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Old 07-26-15, 11:47 AM   #1
marx290
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Default Ejector Refrigeration, RV Heat Pump, R-290

Hi everybody! I thought I would start a new thread, because my work is sort of all over the place, and doesn't fit well in any particular thread. Since the last time I contributed, I've gotten a fair amount of hands on experience with vapor compression refrigeration. If you check out my blog, you can see how I got into things. Refrigeration Test Bench - Part I

The blog has not been updated for some time, but you can get an idea of where I am, or better yet, check out the Youtube channel.

It is so hard to find any good DIY refrigeration projects on the net (other than here, course. ) I'll try give a brief description of my main project coming up, and if anyone is interested, this could be a good place to answer questions or receive feedback. Refrigeration can be a lonely hobby.



I have many refrigeration projects planned, but my main focus is in building a heat pump to reduce my propane consumption in heating my motorhome this winter. I have logged my LP usage over the past heating season (number of days per 20lb cylinder), and along with the rating on the forced air heater, and the observational evidence of how often it runs, I've decided to build a system with approximately 1/2 ton capacity. This is likely too small to meet all of my heating needs, but I'd rather go to small, with a higher COP and supplement with other sources, than go to large with a lower COP and more cycling.

The compressor will likely be a small rotary unit from an air conditioner. The evaporator will probably be from a larger tonnage unit, and be plumbed up as a gravity flooded system, for greater heat conductivity, and smaller delta T. I have yet to develop a liquid level metering device, but I hope my research provides a solution by fall. Because the refrigerant charge will be rather large, I'm pursuing propane as my refrigerant of choice. This of course alarms some folks, so I will be designing the condenser to heat water, which will be pumped to a radiator in the motorhome. This also allows me to disconnect and move the unit when it comes time to pull up stakes and get out of Dodge.

The condenser / water heat exchanger is planned to be a chest freezer, perhaps further insulated. A series of thermostats will regulate the water temperature, and separate thermostats will regulate the indoor fan and pump.

Compression may very well be two stage, with the first provided by a handmade ejector. I recently constructed one, and I'm having some success with it in an air conditioner I've built in my shop. Anyhow, I'm still learning, and with luck, I will have developed the technologies I'll need to construct this heat pump for the fall. I hope to share my progress as it develops, and look forward to discussing it with any of you interested in such matters.



-Mike

P.S. I was recently turned on to the ejector thread by NiHaoMike (here), and I'd love to here from him on his progress.

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Old 08-04-15, 10:03 PM   #2
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Default A Summary

Hoping to spawn some interest, I wrote up a summary of my understanding regarding how ejectors can be used to improve performance in heat pumps. I hope it is of interest. I plan on doing more writing to document my progress.

Ejectors in Refrigeration – an Expressor | musings on entropy

-Mike
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Old 08-05-15, 10:59 AM   #3
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Quote:
Originally Posted by marx290 View Post
Hi everybody! I thought I would start a new thread, because my work is sort of all over the place, and doesn't fit well in any particular thread. Since the last time I contributed, I've gotten a fair amount of hands on experience with vapor compression refrigeration. If you check out my blog, you can see how I got into things. Refrigeration Test Bench - Part I

The blog has not been updated for some time, but you can get an idea of where I am, or better yet, check out the Youtube channel.

It is so hard to find any good DIY refrigeration projects on the net (other than here, course. ) I'll try give a brief description of my main project coming up, and if anyone is interested, this could be a good place to answer questions or receive feedback. Refrigeration can be a lonely hobby.



I have many refrigeration projects planned, but my main focus is in building a heat pump to reduce my propane consumption in heating my motorhome this winter. I have logged my LP usage over the past heating season (number of days per 20lb cylinder), and along with the rating on the forced air heater, and the observational evidence of how often it runs, I've decided to build a system with approximately 1/2 ton capacity. This is likely too small to meet all of my heating needs, but I'd rather go to small, with a higher COP and supplement with other sources, than go to large with a lower COP and more cycling.

