Propane (R-290) for heat pumps?

[AC_Hacker]

Originally Posted by BradC

At the moment, I'm struggling to come up with a method for "purifying" the Propane that does not rely on a compressor, condenser and 2 valve bottle.

BradC,

I wish you well on this project. I don't know of anyone else who is attempting to improve the quality of BBQ gas on a hobbyist scale.

From what I have seen of your work so far, you are definitely keeping the reputation alive and well, of Aussies as a determined and resourceful lot.

Best,

-AC_Hacker

[MN Renovator]

Originally Posted by Xringer

It has been discussed before. And, I'm sure more than a few folks are still interested.
The question of replacing R410A with Propane has been asked and so far,
I've only read one case where it was done. (And was very successful per a Youtube poster).
http://ecorenovator.org/forum/geothe...html#post12152

And there was a study done, where they changed the cap tube in an R410A system..(IIRC).
Experimental Investigation OPTIMUM Charge R290

So, it seems that R410A can be replaced with Propane, and maybe without any mods in some systems..

It's the inverter part of the equation that makes it tough.

With a normal 'dumb' system there is a low-pressure switch that is designed to prevent the compressor from operating if there is a loss of charge, easy to defeat, just short the switch for most systems.

A simple air conditioner is just a thermostat, compressor, condensor coil, evaporator coil, a capillary tube based evaporator coil, two air movers and some gas lines plus a few other parts. It really is only controlled by the thermostat that triggers the relays to close to power up the blowers and compressor. It will run until the thermostat is satisfied or a switch somewhere in the system is triggered because a component is screaming in pain. A heat pump includes a reversing valve and if its an efficient heat pump by any stretch of the imagination it will have a TXV.

The refrigerant pressure differences aren't so bad on a simple system, you can charge your gas to a level that works with the capillary tube and condenser without much issue. With a TXV you will likely have to swap that for one designed for a lower pressure something from a R22 system of the same capacity is probably good. Then you would need to be sure the oil is compatible but I don't know the details of which refrigerants and oils go together.

Then you get complicated with the inverter. If that thing looks anything like a Fujitsu inverter you could easily be in trouble. I've seen a Fujitsu inverter system before and it has a dozen pressure, temperature, and other sensors wired all over the place on both gas lines. It has weird electronic valves that dump pressure between the suction and liquid lines. There is other weird stuff that you'll never see in any non-inverter system including control boards with tons of stuff on them.
When you have an inverter with a pressure sensor that is running the compressor faster and faster trying to get your propane to a certain pressure and it doesn't happen or it happens and its suddenly made your system belt out tons of hot or cold air when you want just a little bit of heat because it thinks the pressure isn't high enough to it just keeps trying to ramp to its max. It is the inverter that adds the struggle.

[Xringer]

You might be right. I don't know if a complicated system will work.
Some might even have it's ROM programed for the type of refrigerant to be used.
I do know that my model of Sanyo isn't very complex..
I think the only pressure switch might be just for over-pressure problems.
It's in line with the contractor (that controls the main AC power).
See lower right hand side. http://i46.photobucket.com/albums/f1...OutdoorSSR.jpg

When my first unit sprung a leak, it would still run, and ran quite a bit..
I'm amazed it's still working perfectly today (after the leak was repaired).

If the electronic expansion valve (TXV) is a throttle,
(like a variable cap tube) controlled by a CPU, (MVO motor?)
based on feed-back from temperature sensors (and not PSI),
it seems like it might be possible, that it couldn't tell it had propane in it's veins..

The indoor unit has an air-input temp sensor and a coil temp sensor.
It's fan will not turn on, until the coil can provide heat to the room.
(Or cooling, during the summer)..
http://i46.photobucket.com/albums/f1...indoorunit.jpg

[BradC]

Originally Posted by Xringer

If the electronic expansion valve (TXV) is a throttle,
(like a variable cap tube) controlled by a CPU, (MVO motor?)
based on feed-back from temperature sensors (and not PSI),
it seems like it might be possible, that it couldn't tell it had propane in it's veins..

My understanding is they tend to work like this :
- The TXV(s) are generally regulated by measuring the temperature differential between the start and end of the coil to determine the superheat accurately.

- The condenser unit measures the suction pressure of the low side and adjusts the compressor speed to maintain a minimum suction temperature.

As the indoor units load decreases, the txv's close down reducing the overall refrigerant mass flow. The suction pressure will then drop unless the compressor capacity is reduced, so the system slows the compressor to maintain the suction pressure above a minimum value.

Now, here's an idea. The car hotrod industry have loads of devices that translate analogue signals. They use them for altering boost levels, changing MAF sensors and the like. If you used one of those to translate the pressure sensor levels seen with R290, to the levels you would normally see with 410 then it might just work!

They are just little micros with A/D & D/A that are able to add/subtract/multiply/divide to alter voltage curves.

[mrd]

The Fujitsu service instruction manual provides alot of details into the control logic of its systems. See:
http://www.goductless.com/v/vspfiles...lq_service.pdf
My system uses the same outdoor unit as this, and I posted the refrigerant diagram over here:
http://ecorenovator.org/forum/12040-post14.html

The only pressure switches are shown on the discharge side of the compressor. Another manual only makes a vague reference to their operation, indicating pressure switch 1 is for 'refrigerant circuit protection' and it cuts off at 609 psi and cuts back on at 464 psi. pressure switch 2 it only states 'for control device'. Both appear wired to the main controller on the outdoor pcb.

[mrd]

The SI manual indicates virtually everything is controlled by thermistors. See the EEV control section. Also, it appears the compressor frequency is controlled to meet a indoor hx target temperature. The indoor fan speed is controlled to meet the indoor thermostat temperature.

So the thermostat calls for more cooling, the fan kicks up, the hx heats up, the compressor frequency increases, cooling the hx, etc. There are also protections to keep the hx from icing over by limited compressor frequency.

Heating mode is pretty much the same, it also has 'cool air prevention' so the fan doesn't run very fast until the hx reaches a decent temp.

The outdoor fan speed appears to operate based on a data table of outdoor temp, compressor speed, and heat/cooling mode.

It also spells out the initialization routine of the compressor, how it slowly ramps up to speed whenever it starts.

[AC_Hacker]

Originally Posted by mrd

The SI manual indicates virtually everything is controlled by thermistors.

I tried to get the same document for the Fujitsu AOU12RLS, which is a single-head HP with very high efficiency.

The SIs seem to be disappearing from the web due to Fujitsu's instruction.

Can you find a SI for that model?

-AC_Hacker

[AC_Hacker]

mrd,

I found what I needed by going to Internet Archive.

-AC_Hacker

[AC_Hacker]

BradC,

I came across this document regarding the use of refrigerant line dryers, from a Scandinavian site (I can't even tell what country).

Anyway, it is about using line dryers and most interestingly for you, quantifying the required dryer's capacity for removing a known (or estimated) quantity of water.

Though it might be useful in your quest for dry BBQ gas.

-AC_Hacker

[BradC]

Originally Posted by mrd

The SI manual indicates virtually everything is controlled by thermistors. See the EEV control section. Also, it appears the compressor frequency is controlled to meet a indoor hx target temperature. The indoor fan speed is controlled to meet the indoor thermostat temperature.

That's really useful, thanks!

The Daikin units I've looked at (and the one I ripped my EEV's from) all had low side pressure sensors, so they use a different control strategy for the compressor speed.



Either way, that Fujitsu SI contains some very useful information (much more so than the Daikin manuals I've looked at).