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Old 06-18-16, 04:39 PM   #1
RB855
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Started up another spur of the moment project, and got quite a bit of progress done before the rain showed up (The then better half talked me into a house without a garage...). To make a long story short, we get TTW a/cs on warranty exchange fairly regularly. TTWs are basically glorified window a/cs designed for Through The Wall install with rear vents instead of side vents. I have had 2 12k btu units that were both out for condenser leaks hanging around for a while, and I had previously experimented with hacking up the blower housing to convert them into ducted units (mostly for my HPWH). It occurred to me, mount 2 evap sections on one base pan, and duct it into a Active heat recovery unit! I have been doing decent keeping the temps under control in the house with a 9k portable, but not in the traditional sense. The unit is completely outside with the cold air ducted in, so it is 100% fresh air, with a window cracked open at the other end of the house. We have a lot of reptiles, there is no smell any longer. So why waste that cold air out the other side when I could pass it through the condenser?





Condenser removed


Interesting bottom coil. Its intention is to make full use of the condensate in the pan for free sub cooling.


Evaporator asym.


Got both evap and blower assyms on the pan... and it just aint gonna fit.


So I cut the arse end off both pans and brazed them together. The pan is not completed as I was more curious to see if this whole idea was going to work first.


About 30-45min later had both sides bolted back down, everything piped up, and reused the original captube. Compressor even bolted down into its original location. And, the evaporator motors are still serviceable, unlike the first attempt.


Lost track of charge, but it was significantly less than the original 20.8oz, as I had to remove quite a bit. The SH was so high because it was frickn raining and I was too stubborn to quit...






Dont mind the kWh reading, its cumulative, and I havnt reset it in several months of using it as a test cord at work.


It was certainly doing a good job of pulling condensate, judging by the stream in less than 15min of run time.


So, all in all, not bad for a 3hr project. Next up, need to modify the blower housings to allow ducting, and build a case around it. Both motors are 3 speed, which will aid in balancing flow, and are only 25-30watts each on high. Unit is actually impressively quiet without that awful 3 blade condenser fan howling out the back. Curious to see how well it will maintain temperatures (at least during off peak times).

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Old 06-19-16, 09:07 AM   #2
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I would imagine your COP would suffer by subbing another evaporator for the original condenser. The window/wall units all have a much larger outdoor HX that flows a lot more air through it. You know what this does. As long as the unit serves your purpose, and the unit increases comfort, no one can tell you how to do what. Surprise us.

I'm anxious to see how it will turn out. Will this look like something from the monster garage, or like something Randen would turn out? His stuff looks like it could process food or be featured in an infomercial. Mine usually ends up looking like Freddy Krueger.

Hey, do those control boards have the ULNxxxx chips in them? They are super easy to assume control of...
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Old 06-19-16, 10:50 AM   #3
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I dont imagin the cop will suffer too much since the condenser will be getting conditioned inside air across it instead of 90 something outside air. I know its not going to be great since im already seeing 15-20* difference between ambient and liquid line temps... But the main thing is I needed ballanced airflow in a ductable form. I could always tack in some extra coil space into the heater cavity. I wasnt totally clear in my descrition, but I used a heatpump evaporator on the conenser side as the plumbing is much more favorable to my uses than the straightcool coils. The direction of flow through the coil results in lower final liquid temperature, and it has more rows. I should have taken side by side photos for yall to pick at. Curiously, the condensers on these units, while nearly double in fin surface, use less passes of smaller tubing than the evaporators. They did use a higher flow fan for sure, that was also significantly higher in wattage and a serious amount more noise due to the high rpm/ static pressures. No good way in this setup to take advantage of evaporating the condensate for free subcooling, but depending on my suction temps, I may gain a little from a small recovery exchanger. Once I get things a little more finalized, Ill get some solid readings to see how it actually does.

As far as controls go, these arnt the most typical of systems. The main relay board is a dumb board with the power supply, optos, relays, thermister filtering, and current sense circuits. The front board does all the thinking and just uses logic level outputs. The brain itself is an EMC950(cant read the rest). Unless the orig logic works to my needs, Im probably just going to ditch it and link a rPi to the existing main board. Least that way I can come up with a stragtigy that accounts for indoor/outdoor temp and humidity.
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Old 06-19-16, 09:11 PM   #4
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Welp, it was a lot dryer this afternoon, so round 2! Worked on the charge a bit, got the SH into target range but ended up with over 20* of SC, so the captube is too long. I have a txv perfect for the application sitting on my desk, so that will be going in on the next round, instead of fooling with captube tuning. Also, since it will have to handle fairly significant temperature swings it only makes sense. Started cutting up the housings a bit trying to come up with a decent ducting plan, and everything was going great. Then I went from 0 to full retard at light speed (see below, que suspense music).

Decided I will be going a bit more radical with the blower modification, but that will be another day when I have sheet metal on hand. At the moment, even at full blow, Im coming up short on airflow on both sides of the equation. That begs to question if the factory setup even had enough cfm. It also makes me wonder since the same evap motor is used on 9k and 12k, how am I under flowing on a 9k? The evap isnt so much of a mind as it will dehumidify better, and the condenser will probably come into spec once its flowing conditioned air instead of outdoor ambient.

A housing I cut up previously while brainstorming.


The thinking stage.


Full Retard... Never go full retard.


14 wires later... pretty significant time detour I was not expecting.


Way too much Subcooling, so the captubes too long, driving the high psi sky high (but still under amp rating). Superheat came in target, which is really high due to the humidity.


A side by side of a evaporator and condenser from same model units. The fin area is certainly different between the two. The evaporator has 36 passes, in a 3 row configuration, whereas the condenser has 34 passes in a 2 row configuration, but it has the added capacity of an 8 pass coil that sits in the condensate.


Got the suction line insulated and the compressor jacket on. Tried to take a video of how quiet it was, played it back, and realized you could barely hear it in the video over the mower on the next block over. These things normally howl due to the condenser fan. Might be next weekend before I get to mocking up the ductwork connections, and txv.

And heres one for anyone who wanted numbers.
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Old 07-02-16, 01:14 PM   #5
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Please excuse the quality of this work... Im not a tin knocker, and my brake isnt big enough for even small work like this.

The evap outlet needed to be redirected to the same side as the condenser inlet, so I cut the top off the blower housing. This left me with a 7x4.5" hole. Admittedly, the size of the radius I used is excessive and made it a bit tall. The fitting is a offset reducing elbow, that takes the 7x4.5 and outlets as a 6x5. From the outlet will be a transition to a 6" round. At the moment Im moving 365cfm at the throat, need to have 300cfm in the final product. 6" is speced at 100cfm, so its not ideal, but it will only be a short run. Still have the option to use 8" if I change my mind. The condenser will have a 6" (or 8) round to rectangle transition for the inlet. The condenser outlet is just a side discharge, which helps prevent mixing with the evap inlet. Im considering adding a small second coil in a side discharge before the existing condenser that will act as a ambient precooler and take better advantage of the cooler indoor air. It will also draw air across the compressor and fan motors, as that interior pocket will become quite stagnant (which originally was cooled by the condenser fan). It draws way more condensate out than I expected which is a plus. The sh/sc numbers are still off, will see how the extra coil and txv change that. Will do a direct before/after numbers comparison in each step for anyone interested.








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