling station.

Wow, “over $2,000 for a couple of chilled water fan coils”, that’s way too steep.

How about this... I came across this paper called, “Low Temperature Heating and High Temperature Cooling”, and researching that idea a bit led me to information that the Germans are experimenting with radiant cooling in the ceiling. The idea is that to achieve the same level of comfort (which is not the same as ‘the same temperature’), the temperature of cooling water in ceiling panels can be warmer that water in air-cooling heat exchangers, thus the power required is less.

I don’t know how things are where you live, but used copper solar heating panels go a-begging here. And the panels, which have water conductive tubing in them, could stripped out of the collectors and used like the Germans are using them.

Might be worth a try in a small room...

I don’t know if you are a digital camera kind of person, but it would be great to see some photos of what you’re doing.

Best Regards,

-AC_Hacker

P.S.: I'm hearing terrible stories about walls of water raging aross parts of Australia.

Sounds just horrible, any of that happening near you?

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