The compressor will likely be a small rotary unit from an air conditioner. The evaporator will probably be from a larger tonnage unit, and be plumbed up as a gravity flooded system, for greater heat conductivity, and smaller delta T. I have yet to develop a liquid level metering device, but I hope my research provides a solution by fall. Because the refrigerant charge will be rather large, I'm pursuing propane as my refrigerant of choice. This of course alarms some folks, so I will be designing the condenser to heat water, which will be pumped to a radiator in the motorhome. This also allows me to disconnect and move the unit when it comes time to pull up stakes and get out of Dodge.

The condenser / water heat exchanger is planned to be a chest freezer, perhaps further insulated. A series of thermostats will regulate the water temperature, and separate thermostats will regulate the indoor fan and pump.

Compression may very well be two stage, with the first provided by a handmade ejector. I recently constructed one, and I'm having some success with it in an air conditioner I've built in my shop. Anyhow, I'm still learning, and with luck, I will have developed the technologies I'll need to construct this heat pump for the fall. I hope to share my progress as it develops, and look forward to discussing it with any of you interested in such matters.



-Mike

P.S. I was recently turned on to the ejector thread by NiHaoMike (here), and I'd love to here from him on his progress.
I put together a heating unit like you describe, minus the ejector. I used a dehumidifier as the outdoor unit. Both heat exchangers were plumbed in series and got airflow from the built in fan. I used a length of copper tubing in a Styrofoam beer cooler for the high side hx, plumbed to a 75 gallon fish tank indoors. The unit started out with a capillary tube for a metering device, then ended up with a txv.

The only problem I had with the heater was defrosting the outside evaporator coils. The unit did not have a reversing valve or a big accumulator, so I couldn't do a proper hot gas defrost. I fiddled with hot gas bypass for a minute, but it didn't work so hot. I ended up putting the hx cooler below the evaporator coils and just spraying some heating water on the intake side with a little pump, I believe it was a fuel pump, when the unit went into defrost.
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Old 08-05-15, 03:17 PM   #4
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Very neat, Jeff! I'm certain I will eventually have an issue with the unit frosting up, but I'll address that when it becomes a problem. A fair amount of Our winter here in Portland stays above freezing, with high humidity (much of the time); a good thing for a heat pump. :-D

I hope to minimize frost ups by utilizing a rather oversized evaporator to keep my delta T to a minimum, and evaporator temperature high. I plan on building a flooded heat exchanger to allow me to accomplish this. Hot gas bypass probably won't work well with a flooded system, but then again, if I designed the liquid / vapor separator to be large enough, I might be able to pull it off. It's not a big concern right now, since I'm not trying to replace my existing heating system, just supplement at a high COP.

One idea I like, if you happened to have two evaporators available, is to plumb them up into a series arrangement, where one acts as a liquid subcooler feeding the TXV on the second one which acts as a conventional evaporator. When the evaporator frosts up, a valving arrangement swaps their functions, and the frosted coil is slowly defrosted by the warm high side liquid, while the other coil picks up heat. I became aware of this idea by reading ice storage patents. I'd love to see someone try it!

What kind of water temperatures did you maintain in the styrofoam cooler? Was the unit effective when it wasn't frosted over?
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Old 08-05-15, 05:55 PM   #5
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It worked very well down to around 40 degF outside. I had the unit rigged to a waterbed thermostat in the aquarium. The unit would hold the tank at max temp (i think it was 90F) until it got cold enough outside to force defrost. As long as it was above freezing outside, the unit would defrost itself and start back up again.

The warm water spray defrost worked well, and got the unit working down into the 20's. With the fish tank as a heat store, it kept my sunroom and living room heated pretty well for a winter. It was a really huge learning experience for such a small rig.

The next season brought a need for cooling, so I retired that rig and found a 9000 btu portable ac unit on cl for cheap and began experimenting with it. I also began playing with window units. These trials eventually led me to build a window shaker heat pump that worked well down to near zero degF. It used a 15kbtu compressor originally made to go in an rv ceiling/roof unit.

I have now caught the bug and cannot help but hack together phase changing monsters. This stuff is amazing! I wish I would've learned about it when I was 10.
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Old 08-05-15, 08:02 PM   #6
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The warm water defrost is interesting. About how much water do you think was used during each defrost cycle? Over the last few months, I have gone back and forth about the merits of subcooling with a heat pump. Beyond the obvious use of pre-heating domestic water, I've wondered if defrosting could be done with some of the heat that can't be readily used to heat the indoor space. One way I thought of doing this is with a water spray or a cascade, similar to what you describe. I would want to do it with a separate water source, other than the heating loop, especially if I used any anti-freeze. I'd also like to catch the runoff and reuse it, as well as the condensate.

What kind of heat exchanger did you use for the water inside your home? Water loops in the floor aren't really an option for me right now, so I'm opting for a water to air heat exchanger and fan, for the RV here. I'm considering something like this:

12x12 Water to Air Heat Exchanger | eBay

Perhaps two of them in series, to produce a counter-flow with the air stream.

I'm 29, and although I did a little bit of hacking about 4 years ago, I also wish I would have gotten into this work when I was a kid. I can't get enough, and really desire more time to work on it. I lose track of time so easily, when I'm out there bending copper.

I truly need to slow down and begin analyzing the contraptions I build, but the empirical method is so much fun! An hour or two of running a machine, and I'm ready to hack it into something better.
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Old 08-05-15, 09:54 PM   #7
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Default Handmade Copper Ejectors

If it is of any use to anyone, I've made several copper "venturis", and tested one copper ejector with some promising results. I will be continuing my work with these, hopefully incorporating one in my heat pump this winter.

Handmade Copper Ejectors | musings on entropy

-Mike
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Old 08-06-15, 10:59 AM   #8
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Originally Posted by marx290 View Post
The warm water defrost is interesting. About how much water do you think was used during each defrost cycle? Over the last few months, I have gone back and forth about the merits of subcooling with a heat pump. Beyond the obvious use of pre-heating domestic water, I've wondered if defrosting could be done with some of the heat that can't be readily used to heat the indoor space. One way I thought of doing this is with a water spray or a cascade, similar to what you describe. I would want to do it with a separate water source, other than the heating loop, especially if I used any anti-freeze. I'd also like to catch the runoff and reuse it, as well as the condensate.

What kind of heat exchanger did you use for the water inside your home? Water loops in the floor aren't really an option for me right now, so I'm opting for a water to air heat exchanger and fan, for the RV here. I'm considering something like this:

12x12 Water to Air Heat Exchanger | eBay

Perhaps two of them in series, to produce a counter-flow with the air stream.

I'm 29, and although I did a little bit of hacking about 4 years ago, I also wish I would have gotten into this work when I was a kid. I can't get enough, and really desire more time to work on it. I lose track of time so easily, when I'm out there bending copper.

I truly need to slow down and begin analyzing the contraptions I build, but the empirical method is so much fun! An hour or two of running a machine, and I'm ready to hack it into something better.
The defrost pump sucked from the foam cooler and was rigged to a couple of raindrip spray emitters that misted a few gallons per hour each. Like any air source unit, the defrost took five minutes or less. Depending on outdoor temp, the thing might go an hour or more between cycles.

The indoor hx was the aquarium. Lots of low grade radiant heat and massive.
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Old 08-15-15, 11:54 AM   #9
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Here's a little information on assembling my ejector system, and some preliminary results. It's a lot of fun!

Ejector Assembly Construction | musings on entropy

Also, I've done some fun copper work recently, with a large focus on carefully reducing copper tubing diameter to make nozzles. I use a simple Yellow Jacket crimping tool. Could be useful.




Enjoy, and be safe!
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Old 08-29-15, 10:17 AM   #10
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Default Mig tip injector

Mike,
dont know if you thought of this but Mig welding guns have interchangeable tips: .024,.030,.045. this might help you Tweek your injector
Like where you going
Kurt

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